Symposium EM12 : Diamond Electronics, Sensors and Biotechnology---Fundamentals to Applications

Over the last decade diamond has emerged as a promising platform for quantum technologies. This is , in part, due to its ability to host optically active single emitters that can act as qubits. While the NV center has been studied thoroughly, other defects like the SiV are up for a renewed interest due to their superior optical properties.
In this talk I will review the recent progress on the SiV defect in diamond and show that even small nanodiamonds can host nearly transform limited emitters. I will show how to couple these emitters to cavities and trigger them electrically.
At the second part of my talk I will review other platforms that host previously unexplored single emitters – namely hexagonal boron nitride, gallium nitride and silicon carbide. This family of wide bandgap materials offer unique platform for exploration of solid state qubits, and I will highlight the challenges and the advantages of each platform.

Diamond transistors potentially have orders of magnitude superior properties for high-frequency high-power transistors than other semiconductor devices. However, many of these superior properties have not been realized in fabricated devices due to diamond’s unique manufacturing limitations. This presentation will discuss these limitations, how they impact device performance as compared to AlGaN/GaN transistors, and potential approaches to improve diamond transistor performance.
The initial diamond device limitation, no effective room-temperature n or p dopants, was addressed by Landstrass’s discovery in 1989 [1] that a hydrogen-terminated diamond surface would form a conductive 2-dimensional hole gas. With this discovery, Kawarada [2] and a few others in Japan [3] and Europe [4] over the next 27 years have reported landmark devices that are demonstrating performance exceeding the best transistors fabricated in other semiconductors. However, a few limitations to device performance still exist: high contact resistance, 2 to 3 Ω-mm (AlGaN/GaN is < 0.1 Ω-mm), high surface resistance, 1,000 to 2,000 Ω sq^-1 (AlGaN/GaN is 330 to 400 Ω sq^-1), device reliability, and metal contact adhesion. In spite of these limitations, diamond’s ~20-times higher thermal conductivity than GaN and higher breakdown voltage give diamond transistors superior properties when compared to other semiconductor devices.
Although it has been >27 years since Landstrass’s discovery, only minimal resources have been directed to diamond transistor development. With recent reports of significant diamond transistor performance [2-4], additional worldwide resources are being directed to device development, some of which will be reviewed.

[1] M. I. Landstrass and K. V. Ravi, “Resistivity of chemical vapor deposited diamond films,” Applied. Physics Letters 55, 975-977 (1989).
[2] H. Kawarada, T. Yamada, D. Xu1, H. Tsuboi, T. Saito, and A. Hiraiwa, “Wide Temperature (10k-700k) and High Voltage (~1000V) Operation of C-H Diamond MOSFETs for Power Electronics Application,” 2014 IEEE International Electron Devices Meeting 15-17 Dec 2014, 11.2.1-11.2.4, 10.1109/Iedm.2014.7047030.
[3] Makoto Kasu, “Diamond epitaxy: Basics and applications,” Progress In Crystal Growth and Characterization of Materials (2016), Doi: 10.1016/J.Pcrysgrow.2016.04.017.
[4] Stephen Russell, Salah Sharabi, Alexandre Tallaire, and David A. J. Moran, “ RF Operation of Hydrogen-Terminated Diamond Field Effect Transistors: A Comparative Study,” IEEE Transactions on Electron Devices 62 (3) 751-756 (2015).

With the high breakdown voltage and current handling ability of GaN, AlGaN/GaN on SiC HEMT structures are the current benchmark for high-power, high-frequency applications¹. However, in such devices the GaN epilayer and particularly the SiC substrate, with thermal conductivity of around 400 W/mK, limit the heat extraction leading to de-rating of the maximum power dissipation². Through replacement of the substrate and capping of the transistor channel with diamond of thermal conductivity of up to 2000 W/mK, large decreases in the thermal resistance should therefore be achievable allowing full utilisation of the properties of GaN based devices³.

In the present work NCD films have been successfully deposited directly on GaN on sapphire wafers, without the addition of a thermally resistant intermediate dielectric layer to aid growth as used within other studies¹. Films were grown through careful utilization of the electrostatic attraction between GaN and diamond at 850 °C, under 5% methane CH₄/H₂ conditions to a thickness of ~150 nm, as judged by in-situ laser interferometry. Raman and SEM characterization of the resulting samples revealed continuous films over the 15 by 15 mm samples, free of pinholes, and highly crystalline with uniform lateral grain size of 100—150 nm.



1. J. W. Pomeroy, M. Bernardoni, D. C. Dumka, D. M. Fanning and M. Kuball, Applied Physics Letters 104 (8), 083513 (2014).
2. J. Pomeroy, M. Bernardoni, A. Sarua, A. Manoi, D. C. Dumka, D. M. Fanning and M. Kuball, presented at the 2013 IEEE Compound Semiconductor Integrated Circuit Symposium (CSICS), 2013 (unpublished).
3. O. A. Williams, Diamond and Related Materials 20 (5-6), 621-640 (2011).

Carbon materials are promising for applications in energy storage, e.g. for batteries and supercapacitors. Composites consisting of diamond nanoparticles (about 5 nm in diameter) with different surface treatment embedded in a porous carbon matrix were synthesized via a sol-gel process. The aim was to provide nanodiamond based carbon composites for analysis as supercapacitor electrodes. The differently annealed nanodiamonds were incorporated by adding them as colloidal dispersions to the aqueous starting solution for a resorcinol-formaldehyde (RF) gel used as carbon precursor and by impregnating porous carbon gels.
Using surface untreated nanodiamond dispersions led to precipitation when adding them to the RF sol containing a base catalyst. To prevent this effect that results in RF-gel composites with a strong gradient we applied surface modified nanodiamond dispersions obtained from oxidized starting material or thermally annealing the nanodiamond. With this approach homogeneous composites with diamond nanoparticle concentrations of up to 10 weight % were successfully prepared. The observed impact of the differently annealed nanodiamonds on the structure formation upon the sol-gel process was compensated by adjusting the catalyst concentration.
The electrochemical properties of these new electrode materials will be discussed with respect to charge storage applications.

Acknowledgment: This research was funded by "Bayerisches Staatsministerium für Umwelt und Verbraucherschutz“ in the network UMWELTnanoTech (http://www.umwelt-nanotech.de).

Boron Doped Diamond (BDD) is known as a remarkable electrode in particular in terms of robustness, reactivity, stability and resilience to corrosion and fouling. Its excellent properties are highly promising for electrochemical sensors measuring e.g. resistivity, permittivity or pH in environments like those commonly found in the oil and gas industry. Indeed those sensors are often exposed to very harsh conditions: high pressure and high temperature, strong corrosion and abrasion, fouling fluids. Most of these sensors generally use metal-based electrodes that are likely to be damaged by such harsh conditions. In this work we investigate the potential of BDD electrodes to improve the sensors reliability, lifetime and detection performances in harsh oil and gas environments including drilling fluids or mix fluids used for cementing.

Over the last few years, anti-fouling processes have been studied using anodic, cathodic or pulsed treatments. The latter was efficiently optimised by Kiran and co-workers [1, 2] to reactivate BDD electrodes and to clean their surfaces in situ, sometimes directly in the sample medium itself. These processes have mostly been developed for biochemical sensing applications where they exhibit high efficiency. However currently the different activation processes have not yet been completely explained and thus their limits are not fully known.
In this study, the cleaning efficiency of BDD electrodes fouled by compounds from drilling fluid containing high conjugated system species was followed by Electrochemical Impedance Spectroscopy (EIS), as well as by fluorescence imaging. We also gained some insights on the role of water for electrochemical cleaning when we observed its inefficacy in anhydrous ionic liquid exhibiting water concentrations below 10ppm.

These results led to better understanding of the electrochemical activation processes in various oil based drilling fluids. The results demonstrated the advantages of BDD against more conventional electrode materials such as Pt and stainless steel alloys. For instance, in the case of a BDD based resistivity sensor, measurement errors have revealed the high BDD resilience to fouling and have proven the efficiency of in situ electrochemical cleaning.

This work was fund and supported by Schlumberger an oilfield service company.

[1] R. Kiranet al, Boron doped diamond electrodes for direct measurement in biological fluids: an in situ regeneration approach, J. Electrochem. Soc., 2013, 160, H67–H73
[2] Method of Activating a Doped Diamond Electrode, Patent WO2012EP52689 20120216

Boron Doped Diamond is an innovative electrode material in particular in terms of robustness, potential for miniaturisation and sensitivity. Its application in electrochemistry levarages numerous assets, and namely a wide electrochemical window in aqueous media, high corrosion resistance, chemical inertness, biocompatibility and low background current. In the recent years, several studies have been carried out on the possibility to deposit metallic nanoparticles, such as Pt or Ir, onto BDD, in order to enhance the electro-catalytic activity of such electrodes. This enables the detection of species that could not be monitored with bare BDD electrodes. For example, such hybrid electrodes have been used in biofuel application for ethanol oxidation and also in biosensor application for detecting derived products from enzymatic reactions such as H₂O₂ oxidation. Pt nanoparticles have also been used widely on BDD electrodes for the detection of H₂O₂, since bare BDD electrodes were found to be not active in redox reactions involving H₂O₂.
Moreover, we reported recently on a new diamond material called SPDia^TM consisting of BDD grown by CVD onto highly porous polypyrrole substrate. The resulting material was shown to exhibit similar electrochemical properties to planar BDD, including a wide potential window in the order of 2.8V in aqueous media and high chemical inertness, but with a large double layer capacitance increased by typically a factor 500 due to the high porosity of the film. These properties render the material very promising for supercapacitor or neural stimulation applications. Since the sensitivity of amperometric sensors is also directly related to the active surface area of the electrode, it is expected to bring some significant advantages over planar electrodes in terms of electrode sensitivity. Thus in this work, we compare the electrochemical properties of SPDia^TM over planar BDD for analytical measurements. Our investigation is focused on the detection H₂O₂. We show that metal nanoparticles can be immobilized over the porous material surface by metal sputtering/dewetting approach and that both the high porosity of the film combined with the presence of Pt nanoparticle allows surpassing drastically the performances of bare BDD electrodes. Moreover, using the new diamond porous material material called SPDia^TM allowed to increase the sensitivity by factor 2 and decreased the LOD by factor 3.

Early and accurate detection of life threatening biomarkers are key aspects for the treatment of many diseases. Biosensors offer the advantage of a cost-effective, highly specific, and portable quantification platform, which in combination with adequate clinical knowledge could help to diagnose and classify different pathologies. Here we are presenting the development and characterization of a surface enhanced polymeric that allows improved performance in term of the biosensor sensitive and robustness. The biosensing platform has been tested for glucose quantification after proper functionalization.
In this investigation nanodiamond particles were used as structural filler to increase the otherwise flat polyaniline polymeric film. The electrochemical deposition of Polyaniline (Pani) and Nanodiamond-Polyaniline (ND-Pani) films was performed using cyclic voltammetry in an aqueous solution containing 0.2 M aniline monomer in 0.5 M sulfuric acid as the supporting electrolyte. Two surface densities of nanodiamond particles, 0.15 𝜇𝑔/𝑚𝑚² and 0.6 𝜇𝑔/𝑚𝑚², have been studied to analyze the effect of nanoparticle addition. Cyclic voltammetry deposition was completed in two steps; one initial wide cycle from -200 mV to 1.1 mV to trigger the polymerization cascade, followed by 9 cycles of a shorter cycle from -200mV to 900 mV. To evaluate the repeatability of the synthesis process intensity of the cathodic current peaks and its corresponding potentials was recorded, showing values within three standard deviations for multiple experiments. The influence of nanodiamond particle inclusion over the surface of regular polyaniline was studied using roughness analysis. Five measurements were taken at different points of each sample. The AFM results indicated a significant surface area increase after ND addition. The aforementioned results were confirmed using electrochemical measurements based on the Randles-Sevcik equation. Later, Glucose oxidase was covalently attached onto the different electrodes materials (Pani, ND(0.15)-Pani and ND(0.6)-Pani) following zero-length covalent bounding. A solution containing N-Hydroxysuccinimide and 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide was prepared, a portion of this solution was used to prepare the stock solution containing glucose oxidase enzyme. From the stock solution, 5𝜇L were coated over the electrodes and let it dry at room temperature. The results obtained from the chronoamperometric experiments demonstrated higher current density for the ND(0.6)-Pani/GOX compare to the signal observed from the ND(0.15)-Pani/GOX and Pani/GOX. Also, the signal-to-noise ratio for all sensing platforms were gathered, with an important improvement for the ND(0.6)-Pani/GOX compare to the ND(0.15)-Pani/GOX and Pani/GOX. Selectivity and robustness of the different biosensors were tested against serotonin, dopamine and ascorbic acid with acceptable deviation from the pure solution sample due to the interference substance.

Highly conducting boron-doped diamond (BDD) films exhibit a number of properties that make them attractive for use as electrochemical electrodes; in particular they have a low background current, extreme electrochemical stability in both acidic and alkaline media, high resistance to fouling, and a wide potential window in aqueous solutions. The performance of BDD electrodes can often be greatly improved by modifying their size, shape and surface structure. Structuring the diamond surface on the micro- or nano-scale has the effect of greatly increasing the effective electrode surface area, leading to higher sensitivity, increased selectivity, and higher capacitance values. This report describes an alternative method to fabricate high-surface-area BDD electrodes using so-called ‘black silicon’ (bSi). This is a synthetic nanostructured material that contains high-aspect-ratio nano-protrusions, such as spikes or needles, on the Si surface produced through a simple RIE technique. We now show that coating a bSi surface conformally with BDD produces a robust, sensitive electrochemical electrode with high sensitivity and high capacitance. We first use a simple dielectric medium (aqueous KNO₃ solution) to measure the electrochemical performance of different BDD-coated bSi samples in comparison to a flat BDD control, and then repeat these with a more complex, one-electron redox system (ferri/ferrocyanide). A more clinically relevant demonstration of the efficacy of these electrodes is shown by measuring their sensitivity for detection of dopamine (DA) in the presence of an excess of uric acid (UA).
Finally, the nanostructured surface of bSi has recently been found to generate a mechanical bactericidal effect, killing both Gram-negative and Gram-positive bacteria at high rates. We will show that BDD-coated bSi also acts as an effective antibacterial surface, with the added advantage that being diamond-coated it is far more robust and less likely to become damaged than Si.

Electrons from cold cathode emitters are usually obtained by applying an electric field, which tunnels the electrons from the material surface into vacuum. A cold cathode emitter is expected to possess certain characteristics, namely, resistance against chemical attack and ion bombardment by residual gases, sustaining plasma discharges, and stability in various gas environments. Because of its superior properties, including a negative electron affinity (NEA) when H-terminated, diamond is considered an excellent candidate for said applications. Also boron nitride has been shown to possess a NEA, with 2D hexagonal boron nitride (hBN) receiving increased attention. Stimulated by the unique possibility to combine two nanostructured materials, this work will focus on novel heterostructures based on hBN nanowalls deposited on doped and undoped nanocrystalline (NCD) diamond films.
NCD films are deposited on silicon substrates by microwave plasma enhanced CVD, followed by hBN nanowall growth on diamond using a home built radio-frequency sputtering system [1]. Employing advanced electron microscopy techniques, both the surface morphology of the individual layers, as the interface between both materials is studied. The initial stage of BN growth is known to lead to unwanted BN phases, such as amorphous and turbostratic BN. Such a non-ideal interface between BN and the substrate material hampers efficient charge transport across the interface. Interestingly, cross-sectional TEM shows that such phases were significantly reduced at the hBN/NCD interface, suggesting that the H-terminated NCD provides an excellent template for hBN nanowall growth. Moreover, using STEM-EELS, a clear incorporation of carbon in the hBN nanowalls is detected, which improves their conductivity via defect states. It is believed that these findings explain the observed superior electron emission from the hBN/NCD heterostructures compared to hBN nanowalls deposited directly on silicon [2]. In addition to a detailed discussion on the influence of doping and nanostructuring the NCD substrate material, the potential application of these heterostructures is further demonstrated by plasma illumination measurements.

[1] D.Q. Hoang, P. Pobedinskas, S.S. Nicley, S. Turner, S.D. Janssens, M.K. Van Bael, J. D’Haen, K. Haenen, Crystal Growth & Design (2016), DOI: 10.1021/acs.cgd.6b00191.
[2] K.J. Sankaran, D.Q. Hoang, S. Kunuku, S. Korneychuk, S. Turner, P. Pobedinskas, S. Drijkoningen, M.K. Van Bael, J. D’Haen, J. Verbeeck, K.C. Leou, I.N. Lin, K. Haenen, accepted for publication in Scientific Reports (2016).

K.J. Sankaran and P. Pobedinskas are FWO Postdoctoral Fellows of the Research Foundation – Flanders (FWO).

Thermionic electron emission as described by the law of Richardson – Dushman presents a means to establish an electron current by application of thermal energy. The magnitude of the emission current can be described in terms of materials parameters, the work function or emission barrier and the Richardson or emission constant. Diamond has long been of interest in electron source applications motivated by its ability to accept donors in its lattice and for its surfaces to attain a negative electron affinity (NEA) that can eliminate the emission barrier at the diamond-vacuum boundary. As doping at energy levels of 0.6eV and 1.7eV can be achieved by phosphorus and nitrogen incorporation, respectively, in conjunction with the NEA surface low work function materials should be feasible. We report on thermionic electron emission from single crystal phosphorus doped diamond prepared on (100) and (111) doped and undoped diamond substrates. Nitrogen doped (~3x10¹⁹cm^-3) HPHT single crystal diamond with (100) surface orientation was exposed to a pure hydrogen plasma to induce NEA properties and thermionic electron emission data communicated a work function or emission barrier of ~2.4eV attributed to band bending. A high Richardson constant of 62A/cm²K², approaching the theoretical value for diamond, warranted application of this type Ib diamond as substrate. Phosphorus doped films were prepared on the (100) type Ib surface by plasma enhanced CVD utilizing a 200ppm trimethlyphosphine in hydrogen gas mixture. The doping concentration was controlled by adjusting the microwave power, substrate temperature and TMP/H₂ flow rate where SIMS data verified phosphorus concentrations from 10¹⁷cm^-3 - >10¹⁸cm^-3 for film thicknesses of 10nm - >50nm. Thermionic electron emission from these thin films was measured with gold contacts prepared on the emitting surface as well as the backside of the substrate and work functions of 0.67eV and 0.84eV were obtained for films grown under TMP/H₂ flow rates of 10sccm and 30sccm, respectively. Utilizing a type IIa (undoped) CVD diamond substrate with (100) surface orientation for the same thin phosphorus doped diamond film resulted in non-detectable emission up to 800°C. By utilizing a boron doped (9x10¹⁹cm^-3) type IIb HPHT plate with (111) surface orientation a phosphorus doped diamond film with increased thickness of 500nm and doping concentration of ~7x10¹⁹cm^-3 was prepared. Thermionic electron emission was observed at levels reduced several orders of magnitude which was attributed to a prominent increase in the emission barrier. We will discuss the role of the substrate in the transport process and the effects of film thickness and doping concentration on the emission behavior.

This research is supported by the Office of Naval Research through grant # N00014-10-1-0540.

Radioactive power sources have become increasingly attractive as the next generation batteries for remote electronic systems due to their high energy density and insensitivity to environment and temperature. To convert radioactive decay energy into electric current, one promising technique is the direct energy-conversion method, which employs a semiconductor diode and a radioisotope source. Taking into account lifetime, energy level and safety, Ni-63 seems to be the most suitable radioisotope source due of its pure beta particle radiation, long half-life (100 years) and low-energy radiation.
Due to wide band gap and large value of electron’s threshold displacement energy a diamond is the most attractive choice for creating betavoltaic microbatteries. Recently we demonstrated a prototype of planar nuclear battery with overall active area of about 15 cm² consisted in 130 single cells of Schottky barrier diamond diodes [1]. In developed prototype the specific energy of about 120 W*hr/kg was obtained. However the power density was only about 0.3 μW/cm³ that has been limited by two main factors. First of all due to a high intrinsic Ni-63 source self-absorbance the radioisotope utilization efficiency in thick low enriched source was only about several percent. In addition a thickness of our diode-based conversion cell structures was more than 10 times higher than typical depth of electron-hole pairs creation in diamond under beta irradiation.
In this work we proposed new three-dimensional battery architecture that provides more than 50 μW/cm³ of electrical power. For this purpose we used ion-beam assisted lift-off technique to smart cut the 15-μm CVD drift layer from the HPHT substrate in order to minimize the substrate parasitic volume. Also it allows us to use multiple times the same IIb type substrates that have been carefully selected to minimize their as-grown structural defects. Moreover we optimized the ion implantation parameters as well as a post annealing regime to reduce irradiation defects density in subsurface layer of substrate to achieve high quality epitaxial diamond drift layer with a large enough value of carrier diffusion length.
Conventional Ti/Pt/Au scheme was used for ohmic contact fabrication to residual HPHT layer of about 1 μm thickness after lift-off process. Thin Ni Schottky contact was deposited at the top of drift layer. To achieve an effective battery the electroless nickel plating technique was used to deposit about 1 μm of highly enriched Ni-63 layer selectively on Schottky contact of each diode-based structure.
We stacked thin diamond diodes vertically with offset to fabricate a ladder-like battery structure. Using special interconnection technique we obtained parallel electrical connections between each conversion cells. Detailed description of each fabrication steps and battery characterization results will be presented in report.

[1] V. Bormashov et al. Phys. Status Solidi A 212 (2015) 2539.

The negative electron affinity of the hydrogen-terminated surface of the boron-doped chemical vapor deposition (CVD) diamond (BDD) makes it an appealing material for electron multiplication. In devices such as photomultiplier tubes, the potential benefits of BDD as a high secondary electron emission (SEE) material for dynodes are numerous. One of them is a smaller number of multiplication stages to achieve the same level of overall gain. In this study, we characterize the SEE in terms of gain with respect to the energy of the primary electron impacting the surface of the BDD and discuss the factors that may affect the gain, such as the boron doping level, the thickness of the CVD layer, hydrogenation process and surface finish. We describe an experimental setup used for the characterization and present results from a prototype photomultiplier tube built using a BDD dynode.

Diamondoids represent a new class of materials bridging the gap between nanodiamond and organic molecules. This crossover gives them diamond-like properties such as negative electron affinity and strong electron-phonon coupling, combined with atomically-precise structures and ultrahigh purity. Diamondoids thus present an intriguing system to explore the properties and applications of diamond at unprecedentedly small scales. In this talk we will present our recent effort on using diamondoid self-assembled monolayers to create electron emitters with low work function, high stability and monochromaticity. First, we found that monolayer diamondoid coating can reduce the surface work function of gold by ~3 eV, representing the largest work-function reduction by organic molecules. Experimental and computational results indicate that the diamondoid radical cations, stabilized by their cage-like structures, are responsible for this effect. Furthermore, we developed a generic approach to enhance the stability of the diamondoid coatings with monolayer graphene coverage. The atomically-thin graphene provides a robust diffusion barrier to inhibit the dissociation of surface-attached diamondoids, while allowing electron transmission with little scattering. Using this strategy, we created diamondoid-based photoelectron emitters with kinetic energy distribution less than 20 meV, by far the narrowest energy dispersion observed in diamond-based electron sources. Moreover, these graphene-protected diamondoid emitters could be operated at room temperature with enhanced long-term stability against both thermal and irradiation disruptions. These developments, combined with the negative electron affinity and strong electron-phonon coupling in diamondoid, provide a new paradigm to design monochromatic electron sources with high robustness, compact structure and low energy consumption.

Significant advances in the understanding of free-exciton dynamics in diamond have been provided recently with ultrapure single crystals studied under high injection conditions at low temperature. In particular, the interplay of free excitons with the condensation of electron hole droplets [1] and the formation of polyexcitons [2] have been evidenced. However, it is indisputable that doping impurities necessarily play a role in the recombination dynamics of excitons in diamond. Yet, a basic knowledge of the corresponding time constants is still missing.

In this work, the dynamics of the free exciton capture by boron acceptors and phosphorus donors in diamond is observed in the picosecond range by time-resolved photoluminescence experiments at 5K. The formation of neutral boron and phosphorus bound excitons are observed with a delay of 410 ps and 120 ps respectively after the formation of free excitons. This is the result of the free exciton capture by B⁰ and P⁰ impurities. The lifetimes of boron and phosphorus-bound excitons are measured and found equal to 270 ps and 70 ps respectively. The bound exciton lifetimes in diamond appear about 4 orders of magnitude shorter than for the same impurities in silicon. E_i being the ionization energy of dopants, these results scale well with the E_i⁴ dependence of the non-radiative Auger recombination rate expected for bound excitons in indirect bandgap semiconductors [3].

[1] M. Nagai et al. Phys. Rev. B 68, 081202(R) (2003).
[2] J. Omachi et al., Phys. Rev. Lett. 111, 026402 (2013).
[3] J. Barjon et al., Phys. Rev. B 93, 115202 (2016).

The preparation of diamond thin films at low temperatures (T < 410 °C) enables a wide range of novel applications, e.g. deposition on flat panel displays, plastics, and other materials that don’t withstand high temperatures. The crucial requirement for diamond growth at low temperatures is a high plasma density at low gas pressure, leading to a low thermal load onto sensitive substrate materials. Such conditions are not within reach for resonance cavity plasma systems, which typically operate at pressures above 20 mbar. Linear antenna microwave delivery systems, however, allow depositions at pressures below 1 mbar [1]. Moreover, large area deposition is feasible over substrate diameters of 30 cm. Nevertheless, the use of linear antenna microwave plasma enhanced chemical vapour deposition systems, and in particular the growth of high quality diamond layers, remains understudied. In addition, for the development of nanocrystalline structures or devices, a bottom-up approach that allows control over the obtained morphology would be highly valuable. In this work the co-deposition of high quality platelets and octahedral diamond grains in nanocrystalline films is reported. In contrast to previous reports claiming the need of high temperatures (T > 1000 °C) [2], low temperatures (320 °C ≤ T ≤ 410 °C) were sufficient to deposit diamond platelet structures. Cross-sectional high resolution transmission electron microscopy studies show that these platelets are terminated by large {111} surface facets. Moreover, the grain boundaries are shown to be quite sharp and clean, which means there is very little disorder in between the grains. The high diamond quality is confirmed by Raman and electron energy loss spectroscopy both showing very small sp² contributions to their respective spectra.
Up to now, literature reports have focused on the characterisation of these platelets and multiple growth models have been proposed [3, 4]. These models start from an initial diamond structure that contains plenty of stacking faults, i.e. layers of so-called hexagonal diamond, and account for the development of platelets by preferential growth sites or by the relative growth rates of crystal facets. Nevertheless, in none of the previous reports an explicit reason for the presence of these stacking faults is given. Optical emission spectroscopy can reveal the plasma characteristics responsible for the growth mechanisms behind this particular morphology. In this work a model is proposed that accounts for the initial development of these platelets full of stacking faults and the growth of this morphology at low temperatures.

References

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Sharp transition between heavily boron-doped ([B] > 5×10²⁰ cm⁻³) and lightly boron-doped ([B] < 10¹⁷ cm⁻³) diamond films are essential to build power transistors based on delta-doping [1], or optical systems [2], as well as boron-doping gradients are desired for high voltage diodes. The main challenge concerns the control of doping level and growth rate in order to obtain the desired boron distribution. In the case of thick and homogeneous doping, the boron flow is typically adjusted to set a (B/C) gas ratio for achieving the suitable doping level. However, we suppose that this technique is insufficient to design nano-scale doping multilayers, and to perform continuous thin films deposition with sharp transitions of boron concentration from 10¹⁷ to 10²¹ cm^–3.
In this study, we take advantage of the boron incorporation efficiency that saturates and decrease at low methane concentration, below 1% to the total gas flow typically, and that falls when a small concentration of oxygen is introduced in the gas mixture (< 0.4%). Dealing with methane and oxygen flows provides a complementary way to control the boron doping. <100>-oriented diamond substrates have been exposed to high power density CVD plasma composed of trimethylboron (TMB)/CH₄/O₂/H₂ gas mixtures. Semi-quantitative in-situ plasma diagnostics have been performed to monitor the deposition. To do so, the relative emission of hydrogen Balmer series of peaks, BH*, CH*, and C₂* have been analyzed by optical emission spectroscopy (OES).
We established correlations between C₂* emission intensity and deposition rate, and between BH*/C₂* and boron doping level. We also identified special gas mixtures, associated to a bright intensity of BH*, where the diamond growth flipped into etching. In our experiment, without oxygen, the diamond etching takes place at large B/C gas ratio (1–4%) and small methane concentration (<0.5%). Such etching degrades the surface roughness (etch pits) and the crystalline quality (defects). Usually, a plasma composed of pure hydrogen is employed to reduce methane and boron concentrations between the depositions of two layers with different doping levels. Then, as soon as the methane concentration drops, and the boron residual is large enough, etching takes place. Consequently, it points out an additional difficulty to realize defects-free doping multilayers. First results of optimized CH₄/O₂/H₂ plasma mixtures indicate that we are able to stay near the equilibrium between growth and etching while the boron concentration in the plasma is changing.

References:
[1] A. Fiori et al, Appl. Phys. Express 6 (2013), 045801
[2] A. Fiori et al, Appl. Phys. Lett. 105 (2014), 081109

With the increased interest in the use of thin film diamond in a wide range of applications from micro-electro-mechanical systems¹ to tribological coatings², compositional and structural analysis of the initial stages of diamond growth is required in order to optimise the growth conditions used. Unlike conventionally used characterisation techniques including Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron (SEM) and atomic force microscopy (AFM), spectroscopic ellipsometry (SE) has robustly demonstrated the quantitative estimation of the composition of diamond films with varying depth^{3, 4}. The aim of this study is to therefore use variable angle spectroscopic ellipsometry to investigate the optical, compositional and structural properties of nanocrystalline diamond films during the early stages of growth.

To this end, a series of nanocrystalline samples of varying thickness (25-75 nm) were grown on (100) silicon wafers. Before growth, each wafer was placed into a mono-dispersed diamond colloid known to produce high seeding densities > 10¹¹ cm^-2, reducing the coalescence thickness⁵. Characterisation with SE was then performed within the spectral range 200-1000 nm using a simple 4-layer model to account for the surface roughness, grain boundary sp² and void fraction within the bulk, and SiC layer thickness at the interface with the Si substrate. With such a model the seeds and individual islands atop a 5-9 nm SiC layer are observed, before continued growth leads to coalescence at a thickness of ~30 nm as indicated by a reduction in the void content. The subsequent peak in non-diamond content from the addition of grain boundaries is then corroborated with Raman, while the increasing thickness of the surface roughness layer arising from columnar growth is validated with AFM, demonstrating the applicability of SE to the initial stages of diamond film growth. Lastly, the evolution from nano-diamond seeded Si to coalesced film was studied with x-ray diffraction.

1. A. Gaidarzhy, M. Imboden, P. Mohanty, J. Rankin and B. W. Sheldon, Appl Phys Lett 91 (20) (2007).
2. M. Amaral, C. S. Abreu, F. J. Oliveira, J. R. Gomes and R. F. Silva, Diam Relat Mater 17 (4-5), 848-852 (2008).
3. J. Mistrik, P. Janicek, A. Taylor, F. Fendrych, L. Fekete, A. Jager and M. Nesladek, Thin Solid Films 571, 230-237 (2014).
4. B. Hong, J. Lee, R. W. Collins, Y. Kuang, W. Drawl, R. Messier, T. T. Tsong and Y. E. Strausser, Diam Relat Mater 6 (1), 55-80 (1997).
5. O. A. Williams, Diam Relat Mater 20 (5-6), 621-640 (2011).

Commercially available high-pressure high-temperature (HPHT) substrates are heterogeneous in terms of structural defects and impurity concentrations. Their surface polishing creates additional defects in the subsurface, which influences the properties of homoepitaxial CVD diamond layers grown upon HPHT substrates. A common strategy to remove the damage of polishing is to etch the top layers of a substrate by plasma prior to CVD diamond growth.
In this work, we investigated the impact of nitrogen concentration in HPHT (111) substrate and substrates’ surface pre-treatment by O₂/H₂ and H₂ plasmas on the structural and electrical quality of phosphorous-doped CVD diamond layers grown upon them. The bulk and surface defects of the substrates were visualized by the X-ray Bragg diffraction imaging technique at ESRF synchrotron. The relative variation of nitrogen impurities in the substrates were analyzed by confocal µ-Raman/photoluminescence (PL). The lifetimes of charge carriers in CVD diamond layers were determined by an optical pump-probe technique, which is based on a differential transmission/reflection of a laser probe-beam (1064 nm) under optical excitation of an epilayer at 213 nm. For a deeper insight, measurements were done at various excitation fluencies and temperatures. The obtained results were compared in detail to µ-Raman/PL data.
P-doped diamond layers, ~4 µm thick, grown on nitrogen-rich substrate sectors after its pre-treatment for 5 min by O₂/H₂ plasma clearly show short lifetimes of charge carriers (40 ps), while layers on nitrogen-poor sectors of the same substrate showed longer lifetimes (2 ns). A longer pre-treatment (≥ 30 min) resulted in 7-fold prolonged lifetimes on N-rich substrate sectors and no improvement for layers deposited over N-poor sectors. The recombination modelling in CVD layers over the N-poor substrate sectors yielded 5 ns lifetime in the bulk with a surface recombination velocity of 10⁵ cm/s. Higher P-doping did not affect the lifetimes for layers over N-rich sectors, tentatively suggesting that dislocations could be the major cause of the short lifetimes.

Acknowledgements
This work was performed within the H2020 Research and Innovation Action Project "GreenDiamond" (www.greendiamond-project.eu) under grant agreement N°640947.

Diamond (111) are now attracting for the applications of the NV centers, due to the recent reports of highly selective alignment of the NV axis on (111) substrate^1,2 In principle, this alignment control should be possible also on highly-oriented diamond (HOD), large-area substrates of HOD(111) contribute to the development of applications. 3C-SiC/Si is a suitable substrate for the heteroepitaxial growth of the diamond film, because thermal expansion of Si is well matched with that of diamond and 3C-SiC can be directly grown on large Si substrates. Although HOD on 3C-SiC/Si with (100) orientation had been already demonstrated^3,4, there have been no reports on the HOD(111).
The sufficient density of epitaxial nuclei is necessary to synthesize HOD. However, we found that enough epitaxial nuclei cannot be obtained with the conventional bias enhanced nucleation (BEN) treatment on 3C-SiC/Si(111) surface. Thus, in this study, we developed a novel pulse bias method, called pulse BEN, and demonstrate the HOD(111) formation on 3C-SiC/Si(111) substrates for the first time.
Usually, conventional BEN on 3C-SiC are held on the condition with several tens of voltage for about 10min. High voltage over 100V must result in non-epitaxial nuclei. However, we found most of the nuclei have epitaxy in a few seconds just after nuclei begin to appear, even with such high voltage. Pulse BEN is a method, employing high voltage to obtain high nucleation density, and for their epitaxy quitting voltage to apply in such epitaxy period. In this study, we use 3C-SiC/Si (111) substrate with 4 degrees off angle toward [11-2] for aligned NV application.
By applying the pulse BEN of 100V and 12sec in antenna-edge microwave plasma CVD³, we achieved a nuclei density of over 10⁹/cm². Reflection high energy electron diffraction (RHEED) showed diamond patterns, suggesting a high epitaxial rate of the synthesized high density nuclei. After the subsequent growth on the nuclei for 2 hours, the SiC surface were completely covered by epitaxial diamond grains. The diamond growth flows to the off-direction of [11-2]. The diffraction in RHEED now became clear spots or streak pattern. Therefore, we successfully synthesized HOD(111) films on 3C-SiC/Si(111). Because the selective alignment of the NV axis can be achieved with the off-direction of [11-2] or [-1-12], the incorporation of the NV centers into our HOD(111) films will lead to the realization of the large-area platform for quantum applications.

[1] J. Michl, T. Teraji, S. Zaiser, I. Jakobi, G. Waldherr, F. Dolde, P. Neumann, M. W. Doherty, N. B. Manson, J. Isoya, and J. Wrachtrup, Applied Physics Letters 104 (10), 5 (2014).
[2] K. Tahara, H. Ozawa, T. Iwasaki, N. Mizuochi, and M. Hatano, Applied Physics Letters 107 (19), 4 (2015).
[3] J. Yaita, T. Iwasaki, M. Natal, S. E. Saddow, and M. Hatano, Japanese Journal of Applied Physics 54 (4), 4 (2015).
[4] H. Kawarada, T. Suesada, and H. Nagasawa, Applied Physics Letters 66 (5), 583 (1995).

Diamond shows superconductivity when the boron concentration is more than 3×10²⁰ cm^-3 [1, 2]. Superconducting transition temperature (T_C) of diamond can be controlled by changing the boron concentration and plane orientation [1, 2], we reported superconducting (111) diamond with T_C (offset)= 10K recently [3]. These results suggest that superconducting diamond is a promising material for superconducting devices. To fabricate high sensitive superconducting devices, high quality and homogeneous crystalline is essential. But heavily boron-doped diamond with certain thickness have many defects induced by lattice relaxation due to the difference in lattice constant of carbon (0.77 Å) and boron (0.88 Å). So the purpose of this study is to investigate the mechanism of the introduction of lattice relaxation, especially identification of the defects.
Superconducting boron-doped diamond were synthesized onto HPHT Ib (111) diamond substrate by custom-built microwave plasma chemical vapor deposition (MPCVD) apparatus. Mixture gas of methane, hydrogen, and tri-methyl-boron (TMB) was used for the growth. The methane concentration was 5% and the [TMB]/[CH₄] ratio was 0.9%. To investigate the effect of the lattice relaxation, we synthesized two samples with different thickness (300nm, 1100nm). Tc of these samples were 10K and the estimated boron concentration were 1× 10²²cm^-3.
Lattice mismatch was measured by two-dimensional reciprocal space mapping (RSM). The RSM of the initial growth (300 nm) showed only the peak of the strained layer with 0.68% for perpendicular lattice expansion. On the other hand, the RSM of the certain thickness (1100 nm) showed the peak of the strained layer with 0.63% for perpendicular lattice expansion and the peak of the relaxed layer with 0.63% for perpendicular and 0.75% for in-plane lattice expansions. This indicated that lattice strains appear due to the large lattice mismatch and relaxation of the lattice strain begins to occur once the doped diamond film reaches a certain thickness. Cross-sectional transmission electron microscope (TEM) observation of the sample with 1100nm thickness showed that high density of planar defects like stacking faults and twins appeared above 300-500 nm from the interface of diamond substrate and boron-doped layer. The diffraction pattern of the planar defects region showed the typical pattern of twins, though that of the interface showed only (111) diffraction pattern. The steric structure of the stacking faults is an upside down regular tetrahedron structure. These results indicated that introduction of planar defects co-occur with the lattice relaxation.
This study revealed that stacking faults and twins with an upside down regular tetrahedron structure are induced by lattice relaxation.

[1] E.Ekimov. et al., Nature 428, 542-545 (2004).
[2] Y.Takano, H.Kawarada. et al., Appl. Phys. Lett. 85, 2851-2853 (2004).
[3] T.Kageura, H.Kawarada, et.al., 2015 MRS Fall meeting abstract (2015).

The adsorption of particular molecular species on hydrogenated diamond produces hole accumulation on the diamond surface [1,2]. The desired hole doping needed for the development of diamond based devices can be controlled by a combination of surface termination and molecular adsorbate. Here we present a quantitatively accurate results of the electronic and structure properties of hydrogenated diamond surfaces and the charge transfer produced by the presence of a number of molecular species. This is made possible by the use of state-of-the-art non-local exchange-correlation functionals within hybrid density functional theory.

[1]: F. Maier, M. Riedel, B. Mantel, J. Ristein, L. Ley, Phys. Rev. Lett. 85 (2000) 3472.
[2]: Y. Takagi, K. Shiraishi, M. Kasu, and H. Sato, Surf. Sci. 609 (2013) 203.

Recent studies have demonstrated that hydrogen terminated diamond can act as a solid-state source of electrons in water when illuminated with above-bandgap light (>5.5 eV, ~225 nm). Excitation of electrons to diamond’s conduction band leads to facile emission of electrons into water due to diamond’s negative electron affinity. This results in the creation of solvated electrons that are potent reducing agents able to initiate many chemical reactions such as the reduction of N₂ to NH₃ and the reduction of CO₂ to CO. The goal of this study is to investigate mechanisms by which electrons can be photoemitted into water using near UV light (~3.4 eV, 360 nm +/- 20 nm) illumination of diamond that has been doped with nitrogen. Due to the deep donor level of nitrogen in diamond (1.7 eV below the conduction band), it is possible a sequential two photon absorption in the near UV range can excite an electron from the valence band to the conduction band of diamond by using the nitrogen donor level as a mid-gap state. Preliminary results indicate that not only does nitrogen doped diamond show a pronounced photocurrent from photoemission into argon when illuminated with the near UV light source, but the diamond films also show a measurable amount of ammonia produced from the reduction of nitrogen in an aqueous environment. In addition to further results from these experiments, changes to the diamond film characteristics due to the introduction of nitrogen during growth such as crystal size and the electronic structure at the surface will also be discussed.

Diamond has attracted considerable attention in the optics community for its high refractive index, low absorption loss and wide transmission window. The potential of its use as a single material platform for nonlinear and quantum optics has motivated new studies in those fields. For instance, frequency generation has been shown in diamonds, while its optically active defects are good candidates as sources for single photon emitters. Although diamond photonics has prompted as an interesting area of fundamental science as well as applications, studies on the third-order optical nonlinearities of diamond are still limited.

Here we used femtosecond laser pulses to investigate third-order optical nonlinearities, from the UV up to the telecom region (260-1500 nm), in diamond. To the best of our knowledge, it is the first time the n₂ spectrum of type II diamond is reported in this range. The experimental data, obtained from Z-scan technique, is compared with a first principles theory on nonlinear refraction in solids, which predicts negative values of n₂ when the wavelength is close to the band gap energy. The nonlinear refractive index (n₂) spectrum and optical Kerr gate investigated herein are fundamental for understanding ultrafast phenomena in diamond. We have also studied the use of femtosecond laser pulses to produce nitrogen-vacancy (NV) centers, aiming at the development of single-photon sources for quantum optics. The threshold energy for diamond modification was found to be ~15 nJ, when focusing 120-fs laser pulses with a microscope objective of NA = 1.25. Diamond modification by fs-laser pulses involves the formation of graphitic and amorphous phases. After an annealing at 680 Celsius for 1h, the irradiated lines became highly fluorescent, suggesting the formation of optically active defects. The properties of such defects for quantum optics are currently under investigation.

Fabricating single-crystalline diamond (SCD) wafers exceeding 1” dimensions, requires serious synthesis effort. For example, with typical growth rates of 30 µm/hour it takes about 2000 hours of growth time to make a 3 cm by 3 cm diamond plate. Stable CVD SCD growth processes for such long deposition times have not yet been demonstrated. Thus, it is very desirable to significantly increase the growth rate, while maintaining or improving the SCD quality.

The recent development of new growth reactor technology increased the safe and efficient diamond synthesis process window toward higher pressures [1]. The main motivation of increasing the process pressure is to achieve higher SCD growth rates while reducing defects [2]. At a process pressure of 300 Torr growth rates of up to 75 µm/hour were demonstrated. However, any further increase in process pressure resulted in unstable plasma conditions due to the use of a microwave power supply pulsed at 120 Hz. In this paper we report on further increasing process pressures to 400 Torr, which is possible with a power supply that can be switched between continuous and pulsed excitation. Previously we reported on the basic discharge behavior using this power supply [3].

In this study we demonstrate high quality SCD synthesis in the so-far unexplored pressure region between 300 and 400 Torr using pulsed power supplies. The effects of several parameters of the multidimensional parameter space, e.g. pressure and methane concentration, are discussed. The samples were analyzed for growth rates, film morphology, optical absorption, birefringence and nitrogen content.

References
[1] Lu et al., Diamond and Related Materials 37 (2013), 17-28
[2] Silva et al., Diamond and Related Materials 18 (2009), 683-697
[3] Muehle et al., MRS Fall Meeting 2015

Negatively charged Nitrogen Vacancy (NV) center in diamond is a promising candidate for nanoscale high sensitivity magnetic sensing, such as detecting nuclear spins of molecules on diamond surface [1], [2]. For this application, to create shallow NV centers while suppressing the degradation of its superior characteristics is significant. It was reported that NV electronic spin coherence time T₂ of shallow NV centers is much shorter than that of NV centers in bulk because of the surface defects [3]. Since this problem limits the potential of NV-based magnetometry, improving the coherence properties of shallow NV centers is desired. Delicate oxidation methods by annealing at 465°C in a dry oxygen environment [4] and oxygen soft plasma treatment [5] were reported to diminish surface undesirable spins and improve the coherence properties of shallow NV centers. Among soft oxidation methods, UV ozone treatment is used to control the coverage of oxygen on diamond surface [6]. Here, we investigated the effect of UV ozone treatment on the charge stability of very shallow NV centers in pure diamond.
¹²C enriched high-purity (nitrogen concentration < 1 ppb) diamond films were epitaxially grown on (001) diamond substrates [7]. Shallow single NV centers were created by low energy (≤ 10 keV) ¹⁵N ion implantation and subsequent annealing. Initial oxygen terminated surface was formed by acid treatment. We evaluated the charge stability of each NV center by the contrast of Rabi oscillation. The charge state of NV centers in 1.2 keV ion implantation region (the expected NV center depth is 2.5 nm below the surface on average [8]) was unstable after acid treatment. For these shallow NV centers, however, after UV ozone treatment, average Rabi oscillation contrast was improved by more than twice. The signal-noise ratio of fluorescence intensity of single NV centers and surface background intensity was nearly unchanged before and after ozone treatment. Therefore we consider that this improvement was due to the charge state stabilization by UV ozone treatment. While the charge stability was improved, no distinct improvement in T₂ was attained, indicating that various sources of the charge instability and/or the shortening T₂ exist.
[1] T. Staudacher, J. Wrachtrup, et al., Science 339, 561 (2013).
[2] S. J. DeVience, R. L. Walsworth, et al., Nature Nanotech. 10, 129 (2015).
[3] B. A. Myers, A. C. Bleszynski Jayich, et al., Phys. Rev. Lett. 113, 027602 (2014).
[4] I. Lovchinsky, M. D. Lukin, et al., Science 351, 836 (2016).
[5] F. F. de Oliveira, J. Wrachtrup, et al., Appl. Phys. Lett. 107, 073107 (2015).
[6] T. Sakai, H. Kawarada, et al., Diam. Relat. Mater. 12, 1971 (2003).
[7] T. Teraji, J. Appl. Phys. 118, 115304 (2015).
[8] J. F. Ziegler et al., SRIM the stopping and range of ions in matter, SRIM co. (2008).
Acknowledgements
We thank Dr. Liam P. McGuinness and Prof. Fedor Jelezko for their help in building CFM setup.

Boron doped diamond (BDD) film is excellent electrode material as an anode for waste water treatments system because of its excellent mechanical properties, wide potential window, low background currents and electrochemical stability. In this paper, we have synthesized BBD electrode to generate ozone high efficiency and more safely compared to traditional lead oxide (PbO2) electrode. The BDD film was deposited on the Ti substrate by surface wave plasma chemical vapor deposition to use as an anode for ozone generator. The morphology of samples were observed by Scanning Electron Microscopy (SEM) and the structural-chemical properties of synthesized diamond layer was investigated by Raman Spectroscopy. Conductivity, carrier concentration and Hall mobility was determined by a hall-effect measurement unit, based on the van der Pauw method. The ozone concentration in water, which was measured by Ozone Colorimeter.

Large size and high quality single crystal diamond (SCD) substrates are required for the commercialization of the many SCD applications. Currently the most commonly used SCD growth method that is employed to produce thick SCD is the (MPACVD) process [1]. Recently [2] polycrystalline diamond (PCD) rimless, smooth and high quality SCD substrates were grown by the MPACVD method where a Michigan State University (MSU) Reactor C [3] was operated at 240 Torr and a diamond seed substrate was placed in a pocket holder. SCD were grown on 3.5mm x 3.5mm x 1.4mm HPHT type 1b, (100)-oriented single crystal diamond seeds. The SCDs substrates were grown in an optimized pocket holder design as discussed previously [2]. The pocket holder has a depth d = 2.3 mm and w = ~1 mm. Diamond substrates were grown in one step over growth times between 40 – 72 hours at an experimental pressure of 240 Torr, with a H₂ flow rate 400 sccm, and 5% CH₄/H₂ methane concentration. The deposited SCD had growth rates of ~ 30 μm/h. When using the optimal growth conditions the morphologies exhibited a very smooth and a flat surface and no growth of any PCD rim.

Here the results of the experimental investigation are presented where the growth process was extended by adding two and three growth steps and, as a result, thicker and larger SCD plates and cubes are grown. The grown SCD was the laser cut from the seed and polished to produce SCD plates and cubes. Thinner diamond plates were fabricated by both laser cutting in the growth direction and along the original seed surface. The quality of these as grown SCD plates will be summarized from the results of the following measurement techniques: (1) SEM, (2) UV/Vis spectroscopy, (3) Etch pit density, (4) Birefringence and (5) SIMS analysis.

[1] M. SSchreck, J. Asmussen, S. Shikata, J.-C. Arnault, and N. Fujimori, MRS Bull., vol. 39, no. June, pp. 504–510, 2014.
[2] S. Nad, Y. Gu, and J. Asmussen, Diam. Relat. Mater., vol. 60, pp. 26–34, 2015.
[3] Y. Gu, J. Lu, T. Grotjohn, T. Schuelke, and J. Asmussen, Diam. Relat. Mater., vol. 24, pp. 210–214, 2012.

We report the development of a new technique of high selective deposition of polycrystalline diamond films on monocrystalline silicon wafers. This technique based on the deposition of desired pattern by using standard photolithography with addition of a nanodiamond suspension in photoresist, and the subsequent ion etching the surface of wafer. Ion etching is allows to remove the remaining parasitic nanodiamond particles in areas where the diamond film should not grow. Etching was carried out with 3.5 keV argon ions generated with closed drift ion source. Diamond films were deposited in selective regions using high-current glow discharge PACVD reactor. The effects of the nanodiamond concentration in photoresist and the thickness of etching layers on the nucleation density of diamond were also investigated. This technique is much simpler than those that are currently in use (eg selective oxidation method), and is very promising for the development of different microelectronic devices, displays, sensors, etc.

CVD diamond deposition on non-diamond substrates requires surface treatment in order to achieve a high nucleation density. One of the most widely used approaches is the substrate seeding with diamond particles dispersed in an appropriate solvent accompanied by ultrasonic agitation. On the other hand, electrostatic self-assemblies of nanodiamond seeding have been shown to provide the highest nucleation density as compared to that of ultrasonic treatment with particles of larger size. In this context, micro/nano diamond film nucleation and growth on metallic titanium (Ti) substrates represents a complex process. Among the difficulties, the poor film adhesion due to diamond/Ti lattice mismatch as well as the difference of the thermal expansion coefficients between them may be highlighted. Thus, the substrate morphology associated to the seeding process can be determinant for the film adhesion. The boron doped micro/nanocrystalline diamond (BDD/BDND) adhesion on Ti substrate was systematically studied taking into account five different Ti roughness in addition to two different seeding processes of ultrassonic dispersion of 0.25 µm diamond powder in hexane and electrostatic self-assembly seeding with diamond 4 nm. Twenty different samples were grown by hot filament chemical vapor deposition technique considering the combination of micro/nanocrystalline particles nucleation and growth, Ti roughness, and seeding methodologies. The samples were characterized by scanning electron microscopy, Raman scattering espectroscopy, and X-ray spectra (XRD). The adhesion tests were provided by hardness Rockweel, according to VDI 3198 standard. The results indicated that both BBD and BDND films grown with electrostatic self-assembly seeding with diamond 4 nm showed the highest adhesion indicating that the chemical interaction has important role in improving the mechanical properties on diamond/Ti interface. This result may be associated to TiC and/or TiH interlayer formation analyzed from XRD patterns. Besides, the substrate roughness may be taking into account by providing the film/substrate mechanical anchorage.

The traditional wastewater treatments comprising physical, chemical, and biological methodologies, which may present advantages or disadvantages depend on the total or partial degradation of the contaminant for the required application. Among them, advanced oxidation processes (AOPs) have received great attention because of their efficient degradation of persistent organic compounds, such as azo-dyes. AEOPs can produce (●OH) from an electrochemical reaction using the most clean agent, the electron, avoiding additional chemical agents during the treatment. Thus, the used anode material is a determinant step and boron doped micro/nanodiamond (BDD/BDND) electrodes have been used as the most efficient. Taking into account the above considerations, a systematic study was performed concerning the production, characterization, and application of BDD/BDND films grown on titanium substrate to degrade brilliant green dye using an electrochemical flow reactor. For this methodology four BDD or BDND samples of 25x25x0.5 mm were used as anodes in this flow reactor while the cathodes were of stainless steel. The films were grown in a hot filament chemical vapor deposition reactor using the balanced H₂/CH₄ (BDD) and H₂/CH₄/Ar (BDND) mixtures. Boron was obtained by dissolution of B₂O₃ in methanol in the appropriate B/C ratio to obtain good conductive electrodes. They were characterized by Scanning Electron Microscopy, Raman spectroscopy, X-ray diffraction, and Mott-Schottky plots. Subsequently, the electrolysis were carried out using BDD and BDND as anode material in an electrochemical reactor to degrade brilliant green dye analyzing the influence of different current densities and flow rates in this process. During the electrolysis, aliquots of the treated solution in the electrochemical reactor were analyzed by analytical techniques of UV-Vis and Total Organic Carbon (TOC) measurements. The electrode efficiencies obtained for electrodes with micro and nano morphologies were compared considering the color removal rate as well as the TOC mineralization in the end of each electrolysis. The absorption bands intensity from UV/Vis spectra clearly decreased up to their completely vanishing at the electrolysis end at current density of 100 mA/cm² for both electrodes. These results were corroborated by TOC measurements where the 50% of the organic material was removed.

The global energy demand is continuously growing as population increases, while the resources to fulfill this demand are becoming scarce. Energy storage can be an option to improve the energy sources performance and the long term sustainability. Supercapacitors, or electrochemical capacitors, are a promising alternative for energy storage systems, due to their combination of good specific energy and high power capability, which places them in a functional position between conventional capacitors and batteries. Therefore, the development of novel supercapacitor materials is essential to attend the energy demand and the optimization of its properties is crucial to provide a good energy storage device. In this context, high surface area electrodes can be obtained by growing boron doped diamond films on carbonaceous porous materials. The electrodes electrical properties as well as its electrochemical reversibility may be enhanced by adding a conductive polymer. Thus, this work presents the production and characterization of the ternary composite formed by polyaniline (PAni)/B-doped diamond/carbon fiber (CF), aiming its application as electrode for supercapacitor device. In order to optimize the composite properties, different CF heat treatment temperatures were evaluated, 1000 and 2000°C (CF1000 and CF2000). Moreover, the diamond films were grown on CF in two different conditions, by Hot Filament Chemical Vapor Deposition technique. The doping process consisted of a H₂ line, passing through a bubbler containing B₂O₃ dissolved in methanol. A gas mixture of CH₄, H₂ and Ar was used to obtain boron doped nanocrystalline diamond (BDND) films whereas a mixture of CH₄ and H₂ was used to grow boron doped microcrystalline diamond (BDD) films. For PAni synthesis, BDD/CF and BDND/CF samples were immersed in NaCl/HCl solution with distilled aniline. An aqueous solution of (NH₄)₂S₂O₈ in NaCl/HCl was used as oxidant. The temperature was kept at -10°C and the deposition time was 60 min. The composites were characterized by Field Emission Gun Scanning Electron Microscopy (FEG-SEM), Raman Scattering Spectroscopy, Cyclic Voltammetry (CV), Charge-Discharge (CD) curves and Electrochemical Impedance Spectroscopy (EIS). FEG-SEM images showed that both PAni and diamond coatings covered and enwrapped the fibers, forming a homogeneous film. Raman spectra showed the differences in the CF structures, induced by the HTT, and in the BDND and BDD structures. In addition, it confirmed the PAni formation on the composites. CV curves indicated that the PAni/BDD/CF2000 composite has the highest current density and capacitance response among the studied composites combinations. It also presented more reversible oxidation and reduction processes as well as greater charge storage capacity, observed from CD curves. Besides, EIS results confirmed its high capacitive response associated to its low charge transfer resistance.

Cadmium is considered a highly toxic heavy metal, even at trace levels, and extended environmental exposure to it can cause serious health issues such as nephrotoxicity, bone demineralization, and cancer. Boron doped diamond (BDD) electrodes have been extensively studied due to their attractive electrochemical properties, which have favored the evolution of their use to detect a variety of analytes, including heavy metals traces as well as pesticide determinations substituting the mercury electrodes in analytical techniques. In this work we investigated the parameter optimizations of square-wave anodic stripping voltammetry using boron doped diamond (BDD) electrodes with different doping levels for cadmium detection. The main parameters studied considered the optimized relation among the peak current with the pulse frequency, the amplitude, and the potential increment for highly (10¹⁹ cm^-3) and heavily BDD (10²¹ cm^-3) electrodes. The films were grown in a hot filament chemical vapor deposition reactor on Si substrate using H₂/CH₄ (99:1). Boron was obtained by dissolution of trimethylborate in methanol (2000 and 20000 ppm of B/C ratios). The films were characterized by Scanning Electron Microscopy, Raman spectroscopy, and X-ray diffraction. The film acceptor concentrations were evaluated by Mott-Schotkky Plots measurements. Cd (II) analyses were performed using SWASV technique in acetate buffer following different steps: (a) pre-conditioning step applying the potential of 0.9 V vs. Ag/AgCl for 45 s before each measurement to ensure the dissolution of the remaining deposits on the electrode surface; (b) the pre-concentration step procedure at -1.0 V vs. Ag/AgCl for 90 s; and (c) the SWASV voltammograms recorded from -1.0 V to 0.0 V. The peak currents were measured around -0.75 V vs. Ag/AgCl for Cd²⁺ concentration ranged from 1 to 20 ppb. Overall, the detection figures of merit for BDD are as good or superior to those for Hg. Both BDD films provided detection limits lower than 5 ppb showing that these electrodes are suitable to use in a mercury-free method to determine cadmium trace levels in water.

Carbon-based materials are increasingly used in electrochemistry due to their relative cheapness, durability, stability and form-tuneable surface area. The popular use of classic carbon electrodes such as glassy carbon (GC) and boron-doped diamond (BDD) stems primarily from the chemical stability of these materials together with the low background current and wide potential window for which BDD is eminent.[1] The sensitivity of GC and BDD is often augmented by the use of nanoparticles dispersed over the area of the underlying electrode. The behaviour of these nanoparticles is known to vary with the allotrope, the surface hydrophobicity and electroactive surface area amongst other factors of the underlying substance.

The surface area of the electrodes can be drastically increased by decorating the surface with particles of high surface area such as conductive carbon black (CB) or acetylene carbon black (ACB). Carbon black powders have different surface oxygen content depending on provenance; although both CB and ACB have very low oxygen contents, ACB is known to have less surface oxygen than CB. GC is sp² hybridised while BDD is predominantly sp³ hybridised and readily forms an oxide surface layer.[2]

We deposited both ACB and CB on GC and BDD electrodes and compared their performance with respect to hydroquinone (HQ) oxidation. HQ, an environmental contaminant, is detected by ex-situ multi-step processes[3] but would benefit from a simpler, cheaper detection method involving electrochemistry that can also be used in-situ. The preliminary results showed differences in electrochemical behaviour and kinetics, which were considered in terms of the contributions owing distinctly to the type of carbon black and the allotrope of the carbon electrode.

Given that BDD can be given stable terminations,[2,4] a comparison was made not only between GC and oxygen-terminated BDD (BDDO) but also between BDDO and BDDH (hydrogen-terminated BDD) and both BDDs and GC. Hence a separate aim arose: to investigate the possibility of using the oxygen-deficient carbon blacks supported on BDDO to mimic the behaviour of BDDH in terms of conductivity and hydrophobicity.

References
[1] Compton, R., Foord, J., Marken, F., Electroanalysis, 2003, 15, 1349–1363.
[2] Salazar-Banda, G., Andrade, L., Nascente, P., Pizani, P., Rocha-Filho, R., Avaca, L., Electrochimica Acta, 2006, 51, 4612-4619.
[3] Devillers, J., Boule, P., Vasseur, P., Prevot, P., Steiman, R., Seigle-Murandi, F., Benoit-Guyod, J., Nendza, M., Grioni, C., Dive, D., Chambon, P., Ecotoxicology and Environmental Safety, 1990, 19, 327-354.
[4] Kawaranda, H., Surface Science Reports, 1996, 26, 205-259.

The union of the unique diamond surface properties (highest hardness, low friction, and high corrosion resistance) with steel (most common substrate material) provides a new solution for machine parts under critical mechanical conditions and severe environmental. However, CVD diamond coating directly on steel comes with several issues. The fundamental reasons for the lack of adhesion are an iron catalytic effect, the high carbon solubility in iron at CVD temperature and high mismatch in thermal expansion coefficient of diamond and steel. Interlayers may solve these issues acting as diffusion barriers, for both iron and carbon, and match thermal expansion coefficients. Several articles describe the PVD deposition or electroplated interlayer to acts as an intermediate barrier. In the present study, the diamond film coated steel with an intermediate barrier deposited by laser cladding. In this novel technique, laser irradiation melts the powder (preplaced) and the substrate surface to create the coating on a steel substrate. We used the SiC/Ti and SiC/Cu powder mixtures to create the intermediate barriers. Each powder has a specific role. A thin layer of SiC/Ti promotes the high CVD diamond nucleation and chemical bond to the substrate. A thick layer of SiC/Cu reduces the high residual stress induced by steel substrate. The Cu powder works as a binder material. During laser irradiation, Cu melts and wets the SiC grains leading to dense intermediate layer. The deposition of diamond films was carried out in an HFCVD reactor (Hot Filament Chemical Vapor Deposition). The samples characterization included X-ray Diffraction (XRD); Field Emission Gun - Scanning Electron Microscopy (FEG-SEM), Energy Dispersive X-ray (EDX) and Raman Scattering Spectroscopy (RSS). Results showed that laser incidence dissociated partially the SiC powder forming Fe₂SiTi, FeSi, Cu₃Si phases. Further, the use of composite layer suggests the accommodation of the high steel thermal stress.

Microelectrodes have attracted great interest for electroanalysis because of their unique properties, such as nonlinear diffusion, increased rate of mass transport, and reduced capacitance, which allows a fast response. In the present work, we created a porous nanocomposite by Boron Doped Diamond (BDD) deposition on Carbon Nanotubes (CNTs) using Hot Filament Chemical Vapour Deposition (HFCVD). The resulting material yielded porous BDD microelectrodes. On the first step, we have grown the CNTs on carbon fiber (CF) surface by Thermal CVD in a tubular reactor. Camphor solution and Fe-Co were carbon and catalyst source, respectively. CNTs functionalization carried out by oxygen plasma improved the surface’s wettability. Nanodiamond dispersed in KCl was the seeding solution to seed nanodiamond particles on CNTs surface. Diamond nanoparticles interact with oxygen-containing groups on CNTs to promote an efficient seeding. BDD film growth occurred in an HFCVD reactor using methane/hydrogen gas mixtures. For doping, we employed a partial hydrogen flow bubbled in a closed vessel containing a solution of boron oxide dissolved in methanol. The microelectrodes were characterized by Raman Scattering Spectroscopy, Scanning Electron Microscopy with Field Emission Gun and electrochemical analysis. The crystalline quality of CNTs and the BDD doping level were studied by Raman analysis. SEM micrographs showed that nanocomposite kept CNTs' morphology. Electrochemical analysis showed that this material presents a low background current, high stability, and low capacitive current in comparison with BDD grown on flat substrates. Further, the porous BDD nanocomposite showed itself to be promising in electroanalysis.

Diamond micro particles are gaining use in composite materials to increase the thermal conductivity of conventional materials such as copper or aluminum. Obtaining the value of the particle thermal conductivity as well as its thermal interface conductance with different metals is essential to correctly determine the overall thermal properties of the composite. Measuring these two thermal properties is challenging due to the particles small size and complex geometry. A technique based on Frequency Domain Thermoreflectance (FDTR) has been developed to characterize both the thermal conductivity of individual diamond particles and the thermal interface conductance between diamond and different metals. This pump-probe technique finds regions on individual diamond particles where the lasers can be focused to perform the measurement. In addition, different oxygen plasma treatments have been conducted on the diamond particles in order to study their effect on the thermal interface conductance. It has been observed that oxygen plasma treatment significantly improves the thermal interface conductance of diamond particles and metals.

Nanodiamonds (NDs) have been used as efficient biosensor in medical procedures that involve ionizing radiation, also they are excellent platforms for drug delivery. The absorbed dose of radiation by the cells generates alterations in the permeability of the membrane affecting their whole function. Most of the external products generated by irradiation are known as a Reactive Oxygen Species (ROS). The ROS mostly comes from water radiolysis following of the oxidation of DNA, lipids, amino acids and carbohydrates. Both, the biological effects on cells and ROS production by radiation are very complex, and they are not fully understood. In this work, we study the effect of gamma radiation on red blood cells (RBCs) using NDs as a multifunctional vehicle to evaluate: 1) mechanical properties (AFM), 2) biochemical changes (Raman spectroscopy) and 3) the interaction with NDs (to use them as nano-carriers). These preliminary results are very important for the evaluation of irradiation of human tissues prepared to transplant, especially blood. In this way, medical doses (25-30 Gy) are recommended to avoid the rejecting of blood in the host. However, the radiation may worsen the quality of blood components, such as red blood cells (RBC). Moreover, in our experiments the same doses hampered the ability to transport oxygen of RBCs and reduced the quality of transplanted blood.

Diamond holds some exceptional properties which makes it an attractive material for many optical and power electronics applications. It has a wide bandgap, high charge carrier mobility, very high thermal conductivity and a high breakdown electric field. Diamond is optically transparent in the entire visible range and partially in the infrared range. However these superior properties are achieved only through proper and optimized growth conditions which may otherwise lead to high defect densities. Threading dislocations are one such defect type which can propagate from the nucleation side to the grown layer and severely affect the charge transport properties of the grown layer. Some studies show that epitaxial growth at different off-axis substrates from the crystalline plane directions <100> and <110> reduces the propagation of threading dislocations [1,2].
In this particular study we try to understand the surface morphology, growth dynamics and defect densities in single crystal diamond (SCD) grown at different offset angles (0°- 10°) from the (100) crystallographic plane. Both thin (~30 microns) and thick layers (~450 microns) are grown on HPHT substrates by the microwave plasma assisted chemical vapor deposition (MPACVD) technique (in MSU reactor B [3,4]). The HPHT seeds are sliced into both off-axis bevels as well as parallel plates. SCD layers have been grown at high pressure (240 Torr) and 5% CH₄/H₂ gas mix for different deposition times. Growth rate and surface roughness of epitaxial layers grown at different angles will be reported In addition, density of etch pits generated by a H₂ plasma will be discussed.
References:
[1] M. Naamoun, A. Tallaire, J. Achard, F. Silva, L. William, P. Doppelt, et al., Influence of surface misorientation of HPHT diamond substrates on crystal morphologies and threading dislocations propagation, Physica Status Solidi (a). 210 (2013) 1985–1990.
[2] M. Naamoun, A. Tallaire, F. Silva, J. Achard, P. Doppelt, A. Gicquel, Etch-pit formation mechanism induced on HPHT and CVD diamond single crystals by H₂ /O₂ plasma etching treatment, Physica Status Solidi (a). 209 (2012) 1715–1720.
[3] K.W. Hemawan, T.A. Grotjohn, D.K. Reinhard, J. Asmussen, Improved microwave plasma cavity reactor for diamond synthesis at high-pressure and high power density, Diamond and Related Materials. 19 (2010) 1446–1452.
[4] S. Nad, Y. Gu, J. Asmussen, Growth strategies for large and high quality single crystal diamond substrates, Diamond and Related Materials. 60 (2015) 26–34.

Introduction
Diamond deep ultraviolet (DUV: 350–190 nm) detectors can be used in various applications such as environment security, information technology, medical treatment, astronomical observation, and military application to inter-satellite communications because of its wide bandgap, highest thermal conductivity (22 W/cm K), high electric breakdown field (~10 MV/cm), low dielectric constant (5.5), high hole mobility (3800 cm²/V s), and high saturation velocity (1.1×10⁷ cm/s for holes). All these outstanding properties offers highest figure-of-merit of high sensitivity, high signal-to-noise ratio, high spectral selectivity, high speed, and high stability for DUV detectors. However, traditional metal electrodes would block the incident of UV lights which reduce the effective detective area so as to affect the responsivity and external quantum efficiency of detectors. Compared with other transparent conducting materials such as ITO, graphene has higher mechanical strength, chemical stability, flexibility, and especially ultraviolet transmittance. The 2% lattice mismatch between diamond and graphene can dramatically reduce the interface states induced by misfit dislocation and enhance the absorption of UV lights. Furthermore, the surface of diamond has relatively high phonon energy and low surface defects which can reduce the charge of impurity scattering and optical phonon scattering at the interface in order to improve the graphene’s mobility. So grapheme should be an excellent candidate of a transparent current spreading layer on diamond for DUV detectors.

Experiment and results
Undoped homoepitaxial diamond films were grown by microwave plasma assisted CVD onto high pressure and high-temperature (HPHT) synthetic Ib diamond (100) substrate. The hydrogen plasma was kept after the deposition to confirm the hydrogen termination, and the samples were cooled down in pure hydrogen atmosphere. Then CVD growth grapheme was transferred to the diamond surface by the common method. After the transfer, Raman spectra was used to examine the quality of graphene. The fabrication process began with the interdigital pattern of graphene using standard lithography and oxygen plasma etching. The extraction electrodes of Pd were then deposited by e-beam. For comparison, the DUV detector with traditional metal interdigital electrodes were also fabricated. Detailed properties of graphene/diamond DUV detector will be presented on the conference.

Diamond has been proved to be a perfect material for X-ray monitoring due to its unique properties, such as low absorption, high thermal conductivity and large bandgap. Diamond detectors are normally made from 50~500 um thick intrinsic SC diamonds with 30 nm platinum deposited on both sides, thus forming a double sided Schottky barrier diode. In most cases, diamond detectors work well in transmission mode, which means the detector is installed upstream of the sample and gives the real-time incident flux. This is a critical feature of diamond detectors compared with traditional Si-based devices. But in soft X-ray regime (500~2000 eV), a 50 um diamond fully absorbs the beam. Therefore, a thinner diamond (~5 um) for soft X-ray monitoring is need for working in transmission mode. Laser slicing and polishing can make diamonds thin to around 30 um. For further thinning, reactive ion etching has been employed. Deep etching diamond while maintaining a smooth and flat surface is challenging since the bulk diamond contains residue internal strain and defects, which will leave deep etching pitches on the surface. We have successfully demonstrated several diamond membranes (5-10 um) detectors. Together with lithographically defined Pt electrodes, the diamond membrane detectors provide flux and position information in transmission to softer x-rays than previously possible. Furthermore, we find that lower quality (higher nitrogen content) diamond can be used in these thin membranes as the thickness becomes less than the charge collection distance allowing for full charge collection. The fabrication and testing of these thin diamond membrane x-ray detectors will be discussed.

Diamond is a promising wide band-gap semiconductor material for use in devices; therefore a thorough understanding of the surface electronic structure is important. The Kelvin Probe (KP), Surface Photovoltage / Surface Photovoltage Spectroscopy (SPV/SPS) and Ambient Pressure Photoemission Spectroscopy (APS) techniques are commonly applied to traditional and organic semiconductor materials, nanowire structures and devices, metals and Transparent Conductive Oxides (TCO). The application of these techniques to synthetic and natural diamond samples provides some challenges: surface charge on the samples, irregular surface structure and atypical capacitive interaction with the KP tip. In this study, the challenges of conducting these measurements on the diamond samples are overcome and measurements using a combination of KP, SPV/SPS and APS techniques are taken of samples of natural and synthetic diamond samples to investigate their surface electronic structure and compare their different properties. These techniques are all non-contact and non-destructive. The Fermi Level position of the diamond samples was found to vary, typically between 4.3 – 4.9 eV, depending on the light illumination. For example, when a natural diamond sample was illuminated with 400 nm light from a 150W Quartz Tungsten Halogen light source, there was a surface photovoltage response of ~250 mV. There was additionally evidence of a shift in the charge characteristics of the material. The charge carriers in the oxygen terminated synthetic diamond sample had sufficient mobility to measure a AC-SPS response peaking at ~530 nm but the natural diamond samples showed no rapid charge movement capability. However, the oxygen terminated synthetic diamond sample required near continuous illumination at low visible wavelengths in order to retain sufficient conductivity to allow measurement with the Kelvin Probe. By contrast, the natural diamond samples measured showed good conductivity in the layers underneath the top surface. In summary, the KP, SPV/SPS and APS measurement techniques provided some interesting information on the diamond samples and an initial investigation of their surface electronic states is performed. These techniques are suitable and could allow greater insight into the surface electronic structure across a range of diamond structures and samples.

The key technology to fabricate quantum devices, i.e. devices that employ single atoms or defects as functional unit is the addressing of single atoms in a solid with high lateral resolution. Whereas the manipulation of single atoms at the surface has been possible since several years, the three dimensional addressing in the bulk requires more effort. The combination of surface manipulation and overgrowth is one possibility but technologically very challenging. Ion beam implantation allows addressing single countable atoms inside a given solid with nanometer precision. To meet this goal we firstly need to focus or collimate the ion beam and to count the ions delivered to the sample. Our approach is to detect a single ion during fly-by using image charge detection and to deliver the ion with nanometer precision employing a modified commercial FIB system.
However, to create a deterministic quantum register based on NV centers a third requirement has to be considered: The implanted nitrogen atom has to be converted into an NV center with nearly 100% efficiency. Unfortunately, the creation of vacancies by ion impact is a statistical process and therefore not predictable. Additionally, the charge state of the NV center has to be converted into the negative state to make it functional.
The talk will discuss the state of the art of single ion nano-implantation methods as well as new developments in material science to overcome the limitations encountered in the creation of NV centers so far.

Full coherent control of quantum systems is a key prerequisite to build quantum information processing (QIP) systems. Moreover, all-optical control techniques are favored as they allow for a spatially resolved and potentially ultrafast manipulation. However, these techniques require optically accessible quantum systems with a large electronic level splitting to allow for the application of ultrafast and thus broadband laser pulses.

Recently, the negatively charged silicon vacancy center (SiV) in diamond has emerged as a novel promising system for QIP due to its superior spectral properties and advantageous electronic structure [1,2]: The SiV offers an optically accessible Λ-type level structure with a large orbital level splitting. For unstrained SiVs this splitting amounts to approximately 48GHz (259 GHz) in the ground (excited) state. Experiments creating steady-state coherence in the Λ-system determined the ground state coherence time to be on the order of 35-45ns [3], limited by phonon-mediated transitions within the ground state manifold [4].

To demonstrate all-optical resonant coherent control of the orbital state of single SiVs we apply ultrashort, 12ps laser pulses resonant with the optical transition between the lower ground and excited state.
Rabi oscillations with high contrast above 90% are clearly evident in the fluorescence signal recorded on the phonon side band of the SiV [5].
We observe no significant damping due to fast decoherence processes (on the time scale of the pulse length). To achieve full coherent control, rotation around a second axis is necessary. This is realized by utilizing the free precession in the equatorial plane of the Bloch sphere in a Ramsey interference experiment. From the visibility of the Ramsey fringes we determine the (lower) excited state coherence time T_2
^* =578ps.

To utilize the full ground state coherence time of the SiV, coherent rotations are realized using a Raman process linking two ground states with a common excited state in a Λ-type configuration. We use a single broadband 1ps rotation pulse that simultaneously addresses both branches of the Λ-scheme (detuning of 500GHz from excited state), giving rise to coherent two-photon Rabi oscillations of up to 2\pi. To verify the coherence of these operations and to demonstrate axis control we performed a Ramsey interference experiment using two subsequent Raman pulses.

The experiments presented here demonstrate the accessibility of a complete set of single-qubit operations relying solely on optical fields and pave the way for high-speed QIP applications using SiV centers such as cavity-assisted Raman transfer schemes, coherent spin-photon interfaces or optical quantum memories.

[1] C. Hepp et al., Phys. Rev. Lett. 112, 036405 (2014).
[2] T. Müller et al., Nat. Commun. 5, 3328 (2014).
[3] B. Pingault et al., Phys. Rev. Lett. 113, 263601 (2014).
[4] K.D. Jahnke et al., New J. Phys. 17, 043011, (2015).
[5] J.N. Becker et al., arXiv:1603.00789 (2016).

To bring practical optical quantum information processing to life, single-photon sources and opical elements such as waveguides, beam splitters and filters need to be integrated into functional quantum-optical chips. The fabrication of such chips, which will likely be hybrid in nature [1], is a demanding task. Defect centers in nano diamonds have proven their suitability as cheap, integrable and stable single-photon emitters. However, in the past, coupling them to photonic structures was mainly based on stochastic methods [2], or time consuming (AFM) micromanipulation techniques [3].
Here, we show a new, scalable, optical localization-selection-lithography procedure for potentially wiring up a large number of single-photon emitters via polymeric photonic wire bonds in three dimensions. First, we localize and characterize nitrogen vacanciy centers in nano diamonds inside a solid photoresist exhibiting low background fluorescence. Next, without intermediate steps and using the same optical instrument, we perform aligned three-dimensional laser lithography. This enables us to create versatile structures with deterministically localized single-photon emitters. As a first proof of concept, we designed, fabricated, and characterized three-dimensional functional waveguide elements on an optical chip. Each element consists of a single emitter in the crossing of two perpendicular arc waveguides. Using a confocal microscope the emitter can be excited from below via one arc while detecting its fluorescence via the perpendicular waveguide. This configuration allows for integrated optical excitation and efficient background suppression at the same time, which is proven by the measured value of the second order correlation function at zero time delay of g⁽²⁾(0) = 0.21.

[1] O. Benson, Nature 480, 193–199 (2011)
[2] A. W. Schell, et al., Sci. Rep. 3, 1577 (2013)
[3] A. W. Schell, et al., Rev. Sci. Instrum. 82, 073709 (2011)

The negatively charged nitrogen vacancy centers (NV^-) is one of the most significant color centers in diamond due to their spin dependent fluorescence properties. One of the key challenges for NV based magnetometry application is to create an ensemble of NV centers in the near surface region. Herein, we report on an innovative nitrogen delta doping technique to engineer shallow NV^- centers in diamond. Nitrogen delta doping was realized by producing a stable nitrogen terminated (N-terminated) diamond surface and subsequently depositing a thin layer of epitaxial diamond on the N-terminated diamond surface. This method produces a nitrogen delta doped layer with a thickness of less than a few nanometers. The obtained nitrogen concentration (n=1.8 x 10²⁰ atoms.cm^-3) in the delta layer is much larger than the traditional delta doping technique, in which N₂ is injected into the reactor during the growth of diamond for a very short period of time. SIMS profile exhibits a positive gradient of 1.9 nm/decade and a negative gradient of 4.2 nm/decade with a full width at half maximum (FWHM) of 7.5 nm. To the best of our knowledge, this is the thinnest nitrogen delta doping profile with abrupt interfaces in single a crystal diamond reported to date. The broadening of the nitrogen profile (FWHM=7.5 nm) is partly attributed to the diffusion of nitrogen as well as to the depth resolution of SIMS measurements (ion mixing and surface roughness effects). This has been experimentally confirmed by performing the delta doping in polycrystalline diamond, which revealed the diffusion of nitrogen through grain boundaries as well as the influence of surface roughness on the broadening of SIMS profile. In addition, SIMS analysis revealed a correlation between nitrogen and hydrogen atoms as well as their concentrations in the delta doped layer. XPS studies confirmed the formation of N-termination, which were stable onto the diamond surface even after expositing to the diamond CVD conditions. Photoluminescence studies using excitation of 531 nm showed the emission at 638 nm, from the NV^- centers. The proposed method would allow a precise control over the depth, which enables a scalable creation of high density NV^- ensemble in the near surface region.

Nitrogen-vacancy (NV) center in diamond can be utilized for quantum sensing of magnetic field. For the improvement of detection sensitivity, selectively aligned high density NV center ensemble is necessary. We have reported the selective alignment of NV ensemble by microwave plasma chemical vapor deposition (MPCVD) growth of N-doped (111) diamonds [1]. In this study, we synthesized N-doped diamonds containing selectively aligned NV ensembles with different internal stress in the diamond film and found that the effect of the internal stress on the measurement contrast of optically detected magnetic resonance (ODMR).
Diamonds containing aligned NV ensemble were grown on the IIa (111) substrates with the off-direction of <-1-12> by MPCVD using CH₄/ /N₂/H₂ as source gasses for formation selectively aligned NV ensemble[1]. We investigated 2 samples: one was grown directly on the IIa diamond substrate (sample A) and another was grown on a phosphorus (P)-doped thin layer (P concentration was 5 × 10¹⁹ cm^-3) on the IIa diamond substrate (sample B). By X-ray diffraction measurement, we confirmed that the lattice spacing of the IIa substrates was about 0.2 % shorter than the original spacing of diamond. Because P in diamond expands the lattice constant, the P-doped layer on sample B can buffer this compression of the lattice.
NV densities were estimated to be 8 × 10¹⁵ (sample A) and 7 × 10¹⁵ cm^-3 (sample B). Moreover, the NV centers in both samples were selectively aligned along the [111] direction, and alignment ratios evaluated by ODMR spectra were 90.3 % (sample A) and 96.7 % (sample B) on average of 10 positions in each sample. In ODMR spectra of sample A, resonance lines from the [111] oriented NV centers shifted – 20 MHz from 2870 MHz. When NV centers are subjected to a pressure parallel to the NV axes, the lines shift by 15 MHz/GPa (compression pressure shifts to higher frequency) [2]. Thus, about 1.3 GPa of internal expansion stress along the [111] direction exists in sample A. In addition, the lines in sample A were split to 2 components due to non-uniformity of the stress. Accordingly, the contrast of sample A in Rabi oscillation became as low as 11 %, despite the high selective alignment. By contrast, there was no shift of the lines in sample B, leading to a high contrast of 21 % in Rabi oscillation. The internal stress of the NV-containing diamond decreases the contrast, but this stress can be effectively removed while keeping the NV density by introducing the buffer layer to negate the lattice expansion of the substrate.

[1] K. Tahara, et al., Appl. Phys. Lett. 107, 193119 (2015).
[2] M. W. Doherty, Phys. Rev. Lett. 112, 047601 (2014).

Silicon Carbide (SiC) has recently garnered attention for its spin-coherent, luminescent defect centers (color centers), occurring in a variety of SiC polytypes. Coupling of these color centers to high quality optical cavities can augment the photonic signature of the defect, allowing for longer-distance, robust information transfer of the color center state. We describe the formation of high quality factor (Q) photonic crystal nanobeam cavities in 4H SiC, whose resonance frequencies have been designed to match either divacancy centers with photoluminescence (PL) emission ranging from 1070-1300 nm or silicon vacancy color centers with PL emission spanning 860-1100 nm. The best coupling conditions require a resonance in frequency between cavity and color center, as well as an overlap between color center position and the spatial extent of the cavity mode.

Color centers were introduced into fabricated 1-dimensional nanobeam photonic crystal cavities, either through ion implantation or electron irradiation. Subsequent thermal annealing resulted in improvements in the cavity Qs, as well as changes in the intensities of the cavity modes. We believe the cavity thus provide a means of sensitively monitoring the spatial diffusion of defects. Ultimately, such behavior may provide insights into approaches for deterministic placement of defects within the cavity.

Tuning of the cavities provided as much as a hundred-fold increase in the intensity of a color center zero phonon line, and lifetime measurements confirm the coupling of the defects to the cavity. The optical data of the tuned cavities-coupled-to-defects will be correlated with corresponding spin lifetimes of the defects. The progress towards strong coupling between cavity and color center, and the understanding of the corresponding spin behavior represent important stepping stones towards the use of such spin centers in quantum information applications.

Efficient interfaces between photons and atoms are crucial for quantum networks and enable nonlinear optical devices operating at the single-photon level. In this talk I will highlight properties of single colour centres at low temperatures and show that single SiV and GeV colour centres in diamond are promising candidates for creating such interfaces. I will also show experiments aiming to create technologies allowing realization of fully integrated, scalable nanophotonic quantum devices.

Long quantum coherence in solid-state systems is the ultimate prerequisite for new technologies based on purely quantum phenomena. In recent years, silicon carbide (SiC) is attracting continuously growing interest for quantum spintronics [1,2] and the longest T₂ reported to date in this system is 1 ms at cryogenic temperature [3]. We observe that T₂ continuously increases up to about 100 ms with the number of decoupling pulses [4]. We estimate the T₂ saturation level to be approximately 0.3 s, which is within the same order of magnitude with the record values for electrons in solid state but achievable without isotope purification of the crystal. Such an exceptional long-lived quantum memory is attained through the suppression of heteronuclear spin cross-talking in a magnetic field above 10 mT, in accord with the theoretical simulations [5].
[1] W. F. Koehl, et al., Nature 479, 84 (2011).
[2] H. Kraus, et al., Nat. Phys. 10, 157 (2014).
[3] D. J. Christle, et al., Nature Mater. 14, 160 (2015).
[4] D. Simin, et al., arXiv:1602.05775 (2016).
[5] Li-Ping Yang, et al., Phys. Rev. B 90, 241203(R) (2014).

Effective fabrication of photonic structures with optically coupled semiconductor spin systems marks an important tool for scalable quantum information processing. To produce aligned nitrogen vacancy centers (NV) with diamond nanostructures, we introduce a lithographic mask with nanoscale implantation apertures for NV creation, together with larger features for producing waveguides and photonic nanocavities. With subsequent nitrogen ion implantation, dry etching and thermal annealing, we obtain self-aligned NV creation at the mode maximum of diamond photonic crystal nanocavities with a single-NV per cavity yield of ∼26%, as well as Purcell induced intensity enhancement of the zero-phonon emission up to five fold. We expect larger enhancement factors by improved fabrication and optimized cavity coupling. Further numerical investigation on the NV formation within nanostructures will also help achieve better alignment between NV and diamond photonic cavities.

The key to the efficient transmission and conversion of low-carbon electrical energy is the improvement of power electronic devices. Diamond is considered to be the ultimate wide bandgap semiconductor material for applications in high power electronics due to its exceptional thermal and electronic properties. Two recent developments - the emergence of commercially available electronic grade single crystals and a scientific breakthrough in creating a MOS channel in diamond technology, have now opened new opportunities for the fabrication and commercialisation of diamond power transistors.
These will result in substantial improvements in the performance of power electronic systems by offering higher blocking voltages, improved efficiency and reliability, as well as reduced thermal requirements thus opening the door to more efficient green electronic systems.
The current research carried out mainly in Japan and Europe will be presented, with the various device architectures explored, including MOSFET, MESFET, JFET and rectifiers. Results obtained in the framework of the first European research collaboration on diamond devices, aiming at fabricating the first HVDC diamond based converter will also be presented.

AlGaN/GaN-on-diamond microwave devices have demonstrated at least three times higher power density than devices grown on SiC substrates. We demonstrate the benefit of optimized seeding of the diamond growth on achieving defect free GaN-on-diamond wafers, high mechanical stability and homogenous thermal properties for use in ultra-high power microwave electronic devices. These material structures benefit from the high electron mobility of the AlGaN/GaN device layer and the high thermal conductivity of the diamond, however, the rather large coefficient of thermal lattice expansion (CTE) between the diamond and the GaN pose challenges.

In situ focused ion beam cross-sectioning was used to study GaN-on-diamond wafers, fabricated at Element-Six, seeded with different size nano/microsize particles to gain insight on the microstructure-properties relationship. Voids can form at the GaN-diamond interface if an inappropriate seeding scheme is used; physical mechanisms for the occurrence of these defects will be discussed. Using an optimized seeding approach, we demonstrate that GaN-on-Diamond wafers with no macroscopic defects can be fabricated. For the investigation of the mechanical strength of the GaN-diamond interface, a novel micro-mechanical testing approach was employed. Micro-size pillars were fabricated containing GaN, diamond and the interface between the two layers; a mechanical load was then applied onto the GaN layer to ‘pull’ it away from the diamond layer to test the strength of the interface. We find that stress in excess of 3 GPa is required to break the ‘bond’ between GaN and the diamond. This has demonstrated high interface mechanical stability, which is essential for real-life deployment of this novel material structure in device applications. To correlate the local microstructure with the thermal properties of the GaN-on-Diamond wafers, mapping of the thermal properties using a transient reflectance technique was applied. The results showed a high homogeneity of the thermal properties for defect free wafers and this provides an excellent basis for achieving high performance ultra-high power electronic devices in a manufacturing environment. The most recent advances and challenges in these areas will be presented and discussed.

This work is in part supported by DARPA under Contract No: FA8650-15-C-7517 monitored by Dr. Avram Bar Cohen, supported by Dr. John Blevins, Dr. Joseph Maurer and Dr. Abirami Sivananthan.

We fabricated hydrogen-terminated (C-H) diamond MOSFETs using the two-dimensional hole gas (2DHG) induced by coating the C-H diamond surface with Al₂O₃ insulator by high temperature atomic layer deposition (ALD) method. We have reported high breakdown voltage (>1600 V) characteristics [1] and wide temperature (10 K-673 K) operations [2, 3]. Generally, the transport properties of C-H diamond MOSFETs shows normally-on because 2DHG is induced even when applying no bias. Normally-off characteristics are required for power devices for safety operations. The normally-off type Diamond FETs have reported by using partially oxidized diamond MISFET [4], HfO₂-gated diamond FETs [5] and JFETs with narrow channel widths [6]. In this paper, we fabricated C-H Diamond MOSFETs aim at gate threshold voltage (V_th) by partial oxidation (partial C-O) and nitrogen-doped to C-H channel. V_th can be controlled by changing the level of valence band maximum. As a result, normally-off operation, high breakdown voltage and high current density characteristics were obtained.
The fabrication process was as follows. First, undoped CVD layer was deposited on Ib (001) diamond substrate and Ti/Au source/drain were deposited. Second, the diamond surface was C-H by remote plasma. Third, the channel region was partial C-O channel or nitrogen-doped. To form partial C-O channel, UV irradiation in oxygen atmosphere. And the dose of nitrogen doping was varied to 10¹⁸–10¹⁹ cm^-3. The sheet resistance of partial C-O and N-doped surface was 10⁵–10⁶ Ωsq, which is one or two orders of magnitude higher than that of typical C-H diamond. Then, Al₂O₃ passivation layer was deposited to cover partial C-O channel by ALD. Finally, Al gate was deposited.
V_th of C-H diamond MOSFETs with partial C-O channel was -3.0 V (@RT) which is high enough for power device application. V_th control and normally-off operation were achieved. The maximum drain current density of -20 mA/mm (V_DS = -50 V) was obtained, which is compatible to C-H diamond MOSFETs with no partial C-O channel. Here, the sizes of the device were L_SG = 4 μm, L_G = 15 μm and L_GD = 21 μm, respectively.The breakdown voltage of a partial C-O channel C-H diamond MOSFET was obtained 1790 V (L_GD = 21 μm, @RT). In addition, the highest breakdown voltage was obtained to 2021 V (L_GD = 24 μm, @RT) with V_th = -3.5 V. The breakdown voltage of >2 kV is the highest for diamond FETs ever reported. Threshold shift characteristics of C-H diamond MOSFETs with N doping will be exhibited on site.

[1] H. Kawarada et al., IEEE IEDM 14933800, pp.279 -282 (2014) and ISPSD pp483-486 (2016).
[2] A. Hiraiwa, H. Kawarada, et al., J. Appl. Phys. 112 (2012) 124504.
[3] H. Kawarada et al., Appl. Phys. Lett. 105 (2014) 013510.
[4] H. Umezawa, H. Kawarada, et al., J. Appl. Phys. Vol. 44, No. 11, pp.7789 -7794 (2005).
[5] J. W. Liu, Y. Koide, et al., Appl. Phys. Lett. 103 (2013) 092905.
[6] T. Suwa, M. Hatano, et al., IEEE Electron Device Lett. Vol. 37, No. 2, pp. 209 -211 (2016).

Gallium Nitiride (GaN) and diamond are two important materials in next generation power electronics and LEDs. Specifically, GaN-based transistors have high breakdown voltages and high carrier densities resulting in low resistance and high efficiency. However, as the gate size of GaN-based transistors decreases to achieve higher operating frequency, heat dissipation worsens due to boundary scattering and growth defects. It is important to limit the temperature rise in these devices because an increase in temperature will reduce electron mobility and degrade the lifetime of the device. Currently, the thermal properties of size-constrained GaN is not well characterized. In this work, we measure the thickness dependent thermal conductivity of a 15-1000nm thick GaN film heteroepitaxially grown on 4H-SiC using a unique pump-probe thermal imaging technique. Additionally, diamond grown on GaN has been proposed as a near-junction heat sink for GaN based devices. However, the thermal conductivity of these thin diamond films is difficult to measure. In this work, we also measure the anisotropic thickness dependent thermal conductivity of 1-100μm thick diamond films grown on silicon.

Diamond as a semiconductor material for electronics has potential due to its material properties including high thermal conductivity, high electric field breakdown strength, and high carrier mobilities. In this paper we will report on the diamond based power electronics work at the MSU/Fraunhofer Center for Coatings and Diamond Technologies (CCD). We will present our work to improve the quality of bulk and epitaxial mono-crystalline diamond material and its use in making vertical diamond diodes for power electronics. The desired diode characteristics in this project includes a reverse bias breakdown voltage exceeding 1000 V and a forward current exceeding 10 A. Work will be described that improves the quality of the bulk substrates by reducing the line defect (dislocation) density. Boron doped epitaxial layers are then grown on the cut substrates with conditions and processes to minimize the generation of new dislocation defects. Diode architectures being studied include a Schottky vertical diode, a Schottky quasi-vertical diode and these same structures with field plates of Al₂O₃. To make the diamond diodes, a heavily-doped p-type layer and a lightly-doped p-type layer are deposited in microwave plasma-assisted CVD reactors using boron as the dopant. Efforts are made during the lightly boron doped deposition to minimize the unwanted nitrogen and other impurity incorporation.

Diodes have been fabricated with both small Schottky contact areas of 150 micrometer diameter and larger Schottky contact areas of 2 mm². Various types of Schottky contacts have been used including gold, platinum and molybdenum. Diodes with the smaller contacts have been fabricated with breakdown voltages of over 1000 V and forward current flow densities of 500 A/cm². Diodes with the larger contacts have been fabricated with current flows up to 18 A and a current density of 900 A/cm². Diode characteristics are measured in the temperature range from 300-600 K and comparisons are made to device simulations using the MEDICI and Sentaurus TCAD semiconductor device simulators. In particular, simulation studies to better understand the reverse bias breakdown voltage and the forward on resistance will be discussed.

The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR0000455.

Diamond is expected to be a promising semiconductor for electronic applications, because of the excellent material properties of high breakdown electric field, high thermal conductivity, and so on. When we apply the diamond to the semiconductor electric devices, pn and pin junctions are the important base structure. However, these junctions have an issue, such as high specific on-resistance R_onS at the forward bias region, which is originated from the high resistivity of the p- and n-layers due to the deep dopant levels of impurities. For practical diamond pn and pin junction diodes, low-resistivity doping layer is needed.
In order to overcome this issue, we have fabricated diamond p⁺in⁺ junction diode (i-layer thickness is 200 nm) using heavily boron- (phosphorus-) doped p⁺ (n⁺) layers with the impurity concentration of the order of 10²⁰ cm^-3, which shows hopping conduction [1]. As a result, R_onS decreased to 2.2 mΩcm² at a forward bias of 20 V. This value is lower by 5 orders of magnitude than that of the conventional pin junction diode. On the other hand, the brocking voltage was maintained high value of 92.5 V (brocking electric field E_block: ~4.6 MV/cm) without any optimization of the device structure, and this E_block is higher than the Si and SiC material limits.
As another type of diamond diode, we have developed Schottky-pn diode, which is merged p⁺n junction with n-type Schottky junction tandemly [2]. By using the hopping p⁺ layer with impurity concentration of ~10²⁰ cm^-3, we can realize extremely high forward current density of over 10⁴ A/cm² (R_onS: ~10^-2 mΩcm²). The diamond pn⁺ and p⁺in⁺ junction structures are also useful for diamond UV-LED [3], electron emitter [4], and so on.
Moreover, the nin junction structure can be applied to the charge control of nitrogen-vacancy (NV) centers, which are the promising candidate for magnetmetry, quantum information science, and so on. For the viewpoint of these applications, the negatively charged centers (NV^-) are needed. By using the band bending of nin junctions, we controlled the Fermi-level in the i-layer as the higher energy level compared to the ground state of NV^-. Under this condition, NV centers in the i-layer are stabilized as the charge state of NV^- , while maintaining the long spin coherence time [5].
In this talk, we show the details of our approach concerning diamond pn, pin, and nin junction devices with various characteristics.
This work is partially supported by SIP (NEDO).

[1] T. Makino, et. al., Jpn. J. Appl. Phys. 53, 05FA12 (2014).
[2] T. Makino, et. al., Appl. Phys. Lett. 94, 262101(2009) .
[3] T. Makino, et. al., Appl. Phys. Lett. 99, 061110(2011) .
[4] D. Takeuchi, et. al., Phys. Stat. Solidi A, 210, 10 (2013).
[5] M. Shimizu, et. al., Diamond Relat. Mater., 63, 192 (2016).

Having a thermal conductivity 17 time greater than GaN along with high free carrier mobilities may allow the speed-power performance of diamond FETs to surpass that of AlGaN based FETs. Already groups have demonstrated transfer doped RF FET performances with Ft = 53 GHz or Fmax = 120 GHz, in a FET structures consisting of an acceptor layer on a hydrogenated diamond surface. Along with high speed, devices require good switching performance for use in communication and radar systems. We will discuss the switching performance and relevant analysis of our transfer doped diamond FETs.
For transfer doped transistors, hydrogenation of the surface leads to the diamond acquiring a negative electron affinity that then gives the surface the proper energy band alignment to provide electrons to the adjacent acceptor layer resulting in a hole conducting channel in the diamond surface region. Transistors we have fabricated in house with gate length of 2.5 micron and gate width of 60 micron, on diamond substrates sourced from several vendors, have demonstrated good gate control, handling current densities of over 80 mA/mm and repeatable performance up to Vds = 60 V, with breakdown voltages over 100 V. Also, the effective mobility in these FET structures has been measured to reach 30 cm²/V/s.
However, transient switching performance has indicated current collapse and gate-lag or drain-lag effects due to traps at the interface and within the diamond layer. Holding the bias to fill or empty traps before the bias scan indicates two different transients, one roughly 150 ms, and the other roughly 1.5 sec. To understand the types of traps present we have used the conductance method and observed interface trap densities up to 1×10¹³ eV^-1cm^-2, and trap lifetimes in the range of ms to microseconds. These measurements utilize a probe station with an instrument guard that completely surrounds the wafer to minimize stray effects of the environment and room. The acceptor layer involved in transfer doping in these devices is formed by atmospheric surface adsorbates. Interface traps, once charged can act as a virtual gate that affects power handling. Because the diamond surface quality has a strong effect on the interface trap density, we also used AFM, SEM and differential contrast imaging to monitor diamond substrate quality both as obtained, and after hydrogenation.
To reduce trap related delays and improve power handling, we are now moving to an electron-beam evaporated MoO₃ acceptor layer instead of the adsorbates. Using this transfer doping layer results in a van der Pauw sheet resistance of the diamond typically 10 times lower than with atmospherics. We are using Raman to verify the phase and stoichiometry of this oxide that is thermally deposited on diamond.

Power devices made of diamond have remarkable potentials based on the highest breakdown field and the thermal conductivity. We have reported high blocking voltages in planar type C-H diamond MOSFETs [1]. Hydrogen terminated diamond surface induces 2 dimensional hole gas (2DHG) layer and become a p-type channel of FETs. The planar C-H diamond MOSFETs have well controlled the source-drain current, but have the difficulty in improving the current density normalized by the device lateral area including large drift region. To achieve high current density, it is inevitable to form vertical-shaped devices to stow the large drift area.
AlGaN/GaN-HEMT is well-known as FET utilizing two-dimensional electron gas (2DEG). Since the 2DEG layer is induced by spontaneous- and piezo- polarization at (0001)AlGaN/GaN interfaces, the 2DEG layer cannot be formed at the surface other than (0001). such as the sidewall of GaN (0001). On the contrary, C-H diamond surface and Al₂O₃ layer formed by atomic layer deposition (ALD) (a passivation layer and a gate insulator), induce two-dimensional hole gas (2DHG). The 2DHG on C-H diamond covered by ALD-Al₂O₃ can be ubiquitously formed on any crystal surface, even on the sidewall. This is very advantageous to fabricate vertical type devices. In this study, we fabricated the vertical type C-H diamond power MOSFETs and confirmed the vertical current through trench.[2]
We fabricated C-H diamond vertical type MOSFETs with trench-channel structure. A nitrogen doped layer about 3μm was grown on p⁺ diamond substrate (boron concentration of 1×10¹⁹ cm^-3). Trench structure with the depth of about 3 μm was formed by inductively coupled plasma ion etching (ICP-RIE). To form 2DHG on to the diamond top surface and the sidewall of trench, 500 nm-thick undoped layer was regrown. The undoped layer conceals the damages by plasma etching. Next, Ti/Au were deposited as a source electrode. Al₂O₃ formed by ALD was deposited as a gate insulator. Finally, Al as gate electrode and Au as backside drain electrode were deposited.
As a result, the maximum of the drain current was ~4 mA/mm and clear drain current modulation by gate voltage was observed, but large on-set [HK1] voltage of -40 V existed. This is due to the existence of 500 nm-thick undoped layer at the bottom of the trench. This undoped layer behaves as intrinsic semiconductor. When applying -40 < VDS < 0 V, the potential of p+ diamond goes up and simultaneously the Fermi level of the i-layer goes up. However, in this condition, the valence band of the i-layer is still convex downward and I_DS hardly increases. When applying VDS < -40 V, the potential of p+ diamond further goes up, the valence band of the i-layer shows monotonic increase, and the hole carrier starts to drift, then IDS starts to increase (on-set).


[1] H. Kawarada, et al., Appl. Phys. Lett. 105, 013510 (2014), IEDM p.279 (2014), ISPSD p.483 (2016).
[2] M. Inaba, H. Kawarada, et al., Appl. Phys. Lett. 2016 (in press).

Due to its superior electrical properties diamond is the ultimate material for power devices. Nowadays, one of the main challenges is to fabricate power metal-oxide-semiconductor (MOS) transistors. In such device, oxide quality and its interface with diamond is the main concern. It affects current and breakdown capabilities. Several groups are investigating on the interface state, band alignment and Fermi-level pinning issues related to the Al₂O₃/p- boron doped diamond interface by performing an electrical characterization of diamond MOS capacitor.
In this study we explored Al₂O₃ in metal-insulator-metal (MIM) capacitors (MIMCAPs), with heavily doped diamond acting as metallic back electrode. Different parameters that influence the oxide quality have been explored: Al₂O₃ deposition temperature, size and pattern of the MIMCAP, substrate crystalline quality and top metallic contact composition. MIMCAP have been characterized by optical profilometry, and electrical measurements (I(V), C(V)).
The starting materials are HPHT Ib diamond crystals of various crystalline quality, with 700 nm of boron p⁺ (10²¹ cm^-3) metallic grown by CVD. Al₂O₃ was grown by ALD between 250 and 380 degree C, prior to Ti/Pt/Au or Pt/Au top metallization.
Results show the importance of capacitance design: The smaller the MIM metal contact, the higher the dielectric constant. In addition, according to the profilometry analysis, the substrate quality might also be responsible for low electric field breakdown of MIMCAP.
Effect of design and process parameters on oxide quality, reproducibility and repeatability will be presented

Attention to diamond as an electronic material is receiving international attention due to the improvements in the growth of synthetic diamond by both chemical vapor deposition (CVD) and high pressure high temperature (HPHT) techniques. Diamond offers significant advantages over other semiconductor materials due to its high electrical breakdown strength, high carrier mobilities, high thermal diffusivity, and other exceptional properties. Diamond semiconductor devices will likely impact applications in high power, high frequency, high temperature, and/or harsh or corrosive environments. One of the strategies for enabling active electronic devices based on diamond is ‘delta doping’ with an electronically active impurity dopant (donor or acceptor).
In this paper the research results on the investigation of boron-doped delta-layer growth are presented. Investigations were made on a new type of CVD reactor designed for growth of delta layers inside the single-crystalline CVD diamond [1]. The reactor consists of a cylindrical cavity resonator with a quartz tube placed inside, in which the plasma is created by the magnetron with 2.45 GHz frequency. Main features of this reactor are an ultra-rapid reactant gas switching system, high velocity laminar flow, independent control of substrate temperature. This approach allowed us to obtain heavily boron doped thin layers and to implement two-dimensional hole "gas" in diamond with high mobility and hole concentrations. At experiments extreme care was taken to substrate preparation, quality and roughness. Boron concentration in the delta layer and the doping profile was determined by SIMS method. As the result of experiments we found the optimal diamond deposition regime which allows obtaining doped delta layers with thickness of 1-2 nm with concentrations of boron greater than 2 10²⁰ cm^-3. Such thin doped layers are highly desirable for the development of diamond-based field-effect transistor and other next generation electronic devices.
[1] A. L. Vikharev, A. M. Gorbachev, M. A. Lobaev, et. al, Phys. Status Solidi RRL, 1–4 (2016) DOI 10.1002/pssr.201510453

NV center in diamond has been extensively interested because the single spin of it can be manipulated and detected at room temperature (RT). Furthermore, coherence time (T₂) of the NV center is very long. T₂ is the time to retain coherence and directly relates to the sensitivity of magnetic sensor. Therefore, the unique and excellent properties are expected to be applied for quantum computing, quantum communication and high-sensitive magnetic sensor with nano-scale resolution. By using the NV center, we previously investigated the quantum entanglement generation [1], spin coherence properties [2], and quantum coupling with a flux-qubit [3]. Furthermore, we realized a stable room temperature electrically driven single-photon source based on a single NV centre by fabricating p-i-n diode [4].
Recently, we realized deterministic electrical charge-state control of single NV- center [5] by using a p-i-n diode that facilitates the delivery of charge carriers to the defect for charge state switching. By developing this technique for the decoupling of nuclear spins from the NV electron spin, realization of quantum memory of nuclear spin with very long T₂ can be expected. Furthermore, we show Fermi level control by phosphorus doping generates pure NV⁻ (more than 99%) [6]. The pure NV⁻ shows a five-fold increase of luminescence and a four-fold enhancement of an optically detected magnetic resonance under 593 nm excitation compared with those in intrinsic diamond. In addition, we also realized nearly perfect alignment (more than 99 %) of the NV axis along the [111]-axis and revealed the mechanism of the alignment during CVD growth [7,8]. This result enables a improvement of optical detection efficiency for spin information in quantum device and a fourfold improvement in magnetic-field sensitivity.
These achievements are considered to be a crucial step towards elaborated diamond-based quantum devices which is operated by single spin, single photon, and single charge.

The research was carried out by Osaka Univ. group, Kyoto Univ. group and the collaboration with AIST group (T. Makino, H. Kato, T. Miyazaki, Y. Miyamoto, D. Takeuchi, M. Ogura, H. Okushi, S. Yamasaki), Tokyo Tech. Univ. (Prof. M. Hatano), Stuttgart Univ. group (M. Nothaft, P. Neumann, F. Jelezko, J. Wrachtrup), A. Gali. The research was supported by CREST and KAKENHI.

[1] P. Neumann, & NM, et al., Science, 320, 1326 (2008).
[2] N. Mizuochi, et al., Phys. Rev. B, 80, 041201(R) (2009).
[3] X. Zhu, & NM, et al., Nature, 478, 221 (2011).
[4] N. Mizuochi et al., Nature Photon. 6, 299 (2012).
[5] Y. Doi, & NM, et al., Phys. Rev. X. 4, 01107 (2014).
[6] Y. Doi, & NM, et al., Phys. Rev. B, 93, 081203 (R), 2016.
[7] T. Fukui, & NM, et al., Appl. Phys. Express 7, 055201 (2014).
[8] T. Miyazaki, & NM, et al., Appl. Phys. Lett., 105, 261601 (2014).

The nitrogen vacancy (NV) center in diamond is a single-spin defect that is highly sensitive to magnetic fields. Because it is an optically addressable, biocompatible sensor that operates under ambient conditions, an NV center ensemble is an excellent candidate for time-resolved, wide-field imaging of magnetic phenomena in biological samples. An outstanding challenge to realizing an NV center-based magnetometer is to improve its sensitivity by increasing NV ensemble density while maintaining long spin coherence times, which are reduced at sufficiently high nitrogen densities. To address this challenge we have developed a technique that combines nitrogen-doped plasma enhanced chemical vapor deposition (PECVD) grown diamond with electron irradiation from a transmission electron microscope (TEM) [1]. This method produces ensembles of NV centers in a nitrogen δ-doped layer that maintain coherence times longer than 1 ms. We extend this work by increasing the thickness of the nitrogen-doped layer from 2 nanometers to several hundred nanometers to achieve an expected magnetic field sensitivity of < 10 nT/√Hz in a diffraction-limited optical spot. We quantify the NV density and the nitrogen density and hence magnetometer sensitivity in the thicker nitrogen-doped material via double electron-electron resonance (DEER) with a homebuilt EPR system operating at 4.1 T and 115 GHz [2]. Optimizing NV concentration, N concentration, and NV spin coherence times is crucial to measuring small biological magnetic fields. We present initial images of biological samples using our tailored NV-ensemble sensors.

[1] C. A. McLellan, B. A. Myers, S. Kraemer, K. Ohno, D. D. Awschalom, A. C. Bleszynski Jayich Nano Lett. 16, 2450-2454 (2016).
[2] V. Stepanov, S. Takahashi, Arxiv Prepr. arXiv:1603.07404 (2016).

The nitrogen vacancy (NV) center in diamond is known as a promising candidate for quantum information processing and sensing of external spins due to its outstanding properties at room temperature. For many applications, near-surface NV centers are created by low-energy nitrogen implantation followed by thermal annealing. In spite of many advantages, the resulting NV centers still show degraded spin properties in comparison to centers hosted in bulk.

In this work we present a novel method to improve the characteristics of near-surface NV centers by means of nitrogen implantation across a p⁺-i junction on the diamond surface (by overgrowth of heavily boron-doped thin layers), coupled to a detailed analysis of spin defects presented within individual ion tracks. We demonstrate T₂ times up to fivefold improved (~ 180 μs) and T₁ times in the range of ~ 6 ms for NV centers with depths below 8 nm (1.1% ¹³C).

Spin noise spectroscopy technique was applied to derive the contribution of the magnetic noise arising from implantation-induced defects within individual ion tracks. This analysis revealed that nitrogen implantation across such p⁺-i junction leads to a suppression of vacancy-related defects within the space charge of out-diffused carriers (holes) at the p⁺-i interface during thermal annealing. Simulation of the implantation/annealing processes by means of Molecular Dynamic and Monte-Carlo tools indicate that the main source of spin decoherence is potentially the formation of divacancies in the nanometric proximity of individual NV centers, which occurs during thermal annealing without the space charge of carriers.

Based on these results, we extend our method towards the creation of strongly coupled pairs of NV centers using low energy molecular ion implantation (i.e. CN^- and N₂⁺) across a p⁺-i junction. The first results demonstrate that the efficiency related to the formation of NV centers might be improved even further.

Color centers in diamond have potential applications in quantum information processing. Other than nitrogen-vacancy center (NV^–), silicon-vacancy (SiV^–) center gains most of the attention due to its outstanding properties. The emission is constituted of ~70% zero-phonon line (ZPL) transition, thus making SiV^– a promising single photon source. Also, SiV^– center is more durable through the nano-fabrication procedures compared to NV^– center. There have been literatures demonstrating that SiV^– centers fabricated inside nanostructures could have nearly lifetime limited optical linewidths and small spectral diffusions.

Plasmonic nano-resonator is one of the cavities that can strongly enhance the spontaneous decay rate and absorption efficiency. This makes them suitable platforms for enhancing single photon emission. In this work, we designed and fabricated plasmonic nano-resonators for SiV^– centers. Simulations show that the Purcell enhancements for circular apertures and for 20 nm gap bowtie apertures are ~15 and ~90, using a 3-D FDTD algorithm (Lumerical). The fabrication started from e-beam patterning on diluted neagative-tone electron resist (hydrogen silsesquioxane, HSQ). Then, reactive ion etching (RIE) was used to create diamond pillars and isolate SiV^– centers. Next, gold was deposited to surround diamond pillars using e-beam evaporation. Later, 650°C annealing for 7 minutes was applied in order to make gold re-flow and fill the gap between gold and diamond. Finally, sonication and lift-off were performed to get clean diamond gold apertures. The device is pumped and collected from top of the substrate, in order to have higher collection efficiency.

A pulsed Ti:Sapphire laser with monochromator generates pico-second laser pulses with 15-20 GHz laser linewidth. This enables us to scan over the transitions of SiV^– centers, and address individual SiV^– in temperature as low as 6-8 K. Some preliminary measurements showed that some SiV^– centers inside circular apertures can have lifetime as short as 0.35 ns, which is a factor of ~5 of lifetime reduction (~1.8 ns lifetime for SiV^– in bulk diamond). Also, we could often see the SiV^– transitions spanning over a relatively wide range (7-8 nm) compared to the transitions in bulk diamond, implying that there might be induced large local strains inside those plasmonic apertures. More measurements are ongoing to investigate the behaviors and fluorescence enhancement of SiV^– centers in those plasmonic nano-resonators.

Quantum single emitters in diamond are expected for various applications, such as quantum information processing, quantum cryptography, and quantum sensing. These applications require quantum emitters fabricated in a deterministic way with site selectivity, the controlled number of emitters, and uniform optical characteristics. So far, it has been shown that focused ion beam is useful for the fabrication of emitters [1]. However, damages to the diamond lattice by ion bombardment is inevitable. Although CVD formation leads to more uniform fluorescence, color centers are randomly formed without the site selectivity. In this study, we demonstrate more controlled CVD formation of emitters by using the dependence of the impurity incorporation on the diamond surface morphology.
NV, SiV, and GeV emitters were formed by microwave plasma CVD using H₂/CH₄ gases. The GeV center is a new quantum emitter which we have recently reported [2]. Gas or solid materials were used as the impurity sources. Sidewalls of pits or steps formed on the diamond surface were utilized as the selective formation sites of the emitters. The crystal faces of the sidewalls of the pits were [112] on the (001) and [113] on the (111) substrates. We found that the color centers can be preferentially incorporated on the sidewalls, while no or less emitters were formed on the flat surface and smooth terraces. The fluorescence intensity (the number of emitters) varied depending on the length and height of the sidewalls. We confirmed for GeV center that the fluorescence intensity decreased as the sidewall length became shorter. When the length went down to 300 nm with 20 nm height, an array of emitters with the diffraction-limited spot size was obtained. Although we observed spots containing a higher amount of the GeV center even on the short sidewall, the emitters show uniform ZPL wavelength at 602 nm. Thus, it is expected that the proposed method can achieve the deterministic CVD formation of emitters with high site selectivity, control of single photon source, and stable optical properties by more precisely controlling the area of the sidewalls, which will be done with sophisticated semiconductor processes we have developed [3,4].

[1] M. Lesik, et al., Phys. Status Solidi A, 210, 2055, 2013.
[2] T. Iwasaki, et al., Sci. Rep., 5, 12882, 2015.
[3] T. Iwasaki, ea at., Appl. Phys. Express 5, 091301, 2012.
[4] T. Suwa, et al., IEEE Electron Device Lett., 37, 209, 2016.

Recent work has demonstrated the potential to increase the carrier density and stability of surface transfer doping in hydrogenated diamond using oxides films such as MoO₃ [1] and V₂O₅ [2]. Understanding the operation and physical and chemical structure of these oxide materials is vital for the successful implementation in diamond-based electronic devices such as field effect transistors.
Progress made and the challenges yet faced in the development of these materials for enhanced surface transfer doping of diamond and advanced electronic device performance and stability will be discussed.
[1] Stephen A. O. Russell et al, Applied Physics Letters, Volume 103, Issue 22, 202112, November 2013
[2] Kevin G. Crawford, Liang Cao, Dongchen Qi, Alexandre Tallaire, E. Limiti, C. Verona, Andrew T. S. Wee and David A. J. Moran, Appl. Phys. Lett. 108, 042103 (2016)

After many years of development, AlGaN/GaN 2-D electron-gas FETs have revolutionized the power RF field. With a similar development effort to harness its superior semiconductor properties, diamond is expected to enable devices with an order of magnitude increase in performance. Primary among the development challenges is a stable, high conductivity active FET channel.

Hydrogen-terminated diamond, with the appropriate surface treatment, forms a 2-D hole gas at its surface. Electron acceptors (NO₂, O₃, and Cl₂) increase the conductance while electron donors (NH₃ and NH₂C₆H₅) diminish the conductance. All these surface dopants are unstable in air with their properties diminishing in time.

We report a different doping approach using UV-generated free radicals. We theorize that these radicals abstract hydrogen from the diamond surface and insert themselves at that site. The resulting surface has stability comparable to ALD-deposited Al₂O₃ and conductivity comparable to the most effective surface treatments reported to date.

Surface conductivity was measured with a Hall – Van der Pauw system to quantify carrier type, density, and mobility. The enhanced conductivity is often observed to be the result of increased carrier mobility instead of increased carrier density. These results indicate that a model of diamond surface conductivity that only considers the dopants as negatively charged states to generate holes is incomplete.

We have also explored the impact of variations in physical properties on surface conductivity. We will report on the relative impacts of surface roughness, sub-surface polishing damage, chemical purity, bulk stress, and growth method.

This presentation will discuss our work on free-radical-doped diamond surfaces and efforts toward maximizing the conductivity and stability.

DISTRIBUTION STATEMENT A. Approved for public release: distribution unlimited. This material is based upon work supported by the Assistant Secretary of Defense for Research and Engineering under Air Force Contract No. FA8721-05-C-0002 and/or FA8702-15-D-0001. Any opinions, findings, conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Assistant Secretary of Defense for Research and Engineering.

The chemical composition and electronic structure in the near surface region of diamond thin films influences the operation of sensors and electronic devices and can also affect the optical and spin properties of diamond quantum devices. Control of the chemical and physical nature of the surface can provide effective methods for developing and controlling diamond-based applications. In this work, we have applied surface analysis methods (PhotoElectron Spectroscopy (PES), REal-time Electron Spectroscopy (REES) and Low Energy Electron Diffraction (LEED)) in parallel and in real-time to investigate the chemical composition and electronic structure of the oxygen-terminated (001) surface of moderately B-doped diamond. These studies have revealed that the desorption of oxygen species does not follow a simple temperature dependence and we have identified specific regimes where surface and sub-surface bonding changes occur that strongly affect the electronic structure.

Single-crystals of CVD-grown diamond with (001) orientation were prepared by mechanical polishing and wet acid etching to produce oxygen-terminated surfaces, whose composition, work function and structure were determined in-situ using ultraviolet and x-ray excited XPS and LEED. Surfaces were characterized following a series of annealing cycles up to a temperature (1000 C) where the oxygen was fully desorbed. By monitoring the desorption in real-time, different temperature ranges and transition points were discovered. The O1s and C1s PES core level peak intensity variation at different temperatures provided the rate of oxygen desorption and the activation energy. The core level peak position is sensitive to chemical and physical changes and in this case, the temperature evolution of the main diamond C1s was used to detect changes in surface conductivity and band-bending. Coupled with ultraviolet PES and LEED measurements, these real-time data provided a model that involved distinct regimes of oxygen desorption from C-O (ether and alcohol) and C=O (ketone) sites with an associated reduction in the surface band-bending, correlated with the amount of surface oxide species remaining. A decrease in the surface work function and a change in the surface periodicity was observed at the highest temperatures (~ 1000 C) that indicated a replacement of oxygen by hydrogen. Control of this process thus enables the selection of processing conditions to provide a composition between fully O-terminated and H-terminated surfaces, a range of work function values of several eV from positive to negative and a surface band-bending variation of over 1 eV.

Detection and identification of Volatile Organic Compounds (VOC) find a real interest in several domains (Security, Pollution, medical). Today progress on the synthesis of CVD diamond offers a real breakthrough for this material to be used for the fabrication of resonant MEMS taking advantage of its high Young’s modulus. We have developed a specific process to achieve diamond cantilevers with embedded polysilicon gauges. A complete mechanical characterization was done to evaluate the Young’s modulus with values between 930 and 1300 GPa. The resonance frequency of cantilevers has also been evaluated by laser Doppler vibrometer and varies from 100 kHz to 160 kHz.
These cantilevers were integrated in a multi-sensor cell to achieve an artificial nose. The specific surface functionalization of each cantilever renders its sensitivity partially specific to a family of species. A range of chemical functions have been selected including halogen groups, chemical functions, proteins(OBPs etc) using adapted grafting and coating techniques (spray coating, covalent binding etc…). To achieve the detection and identification of these VOCs we developed an electronic nose using 8 individual diamond cantilevers mounted in a specific gas cell. To record the evolution of the cantilevers a low noise and reconfigurable electronics has been designed as well as a dedicated human-machine interface. The system has been evaluated in lab with different gas and concentration to evaluate the sensitivity and the limits of detection.

Nanocrystalline diamond (NCD) is well known for its superior mechanical, optical and chemical properties. Also, its outstanding electrical properties are moving more and more in the focus of interest. Ultra-nanocrystalline diamond (UNCD) films are deposited by using hot filament chemical vapor deposition (HFCVD) technique with varying electrical conductivity depending on processing conditions.
UNCD films exhibit generally n-type conductivity, temperature stability up to almost 1000 °C and adjustable specific resistivity from 10^-8 S/cm to 100 S/cm without the loss of the outstanding mechanical properties. The specific conductivity seems to be influenced by the microstructure, the ratio of sp²-to-sp³ carbon bonds and the atomic structure of the sp² carbon bonds within the grain boundary region. The average grain size of electrically conductive nanocrystalline diamond films, measured by X-ray diffraction and electron microscopy is less than 8 nm and shows statistically randomly distributed orientations. Temperature dependent measurements of the electrical resistivity demonstrate a negative temperature coefficient in the entire temperature range from 4 K to 1200 K. Hall effect measurements reveal a constant carrier concentration of 3×10¹⁹ cm^-3. These electrical properties are further correlated with experiments using Raman spectroscopy and electron energy loss spectroscopy (EELS). Both measurements reveal differences in the structure of the sp² carbon bonds within the grain boundary region.
Concerning applications in biomedical engineering it turns out that long-term stability, biocompatibility, chemical inertness and a variable surface chemistry leads to a biointerface with enormous potential. Cavitation generating diamond devices have been realized by micro diamond devices. Due to their small size of about half a square millimeter and their outstanding mechanical stability, this technique allows minimally invasive surgery. That represents a new method to remove human tissue, for example in eye surgery and other situations where organic matter has to be removed.

Optically active impurity defects in diamond have attracted enormous interest in biolabeling^[1], quantum computing, quantum entanglement and encryption, owing to their unique physical, mechanical, and electronic properties. Today, diamond can be synthesized by high-pressure-high-temperature (HPHT) and chemical vapor deposition (CVD)^[2] methods. However, formidable challenges remain in the synthesis of nano-meter size single crystal diamonds with desired internal color-centers. Here we present a novel diamond synthesis method using diamondoid^[3] seeds chemically attached to a substrate, and a vertical, rather than horizontal, stage-substrate geometry. In this configuration there is a large gradient in the plasma electron density, temperature, and atomic hydrogen concentration along the length of the substrate, effectively exploring numerous growth conditions simultaneously. This process allows for rapid identification of the optimal conditions for diamond growth, producing a range of diamond nanocrystal sizes and qualities as a function of the vertical gradient. Using this novel process, we have demonstrated the controlled growth of high-quality, single-crystal nanodiamonds down to the 10 nm size range. In addition, this technique can readily incorporate optically active centers in the 75 nm size range, including Silicon-Vacancy (Si-V) color centers. This new methodology allows facile growth of very small, high-quality diamonds with a wide variety of different color centers (e.g. Chromium, Germanium, Europium, and Nickel.) without ion irradiation damage.

Reference:
[1] Wu, T.-J. & Tzeng, Y.-K. et al. Tracking the engraftment and regenerative capabilities of
transplanted lung stem cells using fluorescent nanodiamonds. Nat. Nanotechnol. 8, 682-9
(2013).
[2] Butler, J. E. & Sumant, A. V. The CVD of nanodiamond materials. Chem Vap. Depos. 14, 145-
160 (2008).
[3] Fokin, A. a. et al. Selective preparation of diamondoid phosphonates. J. Org. Chem. 79, 5369–5373
(2014).

Following the discovery that diamond undergoes a metal-insulator transition through increasing the concentration of boron dopants, it was also found to become a superconductor. By understanding the low temperature properties of this material, the superlative mechanical properties of diamond may be harnessed whilst exploiting the superconductivity to fabricate Nano Electro-Mechanical devices alongside and integrated with other quantum devices.

Through efforts to understand the impact of the material growth on the superconducting properties, results are presented obtained from a series of films with varying thickness, boron concentration, and surface roughness systematically controlled during growth. The transport and magnetisation properties of these films have been studied at low temperatures. The experimental results are presented, and the anticipated impact on device fabrication is discussed.

Nitrogen-Vacancy (NV) color center in diamond is an exceptional material platform for quantum sensing applications. Electron spin state of NV centers works as a quantum magnetometer with optical read out which can be operated at room temperature. Its applications are limited by magnetic sensitivity which is determined by alignment, density and spin coherent time T₂ of NV centers. Quantum sensing applications such as Nano NMR requires highly aligned, high density delta doped NV center film close to the surface for high magnetic sensitivity. Previous studies on obtaining delta doped NV center diamond films are limited only on (100) substrates[1,2,3]. For growth of highly aligned NV center diamond films, CVD growth using (111) substrates has been shown to be effective[4]. In this study, step-flow growth mode was used to obtain highly aligned delta doped NV center diamond films less than 34nm from surface on the (111) substrates. High magnetic sensitivity was confirmed by detection of hydrogen nuclear spin using XY8 pulse sequence.
For realization of step-flow growth, Ib (111) HPHT substrate was polished along <-1-12> direction with 2°off angle. Intrinsic diamond film with 2um thickness was grown by CVD system on top of substrate with CH4/H2(0.05%). Finally, N₂ gas was introduced into CVD system (0.04%) to form delta doped diamond layer with nitrogen. Intrinsic layer was introduced to avoid influence of the Ib (111) HPHT substrate on the photoluminescence obtained from delta doped layer.
Nitrogen layer (>10¹⁸ [cm^-3]) with varied thicknesses for different growth time was confirmed by SIMS (Secondary Ion Mass Spectrometry) measurement. SIMS measurement confirmed delta doped layer to be within 34nm of surface. In the intrinsic layer, background level nitrogen (<5x10¹⁶ [cm^-3]) was confirmed from SIMS measurement. ODMR (Optically Detected Magnetic Resonance) spectrum obtained from 34nm delta doped layer of NV diamond film confirms alignment of NV center along [111] direction with more than 85% of alignment ratio.
Finally, Nano NMR was performed using highly aligned, high density delta dope NV center film using XY8 pulse sequence. Nuclear spin signal corresponding to hydrogen nuclear spin was confirmed by its Larmor frequency observed in Nano NMR. Nano NMR was used to investigate effective depth of delta doped NV center layer for nuclear spin detection.

[1] K.Ohno et al. APL 101, 082413 (2012)
[2] K.Ohashi et al. Nano Letters 13, 4733-4738 (2013)
[3] C.Osterkamp et al. APL 106, 113109 (2015)
[4] K.Tahara et al. APL 107, 193110 (2015)

The high electron and hole mobilities and the high breakdown field make diamond an ideal material for bipolar vertical high power, high voltage devices. Using B-doped diamond substrates this research reports optimization of the phosphorus-doped n-type layer, and the undoped intrinsic layer to obtain high voltage and high current diodes. The p-i-n diodes on (100) diamond show characteristics that indicate a fully depleted n-type layer. These devices show a blocking voltage that approaches 1000V, a forward turn on at less than 1V and current densities greater than 100A/cm² at 4V. The p-i-n diodes on (111) diamond substrates show a high breakdown field of ~4MV/cm and light emission indicating bipolar operation. The potential blocking voltage and current characteristics for the p-i-n device structures are discussed in terms of the diamond materials properties that have led to projections of mobilities greater than 4000 cm²/V-s and breakdown fields greater 10 MV/cm.
This research supported through the ARPA-E SWITCHES program.

Due to its extraordinary properties of radiation hardness, thermal conductivity and large bandgap, diamond is an ideal material for X-ray detectors. Traditional diamond X-ray detectors are fabricated with metal contacts, such as platinum, and provide absolute flux calibration and position resolution better than 50nm. However, for many energy scanning applications the absorption edges from the metallic contacts effect the downstream experiment. Therefore, we have incorporated a thin conducting ultrananocrystalline diamond (UNCD) as the contact material, which shares all the benefits of diamond without the absorption edges associated with metal contacts. We will present results from several detectors fabricated with UNCD contacts where the contacts have been patterned with reactive ion etching into quadrant or pixelated channel devices. The UNCD is grown at the Center for Nanoscale Materials at Argonne National Laboratory. The design, preparation and patterning are done at the Center for Functional Nanomaterials at Brookhaven National Laboratory. The detectors were tested at Cornell High Energy Synchrotron Source and they display uniform response and full collection.

Diamond is naturally an electrical insulator, but shows superconductivity when the doped boron concentration is more than 3×10²⁰ cm^-3 [1][2]. Superconducting transition temperature (T_C) of boron-doped diamond can be controlled by boron concentration and plane orientation [3][4]. The maximum Tc of (111) diamond is 10K with high critical fields and its tolerance to heat and acid supports fabrication of complex micro superconducting devices. However, there are few reports on boron-doped diamond superconducting devices [5][6]. So we report the fabrication process and characteristics of superconducting (111) boron-doped diamond Josephson junction with regrowth-induced (100) step edge structure. Josephson junction is a significant parameter of Superconducting Quantum Interference Devices (SQUID), which can measure micro-magnetic field with high sensitivity. The structure of step edge affects the characteristics of Josephson junction, so we investigated the characteristics of regrowth-induced (100) step edge structure.
We formed the vertical step of 230 nm on the High Pressure and High Temperature (HPHT) Ib type (111) diamond substrate by selective O₂ plasma etching. Then un-doped diamond layer of 200 nm was synthesized by Micro-wave Plasma enhanced Chemical Vapor Deposition (MPCVD) method in order to form the regrowth-induced (100) step edge structure. Superconducting boron-doped diamond layer of 200 nm was selectively grown by MPCVD method. Formation of the step edge structure was observed by Scanning Electron Microscopy (SEM). The angle of regrowth-induced (001) step was in agreement with that of the theoretical plane orientation (55° from (111) axis). The temperature dependence of resistivity shows that the resistivity slightly increases with decreasing temperature from 300K to 9K. When it decreases to less than 2 % of the maximum resistivity of the normal-conducting state at 9K, it shows zero resistivity at 4K. These values correspond to the transition temperature of (111) and (001) diamond [4]. Current-Voltage (I-V) characteristics of Josephson junction from 1.3K to 3.0K show over-dumped type I-V curve with no hysteresis. The critical current density of Josephson junction exponentially increased with decreasing temperature. This trend suggests a weak link type Josephson junction. The maximum critical current density was 8300 A/cm² at 1.5K. Shapiro steps was observed at 20 μV with microwave radiation of frequency ω/2π =10 GHz at 2.8K.
We observed DC and AC Josephson effect, achieved the fabrication of superconducting boron-doped diamond Josephson junction with regrowth-induced step edge structure.

[1] E. A. Ekimov et al., Nature. 428 (2004) 542.
[2] Y.Takano, H.kawarada et al, Appl. Phys. Lett. 85 (2004) 2851.
[3] E. Bustarret et al., Phys. Rev. Lett. 93 (2004) 237005.
[4] A.Kawano, H.kawarada et al., Phys. Rev. B 82 (2010) 085318.
[5] S. Mandal et al., ACS Nano. (2011) 5(9) pp7144–7148
[6] M.Watanabe, H.kawarada et al., Phys. Rev. B 85 (2012) 184516.

Nitrogen-vacancy (NV) centers in diamond are the most promising candidate for various applications such as quantum information science, magnetometry, and biosensing. For these applications, controlling the charge state of the NV centers is crucial, because optical initialization and readout of the spin state of the NV centers are only possible in negatively charged one (NV⁻). However, upon illumination, the NV centers undergo stochastic charge-state transitions between NV⁻ and neutral charge state of the NV center (NV⁰). In case of 532 nm excitation, the steady-state-population of NV⁻ is about 70%. This charge-state interconversion occurs upon illumination at any wavelength, so the steady-state NV⁻ population is always less than 75%–80%.
Recently, we showed Fermi level control by phosphorus doping generates 99.4 ± 0.1% NV⁻ under 1 mW and 593 nm excitation which is close to maximum absorption of NV⁻. [1] However, the results of spin coherence time (T₂) are shorter than the expected values. The reason can be attributed to other impurities or defects generated during CVD growth [2] because phosphorus concentration about 10¹⁶ atoms/cm³ in the n-type diamond is not high enough to cause the short T₂. In other words, if these impurities or defects could be removed, T₂ in n-type diamond should become comparable to the long T₂ of high-quality intrinsic undoped (i-) diamond.
On the other hand, from the theoretical estimation of a band bending of an nin diamond junction, the stabilization of the charge state of NV⁻ in i-diamond can be expected. Therefore, by using the nin diamond junction, both of the long T₂ and the stabilization of the charge state of NV⁻ can be expected. Here, to realize such stabilization of the charge state of NV⁻ in i-diamond film, we investigate nin diamond junction. In our experiment, we observed the effects on the charge states, which can be attributed to the band bending in the nin diamond junction. In the presentation, the details of the experimental results will be shown.
This work was supported by CREST and KAKENHI (No. 15H05868, 16H02088).

[1] Y. Doi, T. Fukui, H. Kato, T. Makino, S. Yamasaki, S. Miwa, F. Jelezko, Y. Suzuki, N. Mizuochi, Physical Review B, 93, 081203 (R), (2016).
[2] N. Mizuochi, H. Watanabe, J. Isoya, H. Okushi, and S. Yamasaki, Diamond and Related Materials, 13, 765 (2004).

To open a route for realization Diamond Metal Oxide Semiconductor Field Effect Transistor (MOSFET), there are numbered investigations on oxygen-terminated diamond (O-Diamond) Metal Oxide Semiconductor capacitors (MOSCAPs). However, high gate leakage currents are generally observed for positive [1-3] and negative gate bias voltage [1,3]. This electrical current is critical for the control of the carrier population at the interfaces and so, is one of the most critical issue for the device fabrication.

In a previous work, we investigated the gate leakage mechanism and its relationship with capacitance-frequency dependence for negative bias [4]. Gate leakage current for positive bias is not systematically observed and its origin is still unclear. Strong reverses leakage current could be at the origin of frequency/bias dependence of the MOSCAP capacitance and then lead Kovi et al. to wrong conclusions about inversion regime [3]. It’s therefore important to understand the origin of reverse leakage current and their relationship with capacitance measurements.
In this work, we investigate the mechanisms responsible of the leakage current for positive bias in O-diamond p-type MOSCAPs. We fabricated O-Diamond MOSCAPs on a stack of a heavily boron doped diamond (p+ layer) and a lightly boron doped diamond (p- layer) on 3*3 mm² Ib high-pressure high temperature (HPHT) (001) diamond substrate. The oxygen termination has been performed by using deep UV Ozone treatment. Then, atomic layer deposition Al2O3 oxide layers were deposited at 250 C. Current-Voltage and Capacitance-Voltage of MOSCAPs have been measured versus temperature.

In order to correlate reverse leakage current with structural characteristics of the substrates, systematical measurements have been done before and after removal of the metal and oxide from the substrate. Combining electron beam Voltage Contrast and in situ I-V, conducting Atomic Force Microscope (c-AFM) and Transmission Electron Microscope (TEM), leakage current spots were identified and correlated with reverse leakage current of MOSCAPs. Impedance measurements have been performed and demonstrated the relationship with reverse gate leakage current. A model related to the presence of dislocations under the MOSCAP will be proposed and then discussed in terms of electrical equivalent circuit. Finally, the ac characteristics extracted from the model will be compared with experimental data in order to describe the unusual frequency/bias dependence of the MOS capacitances under positive bias.

[1] G. Chicot, A. Maréchal, R. Motte, P. Muret, E. Gheeraert, and J. Pernot, Appl. Phys. Lett., 102 242108, (2013).
[2] A. Maréchal, M. Aoukar, C. Vallée, C. Rivière, D. Eon, J. Pernot and E. Gheeraert, Appl. Phys. Lett., 107, 141601 (2015).
[3] K.K. Kovi, O. Vallin, S. Majdi, and J. Isberg, IEEE Electron Device Letters., 6, 603 - 605 (2015).
[4] T.T. Pham, A. Marechal, D. Eon, P. Muret, N. Rouger, J. Pernot, EP15. 5.05, MRS Spring Meeting 2016.

The negatively charged nitrogen-vacancy center (NV) in diamond is a point-like defect that has focused a lot of attention in the past few years due to a number of emerging quantum mechanical applications in cryptography, information processing and magnetic sensing. It has bright single photon emission and the electronic spin state of the defect can be optically read-out and manipulated leading to exceptionally long coherence time even at room temperature.
Harnessing the outstanding properties of NVs mainly relies on the progresses obtained in the synthesis of high quality and purity diamond material using the microwave plasma assisted chemical vapor deposition technique (MPACVD). Individual or ensembles of NV centers can be produced by nitrogen implantation of high-purity isotopically ¹²C-enriched CVD diamond plates. On the other hand, the direct creation of NVs during growth allows creating defects with improved properties in terms of coherence time and orientation as compared to implantation. The requirements though are very challenging and are setting an increasing pressure to the diamond synthesis capabilities by MPACVD. They include the control of NV creation yield and density over a wide range of concentration, from a few ppb to a few ppm and the control of defects spatial localization both in-depth (creation of delta-doped layers for example) and in-plane (creation of arrays). Moreover the ability to promote one orientation among the 4 possible axes of the NV dipole by growing on specific orientations such as (111) and (113) represents a strong advantage for the foreseen applications.
In this talk the growth of nitrogen-doped CVD diamond single crystals by MPACVD will be described. Special emphasis will be given to the control of the orientation and localization of NV centers and the optimization of their density and properties.

Precise generation and positioning of high-quality single colour centres in diamond will be important for many quantum applications. Although ion implantation can achieve nanoscale positioning of impurity atoms, it can only generate shallow colour centres (less than a few micrometres below the surface), and the ions create extensive damage to the diamond lattice as they penetrate, resulting in colour centre properties that are inferior to those of ‘grown-in’ defects.

Laser processing is a powerful technique for generating damage within diamond. The physical mechanism by which damage is generated is highly non-linear, so that with adaptive optics [1] and careful selection of laser pulse energy one can generate damage localised to a volume of submicron dimensions at any position within a sample. Here we make use of this capability to generate vacancies at desired locations in high purity CVD diamond, then annealing to mobilise the vacancies and produce nitrogen-vacancy centres, using native nitrogen in the lattice. The aim is to produce single high quality NV^- defects in desired positions within the crystal.

We use single, femtosecond pulses from a Ti:Sapphire laser (l = 790 nm, t = 250 fs) to generate a damage array at a depth of 50 μm in a commercial high purity CVD diamond (Element Six electronic grade, [N] < 5 ppb). To determine the optimal conditions for single NV generation, the pulse energies are varied between 16 nJ and 61 nJ in 24 even increaments, with 20 repeats to gather statistics. The fluorescence spectra of these damage sites prior to annealing are similar to that of GR1 centres, implying successful generation of vacancies. After annealing at 1000°C for three hours, NV^- centres are observed to form. The spectrum of the generated NV^- centres show clear ZPLs at 637nm and the excitation power dependence measurement show saturation behaviour. Most of the laser-generated NV^-centres are determined as single NV^- centres by photon autocorrelation measurements. The positional accuracy of the generated defects is determined to be about 200 nm on average. Most of the NV^-centres produced also possess clear spin resonance signals, sufficient to resolve hyperfine coupling to the Nitrogen-14 nuclear spin. The T₂ spin-coherence time of the laser-generated NV^- centres is measured to be about 50μs. Finally, we also present optical studies on their zero-phonon linewidths at 4K. Most NVs show narrow, stable transitions including a selection which were at the lifetime limit of 13MHz. These artificially generated defects therefore show promise for applications which require both optically coherent emission and long spin coherence, such as the formation of a quantum network[2].
Reference
1. R. D. Simmonds et al. OPTICS EXPRESS. Vol. 19, No. 24. (2011).
2. A. Dzurak. Nature 479, 47 (2011).

The status of color center yield is a critical limitation for their integration with microfabricated devices and realizing architectures to couple individual centers. Although great progress has been made with deterministic spatial formation both by focused ion beam implantation and nanometer scale masking of broad beams, a process for the reliable activation of implanted centers has not been developed. A primary factor impeding the development of such a process is the inherent uncertainty in the number of implanted ions due to the Poisson statistics of ion implantation. As well, yields <10% are typical for SiV center formation by ion implantation. These two factors limit progress in improving color center yield. We propose a novel path for improving color center yield.
We have adapted the technique of in-situ ionization detection used for low energy counted ion implantation into Silicon and applied it to the diamond substrate. The in-situ diamond detector, we have developed, allows for the counting of single ions with an SNR approaching 10 for a 200 keV Silicon implant. This SNR results in an expected ion counting error rate of less than 1%, thereby removing a known source of Poisson statistics. We will present yield measurements of SiV center formation via counted implantation of Silicon atoms from a focused ion beam system with a 20 nm spot size. Additionally, we will test the feasibility of counted ion implantation as a platform for yield optimization by measuring the change in yield when additional vacancies are introduced local to a Silicon implantation by the subsequent implantation of light ions. We anticipate that the technique of counted implantation will serve as a platform to develop a more certain understanding of how color center yield depends on factors such as the local number of vacancies, anneal parameters, and surface termination.
This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy Office of Science. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Nitrogen-vacancy (NV) centers in diamond can realize a magnetometer with scalable applications from microscopic to macroscopic range. A prototype magnetometer to cover both the microscopic and macroscopic operation has been developed in a shoulder-bag size. The prototype magnetometer consists from semiconductor chips of laser diode, image sensor or photo diode, microwave synthesizer, and timing controller, as well as an optical system functionally equivalent to a microscope.

The NV centers in the diamond crystal under the microscope are fabricated in the top thin surface using the delta-dope CVD process for microscopic measurements where magnetic field from a short distance be measured. On the other hand, the NV centers are uniformly distributed throughout the whole thickness of the diamond crystal using the EB irradiation process for the macroscopic applications where magnetic field from a distance be measured. The image sensor detects the fluorescence from the diamond crystal in the microscopic measurement and the photo diode for the macroscopic measurement. LED could be used instead of laser diode where pulse modulation for high sensitivity was not essential.

As a numerical example of the macroscopic measurement, the DC magnetic sensitivity, observed as the noise level, was 0.12μT/√Hz, using the diamond crystal for which 10^17/cm^2 EB was irradiated in the whole thickness of 0.5mm. The nuclear magnetic resonance (NMR) signal at 3.2MHz from the water in the test tube placed in the 75mT DC magnetic field could also be detected using the same diamond.

The concentration of the electromagnetic field in plasmonic antennae allows for significant improvement of nanophotonic devices. The main advantage of plasmonics compared to resonant dielectric structures is their small size, which is in the subwavelength regime [1]. However, this advantage vanishes when metallic collimating antennas, such as bull’s eye or spiral antennas are considered. Their sizes are typically in the range of a few (tens) of the operating wavelength [2, 3]. Furthermore, losses are correlated to the size of metallic antennae.
In this contribution we will introduce a dielectric antenna with a subwavelength size and discuss the coupling to the nitrogen vacancy center in nano diamond. Therefore, our approach of local functionalization of an antenna using atomic force microscope manipulation [4] will be shown. The experimental results will be complemented by full numerical calculations.


[1] Schietinger, S., Barth, M., Aichele, T., & Benson, O. (2009). Plasmon-enhanced single photon emission from a nanoassembled metal− diamond hybrid structure at room temperature. Nano letters, 9(4), 1694-1698.

[2] Lezec, H. J., Degiron, A., Devaux, E., Linke, R. A., Martin-Moreno, L., Garcia-Vidal, F. J., & Ebbesen, T. W. (2002). Beaming light from a subwavelength aperture. Science, 297(5582), 820-822.

[3] Rui, G., Nelson, R. L., & Zhan, Q. (2011). Circularly polarized unidirectional emission via a coupled plasmonic spiral antenna. Optics letters, 36(23), 4533-4535.

[4] Schell, A. W., Kewes, G., Schröder, T., Wolters, J., Aichele, T., & Benson, O. (2011). A scanning probe-based pick-and-place procedure for assembly of integrated quantum optical hybrid devices. Review of Scientific Instruments, 82(7), 073709.

The aim of this work was to determine a defining characteristic for the chemical process in the Chemical Mechanical Polishing (CMP) of Nanocrystalline diamond. Earlier work in the group has focussed on polishing rough diamond films using Logitech SF1 slurry only on both poly and single crystal diamond for device applications. Further optimisation of the process has involved testing other polishing particles common to the semiconductor industry namely ceria (CeO₂) and alumina (Al₂O₃) along with silica (SiO₂) under different pH environments i.e. acidic and basic. For each particle two slurries were used one with a pH of ≈ 5 and the other ≈ 10. A series of diamond thin films were grown to 360 nm on a 500 nm silicon dioxide buffered 2” silicon wafer. The root mean square (rms) roughness of each as grown film was approximately 24 nm over 25 µm² as measured using atomic force microscopy (AFM). The films were polished using a Logitech Tribo polishing system in conjunction with a SUBA-X polishing pad for a minimum of 3 hours. After each hour of polishing Spectral Reflectance and AFM measurements were taken in order to observe the change in roughness and thickness of each sample. The final surface chemistry of these films was also examined using X-ray Photoelectron Spectroscopy and Scanning Electron Microscopy. We present the final results comparing and contrasting the effects of the different polishing slurries on the thin films.

Nitrogen-vacancy (NV) centers in diamond have remarkable optical, electrical and magnetic properties. It’s being widely used in a variety of applications ranging from drug delivery to quantum computing. We report a unique method for synthesis of pure and nitrogen doped nanodiamonds at room temperatures and atmospheric pressure in air. Amorphous carbon films are deposited onto c-sapphire substrates using pulsed laser deposition technique employing 248 nm KrF nanosecond excimer laser. N doped carbon films are formed by simultaneous bombardment with N₂⁺ (0.5-1.0 KeV) ions using RF plasma during the pulsed laser deposition technique. Subsequently, the N doped and undoped carbon films^1,2 are irradiated with nanosecond laser pulses of ArF excimer laser having energy density 0.5-1.0Jcm^-2 to form diamond micro and nano structures. The carbon film is melted in the highly super undercooled state and quenched within 200-250 nanoseconds. By controlling the quenching from the liquid, we can nucleate diamonds in the form of nanodiamonds (2-8 nm), microdiamonds (100-1000 nm), nanoneedles and microneedles up to 3000 nm long, and large-area films measuring up to 50 mm. N atoms and vacancies are incorporated in the diamond lattice during the liquid phase growth where the solubility exceeds the thermodynamic limit of 2.0x10¹⁸Ncm^-3. High resolution SEM, electron back scattered diffraction (EBSD), Raman spectroscopy, high resolution TEM, and electron emission loss spectroscopy (EELS) are performed to characterize various physical properties of the synthesized diamond micro and nanostructures. Photoluminescence (PL) spectroscopy using 532 nm laser is employed to characterize the NV⁰ (575 nm) and NV^- (637 nm) centers in the NV diamond. Electrical pumping of NV centers in diamond are performed with the application of an external electric field in the presence of 532 nm excitation laser wavelength, where we have achieved NV^-/NV⁰ ratio as high as 12%. For the very first time we can synthesize array of nanodiamonds onto sapphire substrates and electrically and optically control NV^- to NV⁰ transitions which have immense application in quantum computing.
References:
1. Narayan, J. & Bhaumik, A. J. Appl. Phys. 118, 215303 (2015).
2. Narayan, J. & Bhaumik, A. APL Mater. 3, 100702 (2015), and two US Patents Pending.

Single photon sources with narrow linewidth fluorescence are essential to realize quantum cryptographic communication. Color centers in diamond are one of most promising candidates. Recently, we have reported germanium-vacancy (GeV) centers in diamond [1]. The GeV center shows strong fluorescence at the zero phonon line (ZPL) at ~602 nm with FWHM of 4-5 nm in bulk diamond. It is known that the characteristics of the color centers depend on the crystal quality and shape of the host diamond [2]. The fluorescence from nanodiamonds can be efficiently collected due to the less reflection at the diamond-air interface [3]. In this study, we fabricated GeV centers in nanodiamonds fabricated by CVD and found that they show very narrow linewidth ZPLs less than 1 nm at room temperature. Furthermore, we demonstrate a single photon emission from a GeV center in nanodiamond.
First, diamond particles were nucleated by a bias enhanced nucleation (BEN) process using antenna-edge microwave plasma CVD on 3C-SiC (111)/Si substrate using CH₄/H₂ as source gases [4]. The size of the fabricated diamond particles was about 20 nm. Then, the particles were subsequently grown by CVD with a solid germanium source placed next to the substrate. The decomposed germanium was incorporated into the nanodiamonds to form GeV centers. Finally, the GeV incorporatednanodiamonds 100-500 nm in diameter were obtained. The fluorescence from the GeV centers were observed by photoluminescence (PL) and confocal fluorescence microscope with a 532 nm excitation laser.
The nanodiamonds show very sharp fluorescence with FWHM of 0.65-1.5 nm at room temperature. This is comparable to those with the narrowest ZPLs reported from SiV [2]. The sharp ZPLs from GeV were well fitted by a Lorentzian function, indicating that inhomogeneous broadening by electron-phonon interaction is suppressed in our high-quality nanodiamonds. On the other hand, the ZPL wavelength is not uniform and ranges from 592 to 613 nm (mean: 604.2 nm). This deviation would originate from the strain and/or distortion in the lattice of the nanodiamonds, as also observed in SiV incorporated in nanodiamonds [2]. In addition, we found a GeV single photon source in a nanodiamond, confirmed by an anti-bunching dip in the second-order autocorrelation function. Although the ZPL shifts from one of a single GeV center in bulk diamond, the estimated excited state lifetime is 1.7 ns close to the bulk results [1]. Thus, in further studies, a high count rate is expected from the GeV-nanodiamonds by making use of the high collection efficiency and coupling with nano-cavity [5].

[1] T. Iwasaki, et al., Sci. Rep. 5, 12882 (2015).
[2] E. Neu, et al., New. J. Phys. 13, 025012 (2011).
[3] A. Beveratos, et al., Phys. Rev. A 64, 061802 (2001).
[4] J. Yaita, et al., Jpn. J. Appl. Phys. 54, 04DH13 (2015).
[5] M. Fujiwara, et al., Opt. Lett. 40, 5702 (2015).

The development of the electronic industry has led to major advancements in chip integration. The dimension of electronic devices has been shrinking fast in the past two decades, and 14 nm is the target dimension in the future. In addition, 3D FinFET / multigate devices and vertical nanowire wrap-gate devices have widespread use in modern electronic equipment design. However, the use of these devices result in a large amount of heat. Heat dissipation severely limits the efficiency, reliability and durability of electronic devices. Meanwhile, the coefficient of thermal expansion (CTE) of thermal management materials, between 5 and 10 ppm K^-1, should be compatible with semiconductor materials. Otherwise, heat stress aggregates at the interface and results in destruction after numerous thermal circulations. Therefore, there is increasing demand for high thermal conductivity thermal management materials with tailorable CTE in high transistor density application and progressive device miniaturization.
In recent years, diamond-copper composites have attracted significant attention for their high thermal conductivity and tailorable CTE. Its only problem is the weak diamond-copper interface binding. In our study, molten salt method was employed in interface optimization with carbide forming elements Cr, Ti and W. Spark plasma sintering (SPS) was applied to prepare the diamond-copper composites. However, the complete density cannot be reached for SPS when the diamond volume is high, even when the diamond is coated with carbide forming elements. The existence of voids severely decreases thermal conductivity. In order to increase the composite density, secondary processing was utilized. But few studies have examined the hot deformation behavior of diamond-copper composites. The hot compressing tests were performed in the range of 700-1000 °C and at different strain rates to true strain of 0.6. Complete density can be achieved after secondary processing, and the void can be removed thoroughly. Residual stress and defects will appear in the processing samples and result in electron scattering. Hence, subsequent heat treatment is necessary to eliminate these defects and further improve thermal conductivity. After heat treatment, the final thermal conductivity reached a maximum of 720 W/mK. The microstructure characterization shows the defects have significantly decreased after heat treatment by transmission electron microscopy. Defects in the interface have a negative impact on the thermal conductivity of diamond-copper composites. Theoretical prediction takes into account the effect of diamond size, volume percentage, interface width and interface defects and has agreed with the results of the current study.

Nanodiamond (ND) has been considered as a biocompatible and feasible platform for efficient cancer drug delivery. Examples have been successfully demonstrated for various cellular and animal models. However, to date, very few or none studies had included the assessment on the effects and efficiency in a quantitative fashion; and the transportation of these ND-drugs to the cancer/tumor sites are still in a less understood state. For drug delivery, ND can interact with blood circulatory system and enter the peripheral tissues; where ND interacts with target cells. When cell encounters and engulfs ND, the cell may try to digest it in a process named autophagy, a survival mechanism for cells.
In this work, we study autophagy effect of ND and ND conjugated with clinically used anti-cancer drug doxorubicin (Dox). ND and Dox internalization in Human Oral Squamous Carcinoma cell, SAS and the effect of autophagy in the SAS cell are analyzed. To observe ND internalization by SAS cell, the cell was treated with ND for several hours. To visualize ND engulfing by cells, confocal microscopy to observe ND’s NV center fluorescence was used. To observe ND’s effect on autophagy in SAS cells, the cells were subject to immunofluorescence analysis by staining with an anti-LC3 antibody. The LC3 protein aggregates during autophagic process and its fluorescence can be monitored via BD Pathway 435 Benchtop System. Analyzing spatial distribution of anti-LC3 antibody allows detecting whether ND induces the autophagy. The conditions and ND properties to induce an autophagy are discussed in terms of optimization of the ND use for drug delivery.
The ND-drug transportation in the animal model is investigated. In vivo investigation of ND in Rat model and laser-scanning confocal microscopic analysis found ND attachment on RBC membrane. The efficiency of the ND-drug as compared to pure drug in the cellular model was assessed. Further, 100 nm carboxylated ND (cND) was conjugated with human serum albumin (HSA) to achieve well dispersed suspension in buffer solution. Then the clinically used anticancer drug Doxorubicin (DOX) was adsorbed on the particles surface. To characterize the conjugation, UV/Visible, Raman and infrared spectroscopies were used. The particle sizes and surface charges of the complex cND-HSA-DOX were measured by Dynamic Light Scattering (DLS). The stability of cND-HSA-DOX in the buffer solution with pH of 7.4 for 1 week was analyzed via UV/Visible spectroscopy. Besides, DOX release from cND-HSA-DOX at different pH was measured. The Cell viability test was performed using SAS cell line to compare the cytotoxic effect of DOX and ND-HSA-DOX complex. The results show ND can be well dispersed and to have stable particles size in buffer solution after the HSA conjugation; pH-dependent drug release from cND-HSA-DOX complex is demonstrated. A possible mechanism of the drug transportation and delivery will be discussed in the work.

Nitrogen Vacancy center (NVC) in diamond is expected as a sensor of nuclear spins in biological technology [1], and the detection of NMR signals from ensemble nuclear spins (¹H, ¹⁹F, ³¹P) by shallow NVC as were reported [2]. The formation of stable shallow NVCs is essential to improve the magnetic field sensitivity, because the charge states of NVCs are strongly affected by surface termination. Surface termination varies the band bending and the density of states near surface. For DNA sensing, NH₂ termination is necessary to immobilize the target DNA on the diamond surface with amid bond [3]. Nitrogen termination is formed by radio frequency (RF) plasma with low damage [4]. Some reports mentioned that the N-terminated diamond surface could be free of unexpected spins[5] and the surface covered by nitrogen has positive electron affinity (PEA) advantageous for negatively charged NVCs [6], and , O termination is also PEA, but the electron spins are unstable because the density of states is large [7]. In this report, we focused on N-termination and investigated the charge states of shallow NVCs before and after DNA immobilization on NH₂ terminated diamond.
We made shallow NVCs by ion implantation and annealing. We implanted ¹⁵N ions (1×10⁹ /cm², with 3 keV and 6.5 keV:the simulated depth is 5.3 nm and 10.1 nm [8] ) into II a (001) Element six diamond substrate, and annealed (1000 °C, 2 h). O-termination was formed by acid treatment, then N-termination was formed by RF plasma with N₂-H₂ gas (H₂:4%). To investigate the effect of the N-termination on the charge states of shallow NVCs, we compared the density of observable fluorescent spots before and after surface treatment by laser scanning confocal fluorescence microscopy (CFM). The density of spots on N-termination diamond is ~ 1×10⁷ /cm^2, which is the same as that before the N₂-H₂ treatment. From X-ray photoelectron spectroscopy, Nitrogen coveraege is several monolayer. This means the density of NH₂ groups is ~10¹³ /cm² and this density is large enough to detect the biomolecules and to obtain NMR signals. In addition, we observed fluorescent spots after the DNA immobilization. The density did not change. In conclusion, NVCs in N terminated diamond by RF plasma could be applied to the analysis of DNA structure.
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[2] S. J. DeVience, R. L. Walsworth, et al., Nature nanotech. 10 (2015) 129.
[3] GJ. Zhang, H. Kawarada, et al.,Langmuir 22 (2006) 3728.
[4] M. Chandran, A. Hoffman, et al., Appl. Phys. Lett. 107 (2015) 111602.
[5] A.Stacey, S. Prawer, et al., Adv.Mater.Interfaces 2 (2015) 1500079.
[6] M.V. Hauf, J.A.Garrido et al., Phys. Rev. B 83 (2011) 081304.
[7] K. M. O’Donnell, D.Cherns, et al., Phys Rev B 82 (2010) 115303.
[8] J. F. Ziegler et al., SRIM the stopping and range of ions in matter, SRIM co. (2008)
Acknowlegment
We thank Dr. Liam P. McGuinness and Prof. Fedor Jelezko for supporting CFM measurements.

Fluorouracil (5-FU) is a widely used drug in the treatment of conditions such as leukaemia and bowel cancer. It is usually delivered through catheters that are often coated with anti-bacterial films such as silver. The interaction between the molecule and the catheter surface is not normally considered, but we have recently shown by x-ray photoelectron spectroscopy (XPS) that a silver surface can catalyse the dissociation of the 5-FU molecule to release HF, while a graphene surface is inert. In order to compare diamond as coating material, the adsorption of 5-FU on the oxygen and hydrogen terminated diamond(001) surfaces has been studied. The oxygen-terminated surface was prepared with an oxidising acid etch, followed by in-vacuo annealing to 300 C to remove surface contamination. The hydrogen-terminated surface was produced by annealing to 1000 C to remove oxygen and then in-situ exposure to a H* plasma source. 5-FU was then deposited on both diamond surfaces by thermal evaporation. XPS quantification of the thick films confirmed the integrity of the 5-FU molecules (C, F, N and O relative abundance = 4:1:2:2). The 5-FU films deposited at room temperature desorbed with time with the intensity reduction of the core levels more pronounced on the H-terminated surface than the O-terminated surfaces indicating a stronger adhesion of the film on the latter.

In the field of oil and gas industry, Inconel alloys are largely used for their high strength and good corrosion resilience to H₂S, CO₂ and carboxylic acid. However despite their excellent properties compare to other alloys, some specific oil and gas parts such as the sensitive areas of some sensors may require a further coating to protect against corrosion and abrasion. Additionally, oil and gas sensors may often be exposed, during the same drilling work, to various drilling fluids containing hydrophilic solid particles or heavy molecules such as asphaltenes, resins or heavy alkanes which tend to aggregate on hydrophilic surface such as alloys. Diamond coatings have thus been identified as very interesting due to their excellent hardness and wear, low friction coefficient, corrosion resilience and chemical inertness further to high natural resilience to fouling. Furthermore their wettability surface properties may be controlled to some extent.

In this study we focused on diamond coatings on Inconel718 alloy. In order to achieve successful diamond coatings on such metal alloys, two major issues had to be overcome: the first one is related to the high Nickel (Ni) content in Inconel which promotes the formation of sp2 carbon during growth. The second issue is related to the mechanical constrains that induce delamination. This stress is caused by the high thermal expansion coefficients mismatch observed between Inconel718 and polycrystalline diamond.

To overcome both difficulties we investigated two processes in parallel. The first process involves the use of two metal interlayers including a first layer of a mechanical absorber material, which absorbs constraints between polycrystalline diamond and Inconel. The second interlayer is a carbide forming material layer which favor chemical adhesion between diamond and the metal. The second process involves the deposition of a nano-diamonds multilayer which is then coalesced by MPCVD. The conditions for MPCVD have been developed to gently initiate diamond growth at low temperatures (<450°C) in order to prevent the catalytic effect of Ni on diamond. The thickness of the coating obtained is around 50nm and the small porosity in the film allows absorbing the mechanical constraints. In the first process a rough but very adherent polycrystalline diamond film was achieved whereas in the second process a very smooth nano-crystalline diamond film was obtained. Diamond coated surfaces were further chemically grafted to improve hydrophobic properties. The developments led to the manufacturing of high performance and high reliability diamond coated MEMS sensors on a preindustrial basis.

Common-gate configuration of electrolyte solution-gate FETs (SGFETs) has been firstly developed. It is fabricated on polycrystalline diamond with variable surface termination has been applied for pH sensing of solutions. Using common-source circuit, we have applied diamond SGFETs for pH sensing so far.[1,2] For ordinal common-source measurement system, it is necessary to apply a finite source-drain voltage (V_DS). Otherwise the FETs cannot enter into the operation state. In the common-gate circuit, however, the FETs are in the operation state even when the gate-drain voltage (V_DG) is zero. Sensing can be carried out by the drain current variation. This is useful for sensing in the electrolyte solution because gate electrode is normally remote from the source and drain. In this study, we fabricated diamond SGFETs and measured pH by common-gate system.
Polycrystalline diamond substrates were terminated by hydrogen and oxygen as channel. For hydrogen terminated channel, surface C-H bonds form electric dipole attracting negative ions to the interface between diamond and solution, inducing two-dimensional hole gas layer for electrical neutrality. For oxygen terminated channel, thin boron doped diamond layer was deposited on surface.
The SGFETs showed ideal FETs modulation in both the common-source and common-gate system. In both measurements, SGFETs worked stably and the similar saturation current density was obtained. The main advantage characteristics of common-gate mode is that a drain-source current is in saturation region without applying drain-gate voltage. It indicates that pH of solution can be measured by only applying voltage to the device (source and drain), not to solution (gate). Thus, no influence on solution is expected. The common-gate measurement system can be used even for other ion-sensitive FETs, and the characteristics will be exhibited on site.


[1] H. Kawarada et al., Phys.Status Solidi A, 185,79,2001.
[2] Y. Sasaki and H. Kawarada 2010 J. Phys. D: Appl. Phys. 43 374020