Electrochemical and surface characterisation of carbon-film-coated piezoelectric quartz crystals

The electrochemical properties of carbon films, of thickness between 200 and 500 nm, sputter-coated on gold- and platinum-coated 6 MHz piezoelectric quartz crystal oscillators, as new electrode materials have been investigated. Comparative studies under the same experimental conditions were performed on bulk electrodes. Cyclic voltammetry was carried out in 0.1 M KCl electrolyte solution, and kinetic parameters of the model redox systems Fe(CN)₆^3−/4− and [Ru(NH₃)₆]^3+/2+ as well as the electroactive area of the electrodes were obtained. Atomic force microscopy was used in order to examine the surface morphology of the films, and the properties of the carbon films and the electrode-solution interface were studied by electrochemical impedance spectroscopy. The results obtained demonstrate the feasibility of the preparation and development of nanometer thick carbon film modified quartz crystals. Such modified crystals should open up new opportunities for the investigation of electrode processes at carbon electrodes and for the application of electrochemical sensing associated with the EQCM.     

Hybrid temperature effect on a quartz crystal microbalance resonator in aqueous solutions

The quartz crystal microbalance(QCM) is an important tool that can sense nanogram changes in mass. The hybrid temperature effect on a QCM resonator in aqueous solutions leads to unconvincing detection results. Control of the temperature effect is one of the keys when using the QCM for high precision measurements. Based on the Sauerbrey's and Kanazawa's theories, we proposed a method for enhancing the accuracy of the QCM measurement, which takes into account not only the thermal variations of viscosity and density but also the thermal behavior of the QCM resonator. We presented an improved Sauerbrey equation that can be used to effectively compensate the drift of the QCM resonator. These results will play a significant role when applying the QCM at the room temperature.     

Potentiostatic and cyclic voltammetric deposition of nanostructured manganese oxide for supercapacitor applications

Nanostructured manganese oxide was produced by potentiostatic and cyclic voltammetric deposition techniques from aqueous KMnO₄ solutions. Scanning electron microscopy (SEM) and X-ray diffraction were used to study the morphology and crystal structure of the deposited films. The electrochemical properties of deposited films, that obtained by two techniques, were investigated via performing the cyclic voltammetric tests. The results showed the higher specific capacitances of the nanostructured manganese oxide electrodes which have been produced via cyclic voltammetric deposition. The good retention was obtained for all synthesized electrode materials.     

Carbon ion beam-induced variation in orientation of crystal planes of polycrystalline Zn nanowires

In the present work, polycrystalline Zn nanowires are synthesised within polymeric templates by the electrochemical deposition technique. Free-standing Zn nanowires with diameters 100, 200, 400 nm were synthesised on copper substrate acting as cathode, using this technique. The synthesised nanowires were irradiated with 40 MeV C⁴⁺ ion beam for various fluencies at Inter University Accelerator Centre, New Delhi, India. The effect of carbon ion beam on the grain size and preferred orientation of crystal planes of Zn nanowires were studied. The Rigaku X-ray diffractometer was used for X-ray diffraction (XRD) spectra of pristine and irradiated Zn nanowires. Post irradiation XRD analysis showed variation in the intensity of peaks, indicating the change in the orientation of crystal planes of the material. The preferred orientation of the crystal lattice planes in the polycrystalline material was found using texture analysis. To quantitatively investigate the degree of preferred orientations, the texture coefficients (TC) were calculated. The variation of TC was used to demonstrate the effect of irradiation on preferred orientation.     

电场作用下5CB液晶分子的近壁面层黏弹性的QCM研究

利用石英晶体微天平(quartz crystal microbalance,QCM)研究了电场对5CB液晶分子的近壁面层黏弹性的影响.对QCM结果的分析发现,电场作用对液晶的黏度影响分为两部分,通过建立含吸附膜的双层膜模型,分析了QCM的两部分结果,发现电场对近壁面吸附层及体相层的影响是不同的.根据QCM的双层膜模型,对近壁面层液晶分子的黏弹性及膜厚进行了定量的分析计算,结果表明5CB在石英晶体上电极附近有一层约100nm厚的近壁面吸附层,其复剪切黏度随电场强度的增加而减小,这与5CB液晶的体相黏度变化规 关键词： 5CB液晶 石英晶体微天平 近壁面 黏弹性     

HCN气体在金属Cu、Zn表面吸附的密度泛函研究

基于密度泛函理论方法研究了HCN气体在Cu(100)、Cu(110)、Cu(111)、Zn(100)、Zn(110)、Zn(111)表面上不同吸附位点的吸附性质,计算并分析了吸附能、电荷转移、电子态密度的特征。研究表明：HCN在Cu不同表面的吸附能分布在-0.42~-0.29 eV区间内,为物理吸附。HCN在Zn不同表面的吸附能相差较大,Zn(111)表面Hollow吸附位点的吸附能为-1.57 eV,为化学吸附。吸附能较大时对应的HCN的键长键角变化率较大。HCN在Zn表面的吸附要强于在Cu表面的吸附。HCN吸附在金属表面后,电子从吸附剂表面转移到HCN上,同一吸附剂表面不同吸附位点的吸附能越大,电子转移数量越多。吸附后HCN态密度曲线整体向低能级移动,峰值降低,其结构变得更加稳定。     

Creation of nanoparticles and luminescence in Al2O3 crystal by Zn ion implantation

Single crystal α-Al₂O₃ wafers were implanted with 45 keV Zn ions up to a fluence of 1×10¹⁷ ions/cm², and were then subjected to furnace annealing in oxygen atmosphere at different temperatures. Various techniques have been applied to study the creation of nanoparticles (NPs), defects and their thermal evolutions, as well as their effects on optical properties of Al₂O₃. Our results clearly show that Zn NPs have been synthesized in the as-implanted sample and they begin to be oxidized at 500 °C. Two broad photoluminescence bands appear in the Zn ion-implanted samples and their intensities depend on the annealing temperatures. The results have been interpreted in view of creation of the defects and NPs, Zn atoms diffusion as well as their thermal evolution during annealing.     

Mechanistic study of the gas-phase chemistry during the spray deposition of Zn(O,S) films by mass spectrometry

The mass spectrometer, is a powerful tool to identify species and investigate reactions in the gas phase. In this work, the mechanism of aerosol assisted chemical vapor deposition (AACVD) of Zn(O,S) films prepared from H₂S and zinc acetylacetonate (Zn(acac)₂) precursor solutions is elucidated by mass spectrometry. The thermochemical behavior of Zn(acac)₂ is investigated by characterizing the influence of the solvent (H₂O or ethanol), the pH value of the precursor solution and the effect of the reactant H₂S, and by tracking gaseous intermediate products using mass spectrometry. Based on these results, a proton-promoted thermolysis mechanism for the AACVD Zn(O,S) film formation is then proposed, which is initiated by the hydrolysis with H₂O as the first stage, followed either by the rearrangement with an intramolecular proton or by the reaction with an extramolecular proton to produce ZnO or Zn(O,S). A real time mass tracking of the AACVD process reveals that only an adequate amount of H₂S promotes the chemical gas-phase decomposition and sulfurization process, while an excess of H₂S depletes the gaseous Zn(acac)₂ concentration and consequently reduces the film growth rate. The knowledge of the thermal decomposition process helps to optimize synthesis conditions and to adjust film properties to meet the requirement of the application in chalcopyrite or kesterite thin film solar cells.     

In Situ Studies on Reaction Mechanisms in Atomic Layer Deposition

During the past decade, atomic layer deposition (ALD) has become an important thin-film deposition method in microelectronics industry, and it has also gained a lot of interest in many other areas, such as nanotechnology. The success of ALD is built on proper surface reactions. In this paper, in situ reaction mechanism studies on ALD processes are reviewed with the aim of building a general understanding on similarities and differences exhibited by various processes and process groups. Also, levels of understanding reaction mechanisms in ALD are discussed. The main methods used to study ALD chemistry in situ under typical process conditions are quadrupole mass spectrometry (QMS), quartz crystal microbalance (QCM), and infrared (IR) spectrometry. These are presented in detail in the review. Various other optical methods, ellipsometry in particular, have been used to study ALD processes too, but they provide little information about the reaction mechanisms. Competent in situ investigations solve the ALD reaction mechanism as balanced equations for the ALD half-reactions. The majority of ALD processes are exploiting ligand exchange reactions, where the ligands of the metal precursor are eliminated by bonding to the Lewis acids of the nonmetal precursors, most commonly hydrogen. These volatile byproducts are usually released during both precursor pulses, and determining their relative amounts is the important task in reaction mechanism studies of such processes. These processes are mechanistically fairly well understood, though some of these also display side-reactions to the ligand exchange reactions. There are also whole groups of processes that are using chemistry almost entirely different from the ligand exchange reactions. The most important such processes involve combustion chemistry, with oxygen, oxygen plasma, or ozone as a precursor or co-reactant. The mechanisms of these processes are complicated and less understood compared with the mechanisms of the ligand exchange reaction processes.     

3 T强磁场对真空蒸发Zn薄膜晶体结构的影响

在3 T强磁场下采用真空蒸发沉积在玻璃基片上制备了三种厚度分别为1,2,3 μm的Zn薄膜,并和无磁场下制备的薄膜进行了对比研究.对施加磁场和无磁场环境下制备的试样分别进行了X射线衍射研究.研究表明,3 T磁场下制备的Zn薄膜都是沿（002）面取向,而0 T磁场下制备的薄膜随着厚度的增加c轴取向逐渐减弱. 3 T磁场的取向作用可以维持Zn晶粒沿着c轴取向.利用扫描电子显微镜对薄膜表面形貌的研究发现,施加磁场制备的Zn薄膜表面晶粒要比无磁场条件下制备的薄膜有明显的细化.对磁场下Zn原子团形成进行了热力学分析,推导了磁场作用下的临界形核半径r^*_M和临界形核自由能ΔG^*_M.初步分析表明,r^*_M和ΔG^*_M减小从而增加临界形核浓度是Zn晶粒细化的原因. 关键词： 强磁场 晶体结构 真空蒸发沉积 薄膜     

Research on tribological behaviors of composite Zn/ZnS coating under dry condition

A composite Zn/ZnS coating was prepared by a novel compound technology-combining high velocity arc spraying and low temperature ion sulfurizing in this paper. The surface and cross-section morphologies were observed by scanning electron microscopy (SEM). The X-ray diffraction (XRD) pattern for the Zn/ZnS coating implies that it mainly consists of Zn and ZnS. The nanohardness and elastic modulus were measured by a nano-indentation tester. The tribological behaviors were investigated on a ball-on-disk wear tester under dry condition. The results showed that the friction coefficient and worn depth of the composite Zn/ZnS coating were low and stable, indicating that it had excellent friction-reduction and anti-wear properties under dry condition.     

Adsorption/desorption behavior of protein on nanosized hydroxyapatite coatings: A quartz crystal microbalance study

Protein separation relates closely to the interactions between proteins and various kinds of adsorbents. To obtain a direct and comprehensive understanding of the protein interaction at the solid/solution interface, quartz crystal microbalance (QCM) technique was employed to in situ investigate the adsorption process of bovine serum albumin (BSA) on nanosized hydroxyapatite coatings, and factors affecting its adsorption such as pH, solution ionic strength and temperature were discussed in detail. The adsorption kinetic parameter and the desorption of adsorbed BSA caused by phosphate buffer solution (PBS) introduction were investigated and discussed as well, and an adsorption/desorption mechanism has been proposed. The obtained information suggests that QCM is a useful method for monitoring the adsorption/desorption behavior of BSA on nanosized hydroxyapatite coating.     

ATR–SEIR study of anions and water adsorbed on platinum electrode

Adsorbed species on bare Pt, and UPD-Pb or UPD-Cu/Pt electrodes were characterized in HClO₄ or H₂SO₄ solutions at various potentials using attenuated total reflection (ATR)–surface enhanced infrared absorption (SEIRA) spectroscopy. On the bare Pt electrode, anions were observed at 1120–1095 cm⁻¹ at +0.0 < E < +0.6 V, solvated by water molecules with OH stretching absorption at 3600 cm⁻¹ and HOH bending mode at 1610–1620 cm⁻¹. In addition to the S–OH totally symmetric mode at 950 cm⁻¹, adsorbed sulfate species gave two bands at 1230–1100 cm⁻¹ between 0.0 V < E < +0.8 V that are assigned to ν₃ (symmetric stretch of S–O in SO₃) of ions with different coordination based on the peak shift by isotope substitution. At more negative potential, solely water molecules adsorb on the bare Pt surfaces. In contrast, it was found that electrolyte anions such as bisulfate and with hydrating water molecules adsorb onto the UPD-Pb/Pt and UPD-Cu/Pt electrodes even at much negative potentials, e.g. −0.2 V for UPD-Pb.     

Dynamic scaling and optical properties of Zn（S,O, OH） thin film grown by chemical bath deposition

The scaling behavior and optical properties of Zn(S, O and OH) thin films deposited on soda-lime glass substrates by chemical bath deposition method were studied by combined roughness measurements, scanning electron microscopy and optical properties measurement. From the scaling behaviour, the value of growth scaling exponent β , 0.38±0.06, was determined. This value indicated that the Zn(S, O, OH) film growth in the heterogeneous process was influenced by the surface diffusion and shadowing effect. Results of the optical properties measurements disclosed that the transmittance of the film was in the region of 70%-88% and the optical properties of the film grown for 40 min were better than those grown under other conditions. The energy band gap of the film deposited with 40 min was around 3.63 eV.     

Overpotential deposition of Ag monolayer and bilayer on Au(1 1 1) mediated by Pb adlayer underpotential deposition/stripping cycles

Ultra-thin Ag films on the Au(1 1 1) surface were prepared via overpotential deposition (OPD) in the presence of Pb²⁺ ions. By carrying out repetitive Pb adlayer underpotential deposition (UPD) and stripping cycles during Ag bulk deposition, the two-dimensional growth of Ag films was significantly enhanced in high OPD. The Ag monolayer sample was made by comparing the voltammetry curves, in which the signatures for Pb adlayer UPD on Au(1 1 1) changed to that on Ag(1 1 1). As demonstrated by the X-ray specular reflectivity measurements, nearly complete monolayer and bilayer films can be made with optimized deposition procedures. On subatomic scale, however, we found that these films have significant higher root-mean-square displacement amplitudes than those underpotentially deposited Ag monolayer and bilayer on either Au(1 1 1) or Pt(1 1 1).     

Enhancements in intensity and thermal stability of Raman spectra based on roughened gold substrates modified by underpotential deposition of silver

In this study, electrochemically roughened gold is modified with underpotential deposition (UPD) silver to investigate the effects on enhancements in the intensity and the thermal stability of surface‐enhanced Raman scattering (SERS). The SERS of Rhodamine 6G (R6G) adsorbed on the UPD Ag‐modified Au substrate exhibits a higher intensity by six‐fold of magnitude, as compared with that of R6G adsorbedon the unmodified Au substrate. Moreover, the SERS enhancement capabilities of UPD Ag‐modified Au and unmodified Au substrates are seriously depressed at temperatures higher than 200 and 150 °C, respectively. It indicates that the modification of UPD Ag can significantly depress the thermal destruction of SERS‐active substrates. Copyright © 2009 John Wiley & Sons, Ltd.     

光谱及电化学方法研究大黄酸与牛血清白蛋白的相互作用

采用荧光光谱、紫外光谱和圆二色光谱法并结合电化学方法,研究了大黄酸与牛血清白蛋白之间的相互作用。结果表明:大黄酸对牛血清白蛋白有较强的荧光猝灭作用且为静态猝灭,并计算得出不同温度下其结合常数(KA)与结合位点数(n)分别为:3.67×105,0.95(298 K);2.60×104,0.83(309 K)。由热力学参数确定它们间的作用力主要是静电引力,并依据F rster能量转移理论求得其结合距离为3.28 nm,同步荧光光谱及圆二色谱表明大黄酸对牛血清白蛋白的构象产生影响。     

利用ICP-AES分析大豆体内Mn和Zn分配及收支平衡

长期定位试验和ICP-AES测试相结合,研究了下辽河平原土壤有效Mn和Zn浓度变化以及不同施肥制度下大豆体内Mn和Zn浓度与含量的变化。结果表明：下辽河平原土壤有效Zn浓度已濒临临界值,应加强对其监测;大豆籽实和秸秆体内Zn浓度受施肥影响变化较小;而籽实中Mn浓度受施肥影响变化较大,且NPK和NPKO处理显著高于O和CK处理;养分循环再利用在增加大豆生物量的同时,Mn和Zn携出亦呈增加趋势;土壤-作物系统中,Mn和Zn均出现收支赤字,其赤字大小顺序为NPKO＜O＜CK＜NPK,表明养分循环可以显著减缓这种赤字,使生态系统更可持续。     

Theoretical study for magnetic effect in dissociative adsorption of oxygen to a platinum monolayer on Ni(110) surface

We investigate oxygen dissociative adsorption to a platinum monolayer on Ni(110) surface (Pt/Ni(110)) by density functional theory. We have shown that the activation barrier on Pt/Ni(110) is lower than that on a clean Pt(001) surface. This may be due to the effect of magnetization of Pt surface. The reason of decrease of activation barrier can be attributed to the flow of electrons from oxygen to platinum surface because the d orbitals have spin polarization at the Fermi level where the down spin d orbitals are unoccupied.