Recently, all-inorganic perovskite (CsPbX3 (X = Cl, Br, I)) nanocrystals (NCs) have caused extensive attention due to their high photoluminescence quantum yield (PL QY), high color purity, and narrow full width at half maximum (FWHM). Although the excellent optical properties of perovskite NCs (PNCs) endow them good application prospects, their inherent instability severely limits the commercialization process. In this paper, highly-luminescence and ultra-stable phosphor were obtained by loading PNCs onto the surface of amino modified hexagonal boron-nitride (h-BN) white graphene (PNCs-BNWG), This structural design can effectively suppress the attenuation of photoluminescence (PL) intensity and enhance thermal stability, thereby realizing the high stability and brightness white LEDs. The synthesis process is simple and can be finished in a few minutes to ensure scalable production. Compared with bare PNCs, it can maintain excellent optical properties. The high PL QY and thermal stability mainly stem from the isolation effect that separates PNCs from each other on the surface of BNWG and their superior high transparency as well as thermal conductivity. In addition, multi-color inks are produced by dispersing PNCs-BNWG nanocomposites in PDMS to form a multicolor painting demonstrating high PL QY and wide color gamut.

用非平衡格林函数理论和紧束缚模型近似计算长沟道弹道输运p型碳纳米管场效应管中电流强度.研究当场效应管介质(SiO2)中存在两个带电缺陷时,载流子散射所引起的电流强度减小和栅极阈值电压偏移量与缺陷位置的关系.介质中两个缺陷所带电荷Q1=Q2=+e(-e为电子电荷),都靠近源极或者都靠近漏极,或者一个电荷靠近源极另一个电荷靠近漏极.在工作状态下,所引起的电流强度相对减小比介质中只存在单个正电荷Q=+e且靠近源极(或漏极)时所引起的电流强度相对减小大得多.如果两个正电荷都在沟道中央附近,随着两个电荷的轴向距离减小,栅极阈值电压偏移的绝对值明显增加.栅极阈值电压偏移可达到-0.35 V.

The many-body perturbation theory is used to study the properties of excited electronic states of the CO molecule adsorbed on LiCl(001)-(1X1) surface, and further investigate the time evolution of the CO exciton state as well as the lifetime of the exciton state. At first, density-functional theory within local density approximation is used to calculate the ground state geometry of CO adsorbed on LiCl(001)-(1X1) surface. Next, the quasiparticle band structures of bulk LiCl, of the LiCl(001)-(1X1) surface, and of CO adsorbed on the surface are evaluated within the GW approximation. Moreover, by taking the electron-hole interaction into consideration, the electron-hole excitation states and their optical spectra are obtained from the solution of the Bethe-Salpeter equation within the theory of the two-particle Green function. The obtained optical spectra are compared with available experimental results. Finally, based on the solution of the BSE for the adsorbate system CO:LiCl(001)-(1X1), the time evolution of the CO exciton state is studied using the time-dependent Schr?dinger equation. At the initial stage, the CO exciton state exhibits a very fast decay due to the coupling of the adsorbate with the substrate, and the lifetime of the CO exciton state is only 0.75 fs. The electron of the molecule exciton state remains on the molecule while its hole is mostly transferred into the LiCl substrate.

基于局域密度近似的密度泛函理论,运用多体摄动理论的GW近似,计算了碱金属锂的卤族化合物LiF (001)-(1Xl)、LiCl (001)-(1X1)、LiBr (001)-(1X1)、LiI (001)-(1X1)表面的准粒子能带结构.GW近似改进了密度泛函理论对于电子交换关联的处理,计算出的带隙与实验值吻合.由GW近似计算得出的LiF、LiCl和LiBr的(001)表面能带具有负亲和能,由于绝缘体表面外真空中电子与绝缘体表面极化电荷的相互作用,在真空中产生了镜像势态.利用GW近似研究了镜像势态波函数沿表面法线方向的分布,并将由GW近似计算得到的镜像势态的单粒子势能与经典的镜像势能进行了比较.但是,从GW近似给出的表面能带结构可看出,LiI (001)表面具有正亲和能,因而不存在镜像势态.

Recently, all-inorganic perovskite quantum dots (QDs) (CsPbX3, X = Cl, Br, I) as the emerging semiconductor materials have been intensively studied owing to superior optical properties. Currently, the strategy for preparation of inorganic perovskite QDs mainly focuses on the hot-injection method, but requires inert gas protection and is difficult to mass-produce. In this work, we developed a simple and low-cost strategy for preparing highly luminescent and air-stable all-inorganic perovskite QDs by directly heating perovskite precursors in octane in air. The emission wavelength of CsPbX3 perovskite QDs can be tunable from ultraviolet (UV) to infrared region by simply controlling their halide composition and display high PLQYs. Moreover, CsPbX3 perovskite QDs in octane can exist more than half a year in air and the film of CsPbX3 perovskite QDs also shows good thermal stability and air stability, especially high iodide-substituted CsPbBr3−xIx perovskite QDs. The CsPbX3 perovskite QDs can be easily blended with PDMS and used as color conversion layer on the blue LEDs chip for high-quality white LEDs. Our work opens a window for the potential application of such highly luminescent material in the fields of multicolor LEDs, backlight display and other related optoelectronic devices.

This paper reports the electronic band structure and the optical absorption spectrum of alkaline-earth metal oxide CaO, using many-body perturbation theory. The quasiparticle band structure is calculated within the GW approximation. By taking the electron-hole interaction into consideration, electron-hole pair states and optical excitations are obtained by solving the Bethe-Salpeter equation for the electron-hole two-particle Green function. The calculated band gap for CaO is 7.0 eV, which is in good agreement with the experimental result of 7.1 eV. The theoretical results of optical absorption spectrum for CaO are also in agreement with the experimental data.

We present the results of first-principles study for the electronic structure and optical absorption spectrum of the alkaline-earth metal oxide BaO. The quasiparticle band structure is evaluated within the Hedin's GW approximation [Phys. Rev. 139, A796 (1965)]. Thereafter, the electron-hole interaction is taken into consideration and the Bethe-Salpeter equation for the electron-hole two-particle Green function is solved. The calculated quasiparticle band gap of BaO is 4.1 eV, which is in good agreement with the experimental result. The calculated optical absorption spectrum of BaO is also in agreement with the experimental data. In particular, the calculated excitation energy for the lowest exciton peak in the optical absorption spectrum of BaO reproduces very well the corresponding experimental result.

We present the quasiparticle band structure and the optical excitation spectrum of bulk LiCl, using many-body perturbation theory. Density-functional theory is used to calculate the ground-state geometry of the system. The quasiparticle band structure is calculated within the GW approximation. Taking the electron-hole interaction into consideration, electron-hole pair states and optical excitations are obtained by solving the Bethe-Salpeter equation for the electron-hole two-particle Green function. The calculated band gap is 9.5 eV, which is in good agreement with the experimental result of 9.4 eV. And the calculated optical absorption spectrum, which contains an exciton peak at 8.8 eV and a resonant-exciton peak at 9.8 eV, is also in good agreement with experimental data.

The current through a carbon nanotube field-effect transistor (CNFET) with cylindrical gate electrode is calculated using the nonequilibrium Greens function method in a tight-binding approximation. The obtained result is in good agreement with the experimental data. The theoretical approach is used to calculate the amplitude of the random-telegraph-signal (RTS) noise due to a single defect in the gate oxide of a long channel p-type CNFET. Considering a composite structure of gate insulators, which contains an inner insulator with a large dielectric constant (ϵ > 3.9) and an outer insulator with a dielectric constant of 3.9 (as for SiO2), the dependence of the RTS noise amplitude on the structure of composite gate insulators is investigated. It is found that the RTS amplitude increases apparently with the decreasing thickness of the inner gate insulator. If the inner insulator is too thin, even though its dielectric constant is as large as 80, the amplitude of the RTS noise caused by the charge of Q = +1e may amount to around 80% in the turn-on region.

Random telegraph signals corresponding to activated charge traps were observed with liquid-gated CNT FETs. The high signal-to-noise ratio that we observe demonstrates that single electron charge sensing is possible with CNT FETs in liquids at room temperature. We have characterized the gate-voltage dependence of the random telegraph signals and compared to theoretical predictions. The gate-voltage dependence clearly identifies the sign of the activated trapped charge.

We report the calculated quasiparticle band structure and optical absorption spectrum of LiI, using many-body perturbation theory. Density-functional theory within local density approximation is used to calculate the ground-state properties of the system. The quasiparticle band structure is evaluated within the GW approximation. Taking the electron–hole interaction into account, electron–hole pair states and optical excitations are derived from the solution of the Bethe–Salpeter equation for the electron–hole two-particle Green function. The band gap is estimated within the GW approximation as 6.3eV, which is in good agreement with the experimental result of 6.4eV. And the calculated optical spectrum is also in agreement with experimental data.

We investigate channel-length scaling characteristics for effects of a single charged defect in a carbon nanotube field-effect transistor (CNFET), using the nonequilibrium Greens function method. We find that the threshold voltage shift due to a single charge in midchannel increases with the decreasing channel length. In a p-type CNFET, the relative current reduction in the on-state due to a positive charge and the relative current change in the turn-on region due to a negative charge increase apparently with the decreasing channel length. The threshold voltage shift and relative current change caused by a single charge for short channel CNFETs increases with the gate-oxide thickness much faster than that for long channel CNFETs. For a short channel p-type CNFET, the current reduction in the on-state due to a positive charge may be larger than 60% and the threshold voltage shift due to a negative charge may amount to 0.6 V.

We report the quasiparticle band structure and optical absorption spectrum of bulk LiBr calculated from first-principles approaches. The quasiparticle band structure is calculated within the GW approximation. Taking the electron-hole interaction into consideration, the optical excitation is investigated by solving the Bethe-Salpeter equation for the electron-hole two-particle Green’s function. The obtained results for the band gap and optical absorption spectrum are in good agreement with experimental measurements.

We present an implementation of the ballistic Landauer-B\"uttiker transport scheme in one-dimensional systems based on density functional theory (DFT) calculations within the full-potential linearized augmented plane-wave (FLAPW) method. In order to calculate the conductance within the Green's function method we map the electronic structure from the extended states of the FLAPW calculation to Wannier functions which constitute a minimal localized basis set. Our approach benefits from the high accuracy of the underlying FLAPW calculations allowing us to address the complex interplay of structure, magnetism, and spin-orbit coupling and is ideally suited to study spin-dependent electronic transport in one-dimensional magnetic nanostructures. To illustrate our approach we study ballistic electron transport in non-magnetic Pt monowires with a single stretched bond including spin-orbit coupling, and in ferromagnetic Co monowires with different collinear magnetic alignment of the electrodes with the purpose of analysing the magnetoresistance when going from tunneling to the contact regime. We further investigate spin-orbit scattering due to an impurity atom. We consider two configurations: a Co atom in a Pt monowire and vice versa. In both cases, the spin-orbit induced band mixing leads to a change of the conductance upon switching the magnetization direction from along the chain axis to perpendicular to it. The main contribution stems from ballistic spin-scattering for the magnetic Co impurity in the non-magnetic Pt monowire and for the Pt scatterer in the magnetic Co monowire from the band formed from states with $d_{xy}$ and $d_{x^2-y^2}$ orbital symmetry. We quantify this effect by calculating the ballistic anisotropic magnetoresistance which displays values up to as much as 7% for ballistic spin-scattering and gigantic values of around 100% for the Pt impurity in the Co wire.

We calculate the amplitude of the random-telegraph-signal (RTS) noise due to a single charged defect in a long-channel p-type carbon nanotube field-effect transistor, using the nonequilibrium Green function method in a tight-binding approximation. We find that the amplitude of the RTS noise caused by a positive charge close to the source (or drain) contact increases with the applied gate voltage and drain voltage. A positive charge located at the nanotube-oxide interface and close to the source (or drain) contact may cause a large RTS noise of about 50% in the on-state. Copyright (C) EPLA, 2012

I present a method to calculate the ballistic transport properties of atomic-scale structures under bias. The electronic structure of the system is calculated using the Kohn-Sham scheme of density functional theory (DFT). The DFT eigenvectors are then transformed into a set of maximally localized Wannier functions (MLWFs) [N. Marzari and D. Vanderbilt, Phys. Rev. B 56 (1997) 12847]. The MLWFs are used as a minimal basis set to obtain the Hamitonian matrices of the scattering region and the adjacent leads, which are needed for transport calculation using the nonequilibrium Green's function formalism. The coupling of the scattering region to the semi-infinite leads is described by the self-energies of the leads. Using the nonequilibrium Green's function method, one calculates self-consistently the charge distribution of the system under bias and evaluates the transmission and current through the system. To solve the Poisson equation within the scheme of MLWFs I introduce a computationally efficient method. The method is applied to a molecular hydrogen contact in two transition metal monatomic wires (Cu and Pt). It is found that for Pt the I–V characteristics is approximately linear dependence, however, for Cu the I–V characteristics manifests a linear dependence at low bias voltages and exhibits apparent nonlinearity at higher bias voltages. I have also calculated the transmission in the zero bias voltage limit for a single CO molecule adsorbed on Cu and Pt monatomic wires. While a chemical scissor effect occurs for the Cu monatomic wire with an adsorbed CO molecule, it is absent for the Pt monatomic wire due to the contribution of d-orbitals at the Fermi energy.

Laser excitation at 7.9eV photon energy leads to the desorption of hydrogen atoms from the H:Si(001)-(2×1) monohydride surface [T. Vondrak, X.-Y. Zhu, Phys. Rev. Lett. 82 (1999) 1967]. In the present paper we address the electronic excitations relevant for this desorption process and investigate the corresponding force on the hydrogen atom. The excited state is described by ab-initio many-body perturbation theory. A particular problem is posed by the resonant character of the excited state in question, leading to delocalization and fast decay. Here we suggest to employ an additional short-range confinement potential to localize the excited state on the Si–H bond which is broken in the desorption process.