Characterization of optoelectronic properties of the ZnO nanorod array using surface photovoltage technique

Well-aligned ZnO nanorod array, synthesized by wet chemical bath deposition (CBD) method on conductive indium-in-oxide (ITO) substrate, was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. Surface photovoltage (SPV) technique based on a scanning Kelvin Probe system was employed to investigate the optoelectronic behavior of ZnO nanorod array. The surface photovoltage and its time-resolved evolution process are used to determine the energy level structure of the ZnO nanorod array.     

The effect of nitrogen incorporation on surface properties of silicon oxynitride films

In order to investigate the surface heterogeneity of silicon oxynitride films, we observed the nanoscale variation of the surface potential by Kelvin probe force microscopy (KFM), the molecular bonding characteristics by Fourier transform infrared spectrometry (FTIR), and the wetting behavior by contact angle measurement. Nitrogen incorporation into silicon oxynitride films influenced the decrease in the surface potential and the polar component of the surface free energy. We present the first correlation between the nanoscale measurement of the surface potential and the macroscopic measurement of the surface free energy in silicon oxynitride films grown by a standard plasma‐enhanced chemical vapor deposition (PECVD) technique. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photovoltage studies of clean and oxygen covered gallium arsenide

The work function and photovoltage of Ar bombarded and thermally annealed surfaces of GaAs have been examined with the retarding potential electron beam technique. The I–V curve obtained by this method is found to fit the theoretically prodicted dependence. The shift of the I–V curve under illumination is related to the photovoltage of the sample. The shift of the I–V curve during the adsorption of oxygen can be explained by a first-order-kinetics dependence of the adsorption on oxygen. The dependence of the photovoltage on light intensity is found to deviate from that measured with the Kelvin technique. The photovoltage is observed to fall off at photon energies below the bandgap energy. At energies above the bandgap, there is structure which is possibly due to excitons. Below the bandgap the photovoltage is sensitive to surface conditions and is much lower for an uncleaned sample.     

Physical properties of ZnS thin films prepared by chemical bath deposition

Zinc sulphide thin films are deposited on SnO₂/glass using the chemical bath deposition technique. X-ray diffraction and atomic force microscopy are used to characterize the structure of the films; the surface composition of the films is studied by Auger electrons spectroscopy, the work function and the photovoltage are investigated by the Kelvin method. Using these techniques, we specify the effect of pH solution and heat treatment in vacuum at 500 °C. The cubic structure corresponding to the (1 1 1) planes of β-ZnS is obtained for pH equal to 10. The work function (Φ_material − Φ_probe) for ZnS deposited at pH 10 is equal to −152 meV. Annealing at 500 °C increases Φ_m (by about 43 meV) and induces the formation of a negative surface barrier. In all cases, Auger spectra indicate that the surface composition of zinc sulphide thin films exhibits the presence of the constituent elements Zn and S as well as C and O as impurity elements.     

A new approach to modelling Kelvin probe force microscopy of hetero-structures in the dark and under illumination

A numerical method is proposed to model Kelvin probe force microscopy of hetero-structures in the dark and under illumination. It is applied to FTO/TiO₂ and FTO/TiO₂/MAPbI₃ structures. The presence of surface states on the top of the TiO₂ layers are revealed by combining theoretical computation and experimental results. Basic features of Kelvin probe force microscopy under illumination, namely surface photovoltage, are simulated as well. The method paves the way toward further investigations of more complicated optoelectronic devices.     

Surface photovoltage investigations of Cd1−xMnxTe for x = 0.01 and 0.10

Surface photovoltage investigations of Cd_1−xMn_xTe monocrystals for x = 0.01 and 0.10 were performed in the temperature range between 100 and 300 K with a modified Kelvin method at a pressure of 10⁻⁵ Pa. The surfaces with orientation (110) were ground, polished with “Gamal”, and rinsed in acetone and alcohol. Three types of effects were observed on the surface spectroscopy curves: A sharp increase in photovoltage, connected with the electron band-to-band transitions for a photon energy equal to the energy gap. Photovoltage quenching attributed to the existence of surface states with energy just above the edge of the valence band. Increase in photovoltage in the range between 0.9 and 1.0 eV resulting from electron transitions between the valence band and energy states connected with manganese ions.     

一维液态泡沫渗流实验研究及表面能和粘性耗散分析

液态泡沫由大量气泡密集堆积在微量表面活性剂溶液中形成，是远离平衡态的软物质. 泡沫强制渗流在微观上是指以恒定流率输入的液体在气泡间隙内的微流动过程，是影响泡沫稳定的主要因素之一. 采用在表面活性剂溶液中添加微量色素以显示泡沫中液体流动的方法，确定了透射率与液体分率的对应关系，测量得到了一维液态泡沫强制渗流中渗流波传播规律以及液体分率的演变规律；理论推导了泡沫基本单元，即开尔文单元结构(Kelvin cell)的粘性耗散能表达式，并依据Surface Evolver软件计算得到了不同液体分率时开尔文单元结构对应的的表面能，并计算出了与实验系统对应的开尔文单元结构的表面能和粘性耗散. 基于开尔文单元结构内液体分率演变的准静态假设，分析了表面能和粘性耗散的演变规律.     

Photovoltage studies of n-type InP (100)

The transient photovoltage signals of n-type InP(100) have been studied by the retarding potential electron beam technique and are a sensitive function of several experimental parameters. The photovoltage decreases as the duration of the light exposure, and/or the intensity of the light is decreased. The photovoltage decreases sharply at energies less than the bandgap energy, which is temperature dependent, and also shows considerable structure at energies above the bandgap energy. The photovoltage is also sensitive to changes in the surface composition. Both the photovoltage and the work function decrease sharply after Ar bombardment.     

Microstrip notch filters based on open interconnected split ring resonators (OISRRs)

Two kinds of inorganic/organic hybrid junctions based on ZnO nanorods (NRs), i.e. two-layer planar heterojunction and embedded bulk composite structures, were fabricated on ITO glass substrates. Surface photovoltage (SPV) methods based on a Kelvin probe and a lock-in amplifier were respectively utilized to study the photogenerated charges at the surface and the interface in the ZnO-based hybrid junctions. Results indicate that the lock-in SPV response of the bulk composite structure is much higher than its planar counterpart in terms of intensity and spectral range. Therefore, ZnO NR/PF (poly(9,9-di-n-octylfluorenyl-2,7-diyl)) embedded bulk composite structures are more suitable and preferred for photovoltaic application.     

高速率沉积磁控溅射技术制备Ge点的退火生长研究

采用磁控溅射技术在Si衬底上以350?C沉积14 nm的非晶Ge薄膜,通过退火改变系统生长热能,实现了低维Ge/Si点的生长.利用原子力显微镜(AFM)和拉曼(Raman)光谱所获得的形貌和声子振动信息,对Ge点的形成机理和演变规律进行了研究.实验结果表明:在675?C退火30 min后,非晶Ge薄膜转变为密度高达8.5×109cm-2的Ge点.通过Ostwald熟化理论、表面扩散模型和对激活能的计算,很好地解释了退火过程中,Ge原子在Si表面迁移、最终形成纳米点的行为.研究结果表明用高速沉积磁控溅射配合热退火制备Ge/Si纳米点的方法,可为自组织量子点生长实验提供一定的理论支撑.     

Electronic structure and defect states of transition films from amorphous to microcrystalline silicon studied by surface photovoltage spectroscopy

In this paper, surface photovoltage spectroscopy (SPS) is used to determine the electronic structure of the hydrogenated transition Si films. All samples are prepared by using helicon wave plasma-enhanced chemical vapour deposition technique, the films exhibit a transition from the amorphous phase to the microcrystalline phase with increasing temperature. The film deposited at lower substrate temperature has the amorphous-like electronic structure with two types of dominant defect states corresponding to the occupied Si dangling bond states (D⁰/D^- and the empty Si dangling states (D⁺). At higher substrate temperature, the crystallinity of the deposited films increases, while their band gap energy decreases. Meanwhile, two types of additional defect states is incorporate into the films as compared with the amorphous counterpart, which is attributed to the interface defect states between the microcrystalline Si grains and the amorphous matrix. The relative SPS intensity of these two kinds of defect states in samples deposited above 300\du increases first and decreases afterwards, which may be interpreted as a result of the competition between hydrogen release and crystalline grain size increment with increasing substrate temperature.     

RF-PACVD of water repellent and protective HMDSO coatings on bell metal surfaces: Correlation between discharge parameters and film properties

Hexamethyldisiloxane (HMDSO) films have been deposited on bell metal using radiofrequency plasma assisted chemical vapor deposition (RF-PACVD) technique. The protective performances of the HMDSO films and their water repellency have been investigated as a function of DC self-bias voltage on the substrates during deposition. Plasma potential measurements during film deposition process are carried out by self-compensated emissive probe. Optical emission spectroscopy (OES) analyses of the plasma during deposition reveal no significant change in the plasma composition within the DC self-bias voltage range of −40 V to −160 V that is used. Raman and X-ray photoelectron spectroscopy (XPS) studies are carried out for film chemistry analysis and indicate that the impinging ion energy on the substrates influences the physio-chemical properties of the HMDSO films. At critical ion energy of 113 qV (corresponding to DC self-bias voltage of −100 V), the deposited HMDSO film exhibits least defective Si-O-Si chemical structure and highest inorganic character and this contributes to its best corrosion resistance behavior. The hardness and elastic modulus of the films are found to be bias dependent and are 1.27 GPa and 5.36 GPa for films deposited at −100 V. The critical load for delamination is also bias dependent and is 11 mN for this film. The water repellency of the HMDSO films is observed to be dependent on the variation in surface roughness. The results of the investigations suggest that HMDSO films deposited by RF-PACVD can be used as protective coatings on bell metal surfaces.     

Effect of annealing on the physical properties of thermally evaporated In2S3 thin films

The structural, compositional, morphological and optical properties of In₂S₃ thin films, prepared by thermal evaporation technique and annealed in sulfur ambient at different temperatures have been investigated. The grazing incident X-ray diffraction patterns have indicated polycrystalline form and predominantly cubic structure of annealed In₂S₃ films. The scanning electron microscopy revealed textured surface with uniformly distributed grains and the grain size increased with increase of annealing temperature. The optical parameters of the films have been determined using conventional transmission and reflection spectra as well as from surface photovoltage measurements.     

Direct determination of the hole density of states in undoped and doped amorphous organic films with high lateral resolution

We investigate the density of states (DOS) for hole transport in undoped and doped amorphous organic films using high lateral resolution Kelvin probe force microscopy. Measurements are done on field effect transistors made of N,N1-diphenyl-N, N1-bis(1-naphthyl)-1,10-biphenyl-4,4II-diamine undoped or p doped with tetrafluoro-tetracyanoquinodimethane. We determine the DOS structure of the undoped material, including an anomalous peak related to interfaces between regions of different surface potential, the DOS doping-induced broadening, and doping-induced sharp peaks on the main DOS distribution.     

Surface and interface dipoles on catalytic metal films

The work function changes introduced by hydrogen on the surface and at the metal-support interface of a thin Pd-film were studied by simultaneous Kelvin probe and C(V)-measurements. It is demonstrated how these techniques can be used at atmospheric pressures to yield information about catalytic metals and on chemical kinetics on the metal surface. The main purpose of the communication is to point out the correlation between the surface and interface dipoles on catalytic metal films. Furthermore since the interface dipole is only created by hydrogen atoms it is shown how this can be used in a more complex situation to independently monitor the hydrogen content of the metal films.     

配位超分子[Cu(phen)(H2O)2·SO4]的合成、结构及表面光电压光谱

采用水热合成法得到了新颖结构的配位超分子[Cu(phen)(H2O)2.SO4]。通过X射线单晶衍射、红外光谱(IR)、紫外光谱(UV-VIS-NIR)及荧光光谱进行了测定和分析指认结构分析表明:标题化合物中Cu离子的配位模式分为两种,与phen分子中的2个N原子和水分子中2个O原子是通过配位键直接配位的;与硫酸根离子中的2个O原子的配位是采取Cu离子与O原子之间形成氢键,该氢键使Cu离子和硫酸根离子中的2个O原子处于亚配位状态,因此使Cu离子处于扭曲的八面体几何构型中。晶体中存在着大量的氢键将化合物连成了1D双链结构。利用表面光电压光谱(SPS)和场诱导表面光电压光谱(FISPS)研究了化合物的表面光电行为。化合物的SPS在300～800nm范围内呈现出明显的2个正的光伏响应带。FISPS的结果显示化合物呈现出一定的p-型半导体的特征。     

Initial interaction of oxygen with aluminium single crystal faces: A LEED,AES and work function study

Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and work function (Kelvin probe) measurements have been used to study the initial interaction of clean Al(111), (100) and (110) surfaces with oxygen at room temperature. The oxidation process was found to be surface orientation dependent, but a common feature has been always observed on the three low-index surfaces: they show two distinct phases, i.e. a chemisorbed phase followed then by an oxidized phase. From analysis of AES, LEED and Kelvin probe results, an adsorption mechanism of O on Al for each surface orientation is proposed.     

The influence of atomic steps on the photoelectric properties of clean cleaved silicon as derived from the surface photovoltage

The correlation of structural and electrical properties of clean silicon surfaces cleaved in UHV was investigated quantitatively by the surface photovoltage, using light with an energy larger than the band gap of silicon. The surface photovoltage, which is a function of band bending and recombination probability, depends strongly on the appearance of atomic steps. The additional surface states vary with density and crystallographic orientation of the steps as well as with adsorption of oxygen. The experimental facts can be explained by accepting a shift of the Fermi level at the surface towards the valence band due to edge atoms. By measuring the change of sign of the surface photovoltage of crystals with various dopings an exponential temperature dependence of the ratio of the recombination probabilities r_v/r_c for transitions from and into the Surface states has been derived.     

Dependence of electron work function of Al-Mg alloys on surface structures and relative humidity

In many fields the determination of electronic structures of a solid material is a prerequisite in order to investigate its physical/chemical properties as well as related applications. The effect of surface structures and ambient environment on the electronic behavior is of both fundamental and practical significance. In this study, the electron work function (EWF) of Al-Mg alloys is investigated using a scanning Kelvin probe. The results show that the EWF decreases with the increase of surface smoothness, whereas surface oxidation layers would result in the increase of the EWF. Furthermore EWF is strongly dependent on the relative humidity, especially when the relative humidity is higher than 70%, implying that considerable care should be takenon such dependence in order to gain a meaningful parameter for the characterization of surface behavior.     

Preparation and probe analysis of Langmuir–Blodgett films with metal-containing dendritic and cluster structures

We aim to reveal the influence of?pH values of the working solution on spatial arrangement of metal-containing inclusions in the monolayer coatings prepared by Langmuir?CBlodgett (LB) technology and transferred to solid substrates with consequent modification of surface electrical properties. Consequently, films with inclusions in the form of dendrites and cluster shapes have been obtained. Submicron and micron lead-containing formations in Langmuir?CBlodgett films have been characterized by using the atomic force microscopy, Kelvin probe microscopy, and scanning electron microscopy methods. The results show that increasing?pH value of the subphase has caused the significant changes in the shape and composition of the inclusions in Langmuir?CBlodgett films. The synthesized inclusions on the solid substrate surface resulted in formation of the regions with the local electric fields and, as consequence, to significant modification of the structure and electrical properties. The location and length of the regions with surface potential disturbance depend on the shape of inclusions, and consequently, on?pH value of the subphase used in LB technology.