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arXiv:2507.00536
[pdf]
cond-mat.mes-hall
cond-mat.mtrl-sci
cond-mat.soft
physics.app-ph
physics.flu-dyn
Interaction-Driven Giant Electrostatic Modulation of Ion Permeation in Atomically Small Capillaries
Authors:
Dhal Biswabhusan,
Yechan Noh,
Sanat Nalini Paltasingh,
Chandrakar Naman,
Siva Sankar Nemala,
Rathi Aparna,
Kaushik Suvigya,
Andrea Capasso,
Saroj Kumar Nayak,
Li-Hsien Yeh,
Kalon Gopinadhan
Abstract:
Manipulating the electrostatic double layer and tuning the conductance in nanofluidic systems at salt concentrations of 100 mM or higher has been a persistent challenge. The primary reasons are (i) the short electrostatic proximity length, ~3-10 Å, and (ii) difficulties in fabricating atomically small capillaries. Here, we successfully fabricate in-plane vermiculite laminates with transport height…
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Manipulating the electrostatic double layer and tuning the conductance in nanofluidic systems at salt concentrations of 100 mM or higher has been a persistent challenge. The primary reasons are (i) the short electrostatic proximity length, ~3-10 Å, and (ii) difficulties in fabricating atomically small capillaries. Here, we successfully fabricate in-plane vermiculite laminates with transport heights of ~3-5 Å, which exhibit a cation selectivity close to 1 even at a 1000 mM concentration, suggesting an overlapping electrostatic double layer. For gate voltages from -2 V to +1 V, the K+-intercalated vermiculite shows a remarkable conductivity modulation exceeding 1400% at a 1000 mM KCl concentration. The gated ON/OFF ratio is mostly unaffected by the ion concentration (10-1000 mM), which confirms that the electrostatic double layer overlaps with the collective ion movement within the channel with reduced activation energy. In contrast, vermiculite laminates intercalated with Ca2+ and Al3+ ions display reduced conductance with increasing negative gate voltage, highlighting the importance of ion-specific gating effects under Å-scale confinement. Our findings contribute to a deeper understanding of electrostatic phenomena occurring in highly confined fluidic channels, opening the way to the exploration of the vast library of two-dimensional materials.
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Submitted 1 July, 2025;
originally announced July 2025.
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Room-Temperature Deuterium Separation in van der Waals Gap Engineered Vermiculite Quantum Sieves
Authors:
Saini Lalita,
Rathi Aparna,
Kaushik Suvigya,
Li-Hsien Yeh,
Kalon Gopinadhan
Abstract:
As the demand for nuclear energy grows, enriching deuterium from hydrogen mixtures has become more important. However, traditional methods are either very energy-intensive because they require extremely cold temperatures, or they don't separate deuterium (D2) from regular hydrogen (H2) very well, with a D2/H2 selectivity of about 0.71. To achieve efficient deuterium separation at room temperature,…
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As the demand for nuclear energy grows, enriching deuterium from hydrogen mixtures has become more important. However, traditional methods are either very energy-intensive because they require extremely cold temperatures, or they don't separate deuterium (D2) from regular hydrogen (H2) very well, with a D2/H2 selectivity of about 0.71. To achieve efficient deuterium separation at room temperature, we need materials with very tiny spaces, on an atomic scale. For the first time, we've successfully created a material with spaces just about 2.1 angstroms wide, which is similar in size to the wavelength of hydrogen isotopes at room temperature. This allows for efficient deuterium separation, with a much higher D2/H2 selectivity of about 2.20, meaning the material can separate deuterium from hydrogen much more effectively at room temperature. The smaller deuterium molecules are more likely to pass through these tiny spaces, showing that quantum effects play a key role in this process. In contrast, a material like graphene oxide, with larger spaces (around 4.0 angstroms) only shows a lower D2/H2 selectivity of approx 1.17, indicating weaker quantum effects. This discovery suggests that materials with very small, atomic-scale spaces could be key to the efficient separation of hydrogen isotopes at room temperature.
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Submitted 12 February, 2025;
originally announced February 2025.
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Can structure influence hydrovoltaic energy generation? Insights from the metallic 1T' and semiconducting 2H phases of MoS$_2$
Authors:
Kaushik Suvigya,
Saini Lalita,
Siva Nemala Sankar,
Andrea Capasso,
Li-Hsien Yeh,
Kalon Gopinadhan
Abstract:
Hydrovoltaic power generation from liquid water and ambient moisture has attracted considerable research efforts. However, there is still limited consensus on the optimal material properties required to maximize the power output. Here, we used laminates of two different phases of layered MoS$_2$ -- metallic 1T' and semiconducting 2H -- as representative systems to investigate the critical influenc…
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Hydrovoltaic power generation from liquid water and ambient moisture has attracted considerable research efforts. However, there is still limited consensus on the optimal material properties required to maximize the power output. Here, we used laminates of two different phases of layered MoS$_2$ -- metallic 1T' and semiconducting 2H -- as representative systems to investigate the critical influence of specific characteristics, such as hydrophilicity, interlayer channels, and structure, on the hydrovoltaic performance. The metallic 1T' phase was synthesized via a chemical exfoliation process and assembled into laminates, which can then be converted to the semiconducting 2H phase by thermal annealing. Under liquid water conditions, the 1T' laminates, having a channel size of 6 angstroms, achieved a peak power density of 2.0 mW m$^{-2}$, significantly outperforming the 2H phase, lacking defined channels, that produced a power of 2.4 microW m$^{-2}$. Our theoretical analysis suggests that energy generation in these hydrophilic materials primarily arises from electro-kinetic and surface diffusion mechanisms. These findings highlight the crucial role of phase-engineered MoS$_2$ and underscore the potential of 2D material laminates in advancing hydrovoltaic energy technologies.
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Submitted 3 January, 2025;
originally announced January 2025.
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Angstrom Scale Ionic Memristors' Engineering with van der Waals Materials- A Route to Highly Tunable Memory States
Authors:
Dhal Biswabhusan,
Puzari Animesh,
Li-Hsien Yeh,
Kalon Gopinadhan
Abstract:
Memristors that mimic brain functions are crucial for energy-efficient neuromorphic devices. Ion channels that emulate biological synapses are still in the early stages of development, especially the tunability of memory states. Here, we demonstrate that cations such as K+, Na+, Ca2+, and Al3+ intercalated in the interlayer spaces of vermiculite, result in highly confined channels of size 3-5 Å. T…
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Memristors that mimic brain functions are crucial for energy-efficient neuromorphic devices. Ion channels that emulate biological synapses are still in the early stages of development, especially the tunability of memory states. Here, we demonstrate that cations such as K+, Na+, Ca2+, and Al3+ intercalated in the interlayer spaces of vermiculite, result in highly confined channels of size 3-5 Å. They host exotic memristor properties through ion exchange dynamics, even at high salt concentrations of 1 M. The bipolar memristor characteristics observed are tunable with frequency, geometric asymmetry, ion concentration, and intercalants. Notably, we observe polarization-flipping memristor behavior in two cases: one with Al3+ ions and another with devices having a geometric asymmetry ratio greater than 15. This inversion is attributed to the over-screening of counter-ions due to their accumulation at the channel entrance. Our results suggest that ion exchange dynamics, ion-ion interactions, and ion accumulation/depletion mechanisms, particularly with multivalent ions, can be harnessed to develop advanced memristor devices.
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Submitted 6 December, 2024;
originally announced December 2024.