Albany high senior Joanna Belding taking STM and BEEM data.

1. Towards an Atomic Scale Understanding of Spin Polarized Electron TransportVincent P. LaBella, College of Nanoscale Science and Engineering, University at Albany / SUNY, DMR0349108 Spintronics - Utilizing the spin of the electron as well as its charge to fabricate novel, multi-functional semiconductor devices. Today,the spin of the electron is utilized in data storage devices such as the read heads on hard disk drives. The fundamental understanding of spin dependant transport helped to fuel the dramatic increase in storage capacity over the past decade. Tomorrow,new spintronic devices for logic and computation are dreamt of that will bring about increases in speed and reductions in power consumption. For example, a single multi-functional spin based device that can replace multiple charge based devices, or a way to make quantum computing using electron spins. To realize these goals,spintronics must move from mostly metal-based devices such as GMR/TMR stacks into semiconductors. Ion implantation of Mn and growth of Mn-doped semiconductors such as Si and GaAs are currently being explored as candidates. In addition, advances in our fundamental understanding of spin polarized electron transport through materials and material interfaces at an atomic level are needed. Spin polarized ballistic electron emission microscopy is being developed which can measure spin transport on the nanometer length scale. Group members (L-R) PI: V. LaBella, Ph.D. Student A. Stollenwerk, Post Doc M. Krause, Post Doc M. Bolduc, Ph.D. Student Chaffra Awo-Affouda Recent achievement of room temperature ferromagnetism in Mn ion implanted Si appeared in Science News and Materials Today. Physical Review B71 033302 (2005)

2. Towards an Atomic Scale Understanding of Spin Polarized Electron TransportVincent P. LaBella, College of Nanoscale Science and Engineering, University at Albany / SUNY, DMR0349108 A Combined MBE and STM system has been constructed to characterize both compound and elemental semiconductor surfaces and interfaces. A custom designed sample transfer mechanism connects the two chambers. The MBE chamber is equipped with electron diffraction and provides substrate temperature measurements and control by means of band-edge thermometry accurate to within ± 0.5 C. In addition, the microscope can operate at temperatures as low as 4 K and perform ballistic electron emission microscopy. The system has a separate preparation chamber with an evaporation source for metals. The entire STM chamber rests on an active vibration isolation table, while still maintaining an all UHV connection to the MBE. This state-of-the-art system is used for the research projects highlighted in these slides. In addition, the group studies compound semiconductor surfaces and Dr. LaBella and post-doc M. Krause just submitted a review article to Surface Science Reports cover the past 40 years of research on the technologically important GaAs(001) surface. Scaled drawing of the interconnected III-V MBE and STM system which is also capable of performing BEEM measurements. See M. Krause et al., Journal of Vacuum Science & Technology B23 1684 (2005) Above Room temperatureferromagnetism in Mn ion implanted Si (left). Integrating ferromagnetism into semiconductors is a first step at achieving semiconductor based spintronic devices. We demonstrate this is possible by ion implanting Mn into Si. Our ultimate goal is to make Si a diluted magnetic semiconductor (DMS). DMS materials are semiconductors doped with an impurity which makes in ferromagnetic. Typically, Mn is utilized in the range from 1-10% per atom giving these materials the novel property of electric field control of its ferromagnetism. The figure to the right shows the temperature dependence of the normalized remnant magnetization (top) for Mn-implanted Si both p-type (solid markers) and n-type (open markers). A Bloch-law dependence is fitted (solid line) with 90% confidence. The ferromagnetic hysteresis loops at 10 K, 77 K, and 300 K from Mn-implanted Si after rapid thermal annealing are shown in the bottom plot. The inset shows a ferromagnetic hysteresis loop at 300 K before annealing. These results show that it maybe possible to produce a Si-based DMS. The current research challenges are in the synthesis of the material to avoid cluster formation. Physical Review B71 033302 (2005) Albany High Seniors Joel Leibo and Josh Hancox give their final presentation on STM and BEEM from summer internship Ph.D. Student Andy Stollenwerk works with Albany High Senior Joanna Belding taking STM and BEEM data.

3. Towards an Atomic Scale Understanding of Spin Polarized Electron TransportVincent P. LaBella, College of Nanoscale Science and Engineering, University at Albany / SUNY, DMR0349108 BEEM Spectra of MnSi/Si(001)(left) shows evidence of multiple thresholds indicating a complex interface band structure [1]. This system is a potential spin injection contact as it has been theoretically predicted that a layered Si-Mn structure on Si(001) has ferromagnetic properties [2]. Spin polarized BEEM is currently in progress. With spin polarized BEEM a ferromagnetic STM tip is utilized to inject a polarized tunneling current. This technique will be utilized to measure the spin dependant attenuation lengths of the hot-electrons in ferromagnetic metal over-layers on Si. Spin dependant scattering is utilized in GMR devices and can also be used to increase the polarization state of a current of electrons for future spintronic devices. [1] A. Stollenwerk et al. JVST (submitted) [2] Wu et al. Phys. Rev. Lett.92 237202 (2004) PI LaBella works with Ph.D. Students Andy Stollenwerk and Chaffra Awo-Affouda on the MBE system. Mn growth on Si(001)is being studied with in situ STM. After Mn deposition and annealing, MnSi islands form. In between the islands evidence of monolayer-high Mn structures which agree with ab inito calculations can be seen (Mn rows) [2]. In addition, the islands undergo Ostwald ripening as annealing time is increased, which is being utilized to extract the activation energy for diffusion of Mn on the Si(001) surface. Part of this work is in collaboration with Peter Kratzer’s theory group at the Fritz Haber Inst. in Berlin. The goal of this research is to learn how to grow ordered MnSi thin films which are ferromagnetic to be utilized as spin injection contacts for silicon. [1] M. Krause et al. PRB (in preparation) [2] Wu et al. Phys. Rev. Lett.92 237202 (2004) 0.1 ML Mn on Si(001) after annealing at 300 C for 1 min MnSi island Albany high senior Joanna Belding taking STM and BEEM data. 50 nm × 50 nm Mn Rows on Si PI LaBella teaching graduate quantum using classroom response system (clickers). “I love the clickers!” say the students. 680 nm × 680 nm 10 nm × 10 nm