Program Highlights

January 19, 2012
University of Minnesota
Research
Imaging ‘Invisible’ Dopant Atoms in Semiconductor Nanocrystals
Imaging ‘Invisible’ Dopant Atoms in Semiconductor Nanocrystals In semiconductor nanocrystals, the physical effects of deliberately included impurities, called dopants, may depend on the dopant position with the crystal. To date, there has not been an effective technique to determine the location of individual dopant atoms in nanocrystals. IRG-4 researchers demonstrated that a combination of scanning transmission electron microscopy and electron energy loss spectroscopy can be used to reveal the position of such “invisible” dopants.
January 18, 2012
University of Minnesota
Research
Why Most Plastics Can’t be Metals
High Efficiency Silicon Nanocrystal Light Emitting Devices

Conductive polymers, i.e. plastics, that conduct electricity, are important in science and technology as they offer the potential for cheap, flexible electronic devices. This work examines the mechanisms by which electrons are transported in such materials, a process that remains far from understood. One of the main results of the work is that the behavior of such materials, at very high densities of charge carriers, is radically different to simple expectations.

January 18, 2012
University of Minnesota
Research
High Efficiency Silicon Nanocrystal Light Emitting Devices
High Efficiency Silicon Nanocrystal Light Emitting Devices

 

Hybrid light-emitting devices based on organic semiconductors and inorganic semiconductor nanocrystals are of great interest for applications in optical displays and solid-state light sources.  Silicon, a poor light emitter in bulk form, can exhibit strong luminescence in nanocrystal form; however, efficient electrical excitation had not been demonstrated. In this study, Cheng et al. showed a silicon nanocrystal device with an external quantum efficiency of 8.6%, the highest reported efficiency for any nanocrystal light emitting device.

January 17, 2012
Cornell University
Research
Patterned Graphene “Scrap” Grows into Continuous “Patchwork Quilt”

New technique produces heterojunctions in single-atom-thick graphene

Many of today’s electronic devices, including solar cells and transistors, are based on heterojunctions — precisely sculpted, atomic-scale interfaces between different materials. To reach the ultimate limit in miniaturization, scientists must learn to make these near-perfect unions in materials that are only a single atom in thickness.

 

January 17, 2012
Cornell University
Research
A Better Way to Store Information in Computer Memory

Spin Hall effect may enable simpler, more reliable magnetic memory

Most computer memory (so-called random-access memory or RAM) is volatile — the computer “forgets” the information when power is removed. The technology for making non-volatile magnetic memory is undergoing rapid progress, because techniques have recently been developed to change the orientation of small magnets without magnetic fields. This allows for denser, more efficient, and

 

October 18, 2011
New York University
Research
Self-Replication of DNA Nanotile Patterns

Self-replication is ubiquitous in the living world but artificial self-replication has been elusive. We have developed a process for self-replication of an arbitrary seed made from nanometer scale DNA tiles. The tiles are constructs of 10 DNA strands which form a bent triple helix, BTX, with four lateral single strands -- ‘sticky ends’ -- for recognition and hybridization with complementary tiles, and six longitudinal sticky ends for joining tiles to form a sequence.

August 31, 2011
University of Pennsylvania
Research
Stressing the Most Important (Dirac) Points

The Valence and conduction energy bands of Bi2Se3 in the (111) plane during the phase transition from topological insulator to conventional insulator. With increasing strain the topological band gap closes, forming a Dirac point, and then reopens as conventional band gap.Recent physics research shows how spin-orbit coupling can rearrange electronic bands in a solid to make a "topological insulator" a new quantum phase of matter that is guaranteed to have conductive surfaces even though its bulk is insulating. What happens if you take a topological insulator and compress or expand it? A team of researchers at the University of Pennsylvania has examined this question.

August 31, 2011
University of Pennsylvania
Education
Workshops on Materials Science Labs for Teachers

Teachers LecturesIn 2008 The Penn MRSEC assisted a high school science teacher, Schuyler Patton, to prepare a year-long elective course on materials science for his high school, Central HS, Philadelphia. It started with one class of 33 students and it was very successful. In 2010-11, it was expanded to two sections with 66 students. In summer 2010, the Penn MRSEC offered a series of three hands-on workshops for teachers based on the laboratory experiments used in this course. The themes of these workshops were a) thermal properties and b) mechanical properties.

August 31, 2011
University of Pennsylvania
Education
Philly Materials Science and Engineering Day

Philly Materials Science & Engineering Day 2011In conjunction with the NOVA TV science program, the Penn MRSEC collaborated with Penn and Drexel University Materials Science Departments to arrange the first Philly Materials Science & Engineering Day on Feb. 5, 2011, which introduced the general public in the Philadelphia region to the world of materials. An extensive program was arranged that included demonstrations from many LRSM graduate research groups. More than 30 MRSEC faculty, staff and students participated.

August 31, 2011
University of Pennsylvania
Research
Using a vice to change topology: theory and modeling insulators under strain The Topological Insulators Seed of the LRSM

Topological InsulatorsThe topological insulating materials offer conductive surface states that can be useful for quantum computing, catalysis, and other applications. In this recent work, we (Young, Chowdhury, Walter, Mele, Kane, and Rappe, under review, 2011) show that compressing the material strengthens the topological insulating state, while expanding the material eventually takes this behavior away completely. Using external pressure as a control parameter suggests general ways to strengthen this important physical effect.