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何丕模, B. Lu, H. J. Zhang, H. Y. Li, S. N. Bao, and P. He *, T. L. Hao
PHYSICAL REVIEW B 68, 125410 (2003),-0001,():
-1年11月30日
Photoemission measurements for N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1, 1'-biphenyl-4, 4'-diamine (NPB) overlayer on Ag (111) are reported. The growth of NPB overlayer from submonolayer on the single-crystal surface of Ag (111), ultraviolet photoemission spectroscopy (UPS) and x-ray photoemission spectroscopy (XPS) measurements at each growth step allowed a better determination of band bending and interface dipole related change in work function. The XPS measurements show a weak interaction between NPB and Ag (111) and the C 1s core level shift provides a measurement of the band bending occurring with the NPB overlayer. UPS measurements show a decrease in work function with increasing thickness of NPB overlayer. The dipole contribution to the work function as a function of NPB thickness is deduced by subtracting the band bending from the change in work function. The dipole contribution has a minimum at a NPB thickness of about a monolayer. The decrease of work function is attributed to both the band bending occurring within NPB overlayer and dipole layer formed due to surface polarization. Additionally, the top of the highest occupied molecular orbital of NPB is located at about 1.7meV below Fermi level.
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【期刊论文】Interaction of Cs and CO on Ru (0001) for Cs submonolayer coverages
何丕模, P. He and K. Jacobi a)
J. Chem. Phys. 106 (8), 22 February 1997,-0001,():
-1年11月30日
The interaction of Cs and CO was studied for submonolayer coverages of Cs on Ru (0001) by means of high-resolution electron energy-loss spectroscopy (HREELS), thermal desorption spectroscopy (TDS), and low-energy electron diffraction (LEED). From the HREEL spectra and the 2×2 LEED pattern it is concluded that two-dimensional islands of Cs+2CO stoichiometry are formed first. For high CO doses CO adsorbs on the bare Ru surface between the islands as concluded from the v(C-O) stretch-mode frequency and the (√3×√3)R30℃ LEED pattern. Besides some local interaction between CO and Cs, there is strong evidence found for a long range, through substrate interaction. Our data can be understood in terms of a charge redistribution model; Cs donates a given amount of charge to the surface which is then backdonated to and shared between the adsorbed CO molecules within the (Cs+2CO)-islands and outside of them on the bare surface. The desorption temperature of CO with θCO→0 increases nearly linearly with θCs indicating CO desorption out of a two dimensional Cs gas in which the lateral interaction increases with θCs .
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【期刊论文】Vibrational analysis of the (Cs+CO)-(2
何丕模, Peimo He, Yabo Xu, Karl Jacobi a)
J. Chem. Phys. 104 (20), 22 May 1996,-0001,():
-1年11月30日
On a Ru (0001) surface Cs and CO form a very well ordered (Cs+CO)-(2×2) compound layer whose structure was analyzed recently (Cs on-top, CO in threefold sites). Here we present a vibrational analysis of the same system using high-resolution electron energy loss spectroscopy (HREELS), thermal desorption spectroscopy (TDS), and low-energy electron diffraction (LEED). The bonding of CO to Ru is both local and nonlocal. Two (C-O) stretch frequencies are observed depending on whether there are one or two CO molecules in the 2×2 cell. They change in energy between 155 and 204meV depending on CO coverage θCO. Setting θmax CO=1.0, the evolution of the C-O stretch intensities indicates that up to θCO=0.22 the 1-CO-(2×2) phase is formed exclusively implying some mobility of the Cs layer. For θCO.0.22 the 2-CO-(2×2) phase grows additionally until at θCO=1.0 only the 2-CO-(2×2) phase is found. Two Ru-CO stretch modes are observed for the first time and are assigned to adsorption in the hcp and fcc hollow sites within the 2×2 unit cell. They are very weak in intensity which is attributed to the threefold-hollow site and some screening in the 2D compound. With CO adsorption a change of the electronic structure of the Cs adlayer is observed; the adlayer loses metallicity and the Cs-Ru stretch becomes visible. Strong changes of the Cs-Ru stretch energies are observed with CO coverage.
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【期刊论文】Epitaxial growth of tetracene on the Ag (110) surface
何丕模, B. Lu a, H.J. Zhang a, H. Huang a, H.Y. Mao a, Q. Chen b, H.Y. Li a, P. He a, *, S.N. Bao a
Applied Surface Science xxx(2004)xxx-xxx,-0001,():
-1年11月30日
Thin film growth of tetracene on Ag (110) has been investigated by using scanning tunneling microscopy (STM). In the monolayer regime, the tetracene molecules formed islands of ordered structure, which is commensurate (4-fold periodicity) in the [110] direction, but incommensurate in the [001] azimuth, with the substrate. All the tetracene molecules align regularly with their longer axes parallel to the [001] direction, and with their molecular planes parallel to the surface. At multilayer coverages, the tetracene molecules form a crystalline film in a novel 3D orthorhombic structure, with their orientations remained unchanged. Growth of tetracene on Ag (110) is in the layer-by-layer growth mode.
Organic semiconductor, Silver surface, Epitaxial growth, Scanning tunneling microscopy
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【期刊论文】Vibrational study of tris-(8-hydroxyquinoline) aluminum/LiF/Al interfaces
何丕模, P. He, S. D. Wang, S. T. Lee, and L. S. Hung a)
Appl. Phys. Lett., Vol. 82, No.19, 12 May 2003,-0001,():
-1年11月30日
Interface studies of tris-(8-hydroxyquinoline) aluminum (Alq3)/LiF/Al were carried out with high-resolution electron-energy-loss spectroscopy. With LiF on Alq3 or Al on LiF, no significant changes in intensity were observed for the loss peak related to the Li-F stretch mode. However, the deposition of less than one monolayer of Al on Alq3/LiF resulted in a strong attenuation of the LiF-loss peak, providing a direct evidence of LiF dissociation in the coexistence of Alq3 and Al with LiF. On the other hand, the LiF-loss peak remained almost unchanged when Al was deposited on poly (9,9-dioctyl-fluorene)/LiF.
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