Charge conduction process and photoelectrical properties of Schottky barrier device based on sulphonated nickel phthalocyanine

In this paper, the optical and electrochemical properties of sulphonated nickel phthalocyanine (NiPcS_mix) were investigated. The ground state of spectra of NiPcS_mix show splitting of Q band in DMF, but the fluorescence spectra have only one band, suggesting that only some component of the sulphonated NiPc fluoresce. Since, the organic materials are described on the basis of molecular orbital energies, i.e. highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) instead of valence band and conduction band. Such energies were estimated from cyclic voltammetry and optical absorption measurements. The dark current–voltage characteristics of ITO/NiPcS_mix/Ag device in dark at room temperature shows a rectification behavior. At low voltages, current in forward direction was found to obey the diode equation, i.e. exponential increase in current with applied voltage and the conduction was controlled by thermionic emission mechanism. For relatively higher voltages, the conduction was dominated by a space charge limited conduction mechanism with single trap level of 0.34 eV. The J–V characteristics in dark and the comparison of photoaction spectra of the device with the optical absorption spectra of NiPcS_mix indicates the formation of Schottky barrier and Ohmic contact at Ag-NiPcS_mix and ITO-NiPcS_mix, respectively, in ITO/NiPcS_mix/Ag device. The junction parameters such as built in potential, potential barrier height, carrier concentration and width of depletion layer were estimated from the capacitance–voltage (C–V) measurement. The J–V characteristic under illumination shows photovoltaic effect. The power conversion efficiency of the device has been improved upon thermal annealing attributed to the enhancement in the both crystallinity of NiPcS_mix and charge carrier mobility due to the thermal treatment. We have also investigated the effect of PEDOT:PSS buffer layer in between ITO and NiPcS_mix on electrical and photovoltaic properties of the device.     

应变影响下单晶Ge薄膜热导率分析

利用非平衡态分子动力学模拟方法研究了应变对Ge薄膜热导率的影响。结果表明系统应变对单晶Ge薄膜热导率产生明显影响,热导率随着拉伸应变的增大而减小,随着压缩应变的增大而增大,得出声子速率降低以及薄膜表面重构是产生该模拟结果的内在原因。同时,采用修正的Callaway模型对NEMD结果进行理论验证,两种方法得到的结果吻合得较好。理论结果表明应变弛豫时间对Ge单晶薄膜的热导率产生了重要影响。     

Grain size effect on structural, electrical and mechanical properties of NiTi thin films deposited by magnetron co-sputtering

In the present study NiTi films have been deposited on Si (100) substrates by dc magnetron co-sputtering in the temperature range from room temperature to 923 K. The crystallization, surface morphology and structural features were studied using X-ray diffraction (XRD), atomic force microscope (AFM), field emission scanning electron microscope (FESEM) and high resolution transmission electron microscope (HRTEM). In situ hot stage atomic force microscope was used to investigate the micro-structural changes during phase transformation in these films. Substrate temperature was found to have a great impact on the structural features and phase transformation behavior of NiTi films. The grain size and the crystallization extent increase with the increase in substrate temperature. Nanoindentation tests of these films were conducted at room temperature. Low hardness and depth recovery ratio was observed in case of the film deposited at substrate temperature of 923 K that could be due to the dominance of martensite phase at room temperature which results in more plastic deformation. The electrical properties of the films were studied using four probe resistivity method. Electrical resistance versus temperature plots show that grain size of NiTi films plays an important role in their electrical properties. NiTi based shape memory alloys exhibit a very interesting martensite to austenite phase transformation as crystal structure changes from monoclinic to cubic upon heating close to room temperature. The characteristics of this transformation are of immense technological importance due to a variety of MEMS applications.     

Effect of the PbOx thickness on the microstructure and electrical properties of PLT thin films prepared by RF magnetron sputtering

The (Pb_0.90La_0.10)Ti_0.975O₃ (PLT) thin films with different thicknesses of PbO_x buffer layers were deposited on the Pt(111)/Ti/SiO₂/Si(100) substrates by RF magnetron sputtering technique. The PbO_x buffer layer leads to the (100) orientation of the PLT thin films. Effects of the PbO_x thickness on the microstructure and electrical properties of the PLT thin films were investigated. The experimental results show that the PbO_x thickness plays an important role on the orientation, phase purity, domain structure, and electrical properties of the PLT thin films. The PLT thin films with proper PbO_x thickness possess highly (100) orientation, high phase purity, strong intensity of out of plane polarization, and good electrical properties. It is concluded that the PbO_x thickness between PLT thin films and Pt coated Si substrate is very critical to obtain good electrical properties.     

Influences of vacancy defects on thermal conductivities of Ge thin films

The effects of vacancy defects on the thermal conductivity of Ge thin films were investigated by employing molecular dynamics(MD) simulations and theoretical analysis based on the Boltzmann equation.Both the MD and theoretical results show that the lattice thermal conductivity dramatically decreases with the increasing of vacancy concentration at 400 and 500 K.In addition,the dependence of vacancy concentration on the thermal conductivity of Ge thin films becomes less sensitive as the temperature increases.Theoretical results also confirm that the major part of the lattice thermal conductivity reduction is associated with the point-defect scattering and phonon-phonon scattering processes.     

Investigation of 3D anisotropic electrical conductivity in TIG welded 5A06 Al alloy using eddy currents

Electrical conductivity undergoes changes in the weld zones of the material. In this study, its anisotropic components along longitudinal, transverse and through-thickness directions have been investigated nondestructively using circular eddy current probe with Hall Effect sensor. The electromagnetic forward model has been solved with material resistivity input profiles corresponding to tensile and compressive residual stresses in a typical welded joint. For reconstruction of 3D anisotropic electrical conductivity, constrained linear least square optimization has been used. Compared with measurements based on calibration with homogeneous specimen or calculated assuming isotropic material properties in forward model, the results indicate that change in conductivity is significantly larger. A quantitative comparison is made between results based on isotropic and anisotropic material models. The conductivity mapping is required for residual stress measurement in components and structures.     

Effective electrical conductivity of functional single-wall carbon nanotubes in aqueous fluids

In this paper, for the first time, we have used a coaxial fixture to successfully obtain the relatively low and precise electrical conductivity values of nanofluids based on functional sulfonated carbon nanotubes. From 0 to 0.5 wt.% nanotube loading, the conductivity increased approximately 13 times. However, no percolation threshold phenomenon is observed. The linear conductivity increase versus the weight percentage indicates that the dominant conduction mechanism might be the ionic conduction, which is in agreement with the chemical structure of functional SWNT (anion SO₃⁻ group).     

Optical and electrical properties of amorphous thin films in Gex Te1-x system

Ge_xTe_1-x thin films of different compositions are prepared on glass substrates by sputtering deposition. The optical transmittance, reflectance, electrical resistivity of the thin films axe measured as a function of composition,x. The optical energy gap and the electrical resistivity is highest when Ge_xTe_1-x enters the GeTe₂ phase due to its very ordered network structure resulting in narrow localized states in the amorphous energy band structure. Also, the refractive index and the extinction coefficient are lowest at the GeTe₂ composition since the absorption tailing near the band edge is minimum.     

沉积参数及退火条件对AlN薄膜电学性能的影响

利用射频反应磁控溅射在Si（100）基底上沉积AlN介质薄膜,并在不同温度下对薄膜进行快速退火。通过抗电强度测试仪、电容电压测试C-V、X射线衍射仪、电子能谱仪、原子力显微镜和椭圆偏振仪等研究薄膜的击穿电压、介电常数、晶体结构、化学成分、表面形貌及薄膜的折射率。结果表明：溅射功率和溅射气压对薄膜的击穿电压有很大的影响,溅射功率为250 W,气压为0.3 Pa时薄膜的抗电性能较好;薄膜的成分随溅射气压发生变化,N与Al摩尔比最高达到0.845;随退火温度的增加,薄膜晶体结构发生非晶-闪锌矿-纤锌矿的转变;薄膜的折射率随退火温度的升高而增加。     

Dependence of activation energy and pre-exponential factor on electric field in amorphous thin films of Se70Te30−xZnx

The present paper reports the effect of electric field on the electrical parameters (activation energy and pre-exponential factor) in amorphous thin films of Se₇₀Te_30−xZn_x (x = 0, 6, 8). It is observed that, in a particular composition, at low electric field up to 10³ V/cm neither activation energy nor pre-exponential factor depend on electric field as expected in case of ohmic region. However, at higher electric fields where non ohmic region is observed, activation energy and pre-exponential factor both vary with electric field. Similar behavior is observed in all the compositions used in this study. A correlation between activation energy and pre-exponential factor is also observed in these alloys, which is known as Meyer-Neldel rule (MN rule). Further MN rule is also observed in the present case which is explained by the model suggested by Yelon and Movaghar responsible for MN rule in chalcogenide glasses.     

Electrical d.c. conduction mechanism in some newly synthesized mono- and dipyridine quaternary salts in thin films

The study of temperature dependence of the electrical conductivity and thermoelectric power, for some recently synthesized quaternary salts of bipyridine and indolisine pyridine, is reported. Thin film samples (d = 0.10–0.60 μm) deposited from dimethylformamide solutions onto glass substrates were used. Organic films with reproducible electronic transport properties can be obtained if, after deposition, they are submitted to a heat treatment within temperature range 290–500 K.The studied organic salts behave as typical p-type semiconductors. The activation energy of electrical conduction laid in the range 1.40–1.75 eV, while the ratio of charge carrier mobilities ranged between 0.77 and 0.93.The correlations between determined semiconducting parameters and specific molecular structure of the compounds have been discussed.In the higher temperature range (360–500 K), the electronic transport in examined compounds can be interpreted in terms of band gap representation model, while for lower temperatures, Mott's variable-range hopping conduction model may be conveniently used.     

Investigation of photoinduced change of dielectric and electrical properties of indium (III) phthalocyanine and fullerene doped nematic liquid crystal

In this work, we have studied photoinduced dielectric and electrical properties of E63 nematic liquid crystal (E63-LC) materials doped with indium (III) metallo phthalocyanine (In-MPc) and fullerene (C₆₀) in dark and under UV illumination. Doping concentration of In-MPc in E63-LC was chosen to be 5 wt%, whereas a trace amount of C₆₀ was used in investigated samples. Real and imaginary parts of dielectric permittivity were investigated in the frequency range of 100 Hz–10 MHz by using dielectric spectroscopy technique (DST). It was observed that doping agents and UV illumination enhanced the real part of dielectric permittivity at low frequencies, which was thought to originate from photoinduced charge transfer between In-MPc and C₆₀ caused by extra dipole strength in LC medium. In addition to that, critical frequency (f_c) and relaxation time (τ) were obtained and analyzed for all investigated samples. Photoelectrical characteristics of hybrid LC structures were carried out by current–voltage measurements. A major increase in electrical conductivity was observed in In-MPc and C₆₀ doped LC structures under UV irradiation.     

Epitaxial PMN-PT thin films grown on buffered Si substrates using ceramic and single-crystal targets

Epitaxial 0.65Pb(Mg_1/3Nb_2/3)O₃-0.35PbTiO₃ (PMN-PT) thin films were deposited on LSCO/CeO₂/YSZ tri-buffered Si substrate by pulsed laser deposition (PLD) using sintered ceramic and single-crystal targets. The PMN-PT films deposited using both targets were single crystalline and exhibited cube-on-cube growth epitaxy with the substrate. The films deposited using the single-crystal target showed higher crystallinity and a smoother surface morphology than those grown using the ceramic target. The crystallinity of films can be affected by the in-plane lattice mismatch of PMN-PT/LSCO interfaces. The low density and low absorption coefficient of the sintered ceramic target were responsible for the severe compositional deviation from the desired stoichiometry of the PMN-PT films. Dielectric constants of approximately 1926 and 1540 at 10 kHz were obtained for the films deposited using the single-crystal and sintered ceramic target, respectively. In addition, the PMN-PT films fabricated using the single-crystal target exhibited well-developed polarization hysteresis loops with a remnant polarization of 11.9 μC/cm². Single-crystal targets are an indispensable candidate for the growth of epitaxial PMN-PT films with high crystallinity and good electrical properties.     

New technique of VAR investigations of thin films on thick substrates

A new technique of variable angle reflectometry (VAR) investigations of thin films on thick, transparent, parallel-sided substrates is presented. This technique uses spatial distribution of intensity of reflected radiation of a sample illuminated with a light beam of finite diameter. The experimental results obtained for amorphous silicon (a-Si) were fitted with theoretical dependencies taking into account the optical inhomogeneity over the film thickness. This inhomogeneity was described by values n_f, α_f, n_b and α_b of the real part of the refractive index and absorption coefficient at the surfaces of the film. The investigated film was also characterized by the average over its thickness values of the real part of the refractive index and absorption coefficient . For the investigated a-Si

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. It can be suggested that the presented investigations of optical inhomogeneity of thin films of a-Si should be taken into serious consideration for optimized technological conditions.     

Antimicrobial properties of diamond-like carbon-silver-platinum nanocomposite thin films

Silver and platinum were incorporated within diamond-like carbon (DLC) thin films using a multicomponent target pulsed laser deposition process. Transmission electron microscopy of the DLC-silver and DLC-platinum composite films reveals that these films self-assemble into particulate nanocomposite structures that possess a high fraction of sp ³-hybridized carbon atoms. Nanoindentation testing of DLC-silver nanocomposite films demonstrates that these films possess hardness and Young’s modulus values of approximately 35 and 350 GPa, respectively. DLC-silver-platinum films demonstrated exceptional antimicrobial properties against Staphylococcus and Pseudomonas aeruginosa bacteria. This paper was presented at the International Symposium on Manufacturing, Properties, and Applications of Nanocrystalline Materials sponsored by the ASM International Nanotechnology Task Force and TMS Powder Materials Committee on October 18–20, 2004 in Columbus, OH.     

Characterization of chromium thin films by sputter deposition

In this study, a systematic investigation on the deposition of Cr-CrO_x bi-layer film was performed by magnetron DC sputtering. The X-ray photoelectron spectrometer (XPS) examining the bare Cr film showed that the peaks of Cr 2P_3/2 and Cr 2P_1/2 appeared in the Cr thin film associated with the presence of a 12 nm oxide layer. The transmission was reduced to zero as the Cr film exceeded 100 nm in thickness. The reflection saturated at a value of ≈55% when the thickness of the Cr film reached 30 nm. The optical density exceeded 3.50 with a Cr film thickness over 150 nm. In order to reduce the reflection of the film to a level of ≤4%, a Cr-CrO_x bi-layer thin film was prepared. Overall, a Cr-CrO_x bi-layer film with the Cr layer 130 nm and the CrO_x layer 40 nm in thickness reported a transmission of zero, a reflection of 3.82% and an optical density of 4.04, all meeting the requirements of anti-reflection black matrix (BM) for display applications.     

Concentration-dependent behavior of hydrogen in Al-doped ZnO thin films

The Al-doped ZnO thin films were synthesized by aerosol-assisted chemical vapor deposition. The concentration-dependent behavior of hydrogen in the films was discussed, finding that as hydrogen is introduced at a relatively low level, it tends to take the oxygen vacancy site and form a hydrogen-oxygen vacancy complex which behaves as a shallow donor, on the other hand it reduces the solubility of the substitutional Al; then higher hydrogen concentration results in the formation of H₂ neutral molecular complex.     

Transmission photoacoustic spectroscopy analysis of CuIn0.75Ga0.25Se2 thin films

Photoacoustic spectroscopy (PAS) has proved to be an effective technique for the evaluation of the inherent defect population in a wide range of materials for various applications. This paper demonstrates the use of this technique in transmission mode, and hence, evaluates the optical properties of flash-evaporated CuIn_0.75Ga_0.25Se₂ (CIGS) thin films. Both the photoacoustic and transmission spectra were recorded at room temperature using high-resolution near-IR of the gas-microphone-type PAS, which revealed a very broad transmission region (about 300 meV) near the fundamental band edge in the as-grown CIGS thin films due to the presence of several shallow defect levels. The postdeposition heat treatment of the samples under Se ambient, followed by annealing under inert and forming gas ambient, showed significant changes in the behavior of the PAS spectra, particularly near the fundamental band edge. The absorption coefficient has been derived from these spectra to determine the energy band gap values and the activation energies for several defect related energy levels. Using PAS, the energy band gap values were in the range of 1.197 to 1.202 eV. The optical transmission spectra were also recorded from the routinely used spectrophotometer. The transmission data was used to determine the energy band-gap values, which were calculated to be in the range from 1.159 to 1.194 eV. These values were found to be in good agreement with each other, as well as with values reported in the literature. This paper was presented at the fourth International Surface Engineering Congress and Exposition held August 1–3, 2005 in St. Paul, MN.     

Cu掺杂对Be薄膜微结构的影响(英文)

利用离子束溅射法在硅基底上制备高纯Be薄膜并实现Cu元素的可控掺杂,利用X射线能谱、扫描电镜、X射线衍射以及透射电镜等对Cu掺杂Be薄膜进行表征分析。研究结果表明:Cu元素在Be膜内分布均一,且Cu掺杂量对Be薄膜的微观结构有显著影响。Cu掺杂能抑制Be晶粒生长,Be晶粒随着薄膜中Cu含量的增多而减小,并且尺寸分布更加均匀;Cu掺杂影响Be晶粒的生长取向,使其形成更为紧凑的薄膜结构。这些因素使得掺杂Cu的Be薄膜的表面粗糙度明显降低。