Direct current magnetron sputter-deposited ZnO thin films

Zinc oxide (ZnO) is a very promising electronic material for emerging transparent large-area electronic applications including thin-film sensors, transistors and solar cells. We fabricated ZnO thin films by employing direct current (DC) magnetron sputtering deposition technique. ZnO films with different thicknesses ranging from 150 nm to 750 nm were deposited on glass substrates. The deposition pressure and the substrate temperature were varied from 12 mTorr to 25 mTorr, and from room temperature to 450 °C, respectively. The influence of the film thickness, deposition pressure and the substrate temperature on structural and optical properties of the ZnO films was investigated using atomic force microscopy (AFM) and ultraviolet-visible (UV-Vis) spectrometer. The experimental results reveal that the film thickness, deposition pressure and the substrate temperature play significant role in the structural formation and the optical properties of the deposited ZnO thin films.     

Exfoliation of metal-organic framework nanosheets using surface acoustic waves

Two-dimensional (2D) metal–organic framework (MOF) nanosheets have recently received extensive attention due to their ultra-thin thickness, large specific surface area, chemical and functional designability. In this study, an unconventional method using surface acoustic wave (SAW) technology is proposed to exfoliate large quantities and uniform layers of 2D MOF-Zn₂(bim)₄ nanosheets in a microfluidic system. We successfully demonstrated that the thickness of 2D MOF is effectively and accurately controlled by optimizing the SAW parameters. The mechanisms for the efficient exfoliation of 2D MOF nanosheets is attributed to both the electric and acoustic fields generated by the SAWs in the liquid. The electric field ionizes the methanol to produce H⁺ ions, which intercalate Zn₂(bim)₄ sheets and weaken the interlayer bonding, and the strong shear force generated by SAWs separates the MOF sheets. A yield of 66% for monolayer MOFs with a maximum size of 3.5 μm is achieved under the combined effect of electric and acoustic fields. This fast, low-energy exfoliation platform has the potential to provide a simple and scalable microfluidic exfoliation method for production of large-area and quantities of 2D MOFs.     

Selectiveness of laser processing due to energy coupling localization: case of thin film solar cell scribing

Selectiveness of the laser processing is the top-most important for applications of the processing technology in thin-film electronics, including photovoltaics. Coupling of laser energy in multilayered thin-film structures, depending on photo-physical properties of the layers and laser wavelength was investigated experimentally and theoretically. Energy coupling within thin films highly depends on the film structure. The finite element and two-temperature models were applied to simulate the energy and temperature distributions inside the stack of different layers of a thin-film solar cell during a picosecond laser irradiation. Reaction of the films to the laser irradiation was conditioned by optical properties of the layers at the wavelength of laser radiation. Simulation results are consistent with the experimental data achieved in laser scribing of copper-indium-gallium diselenide (CIGS) solar cells on a flexible polymer substrate using picosecond-pulsed lasers. Selection of the right laser wavelength (1064 nm or 1572 nm) enabled keeping the energy coupling in a well-defined volume at the interlayer interface. High absorption at inner interface of the layers triggered localized temperature increase. Transient stress caused by the rapid temperature rise facilitating peeling of the films rather than evaporation. Ultra-short pulses ensured high energy input rate into absorbing material permitting peeling of the layers with no influence on the remaining material.     

Theoretical evaluation of zirconia and hafnia as gate oxides for si microelectronics

Parameters determining the performance of the crystalline oxides zirconia (ZrO2) and hafnia (HfO2) as gate insulators in nanometric Si electronics are estimated via ab initio calculations of the energetics, dielectric properties, and band alignment of bulk and thin-film oxides on Si (001). With their large dielectric constants, stable and low-formation-energy interfaces, large valence offsets, and reasonable (though not optimal) conduction offsets (electron injection barriers), zirconia and hafnia appear to have considerable potential as gate oxides for Si electronics.     

Internal Structure Tailoring in 3D Nanoplasmonic Metasurface for Surface-Enhanced Raman Spectroscopy

Tunable nanoplasmonic metasurfaces have resulted in many versatile platforms for sensing applications including surface-enhanced Raman scattering (SERS)-based detection. However, to date, their fabrication still faces challenges in uniformity, repeatability, and controllability. Here, a novel large-area and hierarchical nanoplasmonic array with controlled internal structure and tunable plasmonic properties is reported, relying on controllably tailoring the single nanosphere on a uniform double-layered array into a well-defined nanoflower structure. The fabrication involves colloidal self-assembly, lithography, and plasmonic metal coating. First, a uniformly distributed double-layered colloidal array is fabricated via an ethanol-assisted self-assembly technique. Next, with the help of inductively coupled plasma dry etching, the lower layer is transformed to the nanoflower array with well-defined petal shape. Subsequently, a gold film with controlled thickness is deposited onto the nanoflower structured array, resulting in a tunable optical and SERS-active enhancement effect. Furthermore, 3D finite-difference time-domain simulation shows multiple enhancement sites inside the nanoflower array. Such a brand-new 3D structured array has the potential for varied applications, ranging from SERS sensors to light regulation.     

Frictional behavior of oxide graphene nanosheets as water-base lubricant additive

Oxide graphene (GO) nanosheets were prepared by modified Hummers and Offeman methods. The products were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectrometry (FTIR), and thermogravimetric analysis (TGA). The tribological properties of GO nanosheets as water-base lubricant additive were investigated using a UMT-2 ball-plate tribotester. By the addition of GO nanosheets in pure water, the antiwear ability was improved and the friction coefficient was decreased. The water with GO nanosheets showed better tribological properties than the water with oxide multiwall carbon nanotubes (CNTs-COOH). It is concluded that the formation of a thin physical tribofilms on the substrate can explain the good friction and wear properties of GO nanosheets.     

喷雾工艺制备的高性能有机光敏薄膜晶体管

以聚3-己基噻吩(P3HT)为有机层、价格低廉的聚甲基丙烯酸甲酯(PMMA)为绝缘层制备了底栅顶接触型结构的有机薄膜晶体管(OTFT)。采用一种新型喷雾工艺来制备器件的有机薄膜层,通过测量有机薄膜晶体管的电学特性,可得出应用喷雾制备的器件有较好的性能。在100 mW/cm2标准模拟太阳光照下,测量基于P3HT的有机薄膜晶体管器源漏电流随时间的变化特性,结果表明基于P3HT的有机光敏薄膜晶体管,不仅具有明显的响应特性,而且具有很好的恢复特性。同时,对比黑暗和光照1,2,4 min下的OTFT特性转移曲线,得到器件的阈值电压随时间的变化曲线。     

Vacuum-deposited, nonpolymeric flexible organic light-emitting devices

We demonstrate mechanically flexible, organic light-emitting devices (OLED's) based on the nonpolymetric thin-film materials tris-(8-hydroxyquinoline) aluminum (Alq(3)) and N, N(?) -diphenyl- N, N(?) -bis(3-methylphenyl)1- 1(?) biphenyl-4, 4(?) diamine (TPD). The single heterostructure is vacuum deposited upon a transparent, lightweight, thin plastic substrate precoated with a transparent, conducting indium tin oxide thin film. The flexible OLED performance is comparable with that of conventional OLED's deposited upon glass substrates and does not deteriorate after repeated bending. The large-area (~1 - cm>(2)) devices can be bent without failure even after a permanent fold occurs if they are on the convex substrate surface or over a bend radius of ~0.5>cm if they are on the concave surface. Such devices are useful for ultralightweight, flexible, and comfortable full-color flat panel displays.     

Self-organized semiconductor surfaces as templates for nanostructured magnetic thin films

Spontaneous pattern formation during epitaxial growth or ion erosion of semiconductor wafers offers an elegant route towards large-area nanostructured surfaces. In homoepitaxy, kinetics may result in rather uniform three-dimensional islands. In the case of semiconductor heteroepitaxy, strain relief leads to the formation of nanofaceted three-dimensional crystallites, which may self-organize into quasiperiodic arrays. By tuning substrate miscut and film thickness, or growing superlattices, a variety of patterns with different symmetries can be obtained, as will be summarized for the model system of SiGe on Si(001). Since these self-organized nanostructure arrays cover the entire wafer on which they are grown, they can serve as large-area nanopatterned substrates for subsequent deposition of magnetic thin films. It will be demonstrated that such templates allow the study of correlations between magnetic and chemical interfacial roughness, as well as the influence of pattern symmetry on the magnetic anisotropy of thin Co films. Furthermore, shadow deposition of magnetic material onto specially faceted nanostructure arrays allows the fabrication of nanomagnet arrays and the study of their magnetic properties. Received: 31 July 2002 / Accepted: 2 October 2002 / Published online: 5 February 2003 RID="*" ID="*"Corresponding author. Fax: +43-3842/402-760, E-mail: teichert@unileoben.ac.at     

Direct observation of dynamic shape transformation and coalescence in platinum nanosheets on graphite surface at room temperature by time-resolved AFM

The shape transformation of platinum (Pt) nanosheets with a uniform thickness of as thin as 3.5 ± 1 nm supported on graphite was investigated by in situ atomic force microscopy (AFM). The AFM observations revealed the shape transformation and the coalescence in preferred directions for the Pt nanosheets at room temperature (25 °C), which is much lower than the melting point of bulk metallic platinum (1769 °C). The behavior may be attributed to the high surface energy for the edge parts of Pt nanosheets with the small curvature of the nanometer scale.     

Investigation of the electrical properties and stability of HfInZnO thin-film transistors

In this study, amorphous HfInZnO (a-HIZO) thin films and related thin-film transistors (TFTs) were fabricated using the RF-sputtering method. The effects of the sputtering power (50–200 W) on the structural, surface, electrical, and optical properties of the a-HIZO films and the performance and NBIS stability of the a-HIZO TFTs were investigated. The films’ N_e increased and resistivity decreased as the sputtering power increased. The 100 W deposited a-HIZO film exhibited good optical and electrical properties compared with other sputtering powers. Optimization of the 100 W deposited a-HIZO TFT demonstrated good device performance, including a desirable μ_FE of 19.5 cm²/Vs, low SS of 0.32 V/decade, low V_th of 0.8 V, and high I_on/I_off of 10⁷, respectively. The 100 W deposited a-HIZO TFT with Al₂O₃ PVL also exhibited the best stability, with small V_th shifts of -2.2 V during NBIS testing. These high-performance a-HIZO thin films and TFTs with Al₂O₃ PVL have practical applications in thin-film electronics.     

甲基蓝-钛酸盐纳米聚合物薄膜的光谱和光学非线性研究

 为了满足光学非线性器件设备对工作材料的要求,探究具有高阶非线性效应的固态薄膜材料的制备方法,并对其光学特性进行表征,采用化学插入法,将甲基蓝染料分子插入到具有纳米量级的层状钛酸盐片间,制备了甲基蓝-钛酸盐纳米聚合物薄膜,通过吸收光谱和荧光光谱的测定,发现薄膜的吸收峰相对于染料溶液发生了明显的蓝移,表明染料分子在纳米片间是H-聚集排列。进一步应用单光束连续He-Ne激光Z-扫描技术研究了样品的非线性光学特性,结果显示：插入染料分子的钛酸盐纳米MB/HTO聚合物薄膜具有“负”的非线性折射率,在低功率连续激光作用下聚合物薄膜的非线性折射率系数n2的量级为10-10 m2/W。     

利用光学薄膜模型研究垂直腔面发射激光器的光学特性

可以把垂直腔面发射激光器看作是多层光学薄膜,应用光学薄膜原理对其光学薄膜的特性进行了研究。计算分析了布拉格反射镜和谐振腔模的反射谱受器件结构变化的影响。通过利用菲涅耳系数矩阵法计算,得到了光在垂直腔面发射激光器器件结构中形成的驻波场分布。结果表明,利用菲涅耳系数矩阵法设计垂直腔面发射激光器的光学薄膜是一种快捷准确的方法。     

Laser applications in thin-film photovoltaics

We review laser applications in thin-film photovoltaics (thin-film Si, CdTe, and Cu(In,Ga)Se₂ solar cells). Lasers are applied in this growing field to manufacture modules, to monitor Si deposition processes, and to characterize opto-electrical properties of thin films. Unlike traditional panels based on crystalline silicon wafers, the individual cells of a thin-film photovoltaic module can be serially interconnected by laser scribing during fabrication. Laser scribing applications are described in detail, while other laser-based fabrication processes, such as laser-induced crystallization and pulsed laser deposition, are briefly reviewed. Lasers are also integrated into various diagnostic tools to analyze the composition of chemical vapors during deposition of Si thin films. Silane (SiH₄), silane radicals (SiH₃, SiH₂, SiH, Si), and Si nanoparticles have all been monitored inside chemical vapor deposition systems. Finally, we review various thin-film characterization methods, in which lasers are implemented.     

Large area,rapid growth of two-dimensional ZnO nanosheets and their field emission performances

We demonstrate an improved and rapid method to synthesize uniform two-dimensional ZnO nanosheets at low temperature. These nanosheets can be prepared within an hour. The compositions and morphologies of the nanosheets produced were characterized by SEM, XRD, Raman and photoluminescence analysis. The nanosheets showed reasonably strong electron field emission properties with good reliability. Emission current density close to 0.3 mA/cm² was obtained. The effects of dimensions and morphologies on the field emission performance of the nanosheets are also discussed. PACS 62.23.Kn; 79.70.+q; 81.16.Be     

In situ growth of ultrashort rice-like CuO nanorods supported on reduced graphene oxide nanosheets and their lithium storage performance

A facile refluxing strategy in aqueous solution was engaged to synthesize ultrashort rice-like CuO nanorods/reduced graphene oxide (CuO-NRs/rGO) composite. The result of the high-resolution transmission electron microscopy shows that the as-synthesized rice-like CuO nanorods have a uniform size of about 8 nm in width and 28 nm in length and are homogenously dispersed on rGO nanosheets. The CuO nanorods are uniformly dispersed and immobilized by the graphene nanosheets reduced from GO. The resultant CuO-NRs/rGO composite as anode material for lithium-ion batteries displays better electrochemical properties than those of pure CuO-NRs and rGO nanosheets. The high reversible capacity and good stability can be ascribed to the presence of rGO nanosheets.     

Electronic Properties of Metallic Nanoclusters on Semiconductor Surfaces: Implications for Nanoelectronic Device Applications

We review current research on the electronic properties of nanoscale metallic islands and clusters deposited on semiconductor substrates. Reported results for a number of nanoscale metal-semiconductor systems are summarized in terms of their fabrication and characterization. In addition to the issues faced in large-area metal-semiconductor systems, nano-systems present unique challenges in both the realization of well-controlled interfaces at the nanoscale and the ability to adequately characterize their electrical properties. Imaging by scanning tunneling microscopy as well as electrical characterization by current-voltage spectroscopy enable the study of the electrical properties of nanoclusters/semiconductor systems at the nanoscale. As an example of the low-resistance interfaces that can be realized, low-resistance nanocontacts consisting of metal nanoclusters deposited on specially designed ohmic contact structures are described. To illustrate a possible path to employing metal/semiconductor nanostructures in nanoelectronic applications, we also describe the fabrication and performance of uniform 2-D arrays of such metallic clusters on semiconductor substrates. Using self-assembly techniques involving conjugated organic tether molecules, arrays of nanoclusters have been formed in both unpatterned and patterned regions on semiconductor surfaces. Imaging and electrical characterization via scanning tunneling microscopy/spectroscopy indicate that high quality local ordering has been achieved within the arrays and that the clusters are electronically coupled to the semiconductor substrate via the low-resistance metal/semiconductor interface.     

二硫化钨纳米片制备及其钙钛矿太阳能电池空穴传输层应用

开发新型无机空穴传输层材料是钙钛矿电池实现商业应用的重要挑战之一。本文开展了二硫化钨纳米片制备及其钙钛矿太阳能电池空穴传输层应用研究。采用液相超声剥离法成功制备了WS 2纳米片,并将其引入钙钛矿太阳能电池中用作空穴传输层。结果表明,当WS 2纳米片溶液浓度为1 mg/mL时,制备的WS 2纳米片空穴传输层具有较合适的厚度,并且后续在其上生长的钙钛矿活性层成膜质量高、结晶性能好,电池取得6.3%的光电转换效率。结果证实WS 2纳米片可作为新型无机空穴传输层材料用于钙钛矿太阳能电池。     

Melt-mediated coalescence of solution-deposited ZnO nanoparticles by excimer laser annealing for thin-film transistor fabrication

Nanoparticle solutions are considered promising for realizing low cost printable high performance flexible electronics. In this letter, excimer laser annealing (ELA) was employed to induce melting of solution-deposited ZnO nanoparticles and form electrically conductive porous films. The properties of the films were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, DC conductance, and photoluminescence measurements. Thin-film field-effect transistors have been fabricated by ELA without the use of conventional vacuum or any high temperature thermal annealing processes. The transistors show n-type accumulation mode behavior with mobility greater than 0.1 cm²/V s and current on/off ratios of more than 10⁴. Optimization and control of the laser processing parameters minimized thermal impact on the substrate. This technique can be beneficial in the fabrication of metal oxide based electronics on heat sensitive flexible plastic substrates using low-cost, large-area solution processing combined with direct printing techniques.     

Two‐Dimensional Au Nanocrystals: Shape/Size Controlling Synthesis,Morphologies, and Applications

The fascinating roles of two‐dimensional (2D) nanomaterials in natural super‐strong bio‐composites (i.e. aragonite platelets in nacre and apatite platelets in bone) have aroused great interest in scientific communities to synthesize their artificial counterparts with controllable geometric and physical properties. The quantum 2D confinement of electrons recently revealed in graphene nanosheets further inspires to explore 2D metal nanocrystals with intrinsic anisotropic properties and quantum size effect. Among them, 2D Au nanocrystals stand out not only due to their unique structure‐ and environmental‐dependent properties, but also due to their rapid development in synthesis approaches and emerging applications in electronics, optics, sensing and biomedicines. In this Review the aim is to rationalize numerous newly published studies on 2D Au nanocrystals and to gain insight into their shape/size controlling synthesis, diverse morphologies, properties, and applications, potentially serving a handy guide to achieve on‐demand 2D Au nanocrystals.