Melting of Shocked Boron Carbide

JETP Letters - The aim of this work is to determine the melting temperature of boron carbide at high shock pressures. To this end, powder boron carbide samples have been compressed by shock waves...     

A Free Energy Model of Boron Carbide

The assessed phase diagram of the boron-carbon system contains a single nonstoichiometric boron-carbide phase of rhombohedral symmetry with a broad, thermodynamically improbable, low temperature composition range. We combine first principles total energy calculations with phenomenological thermodynamic modeling to propose a revised low temperature phase diagram that contains two boron-carbide phases of differing symmetries and compositions. One structure has composition B₄C and consists of B₁₁C icosahedra and C-B-C chains, with the placement of carbon on the icosahedron breaking rhombohedral symmetry. This phase is destabilized above 600 K by the configurational entropy of alternate carbon substitutions. The other structure, of ideal composition B₁₃C₂, has a broad composition range at high temperature, with rhombohedral symmetry throughout, as observed experimentally.     

Evolution of Shock Waves in Hot-Pressed Ceramics of Boron Carbide and Silicon Carbide

Technical Physics - In this paper we studied the evolution of shock compression waves in hot-pressed ceramics based on boron carbide and silicon carbide at a maximum compressive stress of 32 and 34...     

Densification of Crystalline Boron Carbide during Shock-Wave Loading

Crystalline powder boron carbide samples are subjected to explosive loading by 2-μs shock waves with an amplitude of 38 GPa and shock heating to 700 K and to subsequent conservation. The samples recovered after shock-wave loading are studied by X-ray diffraction, and new effects of shock-wave loading on boron carbide are revealed. The explosive treatment is shown to shift the X-ray diffraction reflections of initial boron carbide toward high angles, which is attributed to an increase in the boron carbide density at the level of atomic volume in the unit cell of boron carbide. The X-ray diffraction reflections are found to broaden, which is interpreted as an increase in the coherent scattering region in the crystalline boron carbide subjected to the explosive treatment.     

硅纳米线的生长及其拉曼光谱研究(英文)

pacc:7830 Nanowiresofferauniqueaccesstolowdi mensionalphysicsandnanotechnology.Silicon nanowires(SiNWs)areparticularlyinteresting duetotheprominentroleofsiliconinelectronics. Variousapproachesforselectivegrowthandbulk productionofSiNWsaredemonstrated.Pla…     

Optical Emission Diagnosis of Boron Carbide Synthesized Using Natural Carbon Precursors

Optics and Spectroscopy - Boron carbide (B4C) is a semiconducting material that finds a wide range of industrial and optoelectronic applications because of its unique structural and physical...     

Growth parameters and shape specific synthesis of silicon nanowires by the VLS method

In this paper the effect of varying temperature, pressure and chemical precursors on the vapour–liquid–solid (VLS) growth of silicon nanowires (Si NWs) have been investigated. Some aspects of nucleation and growth mechanisms are discussed. Control on Si NW morphology by varying the choice of gaseous precursor (silane or dichlorosilane) at elevated temperatures is reported.     

硅纳米线的PEOVD生长研究

本文以硅烷（SiH4）为反应气体,利用等离子体化学气相沉积（PECVD）方法在硅（100）衬底上生长硅纳米晶体、纳米线。应用扫描电镜观察不同条件下生长的样品表面,发现衬底条件对硅纳米结构的影响十分显著。在温度、压强等其它条件相同的情况下,对硅衬底应用Fe^3＋催化剂处理后,呈纳米线状结构生长,而无Fe催化剂涂覆情况下,基本呈纳米晶体状生长,说明催化剂对si纳米线的生成起了重要的促进生长作用。通过进一步研究硅纳米晶体、纳米线的等离子增强化学气相生长机理,发现它们以气-液-固（VLS）机制生长。     

常压下金催化硅纳米线生长实验研究

采用固一液一固（SLS）生长机制,研究常压下金催化硅纳米线的制备方法。实验中将硅基Au薄膜在氩氢气中退火,退火温度为1050℃和1080℃,退火完成后在扫描电镜下观察硅片表面的形貌变化,分析不同退火温度、通气量和金膜厚度下的实验结果,并在此基础上进一步讨论了各变量对硅纳米线的生长影响及其机理。     

六方氮化硼薄膜对石墨烯-碳化硅结构近场热辐射的增强

六方氮化硼(hBN)具有跟石墨烯类似的层状结构和晶格参数,研究发现hBN薄膜具有良好的热传导、电绝缘、光学和力学等性能.本文从理论上研究了 hBN薄膜对石墨烯-碳化硅(G/S)结构的近场热辐射的影响.研究发现在红外频段,hBN薄膜在低频率区和高频率区会增强G/S结构的近场热辐射,经计算在G/S结构中加入厚度为10 nm...     

单晶ZnO纳米线的合成和生长机理研究

用化学气相输运(CVT)方法合成了直径在20～120nm呈单晶结构的ZnO纳米线.利用场发射扫描电 镜(FESEM)、高分辨透射电镜(HRTEM)以及选区电子衍射(SAED)等技术对ZnO纳米线的生长机理和结构进行 了系统研究,结果表明,纳米线的成核与Au Zn合金催化颗粒的饱和度有直接的关系,先饱和的颗粒上纳米线首 先成核.纳米线顶端合金颗粒组成的变化是导致纳米线生长终止的重要原因,大量纳米线的生长不是同时进行 的.本工作提供了支持纳米线气液固(V L S)生长机理的新实验证据,提出了氧化物纳米线的生长机理.     

Growth Feature of Cubic Boron Nitride on c-BN Crystal Substrates

Cubic boron nitride （c-BN） films were deposited on highly-oriented （111） bulk c-BN crystal by using the rf magnetron sputtering method. The growth films are characterized by micro-Raman spectroscopy （μ-RS） and scanning electron microscopy （SEM）, The results show that the high crystallization electron transparent c-BN films in thickness of about 10μm are obtained, Island and step growth models are clearly shown.     

氧化物辅助生长法合成氮化硼纳米管

硼、氧化硅、硅的混合粉末与氨气在1423K反应生成了氮化硼纳米管.产物用X射线衍射(XRD),透 射电镜(TEM)和傅立叶红外光谱(FTIR)进行了表征.氮化硼纳米管的直径为20～50nm,长达几十微米.氮化硼 纳米管的头部是开口或封口的,没有观察到纳米颗粒被包覆在纳米管的端部.因此,氮化硼纳米管的生长被认为 是一种氧化物辅助生长的机理.同多晶六方氮化硼的红外光谱相比,在1520cm-1处的小吸收峰表现了氮化硼纳 米管的一维结构特征.     

Epitaxial Growth of Cadmium Selenide Films on Silicon with a Silicon Carbide Buffer Layer

An epitaxial cubic 350-nm-thick cadmium selenide has been grown on silicon for the first time by the method of evaporation and condensation in a quasi-closed volume. It is revealed that, in this method, the optimum substrate temperature is 590°C, the evaporator temperature is 660°C, and the growth time is 2 s. To avoid silicon etching by selenium with formation of amorphous SiSe₂, a high-quality ~100-nm-thick buffer silicon carbide layer has been synthesized on the silicon surface by substituting atoms. The powder diffraction pattern and the Raman spectrum unambiguously correspond to cubic cadmium selenide crystal. The ellipsometric, Raman, and electron diffraction analyses demonstrate high structural perfection of the cadmium selenide layer and the absence of a polycrystalline phase.     

Nucleation of Plasticity in Alpha-Iron Nanowires

Russian Physics Journal - The paper presents research results of the defect nucleation and propagation in the structure of nanosized iron samples with a perfect body-centered cubic lattice under a...     

GaN直纳米线的光学性能

对 Ga N直纳米线的拉曼光谱及光致发光光谱进行了研究。拉曼光谱表明 ,与计算值相比 ,E2 ( high)声子频率在 560 cm- 1有 -9cm- 1的移动 ,这种声子频率显示出向低能带频移及带变宽的特征 ,是由于纳米尺寸效应所引起的结果。体系的光致发光光谱在 3 44 .8nm附近的近带隙发光 ,与文献报道的 Ga N体材料的数值3 65nm相比有一蓝移 ,这是由于量子限制效应造成的