Magnetic force microscopy on high-T c superconductors

Abstract

We demonstrate that magnetic force microscopy is able to detect the superconducting state and to distinguish between the Meissner and Shubnikov phase of a high temperature superconductor. In the Meissner phase we observe an increasing, repulsive force with decreasing tip-to-sample distance. The force depends on the screening current density and therefore on the London penetration depth. Indeed, we detect a decrease in the maximum force as the temperature increases. In the Shubnikov phase a different behavior i.s observed. If the tip is approached staircase-like to a superconductor the repulsive force first increases and then decays rapidly. The superconductor has reacted to the increased stray field of the tip by readjusting the vortex structure to lower the total energy. The experiments are discussed in relation to existing theoretical predictions. We point out that magnetic force microscopy might hecome an important tool to directly observe the vortex structure and its complcx phase transitions.

Scanning tunneling microscopy investigation of nanostructures produced by Ar+ and He+ bombardment of MoS2 surfaces

“…Despite the inert basal plane, MoS 2 has been of interest due to its catalytic activity for hydrodesulfurization ͑HDS͒ where organic sulfur is removed from petroleum and coal feedstocks by reaction with hydrogen gas to form H 2 S. 3,4 The catalytic activity of MoS 2 for HDS has been associated with edge sites, which are more numerous on the small particles employed in supported HDS catalysts. [14][15][16] The easy cleavage of MoS 2 and other layered transition metal dichalcogenides ͑TMDs͒ ͑MoSe 2 , WS 2 , WSe 2 ...͒ can produce large, stable, and atomically flat areas, making these materials ideal substrates for scanning tunneling microscopy ͑STM͒ investigations. 12,13 The structure of MoS 2 also gives it lubricating properties due to the ease of slippage between cleavage planes.…”

Work of Adhesion Measurements of MoS2 Dry Lubricated 440C Stainless Steel Tribological Contacts

“…Indeed, the inside is shown to be comprised of a MoS x O y material, while the outside shows higher detection of Mo 2 S 3 À molecular ions and lower detection of MoS x O y À molecular ions (Table 1). Additionally, the coating is made of nano-sized crystallites mostly oriented perpendicular to the substrate, [52,53] which is a hydrophilic orientation (CA % 40 ). [50] That coupled with the inherent carbonaceous contamination of the pristine coating [41] makes the CA measured outside the contact highly relevant to the nature of the surface.…”

A low temperature ultrahigh vaccum scanning force microscope

“…23 We have used a similar fiber optic interferometer 24 as a deflection sensor for our first low temperature scanning force microscopy instrumentation. 12 We have then measured the levitation force 25 on YBa 2 Cu 3 O 7Ϫx ͑YBCO͒ single crystals cooled with and without an applied external field 26 and imaged a͒ Electronic mail: hug1@ubaclu.unibas.ch single vortices using a low temperature magnetic force microscope ͑LTMFM͒ for the first time. 27 Furthermore, we have used the magnetic stray field of the tip to nucleate vortex bundles.…”