Shape‐Controlled Synthesis of Polyhedral Nanocrystals and Their Facet‐Dependent Properties

Growth of inorganic polyhedral nanocrystals with excellent morphology control presents significant synthetic challenges, especially when the development of synthetic schemes to make nanocrystals with systematic shape evolution is desired. Nanocrystals with fine size and shape control facilitate formation of their self‐assembled packing structures and offer opportunities for examination of their facet‐dependent physical and chemical properties. In this Feature Article, recent advances in the synthesis of nanocrystals with systematic shape evolution are highlighted. The reaction conditions used to achieve this morphology change offer insights into the growth mechanisms of nanocrystals. A novel class of polyhedral core–shell heterostructures fabricated using structurally well‐defined nanocrystal cores is also presented. Facet‐dependent photocatalytic activity, molecular adsorption, and catalytic and electrical properties of nanocrystals have been examined and are discussed. Nanomaterials with enhanced properties and functionality may be obtained through continuous efforts in the synthesis of nanocrystals with well‐defined structures and investigation of their plane‐selective properties.     

On the Synthesis of Carbon Nanofibers and Nanotubes by Microwave Irradiation: Parameters,Catalysts, and Substrates

The microwave (MW)‐assisted synthesis of one dimensional carbon systems is introduced as a promising approach to improve the speed and cost‐effectiveness of the fabrication process. Improved reaction conditions are generated by direct MW heating and synthesis under advanced reaction conditions. The influence of the reaction conditions is investigated and the importance of individual process parameters on the synthesis is discussed. Temperature and pressure data recorded during the irradiation process are analyzed in detail and allow the determination of essential process parameters. This leads to improved reaction conditions, better control of the one‐dimensional carbon nanosystems by tuning the catalyst materials, and allows expanding this approach to initiate the synthesis on a variety of different substrates, such as quartz glass and mica.     

Synthesis of Silver Nanocrystallites by a New Thermal Decomposition Method and Their Characterization

We formed silver nanocrystallites by the thermal decomposition of a Ag+¹‐oleate complex, which was prepared by a reaction with AgNO₃ and sodium oleate in a water solution. The resulting monodispersed silver nanocrystallites were produced by controlling the temperature (290 °C). Transmission electron microscopic (TEM) images of the particles showed a 2‐dimensional assembly of the particles with a diameter of 9.5 ± 0.7 nm, demonstrating the uniformity of these nanocrystallites. An energy‐dispersive X‐ray (EDX) spectrum and X‐ray diffraction (XRD) peaks of the nanocrystallites showed the highly crystalline nature of the silver structure. We analyzed the decomposition of the Ag⁺¹‐oleate complex using a Thermo Gravimetric Analyzer (TGA) and observed the crystallization process using XRD.     

Synthesis of MnO2 Nanoparticles Confined in Ordered Mesoporous Carbon Using a Sonochemical Method

A sonochemical method has been successfully used in order to incorporate MnO₂ nanoparticles inside the pore channels of CMK‐3 ordered mesoporous carbon. Modification of the intrachannel surfaces of CMK‐3 to make them hydrophilic enables KMnO₄ to readily penetrate the pore channels. At the same time, the modification changes the surface reactivity, enabling the formation of MnO₂ nanoparticles inside the pores of CMK‐3 by the sonochemical reduction of metal ions. The resultant structures were characterized by X‐ray diffraction (XRD), nitrogen adsorption, and transmission electron microscopy (TEM). CMK‐3 with 20 wt.‐% loading of MnO₂ inside CMK‐3 delivered an improved discharge performance of 223 mA h g^–1 at a relatively high rate of 1 A g^–1. Almost no decrease in specific capacity is observed for the second cycle, and a discharge capacity of more than 165 mA h g^–1 is retained after 100 cycles. This is attributed to the nanometer‐sized MnO₂ formed inside CMK‐3 and the high surface area of the mesopores (3.1 nm) in which the MnO₂ nanoparticles are formed.     

Synthesis and Characterization of Crystalline Ag2Se Nanowires Through a Template‐Engaged Reaction at Room Temperature

Single‐crystalline Ag₂Se nanowires have been successfully synthesized through a template‐engaged topotactic reaction in which nanowires of trigonal selenium were transformed into Ag₂Se by reacting with aqueous AgNO₃ solutions at room temperature (RT). An interesting size‐dependent transition between two crystal structures has also been observed for this newly synthesized one‐dimensional system: The Ag₂Se nanowires adopted a tetragonal structure when their diameters were less than ∼40 nm; an orthorhombic structure was found to be more favorable as the diameter of these nanowires was increased beyond 40 nm. Since this reaction can be carried out at ambient pressure and temperature, it should be straightforward to scale up the entire process for the high‐volume production of Ag₂Se nanowires with well‐controlled sizes and crystal structures. These highly uniform nanowires of single‐crystalline Ag₂Se are potentially useful as photosensitizers, superionic conductors, magnetoresistive compounds, or thermoelectric materials. This work also represents the first demonstration of a template‐engaged process capable of generating single‐crystalline nanowires from the solution‐phase and at RT.     

Device characteristics of a 10.1% hydrazine‐processed Cu2ZnSn(Se,S)4 solar cell

A power conversion efficiency record of 10.1% was achieved for kesterite absorbers, using a Cu₂ZnSn(Se,S)₄ thin‐film solar cell made by hydrazine‐based solution processing. Key device characteristics were compiled, including light/dark J–V, quantum efficiency, temperature dependence of V_oc and series resistance, photoluminescence, and capacitance spectroscopy, providing important insight into how the devices compare with high‐performance Cu(In,Ga)Se₂. The record kesterite device was shown to be primarily limited by interface recombination, minority carrier lifetime, and series resistance. The new level of device performance points to the significant promise of the kesterites as an emerging and commercially interesting thin‐film technology. Copyright © 2011 John Wiley & Sons, Ltd.     

Nd2(S,Se, Te)3 Colloidal Quantum Dots: Synthesis,Energy Level Alignment,Charge Transfer Dynamics,and Their Applications to Solar Cells

Novel and less toxic quantum dot (QD) semiconductors are desired for developing environmentally benign colloidal quantum dot solar cells. Here, the synthesis of novel lead/cadmium‐free neodymium chalcogenide Nd₂(S, Se, Te)₃ QDs via solution‐processed method is reported for the first time. The results show that small‐bandgap semiconductor QDs with a narrow size distribution ranging from 2 to 8 nm can be produced, and the wide absorption band can be achieved by the redshift owing to the size quantization effect by controlling the initial loading of chalcogenide precursors. By analyzing the band structure of QDs and the energy level alignment between QDs and TiO₂, the influence of energy offset between the conduction band edges of QDs and TiO₂ on the charge transfer dynamics and photovoltaic performance of QD solar cells (QDSCs) is investigated. It is revealed that among the three types of QDs studied, Nd₂Se₃ QDSCs with the smallest energy offset exhibit the best performances and a decent power conversion efficiency of 3.19% is achieved. This work clearly demonstrates the promising potentials of novel rare earth chalcogenide quantum dots in photovoltaic applications.     

Fabrication of Cu(In,Ga)Se2 thin films by sputtering from a single quaternary chalcogenide target

Single‐layered Cu‐In‐Ga‐Se precursors were fabricated by one‐step sputtering of a single quaternary Cu(In,Ga)Se₂ (CIGS) chalcogenide target at room temperature, followed by post selenization using Se vapor obtained from elemental Se pellets. The morphological and structural properties of both as‐deposited and selenized films were characterized by X‐ray diffraction (XRD), Raman spectroscope and scanning electron microscope (SEM). The precursor films exhibited a chalcopyrite structure with a preferential orientation in the (112) direction. The post‐selenization process at high‐temperature significantly improved the quality of the chalcopyrite CIGS. The CIGS layers after post‐selenization were used to fabricate solar cells. The solar cell had an open‐circuit voltage Voc of 0.422 V, a short‐circuit current density J = 24.75 mA, a fill factor of 53.29%, and an efficiency of 7.95%. Copyright © 2010 John Wiley & Sons, Ltd.     

Nanoliter Liquid Packaging in a Bioresorbable Microsystem by Additive Manufacturing and its Application as a Controlled Drug Delivery Device

Precise packaging of nanoliter amounts of liquid in a microsystem is important for many biomedical applications. However, existing liquid encapsulation technologies have limitations in terms of liquid waste, evaporation, trapped bubbles, and liquid degradation. In this study, multiple additive manufacturing techniques for nanoliter liquid packaging in bioresorbable microsystems is used. Two-photon photolithography is used for bioresorbable reservoir fabrication, while inkjet printing (IJP) is used for precise nanoliter liquid packaging. Dual IJP allows for micro-reservoirs to be filled with precise amounts of drug solution and subsequently and rapidly sealed with a layer of lipids mixed with Fe₃O₄ nanoparticles. Combining these two printing techniques can overcome the previous limitations of liquid encapsulation technologies. To demonstrate the relevance of this technique, a wirelessly activated, bioresorbable multi-reservoir microcapsule that can be used for controlled drug delivery is presented. The microcapsules and their content are shown to be stable during fabrication, storage, and operation. Multiple cargo release events are triggered independently by the local melting of the sealing layer, resulting from magnetically induced Fe₃O₄ nanoparticle heating. The operation of the capsule is demonstrated in tissue phantoms and in vitro cell cultures.     

剥离技术制作金属互连柱及其在MEMS中的应用

介绍了利用AZ5214光刻胶及ZKPI-305ⅡD型非光敏聚酰亚胺制作的两种不同的剥离层,即双层AZ5214和ZKPI AZ5214.此两种剥离工艺简单易操作,可剥离出1 μ m金属镍柱,并可在MEMS 工艺制作中获得了良好的效果.     

Photosensitivity of the structures on the Cu(In,Ga)(S,Se)<Subscript>2</Subscript> films obtained by thermal treatment in the S and Se vapors

Using the method of simultaneous sulfurization and selenization of intermetallic Cu-In-Ga layers, single-phase thin films of the Cu(In,Ga)(S,Se)₂ (CIGSS) alloys are obtained. On these films, rectifying photosensitive surface-barrier structures In/p-CIGSS are obtained by vacuum thermal evaporation of pure In. The photosensitivity spectra of the originally obtained structures are studied. The effect of the composition of the alloy films and illumination conditions on the photoelectric parameters of new structures In/p-CIGSS is studied. It is concluded that the obtained CIGSS films are promising for fabrication of high-efficiency thin-film photoconverters.     

As2S8薄膜光致折射率效应及其在条波导制备中的应用研究

分别采用紫外光和He-Cd激光辐照，实验研究了As2S8非晶态薄膜的光致折射率变化以及膜厚变化的现象，归纳了实验规律，初步分析了机理。利用光诱起折射率变化效应试制了As2S8玻璃条波导，实现了良好的导波特性。     

Two-Step Cooling Strategy for Synergistic Control of CuZn and SnZn Defects Enabling 12.87% Efficiency (Ag,Cu)2ZnSn(S,Se)4 Solar Cells

Abundant intrinsic defects and defect clusters in Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cells lead to severe nonradiative recombination and limited photoelectric performance. Therefore, developing effective method to suppress the detrimental defects is the key to achieve high-efficiency solar cell. Herein, a convenient two-step cooling strategy in selenization process is reported to suppress the Cu_Zn and Sn_Zn defects and defect clusters synergistically. The results show that rapid cooling during section from selenization temperature to turning temperature can inhibit the volatilization of Sn and restrain the corresponding Sn-related defects, while slow cooling during the subsequent temperature section can reduce the degree of Cu-Zn disorder. Benefitting from the synergistic effect of two-step cooling, a significantly lowered concentration of Sn_Zn and Cu_Zn defect and their defect clusters [2Cu_Zn+Sn_Zn] in absorber is observed, meanwhile, a reduced band tailing effect and promoted carrier collection efficiency of the photovoltaic device is obtained. Finally, a device with improved open-circuit voltage (V_oc) of 505.5 mV and efficiency of 12.87% is achieved. This study demonstrates the impact of cooling process on defects controlling for the first time and provides a simple and effective new strategy for intrinsic defect control, which may be universal in other inorganic thin film solar cells.     

Advance in Using Plasma Technology for Modification or Fabrication of Carbon-Based Materials and Their Applications in Environmental,Material, and Energy Fields

Plasma technology is an eco-friendly way to modify or fabricate carbon-based materials (CBMs) due to plasmas’ distinctive abilities in tuning the surface physicochemical properties by implanting functional groups or incorporating heteroatoms into the surface without changing the bulk structure. However, the mechanisms of functional groups formation on the carbon surface are still not clearly explained because of the variety of different discharge conditions and the complexity of plasma chemistry. Consequently, this paper contains a comprehensive review of plasma-treated carbon-based materials and their applications in environmental, materials, and energy fields. Plasma-treated CBMs used in these fields have been significantly enhanced in recent years because these related materials possess unique features after plasma treatment, such as higher adsorption capacity, enhanced wettability, improved electrocatalytic activity, etc. Meanwhile, this paper also summarizes possible reaction routes for the generation of functional groups on CBMs. The outlook for future research is summarized, with suggestions that plasma technology research and development shall attempt to achieve precise control of plasmas to synthesize or to modify CBMs at the atomic level.     

Size‐Controlled Synthesis of Cu2‐xE (E = S,Se) Nanocrystals with Strong Tunable Near‐Infrared Localized Surface Plasmon Resonance and High Conductivity in Thin Films

A facile method for preparing highly self‐doped Cu_2‐xE (E = S, Se) nanocrystals (NCs) with controlled size in the range of 2.8–13.5 nm and 7.2–16.5 nm, for Cu_2‐xS and Cu_2‐xSe, respectively, is demonstrated. Strong near‐infrared localized surface plasmon resonance absorption is observed in the NCs, indicating that the as‐prepared particles are heavily p‐doped. The NIR plasmonic absorption is tuned by varying the amount of oleic acid used in synthesis. This effect is attributed to a reduction in the number of free carriers through surface interaction of the deprotonated carboxyl functional group of oleic acid with the NCs. This approach provides a new pathway to control both the size and the cationic deficiency of Cu_2‐xSe and Cu_2‐xS NCs. The high electrical conductivity exhibited by these NPs in metal‐semiconductor‐metal thin film devices shows promise for applications in printable field‐effect transistors and microelectronic devices.     

Nanocrystalline Metal Oxides from the Injection of Metal Oxide Sols in Coordinating Solutions: Synthesis,Characterization, Thermal Stabilization,Device Processing,and Gas‐Sensing Properties

Metal oxide (SnO₂, TiO₂, In₂O₃, ZnO) sols are prepared by various sol–gel processes in such a way as to hinder the condensation reactions. The obtained sols are injected at 160 °C into a solution of tetradecene and dodecylamine, and kept under heating for different periods of time. Depending on the starting sol, variously crystallized oxide nanoparticles are obtained, whose phase compositions and chemical structure have been studied by X‐ray diffraction (XRD) and Fourier transform IR spectroscopy. The elimination of the organic residuals has been carried out by thermal treatment, and the thermal evolution of the nanoparticles has been studied by thermal analyses and Raman spectroscopy. High‐resolution transmission electron microscopy studies coupled with XRD measurements show that the thermal treatment does not markedly affect the particle size, which remains in the nanometer‐sized regime (from 3.5 to 8.5 nm, depending on the system), except in the case of ZnO. The thermally purified and stabilized powders, drop‐coated onto alumina substrates with pre‐deposited electrical contacts, have been tested as gas‐sensing devices, displaying outstanding sensing properties even at room temperature.     

Bipolar Electrochemical Synthesis of WS2 Nanoparticles and Their Application in Magneto‐Immunosandwich Assay

WS₂ nanoparticles are prepared using bipolar electrochemistry. Obtained material exhibits high activity for hydrogen evolution reaction (HER) and it is used as a label in standard magneto‐immunosandwich assay for protein detection through HER. This new system shows high analytical performance in terms of a wide range, selectivity, sensitivity, and reproducibility.     

Large‐Scale Fabrication of MoS2 Ribbons and Their Light‐Induced Electronic/Thermal Properties: Dichotomies in the Structural and Defect Engineering

Controlled design and patterning of layered transition metal dichalcogenides (TMDs) into specific dimensions and geometries hold great potential for next‐generation micro/nanoscale electronic applications. Herein, the large‐scale fabrication of MoS₂ ribbons with widths ranging from micro‐ to nanoscale is reported. Their unique electric and thermal properties introduced by the shape change and defect creation are also demonstrated, with particular focus on the performance associated with light–matter interactions. The theoretical calculation indicates significantly increased absorption and scattering efficiency of the MoS₂ ribbons with decreasing width. As a result, enhanced photocarrier generation ability is detected on their phototransistors with defect‐modulated light‐response behavior. The light‐induced thermal transport properties of the MoS₂ ribbons are further studied. A decreased thermal conductivity is observed on narrower ribbons, attributed to the defects created during fabrication. It is also found that the effect of phonon scattering at ribbon edges on their thermal conductivity is insignificant, and the thermal transport has no obvious dependence on the ribbon direction at such width scale. This study evaluates the prospects for designing and fabricating TMD semiconductors with specific geometries for future optoelectronic applications.     

The Zn(S,O,OH)/ZnMgO buffer in thin film Cu(In,Ga)(S,Se)2‐based solar cells part I: Fast chemical bath deposition of Zn(S,O,OH) buffer layers for industrial application on Co‐evaporated Cu(In,Ga)Se2 and electrodeposited CuIn(S,Se)2 solar cells

This paper is focused on the basic study and optimization of short time (<10 min) Chemical Bath Deposition (CBD) of Zn(S,O,OH) buffer layers in co‐evaporated Cu(In,Ga)Se₂ (CIGSe) and electrodeposited CuIn(S,Se)₂ ((ED)‐CIS) solar cells for industrial applications. First, the influence of the deposition temperature is studied from theoretical solution chemistry considerations by constructing solubility diagrams of ZnS, ZnO, and Zn(OH)₂ as a function of temperature. In order to reduce the deposition time under 10 min, experimental growth deposition studies are then carried out by the in situ quartz crystal microgravimetry (QCM) technique. An optimized process is performed and compared to the classical Zn(S,O,OH) deposition. The morphology and composition of Zn(S,O,OH) films are determined using SEM and XPS techniques. The optimized process is tested on electrodeposited‐CIS and co‐evaporated‐CIGSe absorbers and cells are completed with (Zn,Mg)O/ZnO:Al windows layers. Efficiencies similar or even better than CBD CdS/i‐ZnO reference buffer layers are obtained (15·7% for CIGSe and 8·1% for (ED)‐CIS). Copyright © 2009 John Wiley & Sons, Ltd.     

The Role of Sulfur in Solution‐Processed Cu2ZnSn(S,Se)4 and its Effect on Defect Properties

Understanding the electrically active defects in kesterite Cu₂ZnSn(S,Se)₄(CZTSSe) is critical for the continued development of solar cells based on this material, but challenging due to the complex nature of this polycrystalline multinary material. A comparative study of CZTSSe alloys with three different bandgaps, made by introducing different fractions of sulfur during the annealing process, is presented. Using admittance spectroscopy, drive level capacitance profiling, and capacitance‐voltage profiling, the dominant defect energy level present in the low sulfur content device is determined to be 0.134 eV above the valence band maximum, with a bulk defect density of 8 × 10¹⁴ cm^?3, while the high sulfur content device shows a deeper defect energy level of 0.183 eV and a higher bulk defect density, 8.2 × 10¹⁵ cm^?3. These findings are consistent with the current density–voltage characteristics of the resulting solar cells and their external quantum efficiency. It suggests that as the sulfur content increases, the bandgap of the absorber is enlarged, leading to an increasing open‐circuit voltage (V_oc), that is accompanied by stronger recombination due to the higher defect density of the sulfur‐rich absorber. This is reflected in large V_oc deficit and poor carrier collection of the high sulfur content device.