- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Structural identification of silicene on the Ag(111) surface by atomic force microscopy
摘要： Silicene is a two-dimensional atomic layer material with buckled honeycomb arrangements of Si atoms. The diversity of those arrangements, which expands its potential applications, makes it dif?cult to determine its structure in any particular case. In this paper, we show that atomic force microscopy (AFM) has the capability of structural determination of unknown phases of silicene. We carried out an AFM observation of (√13×√13)R13.9? silicene of unknown structures on Ag(111). Remarkably, it was shown that all constituent Si atoms forming a honeycomb lattice can be resolved by AFM whereas scanning tunneling microscopy (STM) can image only the topmost Si atoms. High-resolution AFM imaging allowed us to identify two types of buckled structure of (√13×√13)R13.9? silicene on Ag(111), which had not been previously discriminated. The structure models obtained by theoretical simulation reproduced AFM images as well as previous STM images. In addition, the mechanism of high-resolution AFM imaging was elucidated by force spectroscopy combined with ?rst-principles calculations. Namely, attractive interaction with the tip pulls up buckled down Si atoms, causing local ?ips of the buckled structures.
关键词： structural determination,buckled structures,Ag(111) surface,silicene,atomic force microscopy
更新于2025-09-23 15:21:21
-
[NanoScience and Technology] Silicene (Prediction, Synthesis, Application) || Properties of Monolayer Silicene on Ag(111)
摘要： The expected properties of silicene and their theoretical background have already been discussed in Chaps. 1–3 and the different ways to synthesize this new 2D material in Chap. 5. It has already been mentioned that such a synthesis requires an adequate substrate material to accommodate the formation of a one-atom-thin silicon layer. Such a material is silver, in particular the Ag(111) surface plane. In this chapter the formation and properties of silicene formed epitaxially on the Ag(111)(1 × 1) surface are discussed. We will see that the properties of these silicene layers are modi?ed with respect to the ones of free-standing silicene, due to the interaction with the substrate. For this reason we will refer to it as epitaxial silicene and look in detail at its two-dimensional (2D) character. A more detailed look at the formation of Si layers on Ag(111) shows that, depending on the speci?c preparation conditions, several 2D Si phase can be formed. Differences and similarities of these structures will be discussed. Furthermore, we will draw the intention on the chemical and temperature stability of these epitaxial silicene layers and unveil the limits for the silicene formation.
关键词： silicene,2D materials,Ag(111),vibrational properties,electronic properties,epitaxial growth
更新于2025-09-23 15:21:21
-
[NanoScience and Technology] Silicene (Prediction, Synthesis, Application) || Atomic and Electronic Structure of Silicene on Ag: A Theoretical Perspective
摘要： The isolation of graphene sheets from its parent crystal graphites has given the kick to experimental research on its prototypical 2D elemental cousin, silicene [1]. Unlike graphene, silicene lacks a layered parent material from which it could be derived by exfoliation. Hence, the efforts of making the silicene dream a reality were focused on epitaxial growth of silicene on substrates. The first synthesis of epitaxial silicene on silver (111) [27, 46] and zirconium diboride templates [16] and next on an iridium (111) surface [31], has boosted research on other elemental group IV graphene-like materials, namely, germanene and stanene [30, 48]. The boom is motivated by several new possibilities envisaged for future electronics, typically because of the anticipated very high mobilities for silicene and germanene [49], as well as potential optical applications [30]. It is also fuelled by their predicted robust 2D topological insulator characters [14, 28] and potential high temperature superconductor character [5, 50]. One of the most promising candidates as a substrate is Ag because from the studies of the reverse system, where Ag atoms were deposited on silicon substrate, it was known that Ag and silicon make sharp interfaces without making silicide compounds.
关键词： theoretical perspective,electronic structure,silicene,Ag(111),epitaxial growth
更新于2025-09-23 15:21:21
-
Substrate-Controlled Synthesis of 5-Armchair Graphene Nanoribbons
摘要： 5-Armchair graphene nanoribbons (5-AGNRs) have been successfully synthesized through on-surface reaction of 1, 4, 5, 8-tetrabromonaphthalene (TBN) on Ag(111) and characterized by scanning tunneling microscopy. Silver-naphthalene chains are observed as intermediate states toward the formation of 5-AGNRs. Similar reaction of TBN has been conducted on Cu(111), but no 5-AGNRs are obtained. Disordered amorphous products prevail on Cu(111) upon high temperature annealing (600 K), which is tentatively explained by the strong aryl-Cu bonds. Scanning tunneling spectroscopy measurements of 5-AGNRs on Ag(111) reveal three prominent peaks at bias voltages of -0.3, 1.0 and 1.5V, determining that the apparent band gap is 1.3 eV.
关键词： Ag(111),scanning tunneling microscopy,scanning tunneling spectroscopy,5-Armchair graphene nanoribbons,Cu(111),on-surface synthesis
更新于2025-09-23 15:21:01
-
Controlled switching of a single CuPc molecule on Cu(111) at low temperature
摘要： Low temperature measurements of the tunneling current as a function of the applied bias voltage have been performed on a dense constant-height grid above individual copper phthalocyanine molecules adsorbed on a Cu(111) surface. By appropriate tuning of the applied bias, the molecule can be reversibly switched between two configurations in which pairs of opposite maxima appear rotated by 90? in the tunneling current map. The underlying conformations are revealed by density functional calculations including van der Waals interactions: a C2v symmetric ground state and two energetically equivalent states, in which the molecule is twisted and rotated around its center by ±7?. For tip biases above 200 mV position-dependent current switching is observed, as in previous measurements of telegraph noise [Schaffert et al., Nat. Mater. 12, 223 (2013)]. In a small voltage interval around zero the measured current becomes bistable. Switching to a particular state can be initiated by sweeping the voltage past well-defined positive and negative thresholds at certain positions above the molecule or by scanning at constant current and a reduced reverse bias.
关键词： density functional calculations,van der Waals interactions,tunneling current,copper phthalocyanine,Cu(111) surface,bistable current
更新于2025-09-23 15:19:57
-
Fluorescent DTPA-Silk Fibroin Nanoparticles Radiolabeled with <sup>111</sup> In: A Dual Tool for Biodistribution and Stability Studies
摘要： This work aims to provide an effective and novel dual tool for the biodistribution studies of biopolimeric nanoparticles by using modified silk fibroin nanoparticles as a model. This is an indispensable step in the evaluation of the applicability of biopolymeric nanoparticles as drug delivery systems. In this paper, we report a new facile method for radiolabeling silk fibroin nanoparticles conjugated to the chelating agent diethylenetriamine pentaacetic acid (DTPA) and tagged with fluorescein isothiocyanate (FITC). Nanoparticles were characterized by means of dynamic light scattering (DLS), scanning electron microscopy (SEM), infrared and fluorescence spectroscopy. The in vitro studies included the stability in biological media and the evaluation of the cytotoxicity of the nanoparticles in a cell culture. The in vivo study was focused in the scintigraphic study over 24 h conducted on New Zealand rabbits, after intra-articular injection of [111In]In-nanoparticles containing 8.03 ± 0.42 MBq. Biodistribution of the nanoparticles was assessed also ex vivo by fluorescence microscopy of post mortem biopsied organs. This radiolabeling method was reproducible and robust with high radiolabeling efficiency (~80 %) and high specific activity suitable for the in vivo studies. Radiolabeled nanoparticles, having hydrodynamic radius of 113.2 ± 2.3 nm, a polydispersity index (PdI) of 0.101 ± 0.015 and Z-potential of -30.1 ± 2.0 mV, showed and optimum retention in the articular space, without activity clearance up to 24 h post injection. Thus, an easy and robust radiolabeling method has been developed, and its applicability is demonstrated in vitro and in vivo studies, showing its value for future investigation of silk fibroin nanoparticles as versatile and stable (steady) local drug delivery systems for consideration as a therapeutic option, particularly in the treatment of joint disorders.
关键词： biodistribution,theragnostic,radiolabeling,mesenchymal stem cells culture,FITC,silk fibroin nanoparticles,Indium-111,stability
更新于2025-09-23 15:19:57
-
Non-parabolic potential dependence of optical second harmonic generation from the Si(111) electrode/electrolyte interface
摘要： We performed potential dependent second harmonic generation (SHG) measurements on the Si(111) electrolyte interface at different azimuthal angles and for different polarization combinations. When the external potential was biased from the equilibrium potential to the flatband potential (Efb), the SHG intensity decreased linearly with the potential when the azimuthal angle was oriented at 301. This linearity extends well beyond the linear region of the Mott–Schottky plot as measured traditionally by capacitance measurements. When the external potential was scanned from Efb toward more negative potentials, the response of SHG intensity showed quadratic behavior and can be described by the parabolic model. The non-parabolic potential dependence cannot be explained with the parabolic model proposed from previous literature. Such asymmetric behavior only implied that the interfacial structure of the Si(111) electrode changes from semiconductor to metal with the applied electric potential biased negatively, i.e. with accumulation of electrons in the surface region. The anisotropic contribution from the Si(111) electrode can also significantly affect the SHG response as seen where the minimum of the potential dependent SHG curve shifts away from Efb.
关键词： potential dependence,Si(111) electrode,electrolyte interface,non-parabolic behavior,second harmonic generation
更新于2025-09-23 15:19:57
-
Theoretical Study on Nanostructural Modifications of the Si (111) Surface
摘要： Modified Si(111) surface with designed nanostructural modifications including grown pits, nanobars and nanoislands as well as deposited hill-, diamond- and cage-like nanoclusters were studied using density-functional theory (DFT) calculations. The thermal stabilities, electronic structures and optical properties of these various nanostructural modifications of the Si(111) surface were calculated and discussed. The results indicate that the optical absorption of the modified Si(111) surface can be enhanced by these surface modifications especially when depositing diamond-like nanoclusters on the surface.
关键词： electronic structures,Si(111) surface modifications,Si nanostructures,optical properties
更新于2025-09-19 17:15:36
-
Temperature Activated Dimensionality Crossover in the Nucleation of Quantum Dots by Droplet Epitaxy on GaAs(111)A Vicinal Substrates
摘要： A temperature activated crossover between two nucleation regimes is observed in the behavior of Ga droplet nucleation on vicinal GaAs(111)A substrates with a miscut of 2° towards (1ˉ1ˉ2). At low temperature (<400 °C) the droplet density dependence on temperature and flux is compatible with droplet nucleation by two-dimensional diffusion. Increasing the temperature, a different regime is observed, whose scaling behavior is compatible with a reduction of the dimensionality of the nucleation regime from two to one dimension. We attribute such behavior to a presence of finite width terraces and a sizeable Ehrlich-Schw?bel barrier at the terrace edge, which hinders adatom diffusion in the direction perpendicular to the steps.
关键词： Quantum Dots,GaAs(111)A,Dimensionality crossover,Droplet Epitaxy,Nucleation
更新于2025-09-19 17:13:59
-
Effect of Nd:YAG pulsed laser welding process on the liquation and strain-age cracking in GTD-111 superalloy
摘要： The weldability of GTD-111 nickel-based superalloy by Nd:YAG pulse laser with an average power of 250 W was studied using several pre- and post-weld heat treatment cycle, and the characteristics of liquation, solidification and strain-age cracks were also investigated. The results revealed that liquation cracks in the GTD-111 Nickel-Based Cast Superalloy were associated with the constitutional liquation of γ′ particle, MC carbides, inter-dendritic γ-γ? eutectic and melting of Cr-rich boride. Also, cracking during welding occurred at the places that the concentration of Al and Ti is high. Crack-free laser welds were observed in the MT1 conditions (1200 ℃ for 2 h) owing to dissolution of deleterious phases before welding. γ′ phase had little effect on the incidence of cracking in the MT1 condition. An analysis of the microstructures indicated that the cracking was caused primarily by liquation in the as-welded condition and was exacerbated by post-weld heat treatment cracking during the subsequent heat treatment. aging heat treatment of samples which were undergone aging heat treatment before welding, resulted in the formation of strain-age cracking due to γ? and γ-γ? eutectic phases precipitation. The results of micro-hardness indicated that the hardness of fusion zone (FZ) was higher than that of HAZ and base metal zone (BMZ). The liquation cracking in the heat affected zone (HAZ) was observed to be affected by the hardness of base-alloy.
关键词： Laser beam welding,GTD-111 superalloy,Liquation cracking,Strain age cracking
更新于2025-09-19 17:13:59