Response of chemical vapor deposition diamond detectors to X-ray

The outstanding properties of diamond, such as radiation hardness, high carrier mobility, high band gap and breakdown field, distinguish it as a good candidate for radiation detectors. The detector's performance is strongly limited by the concentration of defects (grain boundaries and/or impurities) in chemical vapor deposition (CVD) diamond. We report the response of free-standing CVD diamond with a thickness of 300 μm and area of 2×2 cm², synthesized by a hot filament chemical vapor deposition (HFCVD) technique, to 5.9 keV X-ray radiation from a ⁵⁵Fe source. The linear I-V characteristics indicate that CVD diamond has good ohmic contacts. This detector also shows good results such as dark-current of 10⁻⁸ A, photocurrent of 10⁻⁶ A, energy resolution <0.4%, and a high ratio of signal to noise.     

Role of surface and interface science in chemical vapor deposition diamond technology

Diamond is well known as the hardest material in nature. It also has other unique bulk physical and mechanical properties, such as very high thermal conductivity and broad optical transparency, which enable a number of new applications now that large areas of diamond can be fabricated by the new diamond plasma chemical vapor deposition (CVD) technologies. However, some of the most interesting properties of diamond, including the ability to be grown over large areas by CVD processes, result not from its bulk properties but from its special and unique surface chemistry. The surface chemistry derived properties are as remarkable as the bulk properties, and in the end may enable the development of new applications, technologies, and industries which are at least as important as those based on the bulk properties. Some of these surface properties are extreme chemical inertness, low surface energy, low friction coefficients, negative electron affinity, biological inertness, and high over-voltage electrode behavior. The surface science and some of the interesting ongoing research in these areas are explored and illustrated, and unresolved questions are highlighted.     

化学气相沉积金刚石薄膜探测器对α粒子的电荷收集效率

实验测量了自行研制的三明治电极结构化学气相沉积(CVD)金刚石薄膜探测器在室温下对241Am, 243Am 与244Cm α粒子的能谱响应,得到了其α粒子响应电荷收集效率随偏压的变化关系;获得了不同偏压下其相对平均电荷收集效率及响应谱下降沿10%处的相对电荷收集效率。结果表明：所研制的CVD金刚石薄膜探测器性能稳定,对α粒子响应的电荷收集效率随偏压的增加而趋于饱和,对α粒子平均电荷收集效率达33.5%,谱下降沿10%处的电荷收集效率达57%。     

化学气相沉积金刚石薄膜探测器对α粒子的电荷收集效率

 实验测量了自行研制的三明治电极结构化学气相沉积(CVD)金刚石薄膜探测器在室温下对241Am, 243Am 与244Cm α粒子的能谱响应,得到了其α粒子响应电荷收集效率随偏压的变化关系;获得了不同偏压下其相对平均电荷收集效率及响应谱下降沿10%处的相对电荷收集效率。结果表明：所研制的CVD金刚石薄膜探测器性能稳定,对α粒子响应的电荷收集效率随偏压的增加而趋于饱和,对α粒子平均电荷收集效率达33.5%,谱下降沿10%处的电荷收集效率达57%。     

PECVD制备AZO（ZnO:Al）透明导电薄膜

采用PECVD（等离子体增强化学气相沉积）工艺在普通玻璃和Si基上制备出了方块电阻低至89 Ω,可见光透过率高达79%,对基体附着力强的多晶态的AZO（ZnO:Al）薄膜.采用PECVD法制备AZO薄膜是一种有益的尝试,AZO透明导电薄膜不仅具有与ITO（透明导电薄膜,如In₂O₃:Sn）可比拟的光电特性,而且价格低廉、无毒,在氢等离子体环境中更稳定,所获结果对实际工艺条件的选择具有一定借鉴作用和参考价值. 关键词： AZO（ZnO:Al） 等离子体增强化学气相沉积 透明导电薄膜     

Deposition of SiOx layer by plasma-enhanced chemical vapor deposition for the protection of silver (Ag) surfaces

Silver surfaces have been treated with plasma-enhanced chemical vapor deposition to produce SiO₂-like coatings for possible applications in the jewelry industry. Different experimental conditions have been tested in order to optimize the protective effectiveness of the deposited layers. Samples were analyzed with optical and scanning electron microscopy and energy-dispersive spectrometry.     

Analyses of surface temperatures on patterned sapphire substrate for the growth of GaN with metal organic chemical vapor deposition

The surface temperature of cone-shaped patterned sapphire substrate (PSS) in GaN epitaxial growth by MOCVD and its relation to forced convection conditions and substrate surface topography were systematically investigated. Calculations using finite element method (FEM) exhibited that increase of substrate thickness would reduce surface temperature variation on PSS in typical growth condition. A hydrodynamics model under different chamber conditions is established, suggesting that carrier gas's velocity V_∞ plays a significant role on surface temperature of PSS in comparison with planar substrate. Also, carrier gas's pressure P_carrier is found to be another important factor on surface thermal distribution. Results of temperatures of surface with different pattern topographies suggested that an ideal PSS structure can confine the in-cell temperature discrepancy on surface into less than 0.4 K. Pattern scales of PSS and their influence on surface temperature variation were also discussed.     

Dynamics of rough interfaces in chemical vapor deposition: experiments and a model for silica films

We study the surface dynamics of silica films grown by low pressure chemical vapor deposition. Atomic force microscopy measurements show that the surface reaches a scale invariant stationary state compatible with the Kardar-Parisi-Zhang (KPZ) equation in three dimensions. At intermediate times the surface undergoes an unstable transient due to shadowing effects. By varying growth conditions and using spectroscopic techniques, we determine the physical origin of KPZ scaling to be a low value of the surface sticking probability, related to the surface concentration of reactive groups. We propose a stochastic equation that describes the qualitative behavior of our experimental system.     

Process characterization and mechanism for laser-induced chemical vapor deposition of a-Si : H from SiH4

The dependence of a-SiH film deposition by laser-induced decomposition of SiH₄ on the different process variables is studied. The gas phase temperature in the beam center, produced by CO₂ laser irradiation in parallel configuration, is estimated using a simple energy balance model. The surface temperature is measured with high accuracy employing a Ni sensor (250°–400 °C). The deposition rate and film properties such as the hydrogen content and the optical energy gap are determined as a function of these parameters. The production of H₂ (10%), Si₂H₆ (2%), and Si₃H₈ in the gas phase during laser irradiation is proved by a mass spectrometric analysis. The chemical reaction processes induced in the gas phase and at the surface are discussed. A mechanism explaining the main features of the complicated chemistry involved is developed.     

Plasma-assisted hot filament chemical vapor deposition of AlN thin films on ZnO buffer layer: toward highly c-axis-oriented,uniform, insulative films

c-Axis-oriented aluminum nitride (AlN) thin film with improved quality was deposited on Si(111) substrate using ZnO buffer layer by plasma-assisted hot filament chemical vapor deposition. The optical and electrical properties and surface morphology as well as elemental composition of the AlN films deposited with and without ZnO buffer layer were investigated using a host of measurement techniques: X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, field emission scanning electron microscopy (FESEM), and current–voltage (I–V) characteristic measurement. The XRD and XPS results reveal that the AlN/ZnO/Si films are free of metallic Al particles. Also, cross-sectional FESEM observations suggest formation of a well-aligned, uniform, continuous, and highly (002) oriented structure for a bi-layered AlN film when Si(111) is covered with ZnO buffer. Moreover, a decrease in full width at half maximum of the E₂ (high)-mode peak in Raman spectrum indicates a better crystallinity for the AlN films formed on ZnO/Si substrate. Finally, I–V curves obtained indicate that the electrical behavior of the AlN thin films switches from conductive to insulative when film is grown on a ZnO-buffered Si substrate.     

The importance of non-local shadowing for the topography evolution of a-C:H films grown by toluene based plasma enhanced chemical vapor deposition

The topography evolution of hydrogenated diamond-like carbon coatings deposited through toluene based capacitively coupled plasma enhanced chemical vapor deposition has been studied experimentally and with continuum growth models. The experimentally observed mound formation and surprisingly large growth exponents (β≈ 0.9±0.1) cannot be reproduced by familiar local stochastic differential equations that are successfully used for other thin film deposition techniques. Here we introduce a novel numerical approach to simulate a continuum growth model that takes into account non-local shadowing effects. We show that the major characteristics of the experimentally observed topography evolution can be accurately represented by this model.     

Uncovering the transformations that occur during the early stages of TiO2 CVD on Si (A perspective on the article, “TiO2 chemical vapor deposition on Si(111) in ultrahigh vacuum: Transition from interfacial phase to crystalline phase in the reaction limited regime” by A. Sandell et al.)

This perspective offers a brief summary of a series of publications that reveal insight into the nucleation of titanium oxide on different surfaces.     

Identification of two Ag‐2,2′:6′,2″‐terpyridine surface species on Ag nanoparticle surfaces by excitation wavelength dependence of SERS spectra and factor analysis: evidence for chemical mechanism contribution to SERS of Ag(0)–tpy

Measurement and interpretation of the excitation wavelength dependence of surface‐enhanced Raman scattering (SERS) spectra of molecules chemisorbed on plasmonic, e.g. Ag nanoparticle (NP) surfaces, are of principal importance for revealing the charge transfer (CT) mechanism contribution to the overall SERS enhancement. SERS spectra, their excitation wavelength dependence in the 445–780‐nm range and factor analysis (FA) were used for the identification of two Ag‐2,2′:6′,2″‐terpyridine (tpy) surface species, denoted Ag⁺–tpy and Ag(0)–tpy, on Ag NPs in systems with unmodified and/or purposefully modified Ag NPs originating from hydroxylamine hydrochloride‐reduced hydrosols. Ag⁺–tpy is a spectral analogue of [Ag(tpy)]⁺ complex cation, and its SERS shows virtually no excitation wavelength dependence. By contrast, SERS of Ag(0)–tpy surface complex generated upon chloride‐induced compact aggregate formation and/or in strongly reducing ambient shows a pronounced excitation wavelength dependence attributed to a CT resonance (the chemical mechanism) contribution to the overall SERS enhancement. Both the resonance (λ_exc = 532 nm) and off‐resonance (λ_exc = 780 nm) pure‐component spectra of Ag(0)–tpy obtained by FA are largely similar to surface‐enhanced resonance Raman scattering (λ_exc = 532 nm in resonance with singlet metal to ligand CT (¹ MLCT) transition) and SERS (λ_exc = 780 nm) spectra of [Fe(tpy)₂]²⁺ complex dication. Copyright © 2014 John Wiley & Sons, Ltd.