Probe Tip Of Scanning Tunneling Microscope Research Articles

Study of the electrode tool wear and the probe tip sharpening phenomena during the nanoscale STM electric discharge lithography of the bulk HOPG surface

Scanning tunneling microscope (STM)-based electric discharge lithography or machining is capable of fabricating nanostructures or nano-devices out of the carbon-based materials with low cost and high accuracy. As a tip-based nanofabrication method, the evolution of the STM probe tip, which functionalized as the electrode tool, is of great importance to the machining capability and performance of the STM electric discharge lithography. In this work, both the electrode tool wear (ETW) and the probe tip sharpening phenomena were investigated during the SPM electric discharge lithography of the bulk highly oriented pyrolytic graphite (HOPG) sample surface. The influence of the electrode tool wear evolution on the machining results was experimentally studied. The geometric parameters of the STM probe tip were measured from SEM imaging. Moreover, the probe tip sharpening phenomenon was specifically observed by applying the negative polarity machining. The evidences of the underlying mechanisms for the tip sharpening effect were revealed experimentally in this study, which have never been reported in the previous work. It is further proved that this effect could be utilized to the in-situ sharpening of the STM probe tip. Finally, the effective methods to improve the machining consistency and the tool lifetime were proposed.

Giant fullerenes formed on C 60 films irradiated with electrons field-emitted from scanning tunneling microscope tips

It has been found that spherical large clusters of carbon atoms are formed by irradiation of crystalline C 60 films grown on Si(1 1 1)-(7 × 7) surfaces with electrons field-emitted from a scanning tunneling microscope probe tip. The size distribution of the clusters deduced from surface profile measurements suggests that the dominant clusters were not necessarily C 60 n ( n = 2–4) expected from the simple fusion of C 60 molecules. It was proposed that electronic excitations of C 60 molecules caused the fragment and coalescence of the molecules to form the giant fullerenes as in the photo-induced similar effects.

Learning the physics of a scanning tunnelling microscope using a computer program

The Scanning Tunneling Microscope (STM) Simulator is an interactive computer program designed specifically for pedagogical purposes, to enable students to learn how an STM works. The program is not designed to substitute a real STM, but rather to give students an insight into the physics of the STM. The program allows the student to start with any real STM image of a sample, taken elsewhere, observe the cross sectional profile of the sample surface along any direction, and relate it to the measured tunnelling current from the STM's probe tip. While the program does not give any quantitatively useful results pertaining to the specific sample that is being observed, it demonstrates how the concepts of potential energy diagrams, wavefunctions and tunnelling probability can be applied to understand the STM. No knowledge of higher-level mathematics is required to use the program, which is available on the and platforms. The flexibility of the program allows it to be used by students over a range of academic levels.Zusammenfassung. Das Scanning Tunneling Microscope (STM) Simulator ist ein interaktives Computerprogramm, das ausdrücklich für pedagogical Zwecke entworfen wird, um Studenten zu ermöglichen zu lernen, wie ein STM funktioniert. Das Programm wird entworfen um ein wirkliches STM einzusetzen, aber um Studenten einen Einblick in die Physik des STM zu geben. Das Programm erlaubt, daß der Student mit einem wirklichen STM Bild, das anderswo genommen wird, anfangt, das Profil der Probenoberfläche entlag irgendeiner Richtung zu beobacgten, um es danumit dem, gemessen Tunnelstrom von der Spitze des STM in Beziehung zu setzu Während das Programm nicht quantitativ nützlichen Ergebnisse gibt, die die spezifische Probe betreffen, die beobachtet wird, vorführt es ver wie Potentiel Energie Diagramme, Wellen Funktionen, und Tunnelwahrscheinlichkeiten verwendet weden können, um STM zu verstehen. Keine Kenntnis höherer ebener Mathematik wird erfordert, um das Programm zu benutzen. Das Programm lauft auf Windows und Macintosh Plattfromen. Die Flexibilität des Programms erlaubt, daß es von Studenten aller Jahrgäuge benutzt wird.

Imaging entire genetically functional DNA molecules with the scanning tunneling microscope

Deoxyribonucleic acid (DNA) can be immobilized on epitaxial gold surfaces treated with 2-dimethylaminoethanethiol preventing removal of the molecules due to forces exerted by the scanning tunneling microscope probe tip. We present reproducible images of entire plasmid molecules on these surfaces and discuss differences in image contrast that we have observed.

Nanoscale study of the as-grown hydrogenated amorphous silicon surface

A scanning tunneling microscope has been used to study the topography of the as-grown surface of device-quality, intrinsic, hydrogenated amorphous silicon deposited by rf discharge from silane. The substrates were atomically flat, oxide-free, single-crystal silicon or gallium arsenide. No evidence for island formation or nanoscale irregularities was seen in studies of 100-Å-thick films on either silicon or gallium arsenide. The topography of 1000- and 4000-Å-thick films has much variation; many regions can be characterized as ‘‘rolling hills,’’ but atomically flat areas have also been observed nearby. Generally, it appears that surface diffusion plays a role in smoothing the film topography. In most regions, the observed slopes were 10% or less from horizontal, but some steep-sided valleys, indicating incipient voids, were observed. The effect of the finite size of the scanning tunneling microscope probe tip is considered; this has an effect on the observed images in some cases.

Nanometer-scale roughness study and indentation test with a scanning tunneling microscope

The surface roughness of four gold surfaces mechanically finished, three by diamond cutting and one by mechanical polishing, were measured with a scanning tunneling microscope (STM) and with a conventional stylus profilometer. The roughness measurements revealed that the maximum height and the center line average of each profile varied with its representative wavelength. The relationship between roughness parameters and wavelength was almost linear on a logarithmic graph. The indentation tests were done on the best gold surface with a Pt STM probe tip. STM images and profile curves between, before, and after indentation were compared. Most of the valleys around the indentation point changed in depth after contact: some valleys became shallow and other became deep. The tip may become blunt during contact, but the variation of change in depth of valleys is not explained only by the damage of the tip.

Field ion-scanning tunneling microscopy of alkali metal adsorption on the Si(100) surface

We have constructed a scanning tunneling microscope (STM) equipped with a field ion microscope (FIM), by which one can monitor and shape the STM probe tip on an atomic scale in situ in the STM chamber. Taking advantage of a well-defined tip prepared by a FIM, we have greatly improved the stability and reproducibility of the performance of the STM. Li and K adsorption on the Si(001) 2×1 surface has been investigated by field ion-scanning tunneling microscopy (FI-STM). The STM images have shown that at the initial stage of adsorption, Li (K) atoms (1) adsorb on top of one of the dimer-forming Si surface atoms and (2) stabilize the asymmetric (buckled) dimerization, and (3) form linear chains, perpendicular to the substrate 2×1 dimer rows. Our observations suggest that alkali metal adsorption on the Si(001) 2×1 surface may be significantly different from the conclusions of earlier reports.

COMBINED FIELD ION AND SCANNING TUNNELING MICROSCOPE

Realizing the importance of characterizing a STM probe tip on an atomic scale, we have constructed a new instrument which combines a field ion microscope and scanning tunneling microscope. A complete STM set-up, which is similar to the one developed by Demuth, is mounted on an 8 O.D. flange and a FIM set-up is mounted on a 10 O.D. flange. FI images of the STM probe tip are observed using a O.D. chevron channelplate-image intensifier screen assembly with liquid nitrogen cooling. A field necessary for field ionization of He imaging gas is provided through a negative electrode placed near the probe tip so that the high voltage system is completely separated from the STM system. A preliminary data is presented for the graphite (0001) plane in vacuum. A scanning tunneling microscope (STM) has been enjoying much publicity and popularity since its invention by Binning and Rohrer in 1981. The excitement of this microscope lies in the expectation that it can resolve the geometric and electronic structures of almost any surfaces on truly an atomic scale without assuming the periodicity of a crystal. However, it is generally assumed that the STM probe tip must consist effectively of a single or few atoms when a true atomic resolution is to be attained. Little information is available so far on this critical issue of the structure of the STM tip. Indeed, there has been only one successful work in this respect, reported by Kuk and Silverman./l/ They have inspected the surface of the tungsten-made STM tip by a field ion microscope (FIM) in-situ of the scanning tunneling microscope before and after the STM scans and showed a preliminary data on the relationship between the STM resolution and tip surface geometry. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987613 C6-80 JOURNAL DE PHYSIQUE Realizing the importance of their work and urgent needs of detailed information on the STM resolution, we have constructed a new instrument which combines the STM and FIM. Fig. 1 is the schematic of this new instrument. The main chamber is a 20 cm diameter cylinder with 63 cm length and houses two identical STM-FIM set-ups at the symmetric positions. The set-up on the right hand side is used as a noise reference to help us evaluate the noise level of the STM. The entire STM set-up is mounted on the 8 O.D. horizontally placed flange and the FIM set-up is placed on the 10 O.D. vertically positioned flange together with a sputtering ion gun. The system is pumped by a 400 11s Riber Ion Pump and a 330 l/s Seiko magnetic levitation turbo-molecular pum (TMP) backed by another TMP. The operation pressure is 2 r 10-lg Torr. A specially designed Ti sublimation pum may be used occasionally to reduce residual hydrogen down to low Torr. The entire system is mounted on a high-leg air-suspended vibration isolation table. Fig. 2 is the photograph of the STM-FIM set-up. The STM drive consists of the coarse mechanical drive for the STM specimen and fine electro-mechanical drive for the STM probe tip. The coarse one is very silimar to the so-called grasshopper type (with a stopper located nearhy the STM tip) used by Demuth group./2/ The STM specimen is mounted on the head of the grasshopper. The external rotary-linear motion feedthrough is used to manipulate a Mitsutoyo n sub1 Lmat Lon pump channel plate-screen