Showing papers by "Stuart T. Smith published in 1996"

A controlled-force stylus displacement probe

Abstract: A novel design of displacement profiler with a controllable stylus force is presented. It provides highly controlled conditions for contact measurement of, for example, small step heights or surface roughness. Incorporating an electromagnetic force actuator and force feedback control, the profiler provides electronically selectable contact force in the range of 0.01–10 mN and gives a constant static and dynamic loading. In a typical configuration, it has a range of a few micrometers with a discrimination to better than 1 nm at a bandwidth higher than that of a conventional stylus instrument.

X-Ray calibrated tunneling system utilizing a dimensionally stable nanometer positioner.

Abstract: To determine to what extent tunneling probes can be used for metrology or as position-sensitive transducers on the atomic scale, accurate characterization of tunneling current as a function of distance must be ascertained. This report describes a system for making such characterizations and observing their repeatability in air. Also, it is often necessary to position two objects to within nanometers in order to perform precision measurements. Included in the narrative, a dimensionally stable screw-wedge-lever system is described for manually moving a tunneling probe to within 15 nm of a conducting surface. The conducting surface is translated via a magnetically actuated single crystal flexure system previously calibrated through direct x-ray interferometry over a 20-nm range. This limited calibration range dictated dimensional positioning below 15 nm. Also, tunneling current measurements demanded dimensional stability below one nanometer. The complete system is demonstrated to hold the relative probe-surface separation to within 1 nm over a 15-minute duration. Also, the vibrational resonance of the structure is determined using the power spectrum analysis during electron tunneling. Resulting data using platinum, palladium, and silver tips in conjunction with a carbon surface show that current-displacement values vary from run to run with a positional difference of up to 1 nm for a given current. These variations suggest limitations for using tunneling probes in air to perform angstrom metrology.

Metrological x-ray interferometry in the micrometre region

Abstract: A `free-standing' microdisplacement calibrator is described which utilizes a previously proposed but untested design of monolithic x-ray interferometer. The monolith is driven by a twist-compensating electromagnetic actuator and a specially designed 1 ppm current source and is held, along with its x-ray source and detectors, within a desk-top-mounted radiation enclosure. It is confirmed that highly traceable displacements resolved to a small fraction of a nanometre can be obtained over a continuous range of at least under conditions typical of a routine metrology room. An overview of the system and its performance is given, but this paper concentrates particularly on the monolith design and on vibration suppression

A metrological scanning force microscope

Abstract: In last decade, there has been a tremendous progress in scanning probe microscopies, some of which have achieved atomic resolution. However, there still exist some problems which have to be solved before the instrument can be used as a metrological measurement tool. The object of the project introduced in this thesis was to develop a scanning force microscope of metrological capability with the aim of making significant improvement in scanning force microscopy from the viewpoint of instrumentation. A capacitance based force probe has been studied theoretically and experimentally with the main concern being its dynamic properties, characterized by squeeze air film damping, which are believed to have direct effects on the fidelity of measurement. The optimization of design is investigated so as to achieve the results of both high displacement sensitivity and force sensitivity. An x-y scanning stage has been designed and built, which consists of a two axis linear flexure system of motion amplifying mode machined from a single aluminium alloy block. The stage is driven by two piezo actuators with two capacitance sensors monitoring the actual position of the platform to form a closed loop control system. The design strategy is introduced and the performances and characteristics of two commonly used types of flexure translation mechanisms, leaf spring and notch hinge spring system, are analyzed. The finite element analysis method is employed in the analysis and design of translation mechanism. Finally, a metrological scanning force microscope has been constructed, combining a constant force probe system, an x-y scanning stage and a 3D coarse positioning mechanism into a metrological system. The performance of the instrument system has been systematically evaluated and its measuring capability investigated on the. specimens of various properties and features. The results from this first prototype of the instrument demonstrated a subnanometer resolution with comparable stability and repeatability in all three axes.

A super-precision linear slideway with angular correction in three axes

Abstract: This paper describes a single-axis ultra-high-precision translation stage designed and built using almost exclusively the very-low-thermal-expansion ceramic Zerodur. The device is a test-bed for design principles which may be widely applied for various purposes of different precision. It has compensation for pitch, roll and yaw built into the mechanism through the incorporation of three angular sub-stages. The sliding carriage stands on five PTFE pads to form a single-degree-of-freedom kinematic constraint giving rectilinear traverse along an optically flat prism. The translation resolution is at the angstrom level and the angular adjustments are at the sub-arc-second level, with some at the milli-arc-second level, while possessing coarse adjustments with large range. Performance tests using an optical interferometer are reported and the stage's behaviour in the elastic and sliding region is studied to understand where the limits of the technology lie.

A portable three-dimensional stylus profile measuring instrument

Abstract: This paper describes the development of an inexpensive, portable three-dimensional (3-D) stylus-based surface profiler with a scan range of 4.5 mm × 5.5 mm and a maximum vertical range of 150 μm (limited by signal conditioning electronic range) with a resolution of better than 0.9 μm and a range of 30 μm with a resolution of better than 30 nm at the highest vertical sensitivity. The instrument occupies a volume with dimensions of approximately 75 × 75 × 40 mm (L × B × H) with scan speeds up to 0.5 mm s −1 . Construction of instrument components from similar material results in a thermally balanced design with a reasonably low thermal coefficient of 0.27 μm K −1 and a first-order time constant of approximately 40 min. The stylus probe sensor has a free resonant frequency of 49 Hz and a low damping ratio of 0.006. When in stationary contact with a steel surface, this increases to above the transducer bandwidth of 900 Hz. Calibration of the probe sensor is achieved through direct comparison against a standard stylus gauge. Lateral calibration of the specimen carriage position has been assessed by the measurement of standard gratings and laser interferometry. Planar errors caused by the motion of the carriage have been assessed by measuring an optical flat and inferring deviation from a perfect plane as an indication of the worst-case error, which in this case, was 0.2 μm (P-V). The design and construction of the internal datum and the portability of the instrument to facilitate in situ measurement of components are emphasized. Images illustrating the surface mapping capabilities of the profiler are presented.