Sefik Suzer

Soft x-ray photoemission studies of the HfO2/SiO2/Si system

Soft x-ray photoelectron spectroscopy with synchrotron radiation was employed to study the valence-band offsets for the HfO2/SiO2/Si and HfO2/SiOxNy/Si systems. We obtained a valence-band offset difference of −1.05±0.1 eV between HfO2 (in HfO2/15 A SiO2/Si) and SiO2 (in 15 A SiO2/Si). There is no measurable difference between the HfO2 valence-band maximum positions of the HfO2/10 A SiOxNy/Si and HfO2/15 A SiO2/Si systems.

Soft X-ray photoemission studies of Hf oxidation

Soft X-Ray Photoemission Spectroscopy using surface sensitive Synchrotron Radiation has been applied to accurately determine the binding energy shifts and the valence band offset of the HfO2 grown on Hf metal. Charging of oxide films under x-rays (or other irradiation) is circumvented by controlled and sequential in-situ oxidation. Photoemission results show the presence of metallic Hf (from the substrate) with the 4f7/2 binding energy of 14.22 eV, fully oxidized Hf (from HfO2) with the 4f7/2 binding energy of 18.16 eV, and at least one clear suboxide peak. The position of the valence band of HfO2 with respect to the Hf(m) Fermi level is determined as 4.05 eV.

Band alignment issues related to HfO2∕SiO2∕p-Si gate stacks

The valence and conduction band densities of states for the HfO2∕SiO2∕Si structure are determined by soft x-ray photoemission and inverse photoemission. First principles calculations are used to help in assigning valence band maxima and conduction band minima. The energies of defect states at the band edges are estimated by comparing the theoretical and experimental results. Determinations of the local surface potentials before and after a forming gas anneal are used to help determine the possible location of the charge in the film.

FTIR spectra of ammonia clusters in noble gas matrices

FTIR spectra of ammonia have been studied from 200 to 5200 cm−1 over a wide range of concentration and temperature conditions in solid neon, argon, and nitrogen matrices. Dimer bands appear between monomer and higher aggregate absorptions and exhibit intermediate growth behavior on sample annealing and concentration changes. Comparison of spectra in solid argon at 5 and 12 K shows unrelaxed monomer absorptions at 12 K, which almost completely vanish at 5 K without any difference in the dimer spectrum; this indicates that the NH3 submolecules are relaxed in the matrix‐isolated dimer. One antisymmetric and two symmetric N–H stretching modes were observed for the dimer, which follow the 14NH3–15NH3 and NH3–ND3 shifts of their monomer analogs. The dimer N–H stretching modes are intensified by fivefold relative to the dimer umbrella bending mode as compared to the same relative monomer band intensities, which is diagnostic of the hydrogen bonding interaction. The matrix dimer spectra show that one N–H bond fro...

Conducting polymers of aniline. II: A composite as a gas sensor

Abstract The gas sensing ability of electrochemically prepared pure polyaniline and polyaniline-poly(bisphenol-A carbonate) films is investigated. The responses of the composite films to several vapours are more well defined and reproducible compared to the pure conducting polymer. The changes in resistance as determined via the two-probe technique are well defined down to a level of 0.025% vol./vol. ammonia. The possible reason for such a difference is discussed. The structure of the composite is examined through pyrolysis FT-IR studies.

Synthesis, characterization and antibacterial investigation of silver–copper nanoalloys

Ag–Cu nanoalloys were synthesized by chemical co-reduction of their metal salts in aqueous solution with hydrazine hydrate, in the presence of complexing agent and stabilizer, preventing the oxidation of copper, as revealed by XPS. Their antibacterial behavior was tested against Escherichia coli strains, attesting far better ability of the Ag–Cu compared to Ag-only nanoparticles.

XPS and water contact angle measurements on aged and corona‐treated PP

Effects of corona treatment and aging on commercially produced corona discharged polypropylene (PP) films were followed via surface sensitive roughness analysis by atomic force microscopy (AFM), water contact angle (WCA), and X-ray photoelectron spectroscopic (XPS) measurements. Roughness analysis by AFM gave similar results for both untreated and corona-treated samples. The measured water contact angle decreased after corona treatment but increased with aging. XPS findings revealed that corona treatment caused an increase in the O-containing species on the surface of the films, but the measured O/C atomic ratio decreased with aging. The angle dependence of the observed XPS O/C atomic ratio further revealed that surface modifications by the corona treatment were buried into the polymer away from the surface as a function of aging. This is attributed to a surface rearrangement of the macromolecules in agreement with the findings of Garbassi et al. on oxygen–plasma-treated polypropylene.

Characterization of degradation products of polyethylene oxide by pyrolysis mass spectrometry

Abstract The techniques of direct and indirect (evolved gas analysis) pyrolysis MS are used to characterize the thermal degradation products of polyethylene oxide. Using direct pyrolysis MS technique the main degradation process is determined to be due to CO and CC scissions yielding fragments characteristic of the polymer. Evolved gas analysis indicates formation of small molecular stable compounds such as C 2 H 5 OC 2 H 5 , CH 3 CHO, CO 2 , CO and C 2 H 4 .

Matrix isolation study of electron impact on H2O. Infrared spectrum of OH− in solid argon

A thermionic electron source capable of delivering 10–200 mA of electrons at low energies (30–200 eV) has been mated to a matrix isolation apparatus and employed to study electron impact on water. Three products were trapped in the argon matrix; OH radical (3452.7, 3478.1 cm−1), ArnH+ (903.7 cm−1), and a new species absorbing at 3548.9 cm−1 with a 3554.0 cm−1 shoulder. The latter is identified as OH− owing to diatomic D and 18O isotopic shifts and agreement with recent gas phase work. The 3548.9 cm−1 absorption is assigned to the R(0) vibration–rotation band of OH−, which is red shifted 42.6 cm−1 by the argon matrix. This shift is slightly more than the 38.4 cm−1 matrix shift for the R(0) line of HF. Product band intensities showed no dependence on electron energy above 30 eV but showed a nonlinear dependence on electron current, which suggests that OH is produced by primary electron impact on water and that OH− and ArH+ solvated by argon are produced by secondary processes.

Spectroscopic characterization of Al2O3-Ni selective absorbers for solar collectors

Optical spectroscopy of electrochemically prepared Ni-pigmented aluminum oxide selective absorbers have been determined in the 200—20 000 nm range. It was found that samples anodized under the same conditions and pigmented using nickel acetate resulted in better thermal emittance values when compared with nickel sulfate although both have comparable solar absorbance values. Electron spectroscopic investigation revealed that only a small fraction of Ni is present on the surface with an oxidation state of *# 2. The O/Al ratio determined by XPS is larger than 1.5. This information together with the measured Al 2p Auger parameter indicated that the surfaces contain additional OH groups which was also confirmed by the presence of a broad hyrogen-bonded band in the region 3000—3400 cm~1 observed in the reflection—absorption IR spectra of these samples. ( 1998 Elsevier Science B.V. All rights reserved.