Electrowetting at a liquid metal-semiconductor junction

Arscott, S.; Gaudet, Matthieu

doi:10.1063/1.4818715

Cited by 11 publications

(20 citation statements)

References 38 publications

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“…In a rst approximation, the integration constant K can be considered to be zero by assuming that at zero bias the stored energy is approximately zeroalthough this is not the case as there is a surface charge and a nite built-in voltage existing when one initially forms the metal-semiconductor contactsee the supplementary information of ref. 45. The value of E at V ¼ 0 for an Si-Hg interface is $0.4 mJ m À2 if N ¼ 1 Â 10 16 cm À3 and for a built-in voltage V bi ¼ 1 V; this is much less than the value of the surface tension of Hg which is 486.5 mJ m À2 .…”

Section: Electrowetting At a Liquid-semiconductor Junctionmentioning

confidence: 95%

“…Note also that the Young-Lippmann equation for EWOD isin principleperfectly symmetrical vis-à-vis the polarity of the applied voltage, this is due to two reasons: rst, the squared voltage term and second the dielectric symmetry of the insulator which dominates the overall capacitance. On the latter point, and in the context of electrowetting, the capacitances at the insulatorsemiconductor 45 and liquid-insulator-semiconductor junctions 46,47 are not symmetrical about zero-bias voltage. Indeed, researchers studying electrowetting applications oen plot just the positive (or negative) applied voltages and do not always systematically consider the possibility of non-symmetrical, voltage polarity-dependent results unless this is the explicit intention of the study.…”

Section: Electrowetting-on-dielectricmentioning

confidence: 99%

“…As we have said, the basic Young-Lippmann equation for EWOD has no intrinsic voltage-polarity dependency. However, many studies have shown electrowetting polarity effects 41,42,[45][46][47][72][73][74][75][76][77][78][79][80] related to materials' properties [72][73][74][75] and attributed to the liquid properties. [76][77][78][79][80] Voltage-polarity dependent electrowetting was observed using silicon-silicon dioxide and glasstantalum pentoxide electrowetting setups.…”

Section: Voltage Polarity Effects In Continuous Electrowettingmentioning

confidence: 99%

“…Voltage polarity effects can also be observed in electrowettingand more importantly, controlledby using semiconductors, as has been see recently. [45][46][47] It has been shown that the material used for the insulating layer can have a role in "asymmetric" voltage polarity-dependent electrowetting. It was reported that while using parylene as the insulator, the change in contact angle was independent of the voltage polarity.…”

Section: Voltage Polarity Effects In Continuous Electrowettingmentioning

confidence: 99%

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Electrowetting and semiconductors

Arscott

2014

RSC Adv.

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Section: Electrowetting At a Liquid-semiconductor Junctionmentioning

confidence: 95%

Section: Electrowetting-on-dielectricmentioning

confidence: 99%

Section: Voltage Polarity Effects In Continuous Electrowettingmentioning

confidence: 99%

Section: Voltage Polarity Effects In Continuous Electrowettingmentioning

confidence: 99%

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Electrowetting and semiconductors

Arscott

2014

RSC Adv.

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“…EGaIn has a melting point of 15.7 °C and a liquid phase viscosity approximately twice that of water . It has metallic conductivity and low toxicity, making it an attractive alternative to mercury for many applications …”

Section: Introductionmentioning

confidence: 99%

Recapillarity: Electrochemically Controlled Capillary Withdrawal of a Liquid Metal Alloy from Microchannels

Khan

Trlica

Dickey

2014

Adv Funct Materials

126

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even at ppm O 2 levels. [ 24,25 ] Though this oxide has historically been considered a nuisance, [ 26,27 ] it provides unique opportunities to control the shape of the metal. [ 28 ] This oxide "skin" envelopes the liquid and provides mechanical stability that allows EGaIn to be molded into non-equilibrium shapes that would usually be disallowed by surface tension. [ 29,30 ] The skin has been harnessed to print the metal in 3-D [ 30 ] and 2-D [ 31 ] and to form stretchable interconnects, [ 32 ] wires, [ 33 ] antennas, [ 13,29 ] sensors, [ 34,35 ] and plasmonic structures [ 36 ] fabricated by injecting the metal into microchannels.Because EGaIn is a liquid, its shape and position can be controlled by inducing it to fl ow. Injecting the metal into a microchannel is straightforward by using pressure differentials. This injection technique has been used to create shape-reconfi gurable antennas and fi lters composed of alloys of gallium that change length in response to pressure. [37][38][39] Inducing the metal to fl ow out of a microchannel, however, is more challenging. The presence of the oxide skin can cause the metal to leave residue on the channel walls ( Figure 1 a), like wet paint fl owing through a tube. [ 40 ] It is possible to use Tefl onlike surfaces or roughened surfaces [40][41][42][43] to reduce the adhesion of the metal oxide, but these approaches limit the materials of construction and increase the complexity of fabrication. It is also possible to use acid or base to remove the oxide skin, but this approach lacks external control and involves the use of possibly hazardous or corrosive materials. [ 44 ] For these reasons, most studies involving the actuation of liquid metals in microchannels focus on Hg despite its toxicity. [45][46][47] The Pourbaix diagram predicts that reductive electrochemical potentials can remove the oxide skin on gallium. [ 48 ] Without the stabilizing presence of the skin, the metal undergoes capillary action to minimize its surface energy. Figure 1 b (and Supporting Information Movie S1) illustrates this concept: A puddle of the metal beads up in response to a reductive potential. Although an applied bias likely lowers the interfacial tension of the metal (relative to bare metal) via electrocapillarity, [ 49 ] the tension is still large enough to induce capillary phenomena. This phenomenon can be exploited to induce withdrawal of the metal in microchannels (Figure 1 c and Supporting Information Movie S2) by capillary action toward a reservoir where the metal may lower its interfacial energy by adopting a larger radius of curvature. [ 50 ] Importantly, in the absence of applied potential, This paper describes the mechanistic details of an electrochemical method to control the withdrawal of a liquid metal alloy, eutectic gallium indium (EGaIn), from microfl uidic channels. EGaIn is one of several alloys of gallium that are liquid at room temperature and form a thin (nm scale) surface oxide that stabilizes the shape of the metal in microchannels. Applying a reductive potential to ...

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Heterogeneous Ice Nucleation Studied with Single-Layer Graphene

et al. 2022

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Control of heterogeneous ice nucleation (HIN) is critical for applications that range from iceophobic surfaces to ice-templated materials. HIN on 2D materials is a particular interesting topic that still lacks extensive experimental investigations. Here, we focus on the HIN on single-layer graphene (SLG) transferred onto different substrates, including silicon, silica, and thermal oxide on silicon. Complemented by other samples without SLG, we obtain a large range of wetting contact angles (WCAs) from 2° to 95°. All pristine SLG samples exhibit a large contact angle of ∼95°, which is close to the theoretical value of 96° for free-standing SLG, irrespective of the substrate and even in the presence of nanoscale wrinkles on SLG, which are due to the transfer process, indicating that the topographical features have little impact on the wetting behavior. Interestingly, SLG displays changes in hydrophobicity upon repeated water droplet freezing–melting–drying cycles due to a shift in Fermi level and/or enhanced water–substrate polar molecular interactions, likely induced by residual adsorption of H2O molecules. We found that a 0.04 eV decrease in SLG Fermi level reduces the SLG/water interface energy by ∼6 mJ/m2, thereby making SLG less hydrophobic. Counterintuitively, the reduction in SLG/water interface energy and the enhanced hydrophilicity after repeated freezing–melting–evaporation cycles actually decreases the freezing temperature by ∼3–4 °C, thereby slightly retarding rather than enhancing HIN. We also found that the water droplet freezing temperature differed by only ∼1 °C on different substrates with WCAs from 2° to 95°, an intriguing and yet reasonable result that confirms that wettability alone is not a good indicator of HIN capability. The HIN rate is rather determined by the difference between substrate/water and substrate/ice interface energies, which was found to stay almost constant for substrates weakly interacting with water/ice via van der Waals or hydrogen bonds, irrespective of hydrophilicity.

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Electrowetting at a liquid metal-semiconductor junction

Cited by 11 publications

References 38 publications

Electrowetting and semiconductors

Electrowetting and semiconductors

Recapillarity: Electrochemically Controlled Capillary Withdrawal of a Liquid Metal Alloy from Microchannels

Heterogeneous Ice Nucleation Studied with Single-Layer Graphene

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