Fanxiu Lu

Low hydrogen content diamond-like carbon coatings of KCl optics for high power industrial CO2 lasers

Abstract Magnetron sputtered low hydrogen content diamond-like carbon (DLC) was studied for possible application as antihygrosity protective coatings of KCl IR optics for high power industrial CO2 lasers. The absorption coefficient of sputtered DLC was shown to vary with sputtering parameters and hydrogen content in the deposition environment. With proper control of the parameters, DLC with an absorption coefficient as low as 80 cm−1 at 10.6 μm is obtainable. Laser damage due to pulsed and continuous CO2 lasers was studied. The damage threshold due to the pulsed CO2 laser was 4–7 GW cm−2, which was relatively insensitive to sputtering power. The damage threshold due to a continuous wave CO2 laser of DLC prepared under favourable conditions was shown to be 7.2–7.4 kW cm−2, which was very sensitive to sputtering parameters, cleanness of the film surface, and defects in the film and the KCl substrate. The damage behaviour of DLC was studied in detail. A DLC protected KCl focusing lens (φ 50 mm, f = 200 mm) was successfully used with an industrial CO2 laser processing machine ar 1.5 kW power for months in a humid atmosphere in Shanghai, China.

Effect of nitrogen ion implantation on the microstructural transformation of boron film

Abstract The structural transformation by nitrogen ion implantation into boron film as a function of film thickness, implant voltage and nitrogen ion dose was systematically investigated. Boron films were deposited on single crystal Si substrates using the electron beam evaporation of pure metallic boron, the thickness being 200, 500, 1000 and 2000 A, respectively. The films were then nitrogen ion-implanted at 25-, 50- and 75-kV implant voltages applied to substrate, respectively, for a fixed nitrogen ion dose of 3×1017 cm−2, and at 1×1017, 2×1017 and 3×1017 cm−2 nitrogen ion doses, respectively, for a fixed implant voltage of 50 kV. The nitrogen ion-implanted boron films were characterized by Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). XPS results showed that the nitrogen ion-implanted boron films were nitrogen-deficient. Boron exists in the form of both metallic boron and boron nitride as indicated by XPS B1s bands. FT-IR spectra revealed that amorphous boron nitride (a-BN) or hexagonal boron nitride (h-BN) formed during nitrogen ion implantation into boron films. As implant voltage and nitrogen ion dose increased, amorphous BN was initially formed, while h-BN occurred at greater implant voltage and nitrogen ion dose. The thinner film led to the formation of h-BN at a relatively low implant voltage and nitrogen ion dose.

Optical characterization of single-crystal diamond grown by DC arc plasma jet CVD

Optical centers of single-crystal diamond grown by DC arc plasma jet chemical vapor deposition (CVD) were examined using a low-temperature photoluminescence (PL) technique. The results show that most of the nitrogen-vacancy (NV) complexes are present as NV− centers, although some H2 and H3 centers and B-aggregates are also present in the single-crystal diamond because of nitrogen aggregation resulting from high N2 incorporation and the high mobility of vacancies under growth temperatures of 950–1000°C. Furthermore, emissions of radiation-induced defects were also detected at 389, 467.5, 550, and 588.6 nm in the PL spectra. The reason for the formation of these radiation-induced defects is not clear. Although a Ni-based alloy was used during the diamond growth, Ni-related emissions were not detected in the PL spectra. In addition, the silicon-vacancy (Si-V)-related emission line at 737 nm, which has been observed in the spectra of many previously reported microwave plasma chemical vapor deposition (MPCVD) synthetic diamonds, was absent in the PL spectra of the single-crystal diamond prepared in this work. The high density of NV− centers, along with the absence of Ni-related defects and Si-V centers, makes the single-crystal diamond grown by DC arc plasma jet CVD a promising material for applications in quantum computing.

Nitrogen in diamond films grown by direct current arcjet plasma process using gas recycling

The nitrogen in polycrystalline diamond films prepared using the direct current arcjet plasma process has been studied using scanning electron microscopy, X-ray diffraction and electron spin resonance (ESR). The ESR spectrum of single substitutional nitrogen was observed, whose intensity showed that the spin concentration decreases with an increase in the substrate temperature. The preferentially orientated growth is influenced by nitrogen. The result indicates that nitrogen plays a special role in the formation and structure of the polycrystalline diamond films studied in this report.