共查询到20条相似文献,搜索用时 15 毫秒
1.
在Au(111)表面自组装制备了不同链长的烷烃硫醇分子膜,并利用导电原子力显微镜研究了 自组装分子膜的输运特性随外加压力的变化.结果发现分子膜的电流随压力的增加而增大, 其变化特征可以较好地用Hertz模型描述.在相同压力和电压下,通过分子膜的电流随分子链 长的增加呈指数衰减,其衰减因子先随压力的增加而减小,后逐渐趋于稳定.此外,长链分 子自组装膜的电流随压力的变化比短链分子膜更为明显.分析表明,自组装硫醇分子膜输运 特征的压力依赖性主要源于电荷在分子膜中的链间隧穿过程.
关键词:
分子自组装
输运特性
原子力显微镜 相似文献
2.
Nele Vandamme 《Surface science》2006,600(14):2894-2899
Using atomic force microscopy we investigated how local capillary phenomena are affected by the deposition of a self-assembled 1,4-benzenedimethanethiol (BDMT) layer on epitaxially grown Au(1 1 1) and Ag(1 1 1) films. Force-distance curves monitored at varying relative humidity show clear differences in the adhesion forces on the different samples, which can be explained in terms of a change in the wetting behavior due to the presence of the molecules. Moreover, we found that not only the chemical structure of the molecules but also their orientation strongly influences the strength of the capillary forces. A detailed analysis of the measurements shows that condensation of water vapor on Au(1 1 1) films is drastically enhanced due to the vertically aligned BDMT molecules, while on Ag(1 1 1) water condensation is reduced due to a parallel molecule orientation. 相似文献
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H. Klein W. Blanc R. Pierrisnard C. Fauquet Ph. Dumas 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):371-376
We report here a preparation for thin gold films on mica substrates. We have investigated the influence of the substrate temperature
and the evaporation rate on the morphology of the films. After careful outgasing of the substrate, 100 nm of Au is evaporated
onto the mica surface maintained at high temperature. After slow cooling, ex situ characterizations are performed using AFM and STM. For our purposes, the best compromise between roughness and grain size
is found to occur for an evaporation rate of 2 ?s-1 onto a mica substrate maintained at 460 C. We have used these substrates for STM and AFM study of decanethiol self-assembled monolayers (SAMs). We present results
for gold samples immersed for a few seconds in decanethiol solutions, revealing an incomplete organization of the films. The
organization process is discussed through comparison between AFM and STM data recorded on the SAMs. Then we present molecular
resolution STM pictures of ordered SAMs for longer immersion times.
Received 25 May 1999 相似文献
6.
基于Hamaker假设、Lennard-Jones势能定律及经典弹性理论建立了一种新型的球体与平面黏着接触的弹性模型,该模型显示黏着力在原子力显微镜(AFM)针尖趋近和撤离样品表面,即加载和卸载的两个过程中存在黏着滞后现象,表明了AFM在轻敲工作模式中存在能量耗散.同时,根据所建的黏着接触弹性模型,建立了AFM在轻敲工作模式下的动力学模型,研究了AFM在轻敲工作模式下的振动幅度、相位差及耗散功率随针尖与样品表面间距的变化规律,仿真结果与现有的实验结果相一致. 相似文献
7.
The periodic impact force induced by tip-sample contact in
tapping mode atomic force microscope (AFM) gives rise to
non-harmonic response of a micro-cantilever. These non-harmonic
signals contain the full characteristics of tip-sample interaction.
A complete theoretical model describing the dynamical behaviour of
tip--sample system was developed in this paper. An analytic formula
was introduced to describe the relationship between time-varying
tip--sample impact force and tip motion. The theoretical analysis
and numerical results both show that the time-varying tip--sample
impact force can be reconstructed by recording tip motion. This
allows for the reconstruction of the characteristics of the
tip--sample force, like contact time and maximum contact force. It
can also explain the ability of AFM higher harmonics imaging in
mapping stiffness and surface energy variations. 相似文献
8.
Kei Kobayashi Hirofumi Yamada Toshihisa Horiuchi Kazumi Matsushige 《Applied Surface Science》1999,140(3-4):281-286
We demonstrated the high resolution imaging of the organic molecules using noncontact atomic force microscopy in ultrahigh vacuum. The sample was C60 molecules deposited on the Si(111)-7×7 reconstructed surface. When the thickness of the C60 film was submonolayer, we could image some isolated C60 molecules and the reconstructed Si surface simultaneously. However, the imaging was highly unstable not only because of the large structure but also due to the large difference between the interaction forces on the molecules and on the Si surface. On the other hand, when the thickness of the C60 molecules was almost monolayer, individual molecules could be stably imaged. 相似文献
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介绍了原子力显微镜在生物物理领域的最新应用:蛋白质去折叠、DNA拉伸、生物膜受力,通过分析实验得到的力谱,可以获取关于蛋白质、DNA、生物膜结构信息.原子力显微镜不仅能反映测量体系的力学性质,由于其具有独特的时间、空间分辨及实时成像,因而能提供更多信息. 相似文献
10.
《中国物理 B》2021,30(7):77306-077306
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. 相似文献
11.
The (0001) surface of highly oriented pyrolytic graphite is studied by scanning force microscopy in both contact and dynamic mode. Low temperatures were necessary for the dynamic mode measurements in order to achieve the required signal to noise ratio. At 22 K, atomic scale structures with 2.46 Å periodicity and trigonal symmetry of the individual maxima were obtained in both modes. Since graphite exhibits a van der Waals surface in good approximation, this result shows that comparatively weak forces of van der Waals type are sufficient for successful imaging in the dynamic mode on the atomic scale. However, since the positions of the observed maxima correspond to the ones found by scanning tunneling microscopy and contact scanning force microscopy, but not to the positions of the carbon atoms, it also opens new questions on the imaging mechanism in the dynamic mode. 相似文献
12.
Franz J. Giessibl Hartmut Bielefeldt Stefan Hembacher Jochen Mannhart 《Applied Surface Science》1999,140(3-4):352-357
True atomic resolution of conductors and insulators is now routinely obtained in vacuum by frequency modulation atomic force microscopy. So far, the imaging parameters (i.e., eigenfrequency, stiffness and oscillation amplitude of the cantilever, frequency shift) which result in optimal spatial resolution for a given cantilever and sample have been found empirically. Here, we calculate the optimal set of parameters from first principles as a function of the tip–sample system. The result shows that the either the acquisition rate or the signal-to-noise ratio could be increased by up to two orders of magnitude by using stiffer cantilevers and smaller amplitudes than are in use today. 相似文献
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Non-contact atomic force microscope is a powerful tool to investigate the surface topography with atomic resolution. Here we propose a new approach to estimate the interaction between its tips and samples, which combines a semi-empirical model with density functional theory (DFT) calculations. The generated frequency shift images are consistent with the experiment for mapping organic molecules using CuCO, Cu, CuCl, and CuOx tips. This approach achieves accuracy close to DFT calculation with much lower computational cost. 相似文献
14.
The growth kinetics of self-assembled monolayers (SAMs) of thiophene compounds on Au(111) surfaces was revealed by Fourier-transform
infrared reflection absorption spectroscopy (FT-IR-RAS). Thiophene and terthiophene form well-ordered SAMs on Au(111) surfaces
by immersing gold substrates into their ethanol solutions for ca. 15 h. Gibbs free energies for the adsorption processes of thiophene and terthiophene were found to be identical. However,
the growth and molecular orientation of SAMs are different between two thiophene compounds. Terthiophene in SAMs orients parallel
to the surface. The SAM growth of terthiophene obeys a time-dependent Langmuir scheme. On the other hand, the thiophene SAM undergoes a two-step growth process with unique molecular orientations.
In the primary phase, thiophene assumes a parallel orientation on the Au(111) surface. In the second phase, thiophene is oriented
close to the normal of the surface. The different growth process between thiophene and terthiophene is attributable to the
topology of sulfur positions in the molecules.
Received 23 May 2001 and Received in final form 11 February 2002 相似文献
15.
Non-contact atomic force microscopy (AFM) was employed following emersion to examine Au nanoclusters deposited from aqueous mixtures of HF and 10−4 M KAu(CN)2 onto Si(111). As the HF concentration is increased, the growth rates both parallel and perpendicular to the substrate of the approximately oblate Au hemispheroids increase. AFM images were obtained for times at which previously reported in situ second harmonic generation signals from the interface reach a maximum. At the time when the second harmonic enhancement is maximized during deposition from 0.500 (5.00) M HF, the Au nanoclusters have an average diameter of 94 (109) nm and an average height of 3.6 (9.5) nm. These cluster diameters can be understood qualitatively by the shift of the plasmon resonance due to depolarization as the cluster size increases, causing the resonant second harmonic enhancement at 532 nm to pass through a maximum at cluster diameters in the range 90–110 nm. 相似文献
16.
《Surface Science Reports》2020,75(4):100509
It was a long-cherished dream for chemists to take a direct look at chemical bonding, a fundamental component of chemistry. This dream was finally accomplished by the state-of-the-art noncontact atomic force microscopy (NC-AFM) equipped with qPlus force sensors and carbon monoxide (CO) functionalized tips. The resolved interconnectivity between atoms and molecules in NC-AFM frequency shift images is interpreted as chemical bonding, providing essential knowledge of the bond length, bond angle and even bond order. The featured contrast of different chemical bonds can serve as fingerprints for further interpretation of chemical structures toward unknown species synthesized on surfaces. This breakthrough enriches characterization tools for surface science and brings our understanding of on-surface reactions to a new level. Beyond bond imaging, the application of NC-AFM has been extended to quantifying interatomic interactions, identifying three-dimensional nanostructures, manipulating molecules and reactions, as well as determining molecular electronic characteristics. Moreover, some recent efforts address the improvement of the usability and versatility of the bond-resolved NC-AFM technique, including high-resolution molecular investigation on bulk insulators, application-specific tip modification, stable bond imaging above liquid helium temperature and autonomous experimentation implemented by artificial intelligence. 相似文献
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Non-contact atomic force microscopy (NC-AFM) has been applied to observe single- and double-stranded DNA. For the wet processes used to prepare the sample, a strong adhesion force at the surface is observed even in vacuum conditions. Despite the presence of this adhesion force, single- and double-stranded DNA images can be obtained by NC-AFM. Because of the high sensitivity of the tip-sample interaction, NC-AFM images provide stronger contrast than tapping mode (TM)-AFM images. NC-AFM images reveal detailed structures of single- and double-stranded DNA which are not revealed by TM-AFM. In addition, several NC-AFM images show contrast artifacts, which might provide information on the detailed structure of DNA. 相似文献
19.
SHAOYI JIANG 《Molecular physics》2013,111(14):2261-2275
A review is presented of this group's recent molecular simulation studies of self-assembled monolayers (SAMs) of alkanethiols on Au(111) surfaces. SAMs are very useful for the systematic alteration of the chemical and structural properties of a surface by varying chain length, tail group and composition. The scientific and technological importance of SAMs cannot be overestimated. The present work has been centred on studies of atomic scale surface properties of SAMs. First, configurational-bias Monte Carlo simulations were performed in both semigrand canonical and canonical ensembles to investigate the preferential adsorption and phase behaviour of mixed SAMs on Au(111) surfaces. Second, a novel hybrid molecular simulation technique was developed to simulate atomic force microscopy (AFM) over experimental timescales. The method combines a dynamic element model for the tip-cantilever system in AFM and a molecular dynamics relaxation approach for the sample. The hybrid simulation technique was applied to investigate atomic scale friction and adhesion properties of SAMs as a function of chain length. Third, dual-control-volume grand canonical molecular dynamics (DCV-GCMD) simulations were performed of transport diffusion of liquid water and methanol through a slit pore with both inner walls consisting of Au(111) surfaces covered by SAMs under a chemical potential gradient. Surface hydrophobicity was adjusted by varying the terminal group of CH3 (hydrophobic) or OH (hydrophilic) of the SAMs. Finally, ab initio quantum chemical calculations were performed on both clusters and periodic systems of methylthiols on Au(111) surfaces. Based on the ab initio results, an accurate force field capable of predicting c(4×2) superlattice structures over a wide range of temepratures for alkanethiols on Au(111) was developed. The extension of current work is discussed briefly. 相似文献
20.
S. Nagaoka K. Ikemoto K. Fujio K. Hiehata A. Sasahara M. Mitsui H. Onishi A. Nakajima 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,52(1-3):103-106
Multiple-decker vanadium-benzene sandwich clusters Vn(benzene)n+1 produced by a laser-vaporization synthesis method were soft-landed onto self-assembled monolayers of alkanethiol (C18H-SAM) and fluorinated alkanethiol (C10F-SAM) at 200 K. Noncontact atomic force microscopy has been used to examine the resulting adsorption states of the clusters landed on the SAMs at room temperature. For each SAM substrate, the aggregates of the deposited clusters were observed at the vacancy islands and near the steps of the SAM surface. The result indicates that, at room temperature, the clusters landed on the SAM substrate thermally diffuse on the surface to form columnar-shape islands around the defect sites of the SAM surface. 相似文献