Scanning tunneling microscopy study of metal-free phthalocyanine monolayer structures on graphite

Abstract

Low temperature scanning tunneling microscopy (STM) studies of metal-free phthalocyanine (H2Pc) adsorbed on highly oriented pyrolytic graphite (HOPG) have shown ordered arrangement of molecules for low coverages up to 1 ML. Evaporation of H2Pc onto HOPG and annealing of the sample to 670 K result in a densely packed structure of the molecules. Arrangements of submonolayer, monolayer, and monolayer with additional adsorbed molecules have been investigated. The high resolution of our investigations has permitted us to image single molecule orientation. The molecular plane is found to be oriented parallel to the substrate surface and a square adsorption unit cell of the molecules is reported. In addition, depending on the bias voltage, different electronic states of the molecules have been probed. The characterized molecular states are in excellent agreement with density functional theory ground state simulations of a single molecule. Additional molecules adsorbed on the monolayer structures have been observed, and it is found that the second layer molecules adsorb flat and on top of the molecules in the first layer. All STM measurements presented here have been performed at a sample temperature of 70 K.

Surface chemistry of porphyrins and phthalocyanines

“…The reported incommensurate adsorption with a near-square unit cell (13.8 Â 13.1 Å 2 , 92.41) disagrees with earlier work, in which a hexagonal unit cell was observed [315]. Second-layer 2HPc molecules were found to adsorb atop of the first-layer molecules [314]. Well-ordered monolayers with a nearly quadratic lattice were also observed for PdPc/HOPG [316] and CuPc/HOPG [317,318].…”

“…Similar findings were reported for FePc submonolayers after annealing to 670 K, whereas apparently kinetically controlled 3D growth occurred during room temperature deposition [313]. For 2HPc on HOPG, Nilson et al [314] observed densely packed islands already in the submonolayer range, when the samples were annealed at 670 K after deposition. The reported incommensurate adsorption with a near-square unit cell (13.8 Â 13.1 Å 2 , 92.41) disagrees with earlier work, in which a hexagonal unit cell was observed [315].…”

Metal-free phthalocyanine (H2Pc) molecule adsorbed on the Au(111) surface: formation of a wide domain along a single lattice direction

“…It was reported that H 2 Pc molecules form a quasi-square lattice on highly oriented pyrolytic graphite surface [25], and similar ordering was observed for FePc [11,12], CoPc [2,[13][14][15], NiPc [11], CuPc [2,15,16] and SnPc [17].…”

“…The diameter of the molecule can be estimated as the nearest-neighbor distance (nnd) of the close-packed molecules. The nnd of H 2 Pc on the graphite surface was reported as ∼1.3 nm [24,25]. The fcc domain is wide enough to accommodate one molecule, but not two molecules.…”

Ammonia adsorption on iron phthalocyanine on Au(111): Influence on adsorbate–substrate coupling and molecular spin

“…On solid supports, phthalocyanines and phthalocyanine derivatives form ordered monolayer structures. [2][3][4][5][6][7] Such monolayers are promising candidates for novel catalytic [8][9][10][11][12] and gas sensing applications. [13][14][15][16][17][18][19][20][21][22][23][24][25][26] Their function will depend critically on the molecular electronic structure, which for phthalocyanines containing certain transition metals (such as Cr, Mn, Fe, Co) is quite complex with an open shell structure of the d orbitals and a number of energetically close-lying electronic states.…”