Mechanism of conductance switching: An optical investigation

Electronic conductance switching in devices based on thin films of an organic molecule has been studied. Switching between two conducting states has been induced by voltage pulse, while the states have been probed by optical and electrical measurements simultaneously. In situ optical measurements showed that electroreduction of molecules led to conductance switching and appearance of high-conducting state in the device. We could “write” or “erase” a state by applying electrical pulse and “read” it by measuring electronic absorbance and conductivity. The “write” and “read” processes have been carried out for many cycles to exhibit a correspondence between conductance switching and electrochromism.     

Mechanism of conductance switching: An optical investigation

Electronic conductance switching in devices based on thin films of an organic molecule has been studied. Switching between two conducting states has been induced by voltage pulse, while the states have been probed by optical and electrical measurements simultaneously. In situ optical measurements showed that electroreduction of molecules led to conductance switching and appearance of high-conducting state in the device. We could “write” or “erase” a state by applying electrical pulse and “read” it by measuring electronic absorbance and conductivity. The “write” and “read” processes have been carried out for many cycles to exhibit a correspondence between conductance switching and electrochromism.     

Electrical and switching properties of InSe amorphous thin films

In this work electrical and switching properties of InSe thin films have been studied.

The semiconductor compound InSe was obtained by direct synthesis from stoichiometric amounts of spectroscopically pure indium and selenium. By slow cooling of the synthesized InSe a polycrystalline material is obtained. The amorphous films were obtained by thermal evaporation under vacuum of the polycrystalline material on glass or pyrographite substrates.

From electrical measurements, it was found that for all films the dark electrical resistivity decreases with an increase in film thickness and temperature. The InSe compound exhibits non-linear I–V characteristics and switching phenomena. The threshold voltage decreases with increasing annealing temperature and increases with increasing film thickness.     

Size- and temperature-dependent thermoelectric and electrical properties of Bi88Sb12 alloy thin films

The thin films of Bi₈₈Sb₁₂ of different thicknesses have been vacuum deposited on glass and silicon substrates using the flash evaporation method. The structural characterization was carried out by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The composition and thicknesses of as-grown and annealed films were measured by the quartz crystal thickness monitor and Rutherford back scattering spectroscopy (RBS). The thermoelectric power and electrical resistivity measurement have been carried out on the films in the temperature range 100-300 K. The thickness dependences of electrical resistivity and thermoelectric power of thin films have been analyzed using the effective mean-free path model. The thermoelectric power factors of films have been calculated and the nature of carrier scattering in these films has been reported.     

Structural and spectral analysis of thin films of Fe---Cr alloys

A structural X-ray analysis and an analysis of chemical composition using X-ray fluorescence have been carried out for thin films of Fe---Cr alloys of different compositions deposited onto glass substrates in a high vacuum. A nomogram which enables the determination of the percentage composition and the thickness of thin films in relation to the intensity of fluorescence radiation has ben derived. Some electrical parameters of the films have also been measured and quantitative changes of these parameters corresponding to films of different crystalline structures and alloy phases have been found.     

Ag-TCNQ薄膜电双稳态特性的XPS研究

本文采用X光电子谱仪 (XPS)研究了Ag TCNQ薄膜的电双稳态特性。对TCNQ粉末、热处理前后的TCNQ薄膜及Ag TCNQ薄膜作了分析。结果发现 ,真空蒸镀及大气环境中热处理不会引起TCNQ化学状态的变化 ,而热处理会促使Ag与TCNQ发生反应 ,薄膜电双稳态特性的优劣则与反应程度有关。最后讨论了这一现象的可能机理     

Studies on the photoconductivity of vacuum deposited ZnTe thin films

The present paper reports the analysis of photoconductivity of vacuum deposited zinc telluride (ZnTe) thin films as a function of substrate temperature and post-deposition annealing. Detailed analyses were first carried out to understand the effect of substrate temperature and annealing on the structure, composition, optical and electrical properties of the films. The films deposited at elevated substrate temperatures showed faster and improved photoresponse. Post-deposition annealing was found to further enhance the photoresponse of the films. Attempts have been made to explain the improvement in the photoresponse on the basis of structural and compositional changes, taking place in the films, due to the substrate temperature and annealing.     

Structural and electrical studies of thermally evaporated nanostructured CdTe thin films

CdTe thin films were deposited on KCl and glass substrates using thermal evaporation technique under high vacuum conditions. CdTe bulk compound grown by vertical directional solidification (VDS) technique was used as the source material to deposit thin films. Powder X-ray diffraction technique was employed to identify the phase of the as grown bulk CdTe compound as well as its thin films. Surface morphology and the stoichiometry of the bulk compound and thin films was carried out by using scanning electron microscope (SEM) with an attachment of energy dispersive spectrometer(EDS). Microstructural features associated with the as deposited CdTe thin films were studied by using transmission electron microscope (TEM). The films deposited on to glass substrates at different temperatures have been used to study the I-V characteristics of the films. These parameters have been studied in detail in order to prepare good quality nanostructured thin films of CdTe compound. CdTe bulk compound grown by VDS method and its thin films prepared by thermal evaporation method found to have single phase with cubic structure. Size of the particles in the as deposited films vary between 5 and 40 nm In the present study efforts have been made to correlate the electrical and optical properties of the CdTe thin films with the corresponding microstructural features associated with them.     

Electrical conductivity studies on carbazole thin films

Thin films of carbazole have been prepared using vacuum evaporation technique. The electrical conductivity studies are carried out in both low and high temperature regions and the activation energies have been determined. In the low temperature region the electrical conduction is due to hopping of charge carriers in a coulomb gap. Carbazole thin films have been used to fabricate capacitors and the variation of capacitance, dielectric constant; conductivity and dielectric loss in the frequency range between 100 Hz and 3.16 MHz are investigated. The effect of annealing on the dielectric properties is also investigated. The surface topography of the deposited films is studied using scanning electron microscopy. Film morphologies are found to change by annealing.     

Electrical,electromechanical and thermal properties of thin tellurium films

Thin films of tellurium of wide range of thicknesses have been deposited by vacuum evaporation and their electrical properties such as electrical resistivity and temperature coefficient of resistance have been measured. The suitability of these films for possible use as strain gauges has been studied and their strain resistivity behaviour is presented. The thermal conductivity of these films have been determined and these results are presented alongwith. An interesting phenomenon has been noticed. In all these effects an extraordinary behaviour is observed at a specific thickness. This smears out with an increase in the thickness of the film. These effects are explained in terms of size effects in thin films.     

Breakdown conduction in thin dielectric films: A bibliographical survey

Interest in the study of thin films has been greatly stimulated in recent years because of thier importance from the point of view of technological and industrial applications. A bibliographical survey limited mainly to breakdown conduction in thin films is presented here. To make the survey a more comprehensive and up-to-date source of information for the workers engaged in this field, the relevant references on some closely related fields, such as electrical conduction and switching phenomena, as well as on some other types of film systems and substances have also been included.The survey covers work published from 1960 onwards (few references appeared before then) and the references have been arranged in roughly chronological order together with the titles of the papers. In addition, a list of books, reviews and monographs has been given. The survey should also prove useful to assess the progress made by the scientific community in the field of breakdown conduction in thin dielectric films.     

The effect of substrate and post annealing temperature on the electrical properties of polycrystalline InSe thin films

The correlation between the electrical properties of vacuum evaporated InSe thin films and the growth conditions as well as post depositional annealing has been investigated. The electrical properties of the deposited films have been studied in the temperature range of 50–320 K. The donor levels present in the InSe films have been analysed by applying the single donor-single acceptor model to the electrical data.     

Influence of ambient atmosphere on the electrical properties of organic thin film transistors

We have fabricated organic thin film transistors (OTFT) using nickel phthalocyanine (NiPc) as an active layer. The organic thin films were deposited via sublimation under a secondary vacuum. The dependence of electrical characteristics on an ambient atmosphere is studied. Transient behaviour of the OTFT is also investigated showing the presence of a time delay in drain current when gate bias is applied. It is found that this time delay depends closely on the ambient atmosphere in addition with electrical field. Tests of ozone detection using NiPc based on OTFTs were carried out exhibiting a high sensitivity to ozone. We have demonstrated that electrical properties of the OTFTs are highly affected by ozone but not by oxygen. Our results show that NiPc-based OTFTs can represent a new class of ozone sensors.     

Effect of gas enhanced metal-semiconductor-metal UV photodetectors based on thermal annealing tungsten oxide thin film prepared by sol–gel method

Metal-semiconductor-metal ultraviolet photodetectors were fabricated on annealed tungsten oxide thin films which were synthesized by the sol–gel reaction. Surface morphology, microstructure, opto-electrical properties and crystal structure tests of the W₁₈O₄₉ thin films were examined by scanning electron microscopy, transmission, photoluminescence, and X-ray diffraction, respectively. The photo-responsivity of the photodetector shows a dependence on atmosphere environments. The photocurrent measured in a vacuum is about ~2 times higher than the illuminated photocurrent in air. The illumination conductance in a vacuum and in air increase by a factor of 100 compared to that in oxygen ambient. Furthermore, the obtained photoresponse curves showed significant changes in dark, under illumination, and during recovery for gas switching experiment. The solid-state process of electron-hole generation/recombination and surface effects of oxygen was discussed to explain the changes in the observed photoresponse.     

Preparation of rare earth CeO<Subscript>2</Subscript> thin films using metal organic decomposition method for metal-oxide–semiconductor capacitors

Investigation of metal organic decomposed rare earth cerium oxide thin films deposited on Si substrate by sol–gel spin coating technique was carried out. The structural properties have been examined by using XRD, Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The XRD confirms the cubic phase of CeO₂ thin films with (111) plane observed at 28.54°. The FTIR and EDAX spectra confirm the formation of CeO₂ films with atomic percentage of 19.39 and 54.82% of Ce and O₂, respectively. Thickness of 60.11 nm of CeO₂ film measured by cross sectional FESEM image, the average roughness of ~0.6 nm of 400?°C annealed CeO₂ films were observed from AFM micrograph. The MOS capacitors were fabricated by using Ti/Au bilayer metal contact depositing by E-beam evaporator on CeO₂/Si thin film for electrical measurements. Capacitance and conductance voltage measurement was carried out to determine the effective oxide charges (Q_eff), interface trap density (D_it) and dielectric constant (k) and are 2.48?×?10¹² cm^?2, 1.26?×?10¹² eV^?1cm^?2 and ~39, respectively. The effective metal work function of 5.68 for Ti/Au bilayer is observed to be higher than the work function of Ti or Au metals in vacuum.     

Pretreatment of polyethylene terephthalate substrate for the growth of Ga-doped ZnO thin film

The effect of the pretreatment of polyethylene terephthalate (PET) substrate on the growth of transparent conducting Ga-doped ZnO (GZO) thin film was investigated. Because of its high gas and moisture absorption and easy gas permeation, PET substrate was annealed at 100 degrees C in a vacuum chamber prior to the sputtering growth of GZO thin film for the outgassing of impurity gases. GZO thin film was deposited on the pretreated PET substrate by rf-magnetron sputtering and significantly improved electrical properties of GZO thin film was achieved. Electrical and structural characterizations of the GZO thin films were carried out by 4-point probe, Hall measurement, and scanning electron microscopy, and the effects of the pretreatment on the improved properties of GZO thin films were discussed. This result is not only useful to PET substrate, but also could be applicable to other plastic substrates which inevitably containing the moisture and impurity gases.     

Electrical characterization of nanocrystalline SnSe and ZnSe thin films: effect of annealing

In this paper, experimental data on the electrical properties of as deposited and annealed nanocrystalline SnSe and ZnSe thin films are reported. The thin films of SnSe and ZnSe are deposited on glass substrate by chemical bath deposition method. The films are studied before and after thermal annealing at temperatures 473 K for 1 h. This annealing is done in vacuum of 2?×?10^?3 mbar. The various electrical parameters like dark conductivity, photoconductivity, activation energy, photosensitivity and carrier life time have been measured on these films before and after annealing.     

Electrical properties optimization of silver nanowires supported on polyethylene terephthalate

ABSTRACT

The aim of this study is the enhancement of the electrical properties of thin films obtained from silver nanowires (AgNWs) deposited on a flexible polyethylene terephthalate (PET) support. First, AgNWs were obtained by the “polyol” liquid phase synthesis method in the presence of chloride ions. After purification, the AgNWs were successively deposited on a flexible support of PET by doctor blade method. To improve the adhesion of the AgNWs coating to the substrate, thin films of polymethyl methacrylate (PMMA) were interposed between the layer of AgNWs and PET substrate. The properties of the thin films have been studied depending on the number of AgNWs layers and heat treatment procedure. Characterization of pure AgNWs as well as of AgNWs/PMMA/PET structures has been carried out by x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray analysis, transmission electron microscopy, UV–Vis spectroscopy, and scanning probe microscopy. The sheet resistance of the transparent conducting films was determined by four point probe measurement. Best results in terms of homogenous conductance across the film and optical transmittance have been obtained for samples prepared by deposition of four successive layers of AgNWs. Further heat treatment improved the conductivity of AgNWs on the PMMA/PET substrate. For these films, the sheet resistance decreased from 41.25 to 29.55 Ω/sq after 40 min of heat treatment in air at 150°C.     

Annealing effects of In2O3 thin films on electrical properties and application in thin film transistors

Considering practical applications in electronic devices, we studied the growth of In₂O₃ thin films on amorphous glasses by magnetron sputtering at room temperature and annealing effect on the structural and electrical properties. The vacuum annealed In₂O₃ thin films display a grain size enlargement and preferential orientation. Electrical characterization shows that the vacuum annealed In₂O₃ thin films exhibit a significant enhancement of both electron density and mobility, while air ambient annealing leads to a remarkable drop. The mechanism of the electrical characteristic changes in In₂O₃ thin films by annealing is explored by using different scattering mechanisms. Finally, a thin film transistor device using vacuum annealed In₂O₃ nano-meter thin films as active channel material is demonstrated.     

N型Bi2Te2.5Se0.5热电薄膜的电阻率与膜厚和温度的关系

在玻璃衬底上通过瞬间蒸发法沉积了厚度为50-400nm的N型Bi2.5Se0.5热电薄膜,沉积温度为473K.采用XRD、EDXA和FESEM技术分别对薄膜的相结构、组成和表面形貌进行了分析研究,在300-350K的温度范围内,研究了薄膜的电阻率与膜厚和温度的相互关系.