Acoustic properties of buried graphitized layers in diamond formed by ion implantation followed by annealing were studied using the picosecond ultrasonic technique with spatial resolution. Two ...methods of elastic pulse generation were used: heating an aluminum film deposited on a diamond sample by femtosecond laser pulses and direct illumination of the graphitized layers by these pulses. We applied a multilayered model of the acousto-optical response to fit experimental results and estimate the distribution of the acoustical parameters (wave resistance, viscoelastic damping, and longitudinal sound speed) of the structures under study in depth. It was found that unique sets of spectral lines are present in the Fourier spectra of measured responses in regions with different internal structures. Mapping of the Fourier spectra made it possible to visualize regions with different internal structures. The combined use of depth profiling and mapping can serve as a tool for hypersound tomography.
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Ge diffusivity from a buried SiO
2
layer of a silicon-on-insulator (SOI) structure has been studied as a function of annealing temperature. It has been shown that, at an annealing temperature lower ...than 900°C, almost all Ge is localized in the implantation region of the SiO
2
layer. As the annealing temperature is raised to 1100°C, migration of ion-implanted Ge is accompanied by several processes: diffusion into SiO
2
, accumulation at Si/SiO
2
interfaces, diffusion into silicon, and evaporation from silicon. At 1100°C, Ge diffuses from SiO
2
to the bonding interface of the SOI structure with the diffusion coefficient of ~2 × 10
−15
cm
2
/s, which is 2 orders of magnitude higher than its equilibrium value. Depending on the thickness of the silicon layer, formation of a Ge or SiGe phase is detected after annealing at a temperature of 1100°C.
The synthesis of diamonds in traditional growth systems based on Fe, Co and Ni does not allow overcoming the semiconductor level of boron doping of diamond, presumably because of a high affinity of ...boron to boride-forming metals. For the first time, noble metals that do not form borides—silver and gold—are used as growth media for the synthesis of heavily boron-doped diamonds at 8–9 GPa. Gold and silver are not catalysts for the transformation of graphite to diamond, whereas elemental boron is catalytically active at eutectic melting temperatures above 2500 K. It is found that the synthesis of diamond in AgB and AuB growth media starts at temperatures close to the melting temperatures of Ag and Au, 1600 and 1800 K, respectively. Calculations show that molten Au and Ag dissolve boron atoms without a significant change in the electronic structure of the solution, suggesting that the metal melts serve as a carrier for the boron catalyst. The resulting polycrystalline diamond contains dispersed inclusions of Ag and Au, as well as traces of boron carbide; the formation of borides is not detected. The transport measurements of the diamond samples reveal a transition to a superconducting state in the temperature range from 4.5 to 2.5 K. Raman spectroscopy confirms the heavy boron doping of diamond. Thus, we show that melts of “non-catalytic” metals that do not form borides can be effectively used to synthesize boron-doped conductive/superconducting diamonds at relatively low temperatures.
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•Boron-doped diamonds were synthesized in Au and Ag solvents at 8–9 GPa and 1600–1800 K.•Experiments and calculations suggest that molten Au and Ag serve as curriers for boron catalyst.•Synthesized diamonds become superconducting at 4.5–2.5 K.•Nano-inclusions of Au and Ag are spread in the polycrystalline diamond matrix.•Borides of Ag and Au are not formed under synthesis conditions.
Abstract
Chemical vapor deposited (CVD) diamonds have been irradiated with fast reactor neutrons at fluencies
F
= 1·10
18
and 3 · 10
18
cm
-2
and then heated at temperatures up to 1600 °C. The ...processes of annealing in and annealing out of various complexes of intrinsic defects responsible for vibrational and electron-vibrational bands in the IR absorption spectra have been studied in detail. Some tens of local vibrational modes and zero-phonon lines with rather small width caused by numerous complexes of intrinsic defects were observed in the 400-11000 cm
-1
range.
Nanostructured near-IR antireflective layer was produced on a GaAs slab surface by direct femtosecond laser fabrication of a surface diffraction grating. The single nanostructured layer on the GaAs ...slab reduces its total reflection at the wavelength λ ≈ 2.5 μm by 42 %, in agreement with the second-order approximation of the effective medium theory, with negligible increase of its absorbance.
Excitation of type IIb synthetic diamond by ultrashort laser pulses in the visible range causes broadband luminescence in the UV visible range; the observed luminescence band can be attributed to the ...A band characteristic of diamonds. The photoluminescence spectra were obtained at different laser pulse durations (0.3–6.2 ps) depending on the pulse energy. A nonlinear dependence of the luminescence yield on the intensity of ultrashort pulses is established.
•CNWs treatment in the air atmosphere leads to the formation of most active sites.•Surface modification using air atmosphere can be used to improve the ORR characteristics of carbon ...materials.•Structural defects of samples before treatment also made a significant contribution to the obtained ORR characteristic.
Carbon materials are of outstanding interest for use in energy sources. One of the latest achievements in improving their specific characteristics is the doping of carbon materials with various heteroatoms. However, the mechanisms that lead to improved performance remain unexplored. In this study, we investigated the influence of structural defects and incorporated heteroatoms on the oxygen reduction reaction (ORR) of highly oriented pyrolytic graphite and carbon nanowalls. Controllable modification in DC plasma in an atmosphere of nitrogen, oxygen and air was used for the incorporation of heteroatoms. We found that treatment in the air atmosphere leads to the formation of most active sites due to incorporation of heteroatoms and partial amorphization of material surface. The DFT calculations reveal these active sites can’t be amplified by substitution to nitrogen atom due to insignificant sorption energy difference of *OOH group compared with undoped carbon. Existed material’s structural defects and appeared after the treatment also make a significant contribution to the obtained ORR characteristics. Plasma-assisted treatment under air conditions can be used for carbon nanomaterials modification for ORR application.
Diamond's unique properties make it attractive for use in a variety of industrial applications. However, this material has not found mass application in microelectronics due to several factors, ...including the lack of large-sized plates, n-type doping, and high-quality metallization. In this article, we address the problem of diamond surface metallization by forming niobium carbide layers. We obtained a niobium carbide film several nanometers thick that exhibits superconducting behavior up to 12.4 K. To our knowledge, this is the highest superconducting transition temperature achieved in the niobium carbide system. The crystal lattice parameter of the film is 4.4659 Å, which is close to the maximum value for niobium carbide lattice parameters. Density functional theory calculations were employed to investigate the thermodynamic stability of niobium carbide compounds at various temperatures and determine the superconducting critical temperature of niobium carbide. The combination of diamond's high thermal conductivity, along with the strong adhesion and superconductivity of niobium cabide films, introduces exciting possibilities for the realization of superconductive sensitive detectors.
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•Adhesion-strong films of stoichiometrically perfect NbC were obtained by niobium deposition and subsequent annealing.•Observation of phase transformation of niobium into niobium carbide during annealing.•Deposition of niobium at high temperatures leads to good adhesion and formation of continuous nanocrystalline films.•The obtained niobium carbide film several nanometers thick exhibits superconducting behavior up to 12.4 K.•The lattice parameter of the film is 4.4659 Å, which is close to the maximum value for the lattice parameters of NbC.
Abstract
We report on the optical properties of He-related color centers created by He-ion implantation and subsequent thermal annealing in natural diamonds, including the temperature (300–700 K) and ...excitation power (1–1800 kW/cm
2
)-dependent photoluminescence (PL) measurements. The prospects for the use of He-implanted diamonds for temperature sensing are discussed. The effect of fast neutron irradiation on the optical properties of Si-V color centers in CVD diamonds were also examined.
Ion-implanted and graphitized layers in diamond are considered as a key element of promising acousto-electronic devices, micro- and nano-electromechanical systems operating in the gigahertz frequency ...range. That is why their acoustical and photo-acoustical properties are of interest. In this work, we show that graphitized layers in diamond irradiated with femtosecond laser pulses are efficient generators of not only bulk but also surface waves. The nature of these waves is similar in structure to Rayleigh waves propagating along a free flat boundary of a half-space. In contrast to the undamaged diamond surface, the propagation of such a wave along the diamond surface with a buried graphitized layer leads to a considerable “spreading” of the surface wave caused by dispersion.
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