We present data showing how the electrical conductivity and Raman spectra of boron doped ‘cauliflower’-type nanocrystalline (c-NCD) CVD diamond films vary as a function of B content. The conductivity is roughly linear as a function of B content between an onset threshold of ∼5×1020 cm−3 up to ∼6×1021 cm−3, with the higher concentrations giving near metallic conductivity values. The onset threshold may be due to compensating donors due to the large number of impurities and defects in these films. The position of the Lorentzian contribution to the 500 cm−1 Raman feature was used to estimate the B content and compared to the value measured using SIMS. We found that the Raman method overestimated the concentration of B by a factor of ∼5 for these c-NCD films. The shortfall may be explained if only a small fraction of the B found in the small-grained films is being incorporated into substitutional sites. We conclude that in diamond films with a high concentration of grain boundaries, the majority of the B (80% in some cases) must be present at or in the grain boundaries.

Raman spectroscopy is a powerful technique often used to study CVD diamond films, however, very little work has been reported for the Raman study of CVD diamond films using near infrared (785 nm) excitation. Here, we report that when using 785 nm excitation, the Raman spectra from thin polycrystalline diamond films exhibit a multitude of peaks (over 30) ranging from 400-3000 cm−1. These features are too sharp to be photoluminescence, and are a function of film thickness. For films >30 μm thick, freestanding films, and for films grown in diamond substrates the Raman peaks disappear, suggesting that the laser is probing the disordered small-grained interface between the diamond and substrate. Some of the peaks change in relative intensity with time (‘blinking’), and the spectra are very sensitive to position on the substrate – this is reminiscent of the behaviour seen in SERS spectra.

Phosphorus doping on (001)-oriented diamond is introduced and compared with results achieved on (111) diamond. Detailed procedures, conditions, doping characteristics, and recent electrical properties of (001) phosphorus-doped diamond films are described. Now the highest mobility is reached to be ∼780 cm2/Vs at room temperature. The carrier compensation ratio, which is still high around 50-80 %, is the most important issues for (001) phosphorus-doped diamond to improve its electrical property. The origin of compensators in phosphorus-doped diamond is investigated, while yet to be identified.

Ultraviolet light emitting diode with p-i-n junction structure is also introduced using (001) n-type diamond. A strong UV light emission at around ∼240 nm is observed even at room temperature. High performance of diamond UV-LED is demonstrated.

We have used Raman spectroscopy with 3 different laser excitation wavelengths (near infrared: 785 nm, green 514 nm, and ultraviolet 325 nm) to study diamond particles as a function of particle size, ranging from 5 nm to 100's of μm. We find that the position of the 1332 cm−1 diamond line varies with particle size as a direct result of heating by the laser. This effect is more significant for lower wavelengths, probably as a result of the increased absorbance by nanodiamond particles in the UV.

A theoretical analysis of the nanodiamond graphitization was presented. Thermodynamic analysis of the nanodiamond showed three kinds of phase-diagram; smaller nanodiamond, nanodiamond-graphite, and larger nanodiamond. In the theoretical analysis, the most probable and the maximum volume fractions of graphite in the nanodiamond were 0.76 and 0.84, respectively regardless of the annealing temperature and the initial radius of the nanodiamond. The highest graphitization probability decreased with increasing annealing temperature.

Phosphorous-doping of predominantly (110) oriented polycrystalline CVD diamond films is presented. Incorporation of phosphorous into the diamond grains was accomplished by using novel microwave plasma enhanced chemical vapor deposition (MW PE CVD) growth conditions. The substitutional nature of the phosphorous atom was confirmed by applying the quasi-steady-state photocurrent technique (PC) and cathodoluminescence (CL) measurements at low temperature. Topographical information and the relation between substrate and P-doped film grain orientation was obtained with scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD). The optimized growth parameters for P-doped layers on (110) oriented polycrystalline diamond differ substantially from the standard conditions reported in literature for P-doping of single crystalline (111) and (100) oriented diamond surfaces.

The extraordinary characteristics of chemically vapor deposited (CVD) diamond such as tissue equivalence, radiation hardness, and lack of solubility in water; makes CVD diamond a very promising material for radiation dosimetry applications. Recent investigations have shown that CVD techniques allowed the growing of good quality diamond films in a diversity of substrates to be used in the form of ionization chambers, thermoluminescence (TL) detectors and dosimeters. In the present work, we report on the TL properties of MWCVD diamond exposed to gamma radiation in the 0.05 -1.0 kGy dose range and 43.5 and 81.11 Gy min−1 dose rates. The CVD diamond displays a linear dose behavior and 5% TL cycle reproducibility, without requiring any annealing or thermal treatment before using it as TL dosimeter. In spite of the significant results, some problems remain and a lot of research work is necessary to improve the synthetic material characteristics to optimize the TL/OSL radiation dosimeter properties.

The chemical stability of three heterosubstrates (Si, 3C-SiC and iridium) has been studied using the same MPCVD reactor during the successive steps of BEN process. An in situ sequential approach allows a monitoring of the chemical modifications induced by interactions between plasma and surfaces. Contrary to silicon, 3C-SiC and iridium underwent weak surface evolutions during BEN. This leads to favourable conditions for the interface formation in agreement with the better Highly Oriented Diamond films reported in the literature. A short description of the nucleation pathways identified for each heterosubstrate is also presented.

Nanocrystalline diamond films have been synthesized on various substrates by 800 nm fs laser irradiation of a variety of organic solvents including acetone, pentane, hexane, heptane, octane, dodecane, and hexadecane in the presence of a transition metal catalyst. 632 nm Raman spectra display a strong vibration mode at 1308 cm−1 characteristic of hexagonal diamond. X-ray photoelectron spectra confirm that the film is mainly sp3-bonded carbon containing a low concentration of sp2-bonded inclusions. Film microstructure shows that these films are assembled from nanoparticles having an average size of < 100 nm. Analysis of the liquid after irradiation using HPLC techniques indicates that polyyne molecules are also synthesized during irradiation. It is possible that these species are formed as the products of ion chemistry following Coulomb explosion. This process may enable a new method for the creation of nanocrystalline hexagonal diamond layers for micro-electronic and other applications.

In this paper, we measured the field emission properties of reconstructed P-doped diamond under various anode-diamond distances and compared with the oxidized surface. Voltage drops in the vacuum was estimated to be 4.95 and 26.6 V/μm for the reconstructed and the oxidized, respectively. Moreover, we calculated the barrier height ratio between each surface. Our data indicates the changes in electron affinity strongly affect on the field emission properties.

The surface density of states of hydrogen and oxygen terminated diamond is an important parameter from the point of view of electrical transport properties at the surface. In addition, the presence of surface states has a detrimental influence on the electrical contact properties. Therefore it is of great importance that the influence of different species on the surface-related properties of the diamond layer is well understood.

In this work (100)-oriented CVD diamond films are terminated using hydrogen plasma with and without small additions of oxygen (1 to 4%). XPS and UPS measurements are performed to look at the influence of this addition on the surface band gap of the diamond samples. Using the TOF (Time-of-Flight) technique a comparison is made between oxidised and differently hydrogenated diamond surfaces. The results clearly show that the different terminations of the diamond surface have an influence on the electrical transport properties. For the oxidised surface, it is found that defect states are created in the surface band gap, increasing trapping. Contrary to this, fully hydrogenated layers behave differently suggesting that the surface DOS is significantly reduced. This fact can be confirmed when applying an electric field on the CVD diamond samples sandwiched between two metallic electrical contacts. In case of a metal deposited on a hydrogen terminated surface we can see a clear UV light emission, related to free exciton recombination in the contact-diamond-junction region. When the surface is oxidised the UV emission is damped, an effect which is attributed to the parallel recombination channels via the surface states.

Electric field of less than 5 V/um is enough to extract electrons from CVD diamond, whereas field of one to two orders of magnitude higher is needed to extract electrons from metal emitter tips. Diamond has various advantages as an electron emitter in addition to the low-threshold voltage, negative electron affinity (NEA), high thermal conductivity, and high chemical stability. The difficulty in clarification of electron emission mechanism is the factor preventing diamond from being used in practical Quite a few numbers of possible mechanisms have been proposed based on conventional emission current-anode voltage (I-V) characteristics, however, difficulty remained in the determination of origin for emitting electrons. In our previous study, we have succeeded in determining the origin for lightly nitrogen (N)-doped CVD diamond by using combined x-ray photoemission spectroscopy / ultraviolet photoemission spectroscopy / field emission spectroscopy (XPS/UPS/FES) system. The origin at 1.47 eV above valence band maximum (VBM) was consistent with donor level for aggregated N. The origin was at VBM for natural IIb diamond measured as a reference, indicating the emitted electrons strongly depend on the dopant In this study, the origin of emitting electrons for heavily N-doped CVD diamond was characterized by the means of combined XPS/UPS/FES. Extremely low-threshold electron emission at 0.5 V/um is still one of the lowest threshold voltages. Such a low-threshold emission may be possible if electrons are somehow injected to conduction band of diamond and emitted into vacuum through NEA surface. Hence, we strongly believe the determination of the origin for heavily N-doped CVD diamond leads to the clarification of mechanism for low-threshold electron emission from diamond. The system in which we have developed for this study consists of ultraviolet source built in an X-ray photoelectron spectrometer. The diamond sample could be negatively biased up to 4kV relative to the mesh grid for FES. Individual spectroscopy of XPS was performed prior to the combined spectroscopy to determine any possible contaminants on CVD diamond. Peaks referred to C1s and O1s of diamond were observed in addition to Gold, used in a mesh grid set above the sample. Combined spectroscopy of UPS/FES was then, conducted on the CVD diamond to identify the origin of field emitted electrons. The diamond was first illuminated by He I excitation for photoemission. NEA with the typical spectra shape for diamond was observed. After confirming stable operation of individual UPS, negative voltage was applied simultaneously for field emission. Exceeding threshold voltage, a sharp peak, which can be referred to field-emitted electrons appeared in addition to typical UPS spectra. The origin of emitting electrons as well as its dependence on the applied voltage will be discussed.

A thin epitaxial single crystal CVD (Chemical Vapour Deposited) diamond detector has been used in order to monitor the X-ray pulses coming out from a standard, portable, medical X-ray apparatus. The current pulses have been acquired and digitized in order to obtain the pulse shape, timing and dose. The obtained data were successfully compared with standard X-ray monitors like air ionization chambers and silicon detector arrays. The results strongly suggest a possible use of CVD epitaxial diamond in the field of X-ray diagnostics for energies up to 120 keV and doses up to 125 mGy and for X-ray pulse timing from 0.1 s or below and 2 s or more.

Single crystal (SC) CVD diamond is known to exhibit superior electronic properties than polycrystalline ones for detection applications. In our study, tested samples were grown using CVD in an ASTEX type reactor, at various microwave powers and keeping all other parameters constant. The crystalline quality and purity of the samples were investigated using Raman spectroscopy and birefringence microscopy measurements.

The diamonds layers were chemically cleaned and oxidized, towards ionization chamber fabrication using Ni and Au contacts for rectifying properties. The devices electronics and detection properties were then evaluated: leakage currents were probed from I(V) measurements and the contacts behavior were tested under 60Co source at various dose rates. Time Of Flight (TOF) and Charge Collection Efficiency (CCE) measurements were evaluated under an 241Am alpha source and enabled the measurement of the mobility, carrier diffusion lengths and lifetime as a function of the growth parameters. Moreover the response under a UV pulsed flash lamp was probed in order to appreciate the CCE as a function of the repetition rate. The measurements demonstrated the importance of the power density during growth on the detection properties.

Photolysis of cyclic disulfides in the presence of carbon materials such as diamond films and single-walled carbon nanotubes led to a surface modification to introduce thioalkylthiol functional groups, confirming by means of Raman, X-ray photoelectron spectroscopy and mass spectrometer measurements. The results on the value of S/C ratio of sulfur-modified diamond films depends on irradiation time by monitoring with XPS. Through thioalkylthiol moieties, an attachment of gold nanoparticles using self-assembly process was performed on carbon materials surfaces.

We report the results of experiments that attempt to deposit n-type CVD diamond in a standard hot filament reactor using 1%CH4/H2 gas mixtures, using (i) AsH3 as a gas phase source of arsenic, and (ii) evaporated Sb or Sb(Ph)3 as a source of antimony. SIMS measurements revealed that under these conditions, neither Sb nor As is incorporated into the diamond film, and the Raman spectra, electrical conductivity and crystallite morphology remain unchanged from that of undoped diamond. These experiments confirm the predicted low incorporation efficiency for As and Sb, and we conclude that doping CVD diamond with these elements cannot readily be achieved in this manner.

The present work reports our attempt in developing diamond nanoparticles with size<50 nm as photoluminescent nanoprobes for biological applications like biomolecule tracking in living cell.

Diamond is a promising semiconductor which shows some unique surface electronic features if grown optimized with low bulk and surface defect densities. The appearance of a highly conducting surface layer if immersed into electrolyte solution is maybe the most striking feature. Scanning tunneling microscopy experiments on diamond in electrolyte solutions are applied to determine the electronic properties governing these transition. These experiments reveal the formation of unoccupied quantized electronic states in the valence band close to the surface. A two-dimensional density of state distribution with three levels from light-, heavy-, and split-off-band holes is detected. Removal of the electrolyte causes a reversible transition into the insulating state and vice versa.

The n-type diamond is known to have high electron emission properties. However, device fabrication on n-type phosphorus doped diamond had 2 difficulties. First, because highly phosphorus doped n-type diamond layer can be grown only on very small (111) diamond substrate, fabrication of highly homogeneous 3 dimensional device such as gate electrode was very difficult. Second problem was that the resistivity of n-type diamond was still over 100 Ω cm and too high for high current electron emission devices. To solve these problems, we developed a new large size composite wafer in which (111) single crystal diamond was buried in polycrystal diamond and a new electrode coated emitter tip structure for conduction support only whose apex was exposed from the electrode. N-type phosphorus doped diamond was grown on the 15 mm composite diamond wafer with high PH3/CH4 concentration of 20% and highly doped active layer was grown on the embedded (111) single crystal. Sharp emitter tip arrays were fabricated by etching the n-type diamond. Electrodes were coated on these tips and exposed area of diamond was less than 200 nm from the apex of the tip. Gate electrodes were fabricated for each emitter tips. Electron emission of these devices were measured in the vacuum of 10−7 Pa. The threshold voltage of the n-type diamond device was 60 V which was lower than 100 V of the p-type diamond device. The threshold voltage of n-type diamond with and without electrode coatings did not changed. This means that electrode coating did not affect the emission properties and electrons were emitted from the diamond surface. The emission current was enhanced by 2 orders by the electrode coatings and total emission current from 1 mm2 reached 1103 mA. This high emission current electron source enables applications to microwave tubes, electron beam processing and integrated micro vacuum devices.

The potential of nanocrystalline diamond films (NDFs) for biological applications has been addressed by a variety of recent researchers. In the present work, we consider the topographical evolution of NDFs fabricated by microwave plasma assisted chemical-vapor-deposition (MPCVD) and its influence on osteoblast (bone forming cells) functions. One group of NDFs formed in this study were grown with 0.67% methane, 5%∼20% hydrogen and argon. The other group of NDFs composed of nano diamond and amorphous carbon was created with indirect exposure to plasma with 0.67% methane, 20% hydrogen and argon. Scanning electron microscope (SEM) images revealed that the nano diamond grains in the first group of NDFs evolved from round shapes into faceted and successively cubic shapes as hydrogen increased, whereas the second group of NDFs consisted of nano platelet grains. Atomic force microscopy (AFM) analysis confirmed this evolution as well as the variation of surface roughness. Cell results demonstrated that osteoblast adhesion and proliferation on NDFs varied dramatically depending on the different topographical features of the films. Specifically, results showed that NDFs with grain size less than 100 nm could be coated on the stem of a hip implant to promote cell adhesion. In contrast, NDFs with grain size greater than 200 nm or NDF with nano platelet grains may be optimal for the inside of acetabular articulation where cell adhesion is not preferred but wear-resistance is important. Further observation by contact angle measurement suggested that the differences in cellular adhesion and proliferation were related to the wettability associated to the topographical features of NDFs surfaces.