E. Sacher

A surface analytical study of GaAs(100) cleaning procedures

X‐ray photoelectron spectroscopy (XPS) and low‐energy electron diffraction (LEED) have been used to examine the chemical composition of GaAs(100) surfaces after different standard cleaning sequences, using aqueous H2 SO4 :H2 O2/ HCl and H3 PO4 :H2 O2/ HCl solutions. XPS measurements show that the oxides, Ga2 O3 and As2 O3 , which remain at a relative concentration of 1.7:1 after H3 PO4 :H2 O2 :H2 O etch, are totally removed by the subsequent aqueous HCl solution. These same oxides, which have a relative concentration of 2.5:1 after H2 SO4 :H2 O2 : H2 O etch, are then not totally removed by HCl. Elemental arsenic was found to increase in concentration as the surface oxides decreased. The surface, initially gallium rich (Ga/As ratio 1.11), became arsenic rich (Ga/As ratio 0.93) after cleaning in HCl. The excess elemental As can be removed by subsequent treatment in NH4 OH. LEED patterns could be obtained only for H3 PO4 :H2 O2 /HCl cleaned surfaces. Au/Ti/GaAs Schottky diodes were made on both types of samp...

Amorphization of c‐Si by the sputter deposition of Au studied by x‐ray photoelectron diffraction

It is well known that Si atoms can be dislodged from a silicon matrix and diffuse through a thin Au overlayer. In the course of studying this phenomenon, we have found x‐ray photoelectron diffraction (XPD) to be a particularly powerful investigative tool: XPD, a relatively new surface analytical technique, is very sensitive to the surface quality of crystalline materials. We have avoided surface contamination by depositing very thin (<5 nm) Au films onto a (100) Si surface, both by sputtering and by thermal evaporation within the surface instrument. XPD reveals that the c‐Si surface is amorphized by the former process and much less damaged by the latter, a fact we attribute to the higher average kinetic energy of incident Au atoms during sputtering. This interpretation is supported by related studies; for example, by the reaction of adventitious carbon to form Si–C bonds on c‐Si during sputter cleaning and sputter deposition. The study illustrates the important role of even relatively low particle energie...

The determination of trace contaminants in polymers

Although not as successful as anticipated, this first study has shown several pitfalls in the determination of trace ions not previously anticipated. It has shown (1) the presence of trace amounts of starting materials or hydrolysis products, both of which attack metallurgy; (2) elements present in the polymer are not always extractable and, therefore, not mobile; (3) pure materials may be contaminated by their containers; (4) several simultaneous analytical methods are necessary, since each has unique properties.

The DC conductivity of polyimide film

Recently, fast transient dc conditions were used1 to study charge transport in polyimide film. Although originally interpreted in terms of thermally-assisted electron tunneling, these data were later shown to be consistent with dipolar orientation.2 Thus, information about the nature of charge transport in polyimide film must come from data on steady-state, rather than transient, currents.

The influence of processing on the structure of poly(ethylene terephthalate) film

Structural motions have been shown to influence such important polymer use properties as impact strength1 and time-dependent fracture.2 Processing is sometimes used to intentionally modify a polymers structure and, thus, influence the motions the structure gives rise to. An example of this is poly(ethylene terephthalate) film, which is oriented during manufacture.3 While the oriented, commercial film is one of the most useful polymers available, the unoriented film is too brittle to handle and has no known uses.

The DC conductivity of poly(vinylidene fluoride) films

Poly(vinylidene flouride), PVDF, has recently attained commercial importance because, when oriented and poled, it becomes both piezo- and pyroelectric [1]. Yet, when determination of the DC conductivity is required over a temperature range, it is this same pyroelectricity which interferes, virtually precluding the determination of the DC conductivity in this material.

Plasma-polymerized organosilicon films for use in electronic circuit technology

Plasma techniques have become widely accepted in the semiconductor industry for a range of applications. These can conveniently be divided into two broad categories, namely 1. plasma deposition, and 2. plasma etching.

Molecular basis of pyroelectricity in PVDF

The piezofilm possessed a slight curl, indicating how it had once been wound on a roll: the convex side was previously the outer side. Invariably the outer side was found to be polarized positively, as determined by the sign of the thermally stimulated currents.

Structural motions in polyimide films: Preliminary assignments

The elucidation of the structure of polyimide, poly (4, 4-oxydiphenyl pyromellitimide), is important insofar as it determines the properties and use limits of the material. For example, an unidentified transition in the 25°–100°C region was believed responsible1 for the drastic decrease in frictional coefficient and increase in wear life found for this material.

Origins of the secondary dielectric losses in polycarbonate

In considering engineering plastics for use as load-bearing materials, it is often necessary that they possess both high tensile properties and impact strength. A perusal of these properties for pure polymers indicates that, with few exceptions, both properties are not found together. Thus, manufacturers, in seeking to obtain both of these desirable properties in the same material, generally blend, graft or fill, using components having one of the desired properties. The resultant composite polymer has a combination of the properties of its components, reduced in magnitude through dilution.