G.L.R. Mair

Investigation and optimization of the emission parameters of alloy liquid metal ion sources

Abstract Liquid metal ion sources (LMIS) are one of the key elements in focused ion beam (FIB) technology. For special tasks, alloy LMIS are needed which have to be operated in the most cases at elevated temperatures. For the adjustment of an optimal beam performance in a FIB system, the source parameters, temperature of the ion emitter and the energy spread of the different ion species used are of fundamental importance. Emitters wetted with Au73Ge27, Au77Ge14Si9 and Co36Nd64 alloys were investigated with respect to the influence of the source temperature on the emission current–extraction voltage characteristics, the mass distribution, as well as the energy spread of the different emitted ions using an equipment containing an ExB mass filter and a retarding field energy analyser. The energy spread significantly determines the available FIB spot size and depends also on the emission current, the charge state, and the mass of ions or clusters. The axial angular intensity and the resulting target current of the FIB were measured as a function of the source parameters. Two operating regimes were found. Either one works in a high stable target current mode with lower resolution (emission current ∼10 μA), or in the high resolution, high chromatic angular intensity mode (emission current a few μA), with a reduced target current and less current stability, both at source temperatures some 10 K above the melting point.

Temperature dependence of the electric characteristics of liquid metal alloy ion sources

In spite of the fact that a great deal of research has been carried out on liquid metal ion sources, surprisingly few results exist on the temperature dependence of their electric characteristics. In this article we study two liquid metal alloy ion sources (LMAISs), namely Co36 Nd64 and Au77 Ge14 Si9 . While the results of the former alloy were as expected, the latter displayed an entirely different dependence of its electric characteristics on temperature. The unusual results of the Au77 Ge14 Si9 LMAIS are explained in terms of the abnormal behaviour of its surface tension coefficient with temperature.

Photoacoustic detection of d-d transitions and electronic structure of three polyamine copper complexes

The potential of photoacoustic spectroscopy to resolve the crystal field levels of Cu2+ ions in three polyamine copper complexes, aqua spermine copper sulfate trihydrate [NH2(CH2)3NH(CH2)4NH(CH2)3NH2Cu2+H2O]SO42-3H2O, norspermine copper sulfate trihydrate [NH2(CH2)3NH(CH2)3NH(CH2)3NH2Cu2+SO42-]3H2O, and homospermine copper sulfate dihydrate [NH2(CH2)3NH(CH2)2NH(CH2)3NH2Cu2+SO42-] 2H2O, has been explored along with UV/VIS and electron paramagnetic resonance (EPR) spectroscopy. Intense absorption is detected in the photoacoustic spectrum corresponding to the d-d transition band weakly traced in the corresponding optical spectrum. The observed fine structure photoacoustic lines are assigned to the individual d-d transitions of Cu2+ ions, which are further exploited to determine the diverse metal-ligand interaction of the studied compound employing simple crystal field analysis.

Parametric investigation of current pulses in a liquid metal ion emitter

The presence of current pulses superimposed on the dc level of the ion current in liquid metal ion sources has been known for a long time. This work investigates the behaviour of the pulses for varying temperature and working liquid metal. Attempts are made to explain the differences observed in the threshold current for the appearance of the pulses and also in their terminal, or saturation, frequency. Differences are also found between sources using the same working metal, although the pulse appearance threshold current is the same for a given metal. The experimental results indicate that a low source operating temperature is desirable if droplet emission is to be minimized.

Electrohydrodynamic instabilities on a liquid anode displaying an anomalous surface tension coefficient

In the search for a deeper understanding of the factors governing the stability of liquid metal field-ion emitters, the behaviour of a liquid anode with an anomalous surface tension coefficient is studied. The main parameter in this experimental study is the emitter temperature. At the conclusion of the work an important result emerged: apart from the surface tension coefficient, space-charge effects constitute a major factor influencing emitter stability.

Temperature dependence of emission frequency spectra of a liquid metal anode

In an attempt to understand the instabilities that develop on an ion-emitting molten metal anode, we study current oscillograms and emission frequency spectra, as a function of emission current and emitter temperature. It is concluded that increasing the temperature affects adversely the stability of the emitter, thus enhancing the emission of droplets. However, a droplet emission mode, as well as an understanding thereof, is useful for deposition purposes.

Fundamental properties of erbium-ions-producing liquid metal alloy ion sources

Abstract We describe the electric characteristics and mass spectra of two liquid metal alloy ion sources; namely Er 70 Fe 22 Cr 3 Ni 5 and Er 69 Ni 31 . Erbium ions are of great interest for optoelectronic applications. For the first time in the literature the energy spread of triply charged ions (Er 3+ ) is reported.

Frequency spectra and electrohydrodynamic phenomena in a liquid gallium field-ion-emission source

A detailed investigation of the emission frequency spectra of a gallium liquid metal ion source is presented. The spectra are correlated with current oscillograms. The current for which pulses appear superimposed on the d.c. level of current is well predicted by existing theory. The pulses are believed to be the result of droplet emission, and their terminal frequency appears to coincide with the frequency of vibration of the sides of the liquid cone at high currents. Better understanding of the instabilities that develop on the liquid anode can be useful for deposition purposes.

Doubly-charged ions from liquid metal alloy ion sources: direct field-evaporation or post-ionization?

We investigate the temperature dependence of the mass spectrum of the ion beam emitted by an Au77Ge14Si9 liquid metal alloy ion source. Our results strongly point towards the co-existence of two mechanisms for the emission of doubly-charged monomer ions: direct field evaporation and post-ionization.

On the onset voltage of liquid metal ion sources

Abstract Various formulae for the onset voltage corresponding to liquid metal ion sources (LMIS) of different design are compared to a wide range of experimental data. Provided the correct formula is used in each particular case, the agreement between theory and experiment is satisfactory. Predicting the source starting voltage correctly is of use in ion source and ion column design.