12,912 research outputs found
Variable - temperature scanning optical and force microscope
The implementation of a scanning microscope capable of working in confocal,
atomic force and apertureless near field configurations is presented. The
microscope is designed to operate in the temperature range 4 - 300 K, using
conventional helium flow cryostats. In AFM mode, the distance between the
sample and an etched tungsten tip is controlled by a self - sensing
piezoelectric tuning fork. The vertical position of both the AFM head and
microscope objective can be accurately controlled using piezoelectric coarse
approach motors. The scanning is performed using a compact XYZ stage, while the
AFM and optical head are kept fixed, allowing scanning probe and optical
measurements to be acquired simultaneously and in concert. The free optical
axis of the microscope enables both reflection and transmission experiments to
be performed.Comment: 24 pages, 9 figures, submitted to the journal "Review of Scientific
Instruments
Improvement of control and analysis techniques of a SPM model
Bakalářská práce se zabĂ˝vá zdokonalovánĂm vĂ˝ukovĂ©ho modelu mikroskopu atomárnĂch sil (AFM). SoučástĂ práce je rešerše stávajĂcĂch analogii mezi makroskopickĂ˝mi jevy a fenomĂ©ny spojenĂ˝mi s mikroskopii rastrovacĂ sondou. Dále byla vybrána vhodná analogie, která byla následnÄ› implementována do jiĹľ existujĂcĂho modelu mikroskopu atomárnĂch sil. Do modelu byl integrován i jednodeskovĂ˝ poÄŤĂtaÄŤ, kterĂ˝ zajistĂ ovládánĂ i bez nutnosti pĹ™ipojenĂ externĂho poÄŤĂtaÄŤe. Na závÄ›r byly vyhodnoceny vlastnosti pouĹľitĂ© sondy a analogie mezi modelem a skuteÄŤnĂ˝mi mikroskopy atomárnĂch sil.This Bachelor Thesis is focused on development of a model of an atomic force microscope (AFM). First part of the thesis is research of already existing analogies between macroscopic phenomena and phenomena connected to scanning probe microscopy. A suitable analogy was chosen and implemented into an existing AFM model. A single-board computer was integrated into the model to enable control without connecting an external computer. In final chapters, probe behaviour and analogies between the model and real atomic force microscopes are discussed.
Scanned-cantilever atomic force microscope
We have developed a 3.6 µm scan range atomic force microscope that scans the cantilever instead of the sample, while the optical-lever detection apparatus remains stationary. The design permits simpler, more adaptable sample mounting, and generally improves ease of use. Software workarounds alleviate the minor effects of spurious signal variations that arise as a result of scanning the cantilever. The performance of the microscope matches that of scanned-sample instruments
Design and Performance of a Practical Variable-Temperature Scanning Tunneling Potentiometry System
We have constructed a scanning tunneling potentiometry system capable of
simultaneously mapping the transport-related electrochemical potential of a
biased sample along with its surface topography. Combining a novel sample
biasing technique with a continuous current-nulling feedback scheme pushes the
noise performance of the measurement to its fundamental limit - the Johnson
noise of the STM tunnel junction. The resulting 130 nV voltage sensitivity
allows us to spatially resolve local potentials at scales down to 2 nm, while
maintaining angstrom scale STM imaging, all at scan sizes of up to 15 um. A
mm-range two-dimensional coarse positioning stage and the ability to operate
from liquid helium to room temperature with a fast turn-around time greatly
expand the versatility of the instrument. By performing studies of several
model systems, we discuss the implications of various types of surface
morphology for potentiometric measurements.Comment: 16 pages, 17 figures, accepted to Review of Scientific Instruments v2
- minor changes: cleaned up figures/figure caption
Biophysical Measurements of Cells, Microtubules, and DNA with an Atomic Force Microscope
Atomic force microscopes (AFMs) are ubiquitous in research laboratories and
have recently been priced for use in teaching laboratories. Here we review
several AFM platforms (Dimension 3000 by Digital Instruments, EasyScan2 by
Nanosurf, ezAFM by Nanomagnetics, and TKAFM by Thorlabs) and describe various
biophysical experiments that could be done in the teaching laboratory using
these instruments. In particular, we focus on experiments that image biological
materials and quantify biophysical parameters: 1) imaging cells to determine
membrane tension, 2) imaging microtubules to determine their persistence
length, 3) imaging the random walk of DNA molecules to determine their contour
length, and 4) imaging stretched DNA molecules to measure the tensional force.Comment: 29 page preprint, 7 figures, 1 tabl
Nanoscale intermittent contact-scanning electrochemical microscopy
A major theme in scanning electrochemical microscopy (SECM) is a methodology for nanoscale imaging with distance control and positional feedback of the tip. We report the expansion of intermittent contact (IC)-SECM to the nanoscale, using disk-type Pt nanoelectrodes prepared using the laser-puller sealing method. The Pt was exposed using a focused ion beam milling procedure to cut the end of the electrode to a well-defined glass sheath radius, which could also be used to reshape the tips to reduce the size of the glass sheath. This produced nanoelectrodes that were slightly recessed, which was optimal for IC-SECM on the nanoscale, as it served to protect the active part of the tip. A combination of finite element method simulations, steady-state voltammetry and scanning electron microscopy for the measurement of critical dimensions, was used to estimate Pt recession depth. With this knowledge, the tip-substrate alignment could be further estimated by tip approach curve measurements. IC-SECM has been implemented by using a piezo-bender actuator for the detection of damping of the oscillation amplitude of the tip, when IC occurs, which was used as a tip-position feedback mechanism. The piezo-bender actuator improves significantly on the performance of our previous setup for IC-SECM, as the force acting on the sample due to the tip is greatly reduced, allowing studies with more delicate tips. The capability of IC-SECM is illustrated with studies of a model electrode (metal/glass) substrate
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