Scanning tunneling microscopy with spin-polarized electrons

We present a short outline of the first STM experiments with spin-polarized electrons performed in ultrahigh vacuum by using ferromagnetic CrO₂ tips and a Cr(001) single crystal surface. A clear distinction can be made between topographic STM line scans obtained with a non-magnetic tungsten tip and those obtained with a ferromagnetic CrO₂ tip, which are modified due to an additional contribution from spin-dependent vacuum tunneling. STM therefore has the potential to measure the local electron spin polarization of the free surface as well as the spatial distribution of spins on the atomic scale.     

Deterministic teleportation of electrons in a quantum dot nanostructure

We present a proposal for deterministic quantum teleportation of electrons in a semiconductor nanostructure consisting of a single and a double quantum dot. The central issue addressed in this Letter is how to design and implement the most efficient--in terms of the required number of single and two-qubit operations--deterministic teleportation protocol for this system. Using a group-theoretical analysis, we show that deterministic teleportation requires a minimum of three single-qubit rotations and two entangling (square root SWAP) operations. These can be implemented for spin qubits in quantum dots using electron-spin resonance (for single-spin rotations) and exchange interaction (for square root SWAP operations).     

Polarization qubit phase gate in a coupled quantum-well nanostructure

We show that a giant Kerr nonlinearity with a relatively large cross phase modulation (CPM) phase-shift can be used for realizing polarization quantum phase gate based on the nonlinear optical response in a coupled semiconductor double quantum well (SDQW) structure via intersubband transitions.     

Scanning tunneling microscopy of a luttinger liquid

Explicit predictions for scanning tunneling microscopy (STM) on interacting one-dimensional electron systems are made using the Luttinger liquid formalism. The STM current changes with the distance from an impurity or boundary in a characteristic way, which reveals the spin-charge separation and the interaction strength in the system. The current exhibits Friedel-like oscillations, but also carries additional modulated behavior as a function of voltage and distance, which shows the spin-charge separation in real space. Moreover, very close to the boundary the current is strongly reduced, which is an indication of the interaction strength in the system.     

Scanning near-field optical microscopy

Scanning Near-field Optical Microscopy (SNOM) allows the investigation of optical properties on subwavelength scales. During the past few years, more and more attention has been given to this technique that shows enormous potential for imaging, sensing and modification at near-molecular resolution. This article describes the technique and reviews recent progress in the field.     

Scanning near-field acoustic microscopy

Scanning near-field acoustic microscopy (SNAM) is a new method for imaging the topography of nonconducting surfaces at a potential lateral resolution in the sub-micron range. The basic element of this method is a distance sensor consisting of a sharply pointed vibrating tip, which is part of a high-Q quartz resonator driven at its resonance frequency. The decrease of the resonance frequency or of the amplitude of vibration when an object comes into the proximity of the tip serves as the important signal. The dependence of this signal on pressure and composition of the coupling gas shows that the hydrodynamic forces in the gas are responsible for the coupling between object and tip. The sensor is incorporated into a scanning device. Well-resolved line scans of a grating of 8 m periodicity, a lateral resolution of 3 m and a vertical resolution of 5nm have been achieved in our first experiments.     

Scanning probe microscopy of graphene

A material with novel fundamental properties that challenge our current understanding is always exciting for research. If the novel properties extend to the realm of device engineering and promise a revolution in applications, then the scope of its research knows no bounds. The story of graphene, the two dimensional form of carbon, has followed this path. Graphene has been the subject of numerous experimental and theoretical investigations since 2004 when an elegant and a simple technique to make monolayer graphene set the stage for extensive research. Many other techniques to make graphene were developed in parallel to this technique. As graphene is replete with unique structural and electronic properties scanning probe microscopy has proved to be an exciting and a rewarding venture. In this review we discuss the findings of scanning probe microscopy and how it has served as an indispensable tool to understand the properties of graphene and further graphene research.     

Scanning photoemission microscopy of surfaces

Design and performance of a novel instrument for imaging surfaces on the basis of work function differences with a lateral resolution of the order of 1microm is described. Its principle consists in recording the total yield of electrons emitted by UV light focussed onto a small spot of the surface while the sample position is continuously varied.     

Scanning photoacoustic microscopy of coal

Scanning photoacoustic microscopy was utilized to investigate the possibility of characterization of coal by its thermal properties. A band of iron pyrite was clearly observed photoacoustically as were CO₂ and argon-ion laser pyrolyzed areas. The change in photo-acoustic data due to laser pyrolysis was analyzed and confirmed by a scanning electron microscope with X-ray fluorescence capability.     

Scattering approach to scanning gate microscopy

We present a perturbative approach to the conductance change caused by a weakly invasive scattering potential in a two-dimensional electron gas. The resulting expressions are used to investigate the relationship between the conductance change measured in scanning gate microscopy as a function of the position of a scattering tip and local electronic quantities like the current density. We use a semiclassical approach to treat the case of a strong hard-wall scatterer in a half-plane facing a reflectionless channel. The resulting conductance change is consistent with the numerically calculated quantum conductance.     

Gibbs distribution-based Bayesian segmentation of electron microscopy nanostructure images

The use of Gibbs distribution-based Bayesian segmentation of electron microscopy images for visualizing nanostructures is investigated. Bayesian segmentation involves dividing an image into nonoverlapping areas that correspond as closely as possible to the observed image. A quantitative characteristic of this correspondence is the a posteriori probability of one variant of division or another. The most likely version is always the division with the greatest a posteriori probability. The Metropolis algorithm for stochastic relaxation is used to obtain Bayesian estimates of the a posteriori probability of a division. Our study of Bayesian segmentation requires visualization of nanostructures on an electron microscopy image of a film made of NiW nanocrystalline alloy.     

扫描多光谱显微成像

文本描述了一种新的显微成像方法,它把光学扫描显微成像技术与成像多光谱技术巧妙地结合在一起,形成扫描多光谱显微成像技术.文中叙述了系统的结构及工作原理,介绍了所采用的图像处理系统,给出了实验结果,并进行了分析讨论.     

Scanning thermal microwave resonance microscopy

Local detection of ferromagnetic resonance in magnetically ordered materials is achieved by local thermal modulation of the microwave resonance absorption with a scanning thermal microscope. A scanning thermal microwave resonance microscope was constructed based on a microwave bridge with an X-band cavity and a thermal nano-probe contacted to the sample at the wall of the cavity. The technique has been tested on an epitaxial iron film which exhibited lateral inhomogeneities due to a partial oxidation of iron. Different types of oxidation could be distinguished. The locally resolved ferromagnetic resonance spectra are compared with the result of an integral measurement using conventional detection techniques of the ferromagnetic resonance with the same set-up. The lateral resolution achievable with the thermally modulated ferromagnetic resonance measurements was about 200 nm for the investigated iron film.     

Scanning tunneling microscopy imaging of nanotubes

Samples of carbon paper containing multiwalled carbon nanotube films are produced by current annealing. A scanning tunneling microscope is used to examine the structure of the modified carbon paper. X-, Y-, and V-shaped nanotubes are found.     

Scanning tunneling microscopy of carbon nanotubes

This article reports on the application of scanning tunneling microscopy for the study of surface structures and electronic properties of carbon nanotubes. Geometric effects resulting from the cylindrical shape of the tubes as well as the particular band structure of the graphitic crystal lattice can lead to a variety of contrast patterns. On the atomic scale, it is sometimes possible to see the full honeycomb lattice structure but often different structures are observed. Besides distortions caused by tip–sample interactions, we find that a complex superstructure superimposed on the simple atomic contrast pattern arises from elastic scattering of the Fermi states at defects or impurities. From a careful analysis of high-resolution images it is possible to extract information about elastic strain of individual tubes. A new combination of scanning tunneling and scanning force microscopy enables near-atomic point resolution of the force signal the tubes can be identified without the need of a conducting substrate. This imaging mode is a crucial step for the characterization of electronic devices based on individual single-wall tubes. This mode can be further enhanced by the use of single-walled tubes as probe tips. Received: 17 May 1999 / Accepted: 18 May 1999 / Published online: 4 August 1999     

磁性金属纳米结构的畴壁特性与磁逻辑电路构筑

自旋电子学由于其丰富的物理内涵和广泛的应用前景受到学术界和工业界的高度重视,成为近年来凝聚态物理和信息技术领域关注的焦点。本文介绍了利用磁性金属纳米结构实现作为自旋电子器件基础的自旋注入的方法,特别涉及利用铁磁金属纳米点接触结构钉扎磁畴的特点,研究自旋极化电流与磁畴壁的相互作用规律, 理解纳米结构中畴壁的动力学行为,并以此为基础构筑结构简单、性能优异的全金属磁逻辑电路,从而实现了由电信号驱动,通过电信号检测,并与CMOS技术兼容的目的。     

Demonstration of intricate gate,Ohmic and interconnect metallizations for nanostructure construction

We describe the fabrication and low temperature characterization of nanostructures defined by submicron-sized gate, interconnect and Ohmic metallizations on the surface of AlGaAs/GaAs heterostructures. A two level metallization architecture is used with Ohmic and gate surface patterns, separated by an inter-layer insulator, linked by patterned interconnects. The procedure, which features a 10nm alignment accuracy, can be used to interconnect metal patterns as small as 100nm. For the Ohmic metallization we discuss the injection properties of the contact as it is reduced to less than 1μm in diameter and present results which indicate the minimum size of Ohmic contacts that can be reliably formed using a Ni-Ge-Au metallization. The approach is illustrated with the fabrication and characterization of submicron-sized Corbino discs.     

Scanning acoustic Doppler microscopy and scanning acoustic correlation microscopy

Acoustic microscopy with vector contrast at 100 MHz in a fluid with immersed particles is used to detect the flow profile in front of a microscopic orifice. The velocity profile concerning the component in axial direction of the focused beam is derived from the phase contrast. Possibilities to resolve the flow profile also for the components in normal direction with respect to the axis are demonstrated. The methods concerning measurement techniques and data evaluation for scanning acoustic Doppler microscopy are presented. For scanning acoustic correlation microscopy the time dependent phase and amplitude signals resulting from sound waves scattered by the immersed particles (aluminium flakes with a typical diameter of 10 microm) have been analysed by correlation procedures. From the obtained autocorrelation functions the velocity distribution can be derived. Both methods can be applied simultaneously. Data analysis is based on the information contained in the originally obtained images in vector contrast derived from temporal and spatial resolved analogue and digital processing of the acoustic signals.     

Scanning microscopy by mid-infrared near-field scattering

2 -laser radiation from an AFM tip. In the microscopic images we find and identify a new type of AFM-induced artifact (crosstalk via the tapping amplitude). Minimizing this by proper scan parameters we obtain evidence of true infrared contrast. The results demonstrate the material-sensitive potential of infrared-spectroscopic imaging and a spatial resolving power of better than 100 nm. Received: 18 November 1997/Accepted: 5 January 1998