Variable-temperature Ultrahigh Vacuum (UHV) Scanning Force and
Tunneling Microscope: Thanks to a generous grant from the Murdock
Foundation and matching funds from the University of Washington, an
instrument located in Physics B009 is being shared among the
groups
of Professors Marjorie
Olmstead and Sam Fain
(Physics), Charles
Campbell
(Chemistry), and Fumio
Ohuchi (Materials Science and Engineering). The
instrument is used to study growth, etching and interface formation of
inorganic materials, with primary emphasis on systems where
one
constituent is often insulating or transparent. These materials are of
interest
both for intrinsic science and for technology. Initial materials
investigated have been calcium fluoride, gallium selenide, indium
selenide,
sapphire, silicon and water ice. Schematic
drawing of the apparatus before
installation of home built items on preparation chamber (the table top
is
1.38 m long). The heart of the apparatus is the Omicron beam deflection
AFM which does atomic resolution Atomic Force Microscopy (AFM) between
25K
and 750K and Scanning Tunneling Microscopy (STM) between 25K and
1000K.
Ion-scattering spectroscopy, x-ray photoelectron spectroscopy, and low
energy electron diffraction are also be available on the spectroscopy
chamber. The vacuum system includes a separate sample preparation
chamber
(upper right of drawing) which has been
instrumented at UW, an entry lock chamber, three large ion pumps, and
two
turbopumps. (The long tube at upper right of the drawing is the magnetically activated
device to
transfer the sample from the preparation chamber to the spectroscopy
chamber.) Shown below are Tracy Lovejoy (U. W. Physics graduate
student), Jeremy
Morales (U. W. Physics hourly employee), Prof. Marjorie
Olmstead, Tanakanori Mitsui (visitor from Japan), and
Chih-Yuan (Claire) Lu (Ph.D. U. W. Materials Science and Engineering,
at Intel starting Oct 2007), gathered around the computer (off camera
left) that
controls the Omicron STM/AFM.
Past topics of Fain research lab:
Dynamics at Ice Surfaces: The environment of molecules of a given material near an interface is different from that of molecules in the bulk of the material, due to bonds missing at the interface. Thus the structure and dynamics near an interface can be quite different than in the bulk. Water ice is important in a number of environments on the earth, in the atmosphere, on comets and planetary satellites, and in space. Below are described briefly two different aspects of the dynamics at ice surfaces that we have studied recently.
a) Dynamics at Ice Surfaces at Low Temperatures: Non-contact mode AFM measurements were used to investigate the structure, morphology, and annealing behavior of ice that was vapor deposited on various single crystal substrates in ultra-high vacuum for temperatures between 80K and 120K using this microscope. The fundamental information obtained by such measurements will aid in understanding the influence of substrate on the growth and annealing behavior of ice at low temperatures such as occurs in the much colder environments in space where comets and dark interstellar media occur. Photos show Jason Donev and Steve Tait taking data for clustering of water on Au(111) on the Omicron instrument. (Donev et al. 2005, Fain 2007)
b) Dynamics at Ice Surfaces near the Triple Point: The objective of a project completed a few years ago was to understand the interaction between ice surfaces and other solids in a controlled environment at temperatures near the triple point. Dynamical measurements of the normal and lateral forces exerted on scanning mechanical probes by the surface of ice were made as a function of temperature, atmosphere above the ice surface, and electric potential between the probe and the ice. We used atomic force microscope (AFM) silicon tips uncoated or coated with a hydrophobic layer to measure the nanoindentation properties of vapor deposited ice surface above -25 Celsius. The hydrophobic coatings were provided by Amy Szuchmacher, who was a graduate student working with Tom Engel of Chemistry and R. Overney of Chemical Engineering. (Pittenger et al. 2001)
Intermittent-Contact Force Microscopy: Atomic force microscopy (AFM) [also known as scanning force microscopy (SFM)] is used to evaluate a wide variety of materials and devices on scales ranging from nanometers to micrometers. As originally conceived, a small probing tip attached to a weak cantilever spring moves over a surface and the distance between the spring support point and the sample is varied to maintain a constant deflection of the spring. Subsequent modifications of the technique involve monitoring the vibrational amplitude of a tip attached to a cantilever whose support point is driven at a frequency in the kilohertz range. In intermittent contact AFM the tip contacts the surface for only a small fraction of its vibration cycle; this avoids lateral frictional effects. We have developed a method to measure directly the average force which occurs during this intermittent contact between silicon tips and the surfaces of piezoresistive cantilevers fabricated from silicon by ThermoMicroscopies (formerly Park Scientific Instruments). A manuscript has been published in Applied Physics Letters. A more detailed talk on this work as 0.4 Mb pdf.
Structure and Dynamics of Physically Adsorbed Layers: Previous projects in this laboratory used electrons interacting with adsorbed layers to determine the structure and dynamics of gases such as ethylene and isotopes of hydrogen adsorbed on graphite single crystal surfaces.
Much of the research in FAIN RESEARCH LAB has been funded
by the National Science Foundation,
most recently under grants DMR 96-23590, KDI 99-80125, NER 05-08216,
and DMR 07-10641.
Any opinions, findings and
conclusions or recomendations expressed in this material are those of
the
author(s) and do not necessarily reflect the views of the National
Science
Foundation (NSF). Other sources of funding are cited in the articles
above.
Information on application to the Physics Department for graduate study can be found at U.W.Physics Gradweb. University of Washington undergraduates and current or prospective graduate students are welcome to inquire about research opportunities in this group.
Updated 15 Oct 2007
