7 research outputs found
Phase Separation and Ion Diffusion in Ionic Liquid, Organic Solvent, and Lithium Salt Electrolyte Mixtures
The highly desirable characteristics of ternary mixtures
of ionic
liquids, organic solvents, and metal salts make them a promising candidate
for use in various electrothermal energy storage and conversion systems.
In this study, using large-scale classical molecular dynamics simulations,
we looked into 10 different ternary electrolyte mixtures using combinations
of [EMIM]+, [BMIM]+, and [OMIM]+ cations
with [NO3]−, [BF4]−, [PF6]−, [ClO4]−, [TFO]−, and [NTf2]− anions, tetraglyme, and Li salt to study the effect of ionic liquid
composition on the phase behavior of ternary electrolyte mixtures.
We uncovered that in these electrolytes, phase separation is mainly
a function of pairwise binding energy of the constituents of the mixture.
To corroborate this theory, several simulations are performed at various
temperatures ranging from 260 to 500 K for each mixture, followed
by calculating the binding energy of ionic liquid pairs using density
functional theory. Our results verify that the transition temperature
for the phase separation of each system is indeed a function of the
pairwise binding energy of its ionic liquid pairs. It is also found
that in some cases, the diffusion coefficient of the Li+ ions decreased even with the increase in the temperature, an effect
that is attributed to the presence of condensed ionic domains in the
electrolyte. This study provides a new insight for the design of multicomponent
electrolyte mixtures for a wide range of energy applications
Stable and Selective Humidity Sensing Using Stacked Black Phosphorus Flakes
Black phosphorus (BP) atomic layers are known to undergo chemical degradation in humid air. Yet in more robust configurations such as films, composites, and embedded structures, BP can potentially be utilized in a large number of practical applications. In this study, we explored the sensing characteristics of BP films and observed an ultrasensitive and selective response toward humid air with a trace-level detection capability and a very minor drift over time. Our experiments show that the drain current of the BP sensor increases by ∼4 orders of magnitude as the relative humidity (RH) varies from 10% to 85%, which ranks it among the highest ever reported values for humidity detection. The mechanistic studies indicate that the operation principle of the BP film sensors is based on the modulation in the leakage ionic current caused by autoionization of water molecules and ionic solvation of the phosphorus oxoacids produced on moist BP surfaces. Our stability tests reveal that the response of the BP film sensors remains nearly unchanged after prolonged exposures (up to 3 months) to ambient conditions. This study opens up the route for utilizing BP stacked films in many potential applications such as energy generation/storage systems, electrocatalysis, and chemical/biosensing
Bimodal Phonon Scattering in Graphene Grain Boundaries
Graphene has served as the model
2D system for over a decade, and the effects of grain boundaries (GBs)
on its electrical and mechanical properties are very well investigated.
However, no direct measurement of the correlation between thermal
transport and graphene GBs has been reported. Here, we report a simultaneous
comparison of thermal transport in supported single crystalline graphene
to thermal transport across an individual graphene GB. Our experiments
show that thermal conductance (per unit area) through an isolated
GB can be up to an order of magnitude lower than the theoretically
anticipated values. Our measurements are supported by Boltzmann transport
modeling which uncovers a new bimodal phonon scattering phenomenon
initiated by the GB structure. In this novel scattering mechanism,
boundary roughness scattering dominates the phonon transport in low-mismatch
GBs, while for higher mismatch angles there is an additional resistance
caused by the formation of a disordered region at the GB. Nonequilibrium
molecular dynamics simulations verify that the amount of disorder
in the GB region is the determining factor in impeding thermal transport
across GBs
Modeling and Analysis of Intercalant Effects on Circular DNA Conformation
The
large-scale conformation of DNA molecules plays a critical role in
many basic elements of cellular functionality and viability. By targeting
the structural properties of DNA, many cancer drugs, such as anthracyclines,
effectively inhibit tumor growth but can also produce dangerous side
effects. To enhance the development of innovative medications, rapid
screening of structural changes to DNA can provide important insight
into their mechanism of interaction. In this study, we report changes
to circular DNA conformation from intercalation with ethidium bromide
using all-atom molecular dynamics simulations and characterized experimentally
by translocation through a silicon nitride solid-state nanopore. Our
measurements reveal three distinct current blockade levels and a 6-fold
increase in translocation times for ethidium bromide-treated circular
DNA as compared to untreated circular DNA. We attribute these increases
to changes in the supercoiled configuration hypothesized to be branched
or looped structures formed in the circular DNA molecule. Further
evidence of the conformational changes is demonstrated by qualitative
atomic force microscopy analysis. These results expand the current
methodology for predicting and characterizing DNA tertiary structure
and advance nanopore technology as a platform for deciphering structural
changes of other important biomolecules
Thermodynamics and Kinetics in Anisotropic Growth of One-Dimensional Midentropy Nanoribbons
One-dimensional
(1D) materials demonstrate anisotropic in-plane
physical properties that enable a wide range of functionalities in
electronics, photonics, valleytronics, optoelectronics, and catalysis.
Here, we undertake an in-depth study of the growth mechanism for equimolar
midentropy alloy of (NbTaTi)0.33S3 nanoribbons
as a model system for 1D transition metal trichalcogenide structures.
To understand the thermodynamic and kinetic effects in the growth
process, the energetically preferred phases at different synthesis
temperatures and times are investigated, and the phase evolution is
inspected at a sequence of growth steps. It is uncovered that the
dynamics of the growth process occurs at four different stages via
preferential incorporation of chemical species at high-surface-energy
facets. Also, a sequence of temperature and time dependent nonuniform
to uniform phase evolutions has emerged in the composition and structure
of (NbTaTi)0.33S3 which is described based on
an anisotropic vapor–solid (V–S) mechanism. Furthermore,
direct evidence for the 3D structure of the charge density wave (CDW)
phase (width less than 100 nm) is provided by three-dimensional electron
diffraction (3DED) in individual nanoribbons at cryogenic temperature,
and detailed comparisons are made between the phases obtained before
and after CDW transformation. This study provides important fundamental
information for the design and synthesis of future 1D alloy structures
Thermodynamics and Kinetics in Anisotropic Growth of One-Dimensional Midentropy Nanoribbons
One-dimensional
(1D) materials demonstrate anisotropic in-plane
physical properties that enable a wide range of functionalities in
electronics, photonics, valleytronics, optoelectronics, and catalysis.
Here, we undertake an in-depth study of the growth mechanism for equimolar
midentropy alloy of (NbTaTi)0.33S3 nanoribbons
as a model system for 1D transition metal trichalcogenide structures.
To understand the thermodynamic and kinetic effects in the growth
process, the energetically preferred phases at different synthesis
temperatures and times are investigated, and the phase evolution is
inspected at a sequence of growth steps. It is uncovered that the
dynamics of the growth process occurs at four different stages via
preferential incorporation of chemical species at high-surface-energy
facets. Also, a sequence of temperature and time dependent nonuniform
to uniform phase evolutions has emerged in the composition and structure
of (NbTaTi)0.33S3 which is described based on
an anisotropic vapor–solid (V–S) mechanism. Furthermore,
direct evidence for the 3D structure of the charge density wave (CDW)
phase (width less than 100 nm) is provided by three-dimensional electron
diffraction (3DED) in individual nanoribbons at cryogenic temperature,
and detailed comparisons are made between the phases obtained before
and after CDW transformation. This study provides important fundamental
information for the design and synthesis of future 1D alloy structures
Thermodynamics and Kinetics in Anisotropic Growth of One-Dimensional Midentropy Nanoribbons
One-dimensional
(1D) materials demonstrate anisotropic in-plane
physical properties that enable a wide range of functionalities in
electronics, photonics, valleytronics, optoelectronics, and catalysis.
Here, we undertake an in-depth study of the growth mechanism for equimolar
midentropy alloy of (NbTaTi)0.33S3 nanoribbons
as a model system for 1D transition metal trichalcogenide structures.
To understand the thermodynamic and kinetic effects in the growth
process, the energetically preferred phases at different synthesis
temperatures and times are investigated, and the phase evolution is
inspected at a sequence of growth steps. It is uncovered that the
dynamics of the growth process occurs at four different stages via
preferential incorporation of chemical species at high-surface-energy
facets. Also, a sequence of temperature and time dependent nonuniform
to uniform phase evolutions has emerged in the composition and structure
of (NbTaTi)0.33S3 which is described based on
an anisotropic vapor–solid (V–S) mechanism. Furthermore,
direct evidence for the 3D structure of the charge density wave (CDW)
phase (width less than 100 nm) is provided by three-dimensional electron
diffraction (3DED) in individual nanoribbons at cryogenic temperature,
and detailed comparisons are made between the phases obtained before
and after CDW transformation. This study provides important fundamental
information for the design and synthesis of future 1D alloy structures