金属氮化物硬质膜层“合金化”的研究进展

通过展示近年来国内外金属氮化物膜层的研究结果,探究了膜层晶体结构、微观组织的变化规律和提高性能的途径;列举了大量文献进行分析.结果表明:添加C或B元素,可形成"替位式"的金属氮碳化物或氮硼化物膜层,具有明显的固溶强化效应;大部分氮硼化物膜层,都可生成细小的金属硼化物,对性能的提高非常有力;加入Si可以细化晶粒,提高膜层的韧性和耐磨性.在TiN和CrN膜层中加入金属合金化元素(如Al、Zr等),除具有明显的固溶强化效应外,还能显著提高膜层的高温氧化阻力和腐蚀阻力,提高膜层的耐磨性.沉积膜层的显微组织结构,可以通过调整"合金化"元素的比率来改变,并由此可以对膜层性能进行调制.通过"合金化",金属氮化物膜层的晶体结构、微观组织都可以调制,综合性能显著改善和提高.

Low pressure synthesis of boron nitride with (C_2H_5)_2O·BF_3 and Li_3N precursor

Cubic boron nitride（c-BN） was synthesized through benzene thermal method at a lower temperature of （300℃） by selecting liquid（（C2H5）2O·）BF3 and Li3N as reactants. Hexagonal boron nitride（h-BN） and orthorhombic boron nitride（o-BN） were also obtained. The samples were characterized by X-ray powder diffractometry and Fourier transformation infrared spectroscopy. The results show that all the BF3, BCl3 and BBr3 in the same family compounds can react with Li3N to synthesize BN since the strongest bond of B—F can be broken. Compared with BBr3, liquid （C2H5）2O·BF3 is cheaper, less toxic and more convenient to operate. Li3N not only provides nitrogen source but also has catalytic effect on accelerating the formation of c-BN at low temperature and pressure.

Electronic Transport Through N24B24 Molecular Junction

We have investigated the electron transport properties of a N24B24 molecule coupled to two metallic contacts with a combination of GW approximation and the non-equilibrium Green＇s- function technique. The calculations indicate that the four and three resonant tunneling peaks are seen for the density of states （DOS） curves in the cases of single and multiple atomic contacts, respectively. The off state and negative differential resistance （NDR） effect are observed in the I-V characteristics of the N24B24 molecule. The NDR behavior is also observed in voltages of about 354.5, 354, 354.6, and 354.3 V for one, four, six, and eight atomic contacts. Also, the I-V characteristics of N24B24 are in off state at low voltages that is independent of the contact types. The current contact types and indicate that N24B24 molecule curves against the gate voltage depend on behaves as a semiconductor.

Length dependence of linear and nonlinear optical properties of finite-length BN（5,0） nanotube

In this paper, we investigate the length dependence of linear and nonlinear optical properties of finite-length BN nanotubes. The recently predicted smallest BN（5,0） nanotube with configuration stabilization is selected as an example. The energy gap and optical gap show the obvious length dependence with the increase of nanotube length. When the length reaches about 24 /~, the energy gap will saturate at about 3.2 eV, which agrees well with the corrected quasi- particle energy gap. The third-order polarizabilities increase with the increase of tube length. Two-photon allowed excited states have significant contributions to the third-order polarizabilities of BN（5,0） nanotube.

The Adhesion Improvement of Cubic Boron Nitride Film on High Speed Steel Substrate Implanted by Boron Element

Cubic boron nitride(c-BN) films were deposited on W6Mo5Cr4V2 high speed steel(HSS) substrate implanted with boron ion by RF-magnetron sputtering. The films were analyzed by the bending beam method, scratch test, XPS and AFM. The experimental results show that the implantation of boron atom can reduce the internal stress and improve the adhesion strength of the films. The critical load of scratch test rises to 27.45 N, compared to 1.75 N of c-BN film on the unimplanted HSS. The AFM shows that the surface of the c-BN film on the implanted HSS is low in roughness and small in grain size. Then the composition of the boron implanted layer was analyzed by the XPS. And the influence of the boron implanted layer on the internal stress and adhesion strength of c-BN films were investigated.

Stability of BN/metal interfaces in gaseous atmosphere

Hexagonal boron nitride （h-BN） is often prepared by epitaxial growth on metals, and stability of the formed BN/metal interfaces in gaseous environment is a key issue for physicochemical properties of the BN overlayers. As an illustration here, the structural change of a BN/Ru（0001） interface upon exposure to 02 has been investigated using in situ photoemission electron microscopy （PEEM） and ambient pressure X-ray photoelectron spectroscopy （AP-XPS）. We demonstrate the occurrence of oxygen intercalation of the BN overlayers in 02 atmosphere, which decouples the BN overlayer from the substrate. Comparative studies of oxygen intercalation at BN/Ru（0001） and graphene/Ru（0001） surfaces indicate that the oxygen intercalation of BN overlayers happens more easily than graphene. This finding will be of importance for future applications of BN-based devices and materials under ambient conditions.

Super-Planckian thermal radiation enabled by hyperbolic surface phonon polaritons

Excitation of surface resonance modes and presence of resonance-free hyperbolic modes are two common ways to enhance the near-field radiative energy transport, which can find wide applications in noncontact thermal management and energy harvesting.Here, we identify another way to achieve the super-Planckian thermal radiation via hyperbolic surface phonon polaritons(HSPhPs). Based on the fluctuation-dissipation theory, the near-field radiative heat flux between bulk hexagonal boron nitride(hBN) planes with the optical axis perpendicular to the radiative energy flow can be 120 times as large as the blackbody limit for a gap distance of 20 nm. When the film thickness is reduced to 10 nm, the radiative heat flux is found to increase by 26.3%.The underlying mechanism is attributed to the coupling of Type I HSPhPs inside the anisotropic hBN film, which improves the energy transmission coefficient over a broad wavevector space especially for waves with extremely high wavevectors. This work helps to deepen the understanding of near-field radiation between natural hyperbolic materials, and opens a new route to enhance the near-field thermal radiation.

Red photoluminescence BCNO synthesized from graphene oxide nanosheets

In this paper,we demonstrate the conversion of graphene oxide(GO) into boron carbon oxynitride(BCNO) hybrid nanosheets via a reaction with boric acid and urea,during which the boron and nitrogen atoms are incorporated into graphene nanosheets.The experimental results reveal that GO is important for the photoluminescence(PL) BCNO phosphor particles.More importantly,in this system,the prepared BCNO phosphors can be used to prepare the materials needed for red light emitting diodes(LEDs).