Spectroscopy of Hybrid Inorganic/Organic Interfaces Electron Spectroscopy Dietrich RT Zahn

Photoemission Spectroscopy: UPS and XPS X-Ray Source (Mg K  / Zr M  ) X-Ray Source (Mg K  / Zr M  ) UV Lamp (He I/ He II) UV Lamp (He I/ He II) Lens System: 5 operation modes Lens System: 5 operation modes Angular Resolved Energy Analyser Angular Resolved Energy Analyser Detector (Channeltron) Detector (Channeltron) Data acquisition system Data acquisition system

OMBD System and Electrical Measurements in situ IV / CV

X5 Determination of using Photoemission Spectroscopy Determination of Energy Diagram using Photoemission Spectroscopy

Reduction of Inhomogeneous Fermi Level Pinning by PTCDA Deposition S.Park, D.R.T. Zahn et al., APL 76 (22) (2000) PTCDA/Se-GaAs(100) Lineshape remains unchanged  Negligible interaction between PTCDA and Se-GaAs(100). Gaussian broadening of Se3d core level is reduced: 0.87  0.78 eV by 0.09 eV.  Reduction of inhomogeneous Fermi level pinning by preferential adsorption of PTCDA on defect sites.

Valence Band Offset at the PTCDA/S-GaAs Interface Valence band – HOMO offset : (1.1eV  0.1)eV No change in band bending of the substrate upon PTCDA deposition.

IE spans from 5.18 to 6.4eV. A wide range of IE of wet S treated surfaces (5.53~5.91eV).  Due to the degree of the surface dipole formation. Similar IE for GaAs(100)- c(4  4) and H-plasma treated GaAs(100). Ionization Energy of Differently Treated GaAs(100) Surfaces

Valence Band Spectra of PTCDA/S-GaAs(100) Assignment - A:  MO in perylene - B,C,D:  MO in perylene and C=O - E: mixture of  and  states No change in energy position of A – E upon PTCDA deposition. Shift of E cutoff towards higher binding energy.

Valence Band Spectra of PTCDA/GaAs(100)-c(4  4) Change in direction of interface dipole is observed.

Band Diagram of PTCDA on Differently treated GaAs(100) IE GaAs =6.40eV Se-GaAs PTCDA IE GaAs =5.75eV S-GaAs PTCDA GaAs PTCDA IE GaAs =5.23eV Possible LUMO position:(E g,o =2.2eV)–(E g,t =2.8eV from Kahn et al.) Correlation between interface dipole and relative energy position of E LUMO to E CBM.  EA difference is the driving force for the formation of the interface dipole.

Interface Dipole vs. Electron Affinity of GaAs(100) Se-GaAs -(2  1) S-GaAs -(2  1) GaAs -c(4  4) Linear relation of interface dipole to  GaAs. At interface dipole=0,  GaAs =(4.12  0.1)eV=  PTCDA E g,t (PTCDA)=2.44–2.55eV  PTCDA =4.12eV

VB Spectra of Ag on PTCDA At low Ag thickness, features from PTCDA are still seen without energy shifts. Very weak charge transfer between Ag atoms and PTCDA molecules.

VB Spectra of Ag on DiMe- PTCDI Very weak charge transfer between Ag atoms and DiMe-PTCDI molecules. Slightly different Ag4d band lineshape. DiMe thyl-3,4,9,10- P erylene t etra c arboxylic d i i mide

Influence of Organic Substrate on Metal Workfunction  Ag(111),  Ag,poly : Dweydari et al., Phys. Stat. Soli. A 17 (1973) 247 Ag film on PTCDA: closer  to  Ag(111), stronger (111) diffraction peak Crystalline structure of underlying organic film strongly influence the crystalline structure and  of metal film.

interface dipole  =-0.68 eV strong surface dipole  good interface properties Energy band alignment DiMePTCDI / S-GaAs(2  1) EFSEFS 1.18eV 2.04eV 6.28eV 6.46eV  =-0.68eV E VBM E HOMO Gianina Gavrila

Density of states for a neutral molecule of DiMePTCDI valence band states corresponding to bonding combinations of C 2s, C 2p, N 2s, N 2p or O 2s, O 2p

Gianina Gavrila Molecular orientation of DiMePTCDI on S-GaAs(100) 56°  deviation from the predicted value by ~ 15 °  better estimation of V 0

Photon energy dependence spectra Gianina Gavrila

Intermolecular energy band dispersion  the final continuum state is a parabolic free-electron-like band in a constant inner potential V 0. * Parameters:  Parameters: V 0 =5.8 eV, t=0.04eV, a  = 4.1 Å  tilt 42° * D. Yoschimura at al, PRB, 60, 12, , 1999

The Transport Gap from Combined PES and IPES Measurements HOMO LUMO EFEF E VAC IEEA