Diamond Band Research Articles

Femtosecond Laser-Induced Electron Emission from Nanodiamond-Coated Tungsten Needle Tips.

We present femtosecond laser-induced electron emission from nanodiamond-coated tungsten tips. Based on the shortness of the femtosecond laser pulses, electrons can be photoexcited for wavelengths from the infrared (1932nm) to the ultraviolet (235nm) because multiphoton excitation becomes efficient over the entire spectral range. Depending on the laser wavelength, we find different dominant emission channels identified by the number of photons needed to emit electrons. Based on the band alignment between tungsten and nanodiamond, the relevant emission channels can be identified as specific transitions in diamond and its graphitic boundaries. It is the combination of the character of initial and final states (i.e., bulk or surface-near, direct or indirect excitation in the diamond band structure), the number of photons providing the excitation energy, and the peak intensity of the laser pulses that determines the dominant excitation channel for photoemission. A specific feature of the hydrogen-terminated nanodiamond coating is its negative electron affinity that significantly lowers the work function and enables efficient emission from the conduction band minimum into vacuum without an energy barrier. Emission is stable for bunch charges of up to 400electrons per laser pulse. We infer a normalized emittance of <0.20 nm rad and a normalized peak brightness of >1.2×10^{12} A m^{-2} sr^{-1}. The properties of these tips are encouraging for their use as laser-triggered electron sources in applications such as ultrafast electron microscopy as well as diffraction and novel photonics-based laser accelerators.

Ultra-thin sectioning and grinding of epoxy plastinated tissue.

With classical sheet plastination techniques such as E12, the level and thickness of the freeze-cut sections decide on what is visible in the final sheet plastinated sections. However, there are other plastination techniques available where we can look for specific anatomical structures through the thickness of the tissue. These techniques include sectioning and grinding of plastinated tissue blocks or thick slices. The ultra-thin E12 technique, unlike the classic E12 technique, starts with the plastination of a large tissue block. High temperatures (30-60°C) facilitate the vacuum-forced impregnation by decreasing the viscosity of the E12 and increasing the vapour pressure of the intermediary solvent. By sectioning the cured tissue block with a diamond band saw plastinated sections with a thickness of <300μm can be obtained. The thickness of plastinated sections can be further reduced by grinding. Resulting sections of <100µm are suitable for histological staining and microscopic studies. Anatomical structures of interest in thick plastinate slices can be followed by variable manual grinding in a method referred to as Tissue Tracing Technique (TTT). In addition, the tissue thickness can be adapted to the transparency or darkness of tissue types in different regions of the same plastinated section. The aim of this study was to evaluate the advantages of techniques based on sectioning and grinding of plastinated tissue (E12 ultra-thin and TTT) compared to conventional sheet-forming techniques (E12).

First‐Principles Studies of Ti‐Related Defects in Diamond

The transition metal‐related centers of diamond exhibit good properties. Herein, a first‐principles method based on density functional theory (DFT) is used to study single‐doped Ti‐related point defect structures and codoped structures of Ti and B or N, which possibly exist in diamond; the electronic structure and formation energy are also calculated. The results from structural calculations show that Ti is more likely to be located adjacent to a vacancy to form a TiV structure, which is more stable than other configurations. Ti doping introduces impurity levels into the pure diamond band gap, and the possible energy level transitions are determined. The results from the calculations of the codoped system show that the incorporation of N or B atoms is beneficial for the formation of defect structures and that the incorporation of N optimizes the energy band structure of the defects. When a substitutional Ti atom is located adjacent to a B atom and forms a Ti–B structure, and when four N atoms replace the corresponding neighboring C atoms around TiV to form a TiV–4N structure (which is similar to the NE8 configuration), the structure shows a better energy band structure, which presents new color centers.

Field emission spectroscopy measurements of graphene/n-type diamond heterojunction

In this study, a graphene/n-type diamond heterojunction was fabricated by a wet-transfer process on hydrogen-terminated heavily phosphorus-doped diamond. Ultraviolet photoelectron spectroscopy (UPS) and field-emission electron spectroscopy were conducted to study the band structure of the graphene/n-type diamond heterojunction and its field emission mechanism. UPS suggests that an internal barrier is formed in the diamond by upward band bending near the graphene–diamond interface. The work function of graphene is estimated to be 3.72 eV. Field emission occurs from the Fermi level of graphene at low voltages, and then electron emission from the valence band of diamond starts at increased voltages. The results indicate that electron emission limited by surface termination changes to graphene-oriented emission following the formation of the heterojunction.

Interradicular Root Canals in Mandibular First Molars: A Literature Review and Ex Vivo Study

IntroductionSuccessful endodontic treatment vastly depends to a high degree on an accurate knowledge of root canal system morphology. It is a prerequisite to be aware of all possible reservoirs where bacteria and/or toxins can persist, compromising the surrounding tissues; such knowledge results in endodontic success. MethodsThe presence of interradicular canals and diverticula between the pulp chamber floor and the bifurcation area surface of 117 mandibular first molars was investigated. Access cavities were prepared, the teeth were embedded in plastic, and the pulp chambers were flooded with methylene blue and then centrifuged. An average of 4.2 (0.145 ± 0.03 mm thickness) slices per tooth were obtained by means of a diamond band saw. The presence of interradicular canals and diverticula was investigated using a light microscope (125×). ResultsInterradicular canals were observed in 9 teeth. Seven teeth had 1 interradicular canal, and 2 teeth had 2 interradicular canals. Diverticula (blind interradicular canals) were observed in 11 teeth originating either on the pulp chamber floor or the bifurcation side. The number of diverticula per tooth varied between 1 and 5 and originated in 3 teeth in the pulp chamber floor and 8 teeth in the bifurcation area. Two teeth had both 1 interradicular canal and 3 diverticula. Of the 117 mandibular molars investigated, 18 had either 1 or 2 interradicular canals, 1 to 5 diverticula, or an interradicular canal and 3 diverticula. ConclusionsBased on the results obtained with this ex vivo study and because of the difficulties involved in the clinical performance of mechanical cleaning of possibly existing interradicular canals, it is highly recommended to perform thorough chemical cleaning and disinfection of the pulp chamber floor area in order to enhance the sealing possibility of such structures and minimize treatment failure.

Preparation and characterization DLC thin films using atmospheric pressure plasma Jet

Diamond-like carbon, amorphous hydrogenated films forms of carbon, were pretreated from cyclohexane (C6H12) liquid using plasma jet which operates with alternating voltage 7.5kv and frequency 28kHz. The plasma Separates molecules of cyclohexane and Transform it into carbon nanoparticles. The effect of argon flow rate (0.5, 1 and 1.5 L/min) on the optical and chemical bonding properties of the films were investigated. These films were characterized by UV–Visible spectrophotometer, X-ray diffractometer (XRD) Raman spectroscopy and scanning electron microscopy (SEM). The main absorption appears around 296, 299 and 309nm at the three flow rate of argon gas. The value of the optical energy gap is 3.37, 3.55 and 3.68 eV at a different flow rate of argon gas. For XRD analysis, The presence of diamond peaks and graphite peaks in the x-ray spectrum for these films Indicates that there is an occurrence of local ordered sp3 and sp2 for carbon domains and graphite respectively. Raman spectroscopy analysis revealed two broad bands D band and G band. The upshift of D band of diamond and downshift of the G band of graphite with is indicative of the presence of DLC films.

The Infrared spectrum of very large (periodic) systems: global versus fragment strategies—the case of three defects in diamond

The calculation of the full vibrational spectrum (Infrared or Raman) of very large systems (say larger than one thousand atoms) is not only very expensive, but also of relatively low interest, as in many (most of the) cases only a subset of modes, well separated from the large, diffuse bands resulting from the superposition of thousands of peaks, is used for the spectroscopic characterization of the specific system under study. Here, a fragment strategy, consisting in computing and diagonalizing a reduced (in size) Hessian matrix centered around the zone of interest, is illustrated, and its accuracy and efficiency documented, by comparison with the full Hessian diagonalization (FHD) scheme. Three test cases are considered, showing different vibrational features. They are defects in diamond: the $${\hbox {VN}}_3$$ H defect (V stands for the vacancy), where the interesting point is the characterization of the bending and stretching modes of H, well separated from the large band resulting from the perturbation of the diamond manifold; the $${\hbox {VH}}_4$$ defect (four H atoms in the vacancy, with vibrational modes related to H appearing both at high and low wave numbers); and the $${\hbox {I}}_{2{\mathrm{N}}}$$ interstitial defect, with modes in which the N atoms are involved, appearing at wave numbers not far from the manifold of the perfect diamond modes. So the three cases, apparently similar, explore three different situations of interest for the fragment strategy: (1) localized modes very well separated from the large diamond continuous band ( $${\hbox {VN}}_3$$ H); (2) modes at upper border of the large diamond continuous band ( $${\hbox {I}}_{2{\mathrm{N}}}$$ ): a case in which the modes of interest appear both as separated from and merged with the large continuous band ( $${\hbox {VH}}_4$$ ). It turns out that in all cases relatively small fragments, containing from 2 to 40 atoms, permit to reproduce with high accuracy (the difference with respect to the FHD being always smaller than 5 cm $$^{-1}$$ for the wave numbers, and a few percent for the IR intensity) the spectral feature(s) of interest, at a computational cost that is only a small fraction of the one required by the FHD.

Ab initio investigation on the experimental observation of metallic hydrogen

The optical spectra of hydrogen at $\sim$500 GPa were studied theoretically using a combination of \emph{ab initio} methods. Among the four most competitive structures, i.e. C2/c-24, Cmca-12, Cmca-4, and I41/amd, only the atomic phase I41/amd can provide satisfactory interpretations of the recent experimental observation, and the electron-phonon interactions (EPIs) play a crucial role. Anharmonic effects (AHEs) due to lattice vibration are non-negligible but not sufficient to account for the experimentally observed temperature dependence of the reflectance. The drop of the reflectance at 2 eV is not caused by diamond's band gap reducing or interband plasmon, but very likely by defects absorptions in diamond. These results provide theoretical support for the recent experimental realization of metallic hydrogen. The strong EPIs and the non-negligible AHEs also emphasize the necessity for quantum treatments of both the electrons and the nuclei in future studies.

Fabrication of DLC nanoparticle clusters by μ-wave oven based plasma reactor with acetylene diluted in air precursor

This work developed a microwave oven based plasma reactor operated under vacuum pressure. This microwave plasma deposition system used to deposit diamond-like carbon (DLC) thin film on silicon substrate. System is custom-made and economically provides a very inexpensive way to conduct film deposition experiments by using a household microwave oven as a microwave source to get plasma discharge. DLC thin films were successfully deposited on silicon substrates by pure acetylene (C2H2) plasma. Plasma species composed of; CN, N2, CO, C2, and H are presented revealed by Optical Emission Spectroscopy. Energy Dispersive X-ray analysis indicated that the deposited film composed of carbon atoms 46.25% and silicon atoms 53.75%. Raman analysis showed D-band, G-band and nanocrystalline diamond band with sp3-hybridization contained in the films in the range of 48.75–64.08% that composed of chemical bonding; CC, CO, CN, CN, CO, CNH, NO, OH and HOH, analyzed by XPS technique. XRD indicated that the grown films are cubic diamond (1 1 1) crystallography and formed in coral-like clusters from nanoparticles of a mixture between sp2 and sp3 hybridization with high porosity in surface texture that introducing the hydrophobic property on the grown DLC surface by changing the hydrophilic property of smooth silicon substrate surface.

Raman Scattering in Lonsdaleite

We present the results of our study of a polycrystalline diamond–lonsdaleite powder from the Popigai crater (Siberia) using UV micro-Raman scattering and synchrotron X-ray diffraction. By subtracting two experimental Raman spectra of diamond–lonsdaleite samples with a close ratio of the diamond and lonsdaleite fractions, when the maximum contribution to the difference spectrum is related to the difference of the lonsdaleite contributions and not to the change in the diamond band width, we have managed to obtain the spectrum of “pure” lonsdaleite. Its deconvolution has allowed us to identify all three Raman-active vibrational modes E2g, A1g, and E1g whose positions agree well with the results of ab initio calculations.

Enhanced Photocatalytic Activity of Diamond Thin Films Using Embedded Ag Nanoparticles.

Silver nanoparticles embedded into the diamond thin films enhance the optical absorption and the photocatalytic activity toward the solvated electron-initiated reduction of N2 to NH3 in water. Here, we demonstrate the formation of diamond films with embedded Ag nanoparticles <100 nm in diameter. Cross-sectional scanning electron microscopy (SEM), energy-dependent SEM, and energy-dispersive X-ray analysis demonstrate the formation of encapsulated nanoparticles. Optical absorption measurements in the visible and ultraviolet region show that the resulting films exhibit plasmonic resonances in the visible and near-ultraviolet region. Measurements of photocatalytic activity using supraband gap (λ < 225 nm) and sub-band gap (λ > 225 nm) excitation show significantly enhanced ability to convert N2 to NH3. Incorporation of Ag nanoparticles induces a nearly 5-fold increase in activity using a sub-band gap excitation with λ > 225 nm. Our results suggest that internal photoemission, in which electrons are excited from Ag into diamond's conduction band, is an important process that extends the wavelength region beyond diamond's band gap. Other factors, including Ag-induced optical scattering and formation of graphitic impurities are also discussed.

Petrography of the carbonaceous, diamond-bearing stone “Hypatia” from southwest Egypt: A contribution to the debate on its origin

The stone named “Hypatia” found in the Libyan Desert Glass area of southwest Egypt is carbon-dominated and rich in microdiamonds. Previous noble gas and nitrogen isotope studies suggest an extraterrestrial origin. We report on a reconnaissance study of the carbonaceous matrix of this stone and the phases enclosed in it. This focused on areas not affected by numerous transecting fractures mostly filled with secondary minerals. The work employed scanning electron microscopy (SEM) with energy-dispersive (EDS) and wavelength-dispersive (WDS) electron microprobe (EMPA) analysis, Proton Induced X-ray Emission (PIXE) spectrometry and micro-Raman spectroscopy. We found that carbonaceous matrices of two types occur irregularly intermingled on the 50–500 μm scale: Matrix-1, consisting of almost pure carbonaceous matter, and Matrix-2, containing Fe, Ni, P and S at abundances analyzable by microprobe. Matrix-2 contains the following phases as inclusions: (i) (Fe,Ni) sulphide occurring in cloud-like concentrations of sub-μm grains, in domains of the matrix that are enriched in Fe and S. These domains have (Fe + Ni)/S (atomic) = 1.51 ± 0.24 and Ni/Fe = 0.086 ± 0.061 (both 1SD); (ii) grains up to ∼5 μm in size of moissanite (SiC); (iii) Ni-phosphide compound grains up to 60 μm across that appear cryptocrystalline or amorphous and have (Ni + Fe)/P (atomic) = 5.6. ± 1.7 and Ni/Fe = 74 ± 29 (both 1SD), where both these ratios are much higher than any known Ni-phosphide minerals; (iv) rare grains (observed only once) of graphite, metallic Al, Fe and Ag, and a phase consisting of Ag, P and I. In Matrix-2, Raman spectroscopy shows a prominent narrow diamond band at 1340 cm−1. In Matrix-1 the D and G bands of disordered carbon are dominant, but a minor diamond band is ubiquitous, accounting for the uniform hardness of the material. The D and G bands have average full width at half maximum (FWHM) values of 295 ± 19 and 115 ± 19 cm−1, respectively, and the D/G intensity ratio is 0.75 ± 0.09 (both 1SD). These values are similar to those of the most primitive solar system carbonaceous matter. The diamond phase is considered to be a product of shock. The (Fe, Ni) sulphide phase is probably pyrrhotite and a shock origin is likewise proposed for it. Moissanite is frequently associated with the Ni-phosphide phase, and a presolar origin for both is suggested. The lack of recrystallization of the Ni-phosphide phase suggests that the Hypatia stone did not experience long-lasting thermal metamorphism, in accord with the Raman D-G band characteristics.A lack of silicate matter sets the stone apart from interplanetary dust particles and known cometary material. This, along with the dual intermingled matrices internal to it, could indicate a high degree of heterogeneity in the early solar nebula.

Photoluminescence excitation spectroscopy of SiV− and GeV− color center in diamond

Color centers in diamond are important quantum emitters for a broad range of applications ranging from quantum sensing to quantum optics. Understanding the internal energy level structure is of fundamental importance for future applications. We experimentally investigate the level structure of an ensemble of few negatively charged silicon-vacancy (SiV−) and germanium-vacancy (GeV−) centers in bulk diamond at room temperature by photoluminescence (PL) and excitation (PLE) spectroscopy over a broad wavelength range from 460 to and perform power-dependent saturation measurements. For SiV− our experimental results confirm the presence of a higher energy transition at . By comparison with detailed theoretical simulations of the imaginary dielectric function we interpret the transition as a dipole-allowed transition from -state to -state where the corresponding a2u-level lies deeply inside the diamond valence band. Therefore, the transition is broadened by the diamond band. At higher excitation power of we indicate signs of a parity-conserving transition at supported by saturation measurements. For GeV− we demonstrate that the PLE spectrum is in good agreement with the mirror image of the PL spectrum of the zero-phonon line. Experimentally we do not observe a higher lying energy level up to a transition wavelength of . The observed PL spectra are identical, independent of excitation wavelength, suggesting a rapid decay to excited state and followed by optical transition to ground state. Our investigations convey important insights for future quantum optics and quantum sensing experiments based on SiV−-center and GeV−-center in diamond.

Raman spectra of polycrystalline microdiamond inclusions in zircons, and ultrahigh-pressure metamorphism of a quartzofeldspathic rock from the Erzgebirge terrane, Germany

ABSTRACTPolycrystalline microdiamonds are rare in ultrahigh-pressure (UHP) rocks worldwide. Among samples collected at Erzgebirge, Germany, we found abundant polycrystalline microdiamonds as inclusions in zircons from a quartzofeldspathic rock. To illuminate their origin and forming age, we investigated morphologies and Raman spectra of 52 microdiamond inclusions, and dated the zircon host. The zircons have low Th/U values (0.03–0.07) and a concordia U/Pb age of 335.8 ± 1.9 Ma. Polycrystalline diamond (10–40 µm) consists of many fine-grained crystals (1.5–3 µm) with different orientations; discrete single diamonds (2–20 µm) are rare. All measured Raman spectra show an intense diamond band at 1332–1328 cm−1 and have a negative correlation with full width at half maximum (FWHM) of 5.8–11.3 cm−1. These data combined with previously reported diamond band data (1331–1337 cm−1) are compatible with those of diamond inclusions in various host minerals from other UHP terranes, but are different from those of ureilite diamonds. The Erzgebirge microdiamonds in zircon do not display visible disordered sp3-carbon, but show downshifting of the Raman band from the ideal value (1332 cm−1), and have a broader diamond band (FWHM >3 cm−1) than those of well-ordered diamonds. These features may reflect imperfect ordering due to rapid nucleation/crystallization during UHP metamorphism and rapid exhumation of the UHP terrane. Graphite inclusions in zircon show a typical G-band at 1587 cm−1. Our study together with previously reported C-isotopic compositions (δ13C, −17 to −27‰) of diamond and occurrences of fluid/melt inclusions in diamond and garnet indicates that Erzgebirge microdiamonds are metamorphic, have an organic carbon source, and crystallized from aqueous fluids. Limited long-range ordering suggested by the Raman spectra is a function of the P–T time of crystallization and subsequent thermal annealing on decompression. Combined with regional geology, our work further constrains the tectonic evolution of the Erzgebirge terrane.

Raman spectra of polycrystalline microdiamond inclusions in zircons, and ultrahigh-pressure metamorphism of a quartzofeldspathic rock from the Erzgebirge terrane, Germany

ABSTRACTPolycrystalline microdiamonds are rare in ultrahigh-pressure (UHP) rocks worldwide. Among samples collected at Erzgebirge, Germany, we found abundant polycrystalline microdiamonds as inclusions in zircons from a quartzofeldspathic rock. To illuminate their origin and forming age, we investigated morphologies and Raman spectra of 52 microdiamond inclusions, and dated the zircon host. The zircons have low Th/U values (0.03–0.07) and a concordia U/Pb age of 335.8 ± 1.9 Ma. Polycrystalline diamond (10–40 µm) consists of many fine-grained crystals (1.5–3 µm) with different orientations; discrete single diamonds (2–20 µm) are rare. All measured Raman spectra show an intense diamond band at 1332–1328 cm−1 and have a negative correlation with full width at half maximum (FWHM) of 5.8–11.3 cm−1. These data combined with previously reported diamond band data (1331–1337 cm−1) are compatible with those of diamond inclusions in various host minerals from other UHP terranes, but are different from those of ureil...

Study on Defects in Ultrananocrystalline Diamond/Amorphous Carbon Composite Films Prepared by Physical Vapor Deposition

Ultrananocrystalline diamond/amorphous carbon composite (UNCD/a-C:H) films was deposited by coaxial arc plasma deposition with a graphite target. UNCD/a-C:H films prepared by physical vapor deposition show large optical absorption coefficients in the photon range from 3 to 5 eV due to disordered structures in a-C:H and grain boundaries. Electron spin resonance measurement indicates the existence of a large number of dangling bonds with a density of ~1022 cm−3. These dangling bonds might cause the formation of localized states in diamond band gap and contribute to the optical absorption properties specific to the UNCD/a-C:H films.

Interface electronic structure and the Schottky barrier at Al-diamond interface: hybrid density functional theory HSE06 investigation

Diamond is regarded as one of the most promising semiconductor materials used for high power devices because of its superior physical and electrical properties, such as wide bandgap, high breakdown electric field, high mobility, and high thermal conductivity. Highpower diamond devices are now receiving much attention. In particular, Schottky diode based on a metal/diamond junction has promising applications, and high breakdown voltage has been achieved, though unfortunately its forward resistance is high. In this paper, the first principles calculations are performed to study the electronic structure of interface and the Schottky barrier height of Al-diamond interface. The projection of the density of states on the atomic orbitals of the interface atoms reveals that the typical Al-induced gap states are associated with a smooth density of states in the bulk diamond band gap region, and these gap states are found to be localized within three atom layers. At the same time, electronic charge transfer makes the Fermi level upgrade on the side of diamond. Besides, the typical Al-induced gap state model gives a simple picture about what determines Schottky barrier height at Al-diamond interface, by assuming an ideal, defect-free and laterally homogeneous Schottky interface in which the only interaction comes from the decay of the electron wave function from the metal into the semiconductor, which in turn induces electronic charges to be rearranged in the region close to the interface. As for the electronic charge transfer, this potential shift can be extracted by subtracting the superimposed planar or macroscopically averaged electrostatic potentials of the Al and diamond surfaces (at frozen atomic positions), from the planar or macroscopically averaged potential of the relaxed Al-diamond interface. The electronic charge transfer suggests that the formation of an interface should be associated with the formation of new chemical bonds and substantial rearrangements of the electron charge density. Especially, we obtain the Schottky barrier height of 1.03 by the first principle, which is in good agreement with the results from phenomenological model and experiment. The research results in this paper can provide a theoretical basis for the research of the metal diamond Schottky junction diode, and can also give a theoretical reference for the research of the metal-semiconductor highpower device based on diamond material.

Graphite-diamond relations in mantle rocks: Evidence from an eclogitic xenolith from the Udachnaya kimberlite (Siberian Craton)

Relations of graphite and diamond have been studied in a garnet-kyanite-clinopyroxene+sulfide+coesite/quartz+diamond+graphite eclogite xenolith from the Udachnaya-East kimberlite pipe in the Yakutian diamond province. Euhedral crystals of diamond and graphite occur in the intra- and intergranular space. The equilibrium conditions of diamond formation reconstructed by geothermobarometry for the Grt-Cpx-Ky-Coe mineral assemblage are 1020 ± 40 °C and 4.7 GPa. Raman imaging of graphite enclosed in diamond shows high ordering and a 9 cm−1 shift of the ~1580 cm−1 band. This Raman shift of graphite, as well as a 5 cm−1 shift of the 1332 cm−1 band of diamond, indicate large residual stress in graphite and in diamond around the inclusion, respectively. According to FTIR spectroscopy, nitrogen in diamond is highly aggregated and exists mainly as the A centers, while no other phases occur near graphite inclusions. Therefore, diamond in the analyzed eclogite sample must be quite old: it likely had crystallized long (~1 Byr) before it became entrained with kimberlite melt. New data show that graphite can stay in the upper mantle for billions of years without converting to diamond. Crystallization of various carbon polymorphs, both in laboratory and natural systems, remains poorly constrained. Graphite present in mantle and UHP rocks may be a metastable phase crystallized in the diamond stability field. This fact should be taken into consideration when deducing petrological constrains and distinguishing diamond and graphite subfacies in upper mantle.

Direct determination of the barrier height of Au ohmic-contact on a hydrogen-terminated diamond (001) surface

The barrier height ϕB of Au ohmic-contact on hydrogen-terminated p-type surface conductive layer (SCL) made on a boron-doped diamond (001) substrate has been directly determined by X-ray photoelectron spectroscopy (XPS). For this purpose, thin layer (thickness~3.6nm) of Au was deposited on the p-type SCL. The formation of nm-size Au-islands was identified by scanning electron microscopy. It became therefore evident that C 1s XPS spectra originate from diamond in the gap areas among Au-islands but not from diamond underneath the Au-islands. Two-dimensional energy band simulation was performed to show that the diamond band diagram in the gap areas among Au-islands become effectively identical to that of diamond underneath the Au-islands when SCL is eliminated only in the gap areas. In order to eliminate SCL in the gap area only, a VUV/ozone irradiation process was applied on the Au-island-covered sample. C 1s and Au 4f7/2 XPS spectra were measured for the sample before and after the VUV/ozone irradiation process. The peak binding energies and widths of C 1s and Au 4f7/2 XPS spectra are carefully considered to reach to the conclusion that ϕB=0.29±0.13eV. For the boron-doped present substrate, the current flow mechanism at the Au ohmic-contacts is expected to be thermionic emission and specific contact resistance RC is thus evaluated to be the order of 10−4Ωcm2.

Spectroscopic Analysis of Nitrogen-Doped Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films Prepared By Coaxial Arc Plasma Deposition

Ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) is a new candidate carbon semiconductor applicable to electrical devices. It has been investigated that nitrogen-doping for diamond is ineffective for realizing n-type conduction at room temperature, because nitrogen form a deep donor level of 1.7 eV below the bottom of a conduction band in diamond. For a-C:H, n-type conduction is realized by nitrogen doping, however it is difficult for the carrier density to be controlled widely. On the other hand, it has been reported that nitrogen doping is effective for UNCD/a-C:H prepared by chemical vapor deposition (CVD) and pulsed laser deposition (PLD)1), 2), the doping mechanism for UNCD/a-C:H seems to differ from those for diamond and a-C:H. In this study, UNCD/a-C:H films were prepared by coaxial arc plasma deposition (CAPD) with nitrogen atmosphere and the effects of the nitrogen doping on the UNCD crystallite formation were structurally investigated. X-ray photoemission spectra (XPS), which were measured with MgKα line, of the UNCD/a-C:H films prepared at different inflow ratio of nitrogen and hydrogen (IN/H ). N1s peaks strengthened with an increase in the IN/H , which evidently indicates that the nitrogen content in the film increased with the IN/H . The nitrogen contents of the films deposited at IN/H of 0.25, 0.5, 1.0 and 1.5 were estimated to be 3, 5, 6 and 8 at. %, respectively. Near-edge X-ray absorption fine structure (NEXAFS), spectral shape of the nitrogen-doped films different from the undoped film were obtained. By increasing the doping amount, the intensity of the π*C=N increased, while the intensity of the σ*C-C is decreased. Which refers to strengthen in sp2 bonds and weaken in sp3 bonds. Furthermore, increasing the electrical conductivity by increasing the nitrogen-doping amount can be ascribed to contribute of sp2bonds. The details will be reported at the conference. 1) Dai, et al.: Phys. Rev. B 71, 075421 (2005). 2) T. Yoshitake, et al.: Jpn. J. Appl. Phys 49, 015503 (2010).