| Philosophy
Before discussing some ideas for student projects, it is worth mentioning
my philosophy of student research, which is simply an extension to my previously
stated philosophy of teaching & learning. Learning is definitely
not confined to the classroom, a good scholar is always improving their
skills and seeking out new knowledge. Similarly, research isn’t even
confined to what happens in the lab or machine shop; rather, research involves
presenting one’s findings, attending conferences, and building a relationship
with the faculty member.
With my current research students, I have tried to play the role of consultant
or mentor, rather than supervisor. The students have been the ones
formulating the questions and designing the apparatus. Now, I have
not left them to reinvent the wheel, rather we have discussions where we
share ideas. Some of their ideas (as well as some of mine) don’t
bear fruit, but learning from mistakes is one of the key aspects of a researcher
and lifelong learner. As I see it, my mentor responsibilities are
not only to share information and experiences with the students, but also
to encourage them to explore on their own. There has been more
than one occasion when we have attempted a technique suggested by a student,
even though I suspected it would not pan out. I wanted the students
to know that it is okay to occasionally fail, and not trying is much worse.
While participating in DePauw’s Science Research Fellows Program, I often
had the opportunity to work with some extremely talented freshmen.
We would find ourselves talking about topics completed unrelated to our
project. I see this as part of the mentor-student relationship.
Particularly for women and underrepresented minorities, this personal connection
can make a difference in their self-esteem and affect their decision whether
or not to pursue a career in science. In affect, the faculty member
is serving as a representative of the entire science community.
Just as courses should contain material that is of interest to students
so should research projects. Particularly, when working with underclassmen
I have tried to think of projects that do not require significant theoretical
background, and may even be familiar to the students. Soap films,
sandpiles, organ pipes, and bicycles are all examples of novel systems
that contain a wealth of physics. For upperclassmen, projects that
employ more advanced techniques or draw on deeper theoretical background
would be appropriate. These could be anything dealing with quantum
fluids, statistical mechanics, and computer modeling.
Future Projects
The wetting behavior of fluid on solid surfaces is of critical importance
to many systems- fabrication of semiconductor devices, application of inks
to paper, and even the survival of animals. One possibility for the
fluid is that it completely wets the surface, forming a thick uniform film.
However, if the surface tensions are altered, the fluid may not wet the
surface and instead bead up like water on a waxed surface. Wetting
phenomena is an issue in all systems where a fluid phase is at an interface
of another fluid and solid (or between two other fluids). For most
systems the substrate is sufficiently attractive that all fluids wet the
interface. However, recently several new systems have been explored
that allow for wetting temperatures where the fluid goes from a wet to
non-wet phase.
Most systems studied display a first order wetting transition, but it is
believed that another variety of wetting was possible- continuous wetting.
For these systems the film thickness is continuous across the wetting temperature.
Continuous, or second order, wetting has not yet been seen in a physisorbed
system. It was recently predicted that xenon on alkali metals, plated
with a monolayer of gold would be a possible candidate for continuous wetting.
With my experience of first order wetting and preparation of alkali metal
surfaces, I believe that it would be possible to construct an experiment
that would look for this new transition. I am currently preparing
an application for funding that will be sent to the Research Corporation.
The experiment would require a cryostat capable of precise temperature
regulation near the bulk triple point of xenon. The design and construction
of such an apparatus would give students hands on experience with temperature
control. The elimination of radiant heat, equilibrium time constants, and
handling of cryogenic liquids would be issues that need addressing.
Because surface contamination is of great concern, students would also
be able to work with UHV techniques such as turbo pumps and leak detection.
Surface preparation would likely be done using evaporative techniques already
used in thin film preparation. Even outside the context of the wetting
experiment, the preparation and analysis of thin films could be a valuable
experience for a student. Measurement of both the substrate and xenon film
thickness could be done with quartz crystal microbalances. These
devices allow for resolutions of fractions of a monolayer, which would
be necessary at all stages of the experiment. Operation of the cryostat
will require some computer programming and interface control for data collection.
This experience with LabVIEW or other similar language would give a student
practical experience for running future experiments.
After completion of the xenon wetting experiment, the cryostat could be
used for any number of low temperature experiments. One perplexing
puzzle in adsorbed films is the solid layer mobility. For warmer
temperatures, when the vapor pressure is significant, the major process
for mass transport is through the vapor. For situations when the
vapor pressure is negligible, there are some questions as to the mechanism
of transport. In my helium experiments it is seen that at low temperatures,
even before the adsorbed film goes superfluid, the mass transport is very
rapid. Experiments have also been performed on the kinetics of solid
hydrogen mobility with little theoretical understanding, as the transport
is not simple diffusion of a 2-D gas. Further work on these and other
systems could be performed with a cryostat that has optical access.
A simple experiment would burn a hole in the adsorbed film using a heater
or laser. Then using ellipsometry techniques a student would be able
to accurately measure the film regrowth as a function of time. Once
optical capabilities have been added to the cryostat, other experiments
on the adsorption and phase transitions of various two-dimensional films
would be possible.
My interests in phase transitions and soft condensed matter have also grown
beyond low temperature physics. Currently I am working with six freshmen
to study two-dimensional fluid dynamics in soap films. Using a soap
film suspended between two nylon wires, we are able to study the turbulence
as the fluid flows past various objects. This system is incredibly easy
to assemble, and yet it provides one of the best apparatuses for testing
fluid dynamics in two- dimensions. Our focus has been to study the
transition from laminar to turbulent flow, identifying the relevant parameters.
For a student who enjoys computer modeling this would be a nice project
as they could perform calculations that can be easily compared with laminar
flow experiments.
Another system that is deceptively simple to assemble is granular materials.
The basic setup for the study of avalanches, pattern formation and convection
only requires a few trips to the hardware and grocery stores, yet there
is much to be learned from granular materials. While the materials
are simple macroscopic particles, which only interact with repulsive forces,
the physics is still a mystery. A sandpile at rest behaves like a
solid, yet if the slope is increased so that it is greater than the angle
of repose the grains will begin to flow. However this movement is
not completely fluid-like, as the Navier-Stokes equations do not hold.
The discrete nature of the particles may imply a gas-like state but the
thermal energy of the system is negligible when compared to the gravitational
energy. After all of the contradictions, one is left to conclude
that new laws need to be found that can predict the behavior of granular
materials. The study of granular materials, much like that of soap
films, can be appealing to students as it is easy to observe the phenomena,
making it easier for the students, particularly underclassmen, to get excited
about the research.
Working on phase transitions and critical phenomena, especially at low
temperatures, is something that I find very stimulating and I think students
would agree. Experiments such as soap films, granular materials,
binary fluids and liquid crystals can offer students the opportunity to
study more novel systems. With the equipment from the wetting experiments
it would even be possible to look at friction and adhesion in various systems,
including biological ones. Studies of quantum chaos would also be
possible with a modest amount of additional equipment. As you
can see, the equipment can be used to investigate many different phenomena,
offering the students different projects to help match the students with
the project that is best for them. When the experiments are
combined with a strong mentor- student relationship, the students are able
to practice valuable skills and begin the lifelong journey of exploring
the world around them, which is the essence of the liberal arts education.
|
|
