Observation of subcellular structures of neurons by an illumination mode near-field optical microscope under an optical feedback control

We propose an illumination mode near-field optical microscope operated under an optical feedback for imaging biological specimens in their natural environment. For feedback control, rapidly varying evanescent signal has been generated over the sample surface. It has been found that evanescent signal can be profitably used as a control signal by utilizing its sample feature dependent discrimination sensitivity. Neurons have been successfully observed both in air and in liquid with a resolution well beyond the diffraction limit.     

Atomic engineering of photon emission with a scanning tunneling microscope

We present measurements of photon emission from individual several-atom silver chains on the NiAl(110) surface, excited by tunneling electrons in a scanning tunneling microscope (STM). The chains were assembled by manipulating single silver atoms on the NiAl(110) surface with the STM. The photon energy of this emission can be tuned by appending a single atom to the chain. These changes in photon emission result from changes in the electronic structure of the silver chain, each electronic state inside the chain being associated with a distinct channel of emission.     

Investigation of localized surface plasmons with the photon scanning tunneling microscope

A Photon Scanning Tunneling Microscope (PSTM) with probe-sample distance control by electron tunneling is used to probe the localized surface-plasmon fields of individual nanometric silver particles. As samples, conventional island films produced by thermal evaporation and regular particle arrays produced by an electron-beam-lithography-based technique, respectively, are used. In either case the strength and spatial localization of the surface-plasmon fields strongly depend on the excitation wavelength. The results are interpreted as different resonance frequencies of individual particles or of different sample areas. On regular arrays consisting of particles with a smallest diameter of 40 nm, the PSTM maps represent the plasmon field strength spatially resolved for individual particles.     

Theory for photon emission from a scanning tunneling microscope

We have calculated the rate of light emission from a scanning tunneling microscope with an Ir tip probing a silver film. In the calculation we model the tip by a sphere. We find a considerable enhancement of the light emission compared with for example inverse photoemission experiments. This enhancement is explained as the result of an amplification of the electromagnetic field in the area below the microscope tip due to a localised interface plasmon. We estimate that one out of 10⁴ tunneling electrons will emit a photon in the visible range. Due to an electromagnetic decoupling of the sphere from the sample the enhanced emission is lost for photon energies above a certain value. We also find that the experimentally observed maximum in the light emission as a function of bias voltage is related to the behavior of tip-sample separation versus bias voltage.     

镀纳米结构薄膜光纤探针的光子隧道扫描显微镜成像数值模拟

利用时域有限差分法,对镀纳米结构薄膜光纤探针的成像特性进行了三维数值模拟。在考虑光纤和样品相互作用的基础上,采用等效入射波法设置入射波和等高扫描。从成像分辨率和灵敏度的角度比较了不同纳米颗粒与样品间距、纳米颗粒大小、排列方式以及排列密度对成像的影响。结果表明,镀纳米结构薄膜光纤探针的光子隧道显微镜无论在制备的可行性上,还是在分辨率和灵敏度上都有显著的改进。     

扫描隧道显微镜在单分子科学中的应用

单分子科学是一门新兴的交叉科学,在当前的科技发展中具有重要意义.扫描隧道显微镜是研究单分子的一种强有力而独特的工具.文章以作者所在研究组近年来在单分子表征、操控和原型器件设计等方面的研究工作进展为例,概述了扫描隧道显微镜在单分子科学中的应用,重点介绍了以下成果:在硫醇分子自组装单层膜上观测到C60分子的本征笼状结构,并发现了一种新颖的由C60分子取向产生的拓扑序;结合实验图像和理论模拟,确定了单个C60分子在Si(111)-7×7表面的吸附取向;通过对金属富勒烯分子Dy@C82进行空间和能量分辨成像及相关理论模拟,确定了金属原子相对碳笼的位置及分子的取向;利用扫描隧道显微镜针尖对吸附在Au(111)表面的单个CoPc分子操作"分子手术",以实现其吸附态和自旋态的量子调控;发现了一种由单电子隧穿和C59N分子的特殊能级结构产生的新的整流机制;发现了一种由针尖电子态和CoPc分子中Co原子轨道的空间对称性匹配产生的负微分电阻效应.     

Controlled lateral manipulation of single molecules with the scanning tunneling microscope

We report on the first successful lateral manipulation of molecules and controlled formation of nanostructures with the Scanning Tunneling Microscope (STM) at temperatures above 4 K as used by Eigler and collaborators. Among the first structures, we built the letters F and U forming the logo of our university at 30 K with CO molecules on a Cu(211) substrate. Our method to manipulate the molecules is analogous to that employed successfully up to now only by Eigler and co-workers. First experiences concerning the manipulation of the CO molecules on the highly anisotropic substrate are presented and the crucial role of the tip composition in imaging the CO molecules is demonstrated.     

扫描隧道显微镜在单分子科学中的应用

单分子科学是一门新兴的交叉科学,在当前的科技发展中具有重要意义.扫描隧道显微镜是研究单分子的一种强有力而独特的工具.文章以作者所在研究组近年来在单分子表征、操控和原型器件设计等方面的研究工作进展为例,概述了扫描隧道显微镜在单分子科学中的应用,重点介绍了以下成果：在硫醇分子自组装单层膜上观测到C60分子的本征笼状结构,并发现了一种新颖的由C60分子取向产生的拓扑序;结合实验图像和理论模拟,确定了单个C60分子在Si(111)-7×7表面的吸附取向;通过对金属富勒烯分子Dy@C82进行空间和能量分辨成像及相关理论模拟,确定了金属原子相对碳笼的位置及分子的取向;利用扫描隧道显微镜针尖对吸附在Au(111)表面的单个CoPc分子操作“分子手术”,以实现其吸附态和自旋态的量子调控;发现了一种由单电子隧穿和C59N分子的特殊能级结构产生的新的整流机制;发现了一种由针尖电子态和CoPc分子中Co原子轨道的空间对称性匹配产生的负微分电阻效应.     

Direct observation of the quantum tunneling of single hydrogen atoms with a scanning tunneling microscope

Single hydrogen atoms were imaged on the Cu(001) surface by scanning tunneling microscopy (STM). The vibrations of individual H and D atoms against the surface were excited and detected by inelastic electron tunneling spectroscopy (STM-IETS). Variable temperature measurements of H atom diffusion showed a transition from thermally activated diffusion to quantum tunneling at 60 K. Regimes of phonon-assisted and electron-limited quantum tunneling were observed. The thermal diffusion rate of D atoms varied over 7 orders of magnitude between 80 and 50 K with no transition to quantum tunneling down to a thermal hopping rate of 4x10(-7) s(-1).     

Imaging of surface plasmon polariton interference using phase-sensitive photon scanning tunneling microscope

We report the surface plasmon polariton interference, generated via a ??buried?? gold grating, and imaged using a phase-sensitive Photon Scanning Tunneling Microscope?(PSTM). The phase-resolved PSTM measurement unravels the complex surface plasmon polariton interference fields at the gold-air interface.     

Quasi interference of perpendicularly polarized guided modes observed with a photon scanning tunneling microscope

The simultaneous detection of TE- as well as TM-polarized light with a photon scanning tunneling microscope leads to a quasi-interference pattern of these mutually perpendicular polarized fields. This interference pattern has been observed in the optical field distribution as a function of both position and wavelength. Comparison of experimental data with simulations confirms the interference of mutually orthogonal fields. This quasi interference is caused by conversion of the linearly polarized light of both modes into elliptically polarized light by a fiber probe.     

Electroluminescence of single CdSe nanocrystals induced by scanning tunneling microscope

Electroluminescence intensity of single CdSe nanocrystals (NCs) excited by the tunnel current of a scanning tunneling microscope (STM) was measured. Samples with NCs do not exhibit plasmon emission. This enables one to measure pure emission from a single NC. Electroluminescence, measured in time, differs considerably from that of photoluminescence in similar NCs. This difference in temporal behavior results from the difference in physical conditions of experiments on photo- and electroluminescence.     

Fluctuation dominated Josephson tunneling with a scanning tunneling microscope

We demonstrate Josephson tunneling in vacuum tunnel junctions formed between a superconducting scanning tunneling microscope tip and a Pb film, for junction resistances in the range 50-300 k Omega. We show that the superconducting phase dynamics is dominated by thermal fluctuations, and that the Josephson current appears as a peak centered at small finite voltage. In the presence of microwave fields ( f = 15.0 GHz) the peak decreases in magnitude and shifts to higher voltages with increasing rf power, in agreement with theory.     

Controlled charge switching on a single donor with a scanning tunneling microscope

The charge state of individually addressable impurities in semiconductor material was manipulated with a scanning tunneling microscope. The manipulation was fully controlled by the position of the tip and the voltage applied between tip and sample. The experiments were performed at low temperature on the (110) surface of silicon doped GaAs. Silicon donors up to 1 nm below the surface can be reversibly switched between their neutral and ionized state by the local potential induced by the tip. By using ultrasharp tips, the switching process occurs close enough to the impurity to be observed as a sharp circular feature surrounding the donor. By utilizing the controlled manipulation, we were able to map the Coulomb potential of a single donor at the semiconductor-vacuum interface.     

Photon emission with the scanning tunneling microscope

By placing a photon detector near the tip-sample region of a scanning tunneling microscope, we have measured isochromat photon-emission spectra of polycrystalline tantalum and Si(111)7×7 at photon energies of 9.5 eV. Such spectra contain electronic-structure information comparable to inverse photoemission spectroscopy, but with high lateral/spatial resolution. The implications of this new observation are discussed.