Profs. Krogstad and Huang of UIUC

AVS hosted a double feature:
Prof. Krogstad (Asst. Professor, Department of Materials Science and Engineering) discussed how a fundamental understanding of local microstructural evolution, thermodynamic and kinetic driving forces, and mechanical response can be used to improve the long-term response of materials under extreme conditions.

Prof. Huang (Asst. Professor, Department of Materials Science and Engineering) then discussed her TEM investigations into 2-d material interfaces with single-atom precision. She focused on methods for investigating the atomic structure around these interfaces and tied these defects to electronic structure and properties.

Joint AVS-MRS Argonne National Laboratory Trip

AVS and MRS went together to visit the beam lines at Argonne National Laboratory.

AVS and Asylum Research, an Oxford Instruments Company seminar on Scanning Microwave Impedance Microscopy and XRD characterization of ion-damaged single crystals

Double Feature:

Dr. Ted Limpoco of Asylum Research, an Oxford Instruments Company discussed the basics of SMIM, an atomic force microscopy-based technique, and the types of information that can be attained using the technique. This technique can be used to probe the impedance of the tip-sample interface and learn about the local electrical properties.

Dr. Kirill D. Shcherbachev of the Russian National University of Science and Technology discussed advanced HR-XRD techniques for characterizing ion-damaged single crystals. The techniques discussed may be used to attain a damage depth distribution using the shape of the diffraction curve, separating coherently and incoherently scattered x-rays.

Engineering Open House 2015

Unfortunately, the camera broke, so here is a picture from a prior year, but we did more vacuum demonstrations for kids at the 2015 Engineering Open House on Mar. 13. Thank you to all who were able to help out!

Outreach to 5th Grade Students with St. Elmo Brady STEM academy

On Oct. 25, the University of Illinois AVS Student Chapter taught ~ 15 4th and 5th grade boys of the St. Elmo Brady STEM academy about vacuum science. The St. Elmo Brady STEM academy gives African-American 4th and 5th grade boys hands-on exposure to science, technology, engineering and mathematics. We showed them what happens to a ringing alarm clock, the speed at which a feather and magnet fall, Peeps, shaving cream, a candle, a balloon, and water in a vacuum and helped them to discover why these materials behave the way that they do in a vacuum. 

Tatyana Kuznetsova and Vladimir Grebennikov of the Russian Academy of Sciences Seminar

On Wednesday, Sept. 17, Drs. Kuznetsova and Grebennikov discussed their investigations into topological insulators using angle-resolved photoelectron spectroscpoy (ARPES) and scanning tunneling microscopy/spectroscopy (STM/STS).

Bismuth tellurohalides including BiTeI belong to a family of layered polar semiconductors lacking inversion symmetry. Much attention has recently been paid to these compounds due to the strong spin-orbit interactions of electrons caused by Bi atoms. The strong correlation between the direction of motion and spin of charge carriers (called the Rashba splitting) in materials without spatial inversion can be used in spintronic devices. The Rashba effect leads to a shift of opposite spin-polarized bands in opposite directions on the momentum scale. In the semiconductor BiTeI, the Rashba effect can be used to control the spin of charge carriers using electric fields providing a pathway for the technological development of spintronic devices.

The near surface layer of BiTeI has been converted to the three-dimensional topological insulator state by doping the surface with Cs. We studied this system by angle-resolved photoelectron spectroscopy (ARPES) and scanning tunneling spectroscopy. We analyzed the electronic structure of the (0001) surface of BiTeI and its modification upon adsorption of Cs using ARPES. A strong shift of the electronic states at the (0001) BiTeI surface by several hundred meV to higher binding energies due to band bending effects as well as the Rashba splitting are observed. Both scanning tunneling microscopy (STM) and spectroscopy (STS) show unusual atomic structures of the surfaces terminated by both tellurium and iodine atoms. Our experiments have shown that the relaxation of the surface atoms in these compounds is significant and can be used to control surface states in topological insulators.

Michael V. Yakushev, University of Strathclyde UK Seminar

On Tues. Sept 16, Dr. Yakushev was able to teach us about the capabilities of optical spectroscopy including photoluminescence by describing his work with chalcopyrites and other semiconductors.

The chalcopyrite semiconductors based on CuInSe2 are key components in the absorber layer of solar cells which are amongst leading thin-film PV technologies in terms of efficiency and stability. These solar cells have been developed mostly using empirical approaches rather than scientific knowledge-based design: it worked first and was explained later. As a result the progress of the chalcopyrite-based solar cells shows a clear saturation towards not 30 %, a theoretical limit for single-junction solar cells, but 21 %. The problem seems to be that the materials are too complicated for an empirical design.

A solution could be in studying first high structural quality model materials and then using the obtained knowledge for technology grade materials. That is how all other successful semiconductor technologies have been developed. A signficant improvement in the quality of the chalcopyrites produced in Strathclyde facilitated the use of fine methods of optical and magneto-optical spectroscopy to study excitonic states and helped to determine a number of fundamental electronic properties.

The next step in the development of the chalcopyrites is the substitution of rare and expensive In and Ga with alternating Zn and Sn: Cu2ZnSn(SeS)4 with a kesterite structure. An encouraging efficiency in excess of 11 % has already been reported for solar cells based on this compound. However, the material might be far too complicated whereas some other compounds like Cu3BiS3 can probably offer a simpler solution.