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     

Characterization of doped diamond-like carbon films deposited by hot wire plasma sputtering of graphite

Diamond-like carbon (DLC) films doped with nitrogen and oxygen were deposited on silicon(100) and polytetrafluoroethylene (PTFE) substrates by hot wire plasma sputtering of graphite. The morphology and chemical composition of deposited films has been characterized by scanning electron microscopy, XPS, Auger, FTIR spectroscopy and micro-Raman scattering. Plasmon loss structure accompanying the XPS C 1s peak and electron energy loss spectroscopy (EELS) in reflection mode was used to study the fraction of sp³ bonded C atoms and the density of valence electrons. Raman spectra show two basic C–C bands around 1575 cm^-1 (G line) and 1360 cm^-1 (D line) . Auger depth profiling spectroscopy was used to measure the spatial distributions of C, N and O atoms in the surface layer of DLC films. The fraction of sp³ bonded atoms of about 40% was detected in DLC films by XPS plasmon loss and EELS techniques. Nitrile and iso-nitrile groups observed in FTIR spectra demonstrated the existence of sp bonded carbon in doped DLC films. The typical for DLC films specific density 1.7–1.8 g/cm³ was obtained from EELS and XPS data. PACS 52.77.Dq; 81.65.-b; 82.80.Pv     

Nitrogen 1s electron binding energy assignment in carbon nitride thin films with different structures

Carbon nitride thin films deposited by dc unbalanced magnetron sputtering have been analyzed by high-resolution X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The XPS data show that N 1s binding states depend on substrate temperature (T_s). By comparison with the Raman spectra, N 1s binding states are assigned in which nitrogen atoms are mainly bound to sp² and sp³ carbon atoms at T_s = 100°C, whereas at T_s = 500°C nitrogen atoms are mainly bonded to sp², sp³ and sp¹ carbon atoms.     

Nitrogen incorporation in amorphous SiCN layers prepared from electron cyclotron resonance plasmas

Electron cyclotron resonance plasma chemical vapor deposition with nitrogen, methane, and argon-diluted silane as precursors has been used to prepare SiCN thin films. Optical emission from CN species in the plasma has been observed. Infrared measurements show that most of the nitrogen is incorporated to the thin solid films in the form of Si-N, C=N and C≡N bonds suggesting a basic structure of incomplete SiN tetrahedra with C=N and C≡N bridging bonds. The deposited films are nearly transparent in the visible range with a weak absorption threshold between 2.2 and 3.5 eV. Received: 3 April 1998 / Accepted: 5 January 1999 / Published online: 31 March 1999     

Annealing effects on the microstructure of amorphous carbon nitride films

Amorphous carbon nitride films, prepared using a dc facing-target reactive sputtering system, were annealed at temperatures up to 650 °C for 1 h in vacuum. The effects of heat treatment on the films, i.e. changes in the composition and structure, were investigated. It was found that annealing at temperatures ranging from 300 to 650 °C, results in the N content decreasing from ∼33 at.% in the as-deposited films to ∼5 at.%. The loss of N, especially those bonded to sp³C, causes the rearrangement of the film's microstructure, and the dual effects of the thermal annealing are quite noticeable: (1) annealing destroys most graphite-like structures, and more non-aromatic sp²C components and C≡N terminal structures are formed at higher annealing temperatures, contributing to a looser film's structure. (2) Annealing makes the remaining aromatic sp²C structure become more order. The results also reveal that N atoms bonded to sp³C are easily removed with the increasing temperature compared to those bonded to sp²C, which indicates that Nsp²C bonds had a higher thermal stability than Nsp³C.     

Molecular mechanism of gelation with ethylene glycol added to a solution of polyacrylonitrile in dimethylsulfoxide

The mechanism of solidifying a solution of polyacrylonitrile (PAN) in dimethylsulfoxide (DMSO) into which ethylene glycol is added is studied by the method of Raman spectroscopy. In the absence of ethylene glycol, DMSO molecules produce dipole-dipole bonds to PAN molecules. Upon adding ethylene glycol, DMSO molecules form hydrogen bonds with it and a line at 1000 cm⁻¹ appears in the Raman spectrum, which is assigned to the valence vibrations of S=O bonds involved in the hydrogen bonds. After DMSO is removed, ethylene glycol molecules produce hydrogen bonds with two neighboring PAN molecules, giving rise to a band at 2264 cm⁻¹, which is assigned to the valence vibrations of C≡N bonds involved in these hydrogen bonds. A high-viscosity gel consisting of PAN molecules arises in which these molecules are bonded to each other through ethylene glycol molecules.     

Formation of CNx thin films by reactive pulsed laser deposition assisted by electron cyclotron resonance microwave discharge

Amorphous carbon nitride thin films were synthesized by pulsed laser deposition combined with electron cyclotron resonance (ECR) microwave discharge in nitrogen gas. The ECR discharge supplies active nitrogen species in the deposition environment and to the growing film surface, enhancing the film growth in complex processes accompanied by chemical reaction. The synthesized films were characterized by Rutherford backscattering spectroscopy (RBS), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy. The films were determined to consist purely of carbon and nitrogen with a nitrogen concentration of 42%, and have a thickness of 550 nm over which carbon and nitrogen are well distributed. Structural characterizations based on XPS, FTIR and Raman analysis showed that these films appear to contain several bonding configurations between carbon and nitrogen with a small amount of C≡N bonds compared with other bonding states. Received: 31 August 2000 / Accepted: 12 December 2000 / Published online: 23 May 2001     

Correlation between photoluminescence, optical and structural properties of amorphous nitrogen-rich carbon nitride films

Amorphous nitrogen-rich carbon nitride (CN_x) films have been prepared by inductively coupled plasma chemical vapour deposition (ICP-CVD) utilizing transport reactions from a solid carbon source. The nitrogen atomic fraction N/(C+N) is about 1 or even higher as detected by various surface and bulk sensitive methods. An investigation of the chemical bonding structure showed that the films are composed of >C=N units with a small fraction of C≡N groups. Based on these findings, several structural units derived from cis- and trans-conjugated carbon–nitrogen chains are proposed. The optical properties of the CN_x films were studied by transmission spectroscopy and spectral ellipsometry; the optical Tauc gap was determined to 2.1±0.05 eV. The photoluminescence characteristics were measured at three different excitation wavelengths (476, 488 and 515 nm) and revealed two individual contributions. These data are interpreted in terms of the different structural units comprising the nitrogen-rich CN_x films. Received: 14 July 2000 / Accepted:17 July 2000 / Published online: 22 November 2000     

XPS study of the chemical bonding in hydrogenated amorphous germanium–carbon alloys

A systematic study of the chemical bonding in hydrogenated amorphous germanium–carbon (a-Ge_1-xC_x:H)alloys using X-ray photoelectron spectroscopy (XPS) is presented. The films, with carbon content ranging from 0 at. % to 100 at. %, were prepared by the rf co-sputtering technique. Raman spectroscopy was used to investigate the carbon hybridization. Rutherford backscattering spectroscopy (RBS) and XPS were used to determine the film stoichiometry. The Ge 3d and C 1s core levels were used for investigating the bonding properties of germanium and carbon atoms, respectively. The relative concentrations of C–Ge, C–C, and C–H bonds were calculated using the intensities of the chemically shifted C 1s components. It was observed that the carbon atoms enter the germanium network with different hybridization, which depends on the carbon concentration. For concentrations lower than 20 at. %, the carbon atoms are preferentially sp³ hybridized, and approximately randomly distributed. As the carbon content increases the concentration of sp² sites also increases and the films are more graphitic-like. Received: 4 May 1999 / Accepted: 24 November 1999 / Published online: 24 March 2000     

Properties of diamondlike films obtained in a barrier discharge at atmospheric pressure

Diamondlike films are synthesized from gaseous hydrocarbons in a barrier discharge at atmospheric pressure. The films were investigated using transmission electron microscopy, electron diffraction, and infrared spectroscopy. A technique for determining the quantitative characteristics of the films (hydrogen content, ratio of different types of carbon-carbon bonds and hydrocarbon groups) using standard samples is described. The highest-quality films were obtained from methane (ratio of hydrogen to carbon atoms H/C=1.04, fraction of diamondlike to graphitelike bonds sp ³: sp ²=100%: 0%) and from a mixture of acetylene and hydrogen in the ratio 1:19 (H/C=0.73, sp ³: sp ²=68%: 32%). Zh. Tekh. Fiz. 67, 100–104 (August 1997)     

Molecular mechanism of gelation upon the addition of water to a solution of poly(acrylonitrile) in dimethylsulfoxide

The solidification of a solution of poly(acrylonitrile) (PAN) in dimethylsulfoxide (DMSO) upon introduction of water into the solution is studied by Raman spectroscopy. In the absence of water, DMSO molecules are found to produce dipole-dipole bonds with PAN molecules. Upon the introduction of water, DMSO molecules produce hydrogen bonds with it and bands at 1005 and 1015 cm⁻¹ appear in the Raman spectrum, which are assigned to the valence vibrations of S=O bonds involved in the hydrogen bonds. Simultaneously, water molecules produce hydrogen bonds with PAN molecules: R-C≡N...H-O-H...N≡C-R, where R is the carbon skeleton of a PAN molecule. Accordingly, a band at 2250 cm⁻¹ arises in the Raman spectrum, which is assigned to the valence vibrations of C≡N bonds producing hydrogen bonds with a water molecule. When the water content is low and the DMSO concentration is high, the length of the hydrogen bonds varies in wide limits and the band at 2250 cm⁻¹ is wide. As the water content rises, DMSO molecules come out of PAN, the variation of the hydrogen bond length in it decreases (the band at 2250 cm⁻¹ narrows), and a high-viscosity system (gel) arises that consists of PAN molecules bonded to water molecules via “equally strong” hydrogen bonds.     

Formation of carbon nitride compounds during successive implantations in copper

Copper substrates are successively implanted with carbon and nitrogen (¹³C⁺ and ¹⁴N⁺) at high fluences (5 × 10¹⁷ and 1 × 10¹⁷ at. cm⁻², respectively) in order to synthesize specific carbon nitride compounds. The concentration as well as the depth distribution of carbon ¹³C and nitrogen ¹⁴N are determined using non resonant nuclear reactions induced by a 1.05 MeV deuteron beam. The use of (d,p) and (d,α) reactions allows us to profile both ¹³C and ¹⁴N elements with a single and relatively rapid measurement and a quite good resolution. The bonded states of carbon and nitrogen are studied as a function of depth by X-ray photoelectron spectroscopy (XPS). The curve fitting of the C 1s and N 1s photopeaks shows that carbon and nitrogen atoms exist in different chemical states depending on the analysis depth, which correspond to specific kinds of chemical bonds. At least two characteristic C–N bonds are detected indicating that different carbon nitride compounds have been formed during the implantations.     

Pulsed laser deposition of amorphous carbon nitride thin films and their electrical properties

Amorphous carbon nitride thin films were deposited by pulsed laser deposition combined with a nitrogen rf radical beam source. A structural characterization of the deposited films was performed using X-ray photoelectron and Raman-scattering spectroscopy. The Raman spectra showed that the dominant hybridization state of carbon atoms in the deposited film is sp². N 1s electron spectra were deconvoluted into three components, N bonded to pyridine-like N and/or N-sp³C (N1), substitutional N in graphite (N2), and N-O and/or N-N (N3). The proportion of N1 increased with increasing N/C atomic ratio in the film. The electrical conductivity at room temperature decreased and the Tauc optical band gap increased with increasing N/C atomic ratio. The temperature dependence of the electrical conductivity indicated that electronic conduction occurred by variable range hopping between electron localized states. The decrease in electrical conductivity with increasing N/C atomic ratio was caused by a strong electron localization due to the increased proportion of N1. PACS 81.05.Uw; 81-15.Fg; 73.61.Jc     

In-depth modifications of implanted amorphous carbon films

Amorphous carbon films (a-C:H) and nitrogen incorporated carbon films [a-C:H(N)] deposited by a self-bias glow discharge have been implanted with 70 keV nitrogen ions at fluences of 0.6, 1 and 2×10¹⁷ N/cm². The in-depth modifications caused by ion implantation were determined by means of nuclear techniques, such as Rutherford Backscattering Spectrometry (RBS), Nuclear Reaction Analysis (NRA) and Elastic Recoil Detection Analysis (ERDA), as well as by Auger Electron Spectroscopy (AES) and Raman scattering. ERDA profiles show that nitrogen implantation causes hydrogen depletion, the amount of which depends on the film composition and on the ion fluence. In a-C:H(N) films nitrogen loss was also measured. The induced structural modifications in both a-C:H and a-C:H(N) films were followed by both AES, using factor analysis, and microprobe Raman spectroscopy. They turn out to be related to the energy deposited by the incident ions. Our results indicate that the ion-beam bombardment causes in both a-C:H and a-C:H(N) films an increase of either the degree of disorder or the ratio between sp²/sp³ bonds across the hydrogen-depleted layer, which depends on the ion fluence.     

On the influence of a TiN interlayer on DLC coatings produced by pulsed vacuum arc discharge: Compositional and morphological study

The influence of a TiN interlayer on DLC coatings grown on silicon (1 0 0), 316 stainless steel and KCl by using the PAPVD pulsed arc discharge technique is presented in this paper. The structure of the coatings was determined by means of FTIR through observation of the absorption band modes of CH₂ between 3100 and 2800 cm⁻¹ and representation of the sp³ and sp² carbon bonds, respectively. The sp³/sp² bonds ratio was calculated by using the base line method and producing a value greater than 1 which was a good prediction of high hardness. XPS analysis of the films was made; the wide spectrum showed the elemental composition of the films (Ti, N, C). A narrow spectrum of C1s at binding energy of 284.48 eV was obtained, and its deconvolution showed peaks of sp³, sp² and Ti–C. Ti–C bonds were formed due to diffusion of carbon atoms into a TiN matrix. The concentration for the XPS spectra was calculated by using the area under the curve of sp³ and sp² peaks. The morphology of the bilayer, including roughness, grain size and thickness was studied through SPM techniques.     

Field emission from nitrogen-implanted CVD diamond film grown on silicon wafer

Nitrogen was implanted into chemical vapor deposition (CVD) diamond films and the electron field emission properties of the nitrogenated diamond films were investigated. Nitrogen implantation was carried out using 10 keV in the dose range from 1×10¹⁶ to 5×10¹⁷ cm^-2 at room temperature. Raman and X-ray photoelectron spectroscopy measurements revealed that nitrogen implantation damaged the structure of the diamond film and promoted the formation of sp² C–C and sp² C–N bondings. Increasing the implantation dose could lower the threshold field of the emission of the diamond film from 18 V/m to 4 V/m. The effective work function of the nitrogen-implanted CVD diamond films was estimated to be in the range of 0.01–0.1 eV. The enhancement of field emission for nitrogen-implanted CVD diamond films was attributed to the increase of the sp² C bonds fraction and the formation of defect bands within the bulk diamond band gap induced by nitrogen implantation, which could alter the work function and elevate the Fermi level. Consequently, the energy barrier for electron tunneling was reduced.     

Effect of nickel on the structure and bond type in amorphous diamond-like carbon films

Experimental data are presented from studies of the structure and bond type of carbon atoms in amorphous carbon-nickel films deposited from pulsed vacuum-arc discharge plasma sources. X-ray photoelectron spectroscopy was used. The characteristics of the plasmon loss spectra depend significantly on the deposition parameters. Carbon exists in a mixed sp²+sp³ hybridized state in the carbon–nickel films. The ratio of sp³/sp² carbon bonds increases when the nickel content is reduced (from 5.5 to 1.0 atomic %) and the deposition angle is increased. The structure closest to that of diamond was with a substrate bias voltage of –80 to –100 V and a deposition angle of 90°.     

Study of optical properties and molecular structure of plasma polymerized diethylene glycol dimethyl ether

This paper deals with plasma polymerization processes of diethylene glycol dimethyl ether. Plasmas were produced at 150 mtorr in the range of 10 W to 40 W of RF power. Films were grown on silicon and quartz substrates. Molecular structure of plasma polymerized films and their optical properties were analyzed by Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy. The IR spectra show C–H stretching at 3000–2900 cm^-1, C=O stretching at 1730–1650 cm^-1, C–H bending at 1440–1380 cm^-1, C–O and C–O–C stretching at 1200–1000 cm^-1. The concentrations of C–H, C–O and C–O–C were investigated for different values of RF power. It can be seen that the C–H concentration increases from 0.55 to 1.0 au (arbitrary unit) with the increase of RF power from 10 to 40 W. The concentration of C–O and C–O–C decreases from 1.0 to 0.5 au in the same range of RF power. The refraction index increased from 1.47 to 1.61 with the increase of RF power. The optical gap calculated from absorption coefficient decreased from 5.15 to 3.35 eV with the increase of power. Due to its optical and hydrophilic characteristics these films can be applied, for instance, as glass lens coatings for ophthalmic applications.     

Electrochemical corrosion behaviors of a-C:H and a-C:NX:H films

The a-C:H and a-C:N_X:H films were deposited onto silicon wafers using radio frequency (rf) plasma enhanced chemical vapor deposition (PECVD) and pulsed-dc glow discharge plasma CVD, respectively. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize chemical nature and bond types of the films. The results demonstrated that the a-C:H film prepared by rf-CVD (rf C:H) has lower I_D/I_G ratio, indicating smaller sp² cluster size in an amorphous carbon matrix. The nitrogen concentrations of 2.9 at.% and 7.9 at.% correspond to carbon nitride films prepared with rf and pulse power, respectively.Electrochemical corrosion performances of the carbon films were investigated by potentiodynamic polarization test. The electrolyte used in this work was a 0.89% NaCl solution. The corrosion test showed that the rf C:H film exhibited excellent anti-corrosion performance with a corrosion rate of 2 nA cm⁻², while the carbon nitride films prepared by rf technique and pulse technique showed a corrosion rate of 6 nA cm⁻² and 235 nA cm⁻², respectively. It is reasonable to conclude that the smaller sp² cluster size of rf C:H film restrained the electron transfer velocity and then avoids detriment from the exchange of electrons.     

Raman spectroscopy of a-C:H:N films deposited using ECR-CVD with mixed gas

Ultraviolet (UV) and visible Raman spectroscopy were used to study a-C:H:N films deposited using ECR-CVD with a mixed gas of CH₄ and N₂. Small percentage of nitrogen from 0 to 15% is selected. Raman spectra show that CN bonds can be directly observed at 2220 cm⁻¹ from the spectra of visible and UV Raman. UV Raman enhances the sp¹ CN peak than visible Raman. In addition, the UV Raman spectra can reveal the presence of the sp³ sites. For a direct correlation of the Raman parameter with the N content, we introduced the G peak dispersion by combining the visible and UV Raman. The G peak dispersion is directly relative to the disorder of the sp² sites. It shows the a-C:H:N films with higher N content will induce more ordered sp² sites. In addition, upper shift of T position at 244 nm excitation with the high N content shows the increment of sp² fraction of films. That means the films with high N content will become soft and contain less internal stress. Hardness test of films also confirmed that more N content is with less hardness.