First-principles studies of the vibrational properties of amorphous carbon nitrides

Raman spectra of amorphous carbon nitride films (a-C:N) resemble those of typical amorphous carbon (a-C), and no specific features in the spectra are shown due to N doping. The present work provides a correlation between the microstructure and vibrational properties of a-C:N films from first principles. The six periodic model structures of 64 atoms with various mass densities and nitrogen contents are generated by the liquid-quench method using Car-Parinello molecular dynamics. By using Raman coupling tensors calculated with the finite electric field method, Raman spectra are obtained. The calculated results show that the vibrations of C=N could directly contribute to the Raman spectrum. The similarity of the Raman line shapes of N-doped and N-free amorphous carbons is due to the overlapping of C=N and C=C vibration bands. In addition, the origin of characteristic Raman peaks is also given.     

非晶碳氮纳米尖端的微结构和发光机理

利用等离子体增强热丝化学气相沉积系统,用CH₄、H₂和N₂为反应气体,在Si衬底上制备了碳氮纳米尖端。用扫描电子显微镜和显微Raman光谱仪对其进行了表征。在室温下测试了它的发光性能,发光谱由中心约为406 nm和506 nm的两条发光带组成。根据Raman散射谱,对其微结构进行了分析。结合非晶碳氮薄膜的结构和发光机理,分析了它的发光性能。     

Ripple surface generated on hydrogenated amorphous carbon nitride films

It is reported for the first time that the periodical ripple surface feature at micrometer-scale was observed on hydrogenated amorphous carbon nitride films deposited by pulse plasma chemical vapor deposition (CVD) technique. Nitrogen incorporation to hydrogenated amorphous carbon films and the different growing environments of pulse dc plasma discharge perhaps played crucial role in the surface morphology transformation of hydrogenated amorphous carbon nitride films.     

Amorphous BeN as a new solid host for rare‐earth‐related luminescent materials

Beryllium‐nitride (BeN) thin films were prepared by sputtering a Be target in an atmosphere of pure nitrogen. The films were doped with samarium simply by placing a piece of Sm metal on the surface of the Be target. Under these deposition conditions the films present an amorphous structure and an optical bandgap of approx. 4 eV. They also exhibit visible light emission due to Sm³⁺ ions as a result of either photon or electron excitation. The present experimental results show that amorphous BeN films are suitable, and efficient, III‐nitride hosts for rare‐earth doping purposes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Further investigation on the formation mechanisms of (NH4)2SiF6 synthesized by dry etching technique

The validity of two formation mechanisms of ammonium silicofluoride (ASF), which are proposed to take place when a silicon surface is exposed to the vapor of HNO₃/HF acid mixture is investigated. Of the two proposed mechanisms regarding the synthesis of ASF on silicon surface, validity of the first predicting the release of hydrofluosilicic acid (H₂SiF₆) at the intermediate stage is examined by FTIR spectroscopy and the second mechanism suggesting O₂ release is investigated using the Winkler technique. IR absorbance bands of SiF₆²⁺ are observed on the fresh samples prepared at low (1/100) HNO₃/HF volume fractions. No significant amount of oxygen is detected during the synthesis of ASF films on silicon surface by dry etching technique. These two observations together provide firmer support for the validity of the second mechanism.     

Adjusting chemical bonding of hard amorphous CSixNy thin films by N*-plasma-assisted pulsed laser deposition

Hard amorphous carbon silicon nitride thin films have been grown by pulsed laser deposition (PLD) of various carbon silicon nitride targets by using an additional nitrogen RF plasma source on [100] oriented silicon substrates at room temperature. The influence of the number of laser shots per target site on the growth rate and film surface morphology was studied. Up to about 30 at. % nitrogen and up to 20 at. % silicon were found in the films by Rutherford backscattering spectroscopy (RBS) and X-ray photoelectron spectroscopy (XPS). The XPS of the films showed a clear correlation of binding energy to the variation of PLD parameters. The films show a universal hardness value up to 23 GPa (reference value for silicon substrate 14 GPa) in dependence on target composition and PLD parameters. The results emphasise the possibility of variation of chemical bonding and corresponding properties, such as nanohardness, of amorphous CSi_xN_y thin films by the plasma-assisted PLD process.     

Carbon nitride films synthesized by nitrogen ion beam bombarding on C60 films

\valunit*{400}{\eV} or ) nitrogen ion beam was used to bombard films to synthesize carbon nitride films. The bombarded films were examined by Raman and X-ray photoelectron spectroscopy (XPS) measurements. The experimental results showed that the destroyed carbon species chemically combined with nitrogen ions to form stable carbon nitride. An appropriate beam energy (possibly ) was proposed in this method. Received: 1 July 1996/Accepted: 27 November 1996     

钼掺杂氧化锌薄膜的结构、光学和表面等离子体特性研究

室温下,通过直流磁控反应溅射在石英衬底上制备一系列钼掺杂氧化锌薄膜。分别采用X射线衍射(XRD)、原子力显微镜(AFM)、分光光度计及拉曼光谱仪研究了钼掺杂浓度对氧化锌薄膜结构、表面形貌、光学性能和表面等离子体特性的影响。XRD测试结果表明,零掺杂氧化锌薄膜结晶良好,呈c轴择优取向,掺杂后薄膜缺陷增多,结晶质量下降,当掺杂浓度达到3.93 Wt%时,薄膜由c轴择优取向的晶态转变为非晶态。AFM测试结果表明非晶态掺钼氧化锌薄膜表面光滑,粗糙度最低可达489 pm。透射光谱表明所有薄膜样品在可见光范围(400～760 nm)平均透过率均达到80%,禁带宽度随着掺杂浓度的提高从3.28 eV单调增加至3.60 eV。吸收光谱表明氧化锌薄膜表面等离子体共振吸收峰随钼掺杂量的增大发生蓝移,而拉曼光谱表明Mo重掺杂时ZnO薄膜表面拉曼散射信号强度显著降低。通过Mo掺杂获得非晶态氧化锌薄膜,拓宽了氧化锌薄膜材料的应用领域,同时研究了Mo掺杂浓度对氧化锌薄膜表面等离子体的调控作用,这对制备氧化锌基光子器件具有重要参考价值。     

Effect of air post contamination on mechanical properties of amorphous carbon nitride thin films

We report in this study the mechanical, structural and compositional characteristics of amorphous carbon nitride films (a-CN_x) deposited on Si(100) using RF magnetron sputtering of graphite targets in pure nitrogen and under different RF powers. The properties of the films were determined in their as deposited state using nuclear reaction analysis (NRA), elastic recoil detection (ERDA), infrared (IR) absorption and Raman spectroscopy. The mechanical properties were obtained combining nanoindentation and residual stress measurements. The presence of various types of C-N bonds, as well as the post-deposition contamination of the deposited films by oxygen and water (voids) is revealed. The measured hardness and Young modulus were 0.9-2.03 and 23-27 GPa, respectively. These results have been analysed in term of the matrix flexibility which results from the nitrogen content and the porous character of the films, which can affect deeply the estimation of the physical-mechanical properties of the films.     

Structure and mechanical properties of titanium nitride/carbon nitride multilayers

The structure and mechanical properties of the multilayers consisting of 5-73 nm thick titanium nitride (TiN) and 4.6 nm thick carbon nitride (CN) have been investigated. It has been found that the CN layers are amorphous and the TiN layers thinner than 17 nm are amorphous. The TiN layers become crystallized as the thickness is increased to 30 nm or thicker. The hardness from the composite response of the multilayered films and their substrates determined using continuous stiff measurement is smaller than the film-only hardness (without substrate effects) calculated using Bhattacharya-Nix empirical equation. The hardness increases with raising the thickness of TiN layers. With the crystallization of the TiN layer, the multilayers become even harder than that calculated based on the rule of mixtures. However, no enhancement in hardness has been observed when the TiN layers are amorphous.     

Preparation and Thermal Characterization of Diamond-Like Carbon Films

Diamond-like carbon （DLC） films are prepared on silicon substrates by microwave electron cyclotron resonance plasma enhanced chemical vapor deposition. Raman spectroscopy indicates that the films have an amorphous structure and typical characteristics. The topographies of the films are presented by AFM images. Effective thermal conductivities of the films are measured using a nanosecond pulsed photothermal reflectance method. The results show that thermal conductivity is dominated by the microstructure of the films.     

Dependence of Optical Absorption in Silicon Nanostructures on Size of Silicon Nanoparticles

The amorphous silicon nanoparticles (Si NPs) embedded in silicon nitride (SiN_x) films prepared by helicon wave plasma-enhanced chemical vapor deposition (HWP-CVD) technique are studied. From Raman scattering investigation, we determine that the deposited film has the structure of silicon nanocrystals embedded in silicon nitride (nc-Si/SiNx) thin film at a certain hydrogen dilution amount. The analysis of optical absorption spectra implies that the Si NPs is affected by quantum size effects and has the nature of an indirect-band-gap semiconductor. Further, considering the effects of the mean Si NP size and their dispersion on oscillator strength, and quantum-confinement, we obtain an analytical expression for the spectral absorbance of ensemble samples. Gaussian as well as lognormal size-distributions of the Si NPs are considered for optical absorption coefficient calculations. The influence of the particlesize-distribution on the optical absorption spectra was systematically studied. We present the fitting of the optical absorption experimental data with our model and discuss the results.     

Preparation of boron carbon nitride thin films by radio frequency magnetron sputtering

Boron carbon nitride films were deposited by radio frequency magnetron sputtering using a composite target consisting of h-BN and graphite in an Ar-N₂ gas mixture. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results suggest that the films are atomic-level hybrids composed of B, C and N atoms. The boron carbon nitride films prepared in the present experiment have a disordered structure. The sputtering power varied from 80 W to 130 W. This sputtering power was shown to have regular effect on the composition of boron carbon nitride films. The samples deposited at 80 W and 130 W are close to the stoichiometry of BC₃N. The sample deposited at 110 W is close to the stoichiometry of BCN. The samples deposited at 100 W and 120 W approach to BC₂N. It is very significant for us to synthesize boron carbon nitride compound with controllable composition by changing the sputtering power.     

57Fe Mössbauer study of Fe/Bi multilayers

Fe/Bi artificially structured films (ASF's) have been prepared by alternate depositions of Fe and Bi in an ultrahigh vacuum. X-ray diffraction measurements in the small angle range confirmed the formation of periodic structures in all the samples prepared on glass substrates cooled down to about 125K. the CEMS at room temperature indicated that the samples are ferromagnetic except the one with 2Å-thick Fe layers. The CEM spectra also indicated that the structure of Fe layers is amorphous when the Fe layer thicknesses are less than 15Å. Magnetization measurement and CEM spectrum at 6K show that Fe monolayers in the Fe/Bi ASF are ferromagnetic.     

Strong Green Light Emission from Low-Temperature Grown a-SiNx:H Film after Different Oxidation Routes

Room-temperature deposited amorphous silicon nitride （a-SiNx ：H） films exhibit intense green light emission after post-treated by plasma oxidation, thermal oxidation and natural oxidation, respectively. All the photoluminescence （PL） spectra are peaked at around 500nm, independent of oxidation method and excitation wavelength. Compared with the PL results from oxidized a-Si：H and as-deposited a-SiNx：H samples, it is indicated that not only oxygen but also nitrogen is of an important role in enhancing light emission from the oxidized a-SiNx：H. Combining the PL results with the analyses of the bonding configurations as well as chemical compositions of the films, the strong green light emission is suggested to be from radiative recombination in luminescent centres related to N Si-O bonds.     

Raman characteristics of carbon nitride synthesized by nitrogen-ion-beam-assisted pulsed laser deposition

Raman characteristics of carbon nitride films synthesized by nitrogen-ion-beam-assisted pulsed laser deposition were investigated. In addition to the D (disorder) band and G (graphitic) band commonly observed in carbon nitride films, two Raman bands located at 1080–1100 and 1465–1480 cm^-1 were found from our carbon nitride films. These two bands were well matched with the predicted Raman frequencies for βC₃N₄ and the observed Raman bands reported for carbon nitride films, indicating their relation to carbon-nitrogen stretching vibrations. Furthermore, the relative intensity ratio of the two Raman bands to the D and G bands increased linearly with increasing nitrogen content of the carbon nitride films. Received: 30 October 2000 / Accepted: 5 February 2001 / Published online: 2 October 2001     

辉光放电等离子体辅助XeCl准分子激光溅射沉积碳氮薄膜

利用直流辉光放电等离子体辅助的脉冲激光沉积技术在Si衬底上生长了碳氮薄膜.通过扫描电子显微镜、X射线衍射、X射线光电子能谱、俄歇电子能谱等多种手段,对薄膜的形貌、成分、晶体结构、价键状态等特性进行了分析和确定.结果表明,沉积薄膜为含有非晶SiN和晶态氮化碳颗粒结构,晶态成分呈多晶态,主要为α-C₃N₄相、β-C₃N₄相,晶粒大小为40—60nm.碳氮之间主要以C-N非极性共价键形式相结合. 关键词： 脉冲激光沉积 直流辉光放电 碳氮薄膜     

Effects of experimental parameters on composition of boron carbon nitride thin films deposited by magnetron sputtering

We have synthesized boron carbon nitride thin films by radio frequency magnetron sputtering. The films structure and composition were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results indicate that the three elements of B, C, N are chemically bonded with each other and atomic-level hybrids have been formed in the films. The boron carbon nitride films prepared in the present experiment possess a disordered structure. The influence of PN₂/PN₂+Ar, total pressure and substrate bias voltage on the composition of boron carbon nitride films is investigated. The atomic fraction of C atoms increases and the fractions of B, N decrease with the decrease of PN₂/PN₂+Ar from 75% to 0%. There is an optimum total pressure. That is to say, the atomic fractions of B, N reach a maximum and the fraction of C atoms reaches a minimum at the total pressure of 1.3 Pa. The boron carbon nitride films exhibit lower C content and higher B, N contents at lower bias voltages. And the boron carbon nitride films show higher C content and lower B, N contents at higher bias voltages.     

Core-level and valence-band characteristics of carbon nitride films with high nitrogen content

Carbon nitride films with high nitrogen content were prepared by reactive pulsed-laser deposition at nitrogen partial pressures varying from 0.1 to 20.0 Torr. It was found that the nitrogen content in the films first increases with increase of the nitrogen pressure, reaches a maximum of 46 at. % at 5.0 Torr, and then decreases to 37 at. % at 20.0 Torr. The almost pure carbon nitride films were systematically characterized by using X-ray photoelectron spectroscopy (XPS) concerning the core-level and valence-band structures. Some fingerprint information, which shows the role of nitrogen in controlling the electronic structure of carbon nitride films, was found based on the XPS studies. With enhancing the nitrogen incorporation, both the binding energy and the peak intensity of the core-level and the valence-band spectra vary systematically as a function of nitrogen content in the films. Received: 26 June 2000 / Accepted: 26 June 2000 / Published online: 20 September 2000     

Incorporation of nitrogen into amorphous-hydrogenated carbon (diamond-like) films

Nitrogen-doped amorphous hydrogenated carbon films (a-C:H) were prepared by mixing nitrogen gas and benzene during dc plasma discharge deposition. The growth rate of the film decreases strongly with increasing nitrogen content in the mixture. The nitrogen concentration in the films was determined by nuclear reaction analysis (NRA) and Auger electron spectroscopy (AES) using suitable calibration samples. The results of AES measurements are generally consistent with NRA values. Nitrogen incorporation in the a-C:H films shows pronounced doping effects as reflected in their optical and electrical properties.Dedicated to Professor J. P. F. Sellschop for his 60^th birthday