摘要:

Drift, slope of sample, and indeterminate sensitivity of piezoceramics are considered as the origin of the linear scanning tunneling microscope (STM) image distortions. A special algorithm of STM scanning and reconstruction of image of unknown atomic structures is suggested and tested. This algorithm allows us to measure three components of the drift velocity and two angles, characterizing the average slope of scanning surface. On the one hand, using this algorithm, one can perform the STM calibration by a known surface structure (for example, the highly oriented pyrolytic graphite surface) even in the presence of a drift. This enables us to determine all the three piezoceramics constants of STM piezoscanner and the deviation of the real scanner axesXandYfrom orthogonality. On the other hand, using such a calibrated STM and the described algorithm, it is possible to obtain the real STM image and make measurements for unknown surfaces with atomic resolution without the distortions mentioned above. As it has been proved, the error of interatomic distance measurements does not exceed 5% (∼0.1 A˚) for any direction along the surface, even in the presence of a drift up to 0.4 A˚/s and the sample slope angle up to 10°.

ISSN:0034-6748    

DOI:10.1063/1.1144890

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Tungsten tips obtained through electrochemical etching have been characterized by scanning electron microscopy, scanning Auger microscopy, and scanning tunneling microscopy. While such tips resulted to be very sharp, a thick oxide layer (∼10 nm) is present at the apex. High‐vacuum annealing at 1800 K removes most of such oxide.

ISSN:0034-6748    

DOI:10.1063/1.1144891

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Nanoindentation measurements performed using the atomic force microscope (AFM) are significantly affected, both with regard to indentation curve shape and quantitative values of the measurements (70% variation in measured modulus), by the well‐known effects of hysteresis and creep in the lead zirconate titanate (PZT) piezoceramic actuators used to control the positioning and motion of the mechanical components of the AFM. A capacitance‐based displacement calibrator has been built and it was discovered that the response of PZT ceramics may vary (up to 66%) depending upon the conditions under which the piezoceramic is calibrated. By replacing the PZT actuators with lead magnesium niobate (PMN) electrostrictive actuators, nanoindentation measurements have been obtained using the AFM that are both reproducible and quantitative.

ISSN:0034-6748    

DOI:10.1063/1.1144892

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A new dynamic model is developed for analyzing the dynamic process of piezoelectric stepmotors. In this model the voltage applied to the piezoelectric stepmotor is equivalent to the force acting on the end of the piezoelectric stepmotor. The model is simple and convenient for applications. As an example, a model of analyzing the rotatable sample stage is presented. The theoretical results are in good agreement with the experimental results. The structural damping of the piezoelectric material is also discussed.  

ISSN:0034-6748    

DOI:10.1063/1.1145213

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

An ultraclean accelerator mass spectrometry negative ion source for semiconductor material mass analysis has been built and is in operation at the University of North Texas’ Ion Beam Modification and Analysis Laboratory (IBMAL). The source is unique in that the active surfaces and apertures of the optical components in the ion source have been fabricated from high‐purity single crystal silicon. This prevents both the133Cs+beam incident on the semiconductor samples and the negative ions from the sample surfaces from ‘‘seeing’’ and sputtering any metal surfaces (mostly stainless steel) in the beamline. The Cs+beam can be rastered across the sample surface and the impact energy is adjustable to control depth‐profiling rates. An ultraclean ion source of this type is necessary to prevent the injection of Fe and other beamline elements onto the sample or into the tandem accelerator, which is equivalent to putting an impurity signal into the mass analysis of the semiconductor sample. Suppression of these elements increases the sensitivity of the analysis to one part in 1012for many masses. The fabrication and alignment of the optical components—einzel lenses, steerers, raster/scanners, and Faraday cups—in the negative ion source will be presented. Also, simulation trajectories are presented to show (1) the interaction of the incident Cs+ion beam, the semiconductor sample, and holder (biased up to −30 kV), the extracted beam in the sample chamber, and associated potential field lines; and (2) the potential field lines of the octupole steerers.

ISSN:0034-6748    

DOI:10.1063/1.1144893

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Medium energy (100–300 keV) time‐of‐flight spectrometry for surface analysis uses the correlated detection of an energetic ion and the secondary electrons emitted as it passes through a carbon foil. When microchannel plates are employed in this detection scheme, a typical mean efficiency of detection of less than 30% is achieved. When instead a surface barrier detector is used to detect the ion, providing simultaneous acquisition of velocity and energy information, certain advantages are realized over the two microchannel plate configuration in the characterization of low level constituents of surfaces. Specifically, energy‐discriminated gating of the start pulse was observed to nearly eliminate count rate dependent background in a time‐of‐flight spectrum. Further reduction in background was obtained by the selective elimination of forward recoil species or backscatters from the substrate. Replacement of the stop microchannel plate by a surface barrier detector has resulted in improved detection efficiency for He, as well as provided a means for further study of the processes which affect time‐of‐flight spectrometer response, including multiple scattering and secondary electron emission in the start foil. In this publication, we describe the application of this particle telescope to the backscattering analysis of gold on silicon and the forward scattering measurement of hydrogen in a self‐supporting carbon film.

ISSN:0034-6748    

DOI:10.1063/1.1144894

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A succinct model is proposed to describe non‐ideal characteristics owing to electric field penetration into the drift region in actual parallel plate energy analyzers. A good agreement has been obtained between the theoretically expected and experimentally observed focus properties of the 30° parallel plate analyzer.

ISSN:0034-6748    

DOI:10.1063/1.1144895

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Exact solutions of the second‐order differential equation describing the energy dependence of ion flight time in a reflectron time‐of‐flight mass spectrometer are derived, from which numerical evaluation of the construction and operation parameters of a dual‐stage reflectron can easily be performed. Considerations in choosing the design parameters are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1144896

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

An electron cyclotron resonance (ECR) plasma is produced at pressures up to 10 mTorr with a circular TE01mode microwave. The plasma density is almost radially uniform even at 10 mTorr. SiC films are formed on silicon wafers by introducing methane gas into the ECR plasma. It is shown that a circular TE01mode microwave is useful for the ECR plasma chemical vapor deposition (CVD).  

ISSN:0034-6748    

DOI:10.1063/1.1144897

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A washer plasma gun for alkali‐metal plasma is developed. This gun is suitable as a source for experiments on alkali‐metal plasmas, plasma diagnostics, and in various applications such as ion‐beam sputter deposition. The gun uses an injector of alkali‐metal vapor based on the principles of laser ablation. Acceleration is performed by a large electrical field provided across eight washers. The gun is compact, stable, and easy to fabricate and use. The gun produces a neutral Li0beam current of 1 A/cm2and a Li+ion current of 50 A/cm2at its exit at 10 kV of capacitor bank voltage. With this intensity, it is possible to produce beams of neutral Li0atoms of density 6×109cm−3and Li+ions of density ∼1011cm−3at 1 m from the gun, moving with a velocity of ∼107cm/s.  

ISSN:0034-6748    

DOI:10.1063/1.1144898

出版商:AIP    

年代:1994

数据来源: AIP