Electron beam evaporated carbon nanotube dispersed SnO2 thin film gas sensor

Carbon nanotube (CNT) is a useful material for gas-sensing applications because of its high surface to volume ratio structure. In this work, multi-wall CNTs are incorporated into tin oxide thin film by means of powder mixing and electron beam evaporation and the enhancement of gas-sensing properties is presented. The CNTs were combined with SnO₂powder with varying concentration in the range of 0.25–5% by weight and electron beam evaporated onto glass substrates. From AFM and TEM characterization, CNT inclusion in SnO₂thin film results in the production of circular cone protrusions of CNT clusters or single tube coated with SnO₂layer. Experimental results indicate that the sensitivity to ethanol of SnO₂thin film increases by the factors of 3 to 7, and the response time and recovery time were reduced by the factors of 2 or more with CNT inclusion. However, if the CNT concentration is too high, the sensitivity is decreased. Moreover, the CNT doped film can operate with good sensitivity and stability at a relatively low temperature of 250–300^∘C. The improved gas-sensing properties should be attributed to the increasing of surface adsorption area of metal oxide produced by CNT protrusion.     

Piezoresistive property of an aluminum‐doped zinc oxide thin film deposited via atomic‐layer deposition for microelectromechanical system/nanoelectromenchanical system applications

The piezoresistive property of an aluminum (Al)‐doped zinc oxide (AZO) thin film (thickness = 20 nm) is evaluated using a microfabricated silicon cantilever structure. The AZO thin film is deposited via atomic‐layer deposition with 5% Al doping. An AZO piezoresistor is patterned at the root of the cantilever. This cantilever device is fabricated using conventional microfabrication techniques such as lithography, lift‐off, ion milling, and dry/wet etching. The cantilever is deflected by pressing the tip of the cantilever by a needle mounted on a micromanipulator. The strain of the AZO pattern caused by the deflection is numerically calculated using a finite element method based on the dimensions and materials of the fabricated device. The output current of the AZO changes almost linearly with increase in the input voltage. The gauge factor of the AZO thin‐film piezoresistor is found to be 8.5.     

COMPARATIVE ANALYSIS FOR THE LOCAL PIEZOELECTRIC PROPERTIES OF ION BEAM AND REACTIVE ION BEAM ETCHED Pb(Zr,Ti)O3 THIN FILMS

ABSTRACT

Piezoelectric properties of highly (111)-oriented unetched, ion beam etched (IBE) and reactive ion beam etched (RIBE) PbZr_0.35Ti_0.65O₃ (PZT) thin films have been investigated on the nanoscale by piezoelectric force microscopy. Crystallization of the films was performed before or after etching. Piezoelectric contrasts imaging reveals a clear modification of the domain architecture for all the films etched after crystallization; also, within grains, local piezoelectric hysteresis loops measurements show that coercive voltage increases about 130% (1.0 V to 2.3 V) for ion beam etched films while there is no significant change for reactive ion beam etched films. No evolution of coercive voltage is evidenced for films crystallized after ion beam etching. These results are explained in terms of domain-wall pinning in the film. Piezoelectric activity is shown to be similar for all the etched films; it is only slightly reduced of about 10% in comparison to the one measured for unetched film. On the other hand, theoretical considerations using a simple charge model indicate that the depth of the ellipsoid taken into account at the surface of the film for these measurements is about 20 nm.     

Structure change of PTFE by low‐energy ion irradiation. Restraint of structure collapse by crosslinking structures

The authors irradiated PTFE (polytetrafluoroethylene) with low‐energy nitrogen ions (100 eV) for surface modification. However, PTFE cannot be expected to show improvement in adhesive strength because it is a degradation‐prone polymer and surface fatigue is produced by ion irradiation. We focused on cross‐linked structure to solve this problem. PTFE was changed from a degradation‐prone polymer into a cross‐linked polymer by raising the temperature above the glass‐transition temperature during ion irradiation. As a result, the formation of CF₃ bonds was inhibited and degradation was prevented by ion irradiation above the glass‐transition temperature. In addition, combined consideration of the C1s spectrum and the density profile suggests that a cross‐linked structure is effective for improvement of adhesive strength. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 178(4): 1–7, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21225     

Fabrication and evaluation of LaCrO3 thin film heaters

Lanthanum chromium oxide (LaCrO₃) has excellent high‐temperature properties. LaCrO₃ doped with alkaline earth metals also has high electric conductivity. The purpose of this study is to fabricate thin film heaters using LaCrO₃ doped with Ca by RF magnetron sputtering method. The crystal structure of thin films was evaluated and the surface form was studied. The results show that the thin film deposited on Si(100) single crystal and quartz glass substrates in Ar gas had a strong orientation and that its surface form was comparatively smooth. The crystal structure of the thin films deposited on Si(100) and quartz glass substrate at temperatures of 700 and 800 °C by sputtering in a mixture of Ar and O₂ gases was the same as the crystal structure of LaCrO₃. The heating characteristics of a thin film heater on Si(100) substrate with Pt electrodes were evaluated by measurement of the equilibrium temperature‐current (T–I) and resistance‐equilibrium temperature (R–T) characteristics. The maximum equilibrium heating temperature was about 1100 °C. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 139(3): 18–25, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.1156     

Fabrication of flat micro‐gap electrodes for molecular electronics

Recently, organic molecular electronic devices such as molecular thin‐film transistors have received considerable attention as possible candidates for next‐generation electronic and optical devices. This paper reports on fabrication technologies of flat metallic electrodes on insulating substrates with a micrometer separation for high‐performance molecular device evaluation. The key technologies of fabricating planar‐type electrodes are the liftoff method by the combination of bilayer photoresist with overhang profile, electron beam evaporation of thin metal (Ti and Au) films, and SiO₂‐CMP (Chemical Mechanical Polishing) method of CVD (Chemical Vapor Deposition)‐deposited TEOS (tetraethoxysilane)–SiO₂ layer. The raggedness of the electrode/insulator interface and the electrode surface of the micro‐gap electrodes were less than 3 nm. The isolation characteristics of fabricated electrodes were on the order of 10¹³ ohms at room temperature, which is sufficient for evaluating electronic properties of organic thin‐film devices. Finally, pentacene FET (Field Effect Transistor) characteristics are discussed fabricated on the micro‐gap flat electrodes. The mobility of this FET was 0.015 cm²/Vs, which was almost on the order of the previous results. These results suggest that high‐performance organic thin‐film transistors can be realized on these advanced electrode structures. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(2): 39–46, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20152     

光学薄膜制备用的多离子束电子束系统

本文介绍一种新型的光学薄膜制备用多离子束电子束系统。     

Surface passivation of the thin‐film LAPS with perhydropolysilazane‐derived silica treated by O2 plasma

Here, we describe a novel method for surface passivation of the thin‐film light addressable potentiometric sensor (LAPS). To form a uniform passivation layer, perhydropolysilazane (PHPS) was utilized as a spin‐coatable precursor of silica. After transformation of PHPS into silica by baking, we introduced an O₂ plasma treatment aiming for enhancement of the water resistance of the PHPS‐derived silica (PDS) film by completing the PHPS‐to‐silica conversion. To confirm the effect of the O₂ plasma treatment, the PDS film was deposited on a thin‐film LAPS electrode and tested by immersion in a cell culturing medium. The immersion test demonstrated that the plasma‐treated PDS film could keep the electrode stable longer than the untreated could. With the treated PSD film of 600 nm in thickness, a lifetime of the thin‐film LAPS was estimated at over 2 weeks, which is sufficient for cell culturing experiments. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

New design and development of size‐selected gas cluster SIMS

A new cluster time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) was developed, using a size‐selected gas cluster ion as a projectile. Because a large gas cluster ion can generate numerous low‐energy constituent atoms during a collision with the surface, multiple and ultralow‐energy sputterings are induced. Dividing the acceleration energy of a gas cluster ion by the number of constituent atoms provides the mean kinetic energy of the constituent atoms. Hence, sputtering can be controlled to minimize decomposition of the sample molecules by precisely adjusting the number of constituent atoms (the cluster size) and/or the acceleration energy of the gas cluster ions. The cluster size was selected by the time‐of‐flight method using two ion deflectors attached along the ion‐beam line. A high resolution of 11.7 was achieved for the cluster size/size width (m/Δm) of the Ar‐cluster ions. The SIM spectra of poly(methyl methacrylate) (PMMA) were measured using the size‐selected gas‐cluster SIMS machine. The large fragment ions emitted from PMMA are enhanced as the cluster size increases. This result suggests that a large cluster ion projectile in which each constituent atom within the cluster has decreased kinetic energy inhibits the decomposition of the polymer structure. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(3): 52–58, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21159     

High‐frequency measurements of the magnetoresistance effect of thin films

The ac magnetoresistance of thin films at frequencies up to 10 kHz was successfully measured. Patterned electrodes with mechanical flexibility were pressed onto the film surface by using a rubber pad. Induction noises were reduced considerably in comparison to the conventional four‐electrode method. A seven‐electrode system was developed to prevent high‐frequency induction noise, typically induced by leakage flux from the sample edges. It was found that the seven‐electrode system enables magnetoresistance measurements with little induction noise at frequencies up to 10 kHz. © 2000 Scripta Technica, Electr Eng Jpn, 132(2): 1–5, 2000     

Characterization of RF sputtered zinc oxide thin films on silicon using scanning acoustic microscopy

Zinc oxide (ZnO) thin films were grown on silicon (100) substrate using radio frequency (RF) sputtering under various processing parameters including deposition time and annealing temperature. A series of characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and scanning acoustic microscopy (SAM) have been used to analyze the crystallinity and crystal orientation, structural morphology, surface roughness, and acoustic properties of these films. In particular, quantitative analysis of elastic wave propagation in ZnO thin films by scanning acoustic microscopy has been performed for the first time in the present work. It has been shown that the propagation properties of acoustic waves on the surface of ZnO thin films strongly depend on film thickness, crystallinity, and surface roughness. The dispersion properties of surface acoustic waves (SAWs) are observed as a function of ZnO film thickness. The velocities of SAWs range from 5328.3 m/s to 4245.7 m/s with increasing film thickness from 32.5 nm to 2.04 μm, while smoother surface contributes to faster propagation of SAWs.     

薄膜锂电池SnOx阳极材料研究进展

锡基氧化物(SnOx)作为全固态薄膜锂离子电池的阳极材料具有熔点高、比容量大、性能稳定、安全性好、易于制备等优点受到人们的重视。介绍了SnOx阳极薄膜的特点,分析了SnOx的贮锂机理,重点评述了不同方法制备SnOx薄膜的结构和电化学性能,旨在进一步优化高性能锂离子电池阳极薄膜的制备过程,为全固态薄膜锂离子电池性能改善提供借鉴和启发。     

Ion Implantation of Optical Ferroelectrics

We discuss ion implantation as a powerful non-equilibrium processing technology and show its potential for optical waveguide formation by damage engineering and by direct doping. Also the strong improvement of photorefractive properties by implantation-induced vacancies is demonstrated. Finally recent results of the growth of thin ferroelectric films by laser epitaxy and metal-organic vapor-phase epitaxy are presented. The combination of thin film growth techniques of optical ferroelectrics together with ion beam modification will prove important in this strongly advancing field.     

Effect of ion damage on the crystallization of PZT thin films

Abstract

Effects of Ar ion damage prior to the phase transformation from pyrochlore to perovskite structure of PZT thin films have been investigated. As the degree of damage increased by increasing the acceleration voltage in the ion mass doping system, the phase transformation temperature decreased such that the temperature could be lowered down to 550°C when the film was damaged at 15kV for 5 minutes. When the films were damaged prior to the heat treatment, the final grain size of the perovskite thin films became less than 300Å. The microstructure showed the granular type rather than columnar structure after ion damage treatment and annealing. It turned out that relatively high value of the remanent polarization (about 30 μC/cm²) as well as improvement of the fatigue characteristics to a large extent are closely related to the fine grain size of thus obtained PZT films.     

碳酸亚乙烯酯添加剂对锂离子电池性能的影响

用循环伏安(CV)、恒电流充放电(GC)、扫描电镜(SEM)以及傅里叶红外光谱(FT-IR)方法研究了添加剂碳酸亚乙烯酯(VC)对锂离子电池负极界面膜性质及电池循环性能的影响。研究表明,在首次充电过程中VC参与了SEI膜的形成,形成的膜主要成分为Li2CO3以及VC的还原聚合物。充放电实验结果表明电解液中加入少量VC能显著提高电池的初始放电容量,电池的循环稳定性也有所提高。     

PZT thin films by multiple target reactive sputtering

Abstract

Lead zirconate titanate thin films have been deposited by reactive sputtering using an independently RF-supplied three-target (Pb, Zr, Ti) system at a substrate temperature of 615[ddot]C. The lead content depended greatly on the input rf power at the Ti target, the highest power among the three targets, indicating resputtering. Remanent polarization (Pr) was 26.6 μC/cm² for a PZT film of 3200 Å thickness. Dependence of etching rate of PZT and Pt on incidence angle of the Ar ion beam in ion milling was investigated to optimize selectivity.     

Spin‐thermoelectric voltage in longitudinal SSE elements incorporating LPE YIG films and polycrystalline YIG slabs with an ultrathin Pt layer

A spin‐thermoelectric (STE) voltage is generated when a temperature gradient ?T is applied to an element having a thin Pt layer coated on a magnetic substance. In this study, yttrium iron garnet (YIG) ferrimagnetic films prepared by liquid phase epitaxy (LPE) were tested as magnetic insulators. In addition, polycrystalline YIG slabs were tested to compare the STE voltages of film and slab samples. In a Pt coating and YIG film bilayer structure made by an ultrathin Pt layer of 1‐4 nm thickness and an LPE film of approximately 10 µm thickness, a large STE voltage of 600 µV was observed at a probe distance of 5 mm with a temperature difference ?T of 30 K. On the other hand, the STE voltage of a Pt layer and YIG slab bilayer structure was 340 µV, which is roughly half of that of the Pt/YIG‐film element. The cause of the large voltage observed experimentally for the longitudinal spin Seebeck effect element incorporating an LPE YIG film was discussed mainly from the viewpoint of the Pt layer resistivity and the effects of YIG specimen surface conditions on crystallinity and the magnetization process.     

Characterization of Ba(Zr0.05 Ti0.95)O3 thin film prepared by sol-gel process

Ba(Zr_0.05Ti_0.95)O₃ (BZT) thin film (∼330 nm) was grown on Pt/Ti/SiO₂/Si(100) substrate by a simple sol-gel process. The microstructure and the surface morphology of BZT thin film were studied by X-ray diffraction and atomic force microscopy. The optical properties of BZT thin film were obtained by spectroscopic ellipsometry. The optical bandgap was found to be 3.74 eV of direct-transition type. Ferroelectric and dielectric properties of BZT thin film were also discussed. The electrical measurements were conducted on BZT films in metal-ferroelectric-metal (MFM) capacitor configuration. The results showed the film exhibited good ferroelectrity with remanent polarization and coercive electric field of 3.54 μC/cm² and 95.5 kV/cm, respectively. At 10 kHz, the dielectric constant and dielectric loss of the film are 201 and 0.029, respectively.     

Relation between breakdown voltage and prebreakdown current in vacuum gap

Two different surface treatments (mechanical polishing, thin film deposition) were performed on cathode surfaces, and the field emission currents from the cathodes were measured with a microchannel plate. In order to discuss the relationship between the breakdown voltage and prebreakdown current in the vacuum gap, the breakdown voltage was measured after field emission measurement. The V–I characteristics of the field emission and breakdown voltage were influenced by surface treatment, and the breakdown voltages of mechanical polished cathodes were lower than those of the thin film deposited cathodes. It was found that the probability of breakdown increased when the field emission current reached 10^–11 A. Atomic force microscope (AFM) measurements showed numerous protrusions on the cathode surface in the case of thin film deposition treatment, but we estimated by the finite element method that these protrusions make the field enhancement effect low. It was inferred that the breakdown voltage in vacuum gaps could be increased by the thin film deposition method. © 2000 Scripta Technica, Electr Eng Jpn, 131(4): 11–18, 2000     

碳纳米管电化学储能的研究进展

由于碳纳米管的特殊结构导致独特的物理化学性质 ,使得它在各个领域的应用引起多方面重视。根据国内外碳纳米管开发利用现状 ,总结了近年来各种不同规格碳纳米管在电化学储氢、电化学储锂、电化学电容器等电化学储能方面的研究进展 ;指出了各方面研究发现的问题 ,如电化学储锂的电压滞后 ,不可逆容量较大 ,电化学储氢时氢在碳纳米管中的存在状态难以确定等 ;今后的工作应从理论及实验两个方面来解释和解决这些问题。研究表明碳纳米管作为电化学电容器电极将是今后应用的主要方向