Liquid Metal Ion Source Research Articles

Comparison of Mg-based liquid metal ion sources for scalable focused-ion-implantation doping of GaN

We compare the suitability of various magnesium-based liquid metal alloy ion sources (LMAISs) for scalable focused-ion-beam (FIB) implantation doping of GaN. We consider GaMg, MgSO4●7H2O, MgZn, AlMg, and AuMgSi alloys. Although issues of oxidation (GaMg), decomposition (MgSO4●7H2O), and excessive vapor pressure (MgZn and AlMg) were encountered, the AuMgSi alloy LMAIS operating in a Wien-filtered FIB column emits all Mg isotopes in singly and doubly charged ionization states. We discuss the operating conditions to achieve <20 nm spot size Mg FIB implantation and present Mg depth profile data from time-of-flight secondary ion mass spectrometry. We also provide insight into implantation damage and recovery based on cathodoluminescence spectroscopy before and after rapid thermal processing. Prospects for incorporating the Mg LMAIS into high-power electronic device fabrication are also discussed.

Review of: "Focused ion beam nanolithography , as a sequential nanolithography technique, is inherently slow and its throughput is much lower than other techniques, and Ga + -based liquid metal ion source"

Review of: "Focused ion beam nanolithography , as a sequential nanolithography technique, is inherently slow and its throughput is much lower than other techniques, and Ga + -based liquid metal ion source"

Study of microchannel structures for measuring emission conductance of indium field emission electric propulsion micro-thrusters

Surface morphology of emitting tip has a significant effect on performance of Liquid-Metal Ion Sources. In this paper, fabrication technics of dynamic micro-electrochemical etching was employed to realize micro-grooves processing of emitting tip surfaces at different depths by regulating roughening time and voltage frequency. Through field emission experiments of indium Field Emission Electric Propulsion micro-thruster, we measured volt–ampere characteristic curves of a batch of emitters with different microchannel structures. By a normalization method, the effect of inconsistency of apex radius between different tips on volt–ampere characteristics was eliminated, and influence law of surface roughness on emission conductance was revealed more clearly. The test results were found to be consistent with the current–voltage characteristics which was deduced from microchannel model based on a semi-cylindrical shape. This study presents an approach for pre-estimating and optimizing the emission conductance through assessment of emitter surface roughness and substantiates the method’s viability.

Mass-selected ion beam generation using two rotating electric-field mass separation technique

This paper describes the origin, principles, practical applications, and future perspectives of mass-selected ion beams generated using two rotating electric-field mass (REF-MS) filters. Our team has been investigating the underlying principles of REF-MS separation and assessing the feasibility of developing suitable systems to realize mass separation and ion beam convergence using rotating electric fields as well as the practicability of this method. This paper focuses on the mechanism underlying the observed cycloid trajectories followed by REF-MS-selected ions. A focused ion beam column with Ga and AuGe liquid metal ion sources (LMISs) was connected to REF-MS optics to assess the mass-selection performance of the filter. The mass-separation ability of this system was demonstrated by the ion projection images of Ga-LMIS (69Ga+ and 71Ga+) and AuGe-LMIS (97Au2+, Au2Ge+, and Au2Ge2+). The column was then replaced with a vacuum electrospray ionization (ESI) source. The size-selected water-cluster ion beams [(H2O)nH]+ were separated based on cluster size, and a microscale crater was created. Co-containing molecular ion beams were revealed using different concentrations of ESI sources, and a mass-separated [Co(DEGBE)4]+ ion beam was constructed.

Imaging of Ancient Microbial Biomarkers within Miocene Dolomite (Kuwait) Using Time-of-Flight Secondary Ion Mass Spectrometry

Time-of-Flight–Secondary Ion Mass Spectrometry (ToF-SIMS) using a bismuth liquid metal ion source was utilized to characterize and image microbial biomarkers within dolomite from early-middle Miocene coastal mud volcano outcrops in Kuwait. ToF-SIMS analysis revealed biomarkers of ancient microbial consortia of sulfate reducers and methane oxidizers participating in the anaerobic oxidation of methane. The identified lipid biomarkers comprised 17α(H),21β(H)-Norhopane, Hop-17(21)-ene or Hop-22(29)-ene (diploptene), non-isoprenoidal dialkyl glycerol diethers (DAGEs), and Diacylglycerol esters (DGs). The ion µ-scale images of carbonate rocks showed two characteristic styles: (1) high signal intensity of dolomite, halite, and biomarkers, where the biomarkers demonstrate a distinctive co-localization pattern with both dolomite and halite; and (2) a lack of dolomite, halite low signal intensity, and an absence of biomarker co-localization patterns. Our results highlight three remarkable observations. Firstly, the concomitance of dolomite and halite suggests a common source of magnesium and sodium supply, likely from the hypersaline Al-Subiya sabkha. This emphasizes the importance of hypersaline seawater for dolomite formation. Secondly, microbial biomarkers correspond to methane- and sulfate-rich conditions under which dolomite was formed. Lastly, the high intensity of biomarker signals and their association with dolomite and halite indicate that the consortia involved in dolomite formation have preferences for high-salinity conditions. The three observations align with previous studies that have highlighted the importance of methane-sulfate redox, high salinity, and halophilic microbes for dolomite formation. This work is the first to acknowledge ancient microbial biomarkers within Miocene dolomite in Kuwait, which aims to broaden the understanding of the biogeochemical processes triggering dolomite formation in similar environments and ancient geologic settings.

Investigation of the milling characteristics of different focused-ion-beam sources assessed by three-dimensional electron diffraction from crystal lamellae.

Three-dimensional electron diffraction (3DED) from nanocrystals of biological macromolecules requires the use of very small crystals. These are typically less than 300 nm-thick in the direction of the electron beam due to the strong interaction between electrons and matter. In recent years, focused-ion-beam (FIB) milling has been used in the preparation of thin samples for 3DED. These instruments typically use a gallium liquid metal ion source. Inductively coupled plasma (ICP) sources in principle offer faster milling rates. Little work has been done to quantify the damage these sources cause to delicate biological samples at cryogenic temperatures. Here, an analysis of the effect that milling with plasma FIB (pFIB) instrumentation has on lysozyme crystals is presented. This work evaluates both argon and xenon plasmas and compares them with crystals milled with a gallium source. A milling protocol was employed that utilizes an overtilt to produce wedge-shaped lamellae with a shallow thickness gradient which yielded very thin crystalline samples. 3DED data were then acquired and standard data-processing statistics were employed to assess the quality of the diffraction data. An upper bound to the depth of the pFIB-milling damage layer of between 42.5 and 50 nm is reported, corresponding to half the thickness of the thinnest lamellae that resulted in usable diffraction data. A lower bound of between 32.5 and 40 nm is also reported, based on a literature survey of the minimum amount of diffracting material required for 3DED.

Fabrication of tungsten tips with controllable shape by a two-step rapid reciprocating electrochemical etching method.

Traditional electrochemical etching methods for the needle of a liquid metal ion source (LMIS) easily produce an exponential profile with an uncontrollable tip length and apex radius. Meanwhile, a ledge forms between the needle tip and the needle rod under the etching of the meniscus, which becomes an obstacle for the flow and replenishment of the liquid metal. This paper proposed a two-step rapid reciprocating etching method, which aims to fabricate LMIS tungsten needles with controllable tip length and apex radius, and also with a smooth transition region between the needle tip and the needle rod. In the first step of rough machining, the needle rapidly reciprocates up and down in the electrolyte and rotates to produce a uniform conical profile. However, an ellipsoidal residual portion is generated concomitantly at the needle tip. In the second step of finish machining, the needle shifts down for a given distance and continues to reciprocate until the sharp tip is formed. The tip length fabricated varied from 0.59 to 5.53mm at different reciprocating strokes. The apex radius ranged from 0.3 to 0.7 µm, and can also be increased to 2 µm by extra reciprocate etching in the electrolyte to meet the LMIS working requirement. A variable named transitivity was defined to quantitatively describe the smoothness of the region between the tip and rod during the etching process. The experimental results showed that a rotation speed of 600 rpm combined with a reciprocating speed of 0.5 mm/s can significantly improve the transitivity of the needle. Those fabricated needle tips have been tested for the indium LMIS and the maximum emission current of the needle tip reached 12 µA.

Development and coupling test of active spacecraft potential control – Next generation (ASPOC-NG)

The active spacecraft potential control (ASPOC) system developed in the 1990s emits positive ions to neutralise the spacecraft potential, such as used in several missions like Geotail, Equator-S, Cluster, Doublestar and MMS. With the experience gained, the next generation of the active spacecraft potential control (ASPOC-NG) instrument has been developed over the last three years. Thereby, three emission technologies were tested including Liquid Metal Ion Source (LMIS), Liquid Metal Electron Source (LMES) and Solid Metal Electron Source (SMES). The development of the emitter module by FOTEC and the corresponding electronics control unit by IWF is presented. Optimisations were carried out with the focus on the reduction of mass and power consumption to comply with the requirements of future scientific missions. Coupling tests of the modules and the electronics control unit were performed including range, accuracy and lifetime tests. Both ASPOC-NG instruments for positive and negative charge compensation and their performance values show excellent results.

Development of a new generation of ion beams

Ion beams have many applications. Junior Associate Professor Masahi Nojima, Research Institute of Science and Technology at the Tokyo University of Science, Japan, is working to create a new generation of ion beams. Already, he has successfully developed new techniques for producing focused ion beams (FIB). In his most recent work, Nojima has developed a metallic solution ion source that will be used to construct unknown functional materials by using ion beams made up of specific elements. The metallic solution ion source can generate a copy of an original structure using elementally selected materials. With support from the Japan Society for the Promotion of Science (JSPS), KAKENHI, the academic incentive system of the KIOXIA Corporation 2021 and the Toshiba Electric Devices & Storage Corporation 2021, Nojima is seeking to open up new materials for use as ion sources utilising electrospray ionisation (ESI) methods. By harnessing the elements of FIBs primarily created from liquid metal ion source (LMIS) by field ionisation processes, Nojima hopes to create new generations of ion beams. To date, he and the team have displayed the result of mass separating metallic ion solution ion beams on random conditions and, looking ahead, intend to estimate the stopping range of mass selected ion beams in solid materials.

Experimental realization of nonlinear demagnification in plasma-based charged particle optics

We experimentally demonstrate nonlinear demagnification (DM) in plasma-based charged particle optics. The nonlinearity originates from the non-uniform penetration of electric fields through the plasma sheath region, when the object beam size (d P ) is reduced to below the Debye length (λ d ). The strength of nonlinearity depends upon d P and λ d , as confirmed from experimental results and a theoretical model. Nonlinear DM is unique to optics of classical Maxwell-Boltzmann systems and unrealized in conventional liquid metal sources where the Fermi Debye length ≪d P . The realization of plasma sheaths being able to control DM can greatly enhance the performance of charged particle optical systems.

Development of a new generation of ion beams

Ion beams have many applications. Junior Associate Professor Masahi Nojima, Research Institute of Science and Technology at the Tokyo University of Science, Japan, is working to create a new generation of ion beams. Already, he has successfully developed new techniques for producing focused ion beams (FIB). In his most recent work, Nojima has developed a metallic solution ion source that will be used to construct unknown functional materials by using ion beams made up of specific elements. The metallic solution ion source can generate a copy of an original structure using elementally selected materials. With support from the Japan Society for the Promotion of Science (JSPS), KAKENHI, the academic incentive system of the KIOXIA Corporation 2021 and the Toshiba Electric Devices & Storage Corporation 2021, Nojima is seeking to open up new materials for use as ion sources utilising electrospray ionisation (ESI) methods. By harnessing the elements of FIBs primarily created from liquid metal ion source (LMIS) by field ionisation processes, Nojima hopes to create new generations of ion beams. To date, he and the team have displayed the result of mass separating metallic ion solution ion beams on random conditions and, looking ahead, intend to estimate the stopping range of mass selected ion beams in solid materials.

Comparative hard x-ray tomography for virtual histology of zebrafish larva, human tooth cementum, and porcine nerve.

Purpose: Synchrotron radiation-based tomography yields microanatomical features in human and animal tissues without physical slicing. Recent advances in instrumentation have made laboratory-based phase tomography feasible. We compared the performance of three cutting-edge laboratory systems benchmarked by synchrotron radiation-based tomography for three specimens. As an additional criterion, the user-friendliness of the three microtomography systems was considered. Approach: The three tomography systems-SkyScan 2214 (Bruker-microCT, Kontich, Belgium), Exciscope prototype (Stockholm, Sweden), and Xradia 620 Versa (Zeiss, Oberkochen, Germany)-were given 36h to measure three medically relevant specimens, namely, zebrafish larva, archaeological human tooth, and porcine nerve. The obtained datasets were registered to the benchmark synchrotron radiation-based tomography from the same specimens and selected ones to the SkyScan 1275 and phoenix nanotom m® laboratory systems to characterize development over the last decade. Results: Next-generation laboratory-based microtomography almost reached the quality achieved by synchrotron-radiation facilities with respect to spatial and density resolution, as indicated by the visualization of the medically relevant microanatomical features. The SkyScan 2214 system and the Exciscope prototype demonstrated the complementarity of phase information by imaging the eyes of the zebrafish larva. The thin annual layers in the tooth cementum were identified using Xradia 620 Versa. Conclusions: SkyScan 2214 was the simplest system and was well-suited to visualizing the wealth of anatomical features in the zebrafish larva. Data from the Exciscope prototype with the high photon flux from the liquid metal source showed the spiral nature of the myelin sheaths in the porcine nerve. Xradia 620 Versa, with detector optics as typically installed for synchrotron tomography beamlines, enabled the three-dimensional visualization of the zebrafish larva with comparable quality to the synchrotron data and the annual layers in the tooth cementum.

Negative-cluster ion beam production from the tip of a sharp needle: Suppression of surface charging and surface analysis of an insulated sample

In focused ion beam technology, liquid metal ion sources (LMISs) are widely used; however, they cannot produce negative ion beams. In this work, we demonstrate stable negative-cluster ion beam production from a point source by a method similar to LMISs. A negative-cluster ion beam is stably produced from the tip of a sharp needle wetted with a protic ionic liquid, diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]). The time rate of change in the negative ion beam current is less than 1% per hour. The beam is estimated to contain two kinds of negative-cluster ions: [TfO]−([dema][TfO]) (m/z 386.02) and [TfO]−([dema][TfO])2 (m/z 623.08). These cluster ions contain reactive protons enhancing protonation. We investigate surface charging in an electrically insulated material irradiated by the negative ion beam, showing that charging voltage is as low as approximately 1 V. We report that secondary ion mass spectrometry of an insulated organic sample is possible using the negative ion beam without charge compensation.

Experimental study of the laser-induced ionization of heavy metal and metalloid ions: Au+ and Si2+ in intense and sculpted femtosecond laser fields

We implement a liquid metal ion source in a 3D coincidence momentum spectroscopy setup for studying the interaction of ionic targets with intense laser pulses. Laser intensities of up to 4 ⋅ 1016 W cm−2 allow for the observation of up to ten-fold ionization of Au+-ions and double ionization of Si2+-ions. Further, by utilizing two-color sculpted laser fields to control the ionization process on the attosecond time scale, we demonstrate the capability to resolve the recoil ion momenta of heavy metal atoms. Simulations based on a semiclassical model assuming purely sequential ionization reproduce the experimental data well. This work opens up the use of a range of metallic and metalloid ions, which have hardly been investigated in strong-field laser physics so far.

Spatial association between platinum minerals and magmatic sulfides imaged with the Maia Mapper and implications for the origin of the chromite-sulfide-PGE association

ABSTRACT The spatial association between Pt minerals, magmatic sulfides, and chromite has been investigated using microbeam X-ray fluorescence (XRF) element mapping and the Maia Mapper. This lab-based instrument combines the Maia parallel energy dispersive (ESD) detector array technology with a focused X-ray beam generated from a liquid metal source. It proves to be a powerful technique for imaging Pt distribution at low-ppm levels on minimally prepared cut rock surfaces over areas of tens to hundreds of square centimeters, an ideal scale for investigating these relationships. Images of a selection of samples from the Bushveld Complex and from the Norilsk-Talnakh ore deposits (Siberia) show strikingly close association of Pt hotspots, equated with the presence of Pt-rich mineral grains, with magmatic sulfide blebs in all cases, except for a taxitic low-S ore sample from Norilsk. In all of the Bushveld samples, at least 75% of Pt hotspots (by number) occur at or within a few hundred microns of the outer edges of sulfide blebs. In samples from the leader seams of the UG2 chromitite, sulfides and platinum hotspots are also very closely associated with the chromite seams and are almost completely absent from the intervening pyroxenite. In the Merensky Reef, the area ratio of Pt hotspots to sulfides is markedly higher in the chromite stringers than in the silicate-dominated lithologies over a few centimeters either side. We take these observations as confirmation that sulfide liquid is indeed the prime collector for Pt and, by inference, for the other platinum group elements (PGEs) in all these settings. We further propose a mechanism for the sulfide-PGE-chromite association in terms of in situ heterogeneous nucleation of all these phases coupled with transient sulfide saturation during chromite growth and subsequent sulfide loss by partial re-dissolution. In the case of the amygdular Norilsk taxite, the textural relationship and high PGE/S ratio is explained by extensive loss of S to an escaping aqueous vapor phase.

Multiplicity of Inertial Self-Similar Conical Shapes in an Electrified Liquid Metal

Liquid metal ion sources (LMIS) are widely used in applications ranging from local ion implantation in semiconductors, to focused ion beam systems for milling and nanolithography, to space micropropulsion devices being developed by NASA. Above a critically large field strength, an electrically stressed liquid metal develops one or more cuspidal protrusions which undergo accelerated conic tip sharpening with runaway field self-enhancement. Zubarev (2001) first predicted from an inviscid model that the electric stresses at the liquid apex undergo self-similar divergent growth in finite time. The inviscid assumption is appropriate to liquid metals since the viscous boundary layer extends only a few tens of nanometers from the moving interface. In this work, we examine in more depth a two-parameter family of far-field self-similar solutions incorporating inertial, electrical and capillary effects, which to leading order describe electric and velocity potential fields corresponding to a rapidly accelerating \textit{dynamic} Taylor cone. These far field solutions are incorporated self-consistently into boundary integral simulations which reveal the entire liquid shape in the near field. By invoking time reversal symmetry inherent to inviscid flow, we unmask an entire family of novel self-similar conic modes exhibiting features such as inertial recoil, tip bulging from accelerated advance and tip counter-current flow as well as multiple interface stagnation points. These dynamic configurations help explain for the first time the origin of decades old experimental observations that have reported phenomena such as tip oscillation, pulsation and breakup during operation. The various liquid tip shapes accessible to such systems should help correct persistent misconceptions of pre- and post-emission behavior in LMIS systems and related technologies.

IFM Nano Thruster performance studied by experiments and numerical simulations

Field emission electric propulsion thrusters are characterised by their low thrust range, which makes them ideal for the precise control of spacecraft. Decisive for precise control are the properties of the thruster ion beam, which includes the beam divergence angle and the thrust vector. The analysis of these properties is also necessary in order to be able to estimate the interactions of the beam with components of the spacecraft. Due to such interactions, solar panels or electrical instruments on board the spacecraft could be damaged by sputtering effects.The spatial ion current density and energy distribution of a test crown emitter beam, with different specifications compared to the IFM Nano thruster, were examined experimentally with a diagnostic system, including Faraday cups and a retarding potential analyser. In addition to the analysis of the beam profile of an emitting crown, a single emitting needle was analysed. Based on these experimental analyses, an ion trajectory simulation model was developed to determine the theoretical ion current density distribution. This model includes the properties of a liquid metal ion source, where the ion trajectories start from their point of origin, the so-called Taylor cone jet cap. The benchmark of the model shows that the thrust vector and divergence angle correspond to the experimental results and shows the identical calculations for different thruster parameters, like emission current and electrode voltage. The simulation allows for the optimisation of existing and novel thruster geometries in terms of performance, reliability and longevity.

Estimation of needle height using relative parallax between two SIM images in single-column focused ion beam instrument

Gallium liquid metal ion source focused ion beam (FIB) instruments are widely used for cross-sectional sample preparation of specific areas of interest for scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Most FIB instruments are equipped with a metal needle for manipulation of the sample in the sample chamber most commonly as a micro-sampling probe for preparing TEM samples. Automatic needle manipulation has not yet been achieved for a conventional single-column FIB instrument without an SEM column because a reliable method for measuring needle height has not been established yet. This study investigated the use of scanning ion microscope (SIM) image processing to measure needle height from the sample surface in a conventional single-column FIB instrument without an SEM column. The needle height is measured using the relative parallax between two SIM images in which the needle is observed from two directions using a conventional aligner without the use of any special devices. It was demonstrated that the relative parallax was proportional to the needle height. The estimation precision was about several 10 μm, which is sufficient for automatic manipulation and safe touchdown of a needle in practical micro-sampling.

Transition frequencies and hyperfine structure in In+113,115 : Application of a liquid-metal ion source for collinear laser spectroscopy

We demonstrate the first application of a liquid-metal ion source for collinear laser spectroscopy in proof-of-principle measurements on naturally abundant In$^+$. The superior beam quality, i.e., the actively stabilized current and energy of a beam with very low transverse emittance, allowed us to perform precision spectroscopy on the $5s^2\;^1\mathrm{S}_0 \rightarrow 5s5p\;^3\mathrm{P}_1$ intercombination transition in $^{115}$In$^+$, which is to our knowledge the slowest transition measured with collinear fluorescence laser spectroscopy so far. By applying collinear and anticollinear spectroscopy, we improved the center-of-gravity frequency $\nu_\mathrm{cg}=1\,299\,617\,759.\,3\,(1.2)$ and the hyperfine constants $A=6957.19\,(28)$\,MHz and $B=-443.7\,(2.4)$\,MHz by more than two orders of magnitude. A similar accuracy was reached for $^{113}$In$^+$ in combination with literature data and the isotope shift between both naturally abundant isotopes was deduced to $\nu(^{113}\mathrm{In})-\nu(^{115}\mathrm{In})=696.3\,(3.1)$\,MHz. Nuclear alignment induced by optical pumping in a preparation section of the ion beamline was demonstrated as a pump-and-probe approach to provide sharp features on top of the Doppler broadened resonance profile.

Preliminary Study on Gallium-Based Particle Synthesis by Ultrasonication for Microfluid Application

Gallium-based liquid metals have been used widely in many industries because of their unique properties such as high electrical conductivity, the superconductive character at low temperature, and high thermal conductivity. For heat management application, Gallium based metal can be used directly in the liquid form, or in solid particle form. The solid form, however, has extensive application because it can be used as a microparticle additive to create a microfluid. In this research, the ultrasonic oscillator was used to synthesize sub-micron Gallium based particles. Ethanol and Polyethylene Glycol was used and compared as a medium during ultrasonication. Up to 15 %wt of the solid particle was successfully synthesized from one gram of liquid metal source using this simple method.