Effects of bending fatigue on the electrical resistance in metallic films on flexible substrates

The increase of electrical resistance during the strain-controlled bending fatigue of 2 μm-thick inkjet-printed or vacuum deposited metallic films (Cu, Ag) on flexible substrates (BT: Bismaleimide Triazine, PI: Polyimide) was investigated. Electrical resistance increased with an increase in the number of fatigue cycles. The rate of increase in the electrical resistance of inkjet-printed Cu films was lower than that of thermally evaporated films. This phenomenon is attributable to the porous microstructure of inkjet-printed Cu films. The porous structure contains a lot of free volume and a large area of free surface, which can be a sinking site for vacancies formed during the cyclic deformation. It was confirmed that a smaller grain size leads to a lower rate of increase in the electrical resistance, which was ascribed to the easy vacancy annihilation due to a short diffusion length of the vacancy to the grain boundary which is a vacancy sinking site. The rate of increase in the electrical resistance was also influenced by the grain boundary geometry. The lower rate of the evaporated Ag film on a BT substrate was attributed to the crack-like grain boundaries, which were expected to behave like pores.     

Effects of Deflection on the Sio2 Barrier Layer and Mo Back Electrode of Cu（In,Ga）Se2 Thin-Film Solar Cells on Stainless Steel Substrates

This paper studies the effects of deflection on the SiO2 barrier layer and molybdenum(Mo)back electrode of Cu(In,Ga)Se2 thin-film solar cells,prepared via magnetron sputtering on type SUS431 stainless steel substrates.The surface micro-cracks and sheet resistance of thin films had been observed and measured for in-situ bend tests.Experimental results show that increasing the thickness of the SiOx barrier has a better property to prevent cracks induced by bending stress.The sheet resistance of a Mo film increases alongside the bending of the curvature radius.The maximum allowed value of the curvature radius of the SiOx barrier layer,molybdenum electrodes,and the thin film CIGS absorbing layer should be 16 mm,20 mm,and 26 mm,respectively.Therefore,the maximum curvature radius limit should be 26 mm or less for CIGS thin-film solar cells prepared via sputtering on type SUS431 stainless steel substrates.     

The Effect of Interface Cracks on the Electrical Performance of Solar Cells

Among a variety of solar cell types, thin-film solar cells have been rigorously investigated as cost-effective and efficient solar cells. In many cases, flexible solar cells are also fabricated as thin films and undergo frequent stress due to the rolling and bending modes of applications. These frequent motions result in crack initiation and propagation (including delamination) in the thin-film solar cells, which cause degradation in efficiency. Reliability evaluation of solar cells is essential for developing a new type of solar cell. In this paper, we investigated the effect of layer delamination and grain boundary crack on 3D thin-film solar cells. We used finite element method simulation for modeling of both electrical performance and cracked structure of 3D solar cells. Through simulations, we quantitatively calculated the effect of delamination length on 3D copper indium gallium diselenide (CIGS) solar cell performance. Moreover, it was confirmed that the grain boundary of CIGS could improve the solar cell performance and that grain boundary cracks could decrease cell performance by altering the open circuit voltage. In this paper, the investigated material is a CIGS solar cell, but our method can be applied to general polycrystalline solar cells.     

Carrier transportation in polycrystalline CuInSe_2 thin films with Cu-deficient grain boundaries

The interface energies and electronic structures of(112) grain boundaries of Cu In Se2 thin films were investigated by first-principle calculations.It is found that the grain boundary with a Cu vacancy has low interface energy and exists widely in the films.The Cu deficiency may cause the charge imbalance and result in an upward band bending at the grain boundary.It also weakens the repulsion between Cu-3d orbital and Se-4p orbital and leads to the downward shift of valence band maximum.The two mechanisms,namely the band bending from the charge imbalance and the depression of the valence band maximum, have effects on the(112) grain boundaries with different defects.The change of band structure forms a potential barrier to prevent electrons or holes from approaching the grain boundary and reduces their recombination.This might be used to explain the effects of the grain boundary on carrier transportation and why polycrystalline Cu(In,Ga)Se2thin film solar cells have better performance than single-crystal cells.     

钨中溶质原子铬与空位的相互作用的第一性原理计算研究

钨铬(W-Cr)合金具有优异的物理性能,被认为是面向等离子体材料(PFM)中最有潜力的候选材料。而合金元素对辐照损伤演化过程的影响规律是钨合金优化设计的关键,深入研究溶质原子与辐照缺陷(如：空位)的相互作用有助于理解辐照损伤演化的微观物理机制。本文基于第一性原理方法,对W-Cr合金的溶质原子Cr占位、Cr与空位的相互作用及Cr含量对其影响规律进行了计算研究。发现相比于间隙位置,原子Cr更易占据置换位置,W中溶质Cr有偏聚的趋势;在辐照环境下,空位和自间隙原子均易与溶质原子Cr相结合,易加速W中富Cr相的析出;随Cr含量的增加,体系的形成能线性增加,因而结构越发不稳定。研究还发现超胞中单原子Cr的第二近邻空位的形成能最低,且低于W的本征空位形成能,因而溶质Cr与空位之间存在微弱的吸引;对于同一Cr含量,不同构型的空位形成能及空位和Cr的结合能均不同,且Cr含量越高,数值越分散;随着Cr含量的增加,平均空位形成能及空位与Cr的平均结合能均略有下降,因而溶质原子Cr附近空位更易形成,空位浓度更高,同样也表明溶质Cr与空位有微弱的吸引。这些结论将有助于深入理解W中溶质元素存在条件下辐照缺陷演化过程的微观物理机制。     

钙钛矿型La1-xSrxMnO3纳米薄膜的制备及其光催化性能

采用溶胶-凝胶法和浸渍提拉技术在载玻片基底上制备出钙钛矿型La1-xSrxMnO3纳米薄膜;采用TG/DTA技术分析前驱体凝胶的热分解历程;利用AFM观察薄膜的形貌特征;通过XRD进行物相分析,并计算其晶粒尺寸。结果表明,La1-xSrxMnO3薄膜在600℃形成,为钙钛矿结构,其平均晶粒尺寸为10.349nm。采用该薄膜对多种水溶性染料进行光催化降解试验的结果表明,掺杂后该类纳米薄膜有较好的光催化效果,当x=0.2时光催化效果最好。     

Al2O3钝化层对a-IGZO薄膜晶体管电性能的增强机制研究

采用空心阴极增强脉冲激光沉积技术(HC-PLD)在室温制备高质量的Al₂O₃薄膜，作为非晶铟镓锌氧(a-IGZO)TFT器件的钝化层，显著增强了Al₂O₃/a-IGZO TFT器件的亚阈值特性，其原因在于空心阴极引入的氧等离子体抑制了Al₂O₃/a-IGZO界面处氧空位的形成。进一步研究发现，针对a-IGZO薄膜的180℃退火处理有利于消除弱结合氧并抑制深能级缺陷，提高载流子迁移率并降低阈值电压漂移；而针对Al₂O₃/a-IGZO TFT器件进行100℃退火处理有助于消除其界面附近的氧空位，降低载流子浓度，改善亚阈值特性。结合2步退火工艺所制备的Al₂O₃/a-IGZO TFT器件迁移率高达22.8 cm²·V^-1·s^-1，亚阈值摆幅为0.6 V·decade^-1，综合电性能优异。     

Characterization of the field-effect conductivity distribution in pentacene thin-film transistors by a near-field scanning microwave microscope

Direct probing of the conductivity distribution in organic materials is motivated by the need to obtain a deeper understanding of carrier behavior in organic thin-film transistors (OTFT), organic electro-luminescent devices, organic photoconductors, and organic biosensors. Here we used a near-field scanning microwave microscope to visualize conductivity profiles in OTFT channel. Applying this technique to pentacene field-effect transistors has revealed changes of the conductivity distribution in the channel arising from the development and exhaustion of an accumulated charge region. The electric field profiles, the complementary image of conductivity profiles, which are visualized by using an optical second harmonic generation method, support the results. We anticipate that direct observation by this microwave method will find wide application in measurement of carrier conductivity in organic and nonorganic materials.     

PEDOT/PSS bending actuators for autofocus micro lens applications

This paper reports on the development of micro autofocus lens actuators using conducting polymer actuators. We propose a hydrophilic treatment for polyvinylidene difluoride (PVDF) membranes and a polyethylenedioxythiophene/poly(styrene sulfonic acid) (PEDOT/PSS) casting method for easily producing bending conducting polymer actuators with high mechanical strength.We first designed micro autofocus lens actuators using bending conducting polymer actuators, and then determined experimentally that the electrical conductivity and breaking strain of the PEDOT/PSS films could be improved by the addition of polyethylene oxide (PEO). Furthermore, we made hydrophobic PVDF membrane surfaces hydrophilic using polyethylene glycol methacrylate (PEGMA) and coated a solution of a mixture of PEDOT/PSS and PEO on the membrane surfaces to form a laminated film. We produced bending conducting polymer actuators by processing this film. Tests simulating the actuator's use in micro autofocus lenses showed the actuators to operate stably for more than a million cycles.     

Epitaxial integration of perovskite-based multifunctional oxides on silicon

We review recent developments in the epitaxial integration of multifunctional oxide thin film heterostructures on silicon (Si). Perovskite oxides have been extensively studied for use in multifunctional devices due to a wide range of functional properties. To realize multifunctional oxide devices, these multifunctional films should be integrated directly on Si, maintaining high crystalline quality. Molecular beam epitaxy growth of epitaxial SrTiO₃ (STO) on Si provides a template for incorporating the epitaxial oxide films on Si. However, the dissimilar physical nature of Si from most oxide materials influences the properties of oxide films on Si, especially with regard to structural defects and thermal strains. Therefore, in this review, we present a comprehensive overview of epitaxial integration of various model oxide systems on Si, addressing how STO/Si can be used to explore the novel phenomenon of oxide heterostructures as well as to realize multifunctional devices.     

A NEW CONCEPT TOWARD INDUSTRIALIZATION OF Cu-III-VI_2 THIN FILM SOLAR CELLS AND SOME PRELIMINARY EXPERIMENT RESULTS

1.IntroductionA fterm ore than tw o decades'extensive w ork,the ultim ate solutionsusing thin film solarcellsforterrestrialapplicationshave em erged m oredefinitely.Itisgenerally believed thatthe PV m odulesm adeofa-Si:H w illdom inate thecurrentm arketso…     

点缺陷模型在2205双相不锈钢中的应用

采用电化学极化曲线和电化学阻抗技术对2205双相不锈钢在0.1%、1.0%及3.5%（质量分数,%）三种不同浓度的NaCl溶液中的腐蚀性能进行测试,采用点缺陷模型(PDM)对测试结果进行建模与分析。研究结果表明,2205双相不锈钢随着溶液浓度的升高抗点蚀能力下降,这是由于在钝化膜的生长过程中,氧离子缺陷产生于金属/膜界面,消耗于膜/溶液界面,而金属离子缺陷产生于膜/溶液界面,消耗于金属/膜界面;氧离子缺陷的迁移导致钝化膜的生长,而金属离子缺陷的迁移使得钝化膜发生溶解。同时,根据PDM模型理论并从金属相角度出发对2205不锈钢建立钝化膜溶解模型,可知2205双相不锈钢奥氏体相γ上的钝化膜可能比铁素体相α优先发生溶解。     

A fluctuation-based characterization of athermal phase transitions: Application to shape memory alloys

We employ a fluctuation-based technique to investigate the athermal component associated with martensite phase transition, which is a prototype of temperature-driven structural transformation. Statistically, when the phase transition is purely athermal, we find that the temporal sequence of avalanches under constant drive is insensitive to the drive rate. We have used fluctuations in electrical resistivity or “noise” in nickel titanium shape memory alloys in three different forms: a thin film exhibiting well-defined transition temperatures, a highly disordered film, and a bulk wire of rectangular cross-section. Noise is studied in the realm of dynamic transition, viz., while the temperature is being ramped, which probes into the kinetics of the transformation at real time scales, and could probably stand out as a promising tool for material testing in various other systems, including nanoscale devices.     

A NEW CONCEPT TOWARD INDUSTRIALIZATION OF Cu-Ⅲ-Ⅳ2 THIN FILM SOLAR CELLS AND SOME PRELIMINARY EXPERIMENT RESULTS

A new concept of full vacuum manufacturing for Cu-Ⅲ-Ⅳ2 thin-film solar cells has been discussed Cu-Ⅲ-Ⅳ2 thin-film solar cells manufactured using full in-line reactive sputtering will result in lower cost than that of the conventional method with CdS layer fabricated with chemical bath deposition (CBS) method. Using reactive sputtering process with organometallic gases, the compositions and electronic properties of Cu-Ⅲ-Ⅳ2 thin-film can be fine-tuned and precisely controlled, n-type Cu-Ⅲ-Ⅳ2 film and ZnS suffer layer can also be deposited using the in-line sputtering instead of using the CdS layer. The environmental pollution problems arising from using CdS can be eliminated and the ultimate goal of full in-line process development can then be realized. Some preliminary experimental results on a modal solar cell fabricated by the new technique in the new concept have been presented.     

Memory mechanism of printable ferroelectric TFT memory with tertiary structured polypeptide as a dielectric layer

Printable nonvolatile memory devices have been attracting considerable interest because of their application to flexible large-area devices. In order to fabricate such memory devices, it is necessary to discover a new ferroelectric material and to develop an efficient process for its preparation. We have previously reported that poly(γ-methyl-L-glutamate) (PMLG) functions as a ferroelectric layer of an organic thin-film transistor (OTFT) memory device [S. Uemura, A. Komukai, R. Sakaida, M. Yoshida, S. Hoshino, T. Kodzasa, T. Kamata, Synth. Met. 153 (2005) 405]. Further, ferroelectricity is observed when α-helical PMLG molecules are aligned in a direction parallel to the film surface. In this study, we investigate the effect of the tertiary structure of PMLG molecules on the hysteresis of OTFT memory devices, i.e., memory performance. From the results, we conclude that the hysteresis of the OTFT is strongly affected by the helical tertiary structure of PMLG molecules, similar to the structure of a cholesteric liquid crystal phase.     

Constrained diffusional creep in UHV-produced copper thin films

The thermomechanical behavior of metallic thin films on stiff substrates is relevant for thin-film devices, but its mechanisms are not fully understood. In this investigation, the mechanical properties of pure Cu and Cu–1 at.% Al films on diffusion-barrier coated Si substrates were studied with the wafer-curvature technique. In ultra-pure films, which were sputtered and annealed under ultra-high vacuum conditions, characteristic stress relaxation at high temperatures was measured, which could be clearly attributed to diffusional creep. Good quantitative agreement with a recent model of diffusional creep constrained by a substrate was obtained. These features were absent in the Cu–Al alloy films, in which Al surface segregation and oxidation had produced a “self-passivating” effect, and in films produced in less clean environments. Based on these results, we propose a model of thin-film deformation based on dislocation glide and constrained diffusional creep.     

A NEW CONCEPT TOWARD INDUSTRIALIZATION OF Cu-Ⅲ-Ⅵ2 THIN FILM SOLAR CELLS AND SOME PRELIMINARY EXPERIMENT RESULTS

A new concept of full vacuum manufacturing for Cu-Ⅲ-Ⅳ2 thin-film solar cells has been discussed. Cu-Ⅲ-Ⅳ2 thin-film solar cells manufactured using full in-line reactive sputtering will result in lower cost than that of the conventional method with CdS layer fabricated with chemical bath deposition (CBS) method. Using reactive sputtering process with organometallic gases, the compositions and electronic properties of Cu-Ⅲ-Ⅳ2 thin-film can be fine-tuned and precisely controlled. n-type Cu-Ⅲ-Ⅳ2 film and ZnS suffer layer can also be deposited using the in-line sputtering instead of using the CdS layer. The environmental pollution problems arising from using CdS can be eliminated and the ultimate goal of full in-line process development can then be realized. Some preliminary experimental results on a modal solar cell fabricated by the new technique in the new concept have been presented.     

Observation of TaB x O y Along the Ta Diffusion Path Through a Boron and Oxygen Containing Tri-layer Structure

Diffusion and migration of elements are commonly observed in the fabrication of multilayer thin-film devices, including those of STT-RAM. The CoFeB/MgO/CoFeB tri-layer thin-film stack has been widely used in the design of STT-RAM devices as the functional magnetic-tunnel-junction (MTJ) structure. Such issues faced in the fabrication of these devices have been extensively researched from the stand point of engineering the materials property and structure to achieve the best MTJ performance. In this work, we conducted a detailed examination of the chemical-state change of the Ta and B in a CoFeB/MgO/CoFeB/Ta film stack by using x-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry. We showed that the chemical-state change of Ta and B is a result of the Ta diffusion phenomena through the CoFeB/MgO/CoFeB tri-layer structure. In particular, we report the evidences of the formation of TaB _x O _y compound at some considerable depth away from the Ta layer. Also of value to XPS spectroscopy, the Ta binding energy for such TaB _x O _y compound is reported for the first time.     

Spectroscopic and travelling-wave lasing characterisation of Gilch-type and Horner-type MEH-PPV

Two different types of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene) (MEH-PPV) (i) a strictly linear, well-defined material of moderate molar mass prepared through polycondensation (Horner-type) and (ii) a commercially available MEH-PPV-sample (Gilch-type, high-molecular and defect-rich) resulting from a dehydrohalogenation process, are carefully analysed by GPC and ¹³C/¹H-NMR spectroscopy. These studies show that for the Gilch-type polymer there is a marked deficiency of regular vinylene groups (≈30%), and therefore, a lack of long-range polyconjugation. The samples are characterized by thin-film optical constants measurements, absorption and fluorescence spectroscopic studies, and thin-film wave-guided travelling-wave laser action investigations. The influence of film-forming solvents (chlorobenzene (CB), tetrahydrofuran (THF)) and of film heating on the absorption, emission and laser behaviour is investigated.

The fluorescence quantum yields of neat films (≈25% for Horner-type MEH-PPV and ≈36% for Gilch-type MEH-PPV) and toluene solutions (≈38% for Horner-type MEH-PPV and ≈32% for Gilch-type MEH-PPV) are similar. The exciton delocalisation (chromophore size) is found to be about four repeat units for both types of MEH-PPV. Remarkably good laser performance with low pump laser threshold (<20 μJ/cm²) was achieved for both polymers independent of the synthesis pathway, the deviations in the molecular fine structure and the film-forming solvents. However, the preparation of high quality optical films is much easier for the Horner-type MEH-PPV than for the Gilch-type MEH-PPV making the Horner-type MEH-PPV easier to use for thin-film lasers and photonic devices.     

TENSILE AND ADHESIVE STRENGTHS OF FINE TiN FILM ON Ti SUBSTRATE

The cantilever bending test,particularly monitored by an acoustic emission technique,was adopted to measure the tensile and interfacial adhesive strengths of the HCD ionplated fine TiN film on pure Ti substrate.The behaviors of film damaging were foundto be characterized by:an internal tensile stress which exceeded its tensile strength forTiN facing upward,and a shearing stress along film substrate interface which exceededits adhesive strength for TiN facing downward.The measured tensile and adhcsivestrengths are 603 and 242 MPa respectively.