Jiandi Zhang

Magnetic nanostructures fabricated by scanning tunneling microscope-assisted chemical vapor deposition

We have successfully used scanning tunneling microscope-assisted chemical vapor deposition to fabricate magnetic nanostructures as fine as 5 nm wide and <2 nm high using ferrocene [Fe(C5H5)2] as the metal-organic source gas. The physical properties of these nanostructures were qualitatively characterized and ex situ magnetic force microscopy measurements indicate these features are strongly magnetic.

Surface lattice dynamics of La0.65Ca0.35MnO3 across the Curie temperature

Abstract We report a temperature-dependent study of the surface optical phonons of La 0.65 Ca 0.35 MnO 3 films using high-resolution electron-energy-loss spectroscopy. Three surface modes have been observed and correspond to the bulk modes which are associated with the internal vibrations of the MnO 6 octahedron. However, analogous to the high- T c superconducting cuperates, the surface phonons have higher energies than the bulk modes, indicating that the surface and the bulk have significantly different lattice dynamics. The small energy dispersion and large linewidth reflect a short phonon life time. The strong temperature dependence of the linewidth corresponds to coupled-random dynamic lattice distortions. A 2–4 meV shift in the phonon energy across the Curie temperature is associated with a static lattice distortion related to the magnetic phase transition. The temperature dependence of the surface phonon modes are compared with the current understanding of the bulk lattice dynamics, above and below the critical temperature for the structural, electronic, and magnetic phase transitions in the “colossal” magnetoresistance materials.

Direct visualization in manipulation of stable molecular radicals at room temperature

Abstract We present a novel approach for room-temperature molecular manipulation which exploits the reduced thermal mobility of chemisorbed molecular radicals, with cyclopentadienyl, C 5 H 5 , on Ag(100) as an example. Several novel manipulation modes are demonstrated, all achieved at room temperature. Most notably, the dynamics of the radicals can be directly visualized during manipulation, revealing their preferred direction of motion to be perpendicular to the tip displacement. Additionally, individual radicals can be selectively desorbed intact. These findings point to the feasibility of controlling surface chemistry and molecular engineering down to the fundamental ligand level.