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Y 2 O 3 anti-reflection films were deposited on freestanding CVD diamond substrates by radio frequency magnetron sputtering. The thermal shock resistance and oxidation resistance of Y 2 O 3 /diamond/Y 2 O 3 samples at 727 °C and 800 °C in atmospheric air were investigated. No delamination of the Y 2 O 3 films occurred after thermal shock, thereby demonstrating extreme adhesion to freestanding diamond substrates. After thermal shock, Y atoms in the films were almost fully oxidized. Moreover, the majority of monoclinic phase in the Y 2 O 3 films transformed into cubic phase, crystallinity was enhanced, and the average grain size significantly increased. The maximum transmittance in the 8–12 μm long-wave IR range of the Y 2 O 3 /diamond/Y 2 O 3 samples increased from 81.3% ± 0.3% to 84.7% ± 0.2% and 83.6% ± 0.4%. These findings indicated that the Y 2 O 3 anti-reflection films displayed good resistance to thermal shock and provided sufficient protection for diamond substrates against elevated temperature oxidation. [ABSTRACT FROM AUTHOR]

Polycrystalline CVD free-standing diamond films have been heat treated through a rapid heating process using a direct current (DC) arc plasma jet system within the temperature range of 1500–2000 °C. The optical transmission of the diamond film decreases when the treatment temperature exceeds 1500 °C. When the diamond film was annealed to 1800 °C for just 1 min, the infrared (IR) transmittance at λ = 10.6 μm of the film was significantly decreased from 60.5% to 4.0%, due to the transformation from diamond to graphite. Further increase of the temperature to 2000 °C leads to complete loss of optical transmittance in only 30 s, due to the detrimental occurrence of graphitization. XRD patterns indicate that graphite ultimately grows preferentially along the (0002) plane by forming disordered or turbostratic graphite as intermediate product. Raman spectra and SEM images verify that at 1500–1850 °C graphitic carbon transforms from the diamond surface in the form of protruding submicron crystallites, which were still containing a number of sp 3 C C bonds. In addition to graphitization on the external surface, the diamond-graphite phase transition also occurs along the grain boundaries and the calculated activation energy of the grain boundary graphitization process is 276 kJ·mol − 1 for the CVD diamond. [ABSTRACT FROM AUTHOR]

Graphene directly grown on an 4H-SiC (0 0 0 1) substrate by chemical vapor deposition was studied: it was shown that Si evaporation process is not completely halted during graphene growth when T G  ≥ 1400 °C, the SiC substrate decomposes at the position of graphene coverage. AFM and Raman spectrum results reveal that carbon concentration significantly influences graphene growth rate and morphology/structure. It is found that the quality of graphene film depends on the growth temperature and the flow of carbon source. We develop a new gradient growth method to produce a feasible graphene material for electronic devices. Graphene grown by this method has a flat-morphology structure, low wrinkle density, high crystal quality, good uniformity, and outstanding electrical transport properties. Nitrogen doping has an n-type doping effect on graphene carrier concentration. The main component of nitrogen-bond type is the graphitic configuration. The graphene material with nitrogen doping reaches a record mobility of 9010 cm 2 /V·s by room temperature Hall effect measurement, indicating graphene grown by gradient method with suitable nitrogen doping could yield a high quality film comparable to that by traditional method. [ABSTRACT FROM AUTHOR]

The CVD diamond films at different growth stages were prepared on the same substrate by DC arc plasma jet CVD. The surface morphologies and residual stress of diamond films were characterized by scanning electron microscope and Raman spectroscopy. The intrinsic stress of diamond films were obtained by subtracting thermal stress from residual stress. The results showed that the intrinsic compress stress was 0.42 GPa for the precoalescence stage due to the sp 2 carbon inclusions in diamond islands. With the diamond islands growing up and even snapping together to form grain boundary at the coalescence stage the intrinsic compress stress was 0.06 GPa. Eventually, the diamond islands coalesced into a continuous polycrystalline film, the intrinsic compress stress vanished and converted to tensile stress, the intrinsic tensile stress reached 1.41 GPa due to the number of grain boundaries increasing. The evolution of intrinsic stress during diamond film initial growth was mainly attributed to the surface free energy of diamond islands changed to the free energy of grain boundaries which was consistent with the Nix-Clemens model. [ABSTRACT FROM AUTHOR]

Y 2 O 3 anti-reflection films were deposited on freestanding chemical vapor deposited (CVD) diamond substrates by radio frequency magnetron sputtering. The effects of oxygen–argon ratio on microstructure, composition, optical property and mechanical property were analyzed by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, spectroscopic ellipsometry, Fourier transformed infrared spectroscopy, and nanoindentation. The results showed that the crystal structure of Y 2 O 3 films transformed from cubic to monoclinic with the increase of oxygen–argon ratio. Meanwhile, the degree of non-stoichiometry of the film with the monoclinic phase was higher than the film with the cubic phase. Both monoclinic and cubic Y 2 O 3 film had an anti-reflection effect on diamond in the 8–12 μm long-wavelength infrared (LWIR) range. However, the maximum transmittance of the Y 2 O 3 film-coated diamond was shifted to lower wavelengths, which were mainly attributed to the reflective indexes of the Y 2 O 3 film that decreased with the increase of the oxygen–argon ratio. The Y 2 O 3 film with a cubic phase had high resistance to abrasion and plastic deformation. Therefore, the Y 2 O 3 film with a cubic phase was much more suitable for long-wave infrared application. [ABSTRACT FROM AUTHOR]

AlGaN/GaN polarization-doped field-effect transistors (PolFETs) were fabricated on the graded AlGaN/GaN heterojunctions grown by metal organic chemical vapor deposition, and the trap behaviors were first systemically evaluated by frequency-dependent conductance–voltage characterizations. It was found that there was no obvious effective traps accumulation in the graded AlGaN/GaN heterojunctions of the PolFETs due to the absence of abrupt heterostructure as in the traditional HFETs. The exactly exponential dependence of the trap state time constants on the bias voltage in PolFETs was observed, which was a typical characteristic for interface traps, indicating a multi-heterointerface feature of the PolFETs. [ABSTRACT FROM AUTHOR]

The excellent electrical properties of graphene make it have broad application in electronic devices [1–2]. Grain boundaries and wrinkles will greatly scatter charge carriers of graphene [3–4]. Graphene with less gain boundaries and wrinkles are highly demanded. At present, the chemical vapor deposition (CVD) of graphene on Cu foil/Cu-Ni surfaces has been known as the simplicity and low cost way to prepare large-sized high-quality graphene films. However, the suppressing nucleation density method also leads to a low growth rate. Here we demonstrate a surface oxygen supply strategy for the Cu Ni substrate on sapphire to form a Cu-Ni-O surface. With the Cu-Ni-O surface, the growth rate of graphene is greatly increased to 240 μm/min. The as-synthesized graphene has less wrinkles, and a small 2D peaks FWHM of 25.2 cm−1. The room temperature sheet resistance reaches 267 Ω/square. This study provides a meaningful method to time-saving synthesis of high-quality graphene. Unlabelled Image • Surface oxygen supply strategy for the Cu Ni substrate on sapphire to form Cu-Ni-O surface. • The high growth rate and high quality of graphene are obtained on Cu-Ni-O surface. • A meaningful method to time-saving synthesis of high-quality graphene. [ABSTRACT FROM AUTHOR]