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.     

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的hBN薄膜时获得的辐射热流是同物理条件下G/S结构的1.5倍;而在中频率区hBN薄膜的厚度阻碍了石墨烯表面等离激元和碳化硅表面声子极化激元的耦合,使得近场热辐射热流随hBN薄膜厚度增加而逐渐减弱。本研究的结果可为下一步实验与应用中对hBN薄膜厚度的选择提供理论基础。     

Optical absorption of hexagonal boron nitride involving nitrogen vacancies and their complexes

The pseudopotential and supercell methods are used to study the optical absorption of graphite-like hexagonal boron nitride involving deep levels of nitrogen vacancies and their clusters. The impurity-induced absorption is shown to be mainly related to electron transitions between the states that are antisymmetric with respect to the horizontal plane. Therefore, this absorption is highly anisotropic and is maximum for light waves polarized normally to the hexagonal axis. The optical absorption and photoconductivity spectra before and after neutron irradiation and thermal treatment are interpreted, and the activation energies for the thermoluminescence and conductivity of nitrogen-depleted boron nitride before and after fast-neutron irradiation and vacuum annealing are found.     

耐高温CrAlON基太阳能光谱选择性吸收涂层的制备与热稳定性

光谱选择性吸收涂层是太阳能光-热利用技术的核心部件,直接决定着整个系统的转换效率,为了提高涂层的选择吸收性和热稳定性,本文提出以金属氮化物替代金属纳米颗粒,构建纳米晶-非晶异质结构的思路,并采用多弧离子镀制备了Cr/CrAlN/CrAlON/CrAlN/CrAlON/CrAlO多吸收层光谱选择性吸收涂层,其吸收率达0.90,发射率为0.15,而且在500℃、大气条件下时效220 h后,涂层的吸收率升至0.94,发射率则降至0.10,并且能够保持稳定1000 h以上.微观组织分析表明,高温时效处理后,吸收层发生部分晶化形成了大量氮化物纳米颗粒,增加了对太阳光的散射和吸收,而CrAlO减反射层中的部分晶化形成了Al2O3和Cr2O3纳米颗粒,这不仅可以保护内部涂层不被氧化,而且Al2O3的形成可以增加太阳光的透过率,减少涂层表面反射,是多吸收层CrAlON基光谱选择性吸收涂层选择吸收性能提高的主要原因.同时,氮化物纳米颗粒被非晶基体均匀地分隔开来,形成了纳米晶-非晶异质结构,非晶在高温时效处理过程中只发生结构弛豫,从而有效地抑制了高温条件下的原子扩散,保证涂层中的纳米颗粒在高温下不发生明显团聚,这是多吸收层CrAlON基涂层具有良好热稳定性的最主要原因.这些研究结果对提高金属陶瓷光谱选择性吸收涂层的综合性能,实现更高效率的太阳能光-热利用具有重大意义.     

含六方氮化硼的一维光子晶体的光学特性

从麦克斯韦方程组出发,结合电磁场边界条件推导出在倾斜光轴条件下的传输矩阵。利用该传输矩阵研究了光轴方向对基于六方氮化硼的光子晶体光学特性的影响。研究表明,当Ф=0~°时,此结构会在六方氮化硼Ⅱ型双曲区域出现全方位禁带。随着Ф的不断增大,TE波和TM波在Ⅱ型双曲区域内的光子禁带逐渐错开,对于TM波,Ⅰ型双曲区域开始产生禁带,且朝着低频方向移动;Ⅱ型双曲区域内的禁带不断变窄,并往高频方向移动。利用这些特性,可实现偏振光分离和禁带加宽。     

用表面热透镜技术测量1 31 5nm高反射硅镜弱吸收的研究

运用表面热透镜技术精确测量了1315nm高反射硅镜的弱吸收,判断引起吸收的原因,从而为工艺上减少吸收降低损耗提供了保证.     

New quasi-planar surfaces of bare boron

New very stable quasi-planar clusters of bare boron are found by systematic ab initio density functional and quantum chemical methods. They are composed of dove-tailed hexagonal pyramids different from the classical forms of - or β-rhombohedral boron crystallines. The quasi-planar structures are considered to be fragments of quasi-planar surfaces, which can easily be obtained and constructed from a basic unit of hexagonal pyramids. A new investigation on double layers of boron quasi-planar surfaces shows an increase in the stability of the system which can be related to the overlap of π-orbitals between the layers. Therefore, we predict the existence of a series of parallel boron layers, as in graphite. These proposed surfaces can serve as lightweight protective armor, as a neutron-absorber material in fission reactions, or as very high temperature semiconductors.     

高压烧结镀Cr、Ti膜金刚石/铜复合材料热导率研究

 采用磁控溅射方法,在金刚石表面镀覆活性金属Cr膜和Ti膜,在高温高压下合成了镀活性金属膜金刚石/铜复合材料。实验发现,活性金属的加入增强了金刚石与铜界面间的结合强度,减少了界面热阻,提高了复合材料的热导率。复合材料热导率随着金刚石体积分数的增加而降低,随着金刚石的粒度增大而提高。这主要是由界面热阻引起的,可以通过增大金刚石粒度和改善界面状态来提高复合材料热导率。     

Charge distribution of a potassium-doped combined system of graphene and hexagonal boron nitride

By using first-principles density functional theory, we investigate the charge distribution of a potassium-doped layered combined system of graphene and hexagonal boron nitride. Two configurations of potassium-doped hexagonal boron nitride layers on graphenes and the reverse geometry of graphenes on hexagonal boron nitride layers are considered. We find that the charge distribution exhibits different features in these two situations. In the former case, the outmost hexagonal boron nitride layer cannot screen the external charges offered by potassium atom completely and most of the transferred charges reside on the two bounding layers. In contrary, the outmost graphene layer near the potassium atom can accept almost all of the transferred charges and only a few of them stay at interior layers in the latter case. A more amazing result is that the characteristics of charge transfer are independent of the number of hexagonal boron nitride layers and graphenes.     

基于高光谱技术建筑反射隔热涂料光谱特征减损规律的分析

受太阳辐射、气象等外界不可控因素的影响,建筑反射隔热涂料的反射隔热性能会逐渐减损。建筑反射隔热涂料性能在时间维度的变化是评价建筑在特定时段内节能效果的关键基础数据,明确建筑反射隔热涂料性能在时间维度的减损规律具有重要的现实与理论意义。建筑反射隔热涂料的反射、吸收特征是其性能的直观体现,借助高光谱技术定量分析涂料反射、吸收特征可正确揭示涂料性能在时间尺度的变化特征。为研究分析建筑反射隔热涂料性能在时间尺度上的减损规律,该研究利用高光谱技术,联合进行室内与外置实验采集涂料样本不同时期的光谱数据,并结合吸收峰深度、图谱分析法等光谱处理方法,定量分析涂料光谱反射特征、吸收特征在时间维度的变化特征,以研究分析涂料光谱反射率在外界环境影响下的减损规律。研究结论如下：（1）在350～2 250 nm波段区间内,建筑反射隔热涂料的光谱反射率随时间的增加而降低;光谱反射率的降低幅度在1月—5月内呈增加趋势,而在5月—10月内呈递减规律,且光谱反射率在可见光区间的降低幅度明显高于近红外区域。（2）建筑反射隔热涂料的吸收峰深度随时间的增加而降低,降低幅度在0~0.163范围内。（3）涂料厚度对涂料光谱反射率（涂料性能）及其在时间尺度的变化规律具有重要影响,且该影响拥有较强的稳定性;涂料厚度对涂料光谱反射率的减弱幅度具有较强影响,单一厚度的建筑反射隔热涂料的光谱反射率随时间的变化具有一致性,随时间的增加而变弱。     

退火温度对聚对苯乙炔MOPPV-ZnSe量子点复合材料太阳电池性能影响

利用原位缩合法制备了聚(2-甲氧基-5辛氧基)对苯乙炔(MOPPV)-ZnSe量子点复合材料,通过对复合材料的X射线衍射、透射电子显微镜、扫描电子显微镜、紫外可见吸收光谱等研究,发现聚合物MOPPV与ZnSe量子点以包覆形式有效地复合在一起,复合材料中ZnSe量子点结晶性良好,尺寸约为4 nm;且两者之间发生光诱导电荷转移,复合材料随着退火温度的升高,其吸收光谱范围发生红移。通过对MOPPV-ZnSe复合材料光电性能的研究发现,复合材料光电性能随着退火温度的升高逐渐表现出明显的二极管特性,转换效率出现先增大后减小的趋势,且在160℃时转换效率达到最大为0.3726%。     

Increasing the thermal conductivity of boron nitride and aluminum nitride particle epoxy-matrix composites by particle surface treatments

The thermal conductivity of boron nitride and aluminum nitride particle epoxy-matrix composites was increased by up to 97% by surface treatment of the particles prior to composite fabrication. The increase in thermal conductivity is due to decrease in the filler-matrix thermal contact resistance through the improvement of the interface between matrix and particles. Effective treatments for BN involved acetone, acids (nitric and sulfuric) and silane. The most effective treatment involved silane such that the coating resulted from the treatment amounted to 2.4% of the weight of the treated BN. The effectiveness of a treatment was higher for a larger BN volume fraction. At 57 vol.% BN, the thermal conductivity reached 10.3 W/ m·K. The treatments had little effect on the specific surface area of the BN particles. Silane treatments were also effective for AlN. At 60 vol.% AlN, the thermal conductivity reached 11.0 W/m·K.     

红外光谱在纤维质文物材料鉴别中的应用研究

纺织纤维和纸张纤维是常见纤维质文物材料,是构成博物馆精美文物如服饰手稿书画的基本材料,近年来寻求通过无损或微损方法对这一类材料的鉴别以及劣化状况评价备受文物鉴赏家和文物保护工作者的关注。借助傅里叶变换红外光谱,研究博物馆常见纺织纤维材料棉、麻、桑蚕丝、柞蚕丝、羊毛的红外光谱特征和它们的分子结构组成异同,研究传统纸纤维稻草、麦草、龙须草、龙旗松、桑皮红外光谱特征。结果表明：衰减全反射傅里叶变换红外光谱无损分析技术可通过比较3 300～2 800 cm-1 CH,NH,OH振动区间光谱形状以及指纹区峰位以区别不同种类纺织品纤维;碳氧振动纸张纤维最明显光谱差异位置出现在与纤维素OH伸缩振动相关波数3 300 cm-1和与C—O—C相关波数1 332,1 203,1 050 cm-1。文章探索研究红外光谱技术结合主成分分析法在快速鉴别纤维材料中的应用。通过对全光谱数据多元散射校正(MSC)预处理后进行主成分分析,可以把红外光谱十分相似的纺织纤维棉和亚麻、桑蚕丝和柞蚕丝明显分类;对光谱相似的纸纤维,可采用选择不同光谱波数段进行主成分分析,比较发现能够把五种纸纤维明显区分的光谱区间为3 800～2 800 cm-1。本研究为分子光谱无损分析技术应用于文物材料鉴别、科学评估纤维材料保存状况提供基础研究。     

锁相热像方法实验测量Nb2O5薄膜吸收率

利用锁相热像方法定量测量了光学镀膜的吸收率。待测薄膜吸收周期调制的激光能量，在表面形成热波，将红外相机记录的热分布信号进行锁相相关处理，获得信噪比提高的热图像。采用标准吸收样品对系统进行定标，可获得光热信号幅度与样品吸收率之间的定量联系，进而在相同实验条件下测量待测样品，可通过光热信号直接计算获得其绝对吸收率。在1 060 nm波长处开展了实验研究，测量获得了不同厚度Nb₂O₅镀膜的吸收率数值，实测的吸收可达80 ppm。     

六方氮化硼单层中一种(CN)3VB缺陷的第一性原理计算

二维六方氮化硼(hBN)的点缺陷最近被发现可以实现室温下的单光子发射,而成为近年的研究热点.尽管其具有重要的基础和应用研究意义,hBN中发光缺陷的原子结构起源仍然存在争议.本文采用基于密度泛函理论的第一性原理计算,研究hBN单层中一种B空位附近3个N原子被C替代的缺陷(CN)3VB.在hBN的B空位处,3个N原子各自带一个在平面内的悬挂键及相应的未配对电子,而通过C替换可以消除未配对的电子.系统研究了(CN)3VB缺陷的几何结构、电子结构以及光学性质,结果表明,缺陷可以由一个对称的亚稳态经过原子结构弛豫变成1个非对称的、3个C原子连在一起的基态结构.缺陷的形成在hBN中引入了一些由缺陷悬挂σ键及重构的π键贡献的局域缺陷态.这些缺陷态可以导致能量阈值在2.58 eV附近的可见光内部跃迁.本文的工作有助于进一步理解hBN中点缺陷的构成及光学性质,为实验上探讨发光点缺陷的原子结构起源及其性质提供理论依据.     

热透镜技术中反射和透射两种探测方式的比较分析

热透镜技术按照测量方式的不同可以分为反射式和透射式两种。这两种方式的灵敏度强烈地依赖于样品的热物理性质,对于不同的样品,选择合适的测量构型尤为重要。采用高斯激光束作为加热光源,分别从理论和实验上比较分析了模式不匹配的反射式和透射式两种热透镜探测构型在测量以BK7玻璃和石英为基底的高反射光学薄膜弱吸收中的应用,结果表明,对以BK7玻璃为基底的样品,采用反射式探测构型具有较高的灵敏度,而对以石英为基底的样品而言,采用透射式探测构型则具有更高的灵敏度,为实际光学薄膜吸收损耗测试灵敏度的提高提供了理论和实验依据。     

山东产大颗粒高温高压合成钻石的多种谱学方法研究

山东济南中乌新材料有限公司利用六面顶油压机生产出大颗粒钻石,为了掌握这些合成钻石的品质及与天然钻石的区分方法,采用宽频诱导发光光谱仪（GV5000）、红外光谱仪、钻石特征光谱检测仪（PL5000）、激光诱导击穿光谱仪和X射线能谱仪,对该公司生产的225粒无色、蓝色和黄色高温高压（HPHT）合成钻石进行检测,并与天然钻石对比。HPHT合成钻石样品的晶形以（111）晶面和（100）晶面共存的聚形为主导。原石切磨成圆钻形成品的出成率在20%~67%之间,净度级别为VVS-P,颜色级别为D-H。通过GV5000分析,三种颜色样品均可观察到立方八面体生长结构发光图案,无色HPHT合成钻石为强蓝色荧光和磷光,发光峰位于495 nm,与晶格中的顺磁氮有关;蓝色HPHT合成钻石为蓝-绿蓝色荧光和蓝色磷光,发光峰位于501 nm,与晶格中的顺磁氮、硼有关;黄色HPHT合成钻石为弱绿色荧光和磷光,显示556和883 nm Ni+相关发光峰,这些特征可与天然钻石相区分。红外光谱分析表明,无色HPHT合成钻石在1 332~1 100 cm-1无明显氮相关吸收,在2 802 cm-1有B0相关吸收,为含有少量硼的Ⅱa型;蓝色HPHT合成钻石位于1 294 cm-1有与B-相关的强吸收,归属为Ⅱb型;黄色HPHT合成钻石位于1 130和1 344 cm-1有与孤氮相关的明显吸收,归属为Ⅰb型。PL5000光致发光光谱显示,三种颜色HPHT合成钻石可检测到659,694,707,714和883 nm等镍相关缺陷发光峰。相比之下,无色和黄色天然钻石通常为Ⅰa型,具有1 282和1 175 cm-1等聚合氮的红外光谱吸收,光致发光光谱通常可检测到415 nm（N₃）零声子线,由孤氮、硼和镍等缺陷导致的光谱特征极为罕见。因此,红外光谱和光致发光光谱特征可作为重要的鉴别依据。激光诱导击穿光谱仪检测到无色HPHT合成钻石的出露包裹体主要成分为Fe。X射线能谱分析显示,对于含包裹体较多的样品,无色和蓝色HPHT合成钻石可检测到Fe,黄色HPHT合成钻石可检测到Fe和Ni,为其中包裹体的成分,这可作为HPHT合成钻石鉴定性特征。综上所述,通过GV5000超短波紫外荧光和磷光测试,配合红外光谱和光致发光光谱特征,结合包裹体成分特征,可以有效区分该研究的合成钻石和天然钻石。     

Crystallinity and degradation of silk: correlations between analytical signatures and physical condition on ageing

Adequately characterising the physical condition of historic textiles, and understanding the microstructural changes that occur in these materials, is essential when considering appropriate conservation, display and storage strategies. Our work has concentrated on developing non-destructive or micro-destructive methodologies that will permit this for one of the most important historic fibres, silk. We have been able to demonstrate that correlations can be drawn between the physical deterioration of silk samples and certain measurable spectroscopic, chromatographic and chemical signatures. Understanding the way in which these signatures arise then allows the microstructural changes within the crystalline and amorphous content of the fibres to be investigated and more fully interpreted. The techniques developed by our group and by other researchers in the field include polarised FTIR-ATR (Pol-ATR) and near infrared (NIR) spectroscopy, HPLC microsampling analyses and pH measurements. The results of these analyses correlate to measurable mechanical properties and thus suggest that the physical state of historic silk fabrics might be adequately characterised for conservation purposes by such indirect micromethodology. PACS 81.05.Lg; 82.80.Gk; 87.14.Ee     

Preparation and characterization of hexagonal boron nitride and PAMPS-NMPA-based thin composite films and investigation of their membrane properties

The preparation, thermal, morphological, and ion-conducting properties of new composite membranes based on poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) and nitrilotri(methylphosphonic acid) (NMPA)/hexagonal boron nitride (hBN) were carried out throughout this work. Fourier transform infrared (FTIR) spectroscopy was used to characterize the interactions between host polymer, NMPA, and inorganic additive, hBN. Thermal properties of the materials were examined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests. TGA results illustrated that all composite membranes are thermally stable up to 200 °C. The surface topography of the films was investigated by scanning electron microscopy (SEM) and verified that hBN uniformly dispersed into the PAMPS-NMPA matrix. The crystallinity of the membranes was characterized by using X-ray diffraction (XRD). X-ray patterns support semicrystalline nature of the composite materials. At anhydrous conditions, the maximum proton conductivity was found as 3.2?×?10^?5 S cm^?1 at 150 °C for PAMPS-NMPA-3hBN via impedance analyzer.     

Extinction mechanisms of hyperbolic h-BN nanodisk

We applied the finite element method to calculate the extinction spectrum of single hyperbolic hexagonal boron nitride(h-BN) nanodisk. We show that the hyperbolic h-BN nanodisk exhibits two extinction mechanisms in the mid-infrared region. The volume confined phonon polaritons resonances of the nanodisk give rise to a series of weak extinction peaks.The localized surface phonon polaritons lead to a robust dipolar extinction, and the extinction peak position is tunable by varying the size of the h-BN nanodisk. These findings reveal the mechanisms of the interaction between light and resonant h-BN nanodisk, which are essential for h-BN related opto-electromagnetic applications.