Fe：ZnSe/ZnS核-壳纳米晶的微乳液法合成及光学性能研究

在环己烷/Triton X-100/水/异丙醇W/O型微乳液体系中制备了Fe：ZnSe/ZnS核-壳纳米晶。采用X射线衍射仪（XRD）分析了产物的结构,利用透射电子显微镜（TEM）观察了产物的形貌,采用光致发光（PL）谱、紫外-可见（UV-Vis）吸收谱测试了产物的光学性能。着重研究了水与表面活性剂的摩尔比（R值）对合成产物的光学性能的影响。并对相关现象潜在的机理进行了讨论。     

缓冲层生长速率对GaSb薄膜二维生长的影响

用分子束外延(MBE)法在GaAs(100)衬底上生长GaSb薄膜,得到了GaSb薄膜的优化生长工艺条件.为了降低因晶格失配度较大所引起的位错密度,采用低温(LT)GaSb作为缓冲层,研究了缓冲层的生长速率对GaSb薄膜二维生长的影响,并以此说明缓冲层在GaSb薄膜生长中所起的作用.通过X射线双晶衍射仪和原子力显微镜测试分析,得到当低温GaSb缓冲层的生长速率为1.43μm/h时,GaSb外延层中的位错密度最小,晶体质量最好.     

Liquid phase epitaxial growth of pure and doped GaSb layers: morphological evolution and native defects

Undoped and Te-doped gallium antimonide (GaSb) layers have been grown on GaSb bulk substrates by the liquid phase epitaxial technique from Ga-rich and Sb-rich melts. The nucleation morphology of the grown layers has been studied as a function of growth temperature and substrate orientation. MOS structures have been fabricated on the epilayers to evaluate the native defect content in the grown layers from theC-V characteristics. Layers grown from antimony rich melts always exhibitp-type conductivity. In contrast, a type conversion fromp- ton- was observed in layers grown from gallium rich melts below 400 C. The electron mobility of undopedn-type layers grown from Ga-rich melts and tellurium doped layers grown from Sb- and Ga-rich solutions has been evaluated. Paper presented at the poster session of MRSI AGM VI. Kharagpur. 1995     

Influence of substrate orientation on low-temperature epitaxial growth of ferromagnetic silicide Fe3Si on Si

Influence of substrate orientation on epitaxial growth of the ferromagnetic silicide Fe₃Si on Si was investigated using low temperature (60-300 °C) molecular beam epitaxy. Transmission electron microscopy (TEM) measurements revealed that Fe₃Si layers were epitaxially grown on Si(110) and Si(111), while random poly-crystal Fe₃Si layers were formed on Si(100). From the Rutherford backscattering spectroscopy measurements, the values of the χ_min of the Fe₃Si layers grown at 60 °C on Si(100), Si(110), and Si(111) were evaluated to be 100%, 97%, and 41%, respectively. This dependence on the substrate orientation was explained on the basis of the atomic alignments at the Fe₃Si/Si interfaces.     

Initial stages of the ion-beam assisted epitaxial GaN film growth on 6H-SiC(0001)

Ultra-thin gallium nitride (GaN) films were deposited using the ion-beam assisted molecular-beam epitaxy technique. The influence of the nitrogen ion to gallium atom flux ratio (I/A ratio) during the early stages of GaN nucleation and thin film growth directly, without a buffer layer on super-polished 6H-SiC(0001) substrates was studied. The deposition process was performed at a constant substrate temperature of 700 °C by evaporation of Ga and irradiation with hyperthermal nitrogen ions from a constricted glow-discharge ion source. The hyperthermal nitrogen ion flux was kept constant and the kinetic energy of the ions did not exceed 25 eV. The selection of different I/A ratios in the range from 0.8 to 3.2 was done by varying the Ga deposition rate between 5 × 10¹³ and 2 × 10¹⁴ at. cm^− 2 s^− 1. The crystalline surface structure during the GaN growth was monitored in situ by reflection high-energy electron diffraction. The surface topography of the films as well as the morphology of separated GaN islands on the substrate surface was examined after film growth using a scanning tunneling microscope without interruption of ultra-high vacuum. The results show, that the I/A ratio has a major impact on the properties of the resulting ultra-thin GaN films. The growth mode, the surface roughness, the degree of GaN coverage of the substrate and the polytype mixture depend notably on the I/A ratio.     

Two dimensional control of electron beam induced orientation selective epitaxial growth of (100) and (110)CeO2 regions on Si(100) substrates

Orientation selective epitaxy (OSE) of CeO₂(100) and CeO₂(110) layers on Si(100) substrates is studied using reactive magnetron sputtering. The former grows in an area simultaneously irradiated by electron beams during the growth process, whereas the latter grows in the area without electron irradiation. In order to control the electron beam irradiation area, we apply an absorbed electron imaging system. Analyses are made on the sample current profile along Si substrate surfaces and the current components of positive ions and secondary electrons. The spatially controlled OSE growth of the (100) and (110) oriented epitaxial regions is attained and crystallographic orientation distribution within the sample surface was analyzed.     

Spatially varied orientation selective epitaxial growth of CeO2(100) and (110) regions on Si(100) substrates by reactive magnetron sputtering utilizing electron beam irradiation

Spatially varied epitaxial growth of CeO₂(100) and CeO₂(110) regions on Si(100) substrates is attained using electron beam induced orientation selective epitaxial (OSE) growth by reactive magnetron sputtering. The spatially controlled OSE grown samples are made on Si(100) substrates with various electric resistivity values. By X-ray diffraction measurements, we obtain the lateral orientation mapping within the epitaxial layer surfaces and reveal existence of the transition regions in between the above mentioned two orientation areas. The width of the transition regions is clarified to decrease proportionally with the logarithm of underlying Si substrate resistivity. A surface potential distribution model is proposed to explain the results.     

A study of Si epitaxial layer growth on SOI wafers prepared by SIMOX

The epitaxial Si layers were deposited onto silicon on insulator (SOI) substrates by chemical vapor deposition technology, and SOI substrates were manufactured with separation by implantation of oxygen technology. The dislocations and stacking faults of epitaxial Si layer and substrate were examined and their densities were calculated, respectively. The surfaces of epitaxial Si layer and SOI substrate were studied by atomic force microscopy. The SOI substrates and the epitaxial Si layers were characterized by Rutherford backscattering and channeling spectroscopy. Transmission electron microscopy was used to observe the defect in epitaxial layer. The result shows that the defects in the epitaxial Si layer on low dose substrate are less than those in the epitaxial Si layer on standard dose substrate, and also that the defects in low dose substrate are less than those in standard dose substrate. The crystallinity of epitaxial Si layer on low dose substrate is better than that of epitaxial Si layer on standard dose substrate.     

Epitaxial growth of CoSi2 on Si(001) by reactive deposition epitaxy: Island growth and coalescence

Epitaxial CoSi₂ layers, which are phase pure but contain {111} twins, are grown on Si(001) at 700 °C by reactive deposition epitaxy. Transmission electron microscopy analyses show that the initial formation of CoSi₂(001) follows the Volmer-Weber mode characterized by the independent nucleation and growth of three-dimensional islands whose evolution we follow as a function of deposited Co thickness t_Co in order to understand the origin of the observed twin density. We find that there are two families of island shapes: inverse pyramids and platelets. The rectangular-based pyramidal islands extend along orthogonal 〈110〉 directions, bounded by four {111} CoSi₂/Si interfaces, and grow with a cube-on-cube orientation with respect to the substrate: (001)_CoSi2||(001)_Si and [100]_CoSi2||[100]_Si. Platelet-shaped CoSi₂ islands are bounded across their long 〈110〉 directions by {111} twin planes (i.e. {111}(001)_CoSi2||{111}_Si) and their narrow 〈110〉 directions by {511}_CoSi2||{111}_Si interfaces. The top and bottom surfaces are {22¯1}, with {22¯1}_CoSi2||(001)_Si, and {1¯1¯1}, with {1¯1¯1}_CoSi2||{11¯1}_Si, respectively. The early stages of film growth (t_Co ≤ 13 Å) are dominated by the twinned platelets due to a combination of higher nucleation rates resulting from a larger number of favorable adsorption sites in the Si(001)2 × 1 surface unit cell and rapid elongation of the platelets along preferred 〈110〉 directions. However, at t_Co ≥ 13 Å island coalescence becomes significant as orthogonal platelets intersect and block elongation along fast growth directions. In this regime, where both twinned and untwinned island number densities have saturated, further island growth becomes dominated by the untwinned islands. A continuous epitaxial CoSi₂(001) layer, with a twin density of 2.8 × 10¹⁰ cm^− 2, is obtained at t_Co = 50 Å.     

The epitaxial growth of Ag on Si(111)-(7 x 7) surface and its (√3x√3)-R30 surface phase transformation

Ag is adsorbed in ultra-high vacuum on to the (7x7) reconstructed Si(111) surface with submonolayer coverage control with a deposition rate of 3-3 x 10¹² atoms/cm²/sec. The initial stages of growth and intermediate equilibrium phase formation are determined by using low energy electron diffraction (LEED) and X-ray photoelectron diffraction (XPD) for structural information, and auger electron spectroscopy (AES) and electron energy loss spectroscopy (EELS) for composition and interaction analyses. Room temperature (RT) adsorption results in the nearly epitaxial (1 x 1) surface phase growth in the simultaneous multi-layer growth mode. The quenching of the dangling bond states during adsorption is observed by monitoring thep-character of the Si LVV auger peak. For depositions carried out at high temperatures (HT), several plateaus in the auger uptake curve with the (√3 x √3)-R30° LEED structures are formed. It is observed that a minimum coverage of 0–33 monolayer (ML) is required for the formation of the (√3 x √3) phase and this phase causes the reappearance of thep-electron-related states that were quenched by 1.0 ML adsorption at RT. However the (√3 x √3) is observed for higher coverages (0.66 and 1.0 ML) also. The polar angle anisotropy of Si(2p) emission in XPD indicates the rearrangement of substrate Si atoms for the formation of the (√3 x √3) phase. The EELS data also shows relevant changes due to adsorption of Ag at RT and upon annealing. The results suggest the importance of controlled deposition parameters, the lack of which may have kept the determination of the nature and coverage of the (√3 x √3) surface phase unresolved in literature.     

A perspective on materials characterization for technology advancement and industrial growth: Emphasis on non-destructive evaluation

Materials are the index of human progress. The evolution of mankind is linked to materials, for example, stone age, bronze age, iron age etc. The success of use of materials towards better quality of human life depends on the capabilities for characterization of these materials, which leads to ensuring reliable performance of the materials and development of new, and more efficient materials. The materials characterization encompasses determining chemical constituents, microstructural characterization down to a few Angstroms level and defect assessment from a few micrometers to few millimeters in a wide variety of materials. Recent progress made in the nondestructive characterization of materials and the future trends and direction are discussed in this paper. Text of the Presidential Address delivered at the Materials Science Section of the 82nd Indian Science Congress held at Calcutta during January 3–8, 1995.     

Nano-hybrid shish-kebab: Isotactic polypropylene epitaxial growth on electrospun polyamide 66 nanofibers via isothermal crystallization

Polyamide 66 (PA 66) nanofibers, with the mean diameter of about 140 nm, were prepared by electrospinning. Nano-hybrid shish-kebab (NHSK) structure was achieved in PA 66 nanofibers/isotactic polypropylene (iPP) composites via isothermal solution crystallization. The morphology of such NHSK was observed by scanning electron microscopy (SEM). It was found that PA 66 nanofibers act as “shish”, and iPP crystals serve as “kebabs”. Furthermore, the concentration of iPP solution remarkably affects the morphology of the NHSK, i.e., the size of iPP crystals becomes much bigger with the increasing iPP solutions' concentration. The reason for this can be explained as that the high concentration of iPP solutions contain more free chains which can participate into the process of crystallization.     

Sb segregation in Si and SiGe: effect on the growth of self-organised Ge dots

The segregation and incorporation coefficients of antimony (Sb) in Si_1−xGe_x buried doped layers were investigated simultaneously using specific temperature sequences. We first showed an exponential kinetic evolution of Sb surface segregation in Si. In contrast such an evolution could not be observed in Si_1−xGe_x because of the Sb thermal desorption, at growth temperatures of 550°C. We also showed an increased surface segregation increasing with the partial Ge concentration in Si_1−xGe_x alloys, which was explained by a decrease of the kinetic barrier for Sb atoms mobility. It was, therefore, possible to determine the growth conditions to obtain a Si_1−xGe_x doped layer with a controlled incorporation level and a negligible surface segregation obtained by the thermal desorption of the Sb surface coverage. Finally, using Sb surfactant mediated growth, we found Ge dots with lateral sizes reduced by a factor of 2.8 and density multiplied by a factor of four as compared to dots directly deposited on Si(001).     

Review on ranking and selection: A new perspective

In this paper, we briefly review the development of ranking and selection (R&S) in the past 70 years, especially the theoretical achievements and practical applications in the past 20 years. Different from the frequentist and Bayesian classifications adopted by Kim and Nelson (2006b) and Chick (2006) in their review articles, we categorize existing R&S procedures into fixed-precision and fixed-budget procedures, as in Hunter and Nelson (2017). We show that these two categories of procedures essentially differ in the underlying methodological formulations, i.e., they are built on hypothesis testing and dynamic programming, respectively. In light of this variation, we review in detail some well-known procedures in the literature and show how they fit into these two formulations. In addition, we discuss the use of R&S procedures in solving various practical problems and propose what we think are the important research questions in the field.     

A three-step process for epitaxial growth of (111)-oriented C60 films on alkali–halide substrates

Epitaxial (111)-oriented C₆₀ films have been grown on alkali–halide substrates, KCl (100), KBr (100) and NaCl (100) by a three-step process: (1), substrate surface cleaning by high temperature heating; (2), initial deposition with a low deposition rate to grow two or three monolayers (ML); and (3), deposition with a high deposition rate to grow a film with expected thickness. It was found that (111)-oriented epitaxial C₆₀ films could be grown at low temperatures in a wide temperature range, from 40 to 120°C. By this three-step process, we can also grow epitaxial C₆₀ films at deposition rates as high as 35 Å/min.     

Impact of sustainable manufacturing practices on consumer perception and revenue growth: an emerging economy perspective

The view that adopting an environmental perspective on operations can lead to improved operations has become commonplace over the past decade. The implication is that any operational system that has minimised inefficiencies is also more environmentally sustainable. In the first phase of our research, we conducted a field research of the green manufacturing techniques in place in two world-class, ISO 14001-certified paint manufacturing firms in India. This phase of the study was undertaken to ascertain the cost benefits that these firms enjoy due to green manufacturing and recycling. Based on the field work in these two companies, a conceptual framework was proposed to investigate any relationship between the consumer's attitude towards the environment and the perceived image of a company that was environmentally conscious. Subsequently, a survey was administered to understand the impact of green marketing on the decision of consumers to buy paint manufactured by a firm that stringently regulates its hazardous waste. Results indicate that there is a strong correlation between the environmental concern of the survey respondent and the perception that the respondent forms of the firm that has implemented green manufacturing techniques. There is also a strong correlation between the decision to buy a green product and the respondent's concern for the environment as well as the perception formed of the firm. Further research is required to substantiate the cost benefits of green manufacturing.     

A systematic review on unmanned aerial vehicles in Sub-Saharan Africa: A socio-technical perspective

In recent times, Unmanned Aerial Vehicles (UAVs) popularly known as drone technology have gradually gained widespread adoption all over the world. UAVs’ relevance within modern society stems from it being able to solve socio-economic issues as well as improve productivity. Sub-Saharan Africa has become a region of global interest with regards to technological development, leapfrogging and foreign investment, despite the lag in socio-economic development in comparison with other regions. Backed by socio-technical theory, the aim of this paper is to investigate UAV adoption and its usage in Sub-Saharan Africa by means of a systematic literature review methodology. Selected papers were reviewed, assessed and results were categorized according to the domain within which UAVs have been and are being deployed in Sub-Saharan Africa. We also determined whether the research reported on existing projects or rather made proposals on the use of UAVs.Our results reveal that UAV adoption in the sub-region is still in its early phase, with a number of implemented cases primarily focusing on healthcare and crop farming. The study makes theoretical and practical contributions to the topic of UAVs/drone technology within the sphere of Sub-Saharan Africa from a socio-technical perspective.     

Perspectives of the concept of van der Waals epitaxy: growth of lattice mismatched GaSe(0001) films on Si(111), Si(110) and Si(100)

The preparation of high quality epitaxial heterointerfaces of lattice mismatched dissimilar materials is one of the challenging tasks for advanced semiconductor devices. We have used the concept of van der Waals epitaxy, namely the deposition of two-dimensional layered materials like GaSe onto properly terminated three-dimensional substrates to prepare new heterointerfaces on Si of different surface orientation. Film growth and properties were investigated in situ by low-energy electron diffraction (LEED) and soft X-ray photoemission (SXPS) using integrated UHV preparation and analysis chambers. On Si(111) a hexagonal GaSe epitaxial layer grows on top of a preformed Si–Ga–Se van der Waals-like termination layer. A distorted Si–Ga–Se layer is also formed on Si(110), which evidently leads to an hexagonal surface mesh as substrate for further growth of crystalline GaSe. On Si(100), two domains of azimuthally aligned GaSe(0001) films are deposited. The usually given constraints in lattice mismatch, and even of different surface symmetry, can evidently be overcome by the use of van der Waals-like surface termination layers of the substrates. Thus, novel device structures combining compound semiconductors with Si seem to be feasible.     

Low-temperature ultrasound synthesis of nanocrystals CoTiO3 without a calcination step: Effect of ultrasonic waves on formation of the crystal growth mechanism

CoTiO₃ nanocrystallites with an average diameter of 50 nm were synthesized successfully by the sonochemical method without a calcination step and using C₁₀H₁₆N₂O₈ (EDTA) as the chelating agent. To reach an in-depth understanding of the scientific basis of the proposed process, an in-detail analysis was carried out for characterization of nanoscale CoTiO₃ particles via XRD, FTIR, FE-SEM and UV–vis diffuse reflectance spectroscopy (DRS). The crystallite size, average particle size and band gap are found to be 10.7 nm, in the range of 50 nm and 4.64 eV, respectively. The mechanism and the formation process of CoTiO₃ in the sonochemical process were proposed. It was found that nanocrystals were formed directly before being oriented and aggregated into large particles in aqueous solution under ultrasonic irradiation. The nucleation in the sonocrystallization process was accelerated by the implosive collapse of bubbles, while the crystal growth process was inhibited or delayed by shock waves and turbulent flow created by ultrasonic radiation. A pure complex perovskite phase of spherical shape was formed completely in a short irradiation time without the calcination process. Sonochemical irradiation could accelerate spherical shape formation of the particles significantly. These results provide new insights into the development and design of better nanomaterial synthesis methods.     

Growth of InAs Quantum Dots on GaAs (511)A Substrates: The Competition between Thermal Dynamics and Kinetics

The growth process of InAs quantum dots grown on GaAs (511)A substrates has been studied by atomic force microscopy. According to the atomic force microscopy studies for quantum dots grown with varying InAs coverage, a noncoherent nucleation of quantum dots is observed. Moreover, due to the long migration length of In atoms, the Ostwald ripening process is aggravated, resulting in the bad uniformity of InAs quantum dots on GaAs (511)A. In order to improve the uniformity of nucleation, the growth rate is increased. By studying the effects of increased growth rates on the growth of InAs quantum dots, it is found that the uniformity of InAs quantum dots is greatly improved as the growth rates increase to 0.14 ML s^?1. However, as the growth rates increase further, the uniformity of InAs quantum dots becomes dual‐mode, which can be attributed to the competition between Ostwald ripening and strain relaxation processes. The results in this work provide insights regarding the competition between thermal dynamical barriers and the growth kinetics in the growth of InAs quantum dots, and give guidance to improve the size uniformity of InAs quantum dots on (N11)A substrates.