December 1-6, 2013 | BostonMeeting Chairs: Charles Black, Elisabetta Comini, Gitti Frey, Kristi Kiick, Loucas Tsakalakos
The high breakdown electric field, the elevated mobility and the outstanding thermal conductivity make diamond the ultimate semiconductor for high power and high frequency applications. Intensive works and important progresses have been done recently in the field of substrate fabrication, epilayer growth and doping control. Unfortunately, the high serial resistance of the low-doped active layer generally limits diamond devices performances. Indeed, the high ionization energy of diamond dopants gives rise to a low ionization rate and so a high serial resistance. Today, the minimization of such resistance is one of the main issue for diamond devices fabrication. One way to overcome this problem is to perform electronic device based on electron or hole channel created by field effect, like Metal Oxide Semiconductor Field Effect Transistor (MOSFET).In this context, we fabricated a diamond Metal Oxide Semiconductor (MOS) structure with aluminum oxide as insulator and pminus;type (100) mono-cristalline diamond as semiconductor. We investigated the samples by capacitance voltage and current voltage measurements. It will be shown that the dielectric aluminum oxide, deposited by atomic layer deposition on an oxygenated diamond surface at low temperature, gives a clean interface with diamond . The capacitance voltage measurements demonstrate that accumulation, depletion and deep depletion regimes can be controlled by the bias voltage. A MOS band diagram will be proposed and discussed. These results will be compared to other works recently reported in the literature [2,3] and discussed in terms of potentiality for diamond based MOSFET.References: G. Chicot et al. “Metal oxide semiconductor structure using oxygen-terminated diamond”, Appl Phys Lett, 102, 242108 (2013) S. Cheng et al., “Integration of high-dielectric constant Ta2O5 oxides on diamond for power devices”, Appl Phys Lett 101, 232907 (2012). J.W. Liu et al., “Electrical characteristics of hydrogen-terminated diamond metal-oxide-semiconductor with atomic layer deposited HfO2 as gate dielectric,” Appl. Phys. Lett., 102, 112910 (2013).
Photosensitivity properties of sulfur-doped nano- (NCD) crystalline diamond films on (100) silicon substrates haven been investigated by Field Emission (FE) trough of photo-induced electrons (PE) with weak visible light. The structure and composition of these diamond materials were characterized by Raman spectroscopy, X- ray Diffraction (XRD) pattern and scanning electron microscopy. The UV sensitivity and time response was studied on NCD surfaces using a steady state broad UV excitation source and UV laser. In our study, we demonstrate that NCD have high sensitivity in the ultraviolet region, linear response in a broad intensity, no dependence of the fluency intensity at short time response. The electron emission intensity, increasing with the electric field applied is increased. The fact that the emission can be controlled by different electric field values allows the possibility to easily switch electrical currents at room temperature.
Thin diamond foils are needed in many particle accelerator operations relevant to nuclear and atomic physics experiments. Particularly, the nanodiamond form is attractive for this purpose as it possesses a unique combination of diamond properties such as high thermal conductivity, mechanical strength and high radiation hardness, and therefore, it is considered as a potential material for ion beam stripping foils. A small set of foils must be able to survive the typically 6 month operation period of the SNS, without the need for costly shutdowns and repairs. A nanodiamond foil about the size of a postage stamp is critical to the production of neutrons at the SNS and similar sources in US laboratories and around the world.We are investigating nanocrystalline, polycrystalline, and their admixture films fabricated using a hot filament chemical vapor deposition system. Process variables such as substrate temperature, process gas ratio of H2/Ar/CH4, plasma biasing, substrate to filament distance, filament temperature, carburization conditions, and filament geometry are optimized to achieve high purity diamond films without significant heavy metal contamination. An in-situ laser reflectance interferometry tool (LRI) is used for monitoring the growth characteristics of diamond thin film materials. The integrated LRI in the HFCVD process provides real time information on the growth of films and can quickly illustrate growth features and control over film thickness. By knowing the wavelength of the laser and by knowing the refractive index of the film, growth rate and film thickness can be determined. This helps to monitor accurately the targeted 350 micro-g/cm2 thickness of the nanodiamond foil to be manufactured for the spallation neutron source. Using LRI integrated HFCVD, we correlated several important growth parameters of poly and nanodiamond films including the seeding process. Our LRI results clearly indicated that the seeding procedure strongly affects initial growth stages of diamond film through the early onset of oscillations. As the film starts to grow the laser reflectance decreases, until the nucleation layer is continuous on the substrate. After that laser reflectance starts to increase and oscillations can be measured. SEM measurements were conducted to confirm the in-situ film thickness measurements using LRI. Using this approach, a nanodiamond foil product is under development. The process parameters are also optimized for thermal and intrinsic stress management to fabricate free standing thin foils with minimal curling during irradiation. An optimization process removes pinholes to the lowest possible density in the foils. The sp3/sp2 bonds are controlled to optimize electrical resistivity to reduce the possibility of surface charging damaging the foils. The results will be presented in the light of development of a nanodiamond foil product that will be able to withstand a few MW of beam power.
Two-dimensional hole gas (2DHG), which is induced on a hydrogen-terminated diamond surface, is promising as a drift layer of diamond field-effect transistors (FETs), and is effectively protected against its environment being covered with an Al2O3 film formed by an atomic-layer-deposition (ALD) method with an H2O oxidant at 450°C . This film initially allowed a large leakage current, but we have recently succeeded in reducing the current, stacking the O3-oxidized Al2O3 on the H2O-oxidized one. However, the breakdown field only slightly improved contrary to expectation. Here, in order to solve this, we report the effect of high-temperature annealing on the dielectric strength of ALD-Al2O3.The Al2O3 films in this study were formed 33-nm thick on p-type (100) Si substrates (0.002-0.004 Omega;cm) using the ALD method at 450°C with Trimethylaluminium and H2O as precursors. Next the films were annealed in Ar at 600-1100°C for an hour. The samples further received Ti/Au sputtering using a metal mask to form gate electrodes (2.5x10-3 - 5.6x10-3 cm2). The leakage current was measured applying a negative voltage to the gate according to the operation condition of diamond 2DHG-FETs. In this study, we used Si instead of diamond as a substrate material as aforementioned, because of the ease of back ohmic contact. However, note that the results obtained here apply equally to diamond substrates under this polarity of biasing.The high-temperature annealing not only reduced the leakage current but also improved the breakdown field. This improvement was more marked for a higher temperature, and the sample annealed at 1100°C exhibited a dielectric strength of as high as 18MV/cm, which is twice the reported value . Because X-ray diffraction patterns did not show a trace of crystallized Al2O3, this revolutionarily high dielectric strength might be simply ascribed to Al2O3 densification, which was caused by the high temperature annealing. The problem is that the breakdown field was widely distributed among the samples, only some of which exhibited the aforementioned high value. The suppression of defective samples and the reduction of annealing temperature are a remaining challenge.To conclude, we found out that, being annealed in Ar at 1100°C, the ALD-Al2O3 film potentially has a breakdown field as high as 18MV/cm, which is twice the conventional value. Presently, however, there are many defective samples that fall short of the best samples. Solving this problem and reducing the annealing temperature, the ALD-Al2O3 film will drastically enhance the breakdown voltage not only of diamond 2DHG-FETs but of other wide-bandgap semiconductor devices.NB. This study was supported by research grants from ALCA (JST). A. Hiraiwa, A. Daicho, H. Kawarada, et al., J. Appl. Phys. 112 (2012) 124504. A. C. Kozen, M. A. Schroeder, K. D. Osborn, C. J. Lobb, and G. W. Rubloff, Appl. Phys. Lett. 102 (2013) 173501.
Diamond is now well-known for its exceptional properties that make it the ultimate semiconductor in particular in the field of power electronic devices. This is illustrated by the recent increase in the number of publications describing the fabrication and characterization of elementary "all-diamond" components. Nevertheless, these works are mainly related, with a few exceptions , to coplanar or pseudo-vertical components. Even if the characteristics in terms of breakdown voltage are promising [2,3], in the area of high energy devices, the reverse characteristics are not enough. It is also of prime interest to ensure high current flow in forward bias which is only compatible with a large cross-section component, i.e. in vertical configuration  as it is usually done in the case of more conventional semiconductors such as silicon, silicon carbide or even gallium nitride . Obviously, the development of such components is conditioned by the availability of heavily-doped diamond substrates (doping level around 1E20 cm-3) with a thickness allowing mechanical handling which has been recently achieved by microwave plasma assisted chemical vapour deposition (MPACVD), this technique allowing having good doping homogeneity that cannot be ensured at such doping level with High Pressure High Temperature substrates.In this paper, starting from heavily boron doped substrates grown by MPACVD, vertical Schottky diodes have been fabricated. Then, a homoepitaxial growth of thin p-layer is performed on a reactor dedicated to low doped diamond. The Schottky contacts have been obtained by evaporation of aluminum, and gold. The vertical component is characterized by ellipsometry, cathodoluminescence, and optical profilometer to determined thickness layer, dopant concentration and surface roughness. Finally, Voltage-Current behavior is carried out. Our preliminary results show a high rectification ratio, higher than 9 orders of magnitude with a low reverse current (1e-10 A). This first demonstration of vertical diode in diamond can help encapsulation and pave the way to electronic power devices.  R. Kumaresan, H. Umezawa and S. Shikata, Diam. Relat. Mat. 19, 1324 (2010). P.-N. Volpe, P. Muret, J. Pernot, F. Omnès, T. Teraji, F. Jomard, D. Planson, P. Brosselard, N. Dheilly, B. Vergne and S. Scharnholtz, Phys. Stat. Sol. (a) 207, 2088 (2010). J. E. Butler, M. W. Geis, K. E. Krohn, J. Lawless, S. Deneault, T. M. Lyszczarz, D. Flechtner and R. Wright, Semiconductor Science and Technology 18, S67 (2003). J. Achard, F. Silva, R. Issaoui, O. Brinza, A. Tallaire, H. Schneider, K. Isoird, H. Ding, S. Kone, M. A. Pinault, F. Jomard and A. Gicquel, Diam. Relat. Mater. 20, 145 (2011). Toyota gears up HEMTs for hybrid electric vehicles, Compound Semiconductor 17, 6, 18 (2011). B. N. Mavrin, V. N. Denisov, D. M. Popova, E. A. Skryleva, M. S. Kuznetsov, S. A. Nosukhin, S. A. Terentiev and V. D. Blank, Physics Letters A 372, 3914 (2008).
Negative ion sources find applicability in materials science, accelerator physics and fusion research. Our research focuses on the direct conversion of heat to electricity which utilizes negative ions to enhance a thermionic electron emission current to increase conversion efficiency. Generation of negative ions scattered from a surface is described by the Saha-Langmuir formalism which relates the ion yield to the surface work function, its temperature and the affinity level of the scattered particle. Practical ion yields are generated when the value of the particle&’s affinity level approaches the work function of the surface. For a diamond based negative ion source the value of the negative electron affinity and the magnitude of the band bending will also affect ion generation efficiency. Single crystal nitrogen - doped diamond has been utilized as a negative ion source for atomic hydrogen. The deep single substitutional states of 1.7 eV with a concentration of about 3.5 x 10-19 cm-3 establishes upward band bending, which, in conjunction with the NEA, significantly affects the ionization phenomenon. We have measured ionization of atomic hydrogen (affinity level of 0.75 eV) scattered from a hydrogenated, N-doped single crystal diamond surface in various temperature regimes. Here, an electron from a populated state in the diamond tunnels to the hydrogen affinity level if the states are energetically aligned. For the N-doped diamond a thermionic work function of about 2.6 eV was derived by a fit to the Richardson-Dushman relation. The ionization results indicate that at low temperatures < 750K no significant hydrogen ionization occurs. In a medium surface temperature regime from sim;750K to sim;950K ionization becomes more pronounced but deviates from the Saha-Langmuir relation. At elevated temperatures > 950K an exponential temperature dependence of the ionization current is observed as is described by the Saha-Langmuir formalism. We will discuss the ionization phenomenon in terms of dopant level, negative electron affinity and band bending and will compare results to surface ionization from a phosphorus doped, shallow donor diamond film. We will also elaborate on its application in direct energy conversion.This research is supported by the Office of Naval Research.
Diamond films can obtain a negative electron affinity (NEA) surface after hydrogen termination. With n-type doping, this leads to a low effective work function, and efficient thermionic electron emission has been observed from these diamond films. Photo-induced electron emission from nitrogen doped diamond films with visible light illumination has also been reported by our group. Phosphorus doping is found to provide the lowest known work function of any non-cesiated material, yet remains mostly unstudied. The focus of this work is the photo-induced emission from phosphorus doped nanocrystalline diamond (NCD) films. The P-doped NCD films have been grown by microwave plasma enhanced chemical vapor deposition (MPCVD) on different substrate materials (silicon or molybdenum), using phosphine as an in-situ dopant gas. In situ laser reflectance interferometry indicates a typical diamond film thickness of 200 to 350 nm. The photo-induced emission spectra have been collected with a hemispherical electron analyzer at elevated temperatures. A Xe arc lamp with associated bandpass filters provides photon illumination from 320 to 600 nm. The results show a low work function of 1.8 to 3 eV, and the photo-induced emission intensity presents a strong temperature dependence, which may be characteristic of Photon Enhanced Thermionic Emission (PETE). The results indicate potential application in concentrated solar energy conversion devices.This research is supported by the Office of Naval Research through grant # N00014-10-1-0540, and by the EU FP7 through the Marie Curie ITN “MATCON” (PITNGA-2009-238201).
Low work function nitrogen-doped diamond films have demonstrated thermionic emission at temperatures less than 500 degree C, motivating the use of the films as electrodes in thermionic energy converters (TECs). Recently, our group has obtained significant enhancement of diamond-based TEC efficiency through a molecule-mediated charge transfer mechanism. We have built up a base of Python code in an attempt to explain these results. This endeavor has involved determining and modeling many practical sources of inefficiency in the converter so as to isolate the effects of molecular charge transfer, including black-body radiation from the electrodes and internal resistance of the device. The limiting factors on efficiency appear to be electronic heat and black-body losses. The model provides an approach for improving the designs of TEC devices. Future work will include the enhancement of thermionic emission through photon illumination.This research is supported by the Office of Naval Research under grant # N00014-10-1-0540.
Diamond has a unique property that holes are accumulated densely on a carbon-hydrogen bond (C-H bond) surface. Using the property based on C-H surface, we have developed high performance field-effect transistors (FET) so far [1,2]. Since the H-termination effect is affected by a surrounding environment (surface adsorbate, high temperature, etc.), passivation technology [3,4] has been investigated. We have recently developed an advanced passivation for the surface p-type conduction operated at high temperature (~500°C)  using atomic layer deposition (ALD) Al2O3 film formed at 450°C. Here, we applied this passiviation for metal-oxide-semiconductor (MOS) FETs. The electrical properties C-H bond diamond MOSFETs were evaluated at high temperature up to 400°C. Two types of channel with different boron concentration were prepared in the following MOS fabrication process. Source-drain electrode are formed by Ti/Au on undoped (B<1016cm-3) and lightly boron-doped (B~1017cm-3) homoepitaxial layer on (001) diamond. Both layers were C-H bonded by remote plasma. The Al2O3 passivation film also employed as gate insulator was deposited by ALD utilizing ozone and H2O as oxidant at 450°C . Al gate electrode was formed for on the Al2O3 gate insulator. In drain current (IDS) - drain voltage (VDS) characteristics such as pinch-off, on resistance and transconductance, the two types of MOSFETs on undoped and lightly doped diamond shows very similar properties at 400°C in vacuum. However, drain leakage current of lightly boron doped FET is much higher than that of undoped FET. In undoped FET, the on-off ratio is 109, 105, and 103 at room temperature, 300°C, and 400°C, respectively. From the activation energy of the leakage current, the leakage path in undoped FET is not due to the residual boron as acceptor, but nitrogen as deep donor or device isolation by oxygen terminated area. It can be highly decreased by purer diamond and perfect device isolation. The breakdown characteristic of MOSFETs at the temperature from 25°C in vacuum we evaluated VDS : 275V. This result is higher than the highest breakdown voltage of diamond FET reported so far . Stable performance at 400°C comparable to SiC or GaN FETs has been achieved using H-terminated diamond MOSFETs.[Acknowledgment] This research was supported by research grants from ALCA (JST).References H.Kawarada Surf. Sci. Rep. 26 (1996) 205. H.Kawarada Jpn. J. Appl. Phys. 51 (2012) 090111. D.Kueck E.Kohn et al. Diam. Relat. Mat. 19 (2010) 166. M.Kasu et al. APEX 5 (2012) 025701. A.Hiraiwa, H.Kawarada et al., J. Appl. Phys. 112 (2012) 124504. P.Gluche, E.Kohn et al. IEEE Electron Device Lett. EDL-18, (1997) 547.
1.Al-first AlN on diamond (111) to get N polarity AlN/diamond structure is an ideal system to form 2-dimensional hole gas because of a large valence band offset at the AlN/diamond interface. This structure is promising to control holes in diamond by the AlN polarity. As to the spontaneous (intrinsic) polarization of AlN, N polarity (C-Al bonds at the interface) induces more holes at diamond side than Al polarity (C-N at the interface) does. We deposited AlN by Molecular Beam Epitaxy (MBE) alternately supplying N radicals and Al atoms. Alternately supplying starting from Al (Al-first) may realize N polarity (C-Al at the interface). In this study, we deposited Al-first AlN on diamond to get C-Al bonds and investigated the AlN crystallinity and the electric properties of the AlN/diamond interface.2.Alternative supply of Al and N on diamond and in-situ observation by RHEED After depositing a homoepitaxial layer on a (111)-diamond substrate (Ib), an AlN was deposited by MBE alternately supplying N radicals and Al atoms. We observed diffraction pattern from [10-1] direction of diamond (111) surface in-situ. By pre-heating, diamond surface caused surface reconstruction 2×1 structure. The pattern emerged immediately after deposition start is derived from AlN phase. The pattern of Al-first AlN shows no substantial difference from that of N-first AlN.3.Properties of Al-first AlN/diamond interface XRD From XRD pole figure measurements of AlN 101 asymmetry reflection, for N-first AlN, 6 fold rotation symmetry spots were observed in the AlN films. By contrast, for Al-first AlN, AlN 101 reflection is arc indicating that AlN crystal has rotational distribution.Sheet resistivity using the van der Pauw method We measured the resistance of 5 Al-first samples. The sheet resistivity RS of the H-terminated diamond surface were originally ~10kOmega;/sq. After the Al-first AlN deposition, RS of the AlN/diamond system were distributed between 1kOmega;/sq-10kOmega;/sq, which were very low resistivity ever reported at AlN/diamond interface. As to the low resistivity, one possibility is that H-terminated diamond surface produced by the small of residual gas such as water molecules and AlN layer show acceptor-like behavior. The second is that the polarization of the AlN film induces the p-type conduction expected in the spontaneous polarization by N polarity. The third is due to the 2×1 diamond (111) surface with partially π-bonded chain having high conductivity like graphene. We are now investigating which is the case.4.Summary We successfully deposited Al-first AlN on diamond (111). The Al-first AlN shows rotational crystal distribution. The sheet resistance RS of the interface is reproducibly obtained in 1kOmega;/sq-10kOmega;/sq. Although the conducting mechanism is still open question, the relatively high conductive layer might be used as a channel of diamond FET operated in a harsh environment.Acknowledgement This study was supported by research grants from ALCA (JST).
In spite of significant progress in diamond electronics typical diamond-based devices are not suitable for power applications due to low forward current in several hundreds of milliamps. This value is limited by a quality of large area diamond crystals.In this work large area diamond Schottky diodes were produced and investigated. We used IIb HPHT diamond plates cut to 5×5×0.3 mm3 size with boron content about 1018 cm-3 as a p+ substrates. The doping level of substrate was limited by abrupt degradation of crystal quality during subsequent increase of boron concentration. We paid a special attention to quality of plates because the presence of extended structural defects in substrate affects strongly on the quality of CVD-grown films. Only defect-free plates were selected by the X-ray topography method.Low doped 20 mu;m thick diamond film was grown on substrates by MP-CVD. For precise boron doping of this p- layer we used laser ablation of the high purity boron sample in hydrogen supply gas line. After surface preparation ohmic contact (Ti/Pt/Au) was made at the bottom of p+ substrate and Schottky contact (Pt) was made at the top of p- layer. To decrease the electrical field enhancement in contact edge we used field plate termination technique with 2 mu;m thick dielectric (Al2O3) layer.Produced diamond Schottky diodes had good electrical characteristics. The forward current was 5 A (31 A/cm2) at bias 7V. Current was limited by serial resistance of substrate that has significant resistivity 5 Ohm×cm at RT. The reverse leakage current was less than 100 mu;A (0.6 mA/cm2) at 600V blocking voltage. The maximum value of breakdown voltage was slightly above 1000V. The reverse recovery time was 5 ns. Stability tests showed capability of diodes in a wide temperature range and under the influence of harsh impacts including high radiation doses.
Laser reflectance interferometry tool (LRI) is developed for in-situ measurement of the growth characteristics of carbon based thin films materials. LRI tool integrated with hot-filament CVD (HFCVD) was used to grow films of diamond, nanodiamond, graphene, and thermal-CVD was used for carbon nano tubes (CNTs). LRI allows the in-situ measurement of the growth rate and the surface roughness of the samples as they were grown. This process provides real time information into the growth of films and can quickly illustrate growth features. The in-situ measurements allow for quick determination of the effectiveness of initial diamond seeding of the films. By knowing the wavelength of the laser and by knowing the refractive index of the diamond film, growth rate and film thickness can be determined. Using LRI integrated HFCVD; growth parameters of poly and nanodiamond films were correlated such as seeding process and optimization, CH4 concentration, negative biasing, filament temperature, and Ar/H2 ratio on nanodiamond growth. LRI results clearly indicate that seeding procedure strongly affects initial growth stages of diamond film through early start of oscillations. As the film starts to grow the laser reflectance decreases, until nucleation layer is continuous on the substrate. After that laser reflectance starts to increase and oscillations can be measured. Since the time from peak to peak is used to measure the growth rate of the sample, LRI can be used to determine how growth parameters affect the growth rate and surface morphology of the deposited sample. Filament temperature had the greatest effect on the growth rate of diamond samples. Increasing CH4/H2 flow decreased time to nucleation, but had little effect on the growth rate once the film had nucleated. Increasing CH4 concentration increased the growth rate. SEM measurements were conducted to confirm the in-situ film thickness measurements using LRI. LRI is also used for characterization of combustion of carbon materials. The materials tested were CNTs, polycrystalline diamond, and nanodiamond films heated in air. Each phase of carbon form (polydiamond, nanodiamond, CNTs) has it its own characteristic behavior. The characteristic onset combustion temperature strongly depends on the form of the carbon (sp3 vs. sp2). The LRI for polydiamond has constant reflectance until it decreases at 700°C. Raman spectroscopy showed this was due to the destruction of the sp2 bond but that the diamond (sp3) counterpart remained intact. CNTs and nanodiamond both showed constant laser reflection until total destruction of the carbon films. CNTs were completely and combusted at 660°C, nanodiamond at 740°C, indicated by a strong change in reflectivity. These results will be presented in the light of laser reflectivity monitoring tool integrated with Blue Wave HFCVD or other CVD or PVD techniques used for monitoring growth and characterization of carbon and related optical thin film and coating materials.
Boron-doped diamond is a promising material for electronic devices due to its attractive electrical properties, namely wide bandgap, high thermal conductivity, high breakdown electric field and high carrier mobility. However, the crucial step before the fabrication of electronic devices is to understand all of the parameters which influence the fabrication process. Whereas single-crystal diamond devices are well-suited for understanding the basic principles, nanodiamond films attract more attention for large-scale applications. Nanodiamond films, in comparison to the single-crystal diamond, consist of large number of small crystallites, whose properties can have strong influence on the electrical properties. One of the basic parameters is the size of the crystallites, which can be well visualized using the AFM microscope. The distribution of sizes is one of the basic characteristics of nanoparticles. The knowledge of the lateral grain size distribution has potential to shed light on growth mechanisms or charge transport and electric properties in diamond films. Here, we propose a novel way to determine the lateral distribution of sizes from AFM topographies. Our algorithm is based on the autocorrelation function and can be applied both on topographies containing spatially separated and densely packed nanoparticles as well as on topographies of polycrystalline B-doped diamond films. As no manual treatment is required, this algorithm can be easily automatable for batch processing. The grain size distributions obtained by the autocorrelation algorithm will be confronted with the most precize but very slow manualy obtained histogram of the lateral grain sizes and an excelent agreement of the both methods will be presented.
In harsh environment, a diamond has many advantages superior to other materials, such as its high thermal conductivity, hardness, high conductivity, and high transparency. Since an excellent p-type conductivity and high optical transmittance are both required for photovoltaic and electroluminescence devices for an efficient hole injection in p-n junctions, a novel p-type nature obtained by boron doping in diamond endows this semiconductor with promising transparent electronics applications. In our previous study, we showed a p-type transparent conductor having a sheet resistance less than 300Omega;/Sq with 70% transparency. The samples were made by a methane (CH4) concentration of 3% on heavily boron-doped nanocrystalline diamond (NCD) on quartz [1.2]. However, it is necessary to obtain a higher transparent with the same or lower sheet resistance for practical uses. Here, we report the optimization of p-type conducting films using boron-doped NCD (B-NCD). B-NCD layers were deposited on the undoped NCD film/quartz substrate. First, undoped NCD films on quartz which was achieved at a low temperature (300-400degreeC). Next, the B-NCD layer was deposited by the MPCVD system using trimethyl boron (TMB) as the doping gas at 80 Torr in 700-800degreeC. This work was carried out in CH4 1-3% together with [B]/[C] ratio of 3000-10000ppm. As a result, the B-NCD layers retain their optical transparency in 80-90% with a low resistance less than 500-2000Omega;/Sq at a CH4 concentration being 1-1.5% together with [B]/[C] ratio of 3000-10000ppm. The top data is an optical transmittance higher than 80% together with a low sheet resistance less than 500Omega;/Sq. It is important to mention that a low sheet resistance can be obtained at a thinner B-NCD layer with higher boron concentration. The optical transmittance of B-NCD layer is better than that of solution-processed grapheme with the same sheet resistance. In the present case, the transmittance decrease is due to the increased thickness of B-NCD layers. Secondary Ion Mass Spectrometry (SIMS) showed that Boron concentration is higher than 1021 cm-3 at the outermost surface of the B-NCD layer. This conclusion is similar to the boron-concentration from metallic concentration in the range 3x1020 - 1x1021 cm-3. In the present case, 30-50% of boron atoms are present inside the grains, occupying substitutional sites and being electrically active. Therefore, B-NCD films indicate an optical transmittance obtain stably-higher 90%. It is an obvious trade-off relationship can be obtained between high optical transmittance and low sheet resistance. If you raise an optical transmittance, B-NCD must be thin film together with boron concentration being higher than 5x1021cm-3. X.Wang, H.Kawarada et al. (Submitted) Tsugawa, Hasegawa et al Phys. Rev. B 2010, 82, 125460-125468 Kawano, Ishiwata, Kawarada, Phys. Rev. B 82, 085318 (2010)
Achieving n-type doping in diamond with high electron mobility and concentration still remains among the final and most challenging problems in diamond materials research, preventing highly promising diamond electronic and optoelectronic device demonstrations. Having a negative electron affinity, n-type diamond is also ideally suited for low-field electron emission. Considerable efforts have been made toward fabricating n-type diamond, only very recently however, were n-type diamond films obtained in the absence of a high degree of crystallographic distortion where crystalline pitting is a known carrier scattering mechanism in diamond. Aside from crystal pitting, other defect structures in diamond are known to be detrimental to carrier mobility and electronic characteristics such as the dangling bond defect structure associated with three-fold coordinated diamond. In connection with experimental reports, hydrogen is believed to deactivate donor phosphorous through passivation of carriers and is further believed to be a source of crystallographic distortion. Therefore, the interaction between hydrogen, phosphorous, and the NCD surface is an important study towards the realization of practical n-type diamond. Motivated by our recent success, we explore the effect of hydrogen termination on phosphorous doping through various analysis techniques. We demonstrate successful h-termination, a first for experimental reports involving donor Phosphorous. In the absence of significant levels of defect density, we demonstrate excellent hall mobility. These results are promising towards the development of next generation high performance diamond electronics.
Nosocomial infections are expensive and responsible for millions of deaths per year. To decrease this problem innovative microcrystalline diamond films with silver nanoparticles incorporated were successfully elaborated, characterized chemically and physically, and tested for antibacterial capacity. Recent studies demonstrated that pure silver films are more effective antibacterial agents compared to microcrystalline diamond films. The incorporation of silver nanoparticles to the microcrystalline diamond films yielded a significant improvement in its antibacterial properties. In order to perform the bacterial characterization of these MCD-Ag films, a rigorous protocol for bacterial culture was executed and the development of the bacterial populations was assessed through growth curves and absorbance measurements with an Ultraviolet-visible Spectrophotometer. Furthermore, the technique of Bacterial Transfer was used to conduct a temporal quantitative analysis of the MCD-Ag bacterial inhibition properties resulting in zero bacterial growth within 24 hours. Additionally, Scanning Electron Microscope (SEM) spectroscopy allowed us to obtain imaging of the colonial behavior of the P. Aeruginosa on the surfaces of the MCD-Ag films. The elaboration of the ground-breaking MCD-Ag films was achieved via the technique of Hot Filament Chemical Vapor Deposition. The chemical and physical characteristics of the MCD-Ag films were assayed through Transmission Electron Microscopy (TEM) and Raman Spectroscopy.
The National Institutes of Health USA reported that 60% of all microbial infections are caused by biofilms, due to microbial presence on the surfaces of implants in the human body and in surgery tools. The medical industry can benefit greatly from coatings designed to reduce the bacterial viability on implants and medical tools. In the present work, we have evaluated the response to the electric current generated by a biofilm formed by bacteria that can be either gram negative or positive on the surface of microcrystalline (MCD) and nanocrystalline (NCD) diamond. The preliminary results demonstrated a change in the effective resistance of NCD and MCD material when a biofilm is formed on its surface. Furthermore, an oscillating behavior was observed in the curves of electric current versus voltage due to the presence of a bacterial strain droplet on the surface of MCD and NCD starting at 1.6 V and ranging from 0.2 V - 4.0V, similar to RC electric circuit. These studies are focused on the hypothesis of the mechanism of bacterial inhibition most accepted that involves an electrostatic relationship between the organism and the substrate in contact. The voltage-current measurements were taken with modified contact angle equipment, elaborated in the laboratory. Other studies of characterization were done using the Scanning Electron Microscope, Atomic Force Microscope, and Raman Spectroscopy. These studies allow us to infer that the formation of biofilm on biomedical instruments can alter their electrical response, thus providing misleading results, which can be prejudicial for patient diagnosis.
Heavy metal pollution, caused by the waste streams of metal plating facilities, mining operations, and tanneries are not biodegradable and tend to accumulate in living organisms, causing various diseases and disorders to the nervous, immune, reproductive and gastrointestinal systems. Electrochemical method is one of the most favorable techniques for the simultaneous determination of environmental pollutants because of its low cost, high sensitivity and easy operation. Here, we explore diamond nanowire (DNW) electrode for a chemical sensing application by employing an electrochemical technique. The DNW electrode has been synthesized on silicon substrate by N2-based microwave plasma enhanced chemical vapor deposition. Further, diamond nanowire (DNW) electrode explored for the electrochemical deposition of samarium hexacyanoferrate  (SmHCF) as electroactive materials for chemical sensors. The DNW electrode has been synthesized on silicon substrate by N2-based microwave plasma enhanced chemical vapor deposition. The SmHCF deposited on the surface of the DNW electrode by potential cycling from +0.8 to -0.2 V. The SmHCF found to grow on the surface of the DNW electrode with each potential cycle, as revealed by the change of peak currents with each cycle. A well-separated voltammetric peaks for the simultaneous detection of Cd2+, Pb2+, Hg2+, Cu2+, and Zn2+ toxic metal ions are obtained using SmHCF/DNW electrodes in differential pulse voltammetry measurements. Consequently, the DNW electrode with large surface area , good chemical stability, and SmHCF makes the electrode an efficient chemical sensor.Keywords: N2 incorporated diamond nanowire electrode, Samarium hexacyanoferrate, Cyclic voltammetry, Differential pulse voltammetry, Heavy metal ion.REFERENCES  Ibrahim A. Darwish and Diane A. Blake, Anal. Chem. 74 (2002) 52-58 Ping Wu, Shan Lu, Chenxin Cai, Journal of Electroanalytical Chemistry, 569 (2004) 143-150 Jayakumar Shalini, Kamatchi Jothiramalingam Sankaran, Chung-Li Dong, Chi-Young Lee, Nyan-Hwa Tai and I-Nan Lin, Nanoscale, 5 (2013) 1159-1167
IntroductionChemical oxygen demand (COD) is used widely as an indication of organic pollution level in water. Conventional titration method for COD measurement has some drawbacks including production of additional waste, and thus development of electrochemical method is desired. Diamond electrode (or boron-doped diamond, BDD electrode) has wide potential window and is stable to electrolysis at high potentials. In this study, organic compounds were oxidized at high potentials with BDD electrode, and electrochemical oxygen demand (ECOD) was calculated from the anodic charge. ExperimentalConstant potential of +2.5 V vs. Ag/AgCl was applied to stirred 0.1 M Na2SO4 and complete electrolysis of organic samples was performed until the current decreased down to the background level. The amount of electric charge was then calculated to ECOD. The estimated ECOD was compared with COD measured with simple COD meter and total-organic-carbon (TOC) analyzer.Result and discussionHighly positive potential (+2.5 V vs. Ag/AgCl) was applied to the aqueous electrolyte using BDD electrode, and a sample aliquot containing 300 nmol of potassium hydrogen phthalate was added. The anodic current increased as the sample was added, and the current decreased down to the background level. The anodic charge for the electrolysis was calculated from the integration of the background-subtracted current to be 0.81 C. Since oxidation with 1 mol of O2 corresponds to electrochemical oxidation with 4 mol of electron, ECOD can be evaluated to be 16.8 mg/L, which is close to the theoretical COD value (17.4 mg/L). This method was found to be valid for other organic compounds, and thus can be useful for a simple and accurate indication of water pollution level.
IntroductionPlatinum nanoparticle (PtNP) catalysts are usually supported on substrates such as alumina in order to improve the performance. However, when catalysts are used under high temperature for a long time, PtNP agglomerates strongly (sintering) on the support, and the catalytic activity decreases. Recently, for a stable catalyst, PtNP@SiO2 coreminus;shell nanocatalysts, where a PtNP is covered with mesoporous silica, has been reported. In this study, we embedded PtNP into a micrometer-sized porous diamond spherical particle (PDSP), and produced a catalyst with high stability to sintering.ExperimentalThe PtNPs were distributed and were fixed in the spherical particle consisting of a diamond nanoparticle (DNP) aggregate formed by spray drying of an aqueous suspension containing DNP, PtNP and polyethylene glycol as a binder. After removal of the binder by thermal oxidation in air at 300°C, diamond was grown with microwave-plasma-assisted chemical vapor deposition method on the particle surface to improve the strength of the particle. After thermal oxidation in air at 425°C to remove graphitic impurities, platinum nanoparticle-embedded diamond spherical particles (PtNP@PDSP) was obtained. The catalytic activities of the catalysts were tested by dehydrogenation reaction of cyclohexane. The mixture of PtNP@PDSP and cyclohexane were refluxed at 180°C for 150 min, and benzene produced was determined with UV-vis spectroscopy.Result and discussionScanning electron microscopy images showed that the PtNP@PDSP were micrometer-sized spherical particles. Nitrogen gas adsorption isotherms of the PtNP@PDSP showed curves with hystereses in the high pressure region, which indicates the presence of mesopores. Scanning transmission electron microscopy images showed that the PtNPs remained dispersed even after heat treatment. Generation of benzene was not detected when the dehydrogenation reaction of cyclohexane was performed without any catalyst or with PDSP. On the other hand, since generation of benzene was detected when the PtNP@PDSP was used, it was found that the PtNP@PDSP has catalytic activity to the reaction.
The semiconducting properties of diamond make it a material of large interest for fabrication of active electronic devices. Doped films grown by chemical vapor techniques (CVD) were shown to be useful to development of new devices like gas sensors or radiation detectors. In order to produce a reliable device the charge density at the active regions of the device should be well determined. This work is aimed on investigating the distribution of the Boron in diamond films (single and multilayered).using the capacitance-voltage profiling technique. The as grown CVD diamond usually has hydrogenated surfaces that behave as a p-type semiconductor, and these surfaces must be removed. We observed that a conventional cleaning solution based on H2SO2/K2CrO4 lead to unexpected results: our p-doped samples exhibited an electrical n-type behavior. Seeking for a more efficient treatment the samples were then exposed to an oxygen plasma (150W @ 100mbar) before making electrical contacts. A significant difference between the capacitance-voltage curves of the films before and after the treatment was observed confirming the efficiency of the plasma treatment. Also capacitance-voltage data provided us with the doping profile of the samples as expected for a p-type boron doped CVD diamond.
Early and accurate detection of life threatening physiological indicators are key aspects for the treatment of many diseases. The cholesterol, for an example, has been reported to associate with coronary heart problems, cerebral thrombosis, and atherosclerosis. Methods such as colorimetric approach and high-pressure liquid chromatography have been previously reported for highly specific and robust cholesterol quantification; however, these methods do not meet the important aspect requirement of high selectivity at low cost. In this research work, we have synthetized different ratios of nanodiamond (ND)-polyaniline (PANI) based conducting composite on imprinted platinum electrodes, and later thoroughly studied for electrochemical biosensing applications. Attempts are made to vary the ND-to-aniline monomer ratio for optimal electroactive surface using comparative studies based on electrochemical response and roughness measurements. Cyclic voltammetry and Atomic Force Microscope (AFM) measurements have demonstrated that the inclusion of ND particles yields to an increment in the active surface area, which promote a higher electron exchange rate at the electrode surface. Choline oxidase (Chx) and acetylcholinesterase (AChE) enzyme were co-immobilized into the surface using covalent binding. The synthetized structures were analyzed under dynamic as well as steady state condition using electrochemical techniques. Phosphate buffer saline (PBS) containing different concentrations of cholesterol were examined to obtain the calibration curve. Also, robustness of the biosensing structure was tested using cholesterol-free PBS buffer and PBS containing analytes different than cholesterol.
Nitrogen dioxide (NO2) is one of air pollution gasses, so that the emission of is regulated. In recent years, the demand for a better gas sensor has been increase from the view point of environment conservation. The sensor material was required having the environment resistance, since the NO2 was corrosive gas and its source was usually high temperature. In generally, the diamond is an isolator. However, p-type surface conductive layer (PSCL) is formed on it, when NO2 was adsorbed on crystal surface terminated by hydrogen. The conductance of the PSCL depends on NO2 concentration in atmosphere. In addition, as the diamond has high chemical stability and heat resistance, the application to a gas sensor was expected. In this study, to improve in NO2 responsivity of PSCL, the surface treatments for the diamond films have been carried out, and its effects have been considered. The poly-crystalline diamond films were deposited on Si substrate by hot-filament chemical vapor deposition (CVD) method and were used for samples. At first, the changes in conductance of the PSCL by atmospheric gases were measured using diamonds before treatment. The NO2 diluted with nitrogen by 12ppm and pure N2 were used for atmospheric gases. As the surface treatments, after the oxygen plasma irradiation for 10 minutes, the hydrogen annealing for 10 to 90 minutes at 900 °C to the diamond films was applied. Then the conductance was measured again. In addition, the surface hydrogen density of treated diamond films was measured by using elastic recoil detection analysis (ERDA). The responsivity of the conductance by change in atmospheric gas was compared with before and after surface treatment. As a result, it was confirmed that the NO2 adsorption became faster than before treatment, by increase in hydrogen annealing time. On the other hands, the surface hydrogen densities of the treated diamond films were varied with annealing time, and it was considered that the adsorption rate was influenced by the surface hydrogen density. The desorption of NO2 also became faster than before treatments. Since the weak correlation with annealing time, that was affected by the oxygen plasma irradiation. It found out that surface treatment in this study was effective for improvement in responsivity as the gas sensor.
Gamma irradiation is a standard method to prepare blood for transfusion and for reduce the risk of Graft-versus-Host-Disease. Most prediction models are based in both counts and viability of lymphocytes after radiation exposure (around 25 Gy). However, the remained cells in blood tissue are not considered and then, important changes in red blood cells (RBC) may interfere with the recovery process in the affected patient. RBC changes include membrane deformation as we presented in our AFM study. In particular, when the depletion of RBC is altered as consequence of radiation dose, the oxygen transportation capacity is compromised. We report, how this RBC oxygen state with Raman spectroscopy using a nanodiamond as a biolabel. Two characteristic peaks were used to measure 1588 cm-1 for oxygenated RBC and 1640 cm-1 for deoxygenated. The ratio I1588/I1640 of these peaks diminished as radiation dose increased. This may indicate that gamma radiation introduced a deformability and loss of oxygen from RBC and should be considered in the irradiation blood protocols.
A study of the thermoluminescent (TL) and afterglow (AG) response of several commercial samples of synthetic HPHT type-Ib diamond crystals is reported. In previous works it has been reported that the TL glow curves of diamonds grown by HPHT techniques are non-reproducible. We obtained the TL and AG curves in "as grown" samples irradiated with 90Sr radiactive source (beta emission) and compared them after a stabilization procedure (SP) which includes a high gamma (60Co) dose irradiation of 500 kGy followed by a thermal treatment (TT) of 800°C for 1 hour in nitrogen atmosphere. After one SP cycle, the TL and AG have enhanced their dosimetric range of linearity of the response; between 0 and 1 Gy and around 2 Gy the TL signal has a saturation behavior. For 2 SP cycles the reproducibility of TL was improved and we obtained a 5% marginal error.
Single crystal CVD diamond has noticeable advantages over conventional semiconductor materials and allows devices with a higher operating temperature, electric power, and radiation resistance to be developed . However, one of the main factors preventing its wide application and the advent of diamond electronics is the small geometric dimensions of diamond substrates on which epitaxial growth occurs. Currently, the technology for fabricating electronic devices on silicon is commercialized for substrates up to 300 mm in diameter . Recently, a Japanese team succeeded in fabrication of one inch mosaic crystal diamond wafers . However, the dimensions of these, although large, wafers are still far from the dimensions of silicon wafers. Nevertheless, it should be noted that polycrystalline diamond wafers 0.2 to 2 mm thick and 75 to 150 mm in diameter are successfully grown in some laboratories. The question arises: how can a single-crystal diamond of the dimensions presently achieved be used as a material for fabricating electronic devices in a large-scale technological process? In our opinion, one of the areas of such application can be as substrates of polycrystalline diamond with single-crystal diamond inclusions. Such combined diamond wafers will have a polycrystalline wafer diameter 75 to 150 mm and contain a large number of ingrown rectangular (or circular) small CVD diamond single crystals (as large as 5×5 mm or less). Processing lines which are already developed for silicon technology can be used to fabricate electronic devices on such 200-500 mu;m thick diamond wafers. To implement this approach, studies directed at fabricating the combined substrates under consideration are required. In this paper, we present the results of a study in which two problems were solved. One problem is the fabrication of substrates in which single-crystalline and polycrystalline diamond form a single wafer. The other problem is wafer polishing and study of the epitaxial growth of diamond on combined substrates containing regions of polycrystalline and (100) single-crystalline CVD diamond. In experiments 2.45 GHz CVD reactor was used. During the experiments, we determined the conditions under which high-quality single-crystalline and polycrystalline diamond films are deposited. Also the conditions of combined substrate polishing by thermal etching were studied. At each experimental stage, the grown diamond was characterized by scanning electron microscopy (SEM) and Raman spectroscopy.  CVD Diamond for Electronic Devices and Sensors, Edited by R.S. Sussmann (John Wiley & Sons, 2009).  Laurent Bosson. Challenges range from 300-mm economies to new cost pressures and technical barriers. - Wafer News. Special Issue. 2005, July 11. H. Yamada, A. Chayahara, Y. Mokuno, N. Tsubouchi, S. Shikata, N. Fujimori. Diamond and Related Materials, 20, 616-619 (2011).
Diamond-like carbon (DLC) coatings have been deposited on Si(100) and stainless steel substrates by high power impulse magnetron sputtering (HIPIMS) system utilizing high peak cathode powers densities of 1260 W/cm2. Adherent deposits on substrates can be obtained through applying gradient Ti/TiC/DLC layers. A pulsed sputter current more than 120 A was generated on the C target in order to make DLC coatings have higher hardness and denser structure. The films properties were correlated with the growth conditions, including deposition partial pressure, duty cycle and pulsed sputter current apply to the target. The microstructure and hardness value of DLC films were analyzed by using X-ray photoelectron spectroscopy and nanoindenter. The experimental results show that the pulsed sputter current had strong influence on the hardness value of the DLC coatings. It has been observed that DLC films prepared by HIPIMS technology have the hardness value as high as 32 GPa. The corrosion behavior of DLC coatings was also studied in 0.5 M H2SO4 solution by using potentiodynamic polarization method. These results showed that DLC coatings on stainless steel exhibited excellent corrosion behavior especially in lower corrosion current which was less than 5×10-7 A/cm2. Furthermore, the thermal stability of the DLC films on Si substrate was evaluated by monitoring the sheet resistance as a function of treatment temperature (30 min). The results reveal that the DLC films can stabilize up to 400°C.
Element Six first started its CVD diamond programme in 1988, twenty five years on this paper will review notable high and low points flagging some lessons learned. Notable recent trends in areas such as diamond quantum based and electrochemical sensing will be discussed. In addition it will summarize recent progress and challenges for microwave grown polycrystalline diamond as an enabling thermal substrate material for high power density rf electronics and optical windows for next generation EUV lithography.
The wide range of applications of CVD diamond single crystals requires the possibility of mass production. Today, the growth of CVD homoepitaxial single crystal diamond (SCD) is prepared mainly by resonance cavity MW PECVD deposition which provides sufficiently high growth rates. This growth has been extensively studied in the past by many research groups [1 - 5]. Limiting factors are not only the substrate quality but also the homogeneity of the plasma over large area and the scalability. Finding a method for reproducible and reliable production of large number of SCD samples with the same characteristics (morphology, doping level, thicknesshellip;etc) remains a challenge.In this study, we employ pulsed MW PECVD apparatus with linear antenna delivery system that is capable of producing a diffuse plasma over large areas using H2/CH4/CO2 gas mixtures. From previous studies it has been shown that nanocrystalline diamond (NCD) can be produced by this technique . However, by tuning the growth conditions, epitaxial growth conditions have been identified leading to significantly reduced secondary nucleation resulting in mosaic growth patterns.Successful homoepitaxial growth was realized on (100) single crystal Ib high pressure high temperature synthetic diamond substrates. Samples were characterized using Raman spectroscopy, photoluminescence (PL), AFM and scanning electron microscopy. R Linares et al: Diamond and Related Materials 8 (1999) 909-915 P Martineau et al: Gems & Gemology, 40 (1): 2-25 SPR (2004) G. Bogdan et al: phys. stat. sol. (a) 203, No. 12, 3063-3069 (2006) N Tranchant et al: Materials research society symposium proceedings, 956, 117-182 (2007) R Balmer et al: J. Phys.: Condens. Matter 21 (2009) 364221 (23pp) A. Taylor et al: Diamond & Related Materials 20 (2011) 613-615
We previously reported the results from a 2-dimensional Monte Carlo simulation of diamond growth which models 300 atomic layers of diamond growth using a PC in around an hour. This simulation reproduced many of the features seen in as-grown CVD diamond, such as apparent step-edge growth, flat surfaces, and hillock formation, as well as correctly predicting growth rates of the order of a few mu;m/h. We have spent the last 2 years refining this model, and in particular upgrading it to a full 3-dimensional model of the surface. We can now model the effects of addition to or etching from sidewalls, step-edges, corners, and vacancies. The results from these simulations will be compared with those from the simpler 2D model to assess which processes occurring on the growing diamond surface are important (i.e. determine the growth rate and or morphology) and so need to be understood in detail, and which processes are less important and can be approximated.The nature of the critical nucleus in a true 3D system can now be determined for the first time using this model, as can other insights into the fundamental diamond growth processes occurring for a range of different deposition conditions.
Diamond is a unique material with exceptional properties, including high hardness, unmatched thermal conductivity, high electronic carrier mobility, high electric field breakdown, radiation hardness, biocompatibility, and unique chemical inertness. Despite these superb material properties, the full potential of diamond for numerous applications has not been realized because material of sufficient size and perfection has not been adequately available. Progress has been made over the past decade on the plasma-assisted chemical vapor deposition (PACVD) of single crystal diamond for numerous applications. This presentation will present recent progress of single crystal diamond PACVD, especially as the advances relate to electronic and optical applications. Two areas that will be discussed include (1) progress on improving the properties/quality of PACVD single crystal diamond and (2) progress on improving the PACVD process to increase substrate area, increase the deposition rate and reduce the cost of single crystal diamond. Progress at Michigan State University/Fraunhofer Center for Coatings and Laser Applications and progress around the world by other researchers will be discussed in this presentation.Important quality factors for improving single crystal diamond for optical and electronic applications include growing the diamond while minimizing defects, controlling the incorporation of dopants with predictable uniformity and high dopant activation percentages for electronic applications, and processing the diamond with techniques to form devices while minimizing the formation of new defects. The objective is to get single crystal diamond for electronic applications that has the high electric field breakdown strength and high carrier mobilities possible with diamond. As diamond electronics looks to compete with other wide bandgap semiconductor materials, selected properties must be at or near the highest values possible with diamond. The other challenge for single crystal diamond is producing substrates of sufficient size and quantity that the availability and price make it a reliable, easy to use, and competitive product. Progress on increasing growth rate, increasing substrate area and decreasing diamond synthesis cost will be discussed in this presentation.
Devices for high end applications which make use of diamond&’s unique physical properties typically require single crystals in order to guarantee that the extreme material properties are not deteriorated by the presence of grain boundaries. In order to synthesize samples with single crystal quality and technologically relevant wafer size dimensions two major concepts are currently explored. Both use chemical vapor deposition (CVD). The first is based on homoepitaxy using substrates grown by the high pressure high temperature (HPHT) technique and applying cloning and tiling steps. In the second approach heteroepitaxial growth is performed on foreign substrates. Amongst all substrates for which generation of epitaxially aligned diamond grains has been shown experimentally, iridium has turned out to be unique since it facilitates unrivaled alignment of the grains. In this talk the recent progress of diamond heteroepitaxy on iridium layers will be reviewed. All work has been performed on Ir/YSZ/Si with on-axis or off-axis Si(001) and Si(111) substrates. The major defects that have to be considered can be distinguished according to their dimensionality, i.e. 2D, 1D and 0D. Two-dimensional grain boundaries are present only during the first 10-30 µm of film growth forming a closed network that separates individual mosaic blocks. After their dissolution the defect structure is dominated by 1D threading dislocations which appear as individual defects or gathered in groups. Their initial density above 1010 cm-2 decreases continuously by several orders of magnitude during film growth up to 1000 µm thickness. This decrease and the concomitant reduction in microstrain as deduced from Raman line width measurements follow simple mathematic laws. In addition it will be shown that dislocations crucially control the formation of intrinsic stress of both signs during film growth. Among the structural / chemical zero-dimensional defects, centers consisting of an impurity atom and a vacancy (NV, SiV) are of special interest. In the talk the state of the art with respect to defect densities will be described and extrapolations to even higher film thicknesses will be discussed. In addition the performance of the crystals in several areas of potential applications will be presented.
Mechanisms leading to heteroepitaxial diamond nucleation on iridium are particularly complex. Indeed, different plasma-surface interactions are taking place during the Bias Enhanced Nucleation (BEN) step [1,2] inducing the formation of “domains” where epitaxial diamond is obtained after CVD growth. Our previous AFM/SEM  study has shown that domains are composed by an amorphous carbon film (8 nm thick) deposited on roughened iridium, the presence of diamond nuclei at the interface after BEN was supported by SEM.However, to correlate the domain evolution on the iridium surface to the BEN parameters, homogeneous and reproducible deposits are required. As a consequence, the process has been developed and optimized to reach these conditions to specifically study the domain evolution versus time. Several reproducible samples with different BEN times (from 20 to 60 minutes) were investigated by Scanning Electronic Microscope (SEM). Pictures were analyzed by image processing with ImageJ software. Density, surface coverage, size, shape and orientation of domains were extracted. The evolution of the size distribution with the BEN time shows that both density and size of each domain increase at the iridium surface. This can be described by a nucleation rate for domains combined with an expansion kinetics for nucleated domains. The kinetic law of domains expansion was investigated and follows a sigmoid law which will be detailed in different steps and discussed. The latter highlights that during 2D expansion of domains, a preferential orientation close to 45° with respect to the  and  orientations of the iridium appears during the BEN process. This new control of domains sizes and density could be used to improve diamond heteroepitaxial film quality (defects, interface stresshellip;) during the first growth step.References: S. Gsell, S. Berner, T. Brugger, M. Schreck, R. Brescia, M. Fischer, et al., Comparative electron diffraction study of the diamond nucleation layer on Ir(001), Diamond and Related Materials. 17 (2008) 1029-1034. A. Chavanne, J. Barjon, B. Vilquin, J. Arabski, J.C. Arnault, Surface investigations on different nucleation pathways for diamond heteroepitaxial growth on iridium, Diamond and Related Materials. 22 (2012) 52-58. N. Vaissiere, S. Saada, M. Bouttemy, A. Etcheberry, P. Bergonzo, J.C. Arnault, Heteroepitaxial diamond on iridium: New insights on domain formation, Diamond and Related Materials. 36 (2013) 16-25.
Materials with extremely high bulk modulus and high hardness are marked with short bond lengths, high coordinate numbers, and low ionicity. Diamond is such a material and it is an excellent wide-band gap semiconductor.The first successful synthesis of diamond was achieved using a high pressure and high temperature (HPHT) method developed by General Electric in the 1960s. However, besides the high price, diamond synthesized by the HPHT process is in the form of small particles, ranging in size from nanometers to a few millimeters, which is too small for large-scale production of diamond devices and materials. In this study, we will demonstrate how silicon carbide (SiC) can be used as a substrate for high quality epitaxial growth of diamond on SiC by nanodiamond seeding. We discuss the conditions, which affect diamond growth on primarily the C face of 6H-SiC, but also discuss growth on other polytypes of SiC and on silicon. The system employed uses a hot-filament chemical vapor deposition reactor in which the distance from the source can be varied. Its basic system configuration allows for excellent and repeatable uniform growth processes for diamond. The diamond players were characterized by a variety of methods including scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS) and Raman spectroscopy. The mobilities of the as grown layers were as high as 420 cm2/V-sec.
Owing to its high carrier mobility, high Young&’s modulus, and high thermal conductivity, graphene has been a center of attraction for researchers around the world particularly for understanding the fundamental physics of electronic transport in 2D materials . However, the fact that the one atom thick graphene membrane strongly affected by the substrate interactions puts limit on exploiting excellent intrinsic properties of graphene for various applications. Diamond offers multiple distinctive properties, such as high phonon energy, low trap density, and high thermal conductivity which make it an ideal substrate for fabricating graphene devices on diamond. Our research in this direction has been initiated earlier  demonstrating fabrication of graphene based devices on diamond and their unique properties for the first time. However, the graphene was transferred onto the diamond surface using mechanical exfoliation process limiting the applicability of this process to the industrial scale. In present studies, we demonstrate a novel process to grow large area single and few layer graphene on the diamond thin film deposited on silicon wafer. The fact that single and few layer graphene can be grown on diamond thin films on wafer scale (100 mm diameter) at relatively lower temperatures (~800oC) than other existing high temperature methods (such as on SiC) without any transfer process makes this approach unique and offers new opportunities for developing graphene based nanoelectronic devices on diamond. We discuss growth process and characterization of graphene in detail as well as fabrication and performance of top-gate graphene devices on diamond.References: K. S. Novoselov, V. I. Fal&’ko, L. Colombo, P. R. Gellbert, M. G. Schwab, K. Kim, “A roadmap for graphene”, Nature, 490, 192, (2012). Jie Yu, Guanxiong Liu, Anirudha V. Sumant, Vivek Goyal, Alexander A. Balandin, “Graphene-on-diamond devices with increased current-carrying capacity: Carbon sp2- on-sp3 planar technology”, Nano Letters, 12(3), 1603 (2012).
Since the discovery of superconductivity in boron-doped synthetic diamonds  it is considered as a result of insulator-to-metal transition at heavily doping of cubic diamond. Despite a number of experimental evidences of superconductivity some properties are still unclear. For example, Raman spectra of such crystals have two main broad bands at 460-480 and 1220-1230 cm-1 which disagree with the cubic lattice. Instead, they are very similar with the Raman spectra of BC5 compounds . Superconductivity of such boron carbide with the critical temperature Tc up to 45K was theoretically predicted . We have grown 4-5 mm large single crystal heavily boron-doped diamonds by the temperature gradient method under high-pressure-high-temperature conditions [4, 5] and investigated their structure and electrical properties. We used X-ray diffraction, electron microscopy, AFM analysis and micro-Raman scattering for the studies of structure and revealed thin, about 1 mu;m thick surface layer with hexagonal structure on the surface of cubic diamond. We cut ~100 mu;m plates with as-grown surface and investigated electrical conductivity of as-grown surface and the opposite one by 4-probe method down to 1.8K using Quantum Design PPMS EverCool-II system with magnetic field up to 9 Tesla. Chemical etching of the surface of heavily boron-doped diamond in ~100 nm depth drastically changed Raman spectra from broad bands to typical crystal diamond narrow line and defect-induced bands with boron content ~0.1 at% . The temperature dependence of electrical resistivity measured by the 4-probe method at as-grown (111) faces showed transition to superconductivity at Tc=2.5-3.5K as reported earlier . However, the opposite side of the plate showed typical semiconductor R(T) behaviour with activation energy about 80 meV at room temperature and variable range hopping with high resistivity at T<220K. According to X-ray diffraction and electron microscopy analysis the structure of the film is hexagonal. The Raman spectra can be attributed to nanometer-thick hexagonal diamond type lattice. The mean boron content in 1 mu;m depth measured by the wavelength dispersive X-ray spectroscopy method was about 2.5 at.%. Thus we conclude that thin hexagonal boron carbide layer at the surface of boron-doped diamond is superconducting. 1. E.A. Ekimov, V.A. Sidorov, E.D. Bauer et al, Nature, 428 (2004) 542.2. V.L. Solozhenko, O.O. Kurakevych, D.Andrault, Y.L. Godec, M. Mezouar, Phys. Rev. Lett. 102 (2009) 015506.3. M.Calandra, F. Mauri, Phys. Rev. Lett. 101 (2008) 016401.4. R.H. Wentorf, H.P. Bovenkerk, J. Chem. Phys. 36 (1962) 1987.5. V.D. Blank, M.S. Kuznetsov, S.A. Nosukhin, S.A. Terentiev, V.N. Denisov, Diamond and Rel. Mat. 16 (2007) 800.6. B.N. Mavrin, V.N. Denisov, D.M. Popova et al., Phys. Lett. A 372 (2008) 3914.
In this paper, we reported a three-dimensional micro-channel structure, which was fabricated by Yb:YAG 1026 nm femtosecond laser irradiation on a single-crystalline diamond substrate. The femtosecond laser irradiation energy level was optimized at 100 kHz repetition rate with a sub-500 femtosecond pulse duration. The morphology and topography of the microfluidic channel were characterized by SEM and AFM. Raman spectroscopy indicated that the irradiated area was covered by graphitic materials. In order to fully remove the residue of the graphitic material, the diamond substrate has been subjected to hydrogen-plasma etching process by using a MPECVD system. By comparing the AFM cross-sectional profiles before/after removing the graphitic materials, it could be deduced that the micro- channel has an average depth of ~410 nm with periodical ripples perpendicular to the irradiation direction. The fs-laser inscription technique offers a faster and more convenient approach to develop 3D structures and/or devices on diamond substrates, when compared with conventional techniques such as FIB and RIE, etc. This work proves the feasibility of using ultra-fast laser inscription technology to fabricate microfluidic channels on biocompatible diamond substrates, which offers a great potential for biomedical sensing applications.
Pulsed microwave plasma enhanced chemical vapour deposition apparatus with linear antenna delivery system using CO2/CH4/H2 gas chemistries is a versatile system that allows large area growth of nanocrystalline diamond (NCD) at low temperatures . However, one of the drawbacks of the system in comparison with conventional resonance cavity MW CVD systems is lower growth rates. High growth rate is essential for many commercial applications. To overcome this problem while maintaining low temperature, we investigate the catalytic effect of nitrogen in the gas phase that is known to enhance the growth rate . Nitrogen concentrations were varied from 0.1 to 5% in the gas phase and the effect of this addition on the growth rate was investigated. The morphology, grain size, structure, and quality (sp3/sp2 ratio) of the NCD samples were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction, and Raman spectroscopy.The complex gas chemistry induced by nitrogen addition led, somewhat surprisingly, to two effects. The growth rate of the diamond films indeed increased when nitrogen was added. However, upon increasing the nitrogen concentration, the morphology changed significantly. For high N concentrations the NCD morphology resembles highly N-doped ultrananocrystalline diamond (UNCD) films grown in Ar rich atmospheres  in terms of clustering nano-grains into larger ordered clusters and is significantly distinguished from so called “cauliflower” nanodiamond which has been prepared in N-containing resonance cavity plasmas. Furthermore, the sp3/sp2 ratio and diamond Raman peak remained unchanged, when compared with samples prepared without nitrogen at the same growth conditions. A. Taylor et al: Diamond & Related Materials 20 (2011) 613-615 S. Dunst, et al: Appl. Phys. Lett. 94, 224101 (2009) D. Gruen: MRS BULLETIN 26, 10, 771-776 (OCT 2001)
Cubic boron nitride (cBN) is isoelectronic to diamond, and H-terminated cBN has been shown to exhibit a negative electron affinity (NEA) surface. An NEA surface enables emission of conduction band electrons into vacuum without experiencing an extra surface barrier. It has been shown that diamond films with NEA surfaces exhibit thermionic emission below 500°C, making them candidates for electron emitters and collectors in thermionic energy conversion (TEC) devices that operate below 700°C. Given the similar properties to diamond, we present a spectroscopic study of cBN films that investigates its electronic structure to assess its potential as an electron emitter and/or collector in TEC devices. In this study, cubic boron nitride is deposited on silicon using electron cyclotron resonance microwave plasma chemical vapor deposition (ECR MPCVD) employing fluorine chemistry. In-situ X-ray photoelectron spectroscopy (XPS) measurements indicate the presence of cBN on the film&’s surface with minimal presence of hexagonal boron nitride (hBN). Fourier transform infrared (FTIR) spectroscopy indicates a transition from hBN to cBN as the film grows. Ultraviolet photoelectron spectroscopy (UPS) is employed to reveal the electronic structure and indicate the presence of a NEA on the film&’s surface. The observed work function of the undoped cBN the film is 2.7±0.2 eV. Additionally, the results show a distinctive peak at the lowest kinetic energy of the spectra which is a feature that is often associated with a NEA surface for diamond films. The results are consistent with a bandgap of 6.7±0.2 eV which is comparable to the reported value of 6.4 eV. These observations suggest the growth results in a surface with NEA-like behavior. Further investigation will explore the potential of cBN films for electron emitters and collectors in TEC devices.This research is supported by the Office of Naval Research through grant # N00014-10-1-0540.
Parametric frequency conversion via optical nonlinearities in an on-chip platform is intriguing for the development of compact, robust, low-power consuming broadband light sources with applications in spectroscopy, metrology, sensing and all-optical information processing [1,2]. Diamond holds promise as an excellent material for photonic applications due to its exceptional physical and chemical properties, extremely wide transparency window, relatively large refractive index and the presence of various color-centers acting as quantum emitters . Here we present the first realization of nonlinear photonics in diamond by demonstrating optical parametric oscillation (OPO) via four-wave mixing (FWM) in fully-integrated, monolithic, single crystal diamond (SCD) micro-ring resonators.Diamond&’s lowest order non-zero nonlinear susceptibility is chi;(3). FWM is a third-order nonlinear parametric process where two pump photons at frequency nu;_P are converted to two different photons at nu;+ and nu;minus; (denoted as signal and idler), such that energy is conserved (2nu;_P = nu;+ + nu;minus;). OPO is achieved when the round trip FWM gain exceeds the loss in a resonator, a process analogous to a laser above threshold, and bright coherent light is generated at the signal and idler wavelengths. The OPO threshold power is inversely proportional to Q^2.Experimentally, a continuous-wave input laser is sent through an erbium-doped fiber amplifier (EDFA) to obtain high pump powers and then coupled into the on-chip device to observe OPO operation. The pump is initially slightly blue detuned and then slowly moved into a cavity resonance. The output light from the chip is continuously monitored on an optical spectrum analyzer (OSA). As the offset of the pump to the resonance minimum decreases, more power is transferred to the ring resonator, eventually resulting in the generation of pairs of new lines, at integer multiples of the resonator FSR, around the pump in the optical spectrum. High quality factor (sim;1 million) resonators operating at telecom wavelengths enable threshold powers as low as 20mW. Further, by measuring the threshold power for different devices, we extract the intensity-dependent refractive index of diamond at telecom wavelengths. Coupling higher pump powers into the OPO device should enable the generation of broadband, high-repetition-rate optical frequency combs that are desirable for numerous applications [1,2], and this technology in diamond can be readily extended to new wavelength ranges.References: Th. Udem, R.Holzwarth and T. W. Haensch, “Optical frequency metrology,” Nature 416, 233 (2002). T. J. Kippenberg, R.Holzwarth and S. A. Diddams, “Microresonator-based optical frequency combs,” Science 332, 555 (2011). I. Aharonovich, A. D. Greentree and S. Prawer, “Diamond photonics,” Nature Photon. 5, 397 (2011).
The NV centre in diamond which associates a nitrogen atom in substitution to a carbon atom and a nearby vacancy is regarded by many as a promising candidate for applications in spintronics, quantum computing or magnetometry. In fact the spin state of the defect can be easily manipulated and read out optically with coherence times up to several milliseconds long. Ion implantation is the most common technique to generate a controlled density of NV centres in high-purity synthetic crystals. However this technique suffers from a reduced spatial resolution due to straggling and channelling effects as well as a limited creation yield. Defects generated during implantation cannot be completely annealed out which also significantly hampers the centre&’s coherence times. On the other hand progresses in diamond growth by plasma assisted CVD has allowed unprecedented control over the purity of the synthetic diamonds produced and NV centres that are directly grown-in have exhibited the best properties so far.Creating NVs requires that N2 is added to the gas mixture during CVD growth. The uptake of nitrogen is generally low, of the order of 10-4 and only a small fraction (typically 10-3) is found in the form of NVs; the most part being substitutional nitrogen (Ns0). In order to achieve an accurate control over the density and distribution of NV defects it is particularly important to understand how incorporation efficiency and creation yield are affected by the growth conditions such as temperature, methane content or plasma power density. In this paper nitrogen incorporation during CVD diamond growth is discussed as a function of process parameters. It was in particular found that NV centres are mostly created when growth is carried out at a reduced temperature whereas at high temperature luminescence from NVs is practically undetectable. This shows that temperature is a useful tuning parameter allowing the stack of high-quality diamond layers having a varying content of luminescent defects. The ability of this method to produce thin highly N-doped diamond layers embedded in a pure matrix that would be relevant for magnetometry applications is assessed.
Diamond exhibits a large amount of optical centers. One among many others is the NV color center which consists of a substitutional nitrogen atom bounded to a neighboring carbon vacancy. Its unique optical and spin properties which prevails even at room temperature lead to a wide panel of applications. Many of those applications require the positioning of NV centers with high spatial control. Formation of NVs can be performed either by creation of vacancies in N-doped samples of type I-b . This approach leads to the deterministic generation of arrays of NV centers, but presence of N-atoms all around in the diamond bath worsten the spin properties of intentionally created centers. Another approach is to implant nitrogen atoms in ultrapure diamond crystals. High-resolution placement of NV centers can then be achieved using for instance the collimation of the ion beam through a pierced AFM tip . Despite its high accuracy in ion placement with a spatial resolution better than 20 nm, this technique can hardly be applied to create large arrays of color centers. We show that a beam of nitrogen ions can be focused to approximately 100 nm using FIB technology and moreover FIB column used in our experiments combined with a scanning electron microscope, it offers new possibilities for the targeted creation of NV centers in already created structures in diamond. This approach can be used, for instance to form a color center inside the cavity of a photonic crystal or in a diamond membrane.The diamond sample (200 µm thick) used in our experiments consists of ultrapure CVD layers, grown on HPHT substrate at LSPM. Nitrogen implantation was performed with a FIB-column developed by Orsay Physics S.A. Implantation was done at fixed energy 15 keV per ion, and accroding to SRIM simulation such energy corresponds to approximately 20 nm depth. Varying the dose of implantation several arrays of NVs were created (dimension 21x21 spots with 2 µm distance). In order to activate implanted nitrogen, sample was annealed at 800° C during 2 hours. The focus of FIB column was estimated to be in the range of 90±20 nm. The number of created NV in several spots of created pattern was estimated by photon correlation technique and by analysis using Ground State Depletion (GSD) microscopy. Both methods used for the NVs number estimation are in good agreement.As conclusion, it sould be pointed that the nitrogen-FIB column combined with a scanning electron microscope offers new possibilities for the targeted creation of single defects in diamond in already created structures, for instance, in diamond tips for scanning magnetometry or in waveguides.References: J. Martin, R. Wannemacher, J. Teichert, L. Bischoff, and B. Köhler, Appl. Phys. Lett. 75, 3096 (1999). S. Pezzagna, D. Wildanger, P. Mazarov, A. D. Wieck, Y. Sarov, I. Rangelow, B. Naydenov, F. Jelezko, S. W. Hell, J. Meijer, Small 6 2117 (2010).
Diamond has excellent characteristics such as high hardness, high thermal conductivity and wide band gap. Recently color centers in nanocrystal diamond (NCD), such as nitrogen-vacancy (N-V) centers, are attracting much attention to apply to luminescent biomarkers and single photon emitters. In particular, silicon-vacancy defects (Si-V centers) in diamond are expected because of their high emission rate and stability at room temperature. Bias-enhanced nucleation (BEN) is a good way to generate diamond nuclei on heterogeneous substrates. Recently we have proposed the nucleation enhancement by atomic silicon micro addition and high microwave power removing a-C during BEN. The surface-enhanced Raman scattering (SERS) spectrum shows the diamond fine peak at 1332 cm-1 and quite similar to the typical spectrum of NCD. In addition, a zero-phonon line emission at 738 nm originated from Si-V luminescent center was observed. In this paper, we discuss the formation of Si-V luminescent centers in high quality NCD by atomic silicon induced diamond nucleation.
Diamond nanoparticles or nanodiamonds (NDs) produced by detonation synthesis have attracted a lot of attention over the last years. Because its potential applications are numerous, studies of this material aim to understand, control and tailor its physical and chemical properties which are given by the combination of an inert diamond core with a surface rich in functional groups . Indeed ND crystallites are composed of diamond cores of a few nanometers in diameter, partially or completely covered by a thin layer of graphitic and / or amorphous carbon, and bearing carboxyl-, hydroxyl and carbonyl functionalities on the surface.Raman spectroscopy is commonly used for the characterization of those detonation nanodiamonds. When observable, the Raman spectrum of those nanoparticles is usually composed by a broadened and downshifted first-order Raman mode of the cubic lattice and a broad peak at about 1600 - 1650 cm-1. Previous studies have shown that this broad peak seems to be sensitive to the NDs surface chemistry. However, the assignment of this peak is still unclear [1,2 and references herein]. In this study, different chemical and thermal treatments were carried out in order to selectively modify their surface chemistry and track the resulting changes in the Raman spectrum. To this end, ex situ and then in situ Raman measurements were performed.Detonation NDs (provided by NanoCarbon Research Institute Ltd) were either hydrogenated using a microwave plasma  or annealed under vacuum to induce their surface graphitisation . In addition, in situ Raman measurements were conducted during annealing treatments of NDs performed in air and in H2 atmospheres. To reduce the strong photoluminescence background of the samples, measurements were systematically conducted in the UV spectral range using the 325 and 244 nm lines of a He-Cd and a frequency-doubled argon lasers respectively. Part of the present results shows that the shape of the Raman spectrum may actually change with the surface chemistry of NDs. For in situ annealing treatments in H2 atmospheres, the results also tend to indicate strong surface modifications, even for moderate annealing temperatures.1. V. N. Mochalin et al, Nat. Nanotechnol. 2012, 7, 11.2. V. Mochalin et al, Chem. Mater. 2009, 21, 273.3. S. Osswald et al, J. Am. Chem. Soc., 2006, 128, 11635.4. H. A. Girard et al, Diam. Relat. Mater. 2010, 19, 1117.5. T. Petit et al, Nanoscale 2012, 21, 6792.
Silica gels are widely used for column packing material for HPLC. However, in a high pH solution, silica gels can be decomposed by hydrolysis, which limit the applicable pH range of the mobile phase. Diamond is extremely chemically stable material. Thus, if we can use diamond for HPLC column packing material, a wide range of pH can be used for the mobile phase. In this study, we fabricated porous diamond spherical particle (PDSP) as a novel mesoporous material. The PDSP surface was modified with octadecyl group and the modified PDSP was applied to a reverse-phase column packing material for HPLC.Aqueous slurry containing diamond nanoparticle (DNP) with various diameters (5minus;50 nm) and polyethylene glycol (PEG) was spray-dried to fabricate DNP/PEG spherical particles with average diameter of 3minus;10 mu;m. After removal of PEG from the particle by thermal oxidation in air, the particle was subjected to chemical vapor deposition to grow diamond on the particle surface for reinforcement. After removal of possible non-diamond carbon impurities by thermal oxidation in air, oxidized PDSP (O-PDSP) was obtained. The O-PDSP was then hydrogenated by H2 plasma treatment or heating in H2 gas (H-PDSP). The H-PDSP was modified with 1-octadecene to obtain octadecyl group-modified PDSP (C18-PDSP).From nitrogen gas adsorption study, the PDSP was found to have mesopores and the BET surface area ranged from 80 to 300 m2/g depending on the primary DNP size. The PDSP was found to be stable to immersion HF or NaOH aqueous solution indicating extreme chemical stability. Photochemical modification of PDSP with 1-octadecene was confirmed by FTIR spectra. HPLC examination using C18-PDSP-packed column showed successful separation of organic compounds with reverse-phase mode, indicating applicability of the PDSP to a highly stable column packing material for HPLC.
Fluorescent nanodiamonds (FNDs) are studied in connection with wide variety of bio-applications including their use as luminescent probes and sensors. Fluorescence of a diamond originates from local disorders in a diamond crystal lattice - the nitrogen-vacancy (NV) centers. NV centre is completely resistant towards photobleaching and, apart from very small ND particles <5 nm, also towards photoblinking. The brightest available FNDs are those prepared under high pressure-high temperature (HPHT) conditions. HPHT nanodiamonds are polydisperse and of irregular shape bearing sharp edges and spiky vertexes. We present a new chemical treatment of polydisperse commercial 50 nm HPHT nanodiamonds (dispersity D = 9.9), which etches their sharp edges and spikes, resulting in pseudospherical nanodiamonds. These spherical diamonds were fractionated by centrifugation, yielding monodisperse (D = 1.6) fraction of NDs 40 nm in diameter. The same fractionation procedure, applied on original spiky diamonds yielded diamonds of higher polydispersity (D = 2.6), showing that particle rounding is essential for their successful fractionation. Presented chemical etching procedure is simple to perform, and can be easily performed in a gram scale. It was also demonstrated, that spherical monodisperse NDs can be irradiated by accelerated particles to yield FNDs. Spherical FNDs represent unique new material, superior to usually used FNDs in particle shape and distribution which makes them perfectly suitable for applications where these properties are essential, including their use as bioprobes or sensors.
Fluorescent nanodiamonds (NDs) are a perspective material for the preparation of fluorescent labels for bioimaging due to their unique and attractive properties such as unlimitedly stable fluorescence and biocompatibility. NDs fluorescence is caused by point defects in its crystal lattice, so called nitrogen vacancy (N-V) centers. Contrary to other compounds, nanodiamonds do not photobleach or photoblink and have long fluorescence lifetime. Furthermore, fluorescence of nanodiamonds is well separated from cell auto-fluorescence and falls in the near-infrared part of the spectrum (so-called imaging window I) suitable for in vivo imaging. Before the employment of nanodiamonds as fluorescent labels in biological systems, several properties have to be improved. Primarily, their colloidal stability in biological media has to be ensured. Preventing of non-specific interactions of nanodiamonds with proteins is next crucial step. Finally, it is necessary to enable their high-yield further modifications with various molecules. To accomplish these properties of NDs we introduce hydrophilic co-polymers coating surrounding a ND particle. The co-polymers are grown directly from the nanoparticle surface and they contain alkyne or azide groups enabling the covalent attachment of targeting moieties by azide-alkyne cycloaddition reation (click chemistry). We will demonstrate an architecture on a polymer-coated fluorescent ND particles designed for cancer cells targeting as well as results of first biological experiments with them.
Diamond nanoparticles or nanodiamonds (NDs) behave several essential assets for biomedical applications: their very weak cytotoxicity and genetoxicity , their carbon-related surface chemistry for covalent functionalization of targeting or labeling moieties (oligonucleotides, proteins, fluorescent dyeshellip;) and their tunable surface charge toward drug delivery [2, 3]. In particular, detonation nanodiamonds synthetized by explosion  combine all this possibilities in a primary size of 5 nm, compatible with kidney filtration for an expected easier elimination.Nanoparticle radiotracers are currently widely used to assess quantitatively the health hazard related to nanotechnologies or as theranostic agents . Radioactive labelling of nanodiamonds would thus be a promising approach that ensures their tracing for biolabelling or biodistribution studies. From our knowledge, such radioactive labelling was not reported yet. Detonation nanodiamonds (3H-ND) were tritiated using a microwave plasma reactor. Tritium is a β- emitter, which disintegrates into 3He, with a 12.32 years half-life (compatible with biodistribution studies) and by emitting an electron having an average energy of 5.7 keV. This experimental approach was previously applied to efficiently hydrogenate detonation NDs . From sequential radioactivity measurements of 3H-ND at different temperature thresholds during an air oxidation, we inferred that stable radioactive labeling of D-ND comes not only from surface C-3H bond but also from the diffusion of 3H deep inside the diamond lattice. At room temperature, no tritium desorption was observed. 75% of the radioactivity was lost from ND at 400 °C, while a temperature of 600 °C is needed to remove all the tritium. These experiments strongly suggest that 75% of the tritium atoms are tightly bound to the ND surface while 25% are deeply buried in the diamond core. These results demonstrate the excellent stability of tritium incorporated into nanodiamonds which can be stably implanted by diffusion. β- activity measurement will be directly related to ND concentration, allowing their quantification and localization in tissue/organ and wastes. References V. Paget et al., Nanotoxicology (under review) T. Petit et al., Nanoscale 4 (2012) 6792. A. Krueger et al., Advanced Functional Materials (2012) DOI: 10.1002/adfm.201102670 V. Y. Dolmatov, Russian Chemical Reviews 76 (2007) 339. H. Hong et al., Nano Today 4 (2009) 399.  H. A. Girard et al., Diam. Relat. Mater. 19 (2010) 1117.
Recently, nanodiamond (ND) has been considered in terms of development of nano-bio applications. ND&’s spectroscopic (Raman and fluorescence) and surface properties, chemical stability and biocompatibility make it a convenient base for novel bio-sensing, imaging and drug delivery materials and methods. Examples of such bio applications as well as ND&’s non-toxicity have been successfully demonstrated for wide number of cells, including different cancer cells and normal cell lines. To date, very limited number of publications exists concerning ND interaction with tissues and organs. However, the study and understanding of the interaction mechanisms of ND with tissues and organs is a necessary step for implementing ND&’s biomedical applications on the highest levels of biological system organization.In our work, the interaction of ND of different sizes alone and ND in complex with biologically active molecules (proteins, drugs) with blood, like integrative tissue, and with some blood&’s components is studied. In this presentation we focus on the ND interaction with red blood cell (RBC). Confocal microscopy, Raman spectroscopy and UV-visible absorption, as well as analysis of RBC diffuse light backscattering aggregometry and diffractometry are used to characterize and to compare the effects of ND on the rat and human RBC. ND effects on oxygenation and deoxygenation processes of whole RBC and of Hb solution are compared. It allows discussing the mechanisms of ND interaction with RBC membrane, influence on the membrane structure and effects on the RBC mechanical properties, which in turn significantly affect the blood rheology.It was shown that preliminary modification of ND surface with blood plasma protein albumin significantly increases the biocompatibility of ND at its interaction with blood, including its effects on RBC functioning and on blood plasma composition and properties, particularly, decreasing the uncontrollable adsorption of plasma components. Finally, interaction with blood and ND biodistribution in vivo will also be discussed.
Microporous sp2-bonded carbon materials are widely used in/for gas storage, sorbents, supercapacitor electrodes, water desalination, and electrocatalyst/catalyst supports. The adsorption and transport of fluids in these porous materials, which would be important in electrochemical systems, depends on the number and size of the pores as well as the surrounding surface microstructure and chemistry. Diamond (sp3-bonded carbon) has a number of technologically-important properties including microstructural stability, corrosion resistance and chemical inertness. Diamond is an electrical insulator with a band gap of >5 eV. The material can, however, be made electrically conducting by doping with boron. The technology for producing single crystal and thin films of conducting diamond is well developed. Electrically conducting (>0.5 S/cm), high surface area (>100 m2/g) diamond powders represent an advanced functional material. Our research has shown that such materials can be produced via a core-shell approach. In this approach, a high surface area substrate powder is overcoated with a thin layer of boron-doped ultrananocrystalline diamond (B-UNCD). The B-UNCD is deposited by microwave-assisted chemical vapor deposition using an Ar-rich CH4/H2/Ar/B2H6 source gas mixture. Preliminary data from our laboratory indicate that B-UNCD layers can be formed on nanometer-sized diamond grit, disordered sp2 carbons (e.g., Ketjen Black) and metal oxide powders (e.g., TiO2). Much remains to be learned about the synthesis of these nanostructured powders, the kind of collective properties they possess as a function of their structure, and how molecules/fluids interact with these materials in electrochemical systems. Our current research is directed toward gaining fundamental insight on the preparation, characterization and properties of new sp3 and hybrid sp2/sp3 nanostructured carbon powders. How these materials function as a corrosion-resistance electrocatalyst support for PEM fuel cells and as a high surface area anode for the electrochemical-remediation of pesticide and pharmaceutical contaminants in water supplies are being investigated. In this presentation, we will describe the preparation and characterization of these high surface area, electrically conducting diamond powders.
Ni-related impurity are known to be the origin of various color centers indiamond which can be interesting for quantum information processing (QIP) or bioimaging in nanodiamonds.We find that W8 center (negatively charged Ni substitutional) is rather an absorption center with zero-phonon line (ZPL) at ~3.1 eV than a luminescence center. As a consquence, it is not a good candidate for QIP or other applications. We also characterize NE4, NE4* and NE8 Ni-related complexes in bulk and ultrasmall nanodiamonds that show sharp, red or near-infrared ZPL emissions in bulk diamonds. We find that the quantum confinement effect is relatively strong for NE4 and NE8 color centers: when the diameter of nanodiamond shrinks downto 2 nm and 1 nm then there is a clear blueshift in the emission, changing from green to violet. Principally, multi-color emission is possible from single NE4 center, for instance, when the diameter of nanodiamonds can be well controlled.
The production of diamond-based electronic devices for optical and electronic applications requires the control of point and extended defects that influence the exceptional properties of the material. Nowadays high quality single crystal diamond with dislocation densities between 104 and 106 cm-2 exhibiting low birefringence and suitable for optical applications can be produced by microwave plasma chemical vapour deposition (MPCVD). However, for the use of diamond in electronic devices designed to operate at high power , diamond crystals with reduced dislocation densities are necessary .Two main sources of extended defects in CVD crystals can be identified: (i) dislocations induced by the substrate&’s surface state and its polishing, (ii) dislocations that directly originate from defects in the bulk of the substrate such as stacking faults. The generated dislocations tend to thread through the CVD film parallel to the growth direction.Different strategies have been investigated to inhibit the formation of these defects, such as surface treatments and surface structuration  but they are inefficient to prevent dislocations already existing in the substrate from extending into the CVD layer. For this purpose, growth strategies inspired from epitaxial lateral overgrowth (ELOG) commonly used to block and bend dislocations in GaN films will be detailed. Ir and Pt thin layers were deposited by MOCVD on diamond substrates. The layer's thickness and subsequent thermal treatment were optimised in order to obtain self-assembled metallic nanoparticles with controlled size  that preferentially cover defects at the surface. CVD diamond growth was then carried out over such a masked diamond substrate. The interaction of dislocations with embedded nanoparticles will be discussed allowing expecting a substantial decrease in dislocation density .In this study, self-assembled metallic masks process is carried out onto several single diamond crystals in order to determine the impact on extended defects propagation mechanism. Friel et al.,Diamond and Related Materials, v. 18, p. 808-815 (2009) J. Achard et al., Diamond and Related Materials, v. 20, p. 145-152 (2011). S. Ohmagari et al. Journal of Applied Physics, v. 110, 056105-3 (2011). M. Naamoun, A. Tallaire, F. Silva, J. Achard, P. Doppelt, A. Gicquel, Phys. Status Solidi A 209,9, 1715-1720 (2012) S. Mitani et al., Diamond and Related Materials, v. 15, p. 1544-1549 (2006). P. Doppelt et al. French Patent n° 1258779 (2012)
Tetrahedral amorphous carbon (ta-C) is a hydrogen-free and mainly sp3-bonded form of amorphous carbon. ta-C is available as thin film coating and has found widespread applications as tribological coating for automotive parts, protective and decorative coating, biocompatible coating for e.g. medical implants and protective coating of hard disk data storage devices. The fabrication of ta-C thin film coatings with diamond-like properties, e.g. a high sp3 bond fraction close to 80%, is usually done by filtered cathodic vacuum-arc deposition, laser ablation or ion beam deposition. The electronic properties of ta-C films are determined by a large mobility gap up to about 3 eV and a high density of localized electronic states in the Urbach tails. The dominating electronic transport mechanism in thin ta-C films is therefore Poole-Frenkel conduction (field enhanced thermal excitation of bound electrons) and variable range hopping at lower temperatures. Incorporation of foreign atoms like B, N or P usually leads to an increased sp2-bond fraction and a corresponding increase in the electrical conductivity.In this contribution I will discuss the electronic properties of ta-C thin films as well as the behaviour of ta-C thin films grown on Silicon substrates. The electrical characterization includes macroscopic and microscopic I-V measurements as well as impedance measurements covering a broad frequency range. The ta-C/Si system leads to Schottky-like diode behaviour which is massively influenced by the amorphous film. I will also discuss the possibility to tune the electrical properties of ta-C by (i) incorporation of small amounts of Cu impurities and (ii) swift heavy ion irradiation, like 1 GeV Au or U ions. ta-C is unique, since it is a material which can be locally transformed from a high resistive sp3-phase into a highly conducting sp2-phase by swift heavy ions. Swift heavy ion irradiation leads to conducting filaments along the ion tracks with less than 10 nm diameter and a current contrast up to 105 between ion track and surrounding non-irradiated matrix. Conducting ion tracks provide a unique possibility to tailor the electronic properties of ta-C on the nano-scale.
The bias-voltage-dependent complex impedance spectra of heterostructures composed of a thin film of tetrahedral amorphous carbon (ta-C) on silicon is measured and a model, explaining the measured results based on the underlying physics, developed.ta-C is an amorphous carbon with predominantly sp3 bonded network and low hydrogen content. The mass-selective ion beam deposited ta-C films, investigated in this work, have a sp3/sp2 ratio of around 80% and negligible hydrogen content.The measured absolute impedance and phase span, due to their dependence on the parameter pair frequency and bias voltage, a four-dimensional space of data points. The complete set of data points for all frequencies and bias voltages is analysed, as a whole, by fitting an electrical equivalent circuit consisting of components based on the underlying physics only, i. e. components representing theoretical models for dc and ac conduction in ta-C or non-crystalline solids in general. Fitting a complete dataset to extract model parameters, instead of small regions with certain dominant influence of one conduction mechanism with the corresponding model, can lead to enhanced fit parameters. Improvement is especially expected for transient regions, where several models contribute simultaneously, since points in those regions are usually not considered for optimisation of parameters of the model.In ta-C/silicon heterostructures with low-doped substrates, the combination of two voltage-dependent conduction models with different capacitive bypasses leads to a salient feature in the transition region, which is remarkably well described by the presented model.It will be shown that the heterostructure can be modelled by at most two Voigt circuits and a serial resistance. All elements can clearly be ascribed to processes within single parts of the heterostructure.The first Voigt circuit, describing the ta-C film, consists of a voltage-dependent resistance resembling the field-enhanced thermal excitation from trapped carriers below the mobility edge, often described as dc conduction mechanism in ta-C, in combination with, as expected for a non-crystalline solid, a constant phase element (CPE) with exponent close to 0.8. In other words, the ac conductivity is dominated by a long-tail distribution of resonances, rather than a sharp resonance peak, which is most likely the result of a long-tail distribution of contributing trap energy differences, which is in agreement with the existence of an Urbach-tail, typically observed for non-crystalline materials.Depending on the doping of the substrate, a depletion layer, described by the second Voigt circuit, forms at the silicon/ta-C interface combining a modified Schottky diode with a CPE with exponent close to unity. While doping type determines polarity of the diode, dopant concentration determines depletion layer width. Higher impurity concentrations reduce the width to a point that the diode and hence the second Voigt circuit vanish.
Ultrananocrystalline diamond (UNCD) films consist of nano-sized diamond grains and amorphous carbon grain boundaries (GBs), which supplies unique chances to improve the n-type conductivity of diamond. We implanted oxygen or phosphorus ions with lower dose into UNCD films, which introduced the dopants with nearly the same proximity into nano-sized diamond grains and GBs. This method prevents the dopants from enriching in the GB sites as the case of N-doped UNCD films synthesized in CVD process. The results show that the conduction type of O+ or P+-implanted UNCD films transits from p-type to n-type when the annealing temperature increases from 500 to 800 omicron;C. The highest mobility with 303 and 500 cm2V-1s-1 has been obtained in the 900 omicron;C annealed O+ and P+-implanted UNCD films, respectively. The mechanism of the conduction type transition and the high mobility n-type conduction are discussed. A novel conduction mechanism that ion-implanted nano-sized diamond grains supply n-type conductivity and the amorphous carbon GBs give a current path to the UNCD films has been proposed.AcknowledgementsThis work was supported by National Natural Science Foundation of China (Grant No. 50972129, 50602039 and 51211120188) and by Qianjiang talent project of Zhejiang province of China (Grant No. 2010R10026). References:1. X.J. Hu, J. S. Ye, H. Hu, X. H. Chen, Y. G. Shen, Appl. Phys. Lett. 99, 2011, 1319022. X.J. Hu, J.S. Ye, H.J. Liu, Y.G. Shen, X.H. Chen, H. Hu, J. Appl. Phys. 109, 2011, 0535243. X.J. Hu, X. H. Chen, and J. S. Ye, AIP Advances 2, 2012, 042109
Hydrogen-terminated diamond surface possesses unique features, such as p-type surface conduction layer (2DHG) and negative electron affinity, and accordingly has been applied to high-performance field-effect transistors and electron emitters, etc. Obviously, the stability of C-H bonds is crucial to these applications. While we expect high thermal stability of C-H bonds because of a high binding enthalpy of C-H bond (412kJ/mol) compared with those of C-O bond (360 kJ/mol) and C-C bond (348 kJ/mol), there is a report that the 2DHG was lost being annealed in vacuum above 300oC and never recovered after exposure to air indicating annihilation of C-H bonds . The purpose of this study is to reinvestigate the thermal stability of surface C-H bonds of diamond from the point of annihilation and recovery of 2DHG.First, we formed p-type surface conduction layers on (001)-, (011)-, and (111)-oriented single-crystalline diamond substrates using a hydrogen plasma. The sheet resistivity of the samples was approximately 1×104 Omega;/sq, which is typical of 2DHG, as measured using the van der Pauw method . Then, the samples were annealed for 20 min in a vacuum of (3~7.5)×10-6 Pa at stage temperatures ranging from 880 to 1205 oC. After cooling down to room temperature and subsequent exposure to air, the sheet resistivity of the samples was measured again.The (001) or (011) diamond retained the 2DHG after annealing at up to 1090oC and subsequent air exposure without any change in the sheet resistivity, but lost the 2DHG above 1125 oC, although atmospheric adsorbates existed on the diamond surface. This result is ascribed to the dissociation of C-H bonds during the annealing. On the other hand, in the case of the (111) diamond, the 2DHG remained without any change of sheet resistivity after the annealing at up to a slightly lower temperature of 1015oC, and disappeared above 1050oC. This decrease in the transition temperature might be associated with the restructuring of the (111) diamond surface from a 1x1 to 2x1 structure, accompanying the dissociation of C-H bonds. In conclusion, there is a distinct difference in the stability of surface C-H bonds among differently oriented crystals. The lowest stability of C-H on (111) surface is caused by the lower surface energy of clean (111) 2x1 surface than those of clean (001) and (011) surfaces where dangling bond density is high. Even in (111) surface, C-H bonds sustain up to 1015 oC (stage temperature). Hence, the diamond devices that utilize the features specific to the surface C-H bonds are expected to operate stably at high temperatures, being properly protected against environment.AcknowledgementsThis study was supported by research grants from ALCA (JST).References H. Kawarada et al., Appl. Phys. Lett. 65, 1563 (1994). M. Riedel et al, Phys. Rev B. 69, 125338 (2004).
Due to properties such as a wide bandgap, high breakdown voltage, and high carrier mobilities, diamond is a potentially exceptional semiconductor for electronic applications, especially high-temperature and high-power devices, such as vertical Schottky barrier diodes. The realization of vertical diode structures requires the ability to reliably produce heavily doped ( > 1020 cm-3), free standing ( > 500 mu;m thick) p-type substrates, however doping issues continue to be a limitation in this field. A problem of current interest in boron-doped single crystal diamond (SCD) is that of the decreasing doping efficiency at higher pressures (higher plasma discharge power) which has been noted by Achard et al. . In our previous work  we reported higher doping efficiencies than predicted by the model of Achard et al., and we theorized that it was due to a higher substrate temperature during growth. Work done on polycrystalline diamond films has shown that the diffusion coefficient of the boron dopant into the diamond lattice is dependent on the temperature of the substrate during growth, and as shown in the analysis in , the diffusion coefficient at 1000°C is nearly twice the value at 700°C. It is therefore reasonable to assume that a similar temperature dependence relationship exists for boron doping in SCD, which will be more fully explored in this work. We have previously demonstrated the characterization of boron-doped SCD, using methods such as Fourier-transformed infrared spectroscopy (FTIR) to investigate dopant concentrations from below 1017 cm-3 to over 1020 cm-3 , and the successful determination of carrier concentrations using a temperature dependent Hall Effect measurement system . This work expands upon our previous effort to grow and characterize high-quality diamond for electrical applications. Films are deposited on high pressure high temperature SCD substrates in a microwave plasma-assisted chemical vapor deposition (MPACVD) bell-jar reactor with feedgas mixtures including hydrogen, methane, and diborane. We report on the results of growth experiments, and discuss the effect of the temperature of the substrate during growth on the gas chemistry to solid-phase doping efficiency, as determined by FTIR and temperature dependent Hall Effect measurements. We will also look at strategies for defect reduction, by characterizing the stress in the grown samples with X-Ray Diffraction, Raman spectroscopy, and Birefringence measurements.References J. Achard, F. Silva, R. Issaoui, O. Brinza, A. Tallaire, H. Schneider, K. Isoird, H. Ding, S. Koné, M. A. Pinault, F. Jomard, and A. Gicquel, Diam. and Rel. Mater. 20 (2011) 145 S. N. Demlow, I. Berkun, M. Becker, T. Hogan, and T. A. Grotjohn, MRS Proceedings, 1395, (2012)H. Li, T. Zhang, L. Li, X. Lü, B. Li, Z. Jin, and G. Zou, J.Crys. Growth 312 (2010) 1986 I. Berkun, S. N. Demlow, N. Suwanmonkha, T. P. Hogan, and T. A. Grotjohn, MRS Proceedings, 1511 (2013)
Diamond growth on several substrates has been demonstrated by combining oxygen attachment of chemically functionalized diamondoids and pulsed MW PECVD apparatus with linear antenna delivery system. Diamond growth by sonicating diamondoids has been reported in the past. Diamond growth from chemically functionalized diamondoids using Ti coating has produced ultra pure diamond nanoparticles with less than 5nm size with no nitrogen impurity. However, diamond growth from chemically functionalized diamondoids without Ti coating has never been reported before due to simultaneous etching and growth during the growth process, which etches off sub nanometer diamondoid molecules in the initial stage of growth. By utilizing the pulsed MW PECVD apparatus with linear antenna delivery system, which enables low temperature diamond growth due to the surface-wave plasma characteristics (diffuse, low power density, but high peak power and low electron temperature), we realized low temperature diamond growth with low diamondoid etching rates. Our results prove that we can produce diamond at temperature as low as 200deg making diamond growth compatible to CMOS electronics. Our results also demonstrate diamond growth from diamondoids without using any type of coating and detailed investigation has also proven pentamante to be critical size to sustain initial etching of diamond molecule to initiate diamond growth. TEM shows lattice fringe of 2.06A for diamond  lattice spacing and EELS measurement proves 290eV peak that shows sp3 bonded carbon on our sample. Seeding density appears much higher for samples that were not coated with Ti for all temperatures and all size of diamondoids, this is probably due to Ti not being etched by the plasma. SEM shows substantial change in seeding density for pentamantane under same growth condition only without Ti coating at 200deg and 450deg. When growth temperature is raised to 520deg this substantial change in seeding density disappears probably due to diamondoids starting to evaporate off the substrate due to bond breaking with oxygen on the surface. Raman shows peak around 1332cm-1 for sp3 carbon as well as peak around 1600cm-1 for sp2 bonded carbon. Molecular seeding for controlled purity and doping could be useful for producing color centers for quantum computing and boundary free high thermal conductor for high power HEMT device.  A. Taylor, M. Nesladek, M. Liehr. Diamond and Related Materials 20 (2011) 613-615  K. Tsugawa et al, J. Phys. Chem. C 2010, 114, 3822-3824.  H. Ishiwata, ZX Shen, N. Melosh to be submitted.
* Both authors contributed equallyIn previous work we reported on the heat-transfer resistance at interfaces as a novel, denaturation-based method to detect single-nucleotide polymorphisms in DNA . We observed that a molecular brush of double stranded DNA grafted onto synthetic-diamond surfaces does not notably affect the heat-transfer resistance at the solid-to-liquid interface. In contrast to this, molecular brushes of single stranded DNA cause, surprisingly, a substantially higher heat-transfer resistance and behave like a thermally insulating layer. In this work , we report on the label-free real-time thermal monitoring of the denaturation of specific DNA fragments and its potential to detect and quantify single nucleotide polymorphisms (SNPs). Probe DNA, consisting of a 36-mer fragment was covalently immobilized on nanocrystalline chemical vapour deposition (CVD) diamond platforms and hybridized with a 29-mer target DNA fragment (full matching and/or with a point mutation). It was observed that the change in heat transfer resistance upon denaturation is dependent on the amount of DNA hybridized to the nanocrystalline diamond (NCD) surface. Furthermore the possibility to distinguish between a full matching sequence and its singularly mutated counterpart, when bound to the same NCD surface, was investigated. NCD surfaces were selectively hybridized with both full matching and mutated DNA fragments at different ratios (3:1, 2:2 and 1:3). A clear bipartite response in heat transfer resistivity was observed upon simultaneous denaturation of these DNA fragments. Denaturation temperature could be used to identify the DNA fragment to which each partial response could be attributed. Moreover, the partial increases in heat transfer resistivity related to the hybridized amount of non-mutated or mutated DNA, respectively. These results imply that heat transfer resistivity is a technique which can be used to (i) quantify DNA fragments of interest, (ii) detect and (iii) quantify SNPs in a mixture of mutated and non-mutated DNA fragments. Moreover, it illustrates the potential of this technique to detect SNPs without the necessity to design complex microarrays.  B. van Grinsven, N. Vanden Bon, H. Strauven, L. Grieten, M. Murib, K.L. Jimenez Monroy, S.D. Janssens, K. Haenen, M.J. Schöning, V. Vermeeren, M. Ameloot, L. Michiels, R. Thoelen, W. De Ceuninck and P. Wagner, ACS Nano, 2012, 6, 2712 - 2721.  K. Bers*, B. van Grinsven*, T. Vandenryt, M. Murib, W. Janssen, B. Geerets, M. Ameloot, K. Haenen, and P. Wagner, Diamond and Related Materials, 2013, accepted
AbstractElectric double layer capacitor (EDLC) is an electric storage device using double-layer at the electrode/electrolyte interface. In general, EDLC is superior to secondary batteries in cycle-life and charge-discharge speed, and is inferior in energy density. In this study, we fabricated a boron-doped diamond (BDD) electrode with specific large surface area by using photolithography and etching technique. We investigated the improvement of the energy density by using a BDD for an electrode of EDLC.ExperimentalSilicon substrate was masked by patterned photoresist and was etched by reactive ion etching to fabricate micropillars on the substrate. The diameter of the pillar was 10 mu;m and the distance between pillars was about 11 mu;m. BDD layer was deposited on the silicon pillar array substrate by microwave plasma-assisted chemical vapor deposition (BDD pillar array, BDD-PA). The Porous-BDD-PA (P-BDD-PA) was fabricated by two-step heat treatment. The first-step was heating the sample at 1000 °C in argon for 10 h, and then the sample was heated at 425 °C in air for 10 h. Result and discussionPolycrystalline BDD with the grain size of 0.5 mu;m was found by the SEM observation to be deposited on the surface of BDD-PA. After the heat treatment, the pores with the size of 0.2-0.3mu;m were formed densely on the surface. The P-BDD-PA was found to exhibit ten times larger electric double-layer capacitance than a flat BDD electrode with larger potential window than activated carbon evaluated by CV in 1 M Na2SO4 at 10 mV/s. Furthermore the potential window of P-BDD-PA in aqueous electrolyte solution was equal to that of the activated carbon in organic electrolyte solution. From the EIS results, the P-BDD-PA showed a Nyquist plot, which can be simulated by an equivalent circuit with transmission line model.
Functional gastrointestinal (GI) disorders, such as irritable bowel syndrome (IBS), dyspepsia, and gastroesophageal reflux disease, take a significant toll on human health. Functional GI disorders are defined as disturbances in motility, absorption/secretion and sensation that do not have an identifiable pathophysiological basis. These functional disorders are particularly problematic in pediatric health. Research is needed to improve our understanding of the normal motility and secretory activities of the GI tract with age and to discover the pathophysiological changes responsible for functional gut disorders that lead to disease. For example, a better understanding of how the nervous system controls GI function and how neural control of the gut is impaired in functional GI disorders is clearly required. Serotonin is an important excitatory neurosignaling molecule in the gastrointestinal tract. About 90% of the 5-HT in the human body is synthesized and stored in enterochromafin cells (EC) cells which line the mucosa of the small intestine and colon. Serotonin plays a key role in visceral sensation and regulating gut motility. The EC cells continuously release 5-HT in response to a number of chemical and mechanical stimuli. 5-HT is cleared from the extracellular space by 5-HT transporter (SERT) which is expressed in enterocyte cells that also line the mucosa. Previous studies have shown that 5-HT availability is greater in the small intestine of neonatal guinea pigs due to low expression of SERT(). We are testing the hypothesis that 5-HT signaling is not fully developed at birth and that release and clearance mechanisms for this neurotransmitter exhibit age-dependent maturation. In this presentation, we will discuss the preparation and characterization of diamond microelectrodes (boron-doped diamond deposited on sharpened Pt wires) and their performance in in vitro electrochemical measurements. These electrodes are particularly well suited for sensitively, reproducibly and stably monitoring 5-HT.