Salvatore Pignataro

Effect of organic contaminants on the oxidation kinetics of silicon at room temperature

The oxidation kinetics of HF‐etched n‐ and p‐doped silicon in air at room temperature have been studied by electron spectroscopy for chemical analysis. No great differences have been found between the n‐ and p‐type oxidation kinetics at the low doping level of the studied samples. The rate of oxide growth on the HF‐etched surface is much lower than that on a silicon surface obtained by fracture in air of a silicon monocrystal. The behavior of a silicon sample fractured in de‐ionized water and then oxidized in air at room temperature is intermediate. The above findings have been interpreted on the basis of surface reactions involving the plasticizers of the HF and water containers. These reactions produce carbon‐rich hydrophobic surfaces which retard the silicon oxide growth. A mechanism for the involved surface reactions is proposed.

Correlation between the modification of the chemical structure and the electrical properties of Ar-ion bombarded polyimide

Abstract The ion beam induced modification of polyimide (Pyralyn 2555, mainly BTDA-ODA) by Ar+ at 150 keV has been studied in details by using XPS and REELS techniques. Ion fluences ranging from 5 × 1012, to 1 × 1016 ions/cm2 have been used in order to study the chemical evolution of the polyimide in the ranges where chemical and electrical characteristics show the major changes. The modification of the chemical structure and electrical resistivity are shown to occur in relatively narrow fluence ranges. The onset of these successive modification steps are determined and a threshold-like dependence upon the ion fluence is observed.

Primary chemical events in ion bombarded polystyrene films: an infrared study

Abstract The chemical phenomenology which occurs in polystyrene films bombarded with low doses 100 keV He+ ions has been investigated by infrared spectroscopy. The results obtained show that the polymer is rapidly transformed into a different chemical compound consistent with high cross-linking as indicated by low solubility in CHCI3. The I.R. finding is in agreement with XPS findings and indicates that the observed phenomenology occurs via a mechanism which eliminates the electronic “π” system of the phenyl ring and gives rise to alkene-type bonding.

Reflection electron energy loss spectroscopy (REELS) of conductive polymers obtained by keV bombardment

Abstract Reflection electron energy loss (REELS) is used to study the modifications in the electronic structure of polystyrene. poly-2-vynilpyridine, polyethersulphone and polyimide bombarded with Ar+ at 150 keV at fluences between 5 × 1012 and 1 × 1016 ions/cm2. Both the bulk plasmon energy and the low-excitation energy region of the REELS spectra are strongly affected by ion irradiation. The ion beam induced spectral features for fluences up to 1 × 1015 ions/cm2 are close to those of hydrogenated amorphous carbons. Starting at a fluence of 5 × 1015 ions/cm2, Poly-2-vynilpyridine, polyethersulphone and polyimide show a drastic drop in resistivity up to value of the order of 10−1 − 10−2 Ω cm. The REELS spectra of these conducting samples are characterized by a peculiar step-like structure at very low excitation energy, attributable to the formation of conduction states in the pristine band-gap.

Effect of ion energy on the implantation products of benzene

Abstract Solid benzene has been implanted with inert-gas ions with energies ranging from 16 to 100 keV. The small variation observed in the relative concentration of the products has been found to depend mainly on the fact that the relative weight of the nuclear and electronic stopping mechanisms is changing along the energy range explored.

Reactions induced by ion bombardment of solid cyclohexane at 77 K

Abstract Cyclohexane at 77 K has been bombarded with He + and Ar + at several keV energies. The main chemical products obtained have been identified by GC/MS. The results were compared with those obtained on benzene implantation. The product formations were interpreted in terms of a previously proposed model involving electronic and nuclear stopping mechanisms of the bombarding particles. Some important physicochemical reaction pathways are proposed and discussed.

Interfacial reactions in polyimide/metal systems

Ultra-thin films of polyamic acid (BTDA-ODA type) are prepared by spin coating a very dilute solution onto bare or metallized silicon wafers (estimated thickness 25 ± 5 A). The XPS analysis of the various polymer/metal interfaces suggests the occurrence of acid-base type interaction between the carboxylic groups of the polymer and the oxides and hydroxides that cover the Ni and Cr surfaces. When these systems are in situ cured, the XPS analysis shows the occurrence of a variety of chemical interfacial reactions. In particular: (i) when the substrate is a naturally passivated Ni layer, the complete destruction of the polymer is observed; (ii) when the substrate is a naturally passivated Si wafer, no relevant interaction occurs; (iii) for a naturally passivated Cr and an oxidized Ni surface, partial decomposition of the polymer is observed. The above effects are explained in terms of the acid or basic properties of the oxidized layers that cover the metal surfaces, and in terms of their stability toward heating.

Electronic excitations in solid ZrO2 from reflection EELS and ESCA multipeak structures

Abstract The nature of electronic excitations in ZrO 2 is investigated by means of ESCA multipeak structures and EELS spectra obtained in reflection mode with primary electron beams having an energy of 0.2–4.5 keV. Comparison between the ESCA multipeak regions and the low-energy region of the reflection EELS spectrum obtained on the same sample discriminates the photoionization final-state structures from those due to inelastic scattering of photoelectrons.

ESCA investigations of amorphous and crystalline zirconium acid phosphates

Amorphous and micro-crystalline α- and γ-zirconium acid phosphates have been investigated by the ESCA technique. α-zirconium phosphate has been also studied as a single crystal. Both the B.E. of zirconium and phosphorous electrons in zirconium phosphates are slightly higher than those reported for zirconium derivatives and trivalent metal phosphates, indicating a stronger polarization of the ZrO and PO bonds. Furthermore, it seems that some ESCA features of the zirconium phosphates investigated are structure dependent. However, no definitive conclusions have been drawn because of the lack of knowledge of the “charging-up” phenomena in protonic conductors such as zirconium phosphates. Satellite structures have been observed in the P2s, P2p, Zr3d and Zr4p regions. The position and the intensity of these “shake-up” effects are again dependent on the nature of the examined phase and they seem to be due to the presence of electron defect structures induced by X-rays or already present in the original samples.

Chemical effects of ion implantation on solid benzene

Abstract N + 2 , CO + and Ar + at keV energy have been implanted on solid benzene. A number of reaction products were found. The most abundant are: biphenyl, 5-phenyl-1,3-cyclohexadiene, 3-phenyl-1,4-cyclohexadiene and phenylacetylene. The experiment shows that the nature of the projectile does not influence the chemical composition of the main products formed in the implantation phenomena. A mechanism explaining the formation of these products is proposed.