LaBella Group www.albany.edu/spin vlabella@albany.edu

cnse.albany.edu

Towards an Atomic Scale Understanding of Spin Polarized Electron TransportTowards an Atomic Scale Understanding of Spin Polarized Electron TransportVincent P. LaBella, College of Nanoscale Science and Engineering,

University at Albany / SUNY, DMR-0349108The objective of this researchThe objective of this research is to study spin polarized electron transport through materials and material interfaces on the atomic scale. Ferromagnetic-metal/semiconductor contacts are one component of high efficiency spin injectors such as magnetic tunnel junctions (MTJ) and magnetic tunnel transistors (MTT). One method for studying the electron transport properties of these interfaces is ballistic electron emission microscopy (BEEM). This three terminal scanning tunneling microscopy (STM) technique injects electrons from a STM tip into a grounded metal base of a Schottky diode as shown in Fig. 1. A small fraction of these electrons will travel ballistically through the metal to the interface and those electrons with sufficient energy to surmount the Schottky barrier will be detected by a backside contact as BEEM current.

To measure the spin dependent transport propertiesTo measure the spin dependent transport properties of these interfaces we developed a new technique called spin polarized BEEM (SP-BEEM) where a ferromagnetic STM tip is utilized to inject spin-polarized electrons into a ferromagnetic metal semiconductor Schottky diode as shown in Fig. 2. This technique allows measurement of hot electron transport as a function of angle between the magnetic field of the tip and the magnetic field of the sample. By measuring this dependence as a function of the thickness of the Fe in the Schottky diode the spin dependent attenuation lengths of the Fe can be extracted as shown in Fig. 3. These spin dependent attenuation lengths quantify the spin dependent scattering in this material which is the underlying physical mechanism that is utilized in magneto-resistive devices. In addition, these attenuation lengths were measured as a function of tip bias above the Schottky height as displayed in the inset of Fig. 3 and show significant variation with bias. We attribute this variation to changes in the amount of allowed transverse momentum for different bands in the semiconductor. Our future focus is on investigating the effects of the interface band structure upon the measured attenuation lengths of the metal as these results suggest that the attenuation length of a metal is not solely a property of the metal but a property of the interface as well.

Fig. 1 Fig. 2

Spin Polarized BEEMSpin Polarized BEEMBEEMBEEM

Fig. 3

- = 1.8 ± 0.2 nm

+ = 2.5 ± 0.3 nm

A. Stollenwerk et al. Phys. Rev. B (in press) (2007)

LaBella Group www.albany.edu/spin vlabella@albany.edu

cnse.albany.edu

Education and Outreach:Education and Outreach: The PI is engaged in several educational outreach activities. These include teaching first year graduate students quantum mechanics using an audience response system or clickers and participating in nano-career day where groups of high school students visit the college for an all day introduction to nanotechnology, which occurs twice a year. His research group is composed of a diverse set of students from all over the world that includes 4 Ph.D. students and 1 undergraduate. Two Ph.D. students graduated this past year including Chaffra Awo-Affouda who is now doing a post-doc at NRL supported by the NRC and Andrew Stollenwerk who is now doing a post-doc at Harvard. In addition, he is tutoring a junior in high school in quantum mechanics and scanning tunneling microscopy. The student, Lexa Vreslovic, is engaged in a special topics research program at her high school (The Academy of the Holy Names in Albany NY) where each student picks an interesting topic to study. Lexa picked quantum mechanics after reading an interesting article in Scientific American! This is an ongoing program that Lexa started in her freshman year and plans to continue until she is a senior. Currently she is learning about tunneling and how the STM works. This study will lead to her competing in local and national level science fairs.

The spintronics research group at the College of Nanoscale Science and Engineering (Left to Right) Joseph Abel, Ilona Sitnitski, John Garramone, Lexa Vreslovick, Evan Spadafora, Vincent LaBella

High school student Lexa Vreslovic (right) and Grad Students Ilona Sitnitski (center) and Joeseph Abel (left) work on the ambient STM/BEEM instrument

Towards an Atomic Scale Understanding of Spin Polarized Electron TransportTowards an Atomic Scale Understanding of Spin Polarized Electron TransportVincent P. LaBella, College of Nanoscale Science and Engineering,

University at Albany / SUNY, DMR-0349108

Second year graduate student John Garramone works on UHV STM/BEEM instrument