Physics 437: projects in experimental biophysics

James A. Forrest
PHY 360 ext. 2161

Polymer Physics

In addition to the projects listed below, there may be more depending on current research developments, contact J. Forrest for alternate possibilities:

Preparing and characterizing thin polymer films

Polymer science has the ability to replace metallurgy in many applications. Polymers can be made with almost any desired property, and in many cases, the applications are in the form of coatings or thin films. It is relatively straightforward to prepare polymer films of submicron thickness by spincoating dilute solutions of polymer. The film thickness of the resulting films can be measured with 0.1 nm resolution with an optical technique known as ellipsometry. The aim of this project is to quantitatively characterize how the various parameters such as spin speed and solution concentration used in the preparation technique affect the final values of film thickness and uniformity. The effects of heat treating the sample above their glass transition and the effect of residual solvent may also be studied.

Growth kinetics of polymer crystals

While many polymers are highly flexible and form an amorphous solid upon cooling (glass) a large number of polymer (including some of tremendous technological relevance) actually do form partially crystalline samples. A fundamental difference between polymer crystals and those of small molecule or atomic crystals is that in the case of polymers, the kinetics has a large influence and to a large extent determines the final crystalline structure. It has become known recently that dynamic processes in thin films can display substantial deviations from the bulk material. This study will look at the crystallization kinetics of the crystalline polymer poly(ethyleneoxide) in thin films from 200 nm to 20 nm using dark field optical microscopy.

Applications of the quartz crystal microbalance to thin polymer films

The quartz crystal microbalance (QCM) is a very sensitive technique for monitoring mass uptake in thin polymer films. This, in turn, is a very important measurement, as it tells us about diffusion of gasses in polymers (how fast does your Cola lose its fizz) or about potential modification of properties by water uptake (like sticky hairspray in humid conditions). We have a state of the art quartz crystal microbalance which we can use to address such problems. In addition we can use this device to monitor polymer crystal formation (see project above) or look at the softening of polymer surfaces, or the formation of colloidal crystals (listening to paint dry).

Robert W. Hill
PHY 248 ext. 6844

Measuring temperature on the verge of absolute zero

Thermometry is a crucial aspect of low temperature experimental physics, but if you ask yourself how one measures temperatures that are fractions of a degree above absolute zero, the answer is not immediately obvious. Recently, the melting pressure of helium-3 was accepted as the Provisional Low Temperature Scale from 0.9 mK to 1 K (PLTS-2000), establishing helium-3 melting-curve thermometry as the technique of choice in this regime of temperature. Essentially this technique involves measuring the pressure of a small cell of 3He and using the melting curve to convert this to a temperature. This apparently simple approach is made significantly more interesting by the unusual shape of the melting-curve of helium-3.

The aim of this research project is to design, construct and test a helium-3 melting-curve thermometry system for use on an ultra-low temperature facility being installed in the Department of Physics. This will involve learning about cryogenic techniques, thermal contact and, of course, the unusual physics of helium-3.

Superconductivity and ferromagnetism

Superconductivity has hit the headlines again with the recent announcement of the 2003 Nobel Prize for Physics. As scientists continue to probe this intriguing phenomenum, it is clear there is still a lot to learn. For example, conventional wisdom has it that superconductivity and magnetism are antagonistic to one another; a material will either be superconductive or magnetic, but not both. In fact, magnetic fields, when applied externally, are known to suppress superconductivity. It was therefore an extraordinary result when the ferromagnetic material ZrZn2 was recently found to be a superconductor at temperatures below 0.25 K.

The aim of this research project is to characterise this exotic material, using transport and thermodynamic measurements, to discover what makes its superconductivity so spectacularly unusual. This will naturally involve making measurements to extremely low temperatures in order to observe this unique behaviour.

Stefan Idziak
PHY 250 ext. 5580

Confinement of complex fluids

Fluids under confinement have important technological applications as lubricants. An understanding of the structure of these confined fluids is important for the development of next generation lubricants. The structure of these model lubricants subjected to various surface treatments and shear forces will be studied using the X-Ray Surface Forces Apparatus.

Flow of complex fluids

An understanding of the structural properties of flowing complex fluid systems is important for the polymer processing and biomedical industries. A specially designed flow cell will be used to study the structure of these fluids using both in-house and synchrotron x-ray diffraction.

Jan Kycia
PHY 373 ext. 5177

Cryogenic Radio Frequency filters

I am interested in studying fundamental quantum effects seen in solid state, single-electron devices. In particular, I am interested in studying the various influences on a single electron, such as Coulomb blockade and Josephson tunneling, and how the electron is coupled to the surrounding local environment. Gaining a better understanding of these influences on a quantum scale could allow these devices to be used in applications such as electrometers, current sources and quantum computers.

In order to be able to measure the behavior of a single elctron, a very clean electromagnetic environment is required. Many steps need to be taken to isolate the single electron device from electromagnetic noise sources. These steps include operating at very low temperatures (< 100 mKelvin) in order to reduce thermal noise, careful lead design to eliminate interference effects and ground loops, dc and radio frequency, (rf), shielding to reduce environment noise pick-up, and thorough filtering and amplification of the probe and signal leads to the device. Recently, there has been a lot of work in improving the design of electromagnetic filters leading to the single electron device.

The research project consists of designing, constructing, and testing high frequency low pass filters in order to remove any signals at frequencies greater than 500 MHz. Another constraint is that these filters need to operate at cryogenic temperatures. The general principal behind the filters is that the signal line is put through a solenoid in a metal powder/epoxy mixture. The high frequency noise produces eddy current heating in the metal powder, which in turn attenuates the high frequency noise. By adjusting the size of the metal particles, their spacing, and the solenoid parameters, and testing the resulting filters, an optimal filter design for single electron experiments can be produced.

Specific heat measurements of MgB₂

An exciting new superconducting material, MgB₂, was discovered in January 2001. It begins to superconduct at the relatively high temperature of 40 Kelvin, and does not contain the Cu-O planes that characterize all other superconductors with such high superconducting transition temperatures. Because of the practical difficulties of manufacturing wires and films containing copper and oxygen compounds, MgB₂ is potentially much more useful for applications. Among the most direct probes of the superconducting phase transition is the specific heat measurement. This is a challenging measurement because it requires careful thermometry and measurement cell design.

The research project will involve designing and building a cell for measuring specific heat. This will be used to measure the properties of MgB₂ samples. The student will learn cryogenics, instrumentation, and superconductivity. Building this system requires dexterity and working with very small delicate objects.

Vortex decoration of various superconductors including MgB₂

This research project is another, complementary experiment on MgB₂. The student's project would be to use Bitter decoration to determine the arrangement of magnetic fields in the superconductor. The Bitter pattern technique consists of evaporating tiny (100 nm) fragments of iron onto the sample while it is in the uperconducting state. The iron particles are attracted to the vortices (single magnetic flux quanta) running through the superconductor. The structure of the vortex lattice depends both on the type of superconductor (type 1 or type 2), and the purity and microstructure of the sample.

A decorating system will need to be designed and built. This system consists of a small magnet and vacuum chamber that is immersed in liquid helium. An accurate amount of argon gas must be loaded into the chamber. Through a computer controlled power supply, a burst of current is applied to a small filament which then evaporates the iron onto the superconductor. Operating the system is tricky and requires optimizing several parameters to get the correct iron particle size quantity. After decorating with iron, the small particles on the surface stick due to Van der Waals attraction. This allows the sample to be warmed to room temperature and viewed in the chemistry department's state of the art LEO scanning electron miscroscope (SEM). The student will learn cryogenics, instrumentation, superconductivity, and scanning electron microscopy.

Please contact Jan Kycia for additional projects involving low temperatures, material physics, and fabrication of nanoscale electronic devices.

Hartwig Peemoeller
PHY 366 ext. 2633

Nuclear magnetic resonance studies of disordered materials

NMR techniques are used to explore, on a molecular level, the details of the dynamics and coordination of water molecules at the surface of large molecules in such materials as polymer bead suspensions, protein solutions, hydrated polypeptides, wood and polyacrylamide gels. Information gained from this research has the potential to further our understanding of these disordered materials and has application in various areas of soft condensed matter physics, material science as well as in biophysics and medical imaging.

A typical project involves a brief literature search, the familiarization with certain NMR techniques, the acquisition and analysis of data and, with the aid of a computer, establishing correlations between experimental results and results predicted by models of molecular dynamics and coordination.

Gunter A. Scholz
PHY 358 ext. 2213

A 'Philips CM20 Super Twin' High Resolution Transmission Electron Microscope (HRTEM) that operates up to 200 kV is available for student project oriented research. An invitation is extended to students wishing to learn how to use this facility for materials analysis. The CM20 along with sample prepartion facilities are located on the ground floor of the Physics building in Rm 115. Come and visit if you have any interest.

The CM20 is a modern analytical TEM capable of near-atomic imaging that has a resolution limit of ~2 Angstrom. Convergent beam electron diffratcion (CBED) is a particularly useful and informative diffraction method and can be a focus for a variety of 4th year research projects. Additionally, all the usual TEM facilities, including chemical microanalysis, allow the CM20 to be an excellent analytical tool.

My research interests have included: Intercalation Physics, Low-Dimensional Materials, Charge-Density Waves, Transitional Metal Chalcogenides, Protein Fibirils and Semiconductors. If you have interests in other types of materials let me know.