One Dimensional Rare Earth Metal Silicides Applications in - PowerPoint PPT Presentation

One Dimensional Rare Earth Metal Silicides Applications in Applied and Fundamental Science Saban Hus University of Tennessee Oct 25 2010

Outline ● Introduction and Motivation Rare Earth Metal Silicide nanowires ● Applications in applied and fundamental sciences ● – Nanowires for DNA sequencing – Nanowires as nano probes – Nanowires for plasmonics ● Experimental Methods STM and 4-probe STM ● ● YSi 2 nanowires Growth and Structure ● Electrical Characterization of YSi 2 nanowires ●

Rare-Earth Metal Silicide Nanowires Epitaxial RESi 2 are formed via self ● assembly of rare earth metal (RE) onto an atomically clean Si (001) surface RE = Dy, Er, Y, Sm, Gd, Ho, Sc ... ● These nanowires exhibit high ● aspect ratios having lengths exceeding 1 micron and widths as small as 1.15 nm 100nm

Applications in ● Applied Sciences ● Fundamental Sciences as quantum devices Understanding the electronic ● ● behavior in 1D systems interconnects for nano ● As a probe to understand nano electronics. ● structures. Molecular level probing ● Charge ordering in YSi 2 nanowires YSi 2 nanowires for DNA sequencing Zeng et al. Nature Mat., Vol. 7, 539 (2006) UTK- UNC- UCSD

Nanowires for DNA sequencing Current DNA sequencing ● technologies perform sequencing on amplified copies of templates These techniques are slow and ● expensive. A nanowire electrode can be used ● to achieve single nucleotide resolution by measuring the tunneling current as DNA pass through a nano channel.

RE Nanowires for Surface Enhanced Raman Scattering Arrangements of nano particles are ● typically employed in SERS experiments A better control on nano particle ● size can further enhance the Raman scattering to a level sensitive enough to detect single molecules Nobel metal particles (gold or ● platinum) aggregate preferentially You et al. Nano Lett., Vol. 6, No. 9, 2006 on top of RESi 2 nanowires forming an ordered array of noble metal nano clusters or nanowires

Nanowires as nano probes Nanowires with thicknesses ~1 nm ● can be used to probe the electronic structure of smallest nano structures.

Experimental Methods

Creating images from tunneling Creating images from tunneling current current 2 piezoelectric tube control the ● lateral position (x,y) of the tip with ≤ 1Å accuracy Another piezoelectric tube ● controls the height (z) of the tip with 0.05 Å accuracy At a given (x,y) coordinate the ● tip is moved up or down (±z)to provide a predefined tunneling current (~0.1 nA) Z position of the tip is plotted as ● a function of (x,y)

Tunneling current Tunneling current is also ● proportional to the local density of states (LDOS) near Fermi level. where f is the Fermi function, ρ s ● and ρ t are the density of states in the sample and tip, respectively M is the tunneling matrix ● between the modified wavefunctions of the tip and the sample surface

4 Probe STM CNMS / ORNL has a ● Ultrahigh Vacuum Cryo 4- ● probe STM 4 STM probes can take atomic ● resolution images A SEM is used to monitor SEM ● tips while approaching to the nano wire or contact paths Gold coated SEM tips can also ● be used for contact fabrication

YSi 2 Nanowires

YSi 2 Nanowires The wires form through self- ● assembly after depositing approximately 0.5 monolayer of yttrium onto an atomically clean Si(001) surface at about 600 C. The silicide form wires due to ● anisotropic lattice mismatch with silicon substrate YSi wires have higher aspect ● ratios and better uniformity compared the other rare-earth silicide nanowires A , Large-scale STM image of YSi 2 nanowires B , High-resolution STM image at room temperature. C , Simulated STM image of a 1.1 nm wide wire D , Cross-sectional line profile of a 1.1 nm wide nanowire. Zeng et al. Nature Mat., Vol. 7, 539 (2006)c

Structure of YSi 2 Nanowires To determine the structure compare ● Experimental ● – STM images – Tunneling spectra with Theoretical ● – image simulations – local density of states calculations, using Density Functional Theory. A , Structure model of bulk YSi 2 . B , Calculated structure of the thinnest, 1.1 nm wide YSi 2 nanowires. C , dI/dV spectra of the 1.1 nm wide YSi 2 nanowires, D , E , Top and cross-sectional view of the calculated wavefunction densities on the 1.1 nm wide YSi 2 nanowire. Zeng et al. Nature Mat., Vol. 7, 539 (2006)

Transport measurements on YSi 2 Nanowires 4 Probe STM Measurements ● Nanowires are conducted by ● very small Pt electrodes, fabricated via EBID, Pt electrodes are connected to ● thick mesoscopic contact pads . Nanowire between the Pt electrodes Approaching the 4 STM tips to mesoscopic contacts for I-V measurements

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