Lj. Atanasoska

Aluminum/polyimide interface formation: An x‐ray photoelectron spectroscopy study of selective chemical bonding

High‐resolution x‐ray photoelectron spectroscopy has been used to study the formation of the aluminum/polyimide (Al/PI) interface at room temperature. Aluminum films up to 80 A thick were vapor deposited onto cured polyimide in situ. Our results show that Al is chemically active for coverages below ∼20 A. Preferential aluminum bonding with PI occurs at carbonyl sites, as evidenced by the rapid attenuation of the carbonyl C 1s core level photoemission intensity. In the initial reaction stage (1–2 A), Al preferentially occupies planar imide rings. These adatoms transfer charge to carbonyl carbon atoms via oxygen and this resonance hybrid state of C–O–Al weakens, but does not break, carbonyl bonds. With increasing Al coverage, the formation of strong Al–O bonds is observed and is attributed to a C–O–Al complex compound. Metallic Al is observed at a nominal coverage of 2 to 5 A. The Al/PI interface exhibits the attenuation behavior characteristic of cluster growth through both reacted and unreacted regions. A...

Surface Modification and Oxygen Reduction on Glassy Carbon in Chloride Media

The reduction of oxygen on rotating disk glassy carbon electrodes was studied in 0.1M HCl. Reproducible single waves with constant limiting currents over a potential range of 0.5V were obtained after the samples were electrochemically treated: anodic polarization at 2.0V vs. SCE and subsequent cathodic reduction. The number of electrons transferred in the oxygen reduction reaction was calculated to be 2.3. The surface of the glassy carbon was examined by XPS at different stages of the electrochemical treatment. After the anodic treatment, the ratio of oxidized carbon vs. graphitic carbon was higher than 1. The predominant oxygen species were carbonyl groups. Following reduction, the surface had an oxidized vs. graphitic carbon ratio below 0.5 with the oxygen distributed between phenolic and carboxylic groups. The role of the chloride ion in the formation of the carbonyl groups is discussed.

X-ray photoemission investigations of clustering and electron emission, injection, and trapping at the gold/polyimide interface

The evolution of the interface formed between clean [N‐N‐(p,p‐oxydiphenylene) pyromellitimide] polyimide (PI) and evaporated gold was followed by high‐resolution x‐ray photoelectron spectroscopy (XPS). Overlayer and substrate core level emission behavior indicates the nucleation and growth of Au clusters on the PI surface. At low gold coverages (<1 A nominal thickness), there was no observed interaction between the adatoms and the substrate. Above 1 A we observe the growth of clusters on the PI surface and a shift of the Au 4f core levels as the clusters become metallic. Significantly, we observe further shifting of the Au 4f emission and the Fermi level at coverages greater than that expected for metallic behavior, and we see Au‐cluster‐induced broadening and shifting of the substrate core level spectra to lower binding energy. This unexpected behavior can be accounted for in terms of the injection and trapping of charge into the PI film from Au during the photoionization process. Angle‐dependent XPS res...

Dynamics of polyimide curing and degradation: an in situ x-ray photoemission study

Dynamic time‐ and temperature‐dependent x‐ray photoemission studies of polyimide (PI) show the evolving valence bands and core level spectra, starting from partially polymerized PI and continuing through PI degradation at 500 °C. For temperatures below∼200 °C, we see little change, but curing above 300 °C is accompanied by changes in core level and valence‐band positions relative to the Fermi level. These changes are associated with the removal of defect induced states in the band gap of the polymer. Comparison of the valence‐band spectrum of the fully cured PI to recent electronic structure calculations shows good agreement. PI degradation occurs at temperatures between 450 and 500 °C, where there is a decrease in carbonyl and pyromellitic dianhydride benzene ring carbon 1s emission due to loss of CO or CO2, and an increase in carbon atom density. Nitrogen 1s spectra exhibit the growth of new low binding energy components which indicate that the feature previously assigned to an isoimide structure is a m...

Single crystal RuO2 (110): Surface structure*

Abstract The surface structure of RuO2 (110) has been studied with LEED, AES and XPS. The “as-grown” surface shows no LEED patterns and both AES and XPS indicate that the surface is depleted in oxygen in high vacuum. After extensive annealing in an O2 atmosphere reproducible LEED patterns characteristic of the (110) surface were obtained. For the well-ordered surface the oxygen XPS results revealed oxygen associated with the bulk RuO2, the presence of RuO3 and oxygen bound to surface atoms.

Semiconductor/polyimide interface formation: An x‐ray photoelectron spectroscopy study of germanium chemical bonding

We have used high‐resolution angle‐dependent x‐ray photoemission to study the evolving interface formed by vapor depositing Ge (0–80 A) onto cured polyimide (PI). The core level line‐shape changes of PI and Ge demonstrate that Ge reacts chemically with PI for coverages below ∼10 A. The rapid attenuation of the carbonyl C 1s photoemission intensity shows that Ge reaction preferentially occurs with carbonyl groups for Ge deposition below ∼0.5 A and charge withdrawal from the imide–benzene ring is reduced. With increasing Ge deposition (between 0.5 and 5 A), more carbonyl groups are involved in reaction with Ge and the excess of charge carried by carbonyl carbon atoms induces a hyperconjugation form of the imide–benzene ring. These rings are more vulnerable to Ge chemical attack and the formation of Ge–C bonds. Our results indicate multiple Ge–O–C and Ge–C bonding configurations. Once the initial reaction is complete, the growth mode of Ge on PI appears to be layer‐by‐layer‐like. Time‐ and temperature‐depend...

XPS study of chemical bonding at polyimide interfaces with metal and semiconductor overlayers

Abstract High resolution X-ray photoelectron spectroscopy has been used to study evolving interfaces formed by vapour depositing Al and Ge (0–8 nm) onto cured polyimide (Pl) at room and elevated temperatures. The data obtained for the interface of Al with Pl showed preferential aluminum bonding at carbonyl sites at room temperatures but less selective chemical interaction at elevated temperatures. Ge interaction with Pl involves carbonyl and imidebemze functional groups. The resulting The resulting oxygen and phenyl organogermane compounds exhibit multiple bonding configurations. The results of the reactive interfaces have been compared with the nonreactive Au/Pl interface.