1. Highly spin-polarized materials play a central role in spin-electronics. Most such materials have a fixed spin polarization P dictated by the band structure, e.g., P = 45% for Co, and P = 37% for Ni. An ideal ferromagnetic electron source would possess a high degree of tunable spin polarization. We have recently demonstrated a simple scheme that can be utilized to control both the magnitude and sign of the spin polarization of ferromagnetic Co 1-x Fe x S 2. Phys. Rev. Lett., 94, 056602 (2005). (a) Conductance curves measured by Andreev reflection, magnitude of (b) theoretical and (c) experimental values of spin polarization. Transport of Nanowires in Suspension C. L. Chien, Johns Hopkins University, DMR-0403849

2. Transport of Nanowires in Suspension C. L. Chien, Johns Hopkins University, DMR-0403849 Materials of high spin polarization P play a central role in the emerging field of spin- electronics. The value of P is determined by the densities of the electrons at the Fermi energy of opposite spins. For example, the performance a magnetic tunnel junction (MTJ) as measured by magnetoresistance (MR) depends directly on P in the form of 2P2/(1-P2). However, the ideal ferromagnetic electron sources would not only possess a large P, but would also offer control over the magnitude of P. This would allow for example, for the measurement of device performance of an MTJ as a controlled function of the P values of the electrodes. In this work, [Phys. Rev. Lett., 94, 056602 (2005)], we demonstrate that a simple scheme can be utilized to control both the magnitude and sign of P of ferromagnetic Co1-xFexS2. CoS2 is a ferromagnetic metal while the isostructural FeS2 compound is a non-magnetic semiconductor. The position of the Fermi level in Co1-xFexS2 substitutional solid solutions can therefore be tuned by composition, providing control over the value of P. Using first principles electronic band-structure calculations, and spin polarization measurement using Andreev reflection we show that with increasing Fe doping the spin polarization first changes sign before acquiring P values as large as 85% at x = 0.15.

3. Education Outreach: An African American high school student (James Keene) from Baltimore Polytechnic Institute, as an summer intern in our lab, demonstrated and measured the characteristics of transporting nanowires in suspension using dielectropheresis (DEP) force through AC electric field, despite the extremely low Reynolds number of 10 -5. Applications: Manipulating and assembling small entities including biological cells in suspension, MEMS devices, micromotors and microstirrers. Au nanowires assembled in 0.3 sec under 10 V at 50 MHz Transport of Nanowires in Suspension C. L. Chien, Johns Hopkins University, DMR-0403849

4. Transport of Nanowires in Suspension C. L. Chien, Johns Hopkins University, DMR-0403849 Moving an object in suspension encounters drag force due to viscosity. The importance of the drag force is measured by the Reynolds number Re = Dvr/h, where D and v are the dimension and the velocity of the moving object, and r and h are the density and viscosity of the fluid. The smaller the value of Re the greater the difficulty in moving the object. For a human swimmer and a small fish, the Reynolds number are 105 and 102 respectively. However, for a nanowire a few µm in length and 300 nm in diameter, Re only 10-5, ten orders of magnitude smaller. An African American high school student (James Keene), working in our lab in the summer of 2005, shows that AC electric field applied to strategically designed electrodes can efficiently, controllably, and efficiently transport nanowires in suspension. He used circular electrodes (with which the electrical field can be calculated) to characterize the force and demonstrated that the nanowires can be rapidly assembled within a fraction of the second into a pattern according to the electric field distribution. This method has important implication in MEMS devices, micromotors, and manipulation of biological entities.