Optical Properties Of Diamond Films Research Articles

Reaction Gas Ratio Effect on the Growth of a Diamond Film Using Microwave Plasma-Enhanced Chemical Vapor Deposition.

In this study, diamond films were prepared using the microwave plasma-enhanced chemical vapor deposition (PECVD) system, which included a DC bias system to enhance the nucleation of the films. The films were synthesized on Si wafers with different ratios of methane (CH4) and hydrogen (H2) gases. We have studied the effects of the CH4-to-H2 ratio on the structural and optical properties of diamond films. The thickness and surface profile of the films were characterized via field emission scanning electron microscopy (FE-SEM). Raman was used to investigate the structural properties of the diamond films. The refractive indexes as functions of the CH4-to-H2 ratio were measured using an ellipsometer. The FE-SEM analysis showed that the 3 and 5 sccm CH4 created diamond films. The Raman analysis indicated that a nanocrystalline diamond film was formed at 3 sccm; a general diamond film, at 5 sccm; and films similar to the a-C:H film, at 7 sccm. The ellipsometer measurement showed that the refractive index of the synthesized diamond film was around 2.42 at 3 sccm. This value decreased as the CH4 volume increased.

Spectroellipsometric and ion beam analytical investigation of nanocrystalline diamond layers

Optical properties of nanocrystalline and ultrananocrystalline diamond films were studied by ex situ variable angle spectroscopic ellipsometry. The films were prepared by Microwave Plasma Enhanced Chemical Vapor Deposition method. In the experiments Ar, CH4, and H2 gases were used as source gases. Elastic recoil detection analysis was applied to measure the hydrogen content of the deposited layers. Three-layer optical models were constructed for the evaluation of the measured ellipsometric spectra. Besides the Cauchy relation, the effective medium approximation and the Tauc–Lorentz dispersion relation were also used for the modeling of the optical properties of the diamond films. Atomic force microscopy was applied to investigate the surface roughness in function of the deposition conditions.

Effect of nanostructured AlN coatings on the oxidation-resistant properties of optical diamond films

Diamond film is an ultra-durable optical material with high thermal conductivity and good transmission in near-infrared and far-IR (8–14μm) wavebands. CVD diamond is subjected to oxidation at temperature higher than 780°C bared in air for 3min, while it can be protected from oxidation for extended exposure in air at temperature up to 900°C by a coating of aluminum nitride. Highly oriented AlN coatings were prepared for infrared windows on diamond films by reactive sputtering method and the average surface roughness (Ra) of the coatings was about 10nm. The deposited films were characterized by X-ray diffraction (XRD) and atom force microscope (AFM). XRD confirmed the preferential orientation nature and AFM showed nanostructures. Optical properties of diamond films coated AlN thin film was investigated using infrared spectrum (IR) compared with that for as-grown diamond films.

Effects of activated hydrogen etching on surface roughness and optical properties of diamond films

Abstract The surface roughness and optical properties of diamond films untreated and treated by activated hydrogen have been investigated. After hydrogen ion treatment the surface of the film is modified effectively. Optical properties of the treated film are better than those of the untreated one.

Effects of deposition conditions on infrared spectroscopic ellipsometry of CVD diamond films

Diamond films deposited by hot filament chemical vapor deposition (HFCVD) under different deposition conditions are characterized using spectroscopic ellipsometric measurements in infrared region of 2.5—12.5 μm. Effects of deposition conditions on infrared spectroscopic ellipsometry of diamond films are investigated. The optical properties of diamond films depend strongls on its quality. The refractive index increases and the extinction coefficient decreases monotonicly with increasing sp3 C content. High quality optical diamond films are obtained under reactor pressure of 4.0 kPa when substrate temperature and carbon concentration are 750℃ and 0.9%, respectively. Refractive index and extinction coefficient of diamond film of high transparency are 2.385 and of the order of 10-4, respectively.

Optical properties of diamond films deposited by low temperature microwave plasma CVD from camphor

Diamond films were deposited on quartz and Si substrates at a relatively low substrate temperature (∼623 K) by microwave plasma CVD technique using camphor as the precursor. The films were characterized by optical and microstructural (SEM) studies. The film quality was found to be dependent on the sp 3/sp 2 ratio. FTIR studies revealed the ratio of sp 3/sp 2 to vary within 1.7–5.67.

Fitting models of IRSE data for diamond films on silicon grown by MPCVD method

The infrared optical properties of diamond films on silicon substrates, grown by means of microwave plasma CVD method, are studied by infrared spectroscopic ellipsometry in the spectral range of 2.5–12.5μm. It has been found that the establishment of appropriate models has the strongest influence on the fit of ellipsometric spectra. The best fit is achieved for a diamond film with a 77.5nm middle layer of SiO2 included by Bruggeman EMA. Finally, the refractive index (n) and the extinctive coefficient (k) are calculated for the diamond films.

Spectroscopic ellipsometric study of CVD diamond films: modelling and optical properties in the energy range of 0.1–0.4 eV

In this paper, the infrared optical properties of diamond films on silicon substrates grown by means of hot filament chemical vapour deposition (HFCVD) and microwave plasma chemical vapour deposition (MPCVD) method, are studied by infrared spectroscopic ellipsometry (IRSE) in the energy range of 0.1–0.4 eV. The establishment of appropriate models has the strongest influence on the fit of ellipsometric spectra. For diamond films grown by HFCVD method, the best fitting model is Si|diamond| (diamond + void)| air with an 879 nm rough surface layer included by Bruggeman EMA, but for MPCVD film with a 77.5 nm middle layer of SiO2. The average refractive index n of the HFCVD film is about 2.19 and the extinction coefficients k are between 1.0 and 10−3. However, for the MPCVD film, the value of n is very close to that of natural diamond and the k values are about 10−12–10−15, which show that the film grown by MPCVD is transparent in infrared region, and is optically much better than the HFCVD film.

Study on optical properties of diamond films by means of infrared spectroscopic ellipsometry

We have made spectroscopic ellipsometric measurement to characterize the structure of diamond films in infrared region (2.5—12.5μm). These films are grown respectively by microwave plasma chemical vapor deposition (MPCVD) and hot filament chemical vapor deposition (HFCVD). It is found that the establishment of appropriate models has the strongest influence on the fit of ellipsometric spectra. The best fit is achieved for MPCVD film with a 77.5nm middle layer of SiO2, and for HFCVD film with a 879nm rough surface layer included by Bruggeman effective medium approximation. Finally, the refractive index (n) and the extinctive coefficient (k) are calculated for both films, which show that the film grown by MPCVD is optically better than by HFCVD apparently.

Infrared optical properties of diamond films and electrical properties of CVD diamond detectors

In this paper, the infrared optical properties of diamond films grown on silicon substrates by means of the microwave plasma chemical vapour deposition (MPCVD) method were first studied by infrared spectroscopic ellipsometry in the photo energy range of 0.1–0.4 eV. Using the effects of annealing treatment on the extinction coefficient k and refractive index n of diamond films, the infrared optical quality of the diamond film can be significantly improved by thermal annealing treatment in N2 atmosphere. After annealing the value of k was about 10−12–10−15. However, for the non-annealed diamond film, the value of k varied in a large range, about 10−3–10−14. After annealing the refractive index n of the diamond film increased and was close to that of a single crystal, Type IIa natural diamond. The graphite on the diamond surface can be removed to some extent after surface oxidizing treatment of the diamond film in a solution of H2O2 and H2SO4, which causes the obvious decrease of the leakage current of the CVD diamond detector. Based on these diamond films, diamond x-ray detectors with a response time of about 3 ns were fabricated. From the temperature behaviour and the time response of the CVD diamond detector to x-ray irradiation, we find that the various defects or impurities that exist in the film may be responsible for the long fall time.

Laser method for the determination of the optical and thermal characteristics of diamond at high temperatures

The temporal and temperature dependences of the reflectivity, transmissivity, and absorptivity and of the heat capacity of thermally thin diamond plates were obtained in the course of heating up to 2500 °C at a rate of 103 — 104 K s-1 by laser radiation with λ = 1.064 μm. The temperature range in which significant irreversible changes take place in the optical properties of diamond films was determined. These changes are associated with the formation of graphite microstructures in a thin surface layer about 100 nm thick. The formation of clusters of aromatic carbon atom groups with the sp2 bonds is described. It is shown that the extinction coefficient of the modified layer is three orders of magnitude higher than that of the unmodified layer.

The origin of the broadband luminescence and the effect of nitrogen doping on the optical properties of diamond films

Raman and various photoluminescence (PL) techniques were employed to investigate the role of nitrogen doping on the optical spectra of chemical-vapor-deposited (CVD) diamond films and to determine the origin of the characteristic broadband luminescence which is observed from approximately 1.5 to 2.5 eV and centered at ∼2 eV. The PL transitions attributed to the zero-phonon lines (ZPL) of nitrogen centers are observed at 1.945 and 2.154 eV. A new possible nitrogen center at 1.967 eV is also observed as well as the band A luminescence centered at ∼2.46 eV. The experimental results preclude the possibility of the broadband PL being due to electron-lattice interaction of the nitrogen ZPL centers. We establish the presence of an in-gap state distribution in CVD diamond films attributed to the sp2 disordered phase and show that its optical transitions are the likely cause of the broadband luminescence. A model of the in-gap state distribution is presented which is similar to models previously developed for amorphous materials.

マイクロ波プラズマＣＶＤ法により作製したダイヤモンド膜の光学特性

Natural II a-type diamond has a high optical transmission ratio from ultraviolet (225nm) to infrared (13μm), and a study on the optical properties of diamond films synthesized by microwave plasma CVD was accordingly carried out with a view to applying the synthesized diamond films in optical parts.Diamond films were synthesized from CH4-H2 and CO-H2 reaction gas systems on quartz substrates. Film thickness was a uniform 1μm.Raman spectroscopy showed that carbon source concentrations that did not contain non-diamond elements (amorphous carbon etc.) in the films was higher for the CO-H2 system than for the CH4-H2 system. This was because the etching rate of oxygen to carbon is higher than that of hydrogen.In terms of optical properties, the transmission ratio of diamond films containing minute amount of non-diamond elements was about 50%, and was uniform from 240nm to 2600nm. But as the amount of non-diamond elements increased, the transmission ratio at 250nm and 500nm decreased.The transmission ratio of the diamond films in the ultraviolet and visible ranges depended on the quantity of non-diamond elements in the films.

Infrared optical properties of CVD diamond films

Diamond films of 15–20 μm thicknesses were prepared by microwave plasma enhanced chemical vapor deposition onto crystalline silicon substrates. The growth surfaces of the films were rough with polycrystalline crystallographic habits, while the substrate sides of these films were smooth and featureless as viewed by optical microscopy. A heated cast iron scaife was used to polish the rough growth surfaces, and free-standing films were removed from the silicon substrates by dissolving the silicon in an aqueous HF. Both infrared optical transmission and reflection spectra were measured over the range of 600–4000 cm−1. For polished films, near 70% transmittance was obtained over the whole range, while the transmittance for nonpolished films was much lower and varied strongly with the wave number. Absorptions due to carbon-hydrogen stretching bands as well as a silicon carbide phase were observed in the transmission spectra. The optical absorption coefficient and the refractive index were found to vary from as high as 150 to as low as 7 cm−1 and 2.41 to 2.49, respectively (depending on the film quality and the wave number). A weak signature of the two-phonon absorption band of diamond was observed. The relationship between deposition conditions and infrared optical properties of diamond films before as well as after polishing is discussed.