Kenneth T. Park

Influence of substrate temperature on epitaxial copper phthalocyanines studied by photoemission spectroscopy

We report the formation of heteroepitaxial copper phthalocyanine (CuPc) overlayers on a “5×20” reconstructed Au(001) substrate, with thicknesses ranging from 0.8 to 26.9 A. The adsorbed CuPc at room temperature forms a quasiepitaxial overlayer, incommensurate with the substrate lattice, aligned with the 〈110〉 and 〈110〉 axes of the Au(001) surface. At elevated substrate temperatures (ET) between 200 and 250 °C, the deposition of CuPc results in a 13.8 A square overlayer structure commensurate with the substrate lattice. The electronic structures of CuPc overlayers grown at both RT and ET are also investigated. While the films grown at both temperatures generally exhibit lowering of the vacuum level, consistent with the presence of an interfacial dipole, it is the ET-grown CuPc overlayer that exhibits a sharp decrease of the surface vacuum level upon completion of a monolayer. The experimental CuPc valence band energies are compared with the calculated ionization potentials of a CuPc molecule. Using the tu...

Interaction of metallophthalocyanines (MPc,M=Co,Ni) on Au(001): Ultraviolet photoemission spectroscopy and low energy electron diffraction study

Thin films of metallophthalocyanine (MPc,M=Co,Ni) evaporated onto a “5×20” reconstructed Au(001) substrate at room temperature have been investigated by employing low energy electron diffraction (LEED) and ultraviolet photoelectron spectroscopy (UPS). The LEED images from NiPc thin films show that the overlayers are highly ordered with a square unit cell of 12.8×12.8A2 aligned along the ⟨110⟩ and ⟨11¯0⟩ axes of the Au(001) substrate. For CoPc, the LEED pattern reveals the superposition of multiple rotationally equivalent domains of a 12.9×12.9A2 square lattice which are rotated by 16° with respect to each other. The contrast between NiPc and CoPc on Au(001) is further demonstrated in the interfacial electronic structure. UPS studies of the interfacial layers of NiPc deposited on the hexagonally reconstructed gold substrate indicate that NiPc physisorbs on the gold surface as evidenced by a uniform molecular orbital (MO) shift. The CoPc MO’s, on the other hand, indicates a charge transfer at the interface,...

Tip-assisted directional growth of atomically thin Ag islands

Abstract The growth and decay of metal nanostructures are important in many areas of physical science and catalytic chemistry. Here, we show the directional growth of Ag island stripes at room temperature via tip-assisted coarsening of hexagonal islands on Ag(111) using scanning tunneling microscope (STM). The mechanism of this process is attributed to the alignment of the adatom and vacancy islands along the scanning direction via tip-sample interaction during the process of the intrinsic decay of the metastable Ag islands. We find that this tip-assisted island growth is not directly related to the tunneling current and the bias voltage. Experiments performed using Ag tips and W tips show similar coarsening effects. The chamber pressure and the O2 exposure also do not have systematic effects on the rate of island growth. The tip-assisted coarsening strongly depends on the tip morphology.