A. Kahn - Academia.edu (original) (raw)

Papers by A. Kahn

$Research paper thumbnail of Atomic structure of the CdS(112¯0) surface: A dynamical analysis of low-energy electron-diffraction intensities$

Physical Review B, 1991

A determination of the atomic geometry of the CdS(1120) surface by dynamical analysis of measured... more A determination of the atomic geometry of the CdS(1120) surface by dynamical analysis of measured low-energy (35~E~250 eV) electron-diffraction (LEED) intensities is reported. The analysis is performed on the average of two data sets, each of which includes fifteen diffracted beams. Intensities are measured from two different CdS surfaces cleaved in ultrahigh vacuum and cooled below 50 K. The measurements are made using a fast LEED data-acquisition system. The scattered intensities are calculated using a relativistic, energy-dependent Hara-exchange electronion-core potential. The search for the best-fit structure is conducted with a combination of the x-ray R factor and integrated-intensity R factor. The best description of the experimental intensities by the calculated ones is obtained for a structure characterized by a bond-length-conserving relaxation of the surface Cd-S-Cd and S-Cd-S triplets by 0 an angle co=30' followed by a 0.1 A contraction of the first layer toward the bulk. This structure is in quantitative agreement with predictions based on total-energy-minimization calculations for this surface.

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2004

$Research paper thumbnail of Dynamical calculation of low-energy electron diffraction intensities from GaAs(110): Influence of boundary conditions, exchange potential, lattice vibrations, and multilayer reconstructions$

Physical Review B, 1979

Dynamical calculations of the intensities of normally incident low-energy electrons diffracted fr... more Dynamical calculations of the intensities of normally incident low-energy electrons diffracted from GaAs (110), performed using a matrix-inversion method, are compared both with earlier kinematical calculations and with measured intensities. The insensitivity of the calculated ...

Physical Review B, 1994

... D. Olego Philips Laboratories, Briarcliff Manor, New York 10510 (Received 24 January 1994) Ch... more ... D. Olego Philips Laboratories, Briarcliff Manor, New York 10510 (Received 24 January 1994) Chemical ... In this paper we present a multiple-technique investi-gation of ZnSe(100) which ... a Zr anode) and contact potential difference (CPD) measurements (vibrating Kelvin probe) to ...

Surface Science, 1984

Abstract The atomic structures of the two inequivalent (211) surfaces of GaAs have been investiga... more Abstract The atomic structures of the two inequivalent (211) surfaces of GaAs have been investigated by LEED. Both surfaces, prepared by etching and heat-cleaning or ion-sputtering and annealing, are unstable and develop large (110) facets which exhibit the atomic geometry of the (110) GaAs surface. These facets entirely cover the surface. Three sets of facets, making 30°, 30° and 54° angles with the (211) plane, are detected on one surface. Only two sets, making 30° angles with the (211) plane, are detected on the other. The reasons for this difference are not understood at this time. The LEED study of Si(211) and Ge(211) shows that the Si surface is flat whereas the Ge surface exhibits reconstructed (311) facets. The structural difference between the (211) surfaces of GaAs and Ge and the facetting of the compound are invoked to explain the problems encountered in the MBE growth of GaAs on Ge(211).

Surface Science, 1979

Cleaved GaAs(ll0) surfaces were exposed to oxygen (106-5 X 10" L) and analysed by LEED and UPS. V... more Cleaved GaAs(ll0) surfaces were exposed to oxygen (106-5 X 10" L) and analysed by LEED and UPS. Very important changes in the electron diffraction occur at lo8 L and the analysis of the LEED pattern shows a bulk-lie diffraction superposed on a high background, implying that a thin layer (l-3 A) disordered by the oxidation covers the GaAs lattice relaxted to its bulk structure.

Physical Review Letters, 2005

Physical Review Letters, 2013

Physical Review B, 2005

We present a mechanism that explains the energy-level alignment at organic-organic ͑OO͒ semicondu... more We present a mechanism that explains the energy-level alignment at organic-organic ͑OO͒ semiconductor heterojunctions. Following our work on metal/organic interfaces, we extend the concepts of charge neutrality level ͑CNL͒ and induced density of interface states to OO interfaces, and propose that the energy-level alignment is driven by the alignment of the CNLs of the two organic semiconductors. The initial offset between the CNLs gives rise to a charge transfer across the interface, which induces an interface dipole and tends to align the CNLs. The initial CNL difference is reduced according to the screening factor S, a quantity related to the dielectric functions of the organic materials. Good quantitative agreement with experiment is found. Our model thus provides a simple and intuitive, yet general, explanation of the energy-level alignment at organic semiconductor heterojunctions.

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1993

ABSTRACT The chemistry, overlayer morphology, and band bending occurring upon room temperature de... more ABSTRACT The chemistry, overlayer morphology, and band bending occurring upon room temperature deposition of Ga and Pb on GaAs(100) are studied via high resolution photoemission spectroscopy, low energy electron diffraction and contact potential difference measurement. Both interfaces are abrupt and unreacted. At submonolayer coverage, Ga and Pb grow two dimensionally on GaAs(100). An ordered (1×2) superstructure is obtained for Pb(1/2 ML)/GaAs(100) by low temperature annealing of the interface (∼300 °C). Clustering is dominant at high coverage. With Ga, the Fermi level (E F ) converges toward a position 0.68 eV above the valence band maximum (VBM), in agreement with the position obtained for the GaAs(110) surface. The room temperature deposition of Pb leads to E F stabilization at 0.57 eV above VBM, independent of the initial surface stoichiometry (Ga or As rich). The evolution of the band bending as a function of metal coverage emphasizes in both cases the importance of adatom‐induced states at low coverages and the transition to final E F position upon metallization, in support of models based on metal‐induced gap states.

Journal of Electron Spectroscopy and Related Phenomena, 2005

We present ultraviolet photoelectron spectroscopy studies on alkali metal-intercalated thin films... more We present ultraviolet photoelectron spectroscopy studies on alkali metal-intercalated thin films of electroluminescent p-sexiphenyl (6P) and the organic hole transporting material N,N-bis-(1-naphthyl)-N,N-diphenyl1-1,1-biphenyl1-4,4-diamine (␣-NPD). The formation of new occupied electronic states in the otherwise empty energy gap of 6P and ␣-NPD is observed, accompanied by a significant shift of the Fermilevel. Depending on the work function φ of the substrate used for the organic thin films, we observe two different scenarios at low intercalation levels: the new electronic states are observed at (and even above) E F for high φ substrates, whereas they are observed below E F for low φ substrates. At high intercalation levels, all the states are observed below E F. The observation of states at and above E F is attributed to a lack of thermodynamic equilibrium across the organic thin film.

Journal of Applied Physics, 2001

We study the effects of lithium ͑Li͒ incorporation in the cathodes of organic light-emitting devi... more We study the effects of lithium ͑Li͒ incorporation in the cathodes of organic light-emitting devices. A thermally evaporated surface layer of metallic Li is found to diffuse through, and subsequently dope, the electron transporting organic semiconducting thin films immediately below the cathode, forming an Ohmic contact. A diffusion length of ϳ700 Å is inferred from analyses of the currentvoltage and secondary ion mass spectrometry data. The conductivity of the Li-doped organic films is ϳ3ϫ10 Ϫ5 S/cm. Photoemission spectroscopy suggests that Li lowers the barrier to injection at the organic/cathode interface, introduces gap states in the bulk of the organic semiconductor, and dopes the bulk to facilitate efficient charge transport.

Critical Reviews in Solid State and Materials Sciences, 1979

The proper description of the electron physics and chemistry of the terminating surface of a soli... more The proper description of the electron physics and chemistry of the terminating surface of a solid lies somewhere between the collective approach successful in the description of infinite lattices and the local approach successful in the description of small molecules. When viewed in the collective approach as the terminating atomic layer of an otherwise perfect, semi-infinite solid, the collective approach

Chemical Physics Letters, 2002

Chemical Physics Letters, 2007

Ultraviolet photoemission spectroscopy, inverse photoemission spectroscopy, and two-photon photoe... more Ultraviolet photoemission spectroscopy, inverse photoemission spectroscopy, and two-photon photoemission spectroscopy are techniques commonly used to examine the electronic structure of surfaces and interfaces. We have used all three to study self-assembled monolayers of 4,4 0-bis(phenylethynyl)benzenethiol on gold, a system often studied for potential application in molecular electronic junctions. We compare the results of these measurements and discuss them in relation to electronic structure calculations. The result is a better understanding of the valence electronic structure for this system, of the spectroscopic methods involved, and of previous measurements.

Applied Surface Science, 1991

We u,e the Kelvin method to study the synchrotron radiation induced surface photovohage (SPV) on ... more We u,e the Kelvin method to study the synchrotron radiation induced surface photovohage (SPV) on GaAM110) as a function of metal co;'erage and temperature. We find that varying the temperature alone does not induce significant change in band bending in the semiconductor, but that the combination of low t~.mperature and synchrotron light illumination on lightly doped n-GaAs induces a large and quasi-permanent SPV. On lightly doped n-GaAs, the Iov,-tcmperature SPV (0.55 eV) is equal to the quasi-totality of the band bending at submtmolayer coverage and discharges ~'ith a time constant of the order of hours. Above a monolayer, the rate of discharging increases dramatically, crrphasizing the role of charge leakage through the overlayer. The room temperature SPV is considerabl~, smaller (0.2 eV). Finally. no significant SPV is detected on highly doped GaAs. The impact of this synchrotron radiation reduced SPV on the photoemission study of metal/semiconductor interfaces is discussed in detail.

Applied Physics Letters, 1996

We present a photoemission investigation of the interface between In and 3, 4, 9, 10 perylenetetr... more We present a photoemission investigation of the interface between In and 3, 4, 9, 10 perylenetetracarboxylic dianhydride (PTCDA). The interfacial region is very wide due to an anomalously fast diffusion of In into the organic layer. In also reacts with the anhydride end groups of the molecules. ...

Advanced Materials, 1999

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