第一性原理计算金属原子对石墨烯光电性能的调制（英文）

基于第一原理计算,研究最活泼的金属(Na,K,Al)以及实验上常用的金属(Ti,Ag,Ru,Au,Pt)等八种金属原子对石墨烯的功函数和光学性质的调制。结果表明,除了Ti和Ru原子外,所有的吸附原子均失去电子,导致石墨烯的狄拉克锥向低能方向移动。所有吸附结构的功函数均低于本征石墨烯。特别是Ti或Ru原子与石墨烯之间存在较强的相互作用,导致Ti和Ru吸附石墨烯的功函数较小。由于吸附原子的存在,使得石墨烯的光学性质发生了很大的变化。不同吸附结构的静态介电函数差别很大;吸附原子后,石墨烯对可见光和红外光的吸收强度大大增加。     

金属原子吸附对GaN（0001）表面光学性能的调制

基于第一性原理计算，研究了实验中常用的金属（Ni、Ru和Au）等三种原子对GaN（0001）表面光学性质的调控。结果表明，电子从吸附原子中转移到GaN（0001）表面，Ni和Ru的吸附降低了GaN（0001）表面的功函数。在GaN（0001）表面的带隙中引入了杂质能级，使载流子跃迁的势垒高度降低，进而调节其光学性 。可以看到在低光子能量区所有光学曲线的主峰红移，而在高光子能量区所有光学曲线都出现收缩现象，所有光学曲线上特征峰的数量和位置都发生了明显的变化。此外，吸附金属原子后，GaN（0001）表面对可见光甚至红外光的吸收增强了，适用于较长波光的探测。     

碳纳米管/石墨烯复合结构的第一性原理计算

为了研究碳纳米管/石墨烯复合结构的电学性质,采用密度泛函理论(DFT)下的第一性原理,对四种T型复合结构进行了几何结构优化,分析了该复合结构的结合能,能带结构,电子态密度,Mulliken电荷分布及功函数.结果表明复合结构均表现出半导体性质,其稳定性及电子结构取决于碳纳米管类型和复合结构的连接方式,而且复合材料的功函数...     

n型4H-SiC上Ni/Pt和Ti/Pt欧姆接触(英文)

研究了Ni/Pt和Ti/Pt金属在n型4H-SiC上的欧姆接触。在1 020℃退火后,Ni/Pt与n型4H-SiC欧姆接触的比接触电阻为2.2×10-6Ω·cm2。Ti/Pt与n型4H-SiC欧姆接触的比接触电阻为5.4×10-6Ω·cm2,退火温度为1 050℃。虽然Ni的功函数比Ti的功函数高,但是Ni比Ti更容易与n型4H-SiC形成欧姆接触。使用能谱分析仪(EDX)分析了Ni/Pt和Ti/Pt金属与4HSiC接触面的元素,观察到C原子相对于Pt原子的原子数分数随退火温度的变化而不同。实验验证了在n型4H-SiC中退火导致的碳空位起施主作用是有利于欧姆接触形成的主要原因。     

二茂铼分子吸附Zigzag型石墨烯纳米带自旋输运性质的理论研究

基于非平衡格林函数结合第一性原理的计算,研究了二茂铼分子(Re(cp)_2)的吸附对Zigzag型石墨烯纳米带(ZGNRs)自旋输运性质的影响。研究发现,对于完美的ZGNRs,当原子宽度m=12时,体系电流异常的小,其余原子宽度的体系都具有良好的导电性;而对于吸附的体系,随着吸附Re(cp)_2数目以及石墨烯宽度的改变,体系的电流出现了负微分电阻效应和开关效应。此外,又进一步通过分析透射谱、局域态密度以及透射通道来深层次的研究其物理本质。     

NEAGaN光电阴极第一性原理研究

采用基于密度泛函理论(DFT)框架下广义梯度近似投影缀加平面波方法,在六方结构GaN结构优化的基础上,计算了GaN(0001)A面吸附Cs后功函数变化,指出吸附系统表面形成了一个有效的GaN－Cs电偶极子层,降低了原本的GaN表面势垒,形成更加有利于电子逸出的外光电发射效应特性。接着图示吸附Cs、O后的电子结构,指出吸附原子和衬底之间的键合。六方结构GaN材料的光学性质通过Kramers-Kronig 关系得出。根据GaN的介电函数谱,得出了254nm光波长下以GaN为激活层材料的反射式光电阴极在不同少子扩散长度下的内量子效率。计算结果表明六方结构GaN(0001)A面是可见光盲光电阴极的优良发射表面,且254 nm处的量子效率可达到60%,远大于碱金属卤化物紫外光电阴极。     

NaPd3O4的电子结构和光学性质

用第一性原理对金属化合物NaPd3O4进行了电子结构与光学性质的理论研究.结果表明该材料导电的主要原因是由于Pd原子d轨道电子的贡献,氧原子P轨道电子对导电性也有影响,实质上钠原子对这种材料的导电性几乎没起作用,并且在O原子和Pd原子之间存在着离子键.基于电子能带结构并对介电函数的虚部作相应的解释,同时对NaPd3O4的反射系数、吸收系数、能量损失系数、折射系数和湮灭系数等光学性质进行了研究.     

3种配合物的非线性光学性能与分子结构的关系

为了探索配合物的分子结构对3阶非线性光学性质的影响,采用z扫描方法对3种具有不同中心金属原子(Ni,Cu和Pd)的金属有机配合物的3阶非线性光学性能进行了研究。通过比较3种化合物的非线性折射率和激发态吸收截面发现,原子序数较大的中心金属原子明显增强了分子的非线性光学系数,而共振吸收效应对化合物的非线性光学性质影响不大。结果表明,在532nm波长的皮秒脉冲激光作用下,3种化合物均表现出自聚焦和反饱和吸收特性。     

金红石相TiO_2(110)面吸附H_2S分子光学气敏效应的微观机制与特性

光学气敏材料吸附气体分子后导致光学性质发生变化,运用这一原理来检测环境中的气体成分,称为光学气敏效应。采用基于密度泛函理论(DFT)体系下的第一性原理平面波超软赝势方法,研究了光学气敏材料金红石相TiO2(110)表面吸附H2S分子的微观特性,计算了TiO2(110)表面吸附能、电荷密度、态密度和光学性质的变化。结果表明,TiO2最稳定的表面是终止于二配位O原子的(110)面,只有含有氧空位的表面才能稳定吸附H2S,且氧空位比例越高,越有助于H2S吸附于表面;表面吸附H2S以水平吸附方式为主,在氧空位比例达到33%时,吸附能为0.7985eV;吸附的实质是表面氧空位具有氧化性,氧化了H2S分子。在可见光400~760nm范围内,存在氧空位的TiO2(110)表面吸附H2S后都可改善表面的光学性质。氧空位缺陷浓度越高,改善材料对可见光的吸收和反射能力越强,光学气敏响应能力越佳。     

高k金属栅NMOSFET器件阈值电压调控方法

实现对器件阈值电压的有效调控是高k金属栅(HKMG)技术面临的一项重要挑战。TiAl薄膜作为n型金属氧化物半导体场效应晶体管(NMOSFET)的功函数层被广泛地应用于HKMG结构中以实现对器件阈值电压的调控。实验采用射频(RF)-直流(DC)磁控溅射的方式沉积TiAl薄膜,通过优化直流功率、射频功率和反应压强工艺参数,实现了对薄膜Ti/Al原子比率的调节,提高了Ti/Al原子比率分布均匀度。基于实验结果,采用后栅工艺流程制造HKMG NMOSFET,讨论不同的Ti/Al原子比率和TiAl层厚度对NMOSFET阈值电压的影响。Ti/Al原子比率增大10%,NMOSFET的阈值电压增加12.6%;TiAl层厚度增加2 nm,NMOSFET的阈值电压下降19.5%。这种方法已经被成功应用于HKMG器件的生产。     

Adsorption on tunable bilayer graphene: A model approach

The problem of the adsorption of atoms on the surface of tunable bilayer graphene is considered within the context of Anderson’s model. Analytical expressions for the densities of states of bilayer graphene and an adatom are derived, and the charge exchange between adatoms and bilayer graphene is studied. The charge of adatoms of some elements is estimated. The change induced in the density of states of tunable bilayer graphene by the adsorption of atoms is explored.     

Calculation of the variation in the work function caused by adsorption of metal atoms on semiconductors

A simple model is suggested for calculating the variation of the work function Δφ, which is caused by the adsorption of metal atoms on semiconductor surfaces. The model accounts for both the dipole-dipole repulsion of adatoms and metallization of the adsorbed layer for large coverages. The results of calculating Δφ for the adsorption of alkali metals on the Si(001) surface are in good agreement with the experimental data.     

Advent of 2D Rhenium Disulfide (ReS2): Fundamentals to Applications

Rhenium disulfide (ReS₂) is a two‐dimensional (2D) group VII transition metal dichalcogenide (TMD). It is attributed with structural and vibrational anisotropy, layer‐independent electrical and optical properties, and metal‐free magnetism properties. These properties are unusual compared with more widely used group VI‐TMDs, e.g., MoS₂, MoSe₂, WS₂ and WSe₂. Consequently, it has attracted significant interest in recent years and is now being used for a variety of applications including solid state electronics, catalysis, and, energy harvesting and energy storage. It is anticipated that ReS₂ has the potential to be equally used in parallel with isotropic TMDs from group VI for all known applications and beyond. Therefore, a review on ReS₂ is very timely. In this first review on ReS₂, we critically analyze the available synthesis procedures and their pros/cons, atomic structure and lattice symmetry, crystal structure, and growth mechanisms with an insight into the orientation and architecture of domain and grain boundaries, decoupling of structural and vibrational properties, anisotropic electrical, optical, and magnetic properties impacted by crystal imperfections, doping and adatoms adsorptions, and contemporary applications in different areas.     

Local electronic structure,optical bandgap and photoluminescence (PL) properties of Ba(Zr0.75Ti0.25)O3 powders

Ba(Zr_0.75Ti_0.25)O₃ (BZT-75/25) powders were synthesized by the polymeric precursor method. Samples were structurally characterized by X-ray diffraction (XRD), Rietveld refinement, X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) techniques. Their electronic structures were evaluated by first-principle quantum mechanical calculations based on density functional theory at the B3LYP level. Their optical properties were investigated by ultraviolet-visible (UV-Vis) spectroscopy and photoluminescence (PL) measurements at room temperature. XRD patterns and Rietveld refinement data indicate that the samples have a cubic structure. XANES spectra confirm the presence of pyramidal [TiO₅] clusters and octahedral [TiO₆] clusters in the disordered BZT-75/25 powders. EXAFS spectra indicate distortion of Ti–O and Ti–O–Ti bonds the first and second coordination shells, respectively. UV-Vis absorption spectra confirm the presence of different optical bandgap values and the band structure indicates an indirect bandgap for this material. The density of states demonstrates that intermediate energy levels occur between the valence band (VB) and the conduction band (CB). These electronic levels are due to the predominance of 4d orbitals of Zr atoms in relation to 3d orbitals of Ti atoms in the CB, while the VB is dominated by 2p orbitals related to O atoms. There was good correlation between the experimental and theoretical optical bandgap values. When excited at 482 nm at room temperature, BZT-75/25 powder treated at 500 °C for 2 h exhibited broad and intense PL emission with a maximum at 578 nm in the yellow region.     

Electric Field Tunable Interlayer Relaxation Process and Interlayer Coupling in WSe2/Graphene Heterostructures

Transition metal dichalcogenides van der Waals (vdWs) heterostructures present fascinating optical and electronic phenomena, and bear tremendous significance for electronic and optoelectronic applications. As the significant merits in vdWs heterostructures, the interlayer relaxation of excitons and interlayer coupling at the heterointerface reflect the dynamic behavior of charge transfer and the coupled electronic/structural characteristics, respectively, which may give rise to new physics induced by quantum coupling. In this work, upon tuning the photoluminescence (PL) properties of WSe₂/graphene and WSe₂/MoS₂/graphene heterostructures by virtue of electric field, it is demonstrated that the interlayer relaxation of excitons at the heterointerface in WSe₂/graphene, which is even stronger than that in MoS₂/graphene and WSe₂/MoS₂ , plays a dominant role in PL tuning in WSe₂/graphene, while the carrier population in WSe₂ induced by electric field has a minor contribution. In addition, it is discovered that the interlayer coupling between monolayer WSe₂ and graphene is enhanced under high electric field, which breaks the momentum conservation of first order Raman‐allowed phonons in graphene, yielding the enhanced Raman scattering of defects in graphene. The interplay between electric field and vdWs heterostructures may provide versatile approaches to tune the intrinsic electronic and optical properties of the heterostructures.     

Manipulation of Edge‐Site Fe–N2 Moiety on Holey Fe,N Codoped Graphene to Promote the Cycle Stability and Rate Capacity of Li–S Batteries

Graphene‐based materials have been widely studied to overcome the hurdles of Li–S batteries, but suffer from low adsorptivity to polar polysulfide species, slow mass transport of Li⁺ ions, and severe irreversible agglomeration. Herein, via a one‐step scalable calcination process, a holey Fe, N codoped graphene (HFeNG) is successfully synthesized to address these problems. Diverging by the holey structures, the Fe atoms are anchored by four N atoms (Fe–N₄ moiety) or two N atoms (Fe–N₂ moiety) localized on the graphene sheets and edge of holes, respectively, which is confirmed by X‐ray absorption spectroscopy and density functional theory calculations. The unique holey structures not only promote the mass transport of lithium ions, but also prohibit the transportation of polysulfides across these additional channels via strong adsorption forces of Fe–N₂ moiety at the edges. The as‐obtained HFeNG delivers a high rate capacity of 810 mAh g^?1 at 5 C and a stable cycling performance with the capacity decay of 0.083% per cycle at 0.5 C. The concept of holey structure and introduction of polar moieties could be extended to other carbon and 2D nanostructures for energy storage and conversion devices such as supercapacitors, alkali‐ion batteries, metal–air batteries, and metal–halogen batteries.     

Role of Charge Density Wave in Monatomic Assembly in Transition Metal Dichalcogenides

The charge density wave (CDW) in transition metal dichalcogenides (TMDs) has drawn tremendous interest due to its potential for tailoring their surface electronic and chemical properties. Due to technical challenges, however, how the CDW could modulate the chemical behavior of TMDs is still not clear. Here, this work presents a study of applying the CDW of NbTe₂, with a high transition temperature above room temperature, to generate the assembling adsorption of Sn adatoms on the surface. It is shown that highly ordered monatomic Sn adatoms with a quasi‐1D structure can be obtained under regulation by the single‐axis CDW of the substrate. In addition, the CDW modulated superlattices could in turn change the surface electronic properties from semimetallic to metallic. These results demonstrate an effective approach for tuning the surface chemical properties of TMDs by their CDWs, which could be applied in exploring them for various practical applications, such as heterogeneous catalysis, epitaxial growth of low‐dimensional materials, and future nanoelectronics.     

Ru Species Supported on MOF‐Derived N‐Doped TiO2/C Hybrids as Efficient Electrocatalytic/Photocatalytic Hydrogen Evolution Reaction Catalysts

The development of efficient catalysts is of great importance for hydrogen evolution reaction (HER) of water splitting via electrocatalytic/photocatalytic processes to remediate the current severe environmental and energy problems. By aid of the stabilization effects of uncoordinated groups and inherent pore‐confinement of amine‐functionalized metal–organic frameworks (NH₂‐MIL‐125), two forms of Ru species including nanoparticles (NPs) and/or single atoms (SAs) can be firmly embedded in NH₂‐MIL‐125 derived N‐doped TiO₂/C support (N‐TC), and thus obtain two kinds of samples named Ru‐NPs/SAs@N‐TC and Ru‐SAs@N‐TC, respectively. In the synthetic process, the initial feeding amount of Ru³⁺ ions not only strongly determines the final size and dispersion states of Ru species but also the morphology and defective structures of N‐TC support. Impressively, Ru‐NPs/SAs@N‐TC exhibit superior catalytic activities to Ru‐SAs@N‐TC for either electrocatalytic or photocatalytic HER. This should be attributed to its larger specific surface area and benefiting from synergistic coupling of Ru NPs and Ru SAs. It is envisioned that the present work can provide a new avenue for development of high‐efficiency and multifunctional hybrid catalysts in sustainable energy conversion.     

Metal Single-Atom Cocatalyst on Carbon Nitride for the Photocatalytic Hydrogen Evolution Reaction: Effects of Metal Species

Single-atom (SA) catalysts exhibit high activity in various reactions because there are no inactive internal atoms. Accordingly, SA cocatalysts are also an active research fields regarding photocatalytic hydrogen (H₂) evolution which can be generated by abundant water and sunlight. Herein, it is investigated whether 10 transition metal elements can work as an SA on graphitic carbon nitride (g-C₃N₄; i.e., gCN), a promising visible-light-driven photocatalyst. A method is established to prepare SA-loaded gCN at high loadings (weight of ≈3 wt.% for Cu, Ni, Pd, Pt, Rh, and Ru) by modulating the photoreduction power. Regarding Au and Ag, SAs are formed with difficulty without aggregation because of the low binding energy between gCN and the SA. An evaluation of the photocatalytic H₂-evolution activity of the prepared metal SA-loaded gCN reveals that Pd, Pt, and Rh SA-loaded gCN exhibits relatively high H₂-evolution efficiency per SA. Transient absorption spectroscopy and electrochemical measurements reveal the following: i) Pd SA-loaded gCN exhibits a particularly suitable electronic structure for proton adsorption and ii) therefore they exhibit the highest H₂-evolution efficiency per SA than other metal SA-loaded gCN. Finally, the 8.6 times higher H₂-evolution rate per active site of Pd SA is achieved than that of Pd-nanoparticles cocatalyst.     

Stacked graphene–TiO2 photoanode via electrospray deposition for highly efficient dye-sensitized solar cells

A series of TiO₂–graphene stacked photoanodes for dye-sensitized solar cells (DSSCs) were fabricated by electrospray (E-spray) deposition. Among devices incorporating single graphene layer with different deposition times, device with 1 min graphene deposition gave the best performance. For multi-graphene-layer involved devices, best result was obtained with 3 layers of graphene. The working principles were analyzed by scanning electron microscopy, transmittance spectra, electrochemical impedance spectroscopy and incident-photo-conversion efficiency data. We found that although graphene layers incorporated in TiO₂ photoanode slightly decreased dye adsorption, they were able to significantly improve the electron transport, and the charge recombination at the interfaces of TiO₂/dye and TiO₂/electrolyte were greatly suppressed, leading to dramatic improvement in power conversion efficiency. When inserting three layers of pure graphene into the TiO₂ photoanode, high efficiency of 8.9% was obtained, constituting an over 23.6% improvement. Further increasing graphene layers to five, although electron lifetimes is the longest, both the largest charge transfer resistance and the least amount of the dye loading lead to the lowest device efficiency. Our work demonstrated, that pure graphene layer can be successfully incorporated into TiO₂ photoanode by E-spray method with easiness of thickness control and the photoanode with graphene/TiO₂ alternatively layered structure is an excellent candidate for DSSCs.