摘要:

A NMR programmer is described which is built around a logic idea and a set of specifications, rather than availability of special or new integrated circuits. We begin by discussing what a quintessential Touring machine can do to solve the problem of outputting words (or pulses) with the resolution of the system clock over arbitrarily long time intervals. We then illustrate a simple realization of this machine, with 4096 program lines, 25‐ns resolution, two 16‐bit output lines, the possibility of nesting loops down to the 256th level, and a component cost in the 102$ range. A software ‘‘human’’ interface has been developed in an IBM‐PC compatible (MS‐DOS) environment, which simplifies the task of debugging the entire NMR spectrometer, and that of designing new experiments. While certainly overspecified for all traditional solid‐state NMR experiments, our programmer may meet the requirements of recently suggested selective excitation and imaging experiments in liquids.

ISSN:0034-6748    

DOI:10.1063/1.1138599

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The design and application of a detector is described, which is capable of simultaneously measuring energy and angular distributions of neutral particles desorbed from surfaces. Specific applications to ion bombardment studies are presented. The detector utilizes the state selectivity, sensitivity, and pulsed characteristics of multiphoton resonance ionization as a time‐of‐flight sensitive postionization technique. A microchannel‐plate element allows position‐sensitive detection of the laser‐ionized particles. Sample data are presented for ground‐state Rh atoms desorbed from clean, ion‐bombarded Rh foil and Rh(111) surfaces.

ISSN:0034-6748    

DOI:10.1063/1.1138600

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Two different signal‐processing systems are described for the conversion of reflection high‐energy electron diffraction (RHEED) patterns, displayed on a phosphor screen, into quantitative data. Both systems are based on the use of a sensitive video camera. One system using a multichannel boxcar integrator is particularly suited to simultaneous temporal measurements of different RHEED beams and integrated line intensities, while the other can be applied to fast data acquisition of line profiles. The system performance is illustrated and discussed.

ISSN:0034-6748    

DOI:10.1063/1.1138601

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

An ultrahigh‐vacuum scattering chamber working in the low 10−9‐mbar range is described. It is attached to a standard O‐ring sealed beam transport system of an electrostatic accelerator. Twelve targets can be preparedinsitu, one by one, by evaporating the material onto backings, which are mounted on tiltable target holders on a wheel. Backscattering spectra are obtained from these targets and the stopping cross section is deduced from their widths. A cooled high‐resolution surface barrier detector is used for this purpose. The integral concentrations of light impurities in the target are obtained using Rutherford backscattering (RBS), whereas Auger electron spectrometry (AES) together with a sputtering device is used to determine the depth composition. As a test of the assembly we determined the stopping power of aluminum for protons and deuterons, respectively. The results are compared to published tables based upon fits to experiments. The influence of impurities on the result is discussed for an aluminum target prepared under standard evaporation conditions.

ISSN:0034-6748    

DOI:10.1063/1.1138602

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A fast computer‐controlled and fully automated deep level transient spectroscopy (DLTS) system is described. Various DLTS techniques can be operated without changing the hardware. Simultaneous data acquisition and data processing considerably reduces the measurement time. The sensitivity of the system is increased by digital compensation of the sample capacitance and by averaging of a high number of transients. All the trap parameters are determined during one temperature scan.

ISSN:0034-6748    

DOI:10.1063/1.1138603

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Pulse‐field evaporation of III–V compound semiconductors was investigated employing our high‐performance time‐of‐flight atom probe, which accommodates the demand for precise knowledge of both mass (focusing type) and energy deficits (straight type) of field‐evaporated ion species. We show that laser‐pulse mode can yield correct compositions only if an appropriate dc holding field range is used, which is 0.35 to 0.65 for the GaAs presently studied.

ISSN:0034-6748    

DOI:10.1063/1.1138604

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A technique is described for attaching thin, conformal, pin‐hole‐free electrically insulating polyethylene films to flat gold surfaces (previously modified by adsorption of a monolayer of an organic disulfide) by plasma polymerization. These polyethylene films are tough enough to support the attachment of gold electrodes.

ISSN:0034-6748    

DOI:10.1063/1.1138605

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The resultant exotherms obtained from the photopolymerization of thin‐film chemical samples have been investigated. The radiant source used is a standard 200‐W in.−1mercury discharge lamp. About 55% of this power is in the infrared (IR) part of the spectrum, which is removed by a water‐cooled quartz tube. Different regions of the remaining spectrum were selected in the range 270–450 nm with cuton filters. A grating spectrometer is used to measure the transmitted spectra. A thin foil heat flow sensor is used as a calorimeter to measure the heat given off by a chemical sample when exposed to 0.5‐s pulses of ultraviolet (UV) radiation. The pulse is formed by means of a bistable electronic shutter. Data were taken for samples ranging from 0.0125 to 0.05 mm [0.5 to 2.0 milli‐inch (mils)] thicknesses. The heat output per gram is largest for the thinner samples and the absorption characteristics were observed to depend on the thickness of the sample.

ISSN:0034-6748    

DOI:10.1063/1.1138606

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The design and the utility of a glove‐box‐based fabrication system for inelastic electron tunneling junctions are described. The system consists of a stainless‐steel, turbomolecularly pumped ultrahigh‐vacuum fabrication system, mounted to the evacuable entrance chamber (vacuum box) of the glove box. The glove box is a recirculating, catalytically purified, argon‐based system, with a reactive impurity concentration below 2 ppm. In particular, there is ≲1‐ppm water vapor. To demonstrate the advantages of the system, junctions prepared with m‐cresol (3‐methylphenol) chemisorbed from both the vapor and the liquid phases are compared, as well as junctions prepared with ethanolamine (2‐aminoethanol) chemisorbed from the liquid phase both inside the glove box and externally in the laboratory atmosphere. Junctions prepared from the liquid phase with m‐cresol exhibit significantly greater intensities (higher surface concentration) compared to the vapor‐phase adsorption. The junctions prepared with ethanolamine exhibit spectral changes characteristic of different surface structures depending upon whether the adsorption is done in an inert atmosphere or in the laboratory atmosphere.

ISSN:0034-6748    

DOI:10.1063/1.1138607

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We have constructed a compact, inexpensive, high‐speed electrometer for use in xerographic voltage measurements. The device consists of a single operational amplifier stage. The type of amplifier is selected to fit the particular experiment. Amplifiers with frequency responses from dc to 100 MHz and input resistances of up to 10+13&OHgr; are available. Measurements on amorphous selenium have shown this type of electrometer to be more versatile than commercially available units.

ISSN:0034-6748    

DOI:10.1063/1.1138608

出版商:AIP    

年代:1986

数据来源: AIP