Luminescence of samarium-activated cubic boron nitride

Under high pressure conditions, we have obtained samples of samarium-activated cubic boron nitride in the form of micropowders, ceramic samples, and polycrystals having high-intensity discrete photoluminescence in the red region of the spectrum that is stable in the temperature range 6 K to 300 K and is assigned to internal f-f electronic transitions in the Sm³⁺ ions. The materials obtained on the basis of cBN are intended for use as phosphors and light emitters (sources of red light) having thermal and chemical stability. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 1, pp. 88–93, January–February, 2008.     

Luminescence centers in cubic boron nitride

Complex and multiband photoluminescence spectra for GB and HBN centers in single crystals of cubic boron nitride (cBN) were recorded in the wavelength ranges 385–400 nm and 365–395 nm and the nature of these centers was studied. The use of models involving resonance vibrations and strongly shifted configuration diagrams for the electronic ground state and excited state made it possible to associate formation of the GB-1 center with the presence of tungsten impurity in cBN. It was established that the HBN band in the 300–350 nm range of the cathodoluminescence spectra of cBN polycrystals, single crystals, and micropowders is associated with luminescence centers present in microinclusions of graphite-like boron nitride (hBN). The nature of the hBN band is tentatively interpreted within the model of recombination of donor and acceptor defects in hBN: respectively nitrogen vacancies and carbon atoms in positions substituting for nitrogen. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 241–246, March–April, 2007.     

第一性原理计算研究立方氮化硼空位的电学和光学特性

对立方氮化硼的空位进行了基于密度泛函理论框架下的第一性原理平面波超软赝势方法的研究. 通过对总能量、能带结构、态密度及电子密度分布图的分析发现, B空位相比起N空位更加稳定. 并且空位仅影响最近邻原子的电子分布, 空位浓度的增加使禁带宽度逐渐变窄. 从复介电函数和光学吸收谱分析中发现, 随着空位浓度的增加, 立方氮化硼在深紫外区的吸收逐渐减弱. 并且B空位还导致在可见光区域出现明显的吸收带. 关键词： 立方氮化硼 空位 第一性原理 电光学特性     

立方氮化硼薄膜的最新研究进展

立方氮化硼(cBN)作为一种在自然界中并不存在的人造材料具有优异的理化特性. 在超硬刀具、高温电子器件和光学保护膜等领域有着广泛的应用前景,已经成为材料科学的研究热点之一. 但是气相生长高质量cBN薄膜仍然还有许多难点需要攻克. 在综述近几年cBN薄膜研究所取得的一些突破性进展后,结合研究现状提出今后可能的主要研究方向. 关键词： 立方氮化硼薄膜 压缩应力 异质外延 掺杂     

The electrical properties of sulfur-implanted cubic boron nitride thin films

Cubic boron nitride (c-BN) thin films are deposited on p-type Si wafers using radio frequency (RF) sputtering and then doped by implanting S ions. The implantation energy of the ions is 19 keV, and the implantation dose is between 10 15 ions/cm 2 and 10 16 ions/cm 2 . The doped c-BN thin films are then annealed at a temperature between 400°C and 800 C. The results show that the surface resistivity of doped and annealed c-BN thin films is lowered by two to three orders, and the activation energy of c-BN thin films is 0.18 eV.     

立方氮化硼薄膜沉积过程的相变研究

从能量和结构两个角度分析了BN四种相的转变过程，以及杂质和缺陷对立方氮化硼(c-BN)薄膜制备的影响.研究了从六角氮化硼(h-BN)到c-BN转变的一个可能的过程，即h-BN→菱形氮化硼(r-BN)→c-BN过程.对纯的h-BN到r-BN的转变需要克服一个很高的能量势垒，在实验室条件下很难能够提供能量来越过这个势垒.而从r-BN到c-BN的转变只需要克服一个很低的能量势垒.这个能量势垒要低于从h-BN到纤锌矿氮化硼(w-BN)转变所需要克服的能量势垒.c-BN薄膜的制备过程中，薄膜在高能粒子轰击下，会产生大量的缺陷，这些缺陷对立方相的形成起到了重要的作用，缺陷和杂质的存在大大降低了从h-BN到r-BN转变的能量势垒.根据这个理论模型，在两步法制备c-BN薄膜的基础上，调整实验参数，形成三步法制备高质量c-BN薄膜.主要研究了三步法中第一步的时间和衬底负偏压对c-BN薄膜制备的影响，找到合适的沉积时间和衬底负偏压分别为5min和-180V.采用三步法制备薄膜，可以重复得到高立方相体积分数(立方相体积分数超过80%)的BN薄膜，并且实验重复性达到70%以上. 关键词： 立方氮化硼 能量势垒 缺陷 衬底偏压     

用射频溅射法制备立方氮化硼薄膜

利用射频溅射方法在n型Si(111)衬底上制备出立方相含量接近100%且粘附性较高的立方氮化硼(c-BN)薄膜.傅里叶变换红外谱(FTIR)的结果表明，基底负偏压对薄膜立方相含量和薄膜压应力有很大影响，另外，衬底的电阻率对c-BN生长和薄膜的压应力也有一定的影响. 关键词： 立方氮化硼 射频溅射 压应力 基底负偏压     

立方氮化硼薄膜的光学带隙

用射频溅射法在p型Si(100)衬底上沉积立方氮化硼(c-BN)薄膜,薄膜的成分由傅里叶变换红外谱标识,用紫外-可见分光光度计测量了c-BN薄膜的反射光谱,利用K-K(Kramers-Kroning)关系从反射谱计算出c-BN薄膜的光吸收系数,进而确定c-BN薄膜的光学带隙.对于立方相含量为55.4%的c-BN薄膜,光学带隙为5.38eV. 关键词： 立方氮化硼薄膜 光学带隙 K-K关系     

等离子体增强化学气相沉积法制备立方氮化硼薄膜过程中的表面生长机理

利用感应耦合等离子体增强化学气相沉积法以Ar，He，N₂和B₂H₆为反应气体制备了高纯立方氮化硼薄膜.用四极质谱仪对等离子体状况进行了系统的分析，发现B₂H₆完全被电离而N₂只是部分被电离.H₂和过量的N₂在等离子体中生成大量中性的H原子和活化的N^*₂，它们与表面的相互作用严重地阻碍了立方 关键词： 立方氮化硼薄膜 等离子体 质谱     

Surface properties of cubic boron nitride thin films

Studying the surface properties of cubic boron nitride (c-BN) thin films is very important to making it clear that its formation mechanism and application. In this paper, c-BN thin films were deposited on Si substrates by radio frequency sputter. The influence of working gas pressure on the formation of cBN thin film was studied. The surface of c-BN films was analyzed by X-ray photoelectron spectroscopy (XPS), and the results showed that the surface of c-BN thin films contained C and O elements besides B and N. Value of N/B of c-BN thin films that contained cubic phase of boron nitride was very close to 1. The calculation based on XPS showed that the thickness of hexagonal boron nitride (h-BN) on the surface of c-BN films is approximately 0.8 nm.     

Influence of oxygen on the growth of cubic boron nitride thin films by plasma-enhanced chemical vapour deposition

Cubic boron nitride thin films were deposited on silicon substrates by low-pressure inductively coupled plasma-enhanced chemical vapour deposition. It was found that the introduction of O₂ into the deposition system suppresses both nucleation and growth of cubic boron nitride. At a B₂H₆ concentration of 2.5\% during film deposition, the critical O₂ concentration allowed for the nucleation of cubic boron nitride was found to be less than 1.4\%, while that for the growth of cubic boron nitride was higher than 2.1\%. Moreover, the infrared absorption peak observed at around 1230--1280~cm^-1, frequently detected for cubic boron nitride films prepared using non-ultrahigh vacuum systems, appears to be due to the absorption of boron oxide, a contaminant formed as a result of the oxygen impurity. Therefore, the existence of trace oxygen contamination in boron nitride films can be evaluated qualitatively by this infrared absorption peak.     

Phonon spectrum boron nitrideof single-wallednanotubes

Based on a force constant model, we investigated the phonon spectrum and then specific heat of single-walled boron nitride nanotubes. The results show that the frequencies of Raman and infrared active modes decrease with increasing diameter in the low frequency, which is consistent with the results calculated by density functional theory. The fitting formulae for diameter and chirality dependence of specific heat at 300K are given.     

高温高压下立方氮化硼和六方氮化硼的结构、力学、热力学、电学以及光学性质的第一性原理研究

本文采用基于密度泛函理论的第一性原理平面波赝势和局域密度近似方法,优化了立方和六方氮化硼的几何结构,系统地研究了零温高压下立方和六方氮化硼的几何结构、力学、电学以及光学性质.结构与力学性质研究表明:立方氮化硼的结构更加稳定,两种结构的氮化硼均表现出一定的脆性,而六方氮化硼的热稳定性则相对较差;电学性质研究表明:立方氮化硼和六方氮化硼均为间接带隙半导体,且立方氮化硼比六方氮化硼局域性更强;光学性质结果显示:立方氮化硼和六方氮化硼对入射光的通过性都很好,在高能区立方氮化硼对入射光的表现更加敏感.此外,还研究了高温高压下立方氮化硼的热力学性质,并得到其热膨胀系数、热容、德拜温度和格林艾森系数随温度和压力的变化关系.本文的理论研究阐述了高压下立方氮化硼和六方氮化硼的相关性质,为今后的实验研究提供了比较可靠的理论依据.     

立方氮化硼薄膜生长过程中的界面控制

在立方氮化硼薄膜气相生长过程中生成的无定形初期层和乱层结构氮化硼中间层，一直是阻碍立方氮化硼薄膜外延生长的主要原因.系统地分析了硅衬底预处理对立方氮化硼薄膜中无定形初期层成分的影响，发现在等离子体化学气相生长法制备薄膜时，硅衬底上形成无定形初期层的可能原因有氧的存在、离子轰击以及高温下硅的氮化物的形成.在H₂气氛中1200K热处理硅衬底可以有效地减少真空室中残留氧浓度，除去硅表面的自然氧化层，保持硅衬底表面晶体结构.控制衬底温度不超过900 K，就能防止硅的氮化物的形成，成功地除去无 关键词： 立方氮化硼薄膜 等离子体化学气相生长 界面 电子显微镜     

六角氮化硼纳米带的几何和电子结构理论研究

本文采用密度泛函B3LYP方法在6-31G*水平上，对一系列不同宽度的锯齿型和扶手椅型六角氮化硼纳米带进行了理论研究。结果表明纳米带宽度对体系的性质有规律性的影响。随着宽度的增加，纳米带不同位置的硼氮键键长差异逐步减小从而提高了整个体系的共轭性；锯齿型纳米带的能隙单调减小而扶手椅型纳米带的能隙在减小的同时出现振荡，且振幅随宽度逐渐减小。锯齿型氮化硼纳米带的化学势在特定宽度出现了极值点。前线分子轨道的分布随着宽度的增加出现了非均匀分布，呈现出向边界偏移的现象。     

六角氮化硼纳米带的几何和电子结构理论研究

本文采用密度泛函B3LYP方法在6-31G*水平上,对一系列不同宽度的锯齿型和扶手椅型六角氮化硼纳米带进行了理论研究。结果表明纳米带宽度对体系的性质有规律性的影响。随着宽度的增加,纳米带不同位置的硼氮键键长差异逐步减小从而提高了整个体系的共轭性;锯齿型纳米带的能隙单调减小而扶手椅型纳米带的能隙在减小的同时出现振荡,且振幅随宽度逐渐减小。锯齿型氮化硼纳米带的化学势在特定宽度出现了极值点。前线分子轨道的分布随着宽度的增加出现了非均匀分布,呈现出向边界偏移的现象。     

A cubic boron nitride P-N diode: Fabrication in a large-volume press

Abstract

A simple method to determine the temperature of synthesis was proposed. (Mishima et al., to be published) This method utilized the melting of NaCl as an indicator of heater temperature. Applying the method to the fabrication of cBN p-n diodes in a large volume belt-type apparatus, we obtained an UV LED of ～2 mm in size.     

无序双层六角氮化硼量子薄膜的电子性质

基于安德森紧束缚模型,本文研究了无序双层六角氮化硼量子薄膜的电子性质. 数值计算结果表明在双层都无序掺杂的情况下,六角氮化硼量子薄膜的电子是局域的, 其表现为绝缘体性质;而对于单层掺杂(无论是氮原子还是硼原子)的双层六角氮化硼量子薄膜, 在能谱的带尾出现了持续的迁移率边.这就说明在单层掺杂的双层六角氮化硼量子薄膜中产生了 金属绝缘体转变.这一结果证实了有序-无序分区掺杂的理论模型,为理解及调控双层六角氮化硼量子薄膜 的电子性质提供了有益的理论指导.     

P213 BN: a novel large-cell boron nitride polymorph

A new boron nitride polymorph, P2₁3 BN (space group: P2₁3), is investigated by first-principles calculations, including its structural properties, stability, elastic properties, anisotropy and electronic properties. It is found that the new boron nitride polymorph P2₁3 BN is mechanically, dynamically and thermodynamically stable. The bulk modulus (B), shear modulus (G) and Young's modulus of P2₁3 BN are 91 GPa, 41 GPa and 107 GPa, respectively, all of which are larger than that of Y carbon and TY carbon. By comparing with c-BN, the Young's modulus, shear modulus and Poisson's ratio of P2₁3 BN show tiny anisotropy in the (001), (010), (100) and (111) planes. At the same time, in contrast with most boron nitride polymorphs, P2₁3 BN is a semiconductor material with a smaller band gap of 1.826 eV. The Debye temperature and the anisotropic sound velocities of P2₁3 BN are also investigated in this work.