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     

六方氮化硼的振动光谱与立方氮化硼的合成

 以X射线衍射分析作参比，分析了高度三维有序到近乱层结构的9种六方氮化硼的红外和拉曼光谱，并进行了立方氮化硼的高温高压合成。光谱分析表明，随着晶性的降低，六方氮化硼的低频红外吸收峰的位置及拉曼谱线等基本振动光谱发生明显的特征性的变化，并伴随出现各自不同的次级光谱结构。合成结果表明，在触媒作用下，立方氮化硼的形成需要六方氮化硼原料有一定的结晶度，但立方氮化硼合成效果与六方氮化硼结晶度并非是简单的单调关系。对振动光谱和合成试验的结果进行了讨论。     

用不同合成体系制备黑色立方氮化硼的研究

 立方氮化硼（cBN）晶体随颜色的加深,晶体的晶形越完整,晶体尺寸也越大。采用Mg+hBN、LiH+hBN、Li₃N+hBN+B和B+Li₃N 4种体系分别合成出了黑色的立方氮化硼晶体。通过光学显微镜、X射线衍射、拉曼光谱等测试分析手段,从合成条件、晶体形貌、颗粒度及残余应力等方面对不同体系合成出的黑色cBN晶体作了比较。结果表明,不同体系的合成效果有很大差别。在实际应用中应该根据需要采用不同的体系,以达到最优化合成目的。     

衬底材料对制备立方氮化硼薄膜的影响

较系统地研究了不同衬底材料对制备氮化硼薄膜的影响。用热丝增强射频等离子体CVD法,以NH3,B2H6和H2为反应气体,在Si,Ni,Co和不锈钢等衬底材料上,成功生长出高质量的立方氮化硼薄膜,还用13.56MHz的射频溅射系统将c-BN薄膜沉积在Si衬底上,靶材为h-BN(纯度为99.99％）,溅射气体为氩气和氮气的混合气体,所得到的氮化硼薄膜中立方相含量高于90%,用X射线衍射谱和傅里叶变换红谱对样品进行了分析表明,衬底材料与c-BN的晶格匹配情况,对于CVD生长立方氮化硼薄膜影响很大,而对溅射生长立方氮化硼薄膜影响不大。     

高压合成立方氮化硼用的新触媒材料的研究

 本文研究了合成立方氮化硼用新触媒材料Mg₃B₂N₄及Ca₃B₂N₄的制备方法，并对它们的稳定性及其催化作用进行了讨论。氮化硼原料的结晶状态及合成温度、合成时间、气流量等对新触媒的合成有着重要的影响。本文还在高温高压下利用新触媒进行了立方氮化硼的合成实验，结果表明，与碱土金属触媒相比新触媒具有合成压力低、转化率高、合成温度和压力范围宽、产物杂志含量低、破碎强度高等优点，是一种应用前景很大的触媒材料。     

高温高压合成立方氮化硼的热力学分析

 从热力学角度计算出了以六角氮化硼为原料、用高压触媒法合成立方氮化硼时所形成稳定的临界晶粒半径r_k的大小,当p=6.0 GPa、T=1 600 ℃时,r_k≈15 nm。分析了r_k的大小与合成温度、压力的关系,以及在给定压力下立方氮化硼晶粒转化率与温度的关系。结果表明：在立方氮化硼稳定区,在相同压力下,r_k随温度的升高而增大;在相同温度下,r_k随压力的升高而减小,r_k越小立方氮化硼晶粒的转化率越高。计算结果与实际合成实验所得结果完全一致。     

不同六方氮化硼向立方氮化硼的转化行为

 利用X射线衍射法分析了7种六方氮比硼原料的结晶度、晶粒度和晶格常数，研究了高温高压下六方氮比硼（hBN）向立方氮比硼（cBN）的转化行为和转化率。结果表明，结晶度高和晶粒度细的六方氮化硼易于转化，有利于cBN的成核。     

基于六角氮化硼二维薄膜的忆阻器

报道了一种基于多层六角氮化硼(h-BN)二维薄膜的忆阻器件.该器件不需要电预处理过程,且具有自限流的双极性阻变行为;具有较好的抗疲劳性和较长的数据保持时间.该器件在脉冲编程条件下具有模拟转变特性,即在连续的电压脉冲下器件的电阻态能被连续地调控,使得该器件能够模仿神经网络系统中的神经突触权重变化行为.综上所述,基于多层h-BN的忆阻器具有应用在非易失性存储和神经计算中的潜力.     

利用X射线衍射研究冲击波合成纤锌矿型氮化硼

 用X射线衍射法，对不同结晶度的石墨型氮化硼（gBN）在冲击波作用下转变成的纤锌矿型氮化硼（wBN）产物进行了研究，对wBN中的杂质含量等进行了分析。结果表明：gBN的石墨化指数G.I值对wBN的产率有明显的影响。     

ZrN-ZrB2纳米复合材料的高压制备及性能表征

 以金属锆粉（Zr）和六方氮化硼粉（h-BN）为原料,结合高能球磨和高温高压合成技术,制备出了ZrN-ZrB₂纳米复合材料。利用X射线衍射、透射电镜和拉曼光谱等测试手段,对材料的结构和合成规律进行了研究。结果表明,高能球磨过程中只合成出了ZrN_x,没有出现ZrB₂,从N、B原子与Zr进行固态反应的热力学和动力学方面分析了原因。利用Zr与BN粉球磨10 h后的混料,在压力为5 GPa、温度为1 300 ℃的条件下,制备出了具有高致密度的ZrN-ZrB₂纳米复合材料。其维氏显微硬度（17 GPa）、热膨胀系数（7.57×10^-6 ℃^-1）和电阻率-温度系数（8.846×10^-4 ℃^-1）等材料参数的测量结果表明,ZrN-ZrB₂复合材料是一种集优良的力学、热学和电学性能于一体的纳米复合材料。     

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.     

锂基触媒体系中不同形状立方氮化硼晶体的高压合成

采用高温高压方法,以六角氮化硼(hBN)为原料、选用氮化锂(Li3N)、氢化锂+氮化锂(LiH+Li3N)、氢化锂(LiH)、氢化锂+氨基锂(LiH+LiNH2)、氮化锂+氨基锂(Li3N+LiNH2)为触媒,在合适的温度、压力及生长工艺条件下,分别得到了厚板状、类球形、八面体或六八面体、扁锥状和片状六边形形貌立方氮化硼(cBN)晶体。总结了不同锂基触媒/添加剂对合成的cBN晶体形貌变化的影响。     

STRESS ANALYSIS IN CUBIC BORON NITRIDE FILMS BY X-RAY DIFFRACTION USING sin2 ψ METHOD

The boron nitride (BN) films containing cubic boron nitride (c-BN) and hexagonal boron nitride (h-BN) were prepared by radio frequency a ssisted thermal filament chemical vapor deposition. The stress and strain in BN films were investigated by X-ray diffraction analysis using the sin² ψ method. The results showed that both c-BN and h-BN in the same film have similar values of elastic strain, however, the compressive stress in c-BN is much greater than that in h-BN for the same film. Both stress and strain gradually decre ased with the increase of substrate temperature (T_s). The effective stress in the films calculated by the effective stress model increased with the increase of T_s. Furthermore, the dependence of effective stress in the films on T_s was also investigated.     

Ultra-hard materials: New developments in c-Bn synthesis under high pressure conditions

Abstract

c-BN is a promoted material for different applications, such as tooling of ferrous alloys but also for future electronic devices. At the present time, due to the fact that boron nitride is a binary system and also to the elimination of the graphitic form, the preparation of c-BN thin film is difficult and not yet achieved. During these last six years, great efforts have been undertaken in the Laboratoire do Chimie du Solide du CNRS in order to improve the h-BN → c-BN flux assisted conversion using the HP-HT route. New fluxes with a nitrofluoride-composition have been developed in order: (i) to reduce the P, T experimental conversion conditions, (ii) to increase the conversion yield (h-BN → c-BN), (iii) to govern the average size of c-BN cristallites, (iv) to improve the crystal growth.

Now, new techniques have also been developed in the doping control of c-BN lattice.     

Young’s modulus and density of nanocrystalline cubic boron nitride films determined by dispersion of surface acoustic waves

Cubic boron nitride (c-BN) films of 200–420 nm thickness and high phase purity were deposited on silicon (100) substrates by ion-assisted pulsed laser deposition (IA PLD)from a boron nitride target using a KrF-excimer laser, and by plasma-enhanced physical vapor deposition (PE PVD)with a hollow-cathode arc evaporation device. In order to improve the c-BNfilm adhesion, hexagonal boron nitride (h-BN) films with 25–50 nm thickness were used as buffer layers. The density and Young’s modulus of the c-BNfilms were obtained by investigating the dispersion of surface acoustic waves. In data analysis a two-layer model was applied in order to take the influence of the h-BNlayer into consideration. The values for the density vary from 2.95±0.25 g/cm³to 3.35±0.3 g/cm³, and those for the Young’s modulus from 420±40 GPa to 505±30 GPa. The results are compared with literature values reported for nanocrystalline films, polycrystalline disks and single crystal c-BN. Received: 26 March 2001 / Accepted: 29 March 2001 / Published online: 25 July 2001     

Chemical Synthesis of C3N and BC2N Compounds

A chemical reaction for the preparation of B-C-N compounds by using carbon tetrachloride （CC14）, boron tribromide （BBr3）, lithium nitride （Li3N） and sodium as reactants has been carried out at the temperature of 400℃. Measurements of FTIR, XRD, TEM and EELS show that two kinds of compounds have been formed in the prepared sample. One is hollow sphere-like C-N with an amorphous, structure; the other is piece-like polycrystalline B-C-N with the hexagonal structure. Their determined compositions are close to C3N and BC2N, respectively.     

Simulation of boron nitride sputtering process and its comparisonwith experimental data

In the paper, TRIM and TRIDYN simulation codes were used to simulate the sputtering processes of boron nitride (BN) films during bombardment of ions. The TRIM and TRIDYN codes are applicable to the simulation of sputtering processes of different target materials with amorphous and polycrystalline structure. The results of the simulations are compared with experimental data. The sputtering experiments of polycrystalline hexagonal BN (h-BN) and cubic BN (c-BN) films were performed in a Commonwealth Scientific Corporation (CSC) 38-cm ion beam source device. The comparison of calculated and experimental results indicated that a) the experimental sputtering yields of h-BN and c-BN films bombarded with Ar⁺ ions versus the angle of incidence are in reasonable agreement with the calculated results; b) the sputtering yields of h-BN and c-BN bombarded with Ar⁺ are nearly of the same values versus the angle of incidence-preferential sputtering of h-BN was not found; c) the calculated sputtering. Yields of BN as a function of Ar⁺ ion energy are very sensitive to values of the surface binding energy (SEE); and d) surface binding energy between 2 and 3 eV for BN appears to be reasonable for the simulation of sputtering process of h-BN and c-BN films     

First-Principles Studies on Properties of Boron-Related Impurities in c-BN

We investigate, by first-principles calculations, the pressure dependence of formation enthalpies and defective geometry and bulk modulus of boron-related impurities （VB, Cs, NB, and OB） with different charged states in cubic boron nitride （c-BN） using a supercell approach. It is found that the nitrogen atoms surrounding the defect relax inward in the case of CB, while the nitrogen atoms relax outward in the other cases. These boron-related impurities become much more stable and have larger concentration with increasing pressure. The impurity CB^＋1 is found to have the lowest formation enthalpy, make the material exhibit semiconductor characters and have the bulk modulus higher than ideal c-BN and than those in the cases of other impurities. Our results suggest that the hardness of c-BN may be strengthened when a carbon atom substitutes at a B site.