Electron emission and charging of natural diamond under irradiation with medium-energy electrons

The processes of charging of a natural diamond crystal irradiated by an electron beam with primary electron energies in the range 1–30 keV have been experimentally investigated. The charging kinetics has been studied as a function of the irradiation dose and the electron-emission properties of the crystal. The following fundamental characteristics have been determined: the second crossover equilibrium energy of the beam electrons and the values of high-voltage surface potentials and accumulated charges.     

Anomalous nonlinearity of IR photoconductivity of diamond polycrystalline films

Nonlinearity of the lux-ampere characteristics of undoped polycrystalline diamond films is revealed. The spectral dependences of this nonlinearity and photoconductivity are analyzed in the framework of the available models with a single impurity level or a single type of traps. It is shown that, for undoped polycrystalline diamond films in the range of impurity photoconductivity, the lux-ampere characteristics exhibit an anomalous nonlinearity when their slopes change from 1/2 to approximately unity with a decrease in the wavelength and an increase in the excitation level and the carrier lifetime. The results obtained are explained within the model of the coexistence of two different channels of conduction in diamond films. Two ranges of carrier photogeneration are established. For photon energies below 1.4 eV, the carrier generation with quadratic recombination is observed in a single channel. At higher photon energies, the carrier generation occurs in two channels simultaneously (in addition, the carriers are excited with linear recombination in the second channel). It is demonstrated that the equilibrium concentration of carriers in the second channel with linear recombination substantially exceeds the equilibrium concentration of carriers in the first channel with quadratic recombination, which hampers the detection of the first channel without photoexcitation.     

Resonances in ferromagnetic gratings detected by microwave photoconductivity

We investigate the impact of microwave excited spin excitations on the dc charge transport in a ferromagnetic (FM) grating. We observe both resonant and nonresonant microwave photoresistance, which are caused, respectively, by spin and charge dissipations of the microwave power into the FM. A macroscopic model based on Maxwell and Landau-Lifschitz equations reveals the mixing of spin and charge dissipations, which shows that the ferromagnetic anti-resonance is shifted when the conductivity is anisotropic. We find that the microwave photoconductivity provides a powerful new tool to study the interplay between photonic, spintronic, and charge effects in FM microstructures.     

The kinetics of the R- and UV-band photoconductivity (PC) in radiation damaged diamond

Illumination in the UV-band of radiation damaged diamond was found to enhance the PC in the red (the RPC). Continuous R-illumination then caused the RPC to decay hyperbolically to zero. R-band illumination also enhanced the PC in the UV band (UPC). Continuous illumination in the UV-band then caused the UPC to decay to a level about half of the maximum UPC. A two-level model was proposed in which exchange of holes between the U- and R-levels via the valence band was assumed to take place under illumination. The differential equations obtained from the kinetics of the transitions were solved with some approximations, and were found to give an excellent agreement with the experimental results. Further support for the model was obtained from numerical integration of the differential equations. When compared with the experimental results this provided information on the crystal parameters involved. The transition rates for valence-band holes into the levels R and U were found to be: A_R= U_U = 2.3 × 10^?11m³sec^?1, which gave for the capture-cross-sections at 290 K of these centres S = 3.2 × 10^?17m². Surprisingly low densities of the order of 10¹²m^?3 were obtained for R and U, indicating that only a small fraction of the damage-produced defects play a role in the UPC and RPC.     

Photoenhancement of the photoconductivity (PC) of electron irradiated semiconducting diamond

The spectrum of the non-enhanced PC of electron irradiated semiconducting diamond extends from the UV towards the visible and near infrared. It's long wavelength tail was found in the present work to exhibit a well defined threshold shifted with temperature from about 1.5eV at 76 K to about 1.25 eV at 500 K. Pre-illumination in the “UV-band” produced an enhanced PC band with a temperature independent threshold at 1.08 0.03 eV. This photoenhanced band was found to be closely related to a thermally-simulated current peak (TSC) at 500 K with an activation energy of 0.50 eV excited by the pre-illumination in the UV-band. The prhotenhanced band was bleached out thermally with the exhaustion of the TSC peak below 600 K. Some of the characteristics of the photoenhanced band including the linear dependence of the square root of the PC on photon energy may suggest that internal photoemission of holes plays a role in the formation of this band.     

Radiation of channeled 800 MeV electrons in diamond crystals

Measured data on γ-ray emission for the low-energy region of the bremsstrahlung spectra produced by 800 MeV electrons in diamond crystals are presented. The obtained spectral and orientational characteristics of the γ-ray yield indicate that the low-energy radiation is associated with the channeling of electrons.     

The application of thermoluminescence theory to natural semiconducting diamond

The main thermoluminescence glow peak at ~ 250°K in natural semiconducting diamond has been analysed by methods proposed by several authors, using the model of the thermoluminescence process developed in the preceding paper as a guide. Kinetic equations appropriate to two conditions of recombination are developed and discussed in the light of the recombination processes in natural semiconducting diamond. A summary of several methods of analysis is given. The various methods are then applied in turn to the 250°K glow peak. The method of initial rise is shown to be appropriate to the model of trapping and recombination given in the preceding paper, and gives a value 0.35 ± 0.02 eV for the trap depth. Halperin and Braner's method for the trap depth is unsuitable owing to the high value of their correction term 2kT_m/E, although their analysis suggests that the order of the kinetics changes from nearly 1st to nearly 2nd as the glow progresses. The methods of Grossweiner, Keating and Luschik apply only when 1st order processes are selected. An estimation of the trapping cross-section gives S_T ~ 10^-20 cm².     

Circular-polarization-dependent study of the microwave photoconductivity in a two-dimensional electron system

The polarization dependence of the low field microwave photoconductivity and absorption of a two-dimensional electron system has been investigated in a quasioptical setup in which linear and any circular polarization can be produced in situ. The microwave induced resistance oscillations and the zero resistance regions are notably immune to the sense of circular polarization. This observation is discrepant with a number of proposed theories. Deviations between different polarizations occur only near the cyclotron resonance where an unprecedented large resistance response is observed.     

Evaluation of local photoconductivity of solar cells by microwave near-field microscopy technique

Local photoconductivity in surface layer of solar elements has been studied by the method of microwave near-field microscopy (MW NFM). Dependences of photoconductivity of a solar cell on the intensity and wavelength of the incident optical radiation are determined by measuring the coefficient of reflection of MW NFM resonator at the frequency 4.1 GHz.     

Energy characteristics of planar-channeling radiation for high-energy electrons in diamond

γ-ray spectra have been measured for (110) and (111) planar channeling of 600–900 MeV electrons in a diamond crystal. It is shown that in the case of (111) crystallographic planes the influence of molecular-type motion on the formation of the spectra is predominant.     

Nearly exponential dependence on photon energy of the photoconductivity of electron irradiated semiconducting diamond

The photoconductivity (PC) of electron irradiated semiconducting diamond was examined over the energy range 1–4 eV (0.3–1.2 μm) and over the temperature range 76–500 K. The PC response spectra exhibited a strong drop below 3 eV. In one sample (RDl) this drop was by a factor of nearly 10⁴ from 3 to 2 eV. In the range of the Ar laser lines (2.41–2.73 eV) the PC depended nearly exponentially on photon energy. A mechanism involving competition for the absorption of the exciting light between the non-photoconductive GRl system and the photo-conductive UV absorption band gives a good account of the experimental results. This includes the photon energy dependence of the PC and its thermal dependence.The proposed mechanism is further supported by the absence of the drop in PC near 2.5 eV in a lightly colored electron irradiated diamond.     

The negative role of the fast electrons in the microwave oxidation of silicon

The influence of the fast electrons (up to approx. 100 eV), created in the magnetoactive oxygen plasma, with respect to the silicon oxide growth and oxide properties has been studied. The low values of the oxide dielectric strength and great density of the oxide defect charges have been found on damaged oxides. An upper energy limit (less than approx. 30 eV) has been introduced for the plasma electrons to prevent the oxide defects and extremal heating of the silicon sample during oxidation process.     

The laboratory confirmed natural crystallization of diamond from carbonized organic compounds

Abstract

In the paper the conception of the natural diamond growth as a result of the organic compounds reaction in the presence of noncompensated spin was checked. They might have played the essential role in the nucleation of diamond crystals. In the experiments, the partly carbonized phenolformal-dehyde resin instead of graphite was used as a carbon source. The final result of the process of the diamond growth depended on the temperature of resin carbonization as well as on the temperature and pressure of synthesis. The 3,8 GPa pressure, which is less than needed for graphite to diamond transformation in the classic industrial process, was sufficient to produce transparent and colourles diamond crystal of the size up to 0,7 mm.     

Self-organization of diamond nanocrystallites in a low-pressure microwave plasma

The self-organization effect is found in diamond nanocrystallites that arise in polymer-like hydrocarbon films growing in the nonequilibrium microwave plasma of volatile carboniferous materials at a low substrate temperature. The nature of this effect (specifically, the conditions of formation of the hydrocarbon substrate, its role during diamond nanocrystallite growth, and ways of controlling the size and concentration of the crystallites) is studied.     

Integrated microwave (centimeter-range) modulator on polycrystalline diamond layers

Measuring data for the parameters of a microstrip switching superhigh-frequency integrated circuit on a 100-μm-thick polycrystalline diamond film are reported. Measurements are taken in the frequency range 3–7 GHz. It is shown that the decay in developmental modulators is no greater than 1.5 dB in the on state and no less than 29 dB in the off state. Physicochemical analysis of the multilayer contact metallization technology as applied to synthetic diamond and a silicon p-i-n diode is carried out. The metallization is shown to be stable up to 400°C.     

Research of microstructural characteristics on nanocrystalline diamond by microwave plasma CVD

In this study, the nanocrystalline diamond (NCD) films were carried out by microwave plasma chemical vapor deposition (CVD) with CH₄/Ar/H₂ gas concoction on Si substrate at moderate temperatures. The characteristics of NCD films were evaluated using scanning electron microscopy, Raman spectroscopy, transmission electron microscopy, optical emission spectroscopy and optical contact angle meter. The analytical results revealed that C₂ radial was the dominant species in the deposited process. From TEM observation, the NCD films were formed via the etching of hydrocarbons and a small amount of H₂ content additive into gas mixture has improved the aggregation of the nucleation film to form the NCD films. The more hydrophobic surfaces imply that NCD films are the potential biomaterial in the application of article heart valve or stent.     

Observation of monochromatic X-ray radiation from 900 MeV electrons transmitting through a diamond crystal

A new source of monochromatic X-ray radiation from a relativisti? electron beam transmitted through a crystal target is experimentally observed.