原子分辨显微分析技术研究进展

非接触原子力显微技术(NC-AFM)近年来发展迅速.NC-AFM对单个分子的成像和谱学实现了原子分辨和单个化学键分辨.NC-AFM自身功能的拓展及其与不同探针技术的联用将为材料、物理、化学和生命科学有关的研究提供崭新的思路.本文首先介绍NC-AFM和qPlus传感器的基本原理,然后讨论原子尺度的相互作用力和短程力的精确测量,总结近年来NC-AFM在原子尺度的化学结构成像、化学识别、电子结构性质分析以及原子操纵技术中的研究进展,并讨论了开尔文探针力显微技术(KPFM)在局域接触势差(LCPD)测量方面的应用.最后展望了NC-AFM面临的挑战和发展机遇.

基于动力学标度法的a-C:H薄膜表面微观形貌的演变机理研究

采用等离子体增强化学气相沉积(PECVD)方法在Si(111)基底上制备a-C:H薄膜,利用原子力显微镜(AFM)和扫描电子显微镜(SEM)对a-C:H薄膜的表面形貌与表面粗糙度进行表征,并从动力学标度法角度出发讨论a-C:H薄膜表面粗糙度的演变机理。研究结果表明:a-C:H薄膜表面微观形貌为自仿射分形表面,可用分形维数来评价薄膜的表面粗糙度;随着H_2流量的增加,薄膜表面粗糙度先减小后增大,在T_2B与H_2流量比为0.2/6时,a-C:H薄膜的表面粗糙度R_q为2.2nm,相对于其他条件下生长的薄膜的表面粗糙度低,薄膜表面较光滑,致密性良好。

Sequence-dependent interactions between model peptides and lipid bilayers

Studying interaction between peptides and lipid membranes is helpful for understanding the working mechanism of amyloidogenic peptides and antimicrobial peptides, which are toxic to cells through disruption of the cell membrane. Although many efforts have been made to find out common mechanisms of the peptide-induced membrane disruption, detailed information on how the peptide's amino acid sequence affects its interaction with lipid bilayers is still lacking. In this study, three peptides termed as Pep11, P11-2, and QQ11, which share a similar backbone, were employed to explore how modifications on the peptide sequence as well as terminal groups influenced its interaction with the lipid membrane. Atomic force microscopy data revealed that the peptides could deposit on the membranes and induce defects with varied morphologies and stiffness. Fluorescence resonance energy transfer(FRET) experiments indicated that the introduction of the three peptides resulted in different FRET effects on either liquid or gel lipid membranes. DPH fluorescence anisotropy and Laurdan's generalized polarization analysis showed that P11-2 could insert into the lipid membrane and impact the lipid hydrophobic region while QQ11 influenced the order of the hydrophilic head of the lipid membrane. With these results, we have illustrated how these peptides interacted differently with the lipid membrane because of the modification of their sequences. Although these peptides did not relate to disease and antibiosis, we hope these results still could provide some clues for partly understanding the working mechanism of amyloidogenic peptides and antimicrobial peptides.

Fabrication of sulfur-doped cove-edged graphene nanoribbons on Au(111)

The on-surface synthesis from predesigned organic precursors can yield graphene nanoribbons(GNRs)with atomically precise widths,edge terminations and dopants,which facilitate the tunning of their electronic structures.Here,we report the synthesis of novel sulfur-doped cove-edged GNRs(S-CGNRs)on Au(111)from a specifically designed precursor containing thiophene rings.Scanning tunneling microscopy and non-contact atomic force microscopy measurements elucidate the formation of S-CGNRs through subsequent polymerization and cyclodehydrogenation,which further result in crosslinked branched structures.Scanning tunneling spectroscopy results reveal the conduction band minimum of the S-CGNR locates at 1.2 e V.First-principles calculations show that the S-CGNR possesses an energy bandgap of 1.17 e V,which is evidently smaller than that of an undoped cove-edged GNR(1.7 e V),suggesting effective tuning of the bandgap by introducing sulfur atoms.Further increasing the coverage of precursors close to a monolayer results in the formation of linear-shaped S-CGNRs.The fabrication of S-CGNRs provides one more candidate in the GNR toolbox and promotes the future applications of heteroatom-doped graphene nanostructures.

Epitaxial synthesis and electronic properties of monolayer Pd2Se3

Two-dimensional(2D)materials received large amount of studies because of the enormous potential in basic science and industrial applications.Monolayer Pd2Se3 is a fascinating 2D material that was predicted to possess excellent thermoelectric,electronic,transport,and optical properties.However,the fabrication of large-scale and high-quality monolayer Pd2Se3 is still challenging.Here,we report the synthesis of large-scale and high-quality monolayer Pd2Se3 on graphene-SiC(0001)by a two-step epitaxial growth.The atomic structure of Pd2Se3 was investigated by scanning tunneling microscope(STM)and confirmed by non-contact atomic force microscope(nc-AFM).Two subgroups of Se atoms have been identified by nc-AFM image in agreement with the theoretically predicted atomic structure.Scanning tunneling spectroscopy(STS)reveals a bandgap of 1.2 eV,suggesting that monolayer Pd2Se3 can be a candidate for photoelectronic applications.The atomic structure and defect levels of a single Se vacancy were also investigated.The spatial distribution of STS near the Se vacancy reveals a highly anisotropic electronic behavior.The two-step epitaxial synthesis and characterization of Pd2Se3 provide a promising platform for future investigations and applications.

应用纳米球刻蚀法在自组装膜修饰的硅表面生成中尺度的网状蛋白层（英文）

在自组装膜修饰的硅表面制备有序的蛋白阵列是研发生物传感器的先决条件之一,因此如何产生有序的表面蛋白阵列一直是生物医药研究方向的前沿。本研究通过应用纳米球刻蚀法在氧化的10-烯基十一烷基三氯硅烷自组装膜修饰的硅表面生成了网状结构溶菌酶蛋白层。网孔的大小(从纳米到微米级别)由表面沉积的纳米球的尺寸来调控。我们利用原子力显微镜和荧光显微镜对样品表面进行了详细表征。结果表明:这种新方法比传统的通过扫描探针在固体表面修饰而聚集溶菌酶蛋白的方法更快捷简便,而且它能够在相对大的硅表面形成网状蛋白层。此外,网孔表面附着具有强吸附活性的羧酸基团层,它可以通过静电吸引或者共价结合来吸附液相中的第二种蛋白分子。

On-surface synthesis and edge states of NBN-doped zigzag graphene nanoribbons

Zigzag graphene nanoribbons(ZGNRs)with spin-polarized edge states have potential applications in carbon-based spintronics.The electronic structure of ZGNRs can be effectively tuned by different widths or dopants,which requires delicately designed monomers.Here,we report the successful synthesis of ZGNR with a width of eight carbon zigzag lines and nitrogen-boronnitrogen(NBN)motifs decorated along the zigzag edges(NBN-8-ZGNR)on Au(111)surface,which starts from a specially designed U-shaped monomer with preinstalled NBN units at the zigzag edge.Chemical-bond-resolved non-contact atomic force microscopy(nc-AFM)imaging confirms the zigzag-terminated edges and the existence of NBN dopants.The electronic states distributed along the zigzag edges have been revealed after a silicon-layer intercalation at the interface of NBN-8-ZGNR and Au(111).Our work enriches the ZGNR family with a new dopant and larger width,which provides more candidates for future carbonbased nanoelectronic and spintronic applications.

界面上配基种类对BSA吸附行为的影响

利用双偏振极化干涉测量仪(DPI)研究了界面上配基种类对BSA吸附行为的影响。采用3-氨基丙基三乙氧基硅烷(APTES)、3-(甲氨基)丙基三甲氧基硅烷(MAPTMS)和N,N-二乙基-3-氨基丙基三甲氧基硅烷(DAPTMS)对DPI芯片进行了修饰,利用X射线光电子能谱比较了芯片上不同配基的密度,采用原子力显微镜(AFM)和DPI对界面上BSA吸附行为进行了研究。结果表明APTES修饰界面上BSA呈饼状,高配基密度易导致BSA多位点吸附。相同偶联密度条件下BSA在DAPTMS修饰芯片的吸附量高于MAPTMS修饰芯片,但吸附层厚度一致,表明DAPTMS表面上BSA存在聚集现象;AFM扫描结果与DPI分析结果一致,证明了配基密度和种类不仅影响界面上蛋白质吸附量,而且影响蛋白质吸附密度和表面聚集行为。

Tuning the translational freedom of DNA for high speed AFM

Direct observation is arguably the preferred way to investigate the interactions between two molecular complexes. With the development of high speed atomic force microscopy （AFM）, it is becoming possible to observe directly DNA-protein interactions with relevant spatial and temporal resolutions. These interactions are of central importance to biology, bionanotechnology, and functional biologically inspired materials. As in all microscopy studies, sample preparation plays a central role in AFM observation and minimal perturbation of the sample is desired. Here, we demonstrate the ability to tune the interactions between DNA molecules and the surface to create an association strong enough to enable high-resolution AFM imaging while also providing sufficient translational freedom to allow the relevant protein-DNA interactions to take place. Furthermore, we describe a quantitative method for measuring DNA mobility, while also determining the individual forces contributing to DNA movement. We found that for a weak surface association, a significant contribution to the movement arises from the interaction of the AFM tip with the DNA. In combination, these methods enable the tuning of the surface translational freedom of DNA molecules to allow the direct study of a wide range of nucleo-protein interactions by high speed atomic force microscopy.

Hole-doping of mechanically exfoliated graphene by confined hydration layers

By the use of non-contact atomic force microscopy （NC-AFM） and Kelvin probe force microscopy （KPFM）, we measure the local surface potential of mechanically exfoliated graphene on the prototypical insulating hydrophilic substrate of CAF2（111）. Hydration layers confined between the graphene and the CaF2 substrate, resulting from the graphene＇s preparation under ambient conditions on the hydrophilic substrate surface, are found to electronically modify the graphene as the material＇s electron density transfers from graphene to the hydration layer. Density functional theory （DFT） calculations predict that the first 2 to 3 water layers adjacent to the graphene hole-dope the graphene by several percent of a unit charge per unit cell.

F-Actin reassembly during focal adhesion impacts single cell mechanics and nanoscale membrane structure

Focal adhesions play an important role in cell spreading,migration,and overall mechanical integrity.The relationship of cell structural and mechanical properties was investigated in the context of focal adhesion processes.Combined atomic force microscopy(AFM) and laser scanning confocal microscopy(LSCM) was utilized to measure single cell mechanics,in correlation with cellular morphology and membrane structures at a nanometer scale.Characteristic stages of focal adhesion were verified via confocal fluorescent studies,which confirmed three representative F-actin assemblies,actin dot,filaments network,and long and aligned fibrous bundles at cytoskeleton.Force-deformation profiles of living cells were measured at the single cell level,and displayed as a function of height deformation,relative height deformation and relative volume deformation.As focal adhesion progresses,single cell compression profiles indicate that both membrane and cytoskeleton stiffen,while spreading increases especially from focal complex to focal adhesion.Correspondingly,AFM imaging reveals morphological geometries of spherical cap,spreading with polygon boundaries,and elongated or polarized spreading.Membrane features are dominated by protrusions of 41-207 nm tall,short rods with 1-6 μm in length and 10.2-80.0 nm in height,and long fibrous features of 31-246 nm tall,respectively.The protrusion is attributed to local membrane folding,and the rod and fibrous features are consistent with bilayer decorating over the F-actin assemblies.Taken collectively,the reassembly of F-actin during focal adhesion formation is most likely responsible for the changes in cellular mechanics,spreading morphology,and membrane structural features.

Chiral structures of 6,12-dibromochrysene on Au(111)and Cu(111)surfaces

Nanoscale low-dimensional chiral architectures are increasingly receiving scientific interest,because of their potential applications in many fields such as chiral recognition,separation and transformation.Using 6,12-dibromochrysene(DBCh),we successfully constructed and characterized the large-area two-dimensional chiral networks on Au(111)and one-dimensional metal-liganded chiral chains on Cu(111)respectively.The reasons and processes of chiral transformation of chiral networks on Au(111)were analyzed.We used scanning tunneling spectroscopy(STS)to analyze the electronic state information of this chiral structure.This work combines scanning tunneling microscopy(STM)with non-contact atomic force microscopy(nc-AFM)techniques to achieve ultra-high-resolution characterization of chiral structures on low-dimensional surfaces,which may be applied to the bond analysis of functional nanofilms.Density functional theory(DFT)was used to simulate the adsorption behavior of the molecular and energy analysis in order to verify the experimental results.

水的核量子效应研究进展

"水的结构是什么"这是Science杂志在创刊125周年的特刊中提出的21世纪125个亟待解决的科学前沿问题之一.水的结构之所以如此复杂,其中一个很重要的原因就是源于水分子之间的氢键相互作用.人们通常认为氢键的本质为经典的静电相互作用,然而由于氢原子核质量很小,其量子效应在室温下都会非常明显,氢核的量子隧穿和量子涨落将减弱经典势垒对氢原子的限制,从而增强或减弱氢键相互作用强度,改变氢键网络构型,甚至影响氢键体系的宏观物性.该综述首先概述了核量子效应的起因和表现,然后介绍核量子效应研究的传统实验手段,以及新兴的基于扫描隧道显微镜和非接触式原子力显微镜的高分辨成像和谱学技术.然后,本文总结了水中氢核量子隧穿和量子涨落的最新研究进展,尤其是深入到原子尺度的核量子效应研究,最后对核量子效应研究所面临的问题和挑战以及未来发展方向进行评述.

Oxidation-based wet-etching method for Al Ga N/Ga N structure with different oxidation times and temperatures

In this article, a detailed analysis of the wet- etching technique for AIGaN/GaN heterostructure using dry thermal oxidation followed by a wet alkali etching was performed. The experimental results show that the oxida- tion plays a key role in the wet-etching method and the etching depth is mainly determined by the oxidation tem- perature and time. The correlation of etching roughness with oxidation time and temperature was investigated. It is found that there exists a critical oxidation temperature in the oxidation process. Finally, a physical explanation of the oxidation procedure for A1GaN layer was given.

Molecular heterostructure by fusing graphene nanoribbons of different lengths through a pentagon ring junction

Graphene nanoribbons(GNRs)have attracted great research interest because of their widely tunable and unique electronic properties.The required atomic precision of GNRs can be realized via on-surface synthesis method.In this work,through a surface assisted reaction we have longitudinally fused the pyrene-based graphene nanoribbons(pGNR)of different lengths by a pentagon ring junction,and built a molecular junction structure on Au(111).The electronic properties of the structure are studied by scanning tunneling spectroscopy(STS)combined with tight binding(TB)calculations.The pentagon ring junction shows a weak electronic coupling effect on graphene nanoribbons,which makes the electronic properties of the two different graphene nanoribbons connected by a pentagon ring junction analogous to type I semiconductor heterojunctions.

Energy band engineering via“Bite”defect located on N=8 armchair graphene nanoribbons

Graphene nanoribbons(GNRs)not only share many superlative properties of graphene but also display an exceptional degree of tunability of their electronic properties.The bandgaps of GNRs depend greatly on their widths,edges,etc.Herein,we report the synthesis path and the physical properties of atomic accuracy staggered narrow N=8 armchair graphene nanoribbons(sn-8AGNR)with alternating"Bite"defects on the opposite side.The intermediate structures in the surface physicochemical reactions from the precursors to the sn-8AGNR are characterized by scanning tunneling microscopy.The electronic properties of the sn-8AGNR are characterized by scanning tunneling spectroscopies and 6//6V mappings.Compared with the perfect N=8 armchair graphene nanoribbons(8AGNR),the sn-8AGNR has a larger bandgap,indicating that the liB\Xen edges can effectively regulate the electronic structures of GNRs.