AlN缓冲层对ZnO薄膜质量的影响

采用脉冲激光沉积法以AlN为缓冲层在Si(100)衬底上制备了ZnO薄膜,并测量了样品的XRD谱、SEM图和PL谱.结果表明,AlN缓冲层可以提高Si衬底上外延生长ZnO薄膜的晶体质量.改变缓冲层的生长温度(50～500 ℃)所制备样品的测量结果表明,较低温度下生长的AlN缓冲层有利于制备高质量的ZnO外延层薄膜,其中AlN缓冲层生长温度为100 ℃时外延生长ZnO薄膜晶体质量最好.     

Effect of filament biasing on nanocrystalline-Si films deposited by hot wire chemical vapor deposition

Nanocrystalline silicon (nc-Si) films were deposited by hot wire chemical vapor deposition with applying positive or negative filament biases. These films were characterized by Raman spectroscopy, field emission scanning electron microscopy and X-ray photoelectron spectroscopy. Plasmon loss of the Si(2p) band region was shifted to higher energy due to dielectric changes with applied filament biases from negative to positive voltage. A semi-quantitative study of the valence band structure was employed to analyze the bias effect of the valance band in nc-Si networks. Nc-Si with a positive filament bias shows better microstructural properties than those with a negative bias and without biasing nc-Si films.     

Characterization of diamond films deposited on Re substrate by magnetic field-assisted hot filament chemical vapor deposition

A periodically magnetic field (PMF) was used in a hot-filament chemical vapor deposited (HFCVD) for diamond growth on the rhenium substrate. The morphology, band structures and crystalline structure of the film were analyzed by the scanning electron microscopy (SEM), Raman spectroscopy and X-ray diffractometer (XRD), respectively. The results show that the thickness of the diamond film is about 2900 nm by 4 h deposition with magnetic field-assisted. There is no interlayer between diamond film and the rhenium substrate. The result shows that the turn on voltage of the sample is enhanced from 3.3 to 2.6 V/μm with the PMF. Also the total emission current density at 6.2 V/μm increased from 6.3 to 21.5 μA/cm².     

等离子体增强热丝CVD生长碳纳米尖端的研究

用CH₄，NH₃和H₂为反应气体，利用等离子体增强热丝化学气相沉积系统在不同偏压电流的条件下制备了碳纳米尖端，并用扫描电子显微镜和显微Raman光谱仪对碳纳米尖端进行了研究.结果表明碳纳米尖端是石墨结构，随着偏压电流的增大，碳纳米尖端的顶角减小，生长速率增大.结合有关等离子体和溅射的理论，分析讨论了碳纳米尖端的形成和碳纳米尖端的生长随偏压电流的变化. 关键词： 碳纳米尖端 等离子体 化学气相沉积     

Plasma-enhanced chemical vapor deposition of organic particle thin films

Five organic precursors, 2,5-dimethyl-2,4-hexadiene, 2,5-norbornadiene, α-terpinine, limonene, and styrene have been studied as precursors for plasma deposition of low-k films. The films have been produced under particle-forming conditions in the plasma. Accordingly, films have a granular structure with grain sizes in the range 40–400 nm, as determined by AFM. Annealing at 400 °C preserves the granular structure of the films while the grain size decreases. Of the five precursors examined, 2,5-dimethyl-2,4-hexadiene and 2,5-norbornadiene produce films with the lowest dielectric constant, with a value of 3.3. While the dielectric constant varies with deposition conditions (pressure, flow rate, concentration of precursor), we find that the grain size of the films correlates most closely with the dielectric constant and conclude that the lowest value of the dielectric constant are obtained under conditions that promote the formation of particles larger than about 200 nm.     

等离子增强原子层沉积低温生长AlN薄膜

采用等离子增强原子层沉积技术在单晶硅基体上成功制备了AlN晶态薄膜, 利用椭圆偏振仪、原子力显微镜、小角掠射X射线衍射仪、高分辨透射电子显微镜、 X射线光电子能谱仪对样品的生长速率、表面形貌、晶体结构、薄膜成分进行了表征和分析, 结果表明, 采用等离子增强原子层沉积制备AlN晶态薄膜的最低温度为200 ℃, 薄膜表面平整光滑, 具有六方纤锌矿结构与(100)择优取向, Al_2p与N_1S的特征峰分别为74.1 eV与397.0 eV, 薄膜中Al元素与N元素以Al-N键相结合, 且成分均匀性良好. 关键词： 氮化铝 等离子增强原子层沉积 低温生长 晶态薄膜     

Pulsed laser deposition of ZnO as conductive buffer layer of (001)-LiNbO3 thin films

1 (LO) mode peak at 579 cm^-1, indicating oxygen deficiency in the films. Significant dependence of the electrical property for the films on substrate temperature was shown. The I–V relation of the films exhibited non-ohmic behavior. Whereas the films deposited above 500 °C showed a metal-like property, at a lower substrate temperature semiconducting thin films were achieved. The (001)-oriented LiNbO₃/ZnO heterostructure was successfully prepared on quartz fused and (001) sapphire plates. Received: 6 April 1998/Accepted: 26 May 1998     

Synthesis of micro- or nano-crystalline diamond films on WC-Co substrates with various pretreatments by hot filament chemical vapor deposition

Diamond films deposited on tungsten carbide can lead to major improvements in the life and performance of cutting tools. However, deposition of diamond onto cemented tungsten carbide (WC-Co) is problematic due to the cobalt binder in the WC. This binder provides additional toughness to the tool but results in poor adhesion and low nucleation density of any diamond film. A two-step chemical etching pretreatment (Murakami reagent and Caro acid, (MC)-pretreatment) and a boronization pretreatment have both been used extensively to improve adhesion of CVD diamond film on WC-Co substrates. Here we discuss the applicability of MC-pretreatment for a range of Co-containing WC-Co substrates, and demonstrate a controlled synthesis process based on liquid boronizing pretreatment for obtaining smooth and dense micro- or nano-crystalline diamond films on high Co-containing WC-Co substrates. Substrate treatments and deposition parameters were found to have major influences on the smoothness, structure and quality of the diamond films. The best quality diamond films were achieved under conditions of relatively high substrate temperature (T_s) and the best adhesion was achieved at T_s = 800 °C.     

Atomic layer deposition and characterization of Ga-doped ZnO thin films

Low-resistivity n-type ZnO thin films were grown by atomic layer deposition (ALD) using diethylzinc (DEZ) and H₂O as Zn and O precursors. ZnO thin films were grown on c-plane sapphire (c- Al₂O₃) substrates at 300 C. For undoped ZnO thin films, it was found that the intensity of ZnO () reflection peak increased and the electron concentration increased from 6.8×10¹⁸ to 1.1×10²⁰ cm⁻³ with the increase of DEZ flow rate, which indicates the increase of O vacancies () and/or Zn interstitials (Zn_i). Ga-doping was performed under Zn-rich growth conditions using triethylgallium (TEG) as Ga precursor. The resistivity of 8.0×10⁻⁴ Ω cm was achieved at the TEG flow rate of 0.24 μmol/min.     

Deposition of thin rhodium films by plasma-enhanced chemical vapor deposition

Thin films of rhodium have been prepared starting from dicarbonyl-2.4-pentadionato-rhodium(I), Rh(CO)₂C₅H₇O₂, by plasma enhanced CVD. The dependence of the deposition rate and film properties on substrate temperature, partial pressure of the organometallic and on hydrogen has been studied. Metal contents of 100% and thin-film resistivities as low as 5 times the bulk resistivity of rhodium have been achieved.     

Effect of high-temperature annealing on AlN thin film grown by metalorganic chemical vapor deposition

The effect of high-temperature annealing on AlN thin film grown by metalorganic chemical vapor deposition was investigated using atomic force microscopy, Raman spectroscopy, and deep ultra-violet photoluminescence(PL) with the excitation wavelength as short as ～ 177 nm. Annealing experiments were carried out in either N2 or vacuum atmosphere with the annealing temperature ranging from 1200℃ to 1600℃. It is found that surface roughness reduced and compressive strain increased with the annealing temperature increasing in both annealing atmospheres. As to optical properties,a band-edge emission peak at 6.036 eV and a very broad emission band peaking at about 4.7 eV were observed in the photoluminescence spectrum of the as-grown sample. After annealing, the intensity of the band-edge emission peak varied with the annealing temperature and atmosphere. It is also found that a much stronger emission band ranging from 2.5 eV to 4.2 eV is superimposed on the original spectra by annealing in either N2 or vacuum atmosphere. We attribute these deep-level emission peaks to the VAL–ONcomplex in the AlN material.     

Pulsed laser deposition of high-quality ZnO films using a high temperature deposited ZnO buffer layer

High-quality ZnO film growth on sapphire was achieved by pulsed laser deposition using a high temperature deposited ZnO buffer layer. This high temperature deposited buffer layer remarkably improves crystallinity of subsequent films. In particular, the full width at half-maximum of X-ray diffraction ω-rocking curves for ZnO films grown with the buffer layer is 0.0076° (27.36 arcsec) and 0.1242° (447.12 arcsec) for the out-of-plane (002) and in-plane (102) reflections, respectively. In addition, ZnO films grown with this buffer layer showed a carrier mobility of 88 cm²/V s, which is three times higher than that realized for ZnO films grown without the buffer layer. The room temperature photoluminescence spectra showed strong band edge emission with little or no defect-related visible emission. PACS 78.55.Et; 81.05.Dz     

Low-temperature MOVPE growth of ZnO thin films by using a buffer layer

ZnO thin films have been grown on a-plane (1,1,−2,0) sapphire substrates by metalorganic vapor phase epitaxy (MOVPE) at low substrate temperature of 350 °C. It is showed that the crystal and electrical quality of the thin films was improved by using a ZnO buffer layer. The photoluminescence (PL) measurements indicate that the ZnO thin films grown at such a low substrate temperature have a strong UV emission.     

Nonpolar a-plane GaN grown on r-plane sapphire using multilayer AlN buffer by metalorganic chemical vapor deposition

Mirror-like and pit-free non-polar a-plane (1 1 −2 0) GaN films are grown on r-plane (1 −1 0 2) sapphire substrates using metalorganic chemical vapor deposition (MOCVD) with multilayer high-low-high temperature AlN buffer layers. The buffer layer structure and film quality are essential to the growth of a flat, crack-free and pit-free a-plane GaN film. The multilayer AlN buffer structure includes a thin low-temperature-deposited AlN (LT-AlN) layer inserted into the high-temperature-deposited AlN (HT-AlN) layer. The results demonstrate that the multilayer AlN buffer structure can improve the surface morphology of the upper a-plane GaN film. The grown multilayer AlN buffer structure reduced the tensile stress on the AlN buffer layers and increased the compressive stress on the a-plane GaN film. The multilayer AlN buffer structure markedly improves the surface morphology of the a-plane GaN film, as revealed by scanning electron microscopy. The effects of various growth V/III ratios was investigated to obtain a-plane GaN films with better surface morphology. The mean roughness of the surface was 1.02 nm, as revealed by atomic force microscopy. Accordingly, the multilayer AlN buffer structure improves the surface morphology and facilitates the complete coalescence of the a-plane GaN layer.     

热丝CVD生长金刚石薄膜喇曼散射研究

本文报道热丝化学气相沉积法（ＨＦＣＶＤ）生长金钢石薄膜的喇曼散射结果。选取多种峰型，对金钢石薄膜喇曼谱（１１０－１８００ｃｍ－１）采用最小二乘法进行非线性拟合，得到最佳拟合模型，其计算得到的拟合曲线怀实验谱图符合得较好。该模型揭示，石墨Ｄ峰（１３５５ｃｍ－１）是金刚石薄膜喇曼谱中不可缺少的一个组份，并且结合石墨Ｄ峰和金刚石喇曼的空间相关线型，可以解释金刚石喇曼区特殊峰形的物理机制，拟合参量的进一步     

Characterization of atomic-layer MoS_2 synthesized using a hot filament chemical vapor deposition method

Atomic-layer MoS_2 ultrathin films are synthesized using a hot filament chemical vapor deposition method. A combination of atomic force microscopy(AFM), x-ray diffraction(XRD), high-resolution transition electron microscopy(HRTEM), photoluminescence(PL), and x-ray photoelectron spectroscopy(XPS) characterization methods is applied to investigate the crystal structures, valence states, and compositions of the ultrathin film areas. The nucleation particles show irregular morphology, while for a larger size somewhere, the films are granular and the grains have a triangle shape. The films grow in a preferred orientation(002). The HRTEM images present the graphene-like structure of stacked layers with low density of stacking fault, and the interlayer distance of plane is measured to be about 0.63 nm. It shows a clear quasihoneycomb-like structure and 6-fold coordination symmetry. Room-temperature PL spectra for the atomic layer MoS_2 under the condition of right and left circular light show that for both cases, the A1 and B1 direct excitonic transitions can be observed. In the meantime, valley polarization resolved PL spectra are obtained. XPS measurements provide high-purity samples aside from some contaminations from the air, and confirm the presence of pure MoS_2. The stoichiometric mole ratio of S/Mo is about 2.0–2.1, suggesting that sulfur is abundant rather than deficient in the atomic layer MoS_2 under our experimental conditions.     

Aligned growth and alignment mechanism of carbon nanotubes by hot filament chemical vapor deposition

Carbon nanotubes (CNTs) growth on Inconel sheets was carried out using hot filament chemical vapor deposition (HFCVD) in a gas mixture of methane and hydrogen. Scanning electron microscopy, transmission electron microscopy and field electron emission (FEE) measurement were applied to study the structure and FEE properties of the deposited CNTs. The effect of bias voltage and substrate surface roughness on the growth of vertically aligned carbon nanotubes was investigated. Well-aligned CNTs were synthesized by bias enhanced HFCVD. The results show that a bias of −500 V generates the best alignment. It has been observed that at the early growth stage, aligned and non-aligned CNTs are growing simultaneously on the unscratched sheets, whereas only aligned CNTs are growing on the scratched sheets. The results indicate that tip growth is not necessary for the electric field to align the CNTs, and larger catalyst particles created by scratching before the heat treatment can induce alignment of CNTs at the early growth stage. In addition, tree-like CNTs bundles grown on the scratched substrates exhibit better FEE performances than dense carbon nanotube forest grown on the unscratched substrates due to the reduced screen effect.     

Low-temperature growth of ZnO epitaxial films by metal organic chemical vapor deposition

ZnO films were grown on Al₂O₃ (0001) substrates by metal organic chemical vapor deposition at temperatures of T_g=150300 °C. Epitaxial growth was obtained for T_g200 °C. The in-plane orientation of the ZnO unit cells was found to change from a no-twist one with respect to that of the substrate at T_g=200 °C to a 30°-twist one at T_g=300 °C. Absorption and photoluminescence were observed from the film grown at 150 °C, although there was no evidence of epitaxial growth. Films grown at T_g200 °C exhibited smoother surfaces. Moreover, all the films grown at T_g=150300 °C revealed acceptor-related emission peaks, indicating the incorporation of acceptors into the films. PACS 81.15.Gh; 78.55.Et; 78.66.Hf     

Synthesis of carbon nanotubes on diamond-like carbon by the hot filament plasma-enhanced chemical vapor deposition method

Carbon nanotubes (CNTs) have attracted considerable attention as possible routes to device miniaturization due to their excellent mechanical, thermal, and electronic properties. These properties show great potential for devices such as field emission displays, transistors, and sensors. The growth of CNTs can be explained by interaction between small carbon patches and the metal catalyst. The metals such as nickel, cobalt, gold, iron, platinum, and palladium are used as the catalysts for the CNT growth. In this study, diamond-like carbon (DLC) was used for CNT growth as a nonmetallic catalyst layer. DLC films were deposited by a radio frequency (RF) plasma-enhanced chemical vapor deposition (RF-PECVD) method with a mixture of methane and hydrogen gases. CNTs were synthesized by a hot filament plasma-enhanced chemical vapor deposition (HF-PECVD) method with ammonia (NH₃) as a pretreatment gas and acetylene (C₂H₂) as a carbon source gas. The grown CNTs and the pretreated DLC films were observed using field emission scanning electron microscopy (FE-SEM) measurement, and the structure of the grown CNTs was analyzed by high resolution transmission scanning electron microscopy (HR-TEM). Also, using energy dispersive spectroscopy (EDS) measurement, we confirmed that only the carbon component remained on the substrate.