Fabrice Amy

Hydrogen passivation of germanium (100) surface using wet chemical preparation

A wet chemical preparation involving de-ionized water, hydrogen peroxide, and hydrofluoric acid is used to passivate germanium (Ge) (100) surfaces. Infrared absorption spectroscopy and x-ray photoemission spectroscopy studies show that oxide free and hydrogen-terminated Ge (100) surfaces can be obtained. As in the case for silicon (100) surfaces etched in hydrofluoric acid, hydrogen-terminated Ge (100) surfaces are atomically rough, with primarily mono- and dihydride terminations.

Band offsets at heterojunctions between SrTiO3 and BaTiO3 and Si(100)

We use thin (∼26A) SrTiO3 and BaTiO3 films epitaxially grown on Si(100) substrates, and ultraviolet and x-ray photoemission spectroscopy to investigate band discontinuities at the SrTiO3∕Si and BaTiO3∕Si heterojunctions. The treatment of the oxide film surface ranges from ex situ ultraviolet generated ozone to annealing in O2 or ultrahigh vacuum. Depending on surface treatment, the valence band offset varies from 2.38 to 2.64eV for SrTiO3∕Si heterostructure and from 2.35 to 2.66eV for BaTiO3∕Si. These values imply that the conduction band minimum of the oxide is below that of the semiconductor, a situation referred to as negative conduction band offset. We demonstrate that the SrTiO3∕Si and BaTiO3∕Si interfaces undergo significant chemical changes during surface cleaning of the oxide film.

Gas phase chlorination of hydrogen-passivated silicon surfaces

A simple method is described to functionalize hydrogen-passivated Si(111) and Si(100) surfaces with chlorine (Cl2) gas. Infrared-absorption spectroscopy provides a positive identification of chlorination and mechanistic information on the chlorination of H-terminated Si surfaces, and on the structure and stability of chlorine-terminated Si surfaces (Cl∕Si). We find that the chlorination process does not change the surface morphology: H∕Si(111)‐(1×1) surfaces and HF-etched Si(100) surfaces remain atomically flat and atomically rough, respectively, upon chlorination. Chlorinated S: surfaces are stable in a nitrogen atmosphere for over 12 hours.

Interaction of H, O2, and H2O with 3C-SiC surfaces

Infrared absorption spectroscopy studies of Si-dimer-terminated 3C-SiC(100) 3×2 and c4×2 surfaces reveal marked differences between their atomic scale reactivity with H, O2, and H2O and that of Si(100) surfaces. While atomic hydrogen is well known to passivate dangling bonds on all Si surfaces, H exposure on both 3C-SiC(100) 3×2 and c(4×2) surfaces induces a metallic state instead. Furthermore, hydrogenated 3C-SiC(100) 3×2 surfaces exposed to O2 clearly show that oxygen atoms are inserted below the top surface without any loss in the H coverage at room temperature. Finally, while H2O decomposes into H and OH on both Si(100) 2×1 and 3C-SiC(100) 3×2, subsequent atomic H exposure induces a metallic state on the latter only, creating a thin oxide strip on the top surface separated by a metallic trough.

Surface and interface chemical composition of thin epitaxial SrTiO3 and BaTiO3 films: Photoemission investigation

In this work, we use SrTiO3 and BaTiO3 films (thickness <10nm) epitaxially grown on Si(100) substrates, and x-ray and ultraviolet (UV) photoemission spectroscopy to investigate the effect of surface preparation on chemical and electronic film and interface properties. Depending on the surface treatment, e.g., ex situ UV generated ozone or annealing in oxygen or vacuum, the valence band maximum position shifts by more than 2eV, whereas the oxide core levels shift by less than 0.6eV. These findings indicate that extremely careful cleaning procedures must be applied, as surface composition and film morphology are of paramount importance in the determination of the electronic structure of the crystalline oxides. In addition, the interfaces between SrTiO3 and BaTiO3 and Si are shown to be unstable at annealing temperatures required to thoroughly clean and order the surface.

Enhancement of iridium-based organic light-emitting diodes by spatial doping of the hole transport layer

The electroluminescence efficiency of Ir-based green emitter devices is very sensitive to the nature of the hole transport layer used. We show that by inserting a 1 nm layer of bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)methane (MPMP) in a 4,4′-bis-(carbazol-9-yl)biphenyl (CBP) hole transport layer, a device that combines the positive attributes of both MPMP (high efficiency) and CBP (low injection voltage) is obtained. These results can be understood based on a combined ultraviolet photoemission spectroscopy/inverse photoemission spectroscopy study, which reveals the very low electron affinity and superior electron blocking capability of MPMP.

Wet Chemical Cleaning of Germanium Surfaces for Growth of High-k Dielectrics

One of the major difficulties preventing the wide use of germanium (epi or bulk) as a gate material is the poor stability of its oxide, leading to reproducibility and reliability issues. In contrast to silicon, the nature and thickness of Ge “native” oxides are history dependent, and most phases of germanium oxide are water-soluble. As a result, the procedures for passivating Ge surfaces with hydrogen (HF last) are more complex and less forgiving. We have used infrared absorption spectroscopy and x-ray photoelectron spectroscopy to investigate the nature of oxidized and H-terminated Ge surfaces. The GeO2, GeO and GeC phases have been identified and quantified as a function of processing conditions. The stability of the H-terminated surfaces has been examined in air and in controlled environments. The H-passivated Ge surfaces are found to be much less stable in air than H-terminated Si surfaces.

Evidence of environmental strains on charge injection in silole based organic light emitting diodes.

Using density functional theory (DFT) computations, we have demonstrated a substantial skeletal relaxation when the structure of 2,5-[bis-(4-anthracene-9-yl-phenyl]-1,1-dimethyl-3,4-diphenyl-silole (BAS) is optimized in the gas-phase comparing with the molecular structure determined from monocrystal x-ray diffraction. The origin of such a relaxation is explained by a strong environmental strains induced by the presence of anthracene entities. Moreover, the estimation of the frontier orbital levels showed that this structural relaxation affects mainly the LUMO that is lowered of

Polarization at the gold/pentacene interface

190\phantom{\rule{0.3em}{0ex}}\mathrm{meV}

Spectroscopic study on sputtered PEDOT · PSS: Role of surface PSS layer

in the gas phase. To check if these theoretical findings would be confirmed for thin films of BAS, we turned to ultraviolet photoemission spectroscopy and/or inverse photoemission spectroscopy and electro-optical measurements. Interestingly, the study of the current density or voltage and luminance or voltage characteristics of an