A simple electrochemical deposition route for the controllable growth of Ce-doped ZnO nanorods

Here we report that the various Ce⁴⁺-doped ZnO nanorods can be successfully synthesized by electrochemical deposition route, which represents a simple, quick and economical method for the controllable growth of Ce⁴⁺-doped ZnO nanorods. The high-resolution transmission electron microscopy (HRTEM) and the selected area electron diffraction (SAED) both proved that the prepared Ce⁴⁺-doped ZnO nanorods consisted of single crystal with preferential growth in the [0 0 0 1] direction. The morphology and size of the nanorods can be tailored by optimizing the synthetic parameters. Furthermore, the flowerlike Ce⁴⁺-doped ZnO nanorod clusters can also be successfully prepared. An obvious blue-shifted absorption peak of Ce⁴⁺-doped ZnO nanorod compared with that of the bulk ZnO phase was observed.     

Formation and characterization of p-type semiconductor CuCrO2 thin films prepared by a sol–gel method

This study adopted the sol–gel method to synthesize p-type semiconductor CuCrO₂ films and analyzed the effects of an annealing treatment, under a controlled argon atmosphere by changing the temperature and time, on the phase transformation, micro- and nano-structure, composition, and semiconductor properties of thin films. In the Cu–Cr–O phase transformation system, CuO, Cr₂O₃, and CuCr₂O₄ were the intermediate phases of the reaction for forming CuCrO₂: in the metastable state reaction process, the composite phases changed into a single phase, CuCrO₂; in the stable-state reaction process of CuCrO₂, carbon elements of precursors were released and eliminated; and finally the optoelectronic properties of the CuCrO₂ thin film were adjusted and changed. The CuCrO₂ thin film possessed cell- and polygon-like shaped microstructures. The carbon content in the CuCrO₂ film decreased, so the copper, chromium, and oxygen contents increased accordingly. The optical band gap of CuCrO₂ thin film increased from 2.81 eV to 3.05 eV, while the resistivity decreased. The nanoscale crystal was identified which also of the delafossite CuCrO₂ structure. Using the sol–gel method to prepare the CuCrO₂ thin films, an appropriate annealing temperature and time were helpful in forming the single-phase CuCrO₂; the decrease of precursor elements in the thin film could enhance the band gap and the conductivity of the material.     

Near-infrared emitting CdTe0.5Se0.5/Cd0.5Zn0.5S quantum dots: synthesis and bright luminescence

We present how CdTe_0.5Se_0.5 cores can be coated with Cd_0.5Zn_0.5S shells at relatively low temperature (around 200°C) via facile synthesis using organic ammine ligands. The cores were firstly fabricated via a less toxic procedure using CdO, trioctylphosphine (TOP), Se, Te, and trioctylamine. The cores with small sizes (3.2-3.5 nm) revealed green and yellow photoluminescence (PL) and spherical morphologies. Hydrophobic core/shell CdTe_0.5Se_0.5/Cd_0.5Zn_0.5S quantum dots (QDs) with tunable PL between green and near-infrared (a maximum PL peak wavelength of 735 nm) were then created through a facile shell coating procedure using trioctylphosphine selenium with cadmium and zinc acetate. The QDs exhibited high PL efficiencies up to 50% because of the formation of a protective Cd_0.5Zn_0.5S shell on the CdTe_0.5Se_0.5 core, even though the PL efficiency of the cores is low (≤1%). Namely, the slow growth process of the shell plays an important role for getting high PL efficiencies. The properties of the QDs are largely determined by the properties of CdTe_0.5Se_0.5 cores and shells preparation conditions such as reaction temperature and time. The core/shell QDs exhibited a small size diameter. For example, the average diameter of the QDs with a PL peak wavelength of 735 nm is 6.1 nm. Small size and tunable bright PL makes the QDs utilizable as bioprobes because the size of QD-based bioprobes is considered as the major limitation for their broad applications in biological imaging.     

A single-step method for synthesis of CuInS2 nanostructures using cyclic microwave irradiation

Pure and well-crystalline CuInS₂ nanostructures were successfully synthesized via a cyclic microwave irradiation method at low microwave power using cupric chloride dihydrate (CuCl₂·2H₂O), indium chloride tetrahydrate (InCl₃·4H₂O) and thioacetamide as starting reagents. The effects of processing cycles (2–75 cycles) and microwave heating powers (180–600 W) on purity, crystallinity, particle size and morphology of the synthesized products were investigated. The synthesized products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and UV–vis spectroscopy. Increasing processing cycles and microwave heating power improved the purity and crystallinity of the synthesized products. Using the microwave powers of 450 and 600 W with 75 cycles, pure CuInS₂ nanocrystallites were obtained. The CuInS₂ crystallites displayed nanoparticles in clusters with decreasing in the diameter sizes from 1.6 to 0.9 µm when the microwave power was increased from 180 to 600 W. The reaction mechanism of the CuInS₂ formation was also provided. A CuInS₂ solar cell, made from FTO/TiO₂/CuInS₂/CdS/Pt-FTO layers, was fabricated to explore the potential use of the CuInS₂ nanoparticles in photovoltaic devices. The photovoltaic properties of the CuInS₂ solar cell including open-circuit voltage (V_oc), short-circuit current density (J_sc) and fill factor (FF) were 281.10 mV, 0.072 mA/cm² and 0.47, respectively, with cell conversion efficiency (η) of 0.01% under 1.5 AM illumination.     

Low-temperature synthesis and optical properties of wurtzite ZnS nanowires

Single-crystal wurtzite ZnS nanowires have been synthesized via a facile solution route with polyethylene glycol-400 as inducing template at low temperature (170 °C). The as-prepared products have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and energy dispersive X-ray analysis (EDX). Raman and photoluminescence spectrum (PL) were used to investigate the optical properties of ZnS nanowires. The strong emission peak centered at 322 nm in PL spectrum could be attributed to the band to band transitions.     

Real-coded genetic algorithm for stochastic optimization: A tool for recipe qualification of semiconductor manufacturing under noisy environments

This paper considers an interesting topic of recipe qualification during each fabrication step of semiconductor manufacturing. In particular, this type of stochastic optimization scheme within a discrete-event simulation process is discussed and a new optimization method, with the capability to anchor robust recipes for batch processing, is proposed, implemented and evaluated. A particular real-coded genetic algorithm (GA) suitable for resolving continuous optimization problems in noisy environments is developed. Four test functions appearing in the literature are used as a test-bed to assess the proposed genetic algorithm via a variety of experimental studies, showing that the new method can produce much more accurate estimates of the true optimum points than the other two optimization procedures, the Nelder-Mead (NM) simplex search procedure and a well-known variant (RS+S9) of Nelder-Mead suitable for stochastic optimization. As such, the new method could serve as a useful tool for process recipe optimization in noisy semiconductor manufacturing environments. Finally, the chemical mechanical planarization (CMP) process, a turnkey process during semiconductor fabrication, is simulated from batch to batch based on the real-data equipment model and the presented algorithm is employed to seek the optimal recipe profile while processing each batch of wafers sequentially through the CMP tool.     

Investigation of field-effect transistors fabricated by metal-ion-doped nano-titania using sol-gel technique

In our present investigations, field-effect transistors (FETs) based on nano-TiO₂ and metal-ion-doped TiO₂ particles were fabricated and their characteristics were studied. Semiconductor characteristics of nano-TiO₂/metal-ion-doped TiO₂ films, which perform as a diode, were used in the fabrication of the FET device. The performance of the FET device was evaluated by analyzing the data obtained from source-drain current vs. voltage (I_ds-V_ds) by controlling the gate voltage (V_g). The on/off conditions of the transistor were feasibly performed and the threshold voltage (V_t) were determined by adjusting V_g for different types of the FET design. In addition, the influential factors, such as type of metal ions, and positions of TiO₂ and metal-ion-doped TiO₂ layers, on the performance of the FET device were also discussed in this study.     

Semiconductor quantum dots: Theory and phenomenology

Research in semiconductor quantum dots (q-dots) has burgeoned in the past decade. The size (R) of these q-dots ranges from 1 to 100 nm. Based on the theoretical calculations, we propose energy and length scales which help in clarifying the physics of this mesoscopic system. Some of these length scales are: the Bohr exciton radius (α_B*), the carrier de Broglie and diffusion length (λ_D andl _D), the polaron radius (α_p), and the reduction factor modulating the optical matrix element (M _x).R<α_B is an individual particle confinement regime, whereas the larger ones are exciton confinement regime wherein Coulomb interaction play an important role. Similarly a size-dependent dielectric constantε(R) should be used forR<α_p<α_B. An examination ofM _x reveals that an indirect gap material q-dot behaves as a direct gap material in the limit of very small dot size. We have carried out effective mass theory (EMT) calculations to estimate the charge density on the surface of the quantum dot. We present tight binding (TB) calculation to show that the energy upshift scales as 1/R ^x, wherex is less than 2 and the exponent depends on the orientation of the crystallite.     

提高半导体器件成品率的有效对策

从技术、管理等方面入手，讨论了影响器件成品率的诸因素及提高成品率的对策。介绍了一种有效、相容 的吸杂工艺；从工艺优化设计角度讨论了提高成品率的各种途径。     

Effect of nitrate ion on formation of TiO2 nanoplate structure in hydrothermal solution

Nanoplate structure of TiO₂ was synthesized by surfactant-assisted hydrothermal method. The existence of nitrate ion with a high concentration prohibited the rolling of the nanosheets and played the key role on the formation of nanoplates of titanate. After calcinations, the titanate was transformed into TiO₂ nanoplates (anatase) of micrometer-size with 20-30 nm in thickness.