B. L. Blackford

A vertical/horizontal two‐dimensional piezoelectric driven inertial slider micropositioner for cryogenic applications

We have developed a simple, two‐dimensional piezoelectric tube device which uses the inertial slider method to achieve remote micropositioning in the vertical and horizontal directions. The motion of the slider car occurs with respect to a quartz rod which is attached to, and accelerated by the piezo tube. The vertical motion, against or with gravity, is achieved by activating the longitudinal mode of the piezo tube. The horizontal motion is a rotation about the quartz rod, achieved by activating the bending mode of the piezo tube. The device is very compact, works at cryogenic temperatures and is ultrahigh vacuum compatible. Step sizes from 10 to 3000 nm and speeds up to 0.2 mm/s are possible. A computer simulation model of the inertial slider process has been developed also, to investigate the effectiveness of various activating waveforms. It confirms the advantage of a cycloidal‐like waveform recently reported in the literature. Also, the model predictions are consistent with the results obtained in th...

A scanning force microscope with a fiber‐optic‐interferometer displacement sensor

We present a simple optic‐fiber displacement sensor for a scanning force microscope (SFM). The design minimizes the alignment difficulties after a cantilever is changed and is easily adaptable to tube scanners so very compact SFM designs should be possible for imaging at low temperatures or in strong magnetic fields. We also provide a theoretical analysis and results to show that the sensitivity of the device can be improved by increasing the reflectivity of the fiber end. The increased sensitivity makes it possible to work under fluids.

Simple two‐dimensional piezoelectric micropositioner for a scanning tunneling microscope

A simple piezoelectric tube device is described which allows remote micropositioning in two dimensions with step sizes from ∼50 to ∼3000 nm. Speeds up to 0.1 mm/s have been achieved. It uses the principle of inertial sliding of a mass on an accelerated support. The design is a modification of a one‐dimensional device which was recently reported in the literature. The device is compact, rigid, and has low thermal drift.

Scanning tunneling microscope with micrometer approach and thermal compensation

A scanning tunneling microscope that uses a micrometer coarse approach mechanism is described. The approach mechanism can be decoupled from the rest of the microscope to result in a thermally compensated instrument. Thirty minutes after establishing tunneling, lateral thermal drift in our instrument is down to 0.5 A/min. Construction details of the microscope and high resolution images of pyrolytic graphite and 2H‐NbSe2 samples are presented.

Piezoelectric bimorph‐based translation device for two‐dimensional, remote micropositioning

We describe a two‐dimensional, remote micropositioning device that uses the bending mode of a piezoelectric bimorph for walking in the forward/reverse direction of motion. For this mode of operation step sizes range from ∼50 to 5000 nm, with a voltage sensitivity of ∼10 nm/V. Speeds of about 1 mm/s are possible. In the lateral direction of motion, the linear extension mode of the bimorph is used, giving step sizes from ∼50 to 1000 nm, with a sensitivity of ∼2 nm/V. For the walking sequence, anodized aluminum feet are electrostatically clamped to an anodized aluminum baseplate. When used as the coarse positioner in a scanning tunneling microscope, the device requires less than 100 V operating voltage, thus eliminating the high‐voltage supply needed for previous piezoelectric walking devices. A circuit diagram for ‘‘joystick’’ control of the micropositioner is also described.

Scanning tunneling microscope imaging technique for weakly bonded surface deposits

An imaging mode for a scanning tunneling microscope is described in which the tunneling needle is periodically withdrawn from the surface under study in order to reduce the elastic interaction effects between needle and substrate during imaging. Examples of images of weakly bonded surface deposits that could not be imaged with the conventional sweep method are presented. The technique also makes it possible to first manipulate and subsequently image deposits that are weakly bonded to a substrate.

Scanning tunneling microscope imaging of hoops from the cell sheath of the bacteria methanospirillum hungatei and atomic force microscope imaging of complete sheathes

This paper describes techniques used to image the cell sheath of the archaebacterium methanospirillum hungatei. Scanning tunneling microscope (STM) studies were done on hoop‐shaped components separated from the cell sheath by chemical treatment. High‐quality images were only obtained when the hoops were dispersed on highly oriented pyrolytic graphite and overcoated with a conductor, although hopping scans occasionally could image uncoated sheath fragments. Atomic force microscope (AFM) studies of the entire sheath showed the characteristic surface corrugation that was also seen in STM and in electron microscope images. We suggest that the STM imaging of any large biological structures may be limited principally by low electrical conductivity, although tip‐sample interactions and poor adhesion to the substrate also contribute to difficulties in the technique.

Tunneling microscopy of NbSe2 in air

We have obtained atomic‐resolution images of NbSe2 single crystals in air. Constant‐height images clearly show the expected atomic structure, and can distinguish the two inequivalent halves of the unit cell. Constant‐current images show an anomalously high atomic corrugation, associated with elastic deformation of the sample. Surface contamination probably plays an important role in transmitting the tip‐sample forces. A larger‐scale apparent buckling of the surface with a period of several times the atomic spacing is sometimes observed.

A simple self‐propelled two‐dimensional micropositioner

A quartz tube is propelled horizontally along a quartz track by the stick‐slip inertial slider method, activated by the longitudinal mode of a piezoelectric tube mounted inside the quartz tube. Two‐dimensional motion is achieved by rotation of the quartz tube, activated by the bending mode of the piezo. With a sample attached to the quartz tube, the device is an excellent replacement for the electrostatic‐clamp type of walker used as the coarse approach mechanism in scanning probe microscopes (SPMs). Alternatively, by attaching the tip (or sample) to the piezo tube, the device can function as a very simple SPM in which the same piezo tube is used for coarse approach and for scanning. The device performs reliably in air and high vacuum, and is ultrahigh vacuum compatible. Step sizes from 10 to 1000 nm, and speeds up to 0.2 mm/s are possible.

Atomic force microscope measurements of long-range forces near lipid-coated surfaces in electrolytes.

The interaction of DMPC (L-alpha-dimyristoyl-1,2-diterradecanoyl-sn-glycero-3-phosphoch oli ne, C36H72NO8P) lipid-coated Si3N4 surfaces immersed in an electrolyte was investigated with an atomic force microscope. A long-range interaction was observed, even when the Si3N4 surfaces were covered with nominally neutral lipid layers. The interaction was attributed to Coulomb interactions of charges located at the lipid surface. The experimental force curves were compared with solutions for the linearized as well as with exact solutions of the Poisson-Boltzmann equation. The comparison suggested that in 0.5 mM KCl electrolyte the DMPC lipids carried about one unit of charge per 100 lipid molecules. The presence of this surface charge made it impossible to observe an effective charge density recently predicted for dipole layers near a dielectric when immersed in an electrolyte. A discrepancy between the theoretical results and the data at short separations was interpreted in terms of a decrease in the surface charge with separation distance.