摘要:

To observe the products of surface reaction mechanisms we combined a standard quadrupole mass spectrometer featuring high‐speed scanning options with fast data acquisition and a computer‐controlled sample heating system. This combination served to obtain a general view (like a ‘‘fingerprint’’) of the reaction occurring on a Pt(100) crystal upon heating the adsorbate covered surface, as well as to allow for a detailed analysis of the gas compounds leaving the surface within a single measurement. The method is denoted by multimass thermal desorption spectroscopy (MTDS). The MTDS device is capable of recording 850 amu/s providing up to 15 complete mass spectra per second of 50 amu width while heating the surface linearly. The data contain the ion currents of both the reaction products and their fractions (cracking patterns) generated in the spectrometer. Thus it is possible to distinguish between gas species with equal mass numbers by subsequent numerical evaluation.

ISSN:0034-6748    

DOI:10.1063/1.1145196

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The spray extractor for sampling volatile organic compounds in water, reported in Rev. Sci. Instrum.63, 3196 (1992), has been modified and optimized for high extraction efficiencies. A low‐flow spray nozzle is placed in the spray chamber, which produces very small droplets at water flow rates around 80 ml/min. Compounds extracted during a 2 min sampling period are trapped in a sorbent tube and analyzed by gas chromatography/mass spectrometry. With carrier gas (nitrogen) flow rates around 250 ml/min, spray‐and‐trap efficiencies up to 62% (tetrachloroethene) were achieved for various volatile organic compounds.

ISSN:0034-6748    

DOI:10.1063/1.1145197

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The decay of coherently prepared excited triplet state can be observed by pulse optically detected magnetic resonance (ODMR). Analysis of this data yields important information about the various relaxation pathways open to a molecule in a given environment. Pulse ODMR requires shorter pulses with higher resolution than those used in pulse nuclear magnetic resonance. Programmable pulse train generators are commercially available, but they can be costly. In this article, a fully programmable photon counter‐pulse train generator interface is described which has the required resolution and speed. The interface cards occupy two slots of a personal computer and are based on advanced Shottky transistor–transistor logic series of logic circuits. This inexpensive, yet highly flexible apparatus for use in pulse ODMR, can be adapted for other applications, such as pulse magnetic resonance and photon counting. In addition, the modular design allows easy expansion to multichannel pulse or photon counting and to the generation of even the most imaginative pulse sequences.

ISSN:0034-6748    

DOI:10.1063/1.1145198

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A very simple and inexpensive electrolytic jet thinning apparatus for rapid thinning of metal foils for transmission electron microscopy has been described. Regarding the specimen holder assembly, either a polytetrafluoroethylene (PTFE) holder or a platinum tipped locking tweezer‐type holder, can be attached electrically and mechanically to a micromanipulator to be used in the same jet thinning apparatus. This gives a unique feature to our unit, in which the specimen remains above the electrolyte during the polishing process. Also the constructional simplicity of the unit provides easy drainage of the electrolyte for lengthy polishing and a simple way of stopping the thinning process. Transmission electron micrographs of bombarded and unbombarded specimens electrothinned in the unit are presented herein.

ISSN:0034-6748    

DOI:10.1063/1.1145141

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

In this article, a theoretical model for type I magnetic contrast calculations in the scanning electron microscope with energy filtering is presented. This model uses an approximate form of the secondary electron (SE) energy distribution by Chung and Everhart [M. S. Chung and T. E. Everhart, J. Appl. Phys.45, 707 (1974). Closed form analytical expressions for the contrast and quality factors, which take into consideration the work function and field‐distance integral of the material being studied, are obtained. This analytical model is compared with that of a more accurate numerical model. Results showed that the contrast and quality factors for the analytical model differed by not more than 20% from the numerical model, with the actual difference depending on the range of filtered SE energies considered. This model has also been extended to the situation of a two‐detector (i.e., detector A and B) configuration, in which enhanced magnetic contrast and quality factor can be obtained by operating in the ‘‘A–B’’ mode.

ISSN:0034-6748    

DOI:10.1063/1.1145243

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We describe the apparatus, instrumentation, and data acquisition techniques which make up the micromagnetic scanning microprobe system (MSMS). This system was developed to study magnetoresistive (MR) thin films used in magnetic recording read heads. It uses a dc, four‐probe resistance measurement coupled with two pairs of orthogonal field sources. Voltage contacts to the thin film are made with microprobe tips 0.1 &mgr;m in diameter on local edge and central regions of the film. Horizontal and vertical microscopes are used to verify tip placement. Results from magnetoresistance measurements of the dynamic response of a MR read head film are shown to demonstrate system operation and performance. The bulk and local magnetoresistance of a 10 &mgr;m×10 &mgr;m NiFe thin film was measured as a function of applied field and angle. Significant variations in MR responses were seen across the width of the device because of local domain formation. The MSMS is an effective tool for characterizing the effects of domain formation on the output of a MR read head.

ISSN:0034-6748    

DOI:10.1063/1.1145142

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We report on the adaptation of a commercially available scanning force microscope (SFM) for the simultaneous measurement of electrical and mechanical surface properties combining the scanning tunneling microscope, the SFM, and the friction force microscope. Furthermore, the microscope may be operated in the noncontact or attractive mode (AC‐SFM) which is specially suited for the nondestructive investigation of soft sample surfaces.

ISSN:0034-6748    

DOI:10.1063/1.1145143

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The conventional deflection‐mode atomic force microscope operates by optically monitoring the slope near the end of a microcantilever in contact with the sample surface. This signal is usually interpreted as a measure of height change. Lateral forces from friction, surface geometry, or inclination of the cantilever to the surface also affect the slope due to cantilever buckling. We calculate the deflection of a hollow triangular model cantilever subject to both lateral and normal forces. The measured response of the servo circuit to an inclined, loaded cantilever is then determined. This shows (1) errors are always present in height measurements of structures on inhomogeneous surfaces; (2) the sensitivity to buckling can be reduced by repositioning the laser; (3) friction measurements can be accurately made by scanning in two directions and applying the proper calibration.

ISSN:0034-6748    

DOI:10.1063/1.1145144

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Details of the construction of a scanning tunneling microscope (STM) are given in this article. This STM enables one to change the atmosphere around the sample easily from air to inert gases or to vacuum. The STM is compatible with a chamber in which metallic clusters are prepared.

ISSN:0034-6748    

DOI:10.1063/1.1145145

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We have studied the feasibility of using carbon as a scanning tunneling microscopy tip material for experiments conducted under electrochemical environments. The tips were found to be stable and durable in acidic or alkaline solution for several hours. The fabricated carbon tips were capable of resolving graphite atoms in electrolyte solution under potentiostatic condition as well as in air.

ISSN:0034-6748    

DOI:10.1063/1.1145146

出版商:AIP    

年代:1994

数据来源: AIP