摘要:

A new and highly sensitive &bgr;‐NMR method to study adsorbates on single‐crystal surfaces is presented. Contrary to conventional NMR, this method combines (via optical pumping) a high, nonthermal polarization of the adsorbed species with a particle counting method. Here, the &bgr;‐active isotope8Li is produced in the nuclear reaction D(7Li,8Li)H using a high‐pressure deuterium gas target. The fast8Li ions are subsequently implanted into a hot graphite block where they thermally diffuse to the surface and desorb. The desorbing thermal velocity8Li atoms are shaped into an atomic beam. Using a frequency modulated laser beam the atoms are transferred into a single hyperfine state by optical pumping. The so‐achieved nuclear polarization of the atoms (before impinging on the single‐crystal surface) is approximately 0.8 and can be switched in sign by an adiabatic high‐frequency transition. The atoms adsorb on the single‐crystal surface and their polarization—either freely decaying on the surface or driven by an external radio‐frequency field—is observed via the decay asymmetry of the nuclear &bgr;‐decay of the8Li nuclei. This method realizes an effective sensitivity to the active NMR isotope of 5×103atoms/cm2, which corresponds to a stationary coverage of 10−11of a monolayer. The typical electron count rate is 400 Hz during &bgr;‐NMR experiments. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145644

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A first generation digital imaging video microscopy system has been developed that is able to provide both quantitative and visual three dimensional information from individual vascular endothelial cells. More specifically, with the combination of optical sectioning, video microscopy, digital image processing and analysis, deconvolution, fluorescence ratio imaging, and scientific visualization we are able to measure the dynamic changes in spatial distributions of intracellular ions. The technique presented involves the following steps: acquiring three dimensional biological data by optical sectioning of a specimen, preprocessing the digitized volume data, experimentally determining the digital imaging system’s point spread function (PSF), deconvolving the volume data with the PSF to remove the inherent out‐of‐focus information, and finally postprocessing and volume rendering in order to display the volume data in a quantitative and comprehensible manner. This technique permits high resolution visualization and quantification of three dimensional spatial distributions of ions as well as traditional temporal changes in ion concentration. It has the potential to aid immensely in research since the three dimensional spatial information is often a prerequisite for understanding the molecular mechanisms involved in many complex cellular processes. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145645

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

This paper describes detection probe‐tip configuration optimization for a photopyroelectric thermal‐wave imaging instrument. In order to obtain reconstructed thermal‐wave tomographic images with high fidelity, it is necessary to obtain the optimum conditions of the detection probe‐tip configuration. These conditions were obtained by analyzing the electric fields around a capacitive‐coupled detection probe‐tip using finite‐element‐method (FEM) analysis. Experimental results are also shown, verifying the FEM analysis results. It was also confirmed that the equivalent probe‐tip diameter determined from our previous experimental work agreed almost perfectly with that obtained using FEM analysis. As a result, high‐fidelity thermal‐wave tomographic images were obtained. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145646

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We describe the design and characterization of a new variable low‐temperature scanning tunneling microscope (STM) which has been proven to give atomic resolution at temperatures between 77 K and room temperature but which is also capable of performing experiments as low as 4 K. The STM ‘‘head’’ itself consists of a unique cold dewar made up of an upper and lower reservoir connected together by two tubes which pass through an 8 in. conflat flange. The STM stage is suspended in between the two reservoirs by three long springs which pass through holes in the upper reservoir and also attach to the top flange. An adjustable cold shroud surrounds the STM stage for radiation shielding while allowing sample and tip transfer when raised. It has the additional advantage of providing a controllable heat leak. By raising the shroud, the temperature can be increased; by lowering it, the temperature can be decreased. The cold reservoirs can be filled with either liquid nitrogen or liquid helium. In the case of liquid helium, an additional liquid nitrogen ‘‘jacket’’ surrounds the STM head. Everything is operated inside a customized ultrahigh vacuum chamber containing low‐energy electron diffraction and various sample preparation facilities. A detailed description of the STM is presented together with performance results. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145647

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The scanning tunneling microscope (STM) has been known for its high lateral resolution, but its unreliable vertical accuracy has prevented it from being widely used as a profiler for roughness and step height measurements. An STM equipped with an optical interferometer to calibrate STM tip feedback controlled motion in theZdirection along with interferometers for monitoringXandYraster scanning has been developed. The resolution of the interferometer was 0.12 nm rms. Maximum line scanning distance is 250 &mgr;m and the motion in this direction is secured by a parallel spring mechanism. Step height and pitch measurements on a surface topography standard agree in nanometer scale with the certified value of the standard. The result of high accuracy roughness measurement with the STM supports the common observation that STM measurement gives larger roughness than interferometric measurement. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145648

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The conductivity of a variety of atomic force microscopy tips was investigated by measuring both current‐voltage characteristics and force profile data for the tip in contact with graphite. This allows the conductivity to be studied as a function of tip‐sample distance. It was found that etched gold wires or levers coated with a conducting diamond film were the best tips to use for experimentation on hard (SiO2) surfaces. Metal‐coated levers, particularly gold, were found to wear rapidly such that the very end of the tip became insulating. ©1995 American Institute of Physics. 

ISSN:0034-6748    

DOI:10.1063/1.1145649

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Calibration of scanning probe microscopes (SPM) for atomic (molecular) resolution scans can be carried out on crystalline surfaces. However, SPM scans with atomic resolution are often affected by drift and hence would give false calibration factors. We propose a method which allows to calibrate the SPM instrument eliminating the effects of drift in a first‐order approximation. Scans of the same surface are taken at different speeds and a linear regression is applied to the calibration factors calculated for each scan speed. Applying this method we succeeded in calibrating a commercial SPM system for atomic resolution scans with a precision of better than 2%. ©1995 American Institute of Physics. 

ISSN:0034-6748    

DOI:10.1063/1.1145650

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The piezoelectric tube scanners used in tunneling microscopy show nonlinear displacements inx,y, andzdirections with applied voltage. A software technique to correct for this nonlinear behavior inxandydirections is proposed. The method calculates the voltages to be applied to thexandyquadrants of the piezotube during the scan, taking into consideration the variations of thex/ypiezosensitivity with voltage. The technique is of importance in scans performed over large areas, typically in the micrometer range, where nonlinear behavior of the tube scanner causes distortions in the images obtained. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145651

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We describe the construction and operation of a large‐range piezoelectric scanner, suitable for various scanning probe microscopies such as magnetic force, atomic force, and Hall probe microscopies. The instrument is compact and inherently thermally compensated. At room temperature, it has a range of over 2 mm; this range is reduced to 275 &mgr;m at 4.2 K. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145652

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

It was confirmed experimentally that a 210° cylindrical energy analyzer with drift spaces has second‐order focusing. The properties of the analyzer are strongly dependent on the fringing field around the entrance and exit of the cylinders. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1145653

出版商:AIP    

年代:1995

数据来源: AIP