6 research outputs found
Graphene Microcapsule Arrays for Combinatorial Electron Microscopy and Spectroscopy in Liquids
Atomic-scale
thickness, molecular impermeability, low atomic number, and mechanical
strength make graphene an ideal electron-transparent membrane for
material characterization in liquids and gases with scanning electron
microscopy and spectroscopy. Here, we present a novel sample platform
made of an array of thousands of identical isolated graphene-capped
microchannels with high aspect ratio. A combination of a global wide
field of view with high resolution local imaging of the array allows
for high throughput <i>in situ</i> studies as well as for
combinatorial screening of solutions, liquid interfaces, and immersed
samples. We demonstrate the capabilities of this platform by studying
a pure water sample in comparison with alkali halide solutions, a
model electrochemical plating process, and beam-induced crystal growth
in liquid electrolyte. Spectroscopic characterization of liquid interfaces
and immersed objects with Auger and X-ray fluorescence analysis through
the graphene membrane are also demonstrated
From Microparticles to Nanowires and Back: Radical Transformations in Plated Li Metal Morphology Revealed via <i>in Situ</i> Scanning Electron Microscopy
Li
metal is the preferred anode material for all-solid-state Li
batteries. However, a stable plating and stripping of Li metal at
the anode–solid electrolyte interface remains a significant
challenge particularly at practically feasible current densities.
This problem usually relates to high and/or inhomogeneous Li-electrode–electrolyte
interfacial impedance and formation and growth of high-aspect-ratio
dendritic Li deposits at the electrode–electrolyte interface,
which eventually shunt the battery. To better understand details of
Li metal plating, we use <i>operando</i> electron microscopy
and Auger spectroscopy to probe nucleation, growth, and stripping
of Li metal during cycling of a model solid-state Li battery as a
function of current density and oxygen pressure. We find a linear
correlation between the nucleation density of Li clusters and the
charging rate in an ultrahigh vacuum, which agrees with a classical
nucleation and growth model. Moreover, the trace amount of oxidizing
gas (≈10<sup>–6</sup> Pa of O<sub>2</sub>) promotes
the Li growth in a form of nanowires due to a fine balance between
the ion current density and a growth rate of a thin lithium-oxide
shell on the surface of the metallic Li. Interestingly, increasing
the partial pressure of O<sub>2</sub> to 10<sup>–5</sup> Pa
resumes Li plating in a form of 3D particles. Our results demonstrate
the importance of trace amounts of preexisting or ambient oxidizing
species on lithiation processes in solid-state batteries
Fabrication, Testing, and Simulation of All-Solid-State Three-Dimensional Li-Ion Batteries
Demonstration
of three-dimensional all-solid-state Li-ion batteries (3D SSLIBs)
has been a long-standing goal for numerous researchers in the battery
community interested in developing high power and high areal energy
density storage solutions for a variety of applications. Ideally,
the 3D geometry maximizes the volume of active material per unit area,
while keeping its thickness small to allow for fast Li diffusion.
In this paper, we describe experimental testing and simulation of
3D SSLIBs fabricated using materials and thin-film deposition methods
compatible with semiconductor device processing. These 3D SSLIBs consist
of Si microcolumns onto which the battery layers are sequentially
deposited using physical vapor deposition. The power performance of
the 3D SSLIBs lags significantly behind that of similarly prepared
planar SSLIBs. Analysis of the experimental results using finite element
modeling indicates that the origin of the poor power performance is
the structural inhomogeneity of the 3D SSLIB, coupled with low electrolyte
ionic conductivity and diffusion rate in the cathode, which lead to
highly nonuniform internal current density distribution and poor cathode
utilization
Doping-Based Stabilization of the M2 Phase in Free-Standing VO<sub>2</sub> Nanostructures at Room Temperature
A new high-yield method of doping VO<sub>2</sub> nanostructures
with aluminum is proposed, which renders possible stabilization of
the monoclinic M2 phase in free-standing nanoplatelets in ambient
conditions and opens an opportunity for realization of a purely electronic
Mott transition field-effect transistor without an accompanying structural
transition. The synthesized free-standing M2-phase nanostructures
are shown to have very high crystallinity and an extremely sharp temperature-driven
metal–insulator transition. A combination of X-ray microdiffraction,
micro-Raman spectroscopy, energy-dispersive X-ray spectroscopy, and
four-probe electrical measurements allowed thorough characterization
of the doped nanostructures. Light is shed onto some aspects of the
nanostructure growth, and the temperature-doping level phase diagram
is established
Enabling Photoemission Electron Microscopy in Liquids via Graphene-Capped Microchannel Arrays
Photoelectron
emission microscopy (PEEM) is a powerful tool to
spectroscopically image dynamic surface processes at the nanoscale,
but it is traditionally limited to ultrahigh or moderate vacuum conditions.
Here, we develop a novel graphene-capped multichannel array sample
platform that extends the capabilities of photoelectron spectromicroscopy
to routine liquid and atmospheric pressure studies with standard PEEM
setups. Using this platform, we show that graphene has only a minor
influence on the electronic structure of water in the first few layers
and thus will allow for the examination of minimally perturbed aqueous-phase
interfacial dynamics. Analogous to microarray screening technology
in biomedical research, our platform is highly suitable for applications
in tandem with large-scale data mining, pattern recognition, and combinatorial
methods for spectro-temporal and spatiotemporal analyses at solid–liquid
interfaces. Applying Bayesian linear unmixing algorithm to X-ray induced
water radiolysis process, we were able to discriminate between different
radiolysis scenarios and observe a metastable “wetting”
intermediate water layer during the late stages of bubble formation
Enabling Photoemission Electron Microscopy in Liquids via Graphene-Capped Microchannel Arrays
Photoelectron
emission microscopy (PEEM) is a powerful tool to
spectroscopically image dynamic surface processes at the nanoscale,
but it is traditionally limited to ultrahigh or moderate vacuum conditions.
Here, we develop a novel graphene-capped multichannel array sample
platform that extends the capabilities of photoelectron spectromicroscopy
to routine liquid and atmospheric pressure studies with standard PEEM
setups. Using this platform, we show that graphene has only a minor
influence on the electronic structure of water in the first few layers
and thus will allow for the examination of minimally perturbed aqueous-phase
interfacial dynamics. Analogous to microarray screening technology
in biomedical research, our platform is highly suitable for applications
in tandem with large-scale data mining, pattern recognition, and combinatorial
methods for spectro-temporal and spatiotemporal analyses at solid–liquid
interfaces. Applying Bayesian linear unmixing algorithm to X-ray induced
water radiolysis process, we were able to discriminate between different
radiolysis scenarios and observe a metastable “wetting”
intermediate water layer during the late stages of bubble formation