S. Kennou

Growth and interfacial studies of conjugated oligomer films on Si and SiO2 substrates

The growth of [2,5-bis(4-styryl)styryl] 1,4-dioctyloxybenzene, (Ooct-OPV5) oligomer films on Si (100)-(2×1) and Si (111)-(7×7) reconstructed surfaces as well as on a SiO2 film over a Si (100) wafer was studied by x-ray photoelectron spectroscopy (XPS). Ooct-OPV5 resembles poly (p-phenylenevinylene) (PPV), a polymer that is widely used in organic light emitting diodes. High purity oligomer films of up to 18 nm thickness were prepared on the clean substrates by stepwise evaporation in ultrahigh vacuum conditions and a layerwise growth of films was observed on all substrates. The electronic structure of the oligomer interface with n-doped Si (111) was investigated by combined x ray and ultraviolet photoelectron spectroscopies (XPS) and (UPS). The C 1s XPS peak of the bulk oligomer consisted of three components, all associated with oligomer functional groups at binding energies 285.05, 285.75, and 287.15 eV, respectively. During growth, both C 1s and O 1s peaks in the film exhibited an upward BE shift of 0.45...

The electronic properties of the interface between nickel phthalocyanine and a PEDOT:PSS film

Thin films of nickel phthalocyanine (NiPc) are deposited on an as-received and on a mildly sputtered PEDOT:PSS film, spin coated on fluorine tin oxide coated glass. The electronic properties of the PEDOT:PSS surface, both as loaded and upon thermal treatment and sputtering, as well as of the interfaces between NiPc and PEDOT:PSS are studied by x-ray and UV photoelectron spectroscopies in order to investigate both the electronic and the chemical properties of the materials. Surface analysis of the PEDOT:PSS films showed that upon sputtering the insulating PSS film is removed leading to lower work function, as well as to an increase of the density of occupied states close to the Fermi level. The investigation of the interfaces between NiPc and PEDOT:PSS revealed charge transfer and a pinning of the Fermi level across the interface. The hole injection barrier was found significantly lower compared with that for the NiPc/Au interface, indicating that the presence of the PEDOT:PSS layer facilitates the carrier...

A study of the Ni-phthalocyanine/gold interface using x-ray and ultraviolet photoelectron spectroscopies

Nickel phthalocyanine (NiPc) thin films (~25 m thick) were grown stepwise on a polycrystalline Au substrate and the interface was characterized by x-ray and ultraviolet photoelectron spectroscopies (XPS, UPS). The C 1s peak of the bulk (~5 nm) NiPc film was resolved into three components reflecting photoemission from multiple sites within the molecule. The peak at 284.8 eV corresponds to C-C bonds, the one at 286.2 eV to C-N bonds, while the last one at 287.9 eV is satellite of the main peak. The Ni 2p and N 1s peaks appear at ~855.9 eV and ~399.3 eV respectively and are due to Ni-N bonds. The NiPc highest occupied molecular orbital (HOMO) cut-off position was determined from the valence band spectrum of the bulk organic film, and was found at ~1.00 eV from the analyser Fermi level. The work function of the Au foil and the bulk NiPc film were found to be 5.20 ± 0.05 eV and 4.20 ± 0.05 eV respectively. The combination of UPS and XPS results led to the determination of the energy level diagram of the NiPc/Au interface.

A photoelectron spectroscopy study of Au thin films on ZrO2 (100)

Abstract The formation and electronic properties of Au deposits on yttria-stabilized ZrO 2 (100) were studied by X-ray and ultra-violet photoelectron spectroscopy (XPS, UPS) from submonolayer coverages up to a fully conducting thin film across the substrate at room temperature and at 680 K. The results show that at both temperatures Au exhibits a 3D particle growth, which is more pronounced at 680 K. The substrate temperature affects the particle density and average coordination number of the gold atoms, however, the interaction between gold and the substrate is very weak at both temperatures. Annealing up to 780 K of Au films deposited at 300 K, results only in particle coalescence and does not affect the chemical state of either Au or zirconia.

ZrO2 and Al2O3 Thin Films on Ge(100) Grown by ALD: An XPS Investigation

Thin films of aluminium oxide (Al2O3) and zirconium oxide (ZrO2) were prepared by Atomic Layer Deposition (ALD) on p-type (100) germanium substrates. In the present work a detailed analysis of the films by X-ray photoelectron spectroscopy (XPS) in order to investigate their chemical composition is presented. This study is dedicated to an XPS investigation of the principal core levels (Al, Zr, O) of Al2O3 and ZrO2 thin films. In particular, wide scan spectra, detailed scans for the Zr 3d, Al 2p, O 1s, and C 1s regions and related data for zirconia and alumina films are presented and discussed. The results point out the formation of Al2O3 and ZrO2 films with the presence of OH groups and carbon contamination on the surface.

An interface study of vapor-deposited rhenium with the two (0001) polar faces of single crystal 6H-SiC

Abstract The interfaces formed on the two (0001) polar faces of single crystal n-type 6H-SiC by Re evaporation and subsequent annealing were investigated by X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and work function (WF) measurements. Rhenium was deposited from submonolayer up to 2 nm thickness and gradually annealed up to 1100 K. Deposition led to a weakening and eventual disappearance of the 1 × 1 LEED pattern of the clean surface, an increase of the WF up to the value of metallic Re and the formation of a Schottky barrier with a height of 0.7±0.2 eV for both faces. The Re 4 f 7 2 peak binding energy decreased during deposition from approx. 41.1 eV below monolayer coverage, to 40.5 eV for a 2 nm film indicating an island growth of the film. Annealing of the Re films up to 1100 K on both faces led to Re particle coalescence without affecting the low Schottky barrier at the interface, however, there are indications of chemical changes at the interface which could affect the electrical characteristics of the contact.

A study of the interface formation between gold and a thin conjugated oligomer film

The interface formation between Au and a five-ring n-octyloxy substituted phenylenevinylene (Ooct-OPV5) oligomer film was studied by X-ray and ultraviolet photoelectron spectroscopies (XPS, UPS), in ultrahigh vacuum. When the oligomer was stepwise deposited on a clean Au polycrystalline foil, an abrupt interface was formed. A high binding energy component present in the oligomer related XPS C1s peak up to the completion of the first monolayer, revealed the existence of an interfacial state. The C1s peak exhibited a total upward BE shift of ∼0.5 eV, related to the band bending in the oligomer film. When Au was stepwise deposited on a ∼5 nm thick oligomer layer, UPS and angle resolved XPS revealed extended diffusion of the Au atoms in the oligomer. The C1s and Au4f peaks exhibited ∼0.5 and ∼0.65 eV downward BE shifts respectively. These shifts are a combination of initial and final state effects in gold and charge transfer between the two materials in contact.

The impact of ultrathin Al2O3 films on the electrical response of p-Ge/Al2O3/HfO2/Au MOS structures

It is well known that the most critical issue in Ge CMOS technology is the successful growth of high-k gate dielectrics on Ge substrates. The high interface quality of Ge/high-k dielectric is connected with advanced electrical responses of Ge based MOS devices. Following this trend, atomic layer deposition deposited ultrathin Al2O3 and HfO2 films were grown on p-Ge. Al2O3 acts as a passivation layer between p-Ge and high-k HfO2 films. An extensive set of p-Ge/Al2O3/HfO2 structures were fabricated with Al2O3 thickness ranging from 0.5 nm to 1.5 nm and HfO2 thickness varying from 2.0 nm to 3.0 nm. All structures were characterized by x-ray photoelectron spectroscopy (XPS) and AFM. XPS analysis revealed the stoichiometric growth of both films in the absence of Ge sub-oxides between p-Ge and Al2O3 films. AFM analysis revealed the growth of smooth and cohesive films, which exhibited minimal roughness (~0.2 nm) comparable to that of clean bare p-Ge surfaces. The electrical response of all structures was analyzed by C–V, G–V, C–f, G–f and J–V characteristics, from 80 K to 300 K. It is found that the incorporation of ultrathin Al2O3 passivation layers between p-Ge and HfO2 films leads to superior electrical responses of the structures. All structures exhibit well defined C–V curves with parasitic effects, gradually diminishing and becoming absent below 170 K. D it values were calculated at each temperature, using both Hill–Coleman and Conductance methods. Structures of p-Ge/0.5 nm Al2O3/2.0 nm HfO2/Au, with an equivalent oxide thickness (EOT) equal to 1.3 nm, exhibit D it values as low as ~7.4 × 1010 eV−1 cm−2. To our knowledge, these values are among the lowest reported. J–V measurements reveal leakage currents in the order of 10–1 A cm−2, which are comparable to previously published results for structures with the same EOT. A complete mapping of the energy distribution of D its into the energy bandgap of p-Ge, from the valence band towards midgap, is also reported. These promising results contribute to the challenge of switching to high-k dielectrics as gate materials for future high-performance metal–oxide–semiconductor field-effect transistors based on Ge substrates. Making the switch to such devices would allow us toexploit its superior properties.

On the wetting properties of human stratum corneum epidermidis surface exposed to cold atmospheric-pressure pulsed plasma

The Stratum corneum is the outermost layer of the skin, acting as a protective barrier of the epidermis, and its surface properties are directly related to the spreading of topically applied drugs and cosmetics. Numerous works have been devoted to the wettability of this layer over the past 70 years, but, despite the extensive application of atmospheric-pressure plasmas to dermatology, stratum corneum wettability with respect to plasma-induced species has never been considered. The present report assesses the treatment of human stratum corneum epidermidis by atmospheric-pressure pulsed cold plasma-jets for various time intervals and both chemical and morphological modifications are probed. The increase and saturation of the surface free energy due to functionalization are demonstrated, whereas prolonged treatment leads to tissue local disruption (tissue integrity is lost, and stratum corneum looks exfoliated, porous, and even thermally damaged). The latter point arises skepticism about the common practice of contacting atmospheric-pressure plasmas with skin without any previous precautions since the lost skin surface integrity may allow the penetration of pathogenic microorganisms.The Stratum corneum is the outermost layer of the skin, acting as a protective barrier of the epidermis, and its surface properties are directly related to the spreading of topically applied drugs and cosmetics. Numerous works have been devoted to the wettability of this layer over the past 70 years, but, despite the extensive application of atmospheric-pressure plasmas to dermatology, stratum corneum wettability with respect to plasma-induced species has never been considered. The present report assesses the treatment of human stratum corneum epidermidis by atmospheric-pressure pulsed cold plasma-jets for various time intervals and both chemical and morphological modifications are probed. The increase and saturation of the surface free energy due to functionalization are demonstrated, whereas prolonged treatment leads to tissue local disruption (tissue integrity is lost, and stratum corneum looks exfoliated, porous, and even thermally damaged). The latter point arises skepticism about the common practice...