具有可逆蓝光发射特性的氧化硅纳米绳

研究了准一维氧化硅绳的生长机理以及对环境敏感的光致发光特性。实验采用化学气相沉积方法在水平管式炉中制备了具有绳索状的准一维氧化硅纳米结构。通过扫描电镜和透射电镜观察，发现这种非晶氧化硅纳米绳是由大量的氧化硅纳米线通过劈裂、粘连而成的自组织结构。反应中引入的水蒸气对产物的形貌和表面状态产生了重要影响。通过光致发光谱发现新鲜制备的氧化硅纳米绳有强烈的蓝光发射，经过潮湿环境处理后，其蓝光发射强度就会变得非常弱；当再把纳米绳经过干燥处理后，这种蓝色荧光强度几乎恢复到最初的水平。这种可逆的蓝色荧光现象有很好的重复性。结合红外光谱的研究，分析这种新奇的可逆发光现象是由氧化硅表面水分子的吸附、脱附造成的。     

生长温度对热蒸发法制备ZnO纳米线的结构与发光性能影响

采用无金属催化剂的简单热蒸发法,在Si(100)衬底上不同生长温度下成功地制备了高密度和大长径比的单晶ZnO纳米线。分别利用X射线衍射仪(XRD)、扫描电子显微镜(SEM-EDS)、透射电子显微镜(TEM)及荧光光谱仪表征样品的结构和发光性质。XRD和TEM研究表明,所制备的样品为沿c轴择优取向生长的单晶ZnO纳米线,具有六方纤锌矿结构。SEM和TEM研究表明,生长温度对ZnO纳米线的形貌及长径比的影响较大。当生长温度为700℃时,制备得到长径比为300(长度约为15μm,直径约为50nm)的ZnO纳米线;低于600℃时,形成花状ZnO纳米锥或纳米棒;高于700℃时,形成小长径比的ZnO纳米棒。此外,室温光致发光(PL)谱上出现一个强而尖锐的紫外发射峰以及一个弱而宽泛的蓝光发射峰。采用的热蒸发法制备ZnO纳米线基于气-固(VS)生长机理且该生长方法可用于大规模、低成本制备高纯度的单晶ZnO纳米材料。     

热处理温度及掺硼对富硅氧化硅发光的影响

利用等离子体增强化学气相沉积制备了未掺杂与掺硼富硅氧化硅薄膜。在高纯N2气氛中经过600℃、800℃和1100℃热处理,发现随着热处理温度的升高,富硅氧化硅薄膜的光致发光发生了明显红移。这表明薄膜的光致发光来源逐渐由薄膜中的发光中心演变为硅纳米晶。在经过1100℃热处理的未掺杂与掺硼样品中,掺硼样品光致发光强度有明显减弱,这是由俄歇复合效应引起的。此外,在ESR测试谱中,掺硼样品的g因子为2.0020,这表明掺硼可以在薄膜基体和硅纳米晶之间的界面引入发光中心。     

ZnO纳米线的催化合成及其光致发光性能

采用气相传输法,以金膜为催化剂,氧化锌和石墨混合粉末为锌源,制备氧化锌纳米材料。研究获得氧化锌纳米线的光致发光性能。初步探索了氧化锌纳米线的生长机理。实验结果表明,当衬底温度为600℃时,金颗粒的催化性能得到了较好的发挥,形成长度大于10μm,直径小于80 nm的均匀致密的氧化锌纳米线膜。这种氧化锌纳米线具有紫外发光特性。低于600℃时,锌氧蒸汽发生了自凝结,进而在金颗粒间隙形成氧化锌带(400℃时),或在金颗粒上吸附聚集形成花状氧化锌纳米棒(200℃时)。而在高于600℃时,金颗粒析出的锌迅速挥发或氧化、长大,出现了稀疏的针状氧化锌和颗粒。氧化锌纳米线可能的生长模式为“底端生长“模式。     

生长温度对热蒸发法制备ZnO纳米线的结构与发光性能影响

采用无金属催化剂的简单热蒸发法,在Si(100)衬底上不同生长温度下成功地制备了高密度和大长径比的单晶ZnO纳米线。分别利用X射线衍射仪(XRD)、扫描电子显微镜(SEM-EDS)、透射电子显微镜(TEM)及荧光光谱仪表征样品的结构和发光性质。XRD和TEM研究表明,所制备的样品为沿C轴择优取向生长的单晶ZnO纳米线,具有六方纤锌矿结构。SEM和TEM研究表明,生长温度对ZnO纳米线的形貌及长径比的影响较大。当生长温度为700℃时,制备得到长径比为300(长度约为15μm,直径约为50nm)的ZnO纳米线。低于600℃时,形成花状ZnO纳米锥或 纳 米 棒。高 于700℃时,形 成 小 长 径 比 的ZnO纳米棒。此外,室温光致发光(PL)谱上出现一个强而尖锐的紫外发射峰以及一个弱而宽泛的蓝光发射峰。采用的热蒸发法制备ZnO纳米线基于气-固(VS)生长机理且该生长方法可用于大规模、低成本制备高纯度的单晶ZnO纳米材料。     

Au/锗/氧化硅纳米多层膜/p-Si结构的电致发光机制研究

用射频磁控溅射法制备了锗/氧化硅纳米多层膜,在室温下测量了Au/锗/氧化硅纳米多层膜/pSi结构的电致发光.利用位形坐标模型分析了锗/氧化硅纳米多层膜的发光中心,并用量子限制-发光中心模型对该纳米结构的电致发光过程作了研究,研究表明锗/氧化硅纳米多层膜的电致发光主要来自SiO2层的发光中心.     

常压条件下制备SnO_2纳米线及其光学性能研究

在常压条件下采用气相沉积方法制备出SnO_2纳米线,X射线衍射和Raman光谱结果均表明制备出来的产物为金红石结构.在样品的光致发光谱中观察到缺陷发光峰.研究还发现蒸发源及其放置时间在SnO_2纳米线的形成过程中起重要的作用.     

高压PLD法生长ZnO和Zn1-xMgxO纳米棒及其荧光性能

利用自主设计、组装的高压脉冲激光沉积(PLD)系统,研究了温度、靶材、催化剂厚度等生长参数对ZnO和Zn1-xMgxO纳米棒生长的影响,并对ZnO纳米棒的生长机理和Zn1-xMgxO纳米棒的光致发光性能进行了探讨.实验发现,当金膜催化剂厚度为2 nm、温度为925℃时,在单晶Si衬底上生长了直径均匀的ZnO纳米棒阵列,且具有明显的(002)择优生长取向.实验发现温度与催化剂厚度是影响ZnO纳米棒的直径和生长密度的重要因素.据此提出了ZnO纳米棒阵列的高压PLD生长过程应为气–液–固和气–固相结合的生长机制.通过在ZnO靶材中掺入氧化镁,获得了Zn1-xMgxO纳米线和纳米带结构,但生长无明显的择优取向.光致发光谱测量表明,镁掺杂明显增大了ZnO的带隙,但也在其禁带中引入了缺陷能级,导致可见发光明显增强.     

硅纳米线的制备及其生长条件探究

Si纳米材料自问世以来便受到研究者的重视，其不同于宏观块体材料的特殊性质可使其应用于各个领域。如何制备形貌较好且具有良好光电性能的纳米材料是在纳米材料应用前必须解决的问题。以Ni膜作为催化剂直接在Si衬底上制备了密集的Si纳米线，获得了Si纳米线较强的蓝紫波段的发光，研究了退火温度、退火气氛N₂流速、Si膜厚度等制备条件对Si纳米线形貌、光致发光强度的影响，并讨论了双层膜制备Si纳米线形成和生长机理。实验结果显示，退火温度、N₂流速对Si纳米线的生长起到关键性的作用，N₂流速能够影响Si纳米线的光致发光强度，且较大的N₂流速能够使Si纳米线定向生长。而在Ni膜催化剂上预沉积一层适当厚度的Si膜也有助于Si纳米线的生长，且有效改善了Si纳米线的光致发光强度。     

蒲公英状ZnO微米球的控制组装与表征

本文用热蒸发气相沉积的方法在镀有金催化剂的锌片上成功合成了蒲公英状ZnO微米球结构。扫描电镜观察结果表明合成的ZnO微米球平均直径约5微米,表面二次生长的纳米线平均直径约20纳米,长度达几微米。透射电镜分析发现二次生长的纳米线具有单晶结构,其生长方向沿[001]方向。同时研究了沉积衬底、原材料种类和比例对合成产物形貌的影响,对合成微米球的室温光致发光性能进行了研究。合成的这种微米球结构在传感器等纳米器件领域有着潜在的应用前景。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...