Electronic structures and transport properties of fluorinated boron nitride nanoribbons

By applying the nonequilibrium Green's functions and the density-functional theory, we investigate the electronic structures and transport properties of fluorinated zigzag-edged boron nitride nanoribbons. The results show that the transition between half-metal and semiconductor in zigzag-edged boron nitride nanoribbons can be realized by fluorination at different sites or by the change of the fluorination level. Moreover, the negative differential resistance and varistor-type behaviors can also be observed in such fluorinated zigzag-edged boron nitride nanoribbon devices. Therefore, the fluorination of zigzag-edged boron nitride nanoribbons will provide the possibilities for a multifunctional molecular device design.     

X-Ray Photoelectron Spectra and Electronic Structure of Solid Solutions Based on Cubic Boron Nitride

The electronic energy structure of substitution solid solutions based on boron nitride B _1-x NR _x and BN _1-x R_x (R = C, O) (x=0.25) in a diamond-like modification of ZnS type has been investigated by the local coherent potential method in terms of multiple-scattering theory. The total and partial densities of states were calculated for each element in a solid solution. The crystalline potential was calculated using an MT approximation. The lattice parameter was chosen based on X-ray diffraction data for c-BN: 0.3615 nm. The electronic energy structures of the solid solutions and binary c-BN are compared in the framework of a single approximation. The calculated partial densities of states are compared with the experimental X-ray emission and photoelectron spectra of boron, nitrogen, and oxygen in these compounds. The calculated partial charges of electrons at the top of the valence band show that charge transfer from boron to nitrogen takes place in the solid solutions. An analysis of the electronic structures of the solid solutions of boron nitride indicates that the quasicore resonances inherent in binary c-BN are delocalized and that chemical bonding in the solid solutions of boron nitride is weakened.     

X-ray spectra and electronic structure of boron nitride in different crystallographic modifications

The electronic energy structure of boron nitride with ZnS (c-BN) and wurtzite (w-BN) type crystal lattices is calculated by the local coherent potential (LCPA) method in a multiple scattering approximation. The local partial 2p states of boron with c-BN and w-BN are compared with the boron K emission spectra in the corresponding compounds. Fine structure is first obtained in the region of the top of the valence band. Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 6, pp. 1083–1087, November–December, 1998.     

One‐Step Exfoliation and Fluorination of Boron Nitride Nanosheets and a Study of Their Magnetic Properties

A novel, simple, and efficient method for the preparation of the fluorinated hexagonal boron nitride nanosheets (F‐BNNSs) and the corresponding magnetic properties is presented. A one‐step route is used to exfoliate and fluorinate the BNNSs by ammonium fluoride (NH₄F) from hexagonal boron nitride (h‐BN) powder. Through related instrument characterizations and theoretical calculations, we confirm that large‐area and few‐layer F‐BNNSs were successfully produced by this method, which can be attributed to a fluorination‐assisted exfoliation mechanism from the bulk h‐BN in NH₄F. More intriguingly, we initially verified that the as‐prepared F‐BNNSs exhibit ferromagnetic characteristics, which would have good potential applications in spintronic devices.     

DFT study on the structural and electronic properties of Pt-doped boron nitride nanotubes

First-principles calculations based on density functional theory were carried out to investigate the structural and electronic properties of Pt substitution-doped boron nitride (BN) nanotubes. The electronic and structural properties were studied for substituted Pt in the boron and the nitrogen sites of the (BN) nanotube. The band gap significantly diminishes to 2.095 eV for Pt doping at the B site while the band gap diminishes to 2.231 eV for Pt doping at the N site. The band density increases in both the valence band and the conduction band after doping. The effects of the hardness and softness group 17 (halogen elements) were calculated by density functional theory (DFT).     

氮化硼诱导聚乙烯分子结晶的分子动力学模拟

采用分子动力学方法(MD)研究熔体条件下聚乙烯分子在氮化硼纳米管表面和氮化硼片层表面的结晶机理。通过对聚乙烯分子结晶过程中晶体构象的演变、空间内分子分布的变化以及分子扩散特性的研究,从微观角度比较了两种结构氮化硼纳米材料对聚乙烯结晶的影响。结果表明一维结构的氮化硼纳米管诱导聚乙烯结晶的能力远高于二维片层状的氮化硼,说明纳米材料的维度影响着高分子材料的结晶性能。     

高导热氮化硼/芳纶沉析复合薄膜的制备及性能

利用多巴胺(DA)的氧化自聚合特性, 对六方氮化硼(h-BN)进行表面修饰, 并以多巴胺改性后的氮化硼(h-BN@PDA)为导热填料, 对基体芳纶沉析纤维(AF)进行填充, 通过真空辅助抽滤法制备多巴胺改性氮化硼/芳纶沉析(h-BN@PDA/AF)复合薄膜, 并对其微观形貌、 表面官能团、 导热性能、 绝缘性能及力学性能进行研究. 结果表明, 聚多巴胺(PDA)包覆在h-BN表面, 并引入活性基团, 与AF纤维产生氢键, 改善了两者的界面结合, 显著提高了复合薄膜导热性能及绝缘性能. 当h-BN@PDA含量为70%时, h-BN@PDA/AF复合薄膜的导热系数为1.36 W/(m·K), 与纯芳纶沉析薄膜相比, 导热系数的增幅约为697.65%, 体积电阻率为5.96×10 ¹⁴ Ω·m, 拉伸模量高达287.19 MPa.     

Electronic structures of organic molecule encapsulated BN nanotubes under transverse electric field

The electronic structures of boron nitride nanotubes (BNNTs) doped by different organic molecules under a transverse electric field were investigated via first-principles calculations. The external field reduces the energy gap of BNNT, thus makes the molecular bands closer to the BNNT band edges and enhances the charge transfers between BNNT and molecules. The effects of the electric field direction on the band structure are negligible. The electric field shielding effect of BNNT to the inside organic molecules is discussed. Organic molecule doping strongly modifies the optical property of BNNT, and the absorption edge is redshifted under static transverse electric field.     

XPS investigations of thick,oxygen-containing cubic boron nitride coatings

Cubic boron nitride (c-BN) coatings produced by PVD and PECVD techniques usually exhibit very high compressive stresses and poor adhesion due to intense ion bombardments of the growing surface that are mandatory during the formation of the cubic phase. Our previous investigations indicate, however, that a controlled addition of oxygen during film deposition can lead to a drastic reduction of the detrimental stress, yet having minor effect on the cubic phase content in the resulting low-stress, oxygen-containing c-BN:O coatings (as already confirmed by various analytical methods like X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and electron diffraction, and Fourier transform infra-red spectroscopy (FTIR)). This stress-reduction technique makes possible the deposition of well-adhered, superhard c-BN:O layer about 2 μm thick through magnetron sputtering on top of an adhesion-promoting base layer and via a compositional-graded nucleation process. In the present paper, we report on the atomic bonding structure relating in particular to the incorporated oxygen within such a thick c-BN:O coating using X-ray photoelectron spectroscopy (XPS). The c-BN:O top layer was found to consist of about 49.8 at% boron, 42.2 at% nitrogen, 5.5 at% oxygen, as well as small amounts of carbon (1.4 at%) and argon (1.1 at%). Because of the low oxygen concentration, it was difficult to categorize the bonding state of oxygen according to the XPS spectra of B 1s and N 1s elemental lines. However, the detailed results in terms of the O 1s spectrum strongly indicated that the lattice nitrogen of c-BN was partially replaced by the added oxygen.     

溶液法制备图案化量子点薄膜的研究进展

量子点发光二极管(QLED)由于具有显色性好、色纯度高和性能稳定等特点而受到广泛关注,可用于制备具有超薄结构和柔性结构的显示器件.量子点(QDs)层是QLED器件的核心发光层,制备高质量的图案化QD薄膜对于提高QLED器件性能至关重要.本文综述了近年来溶液法制备QD薄膜的研究进展,探讨了目前主要使用的各种溶液法的优势和前景,并对最近新发展的纤维辅助的溶液可控转移制备QD薄膜方法的优势和发展前景进行了评述.     

Interfacial self-assembly growth of mesoporous polydopamine nanofilms for formaldehyde sensing

Mesoporous polymer nanofilms combine the advantages of the unique structure of mesopores, the quasi-2D configuration of the films, and the inherent properties of polymers, and have become a kind of ideal candidate for the high-performance micro-nano devices due to their highly accessible surface area and exposed active sites. However, the facile preparation of polymer nanofilms with well-defined mesostructures has remained a great challenge due to the lack of synthetic strategies. In this study, we developed a simple soft-template interfacial co-assembly strategy to in-situ construct mesoporous polydopamine nanofilms with uniform thickness (30 nm) and regularly distributed mesopore arrays (average pore size of 12 nm) on surfaces with different types and morphologies. Furthermore, a single-layer mesoporous polymer nanofilm was directly grown on a quartz crystal microbalance substrate and its performance for sensing formaldehyde was studied. The resulted sensor showed excellent sensing response, fast response/recovery dynamics, and great stability, presenting a great promising landscape for trace detection of formaldehyde gas.     

The First Principle Study on C-doped Armchair Boron Nitride Nanoribbon Rectifier

The electronic transport properties of armchair-edged boron nitride nanoribbons(ABNNRs) devices were investigated by the first principle calculations. The calculated results show that the ABNNR device doped with carbon atoms in one of the electrodes acts as a high performance nanoribbon rectifier. It is interesting to find that there exists a particular bias-polarity-dependent matching band between two electrodes,leading to a similar current-voltage(I-V) behavior as conventional P-N diodes. The I-V behavior presents a linear positive-bias I-V characteristic,an absolutely negligible leakage current,and a stable rectifying property under a large bias region. The results suggest that C doping might be an effective way to raise ABNNRs devices' rectifying performance.     

Controllable n-type doping in WSe2 monolayer via construction of anion vacancies

The successful applications of two-dimensional (2D) transition metal dichalcogenides highly rely on rational regulation of their electronic properties. The nondestructive and controllable doping strategy is of great importance to implement 2D materials in electronic devices. Herein, we propose a straightforward and effective method to realize controllable n-type doping in WSe₂ monolayer by electron beam irradiation. Electrical measurements and photoluminescence (PL) spectra verify the strong n-doping in electron beam-treated WSe₂ monolayers. The n-type doping arises from the generation of Se vacancies and the doping degree is precisely controlled by irradiation fluences. Due to the n-doping-induced narrowing of the Schottky barrier, the current of back-gated monolayer WSe₂ is enhanced by an order of magnitude and a ∼8× increase in the electron filed-effect mobility is observed. Remarkably, it is a moderate method without significant reduction in electrical performance and severe damage to lattice structures even under ultra-high doses of irradiation.     

选相原位法合成立方氮化硼的关键影响因素

利用选相原位法在水溶液中成功制备出了立方氮化硼晶体，对反应条件进行了优化。结果表明，利用选相原位法合成立方氮化硼的最佳实验条件是：反应压力为10.0 MPa，在氯离子加入下利用混合氮源进行反应。在该条件下得到了纯相的立方氮化硼晶体。     

SiC-doped boron nitride nanotubes: computations of 11B and 14N quadrupole coupling constants

Abstract  

Density-functional theory calculations have been performed to investigate the properties of the electronic structures of silicon–carbon-doped boron nitride nanotubes (BNNTs). The geometries of zigzag and armchair BNNTs were initially optimized and the quadrupole coupling constants subsequently calculated. The results indicate that doping of B and N atoms by C and Si atoms has more influence on the electronic structure of the BNNTs than does doping of B and N atoms by Si and C atoms. The changes of the electronic sites of the N atoms are also more significant than those of the B atoms.     

Self-assembly of discotic liquid crystal porphyrin into more controllable ordered nanostructure mediated by fluorophobic effect

The novel nanoscale discotic liquid crystal porphyrin with partial chain perfluorination, which has the same basic structure as the best photoreceptor in nature (chlorophyll), shows an exceptionally enhanced tendency to self-assemble into ordered nanostructure. Defect-free homeotropically aligned fluorinated porphyrin thin films were, for the first time, fabricated and characterised. The ability to self-assemble large π-conjugated discotic molecules into highly ordered nanostructure via partial chain perfluorination provides new insight for the bottom-up nanofabrication of molecular devices. The controllable ordered porphyrin nanostructure with directed molecular arrangement holds great promise for use in high-performance electronic devices.     

Free-standing poly(L-lactic acid) nanofilms loaded with superparamagnetic nanoparticles

Freely suspended nanocomposite thin films based on soft polymers and functional nanostructures have been widely investigated for their potential application as active elements in microdevices. However, most studies are focused on the preparation of nanofilms composed of polyelectrolytes and charged colloidal particles. Here, a new technique for the preparation of poly(l-lactic acid) free-standing nanofilms embeddidng superparamagnetic iron oxide nanoparticles is presented. The fabrication process, based on a spin-coating deposition approach, is described, and the influence of each production parameter on the morphology and magnetic properties of the final structure is investigated. Superparamagnetic free-standing nanofilms were obtained, as evidenced by a magnetization hysteresis measurement performed with a superconducting quantum interference device (SQUID). Nanofilm surface morphology and thickness were evaluated by atomic force microscopy (AFM), and the nanoparticle dispersion inside the composites was investigated by transmission electron microscopy (TEM). These nanofilms, composed of a biodegradable polyester and remotely controllable by external magnetic fields, are promising candidates for many potential applications in the biomedical field.     

表面配位金属-有机框架薄膜HKUST-1在光电应用中的研究进展北大核心CSCD

金属-有机框架(MOFs)作为一种无机-有机杂化材料,由于其结构的多样性和独特的功能而在众多领域有着潜在的应用价值。尤其是液相外延层层组装的MOFs薄膜(称为表面配位MOFs薄膜,SURMOFs)因其具有可控的厚度、优选的生长取向以及均匀的表面等优点备受关注。本文总结了液相外延(LPE)层层组装MOFs薄膜的技术方法,如层层浸渍法、层层泵式法、层层喷雾法、层层旋涂法等组装方法,并介绍了经典的SURMOF HKUST-1的层层组装策略以及其在光致发光、光致变色、光催化以及电催化方面的相关应用。HKUST-1是经典的SURMOF材料之一,在光电领域具有广泛的应用,SURMOF HKUST-1具有以下独特的性能:可以作为发光载体实现良好的光学性能;具有独特的Cu催化活性位点的优势,有效地降解水中的污染物;因其具有介电特性而在电子器件方面有着潜在的应用。虽然HKUST-1在许多方面均具有独特的性能,但也面临着一些挑战:需要将薄膜的合成步骤简单化;薄膜结构和电催化行为间的机理也需要进一步的研究;降低HKUST-1的内阻的方法也需要进行改进。SURMOFs在大规模工业应用和扩展到其它未探索的领域还任重道远。     

Reversible Modification of the Structural and Electronic Properties of a Boron Nitride Monolayer by CO Intercalation

We demonstrate the reversible intercalation of CO between a hexagonal boron nitride (h‐BN) monolayer and a Rh(111) substrate above a threshold CO pressure of 0.01 mbar at room temperature. The intercalation of CO results in the flattening of the originally corrugated h‐BN nanomesh and an electronic decoupling of the BN layer from the Rh substrate. The intercalated CO molecules assume a coverage and adsorption site distribution comparable to that on the free Rh(111) surface at similar conditions. The pristine h‐BN nanomesh is reinstated upon heating to above 625 K. These observations may open up opportunities for a reversible tuning of the electronic and structural properties of monolayer BN films.     

First-principles study on the adhesive and electronic property of c-BN(111)/Cu(111) interface

The interface properties of c-BN/Cu composite play an important role in its application. In this work, we employed first-principles calculation to investigate the bonding properties and electronic characteristics of the c-BN(111)/Cu(111) interface. The adhesion properties, partial density of states (PDOS), charge density, and charge density difference of different interfaces were analyzed. The results show that the interface of B-termination “OT” stacking mode is the most stable one. The density of states at the c-BN(111)/Cu(111) interface is similar to that of c-BN bulk phase, indicating that the electronic states of the c-BN layer are not affected by the Cu atoms. The PDOS diagram shows that the 2p orbital of B atoms and the 2p orbital of N atoms are hybridized in the c-BN layer. Besides, 2p orbital of B(N) atoms and 3d orbital of Cu atoms are hybridized in the interface. The covalent bonds and ionic bonds in the interface of N-termination and B-termination OT stacking mode structures are stronger than that of “SL” and “TL” stacking mode. So, the OT stacking mode has larger adhesive energy. Furthermore, Cu and c-BN can form a good coherent interface, which can be used to prepare c-BN/Cu composites and functional materials with excellent mechanical properties.