压力对热丝化学气相沉积的CH_4/H_2/Ar气氛中的纳米金刚石薄膜生长的影响(英文)

在热丝化学气相沉积体系中,系统研究了气压对CH4/H2/Ar气氛中纳米金刚石薄膜生长的影响.研究发现,体系气压对纳米金刚石的生长有很大的影响.在40torr的气压下,在CH4/H2/Ar气氛中的Ar气含量需高达90%才能保证纳米金刚石薄膜的生长,但降低气压至5torr时,50%的Ar气含量即可保证纳米金刚石薄膜的生长.压力对薄膜生长表面的气体浓度的影响是这个转变的主要原因.在同样的Ar含量下,在5torr下的C2活性基团的浓度高于40 torr的浓度,因而低的Ar含量会保证纳米金刚石薄膜的生长.     

Ultra-smooth nanostructured diamond films deposited from He/H2/CH4/N2 microwave plasmas

Addition of He to a high CH4 content (10.7 vol%) H2/CH4/N2 feedgas mixture for microwave plasma chemical vapor deposition produced hard (58-72 GPa), ultra-smooth nanostructured diamond films on Ti-6AI-4V alloy substrates. Upon increase in He content up to 71 vol%, root mean squared (RMS) surface roughness of the film decreased to 9-10 nm and average diamond grain size to 5-6 nm. Our studies show that increased nanocrystallinity with He addition in plasma is related to plasma dilution, enhanced fragmentation of carbon containing species, and enhanced formation of CN radical.     

Gas Sensing Properties of Hydrogenated Amorphous Silicon Films

Gas sensing experiments on hydrogenated amorphous silicon (a-Si:H) films have been performed. We show that a-Si:H exhibits a low-temperature gas response that is distinctly different from the more familiar combustive gas response operative on heated metal-oxide surfaces. In particular, we show that at room temperature and above, a-Si:H samples exhibit a dissociative gas response which has first been observed on hydrogenated diamond (HD) samples. Whereas this dissociative gas response disappears at HD surfaces upon evaporation of the adsorbed surface electrolyte layer, a gas response with a similar cross sensitivity profile is observed on a-Si:H surfaces that persists up to the original deposition temperature of the a-Si:H films. We argue that this latter kind of gas response is due to a coordinative gas response that takes place when surface H-atoms of the a-Si:H film enter the coordination sphere of adsorbed analyte gas molecules.     

氧气对MWPCVD制备金刚石膜的影响

在水冷反应室式微波等离子体化学气相沉积装置中以混合的CH4/H2/O2为反应气体,研究了O2浓度对制备金刚石膜的影响.实验发现,很低浓度的O2会显著促进金刚石的沉积,并稍稍抑制非晶C的沉积,因而沉积膜中非晶C的含量急剧下降;较高浓度的O2会同时抑制金刚石和非晶C的沉积,但由于抑制金刚石的作用更强烈,沉积膜中非晶C的含量反而有所升高.另外,O2的存在,有利于沉积颗粒较小的金刚石膜.     

无支撑优质金刚石膜研制中的相关问题探讨

无支撑优质金刚石膜在微波真空器件和光学器件中的广泛应用,有赖于制备成本的下降和工艺的完善。结合微波等离子体化学气相沉积(MPCVD)金刚石膜的工艺研究结果,本文就沉积速率、晶面取向以及内应力的相关问题进行了初步探讨。对于给定的设备,沉积速率与多种因素有关,包括膜的质量、膜厚均匀性和有效沉积面积、以及形核的密度。在通常情况下,金刚石膜呈(111)择优取向,而样品位置下移5mm后,观察到(100)取向。对内应力的初步研究表明,CH4/H2比例较低(1.5)时,金刚石膜的内应力趋向于压应力,而(100)取向的出现则有助于使内应力降到最低。     

Synthesis of ultrasmooth nanostructured diamond films by microwave plasma chemical vapor deposition using a He/H(2)/CH(4)/N(2) gas mixture

Ultrasmooth nanostructured diamond (USND) films were synthesized on Ti-6Al-4V medical grade substrates by adding helium in H(2)/CH(4)/N(2) plasma and changing the N(2)/CH(4) gas flow from 0 to 0.6. We were able to deposit diamond films as smooth as 6 nm (root-mean-square), as measured by an atomic force microscopy (AFM) scan area of 2 μm(2). Grain size was 4-5 nm at 71% He in (H(2) + He) and N(2)/CH(4) gas flow ratio of 0.4 without deteriorating the hardness (~50-60 GPa). The characterization of the films was performed with AFM, scanning electron microscopy, x-ray diffraction (XRD), Raman spectroscopy, and nanoindentation techniques. XRD and Raman results showed the nanocrystalline nature of the diamond films. The plasma species during deposition were monitored by optical emission spectroscopy. With increasing N(2)/CH(4) feedgas ratio (CH(4) was fixed) in He/H(2)/CH(4)/N(2) plasma, a substantial increase of CN radical (normalized by Balmer H(α) line) was observed along with a drop in surface roughness up to a critical N(2)/CH(4) ratio of 0.4. The CN radical concentration in the plasma was thus correlated to the formation of ultrasmooth nanostructured diamond films.     

HFCVD金刚石膜过程的气氛模拟与分析

对热丝法化学气相沉积金刚石膜过程的气氛进行了模拟与分析。使用GRI－Mech3.0甲烷燃烧过程C／H／O／N四元体系热化学反应机理和动力学数据，模拟并分析了HFCVD金刚石膜的C／H气相化学反应，通过对反应流的简单模拟得到了衬底位置气相组成，结果与前人实验数据吻合，探讨了灯丝温度、碳源浓度和碳源种类等因素变化对衬底位置气相组成的影响。结果表明甲基是金刚石膜生长最主要的前驱基团，其作用远高于乙炔，而超平衡态原子氢的存在对金刚石膜的质量至关重要。     

CVD金刚石薄膜(111)与(100)取向生长的热力学分析

用非平衡热力学耦合模型计算了CVD金刚石薄膜生长过程中C2H2与CH3浓度之比[C2H2]/[CH3]随衬底温度和CH4浓度的变化关系,从理论上探讨了金刚石薄膜（111）面和（100）面取向生长与淀积条件的关系。在衬底温度和CH4浓度由低到高的变化过程中,[C2H2]/[CH3]逐渐升高,导致金刚石薄膜的形貌从（111）晶面转为（100）晶面。添加氧后C2H2与CH3浓度都将下降,但C2H2下降得更多,因而添加氧也使[C2H2]/[CH3]下降,从而有利于生长（111）晶面的金刚石薄膜。     

Growth of metal-free carbon nanotubes on glass substrate with an amorphous carbon catalyst layer

We have investigated the direct growth of metal-free carbon nanotubes (CNTs) on glass substrates with microwave-plasma enhanced chemical vapor deposition (MPECVD). Amorphous carbon (a-C) films were used as a catalyst layer to grow metal-free CNTs. The a-C films were deposited on Corning glass substrates using RF magnetron sputtering with the use of a carbon target (99.99%) at room temperature. They were pretreated with hydrogen plasma using a microwave PECVD at 600 degrees C. Then, CNTs were prepared using microwave PECVD with a mixture of methane (CH4) and hydrogen (H2) gases. The CNTs were grown at different substrate temperatures (400 degrees C, 500 degrees C, and 600 degrees C) for 30 minutes. Other conditions were fixed. The growth trends of CNTs against substrate temperature were observed by field emission scanning electron microscopy (FE-SEM). The structure of a-C catalyst layer and grown CNTs were measured by Raman spectroscopy. High-resolution transmission electron microscopy (HR-TEM) images showed that the CNTs had bamboo-like multi-walled structures. Energy dispersive spectroscopy (EDS) measurements confirmed that the CNTs consisted of only carbon.     

Material and sensing properties of Pd-deposited WO3 thin films

The physicochemical and electrical properties of Pd-deposited WO3 thin films were investigated as a function of Pd thickness, annealing temperature, and operating temperature for application as a hydrogen gas sensor. WO3 thin films were deposited on an insulating material using a thermal evaporator. X-ray diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used to evaluate the crystal structure, microstructure, surface roughness, and chemical property of the films, respectively. The deposited films grew into polycrystalline WO3 with a rhombohedral structure after annealing at 500 degrees C. Adding Pd had no effect on the crystallinity, but suppressed the growth of WO3 grains. The Pd was scattered as isolated small spherical particles of PdO2 on the WO3 thin film after annealing at 500 degrees C, while it agglomerated as irregular large particles or diffused into the WO3 after annealing at 600 degrees C. PdO2 reduction under H2 and reoxidation under air were dependent on both the Pd deposition thickness and annealing conditions. The WO3 thin film with a 2-nm-thick Pd deposit showed a good response and recovery to H2 gas at a 250 degrees C operating temperature.     

掺硼对超纳米金刚石薄膜的影响

采用微波等离子体化学气相沉积(MPCVD)技术,利用氩气、甲烷、二氧化碳混合气体,制备出平均晶粒尺寸在7.480 nm左右,表面粗糙度在15.72 nm左右的高质量的超纳米金刚石薄膜;在此工艺基础上以硼烷作为掺杂气体,合成掺硼的金刚石薄膜.表征结果显示在一定的浓度范围内随着硼烷气体的通入,金刚石薄膜的晶粒尺寸及表面粗糙度增大、结晶性变好,不再具有超纳米金刚石膜的显微结构和表面形态;同时膜材的物相组成也发生改变,金刚石组份逐渐增多,并且膜层内出现了更明显的应力以及更好的导电性能.     

Atomic layer deposition of SiO2 thin films using tetrakis(ethylamino)silane and ozone

We examined the atomic layer deposition (ALD) of silicon dioxide thin films on a silicon wafer by alternating exposures to tetrakis(ethylamino)silane [Si(NHC2H5)4] and O3. The growth kinetics of silicon oxide films was examined at substrate temperatures ranging from 325 to 514 degrees C. The deposition was governed by a self-limiting surface reaction, and the growth rate at 478 degrees C was saturated at 0.17 nm/cycle for Si(NHC2H5)4 exposures of 2 x 10(6) L (1 L = 10(-6) Torr x s). The films deposited at 365-404 degrees C exhibited a higher deposition rate of 0.20-0.21 nm/cycle. However, they contained impurities, such as carbon and nitrogen, and showed poor film qualities. The concentration of impurities decreased with increasing substrate temperature. It was found that the films deposited in the high-temperature regime (478-514 degrees C) showed excellent physical and electrical properties equivalent to those of LPCVD films.     

Diamond growth with CF4 addition inhot-filament chemical vapour deposition

Tetrafluoromethane (CF4) was added to standard CH4/H2 mixtures for diamond growth in hot-filament-assisted chemical vapour deposition. CF4 concentrations in the range of 0.3%–3% were studied. Mass spectrometry of the exhaust gas showed that only a small fraction (< 15%) of CF4 was thermally dissociated for filament temperatures over 1800 °C. The observed stable products of its dissociation were mainly C2H2, CH4 and HF. This CF4 addition considerably enhanced the nucleation and growth characteristics on silicon and molybdenum. Diamond growth was observed with substrate temperature as low as 390 °C. A comparative study for the growth dependence on substrate temperature with and without CF4 addition in the gas mixture is presented. The growth rate was measured by post-growth weighing with a micro balance. An activation energy of 11 kcal mol-1 for growth with CF4 addition was obtained. Raman spectra and atomic force microscopy were used to characterize the diamond films. This revised version was published online in November 2006 with corrections to the Cover Date.     

Homogeneous nanocrystalline cubic silicon carbide films prepared by inductively coupled plasma chemical vapor deposition

Silicon carbide films with different carbon concentrations x(C) have been synthesized by inductively coupled plasma chemical vapor deposition from a SiH(4)/CH(4)/H(2) gas mixture at a low substrate temperature of 500?°C. The characteristics of the films were studied by x-ray photoelectron spectroscopy, x-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared absorption spectroscopy, and Raman spectroscopy. Our experimental results show that, at x(C) = 49?at.%, the film is made up of homogeneous nanocrystalline cubic silicon carbide without any phase of silicon, graphite, or diamond crystallites/clusters. The average size of SiC crystallites is approximately 6?nm. At a lower value of x(C), polycrystalline silicon and amorphous silicon carbide coexist in the films. At a higher value of x(C), amorphous carbon and silicon carbide coexist in the films.     

Surface activation pre-treatments for NCD films grown by HFCVD

The control of the nucleation density is essential for the production of ultra-thin, continuous and well adhered nanocrystalline diamond coatings. Surface pre-treatments such as abrasive scratching with diamond powder or bias enhanced nucleation are commonly used methods. In this work, surface activation by a pre-growth step is done using the hot-filament chemical vapour deposition (HFCVD) technique prior to seeding with diamond. The Si surface is modified during exposure to typical CVD diamond growth conditions. After ultrasonication with suspension of diamond in ethanol or n-hexane, an amorphous carbon layer is revealed at the surface of the Si substrates. The densest NCD films were obtained for the surface activation step done using a lower temperature and poorer methane mixture due to the improved seeding allowed by the amorphous carbon layer. Intermediate growth temperature of 750 °C resulted in high nucleation density while lower temperatures decrease it and higher ones produce a DLC nanostructured layer along with moderate NCD nucleation density.     

Adhesion improvement of diamond films on cemented carbides with copper implant layer

The deposition of diamond films on cemented carbides is strongly influenced by the catalytic effect of cobalt under typical deposition conditions. Decreasing the content of Co on the surface of the cemented carbide is often used for the diamond film deposition. But the leaching of Co from the WC-Co substrate leads to a mechanical weak surface, often causing poor adhesion. In this paper we adopt a copper implant layer to improve the mechanical properties of the Co leached substrate. The copper implant layer is prepared with vaporization. The diamond films are grown by microwave plasma chemical vapor deposition from the CH₄/H₂ gas mixture. The morphology and the quality of the diamond films have been characterized by scanning electron microscopy and Raman spectroscopy. A Rockwell apparatus has evaluated the adhesion of the diamond on the substrate. The results indicate that the diamond films have good adhesion to the cemented carbide substrate due to the recovery of the mechanical properties of the Co depleted substrate after the copper implantation and less graphite formation between the substrate and the diamond film.     

Study of the moderate-temperature growth process of optical quality synthetic diamond films on quartz substrates

Growth of undoped and boron-doped diamond films on quartz substrates at moderate temperature of 500 °C by microwave plasma chemical vapor deposition method was studied in terms of growth rate, surface roughness and optical transmittance. Similar density of diamond seed particles on quartz surfaces seeded mechanically before the deposition process and diamond grains within diamond films grown on those substrates is observed. The growth rate is found similar to that reported for diamond deposited on silicon substrates in the same plasma deposition system, although with substantially higher activation energy. Furthermore, increased level of dopant concentration in the gas mixture resulted in a decrease of the growth rate, while a gradual reduction of the surface roughness occurred at high dopant levels. Overall, the highest measured regular optical transmittance of the undoped diamond film on quartz was 45% at 1100 nm (including quartz absorption), whereas that of boron-doped diamond peaked 5% at 700 nm (tail absorption of boron centers).     

Low Resistance Polycrystalline Diamond Thin Films Deposited by Hot Filament Chemical Vapour Deposition

Polycrystalline diamond thin films with outgrowing diamond (OGD) grains were deposited onto silicon wafers using a hydrocarbon gas (CH4) highly diluted with H2 at low pressure in a hot filament chemical vapour deposition (HFCVD) reactor with a range of gas flow rates. X-ray diffraction (XRD) and SEM showed polycrystalline diamond structure with a random orientation. Polycrystalline diamond films with various textures were grown and (111) facets were dominant with sharp grain boundaries. Outgrowth was observed in flowerish character at high gas flow rates. Isolated single crystals with little openings appeared at various stages at low gas flow rates. Thus, changing gas flow rates had a beneficial influence on the grain size, growth rate and electrical resistivity. CVD diamond films gave an excellent performance for medium film thickness with relatively low electrical resistivity and making them potentially useful in many industrial applications.     

Tuning the conditions for the deposition of nanocrystalline diamond by hot filament chemical vapour deposition

Although large focus has been placed into the deposition of nanocrystalline and ultra-nanocrystalline diamond films, most of this research uses microwave plasma assisted CVD systems. However, the growth conditions used in microwave systems cannot be directly used in hot-filament CVD systems. This paper, aims to enlarge the knowledge of the diamond film depositing process. H2/CH4/Ar gas mixtures have been used to deposit micro, nano and ultra-nanocrystalline diamond films by hot-filament CVD systems. Additionally, the distance between the filaments array and the substrate was varied, in order to observe its effect and consequently the effect of a lower substrate temperature in the nucleation density and deposition. All the samples were characterized for microstructure and quality, using scanning electron microscopy and Raman spectroscopy.     

氮气氛下金刚石薄膜生长过程中的光发射谱研究

利用原位光发射谱对衬底附近的化学气相性质进行了研究．研究表明,氮气的引入使得金刚石生长的气相化学和表面化学性质发生了很大变化．含氮基团的萃取作用提高了金刚石表面氢原子的脱附速率,从而提高了金刚石膜的生长速率．而含氮基团的选择吸附使金刚石（１００）取向变得化学糙化,这种化学糙化使得（１００）晶面生长速率远大于其它晶面,最终使金刚石薄膜呈现（１００）织构．还利用化学气相沉积方法研究了氮气浓度对金刚石生长的影响,结果与光发射谱分析是一致的．