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Low-temperature (5K) photoluminescence of silicon substrates in the range 0.8–1.2 eV is studied before and after deposition of polycrystalline diamond films. The diamond films were deposited in the microwave plasma onto high-purity dislocation-free silicon (with the resitivity ρ ≈ 3 kΩ cm) subjected to mechanical polishing or more delicate chemical and mechanical polishing. The deposition temperature was 750–850°C. In the photoluminescence spectra of the samples with the substrates polished chemically and mechanically, two lines, D1 and D2, corresponding to the dislocation-related emission are recorded. Generation of dislocations in the substrates is caused by efficient adhesion of the diamond film and, as a result, by internal stresses that relax with the formation of dislocations. The experimental spectra are practically identical to the photoluminescence spectra observed in silicon (ρ ≈ 100 Ω cm) with the density of dislocations ∼104 cm−2.

The aim of this work was to investigate the excimer laser action (λ = 248, T = 20 ns) on the ultrananocrystalline diamond films grown by CVD technique with different nitrogen gas phase content (0% and 30%). The origin of the films ablation was found to be strongly dependent on laser fluence. A high radiation intensity induces the surface graphitization of the film and a consequent ablation with the rate over 10 nm/pulse. Contrariwise at the fluence below the certain threshold the ablation rate was found to be extremely low (∼10 -2 nm/pulse) and not constant across the thickness in case of the nitrogen doped ultrananocrystalline diamond film. Though the low-rate etching is not accompanied by graphitization a certain structure modification has been detected by a Raman spectroscopy.

A highly-efficient phase photothermal method is developed for quantitative measurements of the small optical absorption coefficient in thin plates made of highly transparent materials in which bulk losses significantly exceed surface losses. The bulk absorption coefficient at 10.6 μm is estimated in polycrystalline diamond plates grown from the vapour phase (a CVD diamond). The results are compared with those for natural and synthetic diamond single crystals and with the concentrations of nitrogen and hydrogen impurities. The absorption coefficient of the best samples of the CVD diamond did not exceed 0.06 cm-1, which, taking into account the high thermal conductivity of the CVD diamond (1800–2200 W mK-1 at room temperature), makes this material attractive for fabricating output windows of high-power CO2 lasers, especially for manufacturing large-size optics.

The heat propagation at room temperature was studied in a heterostructure consisting of a polycrystalline diamond film deposited from a hydrocarbon plasma on an oriented silicon substrate. The dynamics of cooling of a thin-film indium thermometer evaporated atop the diamond film was measured following its heating by nanosecond nitrogen laser pulses. The experimental data were compared with the values calculated in the framework of the theory of thermal conductivity for multilayer systems. This analysis permitted the determination of both the thermal conductivity of the diamond film and the thermal resistance of the diamond/Si and In/diamond interfaces.

Polycrystalline CVD diamond has been annealed in vacuum at temperatures t an = 1550 °C-1690 °C to investigate an influence of modifications of grain boundaries (GB) and defects on thermal conductivity and optical properties of originally optical quality material. While the sample was converted by this heat treatment to "black diamond", excitons still could be observed in cathodoluminescence spectra. Photoluminescence spectra revealed an aggregation of nitrogen (formation of H3 optical center) after annealing at 1690 °C. In-plane thermal conductivity k(T) measured by a heated bar method in the temperature range T= 5-410 K shows a strong (up to 5 times) and monotonic decrease at T < 45 K upon annealing, while room temperature k (298 K) value remains almost constant (ca. 19.0 W/cm K) till t an = 1650°C, rapidly degrading at higher t an . The experimental data on thermal conductivity are analyzed in the framework of full Callaway theory taking into account three-phonon scattering processes, phonon scattering on point defects, sample boundaries, and GB. The proposed model reproduces well the observed k(T) behavior, the phonon scattering on the modified GB playing an important role.

The temperature dependences of thermal conductivity κ of polycrystalline CVD diamond are measured in the temperature range from 5 to 410 K. The diamond sample is annealed at temperatures sequentially increasing from 1550 to 1690°C to modify the properties of the intercrystallite contacts in it. As a result of annealing, the thermal conductivity decreases strongly at temperatures below 45 K, and its temperature dependence changes from approximately quadratic to cubic. At T > 45 K, the thermal conductivity remains almost unchanged upon annealing at temperatures up to 1650°C and decreases substantially at higher annealing temperatures. The experimental data are analyzed in terms of the Callaway theory of thermal conductivity [9], which takes into account the specific role of normal phonon-phonon scattering processes. The thermal conductivity is calculated with allowance for three-phonon scattering processes, the diffuse scattering by sample boundaries, the scattering by point and extended defects, the specular scattering by crystallite boundaries, and the scattering by intercrystallite contacts. A model that reproduces the main specific features of the thermal conductivity of CVD diamond is proposed. The phonon scattering by intercrystallite contacts plays a key role in this model.

The present article presents the results of triboengineering tests of polycrystalline diamonds deposited chemically from the gaseous phase together with intermetallides of the Al-Ti system. The conditions are determined when the diamond wears intensively; these conditions appear due to the use of a metallic catalysis precursor as a counterbody. The study results are expected to contributed to the development of techniques for machining of diamonds of industrial dimensions.

Polarized negative muons were used to study the dynamics of non-equilibrium charge carriers in diamond. From the behavior of the muon polarization it is concluded that the acceptor center μ B in diamond is formed in the diamagnetic state (with the probability close to unity) and then, by capturing a hole, turns to the paramagnetic state. The hole capture rate by an ionized acceptor center μ B − in synthetic diamond was found to depend on temperature as 1/ T α , where α = (1.5–2.5) at T > 80 K.

Nitrogenated nanocrystalline diamond thin films are grown from arc-plasma in CH4/Ar/H2/N2-gas mixtures and characterized by AFM-and Raman spectroscopy, X-ray diffraction and resistivity measurements. It is shown by Mott-Schottky plots taken in indifferent electrolyte (0.5 M H2SO4) that the behavior of the nitrogenated nanocrystalline diamond thin-film electrodes resembles that of n-type semiconductor; the donor effective concentration therein is estimated.

The film quality and electrochemical properties of BDD (boron-doped diamond) thin films grown by hot-filament chemical vapor deposition technique on titanium substrates that had been subjected to a range of pre-treatment processes were evaluated. The pre-roughened Ti-substrates are shown to support more adherent BDD films. It is evident that acid-etching the Ti-substrate involves surface hydrogenation that enhances nucleation and formation of diamond thereon. The prepared BDD film exhibits wide potential window and electrochemical reversibility. It also demonstrated a better long-term electrochemical stability based on the low variation in voltametric background current upon the exposing of the electrodes to repeated cycles of electrochemical metal deposition/stripping process.

Thermal conductivity at room temperature of diamond composites of two types: with a diamond skeleton and with diamond grains imbedded in a non-diamond matrix was evaluated in dependence of the diamond grain size (d) varied from a ten of microns to 500 μm. The thermal conductivity of the compacts with diamond skeleton obtained in the Cu–diamond system at high pressure of 8 GPa strongly increases with diamond particles size approaching the maximum value of 9 W/cm K at d ≈ 200 μm. The compacts sintered in the Cu–Ti–diamond, Al–Si–diamond and Si–diamond systems at lower pressure (2 GPa) are formed predominantly owing to the presence of the binder. It was found for these conditions that the thermal conductivity is less sensitive to the diamond grain size, reaching the value of 6 W/cm K for the composites with SiC–Si matrix.

We have studied the effect of the particle size of diamond (several microns to 500 μm) on the thermal conductivity of high-pressure-sintered diamond composites. The results demonstrate that the thermal conductivity of diamond-matrix composites prepared at 8 GPa in the presence of copper rises steeply with increasing diamond particle size, reaching a maximum, 9 W/(cm K), at a particle size of 200–250 μm. In the case of the samples prepared at 2 GPa and containing isolated diamond grains in a Cu-Ti binder, the grain size has a weaker effect on the thermal conductivity of the material, which can be accounted for by the low thermal conductivity and key microstructural features of the binder.

X-ray planar compound refractive lenses were fabricated from a polycrystalline diamond plate grown by chemical vapor deposition, by precise through cutting with femtosecond laser pulses. The lens geometry and the surface morphology were investigated with optical and scanning electron microscopy, while the material structure modification was analyzed by Raman spectroscopy. The results of the preliminary lens test at 9.25-keV X-rays are presented.

We report on the response of metal-less CVD polycrystalline-diamond pixel sensors under β-particles irradiation. A 21×21 array of 0.18×0.18 mm 2 pixels was realized on one side of a 10.0×10.0×0.5 mm 3 polycrystalline diamond substrate by means of laser induced surface graphitization. With the same technique, a large graphite contact, used for detector biasing, was fabricated on the opposite side. A coincidence detecting method was used with two other reference polycrystalline diamond detectors for triggering, instead of commonly used scintillators, positioned in the front and on the back of the sensor-array with respect to the impinging particles trajectory. The collected charge distribution at each pixel was analyzed as a function of the applied bias. No change in the pulse height distribution was recorded by inverting the bias voltage polarity, denoting contacts ohmicity and symmetry. A fairly good pixel response uniformity was obtained: the collected charge most probable value saturates for all the pixels at an electric field strength of about ±0.6 V/μm. Under saturation condition, the average collected charge was equal to Q coll >=1.64±0.02 fC, implying a charge collection distance of about 285 µm. A similar result, within 2%, was also obtained for 400 MeV electrons at beam test facility at INFN Frascati National Laboratory. Experimental results highlighted that more than 84% of impinging particles involved only one pixel, with no significant observed cross-talk effects.

The effect of the nitrogenation on the electrochemical properties of nanocrystalline diamond films produced by microwave plasma CVD in CH 4 –Ar–H 2 –N 2 gas mixtures was studied systematically, using cyclic voltammetry and electrochemical impedance spectroscopy measurements, for the first time. Differential capacitance, kinetic parameters of reactions in [Fe(CN) 6 ] 3-/4 -redox system and potential window were found to be sensitive to the nitrogen concentration in the process gas. With its increase (from 0 to 25%), a transition of the NCD film behavior from “poor conductor” to metal-like character takes place. The heavily N-doped nanocrystalline diamond films have satisfactory electrochemical properties to be used as electrodes.

The wettability of nanocrystalline CVD diamond films grown in a microwave plasma using Ar/CH4/H2 mixtures with tin melt (250–850 °C) and water was studied by the sessile-drop method. The films showed the highest contact angles θ of 168 ± 3° for tin among all carbon materials. The surface hydrogenation and oxidation allow tailoring of the θ value for water from 106 ± 3° (comparable to polymers) to 5° in a much wider range compared to microcrystalline diamond films. Doping with nitrogen by adding N2 in plasma strongly affects the wetting presumably due to an increase of sp2-carbon fraction in the films and formation of C–N radicals.

Ultrananocrystalline diamond (UNCD) films grown in an argon-rich Ar/CH 4 /H 2 microwave plasma with nitrogen gas added in amounts of 0%–20% were studied by Raman spectroscopy with multiple excitation wavelengths in the range of 244–647 nm and by optical absorption in UV–visible. The Raman spectra have demonstrated the presence of diamond, amorphous carbon and polyacetylene in the UNCD films. Analysis of vibrational and optical properties of amorphous carbon phase proves that nitrogen stimulates the transition from amorphous carbon into an ordered graphite-like structure with narrowed optical band gap, which is supposed to be responsible for the high electrical conductivity of the N-doped UNCD.

Ultrananocrystalline diamond films have been grown by microwave plasma CVD using CH 4 H 2 /Ar mixtures with N 2 added in plasma in amounts up to 25%. The films were characterized with AFM, Raman, XRD, and UV-IR optical absorption spectroscopy mainly focusing on optical and thermal properties. In comparison with polycrystalline CVD diamond the UNCD are very smooth (R a

We measured the temperature dependence of thermal conductivity of a polycrystalline CVD diamond with natural isotope composition and an isotope enriched (99.96% 12C) sample at temperatures from 5 to 420 K. The isotope enriched diamond demonstrates a considerable growth of thermal conductivity at temperatures above 80 K compared to the diamond with natural composition of isotopes. At room temperature the thermal conductivity reaches 24.3 W·cm−1K−1, and the isotope effect makes up not less than 34%.

Nitrogenated nanocrystalline diamond films with controlled conductivity are deposited from microwave plasma in CH4-Ar-H2-N2 gas mixtures. They are characterized using atomic force microscopy, Raman spectroscopy, and electrophysical measurements. Their electrochemical properties are studied by cyclic voltammetry and electrochemical impedance spectroscopy. Kinetic parameters of reactions in [Fe(CN)6]3-/4- redox system are determined. The character of electrode behavior is controlled by the degree on nitrogenation. With the increasing of the nitrogen content in the reaction gas mixture (from 0 to 25%), the potential window somewhat narrows, the background current increases, the reversibility of reactions in the [Fe(CN)6]3-/4- redox system increases. By and large, the transition occurs from the electrochemical behavior of a “poor conductor” to that of a metal-like electrode.

Nitrogenated nanocrystalline diamond thin-film electrodes with controlled conductivity are grown from microwave- or arc-plasma in CH 4 –Ar–H 2 –N 2 gas mixtures. Their electrochemical behavior is studied using cyclic voltammetry and electrochemical impedance spectroscopy techniques. It is concluded from Mott–Schottky plots that the studied material has n-type conductance; the donor concentration is estimated. The character of electrode behavior is controlled by the degree of nitrogenation of the material. In particular, with the increasing of nitrogen concentration in the feeding gas (0–25%) supplied to plasma-chemical reactor, the potential window in the supporting electrolyte (2.5 M H 2 SO 4 ) becomes somewhat narrower, the reversibility of electrochemical reactions in the [Fe(CN) 6 ] 3−/4− redox couple becomes more pronounced. Kinetic parameters of redox reactions in this couple are determined. By and large, with the increasing of the nitrogenation the electrochemical behavior of “poor conductor” gives way to that of metal-like conductor.

A fast bolometric detector embedded in a plate of chemical-vapor-deposited polycrystalline diamond was developed and fabricated. The working element of the bolometer is a buried graphitized layer (with temperature-sensitive resistance) fabricated in the bulk of a diamond by C+ ion implantation followed by annealing. The kinetics of the response of the structure to irradiation with light from an LGI-21 pulsed nitrogen laser (λ = 337 nm, τP ∼ 8 ns) were studied. The room-temperature response width at half-maximum is ∼ 20 ns. Using the space-time distribution of responses of the structure, thermal (bolometric) signals were resolved from signals of different nature (photoconductivity or photovoltage).

With the aim of contributing to the development of two-dimensional UV and X-ray detectors, also stimulated to evaluate specific amplification, handling and addressing electronics, we present a 16-pixel matrix sensor based on high quality polycrystalline diamond. Thick polycrystalline diamond specimens, in the 0.2–0.6 mm range, have been used for the tests and the development of the prototype. Crossed 1 mm large chromium strips have then been realized by lithography on the metal deposited on both the two sample surfaces. The single pixel structure of a matrix appears like a metal-diamond-metal vertical device with a volume which is directly related to the diamond thickness (0.2–0.6 mm3). Initially, to evaluate the sensor-grade quality of the diamond films, each pixel has been characterized by means of: I–V characteristic in the dark and under ns pulsed excimer laser irradiation; linearity with the photon flux; spectral photoresponse in the 200–1000 nm range. The lateral charge collection at the non-illuminated sensing elements has also been measured to estimate the cross-talk between pixels. Successive tests have been devoted to study the whole matrix response by addressing the pixels singly through the realized electronics both in CW and chopped monochromatic UV illumination. The implemented low-noise transimpedance amplifiers (1 V/1 nA) showed a good linearity whereas the bandwidth was limited just to 20 Hz. Finally, the intensity distribution of a 1 × 1 cm2 monochromatic UV beam, extracted by a xenon discharge lamp source, as acquired by a realized prototype is illustrated and analyzed.

We report on the first observation of stimulated Raman scattering (SRS) in single crystal diamond synthesized by chemical vapor deposition (CVD). An efficiency of 45% of energy conversion from the pumping Nd3+:Y3Al5O12 laser radiation to all Stokes and anti-Stokes components is achieved. This makes single crystal CVD diamond an attractive χ(3) nonlinear crystalline material as a Raman laser converter.

This review focuses on high-pressure diamond synthesis processes, some of which have been used in commercial-scale production of diamond powder and large single crystals for more than forty years now, and on the role and types of vapor-phase activation in rapidly developing technologies of diamond films and wafers—excellent candidates for near-term industrial application.

The experimental data and calculations of the dielectric loss in polycrystalline CVD diamonds in the millimeter wave range and in wide temperature range of 1–300 K are analyzed. The theoretical temperature dependencies of the loss were calculated in assumption that the loss is due to the electrical conductance induced by thermal excitation of shallow levels. The continuous uniform activation energy distribution of shallow levels was assumed with additional narrow band at energies ∼ 0.001 eV and graphite-like inclusions were taken into account. A good coincidence was found for the theoretical temperature dependence with the experimental data on loss. These results correlate with the Q-DLTS continuous spectra corresponding to shallow levels obtained in the same samples. The results show the presence of acceptor shallow levels with a continuous energy spectrum and quasi-uniform activation energy distribution from ∼ 0.1 up to ∼ 0.003 eV. It is concluded that the millimeter wave losses in the CVD diamonds at the temperatures ∼ 30–300 K are mainly due to the thermal excitation of charge carriers from native shallow levels. An essential reduction (in the order of magnitude) of the dielectric loss at the edge of the CVD diamond disk after laser cutting (compared to the value in the center) was observed.

We report on experimental study of photosensitivity and Q-DLTS spectra of polycrystalline CVD diamond UV photodetectors. The measured characteristics of Schottky photodiode on boron-doped diamond films are compared with those obtained for planar photoconductive structures (photoresistor type) based on undoped CVD diamond. The Schottky photodiode exhibited a sharp cut-off in photoresponse with spectral discrimination ratio (between wavelengths of 190 nm and 700 nm) as high as 5 · 105 at zero bias voltage (at zero dark current). The photodiode showed the maximum of photoresponse at wavelength

Diamond films produced by chemical vapor deposition (CVD) technique must be polished and machined in order to be used for many applications (windows, heat spreaders, surface acoustic wave devices, etc). We present an Atomic Force Microscopy study of the effects of mechanical polishing, hydrogen plasma etching, and ion implantation followed by annealing and chemical etching, on the morphology of Microwave Plasma CVD polycrystalline diamond films. Both growth and nucleation sides of 0.3-0.5 mm thick free-standing films were characterized. We found that grain boundaries and anisotropy of mechanical properties (hardness and wear rate) mostly contribute to the overall roughness of Microwave Plasma CVD diamond films, which is below 0.2 nm at the single-grain scale. The further deposition of a diamond overlayer, even of small thickness, on highly polished polycrystalline diamond, results in a variety of growth modes and different growth rates depending on the grain orientation, leading to the roughness increase. Hydrogen plasma etching proved to be effective for inducing morphological and chemical changes on the surface, while an ion implantation/annealing/etching can be used for precise removal of thin diamond layers. The latter approach is promising for diamond lithography. (c) 2005 Elsevier B.V. All rights reserved.

The electrode behavior of nanocomposite films deposited onto a sitall substrate is studied, the films containing a titanium-based conducting phase in a dielectric silicon-carbon matrix. With the films’ resistance decreasing, their electrochemical behavior changes from that of “poor conductors” to a nearly “metal-like” one. The electrode’s differential capacitance increases, and the electron transfer in the [Fe(CN)6]3-/4- redox system accelerates. This is explained by an increased number of conducting metal-containing clusters at the film/electrolyte interface.

Polycrystalline diamond coatings over 100 μm thick are produced on AlN ceramic substrates by microwave-plasma CVD from a CH4-H2-O2 mixture. Their Raman spectra indicate good phase purity and a compressive stress as high as about 4 GPa due to the thermal-expansion mismatch between the diamond and the ceramic. Measurements by the laser flash technique at room temperature show the coatings to have a thermal conductivity of 970 W m−1 K−1 as against 290 and 170 W m−1 K−1 for mono-and polycrystalline aluminum nitride, respectively. It is concluded that a diamond coating of appropriate thickness significantly enhances the thermal conductivity of the surface region of AlN substrates and therefore could be useful for creating more efficient AlN heat sinks.

We have opened up nonlinear-laser potential of polycrystalline CVD diamond. At room temperature under laser pulse excitation in the visible and near-IR (0.53, 1.06, and 1.32 μm) high-order Stokes and anti-Stokes generation was observed. The investigated material is classified as promising stimulated Raman scattering active medium for Raman laser converters.

The results of investigating the behavior of the boron impurity in synthetic diamond and the effect of uniaxial static pressure on the aluminum acceptor in silicon are presented. The data on the hyperfine interaction and on the relaxation of the magnetic moment of Al acceptor in silicon were obtained. It was found that the uniaxial stress changed both the absolute value and the temperature dependence of the relaxation rate of the acceptor. Unlike the case in silicon, in CVD diamond the paramagnetic shift in the muon spin precession frequency was not observed within the accuracy of the measurements, and a missing fraction of muon polarization was found at T

The response of graphite-diamond pixel detectors to 90Sr β-particles is reported. Laser induced graphitization was used to realize 200 μm × 200 μm square conductive graphite pads on one detector side whereas a large area graphite contact was realized on the other face for biasing. A board with nine hybrid charge sensitive pre-amplifier channels was used to test homogeneity of response of nine pixels at a time. In the dark the current is Ohmic up to 100 V where the current increases with a power law. While the bulk pixel resistance is 2.5 × 1012 Ω, the resistance between adjacent pixels depends on voltage following a power law. Under irradiation a resolved β-spectrum well separated from the noise contribution was observed on each pixel. The most probable value of the collected charge distribution is voltage dependent and saturates around ±300 V (0.6 V/μm) with a value of 0.70±0.05 fC (4300±300 equivalent electrons charge).

One-dimensional position-sensitive device prototypes were developed for monitoring the position and intensity of a continuous or chopped X-ray beam. The response in terms of linearity and sensitivity were studied on voltage division structures, in the photoconductive charge-generation regime. High-quality polycrystalline diamond samples, mechanically polished for photolithography processing, were used as photoconductor material. Chromium deposits were patterned to realize resistive elements with kΩ resistance values. Developed prototypes were characterized by using a monochromatic 8.06 keV X-ray beam delivered by a collimator 1 mm in diameter. An average non-linearity of 5.5±0.5% on 6 mm long active devices was observed. Sensitivity on the beam intensity variations over one order of magnitude was also evidenced, together with lateral resolutions in the range 0.2–1.2 μV/25 μm.

The electrochemical behavior of B-doped diamond films on Ti substrates subjected to different pretreatment procedures (annealing, sand-blasting, and etching in HCl) is evaluated as a function of surface microroughness. Generally, the differential capacitance follows the true surface area of the electrodes. The width of the potential window also increases, but slightly, with the roughness. The electrode reversibility in the [Fe(CN)6]3−/[Fe(CN)6]4− redox system increases with increasing surface roughness. The apparent increase in the reversibility of the reaction may be also explained by the decrease in the true current density. Although the variations in the electrochemical parameters are not strongly pronounced, the tendencies observed can be used to optimise the electrode properties.

Microstructural changes and annealing/graphitization processes induced by thermal annealing in vacuum at 200–1700 °C and by irradiation of a KrF excimer laser are studied in deuterium-implanted (doses 0.5–12×10 16 cm −2 ) diamond single crystals and polycrystalline CVD diamonds. The specific features of D + implanted samples—low critical doses, island-type graphitization and laser-induced explosive-like ablation—are discussed in terms of deuterium high reactivity and mobility in diamonds.

Free-standing undoped polished MPCVD diamond films (200–300 μm thick) have been used to fabricate photoconductive and photodiode structures for UV light detection. Multifinger planar Au/Cr electrodes of the photoconductive structures were realized on the diamond surface by lithographic technique. The sandwich semitransparent Ni electrodes of the photodiode structures were deposited by a magnetron sputtering on both sides of the diamond films. The films showed conductivity less then 10−15 S/cm at room temperatures with activation energy close to 1 eV and low concentration of the electrically active defects according to charge-based deep-level transient spectroscopy (Q-DLTS). The distinct trap levels with activation energy of 0.5, 0.7 and ∼1.3 eV were evaluated. Planar photoconductive detectors with electrodes on the growth side showed the dark current below 1 pA at 10 V bias voltage with spectral discrimination ratio higher than 5×105 (at 50 V bias) in the 210–270 nm wavelength range. Two orders of magnitude lower responsivity were found on the nucleation side. The sandwich photodiodes showed a sharp cut-off in photoresponse at 220 nm and photovoltage as high as 2.3 V in open circuit regime.

The native and impurity-induced defects, conductivity, and dielectric loss at frequencies 145–182 GHz in undoped and boron-doped CVD diamond films were investigated. The as-grown undoped diamond films displayed the acceptor point defects with a continuous energy spectrum and the activation energy of conductivity Ea∼0.7 eV in the temperature range T=80–540K. The B-doped film showed two discrete boron-induced levels with activation energy EA∼0.37 and 0.25 eV, and the activation energy of conductivity Ea∼0.3 and∼0.13 eV at the high and low temperatures, respectively. The activation energies EAL determined from the temperature dependencies (275–900 K) of the dielectric loss in millimeter wave range are in good agreement with the values Ea and EA deduced from the electrical measurements. This indicates that the millimeter wave losses in CVD diamond are mainly due to excitation of electrically active native and impurity-induced defects. The electron irradiation (2 MeV) changes the parameters of boron-induced levels, reduces the concentration of the native defects with the continuous energy spectrum, and strongly, by four orders of magnitude, reduces electrical conductivity.

It is shown that the wettability of diamond can be tailored in a broad range by the surface modification via ion bombardment. The polished MPCVD diamond films were oxidized in air at 550 °C to make the surface hydrophilic and then were irradiated with Ar+ ions at 1 keV energy at doses ranging from 1×1014 to 5×1016 cm−2. The surface state evolution was monitored in situ with X-ray photoelectron spectroscopy (XPS) and X-ray excited Auger electron spectroscopy (XAES). A progressive sp3 to sp2 bond transformation took place with the dose increase, while the irradiated surface becomes hydrophobic with the water contact angle increasing from 24° to 67° as measured with a sessile drop method. The heating of the ion-treated samples in air at 450 °C restores the hydrophilic properties inherent to oxidized diamond surface.

CVD diamond detectors with metal diamond metal (MDM) microstrip structures have been constructed and characterized for image sensor and large area applications. These sensors are suitable for UV and soft X-ray detection. The device photoelectrical characterization under deep UV (λ=193 nm) laser pulses has been performed both on the nucleation and growth sides of a diamond slab, by varying bias voltage, contacts interspacing and light intensity. Such a characterization was also performed on a laser-smoothed part of the growth side. Reflecting the true electronic quality, largely different photocurrent peak shapes were detected on the untreated and laser-treated parts of the growth side, as well as on the nucleation side. Pulse amplitude and duration appear to decrease according to the different defect density value, which turns out to be larger on the laser-treated growth side of the diamond slab. Independent of pulsed illumination intensity, a linear photoresponse increase with the applied electric field is found in the range 101–104 V/cm. Depending on the defect density value, the photocurrent versus pulse energy changes according to a different power law, the linear dependence extending into a wider pulse energy range when larger defect densities are involved. Such a characteristics is also a figure of the wide signal dynamics. The sensor uniformity has been also tested both on as grown and laser-treated surface, as well as on the nucleation side surface where a linear signal increase has been found by adding adjacent strips connected in parallel. These results suggest the suitability of the sensor for image acquisition.

Transient thermal grating and laser flash techniques have been used to measure in-plane (k∣∣) and perpendicular (k⊥) thermal conductivity of 0.3–0.6 mm thick polycrystalline MPCVD diamond films. A small (

A deep UV photodetector with Metal/Diamond/Vacuum (MDV)-type structure has been developed on CsI coated polycrystalline diamond film. The device operation is based on the simultaneous collection of both photogenerated carriers by internal drift and photoelectrons emitted in the vacuum. The performance of the detectors have been analyzed by measuring the total photosignal obtained when only an anode voltage is applied. The spectral distribution of such a photosignal reflects both the photoemission and photocurrent characteristics, which are combined together. In a simple model, the principle of operation of such device has been described in terms of two capacitors connected in series, with the applied anode voltage partitioned between the diamond film and the vacuum, depending on their dielectric constant and thickness values. It will be shown that photomodulation of the diamond surface voltage is able to add the spectral characteristics of photocurrent signal to those of photoemission and to increase the device responsivity with respect to conventional detector structures.

Electrochemical behavior of the diamond-based composites: a nanodiamond—pyrocarbon composite and Carbal, as well as vacuum-high-temperature-annealed polycrystalline diamond is studied by the cathodic lithium incorporation from LiPF 6 solution in a (1 : 4) propylene carbonate—diethyl carbonate mixture. The amount of incorporated lithium steadily increases with the nondiamond (graphite-like) carbon content in the composite. The intercalation capacity of Carbal equals ~33 mA-h per g of the graphite-like carbon. It is concluded that the graphite-like carbon distributed in the nano-(or micro-)diamond carcass is the electrochemically active phase in the composites.

The electrochemical impedance, photocurrent, and photopotential are measured in the supporting electrolyte solution (2.5 M H 2 SO 4 ) for electrodes made of the undoped polycrystalline CVD diamond films annealed in vacuum at 1500–1640 °C. Analysis of the impedance spectra allowed concluding that both the amount of a nondiamond conducting phase in the electrode bulk and its conductivity increased upon annealing. With increasing annealing temperature, the photopotential passed through a maximum at ∼1570 °C. The photosensitivity of “metal-like” samples (annealed at temperatures ≥1630 °C) is negligibly small. Judging from the sign of the photopotential (positive) and photocurrent (cathodic), the studied material formally behaves as a p-type semiconductor. It is suggested that the photoeffects are caused by the structure defects, in particular, dislocations in diamond crystallites, formed close to intercrystalline boundaries during the high-temperature annealing.

It is shown that the rate of laser oxidation of ultrananocrystalline films in the nanoablation mode is limited by the presence of physically and chemically adsorbed hydrogen-containing molecules on the surface and can be increased by preliminary thermal annealing. It is proposed to explain the observed saturation of the laser etching rate with the number of pulses by water molecule dissociation on the surface and film saturation with hydride and hydroxyl groups.

A diamond polycrystalline composite material with improved physico-mechanical characteristics has been obtained at high pressure and temperature using nickel and cobalt powders and tungsten carbide nanopowder as sintering aids. Samples of this material reinforced with CVD polycrystalline diamond at high pressure and temperature have been manufactured.

We report the first experimental observation of a nonlinear laser effect, stimulated Raman scattering (SRS), in manmade diamond grown from the gaseous phase by the chemical vapor deposition (CVD) technique. Multiple Stokes and anti-Stokes generation in the visible and near-IR ranges was excited under nanosecond and picosecond pumping in a 350-μ-thick plate. All the registered Raman-induced lasing wavelengths were identified. We classify the CVD-diamond as a promising χ(3)-active material for Raman laser converters in a record wide spectral range.

(Eth = 1‐2 V µm −1 compared with Eth = 4‐6 V µm −1 for non-oxidized samples) and improved emission uniformity (the number of emission sites per unit area). The composites with low sp 2 -bonded carbon content, i.e. the more porous samples, typically show better results. The structure of the samples was studied using a C KVV Auger spectrometer, with x-ray excitation of Auger emission. Possible reasons for the emission improvement by oxidation in this two-phase carbon system are discussed. Copyright  2004 John Wiley & Sons, Ltd.

To overcome any difficulty related to the fabrication of diamond ultraviolet (UV) sensors based on p–n junction, in this work we describe the realisation and characterisation of a very simple chemical vapour deposited diamond position sensitive detector based on a voltage-division structure. The photosensor, tested under UV excimer laser illumination, shows a non-linearity of the output signal vs. the beam position of approximately 6% but the response repeatability under stable excitation conditions indicates an rms signal fluctuation as low as 1%. A very low sensitivity to light intensity variation has been also evidenced. Moreover, the device shows a high stability and preliminary results seem to indicate a good robustness to repetitive use. Compared to silicon, the high thermal conductivity and the large threshold energy for radiation damage of diamond would largely extend the lifetime of the device under high intensity UV irradiation.

The photoresponse of different photoconductive diamond sensors to excimer laser pulses is investigated as a function of the pulse energy E over three order of magnitude. The integrated photoresponse pulse intensity changes according to the power law I Eβ. Initially, the pulse intensity increases linearly with the pulse energy up to a turning point, which depends on the electronic quality of the diamond film, where a sublinear behavior (β=0.5) is found. The photoresponse pulse shape also changes accordingly, largely broadening at high pulse energies. Such behavior has been interpreted in terms of monomolecular and bimolecular recombination mechanisms acting in different pulse intensity ranges. A further reduction of β is also observed at very high intensity in less defected samples, where the induced carrier density is high enough to cause carrier–carrier scattering and mobility reduction.