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).
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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).
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[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).
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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