摘要:

An instrument which incorporates an electrostatic scanning electron microscope and a scanning tunneling microscope in an ultrahigh vacuum environment has been developed to study nanostructures. To facilitate positioning the nanostructures for examination with the instrument a high precision orthogonal motion sample stage has been designed. The instrument has been applied to locate and study both nanometer size trenches and wires. These structures have been fabricated using electron beam lithography and a polymethlymethacrylate lift‐off process.

ISSN:0034-6748    

DOI:10.1063/1.1143262

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

When scanning steeply sloped features which are near micron size or taller, scanning tunneling microscopes with conventional feedback control loops exhibit slower response on downhill slopes than on uphill slopes. This effect is caused by the exponential dependence of the tunneling current on the tip‐sample distance. A gap smaller than the setpoint produces a sizable error signal, whereas a gap larger than the setpoint gives only a weak error signal. As the scan rate is increased, the tip begins ‘‘flying’’ well above the surface on steep downhill regions. We have developed a modification of the conventional integral feedback system which eliminates this problem. This circuit makes the error signal growth withincreasingdistance between the tip and sample similar to the usual exponential growth when the tip‐sample distance decreases. This modification allows an increase in scan rates by a factor of 5–10 with no reduction in image quality. The modification can be dialed in or out of circuit as needed, such as when switching between large scale images and atomic scale images, and can easily be installed in any existing scanning tunneling microscope that uses an analog feedback circuit.

ISSN:0034-6748    

DOI:10.1063/1.1143263

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A design is presented for a scanning tunneling microscope (STM) capable of operation over a temperature range of approximately 80–350 K in ultrahigh vacuum. An integral inchworm‐like sample translation device avoids problems with unreliability and lock‐up by using clamping elements which have an unusually large range of motion. The entire STM, including the sample and the tip, are held isothermal. Temperature drift is less than 0.1 A˚/min. A set temperature may be maintained, within 2°, for over 10 h. Operation of the instrument is demonstrated with an image of the Si(001) surface recorded at 120 K.

ISSN:0034-6748    

DOI:10.1063/1.1143264

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A chemical vapor deposition method is described for fabricating force microscope cantilevers with single‐crystal diamond tips. The &bartil;1‐&mgr;m‐diam diamond tips have corner radii of 30 nm, and have been used to study diamond–diamond friction on well‐characterized surfaces in UHV. The tip size and orientation can be determined by electron microscopy without altering the surface atomic structure.

ISSN:0034-6748    

DOI:10.1063/1.1143265

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An automatic system has been completed for conditioning cold field‐emission tips to obtain high flux density and low‐noise emission. It was designed as a real‐time control and operating system for the electron source of a new sextupole‐corrected scanning transmission electron microscope and is able to condition the tipinsitu. All of the control devices in this system are interfaced to a computer and communication across the electric field created by the 200‐kV acceleration voltage is accomplished with light pipes. A program, written in Pascal, controls the conditioning process. This system has been utilized to experimentally determine the optimal flash level for a newly fabricated tip as well as performing corrective maintenance to the conditioned tip to extend its maximum useful lifetime.

ISSN:0034-6748    

DOI:10.1063/1.1143211

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

In this paper it is demonstrated that glass micropipettes have unique applicability as force probes for a variety of imaging conditions and a variety of scanned tip microscopies. These probes are characterized in terms of the parameters that determine their force characteristics. Measurements are presented showing that one can readily achieve force constants of 10 N/m and it is anticipated that a reduction in this force constant by two orders of magnitude can be achieved. Such probes can be produced simply with a variety of geometries that permit a wide range of force imaging requirements to be met. Specifically, the glass micropipette probes reported in this paper are readily produced with apertures at the tip and can thus be applied to near‐field scanning optical microscopy (NSOM). This opens the possibility of the long‐awaited development of a universal feedback mechanism for NSOM.

ISSN:0034-6748    

DOI:10.1063/1.1143212

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A computer‐controlled scan system has been completed for a sextupole‐corrected high‐resolution Scanning Transmission Electron Microscope. It is capable of driving 24 coils and 2 sextupoles in the microscope for beam scan, unscan, alignment, and correction of aberration. A PC‐AT is employed to manage this system and control the system devices. By means of these devices the raster size, shape, rotation angle, and dc offset can be controlled by subroutines for image generation/transformation. Computer control provides numerous advantages for the management of such a complicated system making it possible to modify many parameters and invoke a new group of settings simultaneously. This provides convenience in microscope operation for such functions as change in magnification, selection of viewing area, locations of objects of interest and montage.

ISSN:0034-6748    

DOI:10.1063/1.1143213

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A procedure is presented for systematically and reproducibly preparing alloy specimens for the study of grain boundary (GB) segregation employing both transmission electron (TEM) and atom‐probe field‐ion microscopies (APFIM) to examine thesameGB; the procedure is illustrated for an Fe(Si) alloy. A commercially available oxygen plasma source is incorporated in the sample preparation procedure to remove all traces of hydrocarbon build‐up introduced during TEM GB analysis, thus allowing controlled backpolishing after a TEM analysis. Specifications for the optimum tip geometry, i.e., how a GB is positioned in a tip via backpolishing to maximize the probability of its observation and subsequent compositional analysis via APFIM, are empirically determined: 30–200 nm for the GB‐to‐tip separation, and 40–80 nm for the GB diam for shank angles less than 20°. It is demonstrated that accurate quantitative APFIM analyses of an Fe‐3 at. % Si alloy are possible for pulse fractions ≥15% and specimen temperatures ≤55 K. Results are presented for a &Sgr;≊3aGB that was first analyzed via TEM to determine its five macroscopic degrees of freedom, and then analyzed via APFIM to measure an average GB segregation enhancement factor for Si of 3.51±0.34 at 823 K.

ISSN:0034-6748    

DOI:10.1063/1.1143214

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A scanning probe microscope has been integrated into a microwave resonator tunable from 2.2 to 3.4 GHz with a quality factorQlarger than 1000. Nonlinear phenomena caused generation of higher harmonics when rf fields in the range of 109V/m were applied between tip and sample. Higher harmonic signals were detected at a bandwidth of 10 kHz on conductor surfaces as well as on thin insulating films and were used as feedback to the control loop for imaging graphite surface features and oxidized silicon surfaces with subnanometer resolution.

ISSN:0034-6748    

DOI:10.1063/1.1143215

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A high‐power, power‐modulated transversely excited atmosphere (TEA) CO2laser system is developed with the intention of applying it to high‐temperature plasmas for diagnostic purpose. Two‐mode pulse injection locking is adopted to obtain the required output pulses of the TEA CO2laser. Together with the power modulation, the gain‐switched spike of the output pulses are also suppressed by the adopted method, resulting in pulse lengthening. Two feedback loops are incorporated for reliable power modulation. The power‐modulated output so obtained is used to excite electrostatic plasma waves in laboratory plasmas.

ISSN:0034-6748    

DOI:10.1063/1.1143216

出版商:AIP    

年代:1992

数据来源: AIP