Ga droplet surface dynamics during Langmuir evaporation of GaAs

Tang, Wing Man; Zheng, Changxi; Zhou, Zhenyu; Jesson, D. E.; Tersoff, J.

doi:10.1147/jrd.2011.2158762

Cited by 13 publications

(7 citation statements)

References 28 publications

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“…Ga droplets were created by annealing above the planar surface congruent evaporation temperature at 670 C and were imaged using MEM. [13][14][15][16] Droplet motion was observed 14,15 and movies of coalescence events were recorded. The sample was then quenched to room temperature and droplets were imaged ex situ by atomic force microscopy (AFM) in non-contact mode.…”

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confidence: 99%

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Asymmetric coalescence of reactively wetting droplets

Zheng

Tang

Jesson

2012

Applied Physics Letters

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Coalescence of droplets during reactive wetting is investigated for the liquid Ga/GaAs(001) system. In situ mirror electron microscopy reveals that coalescence predominantly involves the motion of one reactive droplet relative to the other. This behaviour differs significantly from coalescence in non-reactive systems and is associated with contact line pinning at a ridge/etch pit edge which is identified using atomic force microscopy and selective etching. A simple geometrical model is presented to describe the pinning.

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“…The droplets appear as uniform dark discs somewhat larger than the actual droplet, surrounded by a concentric bright halo. 14,15 In panel (a), droplet 1 translates across the substrate and coalesces with droplet 2. The coalescence event is rapid, occurring in less than a movie frame (0.1 s) giving a minimum contact line velocity of 18 lms…”

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confidence: 99%

Asymmetric coalescence of reactively wetting droplets

Zheng

Tang

Jesson

2012

Applied Physics Letters

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“…Gallium‐based alloys can be found in a liquid form at both room and elevated temperatures. At high temperatures (>600 °C), researchers have controlled the motion of liquid gallium arsenide via chemical decomposition of the alloy, controlling the direction of motion via surface crystallinity of the substrate . Other high‐temperature gallium alloys have been controlled and directed by surface roughness .…”

Section: Contact Angles Of Galinstan Droplets On Various Substrates mentioning

confidence: 99%

Liquid Metal Switches for Environmentally Responsive Electronics

Bilodeau

Zemlyanov

Kramer

2017

Adv Materials Inter

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providing a second system for non-mechanical liquid metal manipulation. Zhang et al. fed aluminum chips to a galinstan droplet as fuel for self-propulsion, [19] and have since developed non-contacting magnetic controls for the droplet. [20] Finally, a large category of recent research has used electricity to create relative motion and shape change in liquid metals, [21][22][23] enabling non-contacting pumps for microfluidic flow [24] and cooling, [25] self-destructive circuitry (path-destructive liquid metal droplet motion), [26] and most recently as a source for rigid-body locomotion. [27] It is well known that gallium oxidizes rapidly in normal atmospheric conditions, or in any environment with oxygen levels above 1 ppm, [11,28,29] forming a gallium oxide that has been studied in detail. [30][31][32] This oxide is solid at room temperature and forms a nanoscale stabilizing shell around liquid gallium indium alloys, enabling the liquid metal to be patterned onto, and subsequently adhere to, many different material surfaces (via a plethora of techniques). [33] If the oxide is removed, the liquid metal loses its adhesion to the substrate and will reflow under the influence of gravity (or other forces), enabling a fixed liquid metal pattern to change. In other words, oxide removal enables real-time, non-mechanical manipulation of liquid metals. This has typically been done either in nitrogen boxes (via passive oxide prevention) or in chemical etchant baths (via active oxide removal). [18,19,21,[24][25][26] Unfortunately, these methods require enclosed (air-tight or water-proof) chambers that limit the practical applications for manipulation of liquid metal circuits on the fly, as the circuits must remain inside the chamber.The two main etchants used for aqueous oxide removal are hydrochloric acid (HCl, a low-pH acid) [15,18,21,30,31,34] and sodium hydroxide (NaOH, a high-pH base). [19,21,22,[24][25][26] Both of these etchants mix readily with water and can be contained safely at high concentrations. A non-aqueous alternative for oxide removal comes through exposing the liquid metals to concentrated HCl vapor, [35][36][37][38][39] but practical applications of this are generally limited to environments that can withstand the presence of a highly corrosive gas.In this work, we demonstrate control over the surface oxide of liquid metal droplets, which in turn controls the wetting and adhesion of those drops on a substrate, using purely environmental stimuli. We compare the use of highly acidic HCl and highly alkaline NaOH (in solution) in removing the oxide to release pinned droplets. We show that although both solvent solutions result in high contact angles between the droplet and the substrate, NaOH achieves this result at a rate that is orders of magnitude faster than HCl. We further explore the use of neutral distilled water to regrow the oxide and manipulate the contact area of the liquid metal droplet on the surface, causing the droplet to readhere to the substrate. Finally, we apply this environmentally control...

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“…Considerable attention has been paid to the dynamics of metallic droplets on surfaces since then. This includes the motion of Ga droplets on GaAs under incongruent evaporation conditions [2,3], thermomigration of PtSi droplets on stepped Si(111) and Si(100) [4][5][6], AuSi-and AuGe-droplets on various Si and Ge substrates [7,8], AuGe on Ge(110) [9], and, recently, electromigration of AuGe [10]. The surface studies were motivated by interest in possibilities for bottom-up fabrication of nanostructures, catalysis of standing up [11] and lying down nanowires [12,13] on surfaces, and, last but not least, genuine interest in the complex physics of the motion of metallic droplets on surfaces.…”

Section: Introductionmentioning

confidence: 99%

Shining new light on the motion of eutectic droplets across surfaces: A PEEM study of PtGe on Ge(110)

Poelsema

Zhang

Solomon

et al. 2021

Phys. Rev. Materials

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Thermally stimulated motion of micron-sized eutectic PtGe droplets on Ge(110) has been studied in situ mainly by photoemission electron microscopy, low-energy electron microscopy, and spatially resolved lowenergy electron diffraction. In line with earlier studies of eutectic AuSi, PtSi, AuGe, and PtGe clusters on, respectively, various Si and Ge substrates we find that the motion toward regions at higher temperature is driven by the entropy gain of substrate atoms which become constituents of the droplet during its journey. At ∼1100 K, i.e., well above the bulk eutectic temperature, the direction is governed solely by the local thermal gradient, irrespective of eventual crystalline preferences. Access to the diffusivity of the host material (in this case Ge) inside the eutectic droplets shows that this is well above one order of magnitude higher than expected if it was rate limiting for the velocity of the moving droplets. This excludes a significant gradient of the (Ge) concentration inside the droplet and disqualifies dissolution-diffusion-deposition flow as the driving force for motion of the droplets on the surface, as assumed widely hitherto, to explain surface diffusion of eutectic droplets on surfaces. In addition, the interface between the droplet and the surface appears flat and we find no indication for "endotaxy." The droplets make direct contact with the flat Ge substrate through atomic steps, which are abundantly present at the interface. The droplets are surrounded by a PtGe 3 wetting layer with an ordered (2 × 1) structure. Dissolution of the edges of the wetting layer at the leading edge of the droplet with an activation energy of 2.2 eV is identified as the rate limiting step for its motion.

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Ga droplet surface dynamics during Langmuir evaporation of GaAs

Cited by 13 publications

References 28 publications

Asymmetric coalescence of reactively wetting droplets

Asymmetric coalescence of reactively wetting droplets

Liquid Metal Switches for Environmentally Responsive Electronics

Shining new light on the motion of eutectic droplets across surfaces: A PEEM study of PtGe on Ge(110)

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