Shenda M. Baker

Integration of self-assembled diblock copolymers for semiconductor capacitor fabrication

We combine a self-organizing diblock copolymer system with semiconductor processing to produce silicon capacitors with increased charge storage capacity over planar structures. Our process uses a diblock copolymer thin film as a mask for dry etching to roughen a silicon surface on a 30 nm length scale, which is well below photolithographic resolution limits. Electron microscopy correlates measured capacitance values with silicon etch depth, and the data agree well with a geometric estimate. This block copolymer nanotemplating process is compatible with standard semiconductor processing techniques and is scalable to large wafer dimensions.

Electric field induced instabilities at liquid/liquid interfaces

External electric fields were used to amplify thermal fluctuations at the interface between two thin liquid films. Similar to the results shown previously for the enhancement of fluctuations at the polymer/air interface, interfacial fluctuations having a well-defined wavelength were enhanced with a characteristic growth rate. A simple theoretical framework to describe the experimental observations is presented. Both experiment and model calculation show a substantial reduction in feature size as a result of the change in surface/interfacial energy when going from the thin film to the bilayer case. Experimentally, features develop nearly 50 times faster for the bilayers in comparison to the polymer/air case. These results point to a simple route by which the nanoscopic feature can be easily and rapidly produced or replicated.

Nanostructures and the proximity effect

Nanostructures have interesting properties due to the confinement of electrons in small structures. In addition, since an appreciable fraction of the electronic wave-function resides outside the physical extension of the nanostructure, proximity effects become more important with decreasing size. Moreover, in magnetic nanostructures the magnetic fields also extend a considerable distance outside the physical extent of the nanostructure. Thus, the interplay between size confinement and proximity effects become particularly interesting in magnetic nanostructures. We give two interesting experimental examples of proximity effects with magnetic nanostructures. In one, small magnetic dots radically modify the magnetotransport properties of superconducting films. In the other, the properties of a ferromagnet with nanoscopic antidots are considerably changed because of proximity with an antiferromagnet.

Nanoporous thin films and porous inorganic substrates for lipid bilayer support materials

Abstract Synthetic lipid bilayers are excellent mimics of cell membranes. In order to experimentally access these thin layers and oriented proteins in membranes, suitable supports which allow for membrane fluidity while assuring membrane stability need to be developed. Nanoporous polymer templates created from the natural phase segregation of immiscible diblock copolymers are uniform arrays with pore sizes naturally on the scale of macromolecules, tens of nanometers, and grain sizes currently on the order of microns. We study the suitability of such templates, appropriately treated to present a hydrophilic surface, as substrates for lipid bilayers with scanning force microscopy and neutron reflectometry. In the process, we use tip deflection curves to establish simple criteria for determining the presence of a lipid layer on the substrates. Gold coated porous polymers and silicon oxide templates in silicon both appear to be suitable support materials.

Shear effects on the geometry of polystyrene-polyethylene oxide copolymers at the solid-solvent interface

Abstract The geometry of polystyrene (PS)-polyethylene oxide (PEO) diblock copolymers at the quartz-solvent interface has been examined as a function of solvent quality and shear by neutron reflectometry. Under conditions where a brush geometry is observed for the static PS free block, extremely large shear rates (∼ 10 000/s) produce little or no effect on the structure, in agreement with the recent theoretical considerations. The geometry of the adsorbed polymer was also examined as a function of solvent quality. Under conditions where the polymer can phase separate, the effect of shear increases. Sparser PS coverage, which tends toward the mushroom geometry in good solvents, increases solvent penetration between the molecules. In poor solvents, the PS film may have lateral inhomogeneity and areas of little coverage. Again, this increased penetration of solvent is suggested to account for the increased sensitivity of the molecules to deformation under conditions of shear.

Success for Women in Academia: Choices, Experiences, and Challenges

C We all make choices in our careers. We make the choice whether or not to have an academic career, to marry, or to have a family. When we are unsatisfied in our careers, we weigh the options of keeping a current position, moving to another, changing fields entirely, or leaving the workplace. This idea of choice was reflected in the luncheon program, where the attendants of the Women in Science and Engineering (WISE) conference were asked, “what criteria do we now use to define success?” This question first was asked of the group in a similar WISE conference 25 years ago. The answer then was direct, “To have a measure of recognition from our peers.” Having the ability to do science and to be recognized as contributing in a meaningful way was sufficient to define success 25 years ago. The general consensus from the 1998 meeting was that peer recognition is now expected, and a measure of success comes from assessing all aspects of life. We thus defined success as “the sum over a lifetime of our satisfaction in career, family, and personal life,” indicating that balance has become much more of an issue. Because the ability to have a career is assumed, the conflicts arising from wanting to have a family, personal time, or outside interests all need to balance to give an overall sense of satisfaction, or success. Success is thus defined more on a personal level and is not derived entirely from external sources. That is, to be successful, a woman will make the choices required to excel in all aspects of life, and success can be different for each woman. Yet, how does this definition fit into the traditional evaluations of success in science? Many ideas of success and the challenges in attaining and evaluating success permeated the discussions that occurred in the meeting of the Clare Boothe Luce Professors in the morning before the conference and in the parallel sessions on Successes in Academia, Industry, and Government on March 13th in the afternoon. I will summarize some of the comments from each of these sessions. I will address children and career, both from my perspective and from comments at the conference. Finally, I will briefly contrast some of the experiences reported by women today with those reported from the conference twenty-five years ago.

Reflectivity studies on adsorbed block copolymers under shear

The authors report neutron reflectivity data on (poly)styrene-(poly)ethylene oxide (PS-PEO) diblock copolymers adsorbed onto quartz from the selective solvent cyclohexane (a non-solvent for PEO and a poor solvent for PS). The PEO ``anchor block`` adsorbs strongly to form a thin layer on the quartz substrate, while the deuterated PS chains dangle into the solvent. They find that under static conditions the density profile of the PS block in a poor solvent can be well described by a Schultz function which is indicative of a polymer ``mushroom.`` Furthermore, they have studied the same system under shear at shear rates from 0--400s{sup {minus}1}. They find that there is a dramatic increase in the thickness of the PS layer under shear in cyclohexane and that the relaxation time from the shear-on profile back to the static profile is on the order of several days.