摘要:

A probehead employing interchangeable loop‐gap resonators and rf coils for multifrequency EPR/ENDOR spectroscopy from 1 to 10 GHz is described. A precision coupling mechanism allows accurate magnetic coupling of the microwaves to the resonators. The Rexolite©support of the resonator acts as a spool for the ENDOR coil. rf fields of 1.0 mT are generated. The coil and resonator can be easily changed to cover the range of 1–10 GHz. Liquid‐phase ENDOR spectra of the stable free‐radical galvanoxyl and of the spin label TEMPONE (4‐oxo‐2,2,6,6‐tetramethyl‐l‐piperidine‐N‐oxyl) dissolved inn‐heptane are shown. The ENDOR enhancement for nitrogen from TEMPONE is 15 times larger at 2.3 than at 9.3 GHz due to the rf enhancement.

ISSN:0034-6748    

DOI:10.1063/1.1144747

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We present the technical details and relevant performance aspects of a dielectric resonator‐based electron paramagnetic resonance probe for stopped‐flow kinetic studies. The major benefits of this system are: (1) It incorporates a small, high sensitivity resonator system that is insensitive to stopped‐flow induced noisy transients. (2) The resonator system is cheap, robust, and easily assembled. (3) It contains a microwave coupling scheme that provides finesse in tuning and freedom from microphonics.

ISSN:0034-6748    

DOI:10.1063/1.1144748

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The construction of an ultrahigh vacuum (UHV) surface science chamber equipped with the standard surface analytical techniques and a connected companion UHV chamber containing a scanning tunneling microscope (STM) has been completed. The novel aspects of this experimental system are: the combination of many spatially averaging techniques with STM; a sample holder which is capable ofinsitutransfer between these various capabilities; variable temperature operation;insitutip‐sample approach without mechanical feedthroughs; and various novel software aspects. The sample transfer mechanism allows the sample to be transferred onto the main manipulator and heated or cooled with thermocouple monitoring while electrical isolation from the chamber ground is maintained. The sample then can be transferredinvacuoto the UHV STM for further study. STM tips can be transferred into and out of vacuum and positioned for sputtering and UHV analysis. The various design details which allow forinvacuotransfers will be discussed.

ISSN:0034-6748    

DOI:10.1063/1.1144749

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We have designed and built a scanning tunneling microscope (STM) suitable for biological applications. A sound‐isolated chamber contains the STM unit; the chamber can be evacuated or filled with inert gas, after the sample and tip are loaded, in order to reduce contamination on sample and tip. The STM unit is mounted inside two separable cylindrical supports. The lower cylinder contains the sample holder mounted on top of a step‐motor controlledx‐y‐zstage, while the upper one contains the piezoelectric tip scanner. AnI/Vconverter preamplifier mounted inside thex‐y‐zstage and a completely digitized feedback circuit, together with a full software package in UNIX X‐window environment and data processing, allow fast sample–tip approach and reduced acquisition time. Atomic resolution images of highly oriented pyrolytic graphite (HOPG) in air and reproducible large scan on a platinum grating are routinely obtained. Images of human liver ferritin deposited on an activated gold substrate have also been obtained.  

ISSN:0034-6748    

DOI:10.1063/1.1144751

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We describe the design and operation of a combined scanning tunneling–atomic force–lateral force microscope [(STM), (AFM), (LFM)]. Including these capabilities in a single instrument reduces construction costs and increases flexibility. AFM and LFM may be performed simultaneously; a simple reconfiguration (requiring removing the AFM/LFM cantilever holder and replacing with a STM tip) changes the instrument into a STM. We present atomic forces depicted in force‐to‐distance curves and experimental imaging applications with all three techniques.

ISSN:0034-6748    

DOI:10.1063/1.1144752

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A novel scan generator for a scanning tunneling microscope (STM) has been developed. The instrument compares tunneling current with three thresholds values, to generate anx‐scanner signal with a dynamically changeable step size for adaptation to sharp topographical changes. It has two advantages compared to conventional STM scan generators (i) a better protection from a tip crash and (ii) minimization of the image acquisition time. The implementation is made with a digital signal processor (DSP) DSP32C from AT&T, mounted on a commercially available PC AT‐compatible plug‐in card. Test images of extremely rough surfaces confirm the usefulness of our novel scan generator. The concept could also be used for different scanning probe microscopes.

ISSN:0034-6748    

DOI:10.1063/1.1144753

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A small‐area high‐Tcsuperconducting bolometer with a dense YBCO meander wire on a (100) Zr(Y)O2substrate has been tested at &lgr;=1.5 &mgr;m using a diode laser as the radiation source. The infrared power absorbed by the bolometer was calibrated using a dc infrared substitution method. Responsivities of hundreds of V/W with a millisecond response time were obtained at a temperature of 86.5 K in the modulation frequency range of 10–3000 Hz. A minimum noise equivalent power of 6×10−11W/Hz1/2was measured at 1000 Hz. The experimental results are compared with those obtained from a thermal analysis of the substrate‐supported microbolometer. No nonbolometric effect was distinguished.

ISSN:0034-6748    

DOI:10.1063/1.1144754

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Performing photothermal surface displacement (PTD) technique at &lgr;=10.6 &mgr;m in a vacuum chamber, the measured signal is obtained by the change in probe beam deflection at the bulge of the reflecting heated sample surface. The influence of the accuracy‐limiting quantities such as angle of incidence of the probe beam as well as its finite lateral extension, and the detector geometry and the temperature‐dependent reflection at the sample surface has been investigated by a numerically performed simulation in order to optimize the measuring procedure. The maximum resolution power is achieved for probe beam diameters small compared to the heating beam diameter. An unambiguous measurement may be carried out satisfying the following condition between the quad‐cell slit widthdslit, the probe beam diameter 2rPB, and the heating beam diameter 2rHB: 2rHB≥2rPB≫dslitkeeping the probe beam angle of incidence &agr;PBas small as possible. Moreover, it has been shown that the contribution of the temperature influenced reflection on the change of the probe beam intensity can be also neglected at &lgr;=10.6 &mgr;m.

ISSN:0034-6748    

DOI:10.1063/1.1144755

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

This article examines the measurement capabilities of a novel, two‐dimensional thermal imaging system based on the fluorescence properties of an europium‐doped lanthanum oxysulfide (La2O2S:Eu+3) thermographic phosphor. The foundation of the technique (i.e., the fluorescence properties of La2O2S:Eu+3), as well as the design of the thermal imaging system, are also described. The technique that is employed in the design of the system utilizes the tripled output of a pulsed Nd:YAG laser to excite the thin phosphor coating applied to a test surface. The resulting fluorescent emission of the temperature sensitive 512‐nm radiative transition, along with that of the relatively temperature independent 620‐nm transition, is acquired using an image‐intensified charge coupled device camera. The ratio of the intensities of these two emissions, integrated during their decay, is then correlated with temperature. Phosphor calibration data that is presented demonstrate the efficacy of the technique, while results of evaluations to assess the spatial resolution and measurement accuracy provide a quantitative measure of system capabilities.

ISSN:0034-6748    

DOI:10.1063/1.1144780

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A reliable method for deconvolving badly convoluted molecular beam time‐of‐flight waveforms using Fourier transform and Wiener filtering techniques is presented. The devised method places no restrictions on the functional form of any factors affecting the shape of the measured time‐of‐flight distribution, but rather uses an accurately determined distribution to estimate an overall response function for the system. The estimated response function may then be used to deconvolve any convoluted time‐of‐flight waveform measured under similar experimental conditions. The mathematical details of the method are discussed and examples of its application to the deconvolution of time‐of‐flight waveforms measured in unchopped pulsed supersonic beams of argon, krypton, CHCl3, and CH3Cl are presented.

ISSN:0034-6748    

DOI:10.1063/1.1144781

出版商:AIP    

年代:1994

数据来源: AIP