This fully custom designed system will provide a platform for growing highly pure samples using Molecular Beam Epitaxy (MBE) and thereafter characterizing them in a ultra high vacuum, low temperature, high magnetic field environment. It is currently being commissioned; imaging and spectroscopy have been achieved at temperatures as low as 50mK.

The STM system all wrapped up for bakeout

CAPABILITIES

Along with standard STM capabilities, this system has two unique capabilities: performing time-resolved STM and spin-polarized STM.

Time-Resolved STM

STM in the constant current mode provides black and white contour plots of the surface while the addition of spectroscopic information provides an equivalent of color. Our objective is to turn the STM into a high speed camera and provide information about dynamic electronic processes on surfaces. Magnetization dynamics occur through thermal activation, spin tunneling and spin precession [1,2,3]. The characteristic time scales range from eternity (stable magnetization) down to a few hundred picoseconds. Access to such fast behaviour with the STM might appear hopeless when the intrinsic STM dynamic bandwidth is limited to a few tens of kHz due to the high gain of the tunneling current amplifier. Nevertheless, Freeman et. al. from the University of Alberta have developed an experimental scheme based on a pump-probe approach and demonstrated a stunning 25 ps time resolution in the junction mixing mode [4] . They were using a room temperature air STM, photo-gated pulse generators and micron sized samples made by lithography. While the time resolution was remarkable, they failed to impress the community due to a lack of atomic resolution, the real benchmark of STM. We are currently improving the technique on a home-built STM with atomically clean graphite samples and fully tunable high speed pulse generators. Preliminary results open the door to dynamic spectroscopy and are highly promising for future adaptation in monitoring the dynamics of single molecular magnets.

[1] Will Spin-Relaxation Times in Molecular Magnets Permit Quantum Information Processing?. Arzhang Ardavan, Olivier Rival, John J. L. Morton, and Stephen J. Blundell PRL 98, 057201 (2007)
[2] Non-equilibrium magnetization dynamics in the Fe8 single-molecule magnet induced by high-intensity microwave radiation. M. Bal1, Jonathan R. Friedman, Y. Suzuki, E. M. Rumberger D. N. Hendrickson, N. Avraham, Y. Myasoedov, H. Shtrikman and E. Zeldov Europhys. Lett., 71 (1), pp. 110-116 (2005)
[3] Quantum oscillations in a molecular magnet. S. Bertaina, S. Gambarelli, T. Mitra, B. Tsukerblat, A. Muller & B. Barbara1
Nature, Vol 453|8 May 2008| nature 06962
[4] Ultrafast time resolution in scanning tunneling microscopy. M.R. Freeman a,A.Y. Elezzabi a, G.M. Steeves a, G. Nunes, Jr.b Surface Science 386 (1997) 290-300

Spin-Polarized STM

The recent progress in spin-polarized scanning tunneling microscopy has enabled access to magnetization down at the atomic level [2]. However, only a few groups in the world have succeeded because of non-trivial experimental problems. Therefore, before entering the novel study of molecular magnets, one has to establish the foundation of SP-STM on more conventional systems. With this aim, we studied the thickness dependence of anisotropy for Co thin films on Cu 111 [3] and explored the peculiar properties of an antiferromagnetic Ising lattice with a face-centered cubic symmetry for epitaxial Cr films on Au 100 [4]. Those studies have demonstrated the capabilities of our current apparatus to succeed in this difficult field. Exploration of the magnetic properties of thin films is important because they can also be used as a substrate to host and control the properties of a subsequently deposited molecular magnet. A literature survey shows strong evidence that adaptation of the spin polarized STM technique to molecular magnets is relatively straight-forward [1,2].

[1] Visualizing the Spin of Individual Cobalt-Phthalocyanine Molecules. C. Iacovita,M. V. Rastei, B. W. Heinrich, T. Brumme, J. Kortus, L. Limot, and J. P. Bucher Phys. Rev. Lett. 101, 116602 (2008)
[2] Spin-polarized scanning tunnelling microscopy M. Bode Rep. Prog. Phys. 66 (2003) 523? 582
[3] Imaging Spin-Reorientation Transitions in Consecutive Atomic Co Layers on Cu Y. Pennec, R. Carron. Private Communication UBC CMS Feb. 2009
[4] Ultrathin FCC Chromium on Au 100 investigated with the Scanning Tunneling Microscope Y. Pennec, R. Carron Private communications UBC CMS Feb 2009, ICN+T 2008 conference. July 2008

Image Gallery

A step edge on graphite imaged at 50mk

Vibration isolation gimbal for the dilution fridge still pumping line

Piping run to the gas handling system in the service hallway outside the low-noise rooms