非晶氧化硅薄膜带尾发光特性

采用等离子体增强化学气相沉积技术,通过改变CO2流量制备了不同氧含量的非晶氧化硅薄膜。利用紫外可见吸收谱、傅里叶红外吸收谱和稳态/瞬态光致发光谱等技术研究了薄膜的微观结构和光学特性。实验结果表明,随着氧含量的增加,薄膜的带隙增大,光致发光强度增加、峰值朝高能方向移动、光谱半峰全宽展宽。时间分辨光谱显示薄膜发光峰值处的衰减时间随氧含量的增加从6.2ns单调增加到21ns,而同一样品的发光寿命随发射波长能量增加而减小。综合分析光学吸收、发射及发光衰减特性表明,薄膜的发光机制主要归结为非晶材料带尾态之间的辐射复合。     

Fe掺杂氢化非晶碳薄膜制备及其热稳定性能

 以H₂、反式-2-丁烯（T₂B）和二茂铁混合气体为工作气体,用金属有机等离子体增强化学气相沉积法（PECVD）制备了Fe掺杂氢化非晶碳（a-C:H:Fe）薄膜。使用X射线光电子能谱（XPS）对a-C:H:Fe薄膜成分进行了分析。使用台阶仪、场发射扫描电镜（FESEM）、热重分析和紫外可见分光光度计（UV-VIS）,对比分析了a-C:H薄膜和a-C:H:Fe薄膜的沉积速率、表面形貌、热稳定性和光学带隙变化。研究表明：相同制备条件下,相比a-C:H薄膜,a-C:H:Fe薄膜的沉积速率高,表面颗粒小,容易碳化,光学带隙变窄。     

Fe掺杂氢化非晶碳薄膜制备及其热稳定性能

以H2、反式-2-丁烯（T2B）和二茂铁混合气体为工作气体,用金属有机等离子体增强化学气相沉积法（PECVD）制备了Fe掺杂氢化非晶碳（a-C:H:Fe）薄膜。使用X射线光电子能谱（XPS）对a-C:H:Fe薄膜成分进行了分析。使用台阶仪、场发射扫描电镜（FESEM）、热重分析和紫外可见分光光度计（UV-VIS）,对比分析了a-C:H薄膜和a-C:H:Fe薄膜的沉积速率、表面形貌、热稳定性和光学带隙变化。研究表明：相同制备条件下,相比a-C:H薄膜,a-C:H:Fe薄膜的沉积速率高,表面颗粒小,容易碳化,光学带隙变窄。     

非晶碳薄膜振动拉曼光谱的第一性原理研究

采用基于第一性原理的赝势平面波方法,对3个不同密度(2.6,2.9和3.2 g·cm-3)非晶碳结构的振动态密度和振动拉曼光谱进行了研究。结构模型由快速“液体-淬火”方法模拟得到,振动频率和本征模由线性响应理论决定,拉曼耦合张量由有限电场方法计算。计算结果表明：当密度从2.6增加到3.2 g·cm-3时,sp3碳含量从50%增加到84.4%,G峰向高频区偏移,D峰和G峰的强度之比I_D/I_G减小,T峰向低频区偏移且T峰和G峰的强度之比I_T/I_G增大。该结果与实验结果显示出很好的一致性。依据原子振动的分析结果证实：拉曼光谱的G峰和D峰均来自于sp2碳原子的振动贡献,且G峰是由任何成对的sp2碳原子的伸缩振动产生的,T峰来自于sp3杂化碳原子的振动贡献,G峰和T峰峰位随结构的色散是由键长变化导致的。     

氮化铬过渡层对四面体非晶碳薄膜在高速钢基底上附着特性影响的研究

利用磁过滤阴极电弧与磁控溅射相结合的薄膜沉积技术在高速钢基底上 制备了氮化铬/四面体非晶碳(CrN/ta-C)复合涂层, 通过改变过渡层氮化铬(CrN)的制备工艺, 研究了四面体非晶碳(ta-C)薄膜在钢基底材料上的附着特性的变化. 结果表明, 随着氮气流量的增大, CrN/ta-C复合涂层中的氮化铬经过了Cr-Cr₂N-CrN的相变过程. 同时涂层的附着力也随着氮气流量的增大而增加, 但是当氮气流量超过30 sccm时, 涂层附着力会有所下降; 通过改变基片偏压, 复合涂层中氮化铬的择优取向与晶粒结构发生改变, 随着偏压的增大, 涂层附着力也会大大改善, 但是当偏压超过200 V, 涂层附着特性会略微降低. 通过涂层耐磨性的测试也表明, 在高速钢基底上, CrN涂层能显著提高ta-C薄膜在高速钢基底上的附着力, 同时显著提高耐磨特性. 关键词： 附着力 四面体非晶碳薄膜 X射线衍射 拉曼光谱     

氢化非晶碳薄膜的光致发光线型及其激发能量依赖关系

本文报道了氢化非晶碳薄膜在2.9-4.5eV光激发下的发光谱。它的光致发光谱是无结构的不对称宽带,半宽度约为0.8eV。在低于3.56eV的光激发下,谱带的峰值能量随激发能量的降低明显红移。在安德森带结构和指数分布的带尾态密度的基础上,考虑了尾态中粒子的两种跃迁过程,实验的PL谱就可得到解释。并用这个简单模型计算了这种材料的光致发光谱特征。     

a-C:N:H纳米尖端荧光产生的机理

用CH4,H2和NH3为反应气体,利用等离子体增强热丝化学气相沉积在沉积有碳膜的Si衬底上制备了a-C:N:H纳米尖端,并用扫描电子显微镜和微区Raman光谱仪对碳膜和纳米尖端进行了表征。结果表明:Raman谱中含有与碳和氮相关的峰,且纳米尖端的Raman谱比碳膜的Raman谱有很强的荧光背景。Raman谱中的峰说明沉积的碳膜和纳米尖端是a-C:N:H薄膜和a-C:N:H尖端。a-C:N:H纳米尖端的Raman谱中强荧光背景的产生表明其在激发光源照射的过程中发射了强荧光,对a-C:N:H纳米尖端产生强荧光的机理进行了探讨。     

Superhard nanocomposite nc-TiC/a-C:H film fabricated by filtered cathodic vacuum arc technique

Superhard nanocomposite nc-TiC/a-C:H films, with an excellent combination of high elastic recovery, low friction coefficient and good H/E ratio, were prepared by filtered cathodic vacuum arc technique using the C₂H₂ gas as the precursor. The effect of C₂H₂ flow rate on the microstructure, phase composition, mechanical and tribological properties of nanocomposite nc-TiC/a-C:H films have been investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy disperse spectroscopy (EDS), microindentation and tribotester measurements. It was observed that the C₂H₂ flow rate significantly affected the Ti content and hardness of films. Furthermore, by selecting the proper value for C₂H₂ flow rate, 20 sccm, one can deposit the nanocomposite film nc-TiC/a-C:H with excellent properties such as superhardness (66.4 GPa), high elastic recovery (83.3%) and high H/E ratio (0.13).     

用椭偏法分析单波段及双波段兼容a－C：H增透膜

讨论了在单晶锗上为获得单波段（３～５μｍ）及双波段（３～５μｍ、８～１２μｍ）兼容ａ－Ｃ：Ｈ增透膜所必需的膜系设计，及用椭偏法对该膜进行的增透结果分析。结果表明，ａ－Ｃ：Ｈ膜是理想的红外增透膜。椭偏法对分析所制备的膜是否符合膜系设计要求及沉积工艺参数的确定具有重要意义。     

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.     

A magnetron sputtering technique to prepare a-C:H films: Effect of substrate bias

Amorphous hydrogenated carbon (a-C:H) films were deposited by magnetron sputtering with a mixture gas of Ar and CH₄. The a-C:H films deposited by this method have relatively low internal stress (<1 GPa) compared to some films deposited by conventional deposition process. The effects of substrate bias voltage on microstructure, surface morphology and mechanical properties of the films were investigated by various techniques. It has been found that the polymer-like structure is dominated at low bias voltage (−100 V), while the diamond-like structure with the highest hardness and internal stress is the main feature of the a-C:H films deposited under high bias voltage (−300 V). With increasing the bias voltage further, the feature of diamond-like structure decreases associating with the increase of graphitization. The frictional test shows that the friction coefficient and wear rate of the a-C:H films are depended strongly on structure and mechanical properties, which were ultimately influenced by the deposition method and bias voltage.     

Deposition of a-C:H films on UHMWPE substrate and its wear-resistance

In prosthetic hip replacements, ultrahigh molecular weight polyethylene (UHMWPE) wear debris is identified as the main factor limiting the lifetime of the artificial joints. Especially UHMWPE debris from the joint can induce tissue reactions and bone resorption that may lead to the joint loosening. The diamond like carbon (DLC) film has attracted a great deal of interest in recent years mainly because of its excellent tribological property, biocompatibility and chemically inert property. In order to improve the wear-resistance of UHMWPE, a-C:H films were deposited on UHMWPE substrate by electron cyclotron resonance microwave plasma chemical vapor deposition (ECR-PECVD) technology. During deposition, the working gases were argon and acetylene, the microwave power was set to 800 W, the biased pulsed voltage was set to −200 V (frequency 15 kHz, duty ratio 20%), the pressure in vacuum chamber was set to 0.5 Pa, and the process time was 60 min. The films were analysed by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, nano-indentation, anti-scratch and wear test. The results showed that a typical amorphous hydrogenated carbon (a-C:H) film was successfully deposited on UHMWPE with thickness up to 2 μm. The nano-hardness of the UHMWPE coated with a-C:H films, measured at an applied load of 200 μN, was increased from 10 MPa (untreated UHMWPE) to 139 MPa. The wear test was carried out using a ball (Ø 6 mm, SiC) on disk tribometer with an applied load of 1 N for 10000 cycles, and the results showed a reduction of worn cross-sectional area from 193 μm² of untreated UHMWPE to 26 μm² of DLC coated sample. In addition the influence of argon/acetylene gas flow ratio on the growth of a-C:H films was studied.     

Nanocomposite TiC/a-C：H film prepared on titanium aluminium alloy substrates by PSII assistant MW-ECRCVD

Thin films of titanium carbide and amorphous hydrogenated carbon have been synthesized on titanium aluminium alloy substrates by PSII assisted MW-ECRCVD with a mirror field. The microstructure, chemical composition and mechanical property were investigated. Using XPS and TEM, the films were identified to be a-C：H film containing TiC nanometre grains （namely, the so-called nanocomposite structure）. The size of TiC grains of nanocomposite TiC/DLC film is about 5 nm. The nanocomposite structure has obvious improvement in the mechanical properties of DLC film. The hardness of a-C：H film with Ti is enhanced to 34 G Pa~ while that of a-C：H film without Ti is about 12 G Pa, and the coherent strength is also obviously enhanced at the critical load of about 35N.     

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.     

Structure and hardness of a-C:H films prepared by middle frequency plasma chemical vapor deposition

a-C:H films were prepared by middle frequency plasma chemical vapor deposition (MF-PCVD) on silicon substrates from two hydrocarbon source gases, CH₄ and a mixture of C₂H₂ + H₂, at varying bias voltage amplitudes. Raman spectroscopy shows that the structure of the a-C:H films deposited from these two precursors is different. For the films deposited from CH₄, the G peak position around 1520 cm⁻¹ and the small intensity ratio of D peak to G peak (I(D)/I(G)) indicate that the C-C sp³ fraction in this film is about 20 at.%. These films are diamond-like a-C:H films. For the films deposited from C₂H₂ + H₂, the Raman results indicate that their structure is close to graphite-like amorphous carbon. The hardness and elastic modulus of the films deposited from CH₄ increase with increasing bias voltage, while a decrease of hardness and elastic modulus of the films deposited from a mixture of C₂H₂ + H₂ with increasing bias voltage is observed.     

RF-PECVD掺溴非晶碳氢膜的Raman光谱分析

在室温条件下,以溴乙烷为单体、氢气为载气,用13.56 MHz射频等离子体化学气相淀积方法(RF-PECVD)在硅片衬底上生长了掺溴非晶碳氢薄膜(a-C:Br:H).通过对其进行Raman光谱分析,研究了工作气压对薄膜结构的影响.结果显示:随着气体工作压力从20 Pa下降至5 Pa,样品D峰强度增强,I_D/I_G值逐步由1.18增加至1.36,G峰的位置向高频轻微移动;与此同时,薄膜生长方式逐步转为低能态形式生长,薄膜中sp~2C逐步由链式结构向环式结构转化.