Ch. Schoppmann

Preparation of ultrathin ferric oxide layers using Langmuir-Blodgett films

Abstract Ultrathin ferric oxide films (1015 Fe ions cm-2) were prepared from Langmuir-Blodgett (LB) films of Fe arachidate. The LB films were heated for this purpose to a temperature of 300 °C. It turns out that the Fe ions remain quantitatively at the substrate during the heating procedure and that a linear dependence exists between the Fe area density in the ferric oxide film and the number of Fe arachidate monolayers. The homogeneity of the ferric oxide films was found not to be satisfactory if LB films with a small number of monolayers are used. The homogeneity increases with increasing number of monolayers. The analysis of the films was performed with mass spectrometric methods, Rutherford backscattering spectroscopy and electron microscopy.

Acceleration of Aun clusters to MeV energies

Abstract Gold clusters Au n with n ⩽ 5 and masses m ⩽ 985 u have been accelerated to MeV energies with the tandem accelerators at Orsay and Erlangen. Singly charged negative cluster ions were obtained from a conventional sputter ion source and accelerated between ground potential at the entrance of the accelerator and the terminal (in the middle) at several MV. In a gas channel positioned in the terminal they lose one or several electrons and become neutral or positively charged clusters, respectively. The ions are then accelerated towards the exit of the tandem accelerator. Identification of Au + n clusters is achieved by measuring the time-of-flight of the clusters.

Ultrathin Fe-oxide layers made from Langmuir–Blodgett films

Abstract Thin Fe-oxide films (15–150 nm thick) have been prepared using Langmuir–Blodgett (LB) films as precursors consisting of a certain number of Fe–arachidate monolayers (ML). The organic component of the LB films was removed by different heating procedures: heating in ambient air at 360 and 900°C, and at 500°C in a H 2 gas flow. The remaining Fe-oxide films were analyzed by a number of methods. The most important results are: all Fe-oxide films are smooth and homogeneous (roughnesses between 0.8 and 4 nm), the magnetic properties are, however, not sufficient for an application as magnetic storage medium. Only a film prepared from 35 ML Fe–arachidate by heating at 500°C in H 2 had magnetic properties (hysteresis loop of the single domain type, large coercivity and saturation magnetization) suited to use the film as a high data density magnetic storage medium. The films heated at ambient air consist mainly of α -Fe 2 O 3 . In addition they contain most probably γ -Fe 2 O 3 and Fe 3 O 4 (films heated at 360°C) or Fe 3 O 4 and FeO (films heated at 900°C). Films heated in H 2 consist of Fe 3 O 4 , FeO and metallic α -Fe.

Experimental investigations of spontaneous desorption

Abstract Experimental investigations of the spontaneous desorption (desorption of ions in an electric field existing between the sample and a grid in front of the sample) show that both sputtering and field desorption processes contribute to the spontaneous desorption yield.

Acceleration of cluster ions to MeV energies

Abstract Gold and C 60 cluster ions have been accelerated to MeV energies with the EN tandem accelerator at Erlangen. Negatively charged cluster ions were produced in the sputter source and accelerated through both stages of the accelerator. The identification of the MeV cluster ions was performed by time-of-flight and energy measurements.

Mass spectra of organic and inorganic samples obtained using spontaneous desorption mass spectrometry

Abstract A number of samples have been investigated by spontaneous desorption mass spectrometry to see whether this simple method can be applied to the analysis of organic and inorganic samples. It is found that negative mass spectra of a large variety of samples can be obtained within short data collection times. Desorption rates of positive ions are usually significantly smaller than those of negative ions. A dependence of the desorption rate on sample preparation is found.

Plasma desorption mass spectrometry of Langmuir-Blodgett films: dependence of salt formation of arachidic acid monolayers on the subphase parameters☆

Abstract The conditions for complete salt formation of an arachidic acid monolayer spread onto an aqueous subphase were investigated by means of plasma desorption mass spectrometry in order to demonstrate that this method is very well suited to characterize Langmuir-Blodgett films. The combinations of subphase pH and metal ion concentration necessary for complete salt formation of arachidic acid monolayers were deduced from this analysis.

Ni oxide thin films prepared by means of Langmuir-Blodgett multilayers

Abstract Very thin Ni oxide films have been prepared using Ni-arachidate Langmuir–Blodgett (LB) films as precursors. The preparation of the precursor films is described in detail. Irradiation of these LB films with UV light and subsequent heating (350°C) at ambient air leads to rather smooth NiO films with an area density of (3.6±0.5)·10 14 cm −2 Ni ions per monolayer of transferred LB film.

Langmuir—Blodgett films made from yttrium arachidate

Abstract Yttrium arachidate multilayer films deposited on gold substrates by the usual Langmuir—Blodgett dipping technique have been investigated by means of Rutherford backscattering and plasma desorption mass spectrometry. It turns out that the cation of the film-forming molecules is Y3+. This is in contrast to a previous analysis where the cation was determined to be Y(OH)2+.

The role of adsorbates in spontaneous desorption

Abstract The role of adsorbates deposited on sample and grid has been investigated with respect to the spontaneous desorption of negative sample specific ions. For this purpose experiments have been carried out in a UHV chamber. Both sample and grid could be cleaned by sputtering with Ar ions. The experiments allow conclusions to be drawn concerning the various processes involved in spontaneous desorption. These processes are discussed.