Wide frequency phonons manipulation in Si nanowire by introducing nanopillars and nanoparticles

The combination of different nanostructures can hinder phonons transmission in a wide frequency range and further reduce the thermal conductivity(TC).This will benefit the improvement and application of thermoelectric conversion,insulating materials and thermal barrier coatings,etc.In this work,the effects of nanopillars and Ge nanoparticles(GNPs)on the thermal transport of Si nanowire(SN)are investigated by nonequilibrium molecular dynamics(NEMD)simulation.By analyzing phonons transport behaviors,it is confirmed that the introduction of nanopillars leads to the occurrence of lowfrequency phonons resonance,and nanoparticles enhance high-frequency phonons interface scattering and localization.The results show that phonons transport in the whole frequency range can be strongly hindered by the simultaneous introduction of nanopillars and nanoparticles.In addition,the effects of system length,temperature,sizes and numbers of nanoparticles on the TC are investigated.Our work provides useful insights into the effective regulation of the TC of nanomaterials.

Si nanopillar arrays with nanocrystals produced by template-induced growth at room temperature

Well-aligned and closely-packed silicon nanopillar （SNP） arrays are fabricated by using a simple method with magnetron sputtering of Si on a porous anodic alumina （PAA） template at room temperature. The SNPs are formed by selective growth on the top of the PAA pore walls. The growth mechanism analysis indicates that the structure of the SNPs can be modulated by the pore spacing of the PAA and the sputtering process and is independent of the wall width of the PAA. Moreover, nanocrystals are identified by using transmission electron microscopy in the as-deposited SNP samples, which are related to the heat isolation structure of the SNPs. The Raman focus depth profile reveals a high crystallization ratio on the surface.

Photoelectric characteristics of silicon P–N junction with nanopillar texture:Analysis of X-ray photoelectron spectroscopy

Silicon nanopillars are fabricated by inductively coupled plasma （ICP） dry etching with the cesium chloride （CsCl） islands as masks originally from self-assembly. Wafers with nanopillar texture or planar surface are subjected to phosphorus （P） diffusion by liquid dopant source （POCl3） at 870 ℃ to form P-N junctions with a depth of 300 nm. The X-ray photoelectron spectroscopy （XPS） is used to measure the Si 2p core levels of P-N junction wafer with nanopillar texture and planar surface. With a visible light excitation, the P-N junction produces a new electric potential for photoelectric characteristic, which causes the Si 2p core level to have a energy shift compared with the spectrum without the visible light. The energy shift of the Si 2p core level is -0.27 eV for the planar P-N junction and -0.18 eV for the nanopillar one. The difference in Si 2p energy shift is due to more space lattice defects and chemical bond breaks for nanopillar compared with the planar one.

Improved light extraction of organic light emitting diodes with a nanopillar pattering structure

We have investigated the properties of organic light emitting diodes （OLEDs） with a nanopillar patterning structure at organic-metal or organic-organic interfaces. The results demonstrate that the introduction of a nanopillar structure can improve the light extraction efficiency greatly. We also find that the number, height, and position of nanopillars all affect the light extraction of OLEDs. The maximum power efficiency of a device with an optimized nanopillar patterning mode can be improved to 2.47 times that of the reference device. This enhancement in light extraction originates from the improved injected carriers, the broadened charge recombination zone, and the intensified wave guiding effects.

The enhancement of light-emitting efficiency using GaN-based multiple quantum well light-emitting diodes with nanopillar arrays

The quest for higher modulation speed and lower energy consumption has inevitably promoted the rapid development of semiconductor-based solid lighting devices in recent years. GaN-based light-emitting diodes （LEDs） have emerged as promising candidates for achieving high efficiency and high intensity, and have received increasing attention among many researchers in this field. In this paper, we use a self-assembled array-patterned mask to fabricate InGaN/GaN multi- quantum well （MQW） LEDs with the intention of enhancing the light-emitting efficiency. By utilizing inductively coupled plasma etching with a self-assembled Ni cluster as the mask, nanopillar arrays are formed on the surface of the InGaN/GaN MQWs. We then observe the structure of the nanopillars and find that the V-defects on the surface of the conventional structure and the negative effects of threading dislocation are effectively reduced. Simultaneously, we make a comparison of the photoluminescence （PL） spectrum between the conventional structure and the nanopillar arrays, achieved under an experimental set-up with an excitation wavelength of 325 mm. The analysis demonstrates that MQW-LEDs with nanopillar arrays achieve a PL intensity 2.7 times that of conventional LEDs. In response to the PL spectrum, some reasons are proposed for the enhancement in the light-emitting efficiency as follows： 1） the improvement in crystal quality, namely the reduction in V-defects; 2） the roughened surface effect on the expansion of the critical angle and the attenuated total reflection; and 3） the enhancement of the light-extraction efficiency due to forward scattering by surface plasmon polariton modes in Ni particles deposited above the p-type GaN layer at the top of the nanopillars.

Strain Induced Nanopillars and Variation of Magnetic Properties in La_(0.825)Sr_(0.175)MnO_3/LaAlO_3 Films

To investigate the process of strain relaxation and resultant variation of microstructure and magnetic properties,low-doped La_(0.825)Sr_(0.175)MnO_3 epitaxial films with different thicknesses are deposited on LaAlO_3 substrates and strain induced nanopillars are discovered inside the La_(0.825) Sr_(0.175)MnO_3 film. Perpendicular oriented nanopillars mainly exist below 30 nm and tend to disappear above 30 nm. The distribution of nanopillars not only induce the variation of lattice parameters and local structural distortion but also lead to the deviation of easy magnetization axis from the perpendicular direction. Specifically, the out-of-plane lattice parameters of the film decrease quickly with the increase of the thickness but tend to be constant when the thickness is above 30 nm. Meanwhile, the variations of magnetic properties along in-plane and out-of-plane directions would also decline at first and they then remain nearly unchanged. Our work constructs the relationship between nanopillars and magnetic properties inside films. We are able to clearly reveal the effects of inhomogeneous strain relaxation.

Plasmon-enhanced self-powered GaN/ZnTe core/shell nanopillar array photodetector

Nanostructure photodetectors,as the core component of optoelectronic devices,are mainly focused on the precise preparation of mixed-component nano-heterostructures and the realization of zero power consumption devices.Herein,we successfully fabricated n-GaN/p-ZnTe core/shell nanopillar array and realized self-power ultraviolet/violet photodetection.The radial heterojunction nanodevice reveals high light-dark current ratio of 104 at 0 V bias,indicating effective carriers’separation.And more,by integrating plasmonic effect,the responsivity and detectivity of the Au nanoparticles decorated device are increased from 3.85 to 148.83 mA/W and 4.45×1011 to 2.33×1012 Jones under 325 nm UV light irradiation.While the rise and the fall time are decreased 1.3 times and 6.8 times under 520 nm visible light irradiation at 0 V bias.The high photocurrent gain is derived from that the oscillating high-energy hot electrons in Au nanoparticles spontaneously inject into the ZnTe conduction band to involve the photodetection process.This work presents an effective route to prepare high-performance self-power photodetector and provides a promising blueprint to realize different functional photoelectronic devices based on core/shell nanostructure.

High energy storage performance in AgNbO_(3) relaxor ferroelectric films induced by nanopillar structure

Inspired by the increasing demand for energy-storage capacitors in electrical and electronic systems, dielectrics with high energy-storage performance have attracted more and more attention. AgNbO_(3) -based lead-free ceramics serve as one of the most promising environmental-friendly candidates. However, their energy storage optimization is seriously limited by the low breakdown strength. Fortunately, thin film as a form of AgNbO3 materials can effectively improve the breakdown strength. In this work, AgNbO_(3)film with ∼550 nm in thickness was deposited on SrRuO_(3 )/(001)SrTiO_(3) using pulsed laser deposition. The AgNbO_(3) film reveals typical relaxor ferroelectric hysteresis loops due to the new nanopillar structure, which contributes to high breakdown strength of up to 1200 kV cm^(-1) . Benefiting from the high breakdown strength, a recoverable energy storage density of 10.3 J cm^(-3) and an energy efficiency of 72.2% are obtained in the AgNbO_(3) film, which demonstrates the promising prospect of AgNbO_(3) film for energy storage applications.

低维InP材料的表征和生长机理研究

磷化铟作为一种重要的Ⅲ-Ⅴ半导体材料,由于其独特的光学和电学特性,近年来备受关注。大量的研究表明,它在光电子、催化、医学等领域具有潜在的应用前景。但目前在低维InP纳米材料的可控制备和大规模合成研究中还存在一些问题有待解决。针对上述问题,采用化学气相沉积法(CVD)在Si/SiO_(2)衬底上成功地制备了大量高质量的InP纳米线,并用原位生长法在多晶InP衬底上生长了大量的InP纳米柱。利用扫描电子显微镜(SEM)观察所制备的纳米材料的形貌,纳米线表面光滑,直径在30~65 nm之间,纳米线组成的薄膜厚度约为35μm;纳米柱直径分布为550~850 nm,纳米柱组成的薄膜厚度约为12μm。利用能量色散谱(EDS)和X射线光电子能谱(XPS)分析了所制备的纳米材料的成分为InP。用拉曼光谱法测定了纳米材料的化学结构,并做了进一步的分析。透射电子显微镜(TEM)用于观察纳米材料的微观结构。研究发现,本研究制备的纳米线具有很高的结晶度,沿着[111]方向生长。使用选区电子衍射(SAED)分析纳米线晶体特性时发现了清晰的衍射点,表明其为单晶结构。使用光致发光光谱仪(PL)分析其发光特性,并进一步分析。最后,我们讨论了纳米线和纳米柱的形成机制,纳米线的生长遵循气-液-固(VLS)机制,纳米柱的生长遵循固-液-固(SLS)机制。这些研究为控制InP纳米材料的制备和大规模生产提供了更多可能性。

基于PS球自组装技术的GaN纳米柱阵列ICP刻蚀工艺研究

选用蓝宝石衬底上生长的P型氮化镓为材料,通过自组装技术制备的PS球为掩膜,采用感应耦合等离子体(ICP)干法刻蚀的方法来制备形状规则、周期均匀的纳米结构。在制备过程中,氮化镓纳米结构的形貌受诸多因素的影响,例如胶体球掩膜自组装的形貌,ICP刻蚀所通入的气体类型、气体比例、刻蚀功率源、刻蚀时间等。系统地研究了刻蚀过程中通入的气体类型、气体比例和刻蚀功率源、刻蚀时间对氮化镓纳米结构形貌的影响,并进行调整优化。利用扫描电子显微镜(SEM)对氮化镓进行的形貌分析表明:(1)随着刻蚀功率源和刻蚀时间的增大,掩膜层PS球的尺寸会随之减小使得刻蚀得到的纳米结构直径减小;(2)氮化镓纳米结构的形貌、刻蚀速率受到刻蚀通入的气体类型和比例影响,在Ar和CF_(4)或SF_(6)的组合气体作用下刻蚀速率相对非常缓慢,最高为15 nm/min,而Cl_(2)和BCl_(3)的组合气体作用速率可达到150 nm/min。

基于TiO_(2)纳米柱的多波段响应Cs_(2)AgBiBr_(6)双钙钛矿光电探测器

全无机无铅双钙钛矿材料(Cs_(2)AgBiBr_(6))具有载流子寿命长、稳定性高和禁带宽度适中等优点,近年来在光电探测器的应用研究上受到广泛关注.本文通过将水热法生长的TiO_(2)纳米柱阵列嵌入到Cs_(2)AgBiBr_(6)层中形成紧密的核壳结构,增大两者的物理接触面积,提高光电探测器电子注入与电荷分离的效率.此外,TiO_(2)纳米柱阵列还可以有效减小光在器件表面的反射损耗,增强Cs_(2)AgBiBr_(6)薄膜的光捕获能力.实验结果表明,基于TiO_(2)纳米柱的多波段响应Cs_(2)AgBiBr_(6)双钙钛矿光电探测器在365 nm及405 nm多个波长均能激发高光响应且有良好稳定性和重复性,所得平均开关比分别为522和2090,以0.056 W/cm^(2)固定光强激发,响应度分别为0.019 A/W和0.057 A/W,比探测率分别为1.9×10^(10)Jones和5.6×10^(10)Jones.相比于传统TiO_(2)薄膜型Cs_(2)AgBiBr_(6)光电探测器,平均开关比分别提升65倍和110倍,响应度分别提升35%和256%,比探测率分别提升6.9倍和25倍.上述结果表明,基于TiO_(2)纳米柱的多波段响应Cs_(2)AgBiBr_(6)双钙钛矿光电探测器可为提高光电器件的效率提供参考方案.

Atomistic Simulation of the Orientation-dependent Plastic Deformation Mechanisms of Iron Nanopillars

Tensile tests were performed on iron nanopillars oriented along [001] and [110] directions at a constant temperature of 300 K through molecular dynamics simulations with an embedded-atom interatomic potential for iron. The nanopillars were stretched until yielding to investigate the onset of their plastic deformation behaviors. Yielding was found to occur through two different mechanisms for [001] and [110] tensions. In the former case, plastic deformation is initiated by dislocation nucleation at the edges of the nanopillar, whereas in the latter case by phase transformation inside the nanopillar. The details during the onset of plastic deformation under the two different orientations were analyzed. The varying mechanisms during plastic deformation initiation are bound to influence the mechanical behavior of such nanoscale materials, especially those strongly textured.

Interface engineering of high performance all-inorganic perovskite solar cells via low-temperature processed TiO2 nanopillar arrays

All-inorganic perovskite solar cells suffer from low performance due to unsatisfactory carrier transport and light harvesting efficiency.Semiconductor nanopillar arrays can reduce light reflection loss and suppress exciton recombination dynamics in optoelectronic devices.In all-inorganic perovskite solar cells,few studies employing TiO_(2)nanopillar arrays(TiO_(2)NaPAs)have been reported to improve the device performance.Herein,well-arranged TiO_(2)NaPAs are chosen to enhance the interfacial contact between perovskite and electron transporting layers for improving the carrier transport.Notably,TiO_(2)NaPAs can be directly fabricated on rigid/flexible substrates at roughly room temperature by unique glancing angle deposition,which is more available than high-temperature hydrothermal/solvothermal methods.By embedding TiO_(2)NaPAs into chemical processable CsPbI2Br layers,continuous and intimate films are readily formed,guaranteeing large physical contact for facilitating more effective electron injection and charge separation.The vertically grown TiO_(2)NaPAs also provide a straightforward electron transporting path to electrodes.In addition,TiO_(2)NaPAs can guide the incident light and enhance the light-harvesting ability of CsPbI2Br films.As a result,the solar cell with TiO_(2)NaPAs displays a power conversion efficiency of 11.35%higher than planar control of 10.04%,and exhibits better long-term thermal stability.This strategy provides an opportunity by constructing direct interfacial regulation towards the performance improvement of inorganic perovskite solar cells.

基于粒子群与遗传算法的消色差超透镜自动设计

本文利用智能优化算法,对宽波段消色差超透镜进行设计优化。首先,研究构建于二氧化硅基底上的硅纳米柱这一微单元结构的光学特性,通过数值仿真扫描单元结构的半径构建相位数据库。之后,通过使用粒子群与遗传算法的混合算法(PSO_GA)在相位数据库中找到最佳相位矩阵,即对应每个位置最佳的单元结构。最后,构建超透镜,通过仿真实验验证其可实现红外波段(1000 nm~1250 nm)的聚焦,且消色差效果优于传统粒子群优化算法所获得的超透镜结构。此超透镜的设计为平面光学器件的自动化设计提供了一种解决方法。

GaN nanopillars with a nickel nano-island mask

Uniform GaN nanopillar arrays have been successfully fabricated by inductively coupled plasma etching using self-organized nickel nano-islands as the masks on GaN/sapphire. GaN nanopillars with diameters of 350 nm and densities of 2.6 × 10^8 cm^-2 were demonstrated and controlled by the thickness of Ni film and the NH3 annealing time. These GaN nanopillars show improved optical properties and strain change compared to that of GaN film before ICP etching. Such structures with large-area uniformity and high density could provide additional advantages for light emission of light-emitting diodes, quality improvement of ELO regrowth, etc.

Application of ZnO nanopillars and nanoflowers to field-emission luminescent tubes

Zinc oxide （ZnO） nanopillars on a ZnO seed layer and ZnO nanoflowers were synthesized by electrochemical deposition on linear wires. The morphologies and crystal orientation of the ZnO nanostructures were investigated by a scanning electron microscopy and an X-ray diffraction pattern, respectively. Detailed study on the field-emission properties of ZnO nanostructures indicates that nanopillars with a high aspect ratio show good performance with a low turn-on field of 0.16 V/#m and a high field enhancement factor of 2.86 x 104. A luminescent tube with ZnO nanopillars on a linear wire cathode and a transparent anode could reach a luminance of about 1.5 x l04 cd/m2 under an applied voltage of 4 kV.

Reduction of proximity effect in fabricating nanometer-spaced nanopillars by two-step exposure

A two-step exposure method to effectively reduce the proximity effect in fabricating nanometer-spaced nanopillars is presented. In this method, nanopillar patterns on poly-methylmethacrylate （PMMA） were partly crosslinked in the first-step exposure. After development, PMMA between nanopillar patterns was removed, and hence the proximity effect would not take place there in the subsequent exposure. In the second-step exposure, PMMA masks were completely cross-linked to achieve good resistance in inductively coupled plasma etching. Accurate pattern transfer of rows of nanopillars with spacing down to 40 nm was realized on a silicon-on-insulator substrate.

A non-lithographic plasma nanoassembly technology for polymeric nanodot and silicon nanopillar fabrication

In this work, we present plasma etching alone as a directed assembly method to both create the nanodot pattern on an etched polymeric (PMMA) film and transfer it to a silicon substrate for the fabrication of silicon nanopillars or cone-like nanostructuring. By using a shield to control sputtering from inside the plasma reactor, the size and shape of the resulting nanodots can be better controlled by varying plasma parameters as the bias power. The effect of the shield on inhibitor deposition on the etched surfaces was investigated by time-of-flight secondary ion mass spectroscopy (ToF-SIMS) measurements. The fabrication of quasi-ordered PMMA nanodots of a diameter of 25 nm and period of 54 nm is demonstrated. Pattern transfer to the silicon substrate using the same plasma reactor was performed in two ways:(a) a mixed fluorine-fluorocarbon-oxygen nanoscale etch plasma process was employed to fabricate silicon nanopillars with a diameter of 25 nm and an aspect ratio of 5.6, which show the same periodicity as the nanodot pattern, and (b) high etch rate cryogenic plasma process was used for pattern transfer. The result is the nanostructuring of Si by high aspect ratio nanotip or nanocone-like features that show excellent antireflective properties.

The dislocation structure of slip bands in deformed high entropy alloy nanopillars

Remarkable diversity is observed in dislocation interactions that are responsible for intermittent and sudden crystal slips.While large crystal slips can be easily observed on the surface of deformed crystals,unraveling the underlying dislocation interaction mechanisms,however,has been a longstanding challenge in the study of single-crystal plasticity.A recent study demonstrated that the sluggish dislocation dynamics in the high entropy alloy(HEA)of Al_(0.1)CoCrFeNi enables the observation of slip bands for a direct link to dislocation avalanches in a nanopillar.Here,we further examined the dislocation structure of slip bands in the HEA nanopillars oriented for single slip.Experimental evidence was provided on the dislocation organization in a slip band based on groups of primary dislocations,secondary dislocations,and dislocation pileups.The results were compared with the previously proposed slip band models.The unique aspects of the HEA that enable such observations were also investigated through an examination of the dislocation microstructure and its response to applied forces in the HEA nanopillars.

Gradient Wetting Transition from the Wenzel to Robust Cassie-Baxter States along Nanopillared Cicada Wing and Underlying Mechanism

Gradient wettability is important for some living organisms.Herein,the dynamic responses of water droplets impacting on the surfaces of four regions along the wing vein of cicada Cryptotympana atratafabricius are investigated.It is revealed that a gradient wetting behavior from hydrophilicity(the Wenzel state)to hydrophobicity and further to superhydrophobicity(the Cassie-Baxter state)appears from the foot to apex of the wing.Water droplets impacting on the hydrophilic region of the wing cannot rebound,whereas those impacting on the hydrophobic region can retract and completely rebound.The hydrophobic region exhibits robust water-repelling performance during the dynamic droplet impact.Moreover,a droplet sitting on the hydrophobic region can recover its spherical shape after squeezed to a water film as thin as 0.45 mm,and lossless droplet transportation can be achieved at the region.Based on the geometric parameters of the nanopillars at the hydrophilic and hydrophobic regions on the cicada wing,two wetting models are developed for elucidating the mechanism for the gradient wetting behavior.This work directs the design and fabrication of surfaces with gradient wetting behavior by mimicking the nanopillars on cicada wing surface.