18 research outputs found
IN-OPERANDO ELECTRON MICROSCOPY AND SPECTROSCOPY OF INTERFACES THROUGH GRAPHENE-BASED MEMBRANES
Electron microscopy and spectroscopy (EMS) techniques enable (near-) surface and interfacial characterization of a variety of materials, providing insights into chemical/electrochemical and morphological information with nanoscale spatial resolution. However, the experimental realization of EMS in liquid/gaseous samples becomes problematic due to their incompatibility with high vacuum (HV)
conditions. To perform EMS under elevated pressure conditions, electron transparent membranes made of thin C, SiO2 or/and Si3N4 are implemented to isolate a liquid/gas sample from HV environment. Nevertheless, even a few ten nanometer thick
membrane deteriorates signal quality due to significant electron scattering. The other challenge of EMS consists in inaccessibility to probe solid state interfaces, e.g. solid-state Li-ion batteries, which makes their operando characterization problematic, limiting the analysis to ex situ and postmortem examination.
The first part of my thesis focuses on developing an experimental platform for operando characterization of liquid interfaces through electron transparent membranes made of graphene (Gr)/graphene oxide (GO). The second part is dedicated to probing Li-ion transport at solid-state-battery surfaces and interfaces using ultrathin carbon anodes. I demonstrated the capability of GO to encapsulate samples with different chemical, physical, and biological properties and characterized them using EMS methods. I proposed and tested a new CVD-Gr transfer method using anthracene as a sacrificial layer. Characterization of transferred Gr revealed the advantages of our route with respect to a standard polymer based approach. A novel platform made of an array of Gr-capped liquid filled microcapsules was developed, allowing for a wide eld of view EMS. I showed the capability of conducting EMS analysis of liquid interfaces through Gr membranes using energy-dispersive X-ray spectroscopy, photoemission electron microscopy, and Auger electron spectroscopy. Using operando SEM and AES, I elucidated the role of oxidizing conditions and charging rate on Li plating morphology in all-solid-state Li-ion batteries with thin carbon anodes. Operando EMS characterization of Li-ion transport at battery interfaces with carbon or Gr anodes will provide valuable insights into safe all-solid-state Li-ion battery with enhanced performance
Scalable and Robust Beam Shaping Using Apodized Fish-bone Grating Couplers
Efficient power coupling between on-chip guided and free-space optical modes
requires precision spatial mode matching with apodized grating couplers. Yet,
grating apodizations are often limited by the minimum feature size of the
fabrication approach. This is especially challenging when small feature sizes
are required to fabricate gratings at short wavelengths or to achieve weakly
scattered light for large-area gratings. Here, we demonstrate a fish-bone
grating coupler for precision beam shaping and the generation of
millimeter-scale beams at 461 nm wavelength. Our design decouples the minimum
feature size from the minimum achievable optical scattering strength, allowing
smooth turn-on and continuous control of the emission. Our approach is
compatible with commercial foundry photolithography and has reduced sensitivity
to both the resolution and the variability of the fabrication approach compared
to subwavelength meta-gratings, which often require electron beam lithography.Comment: 10 pages, 6 figure
Immobilization and Encapsulation of Micro- and Nano- Objects with Electron Transparent Graphene Oxide membranes
In Aqua Electrochemistry Probed by XPEEM: Experimental Setup, Examples, and Challenges
Recent developments in environmental and liquid cells equipped with electron transparent graphene windows have enabled traditional surface science spectromicroscopy tools, such as scanning X-ray photoelectron microscopy, X-ray photoemission electron microscopy (XPEEM), and scanning electron microscopy to be applied for studying solid–liquid and liquid–gas interfaces. Here, we focus on the experimental implementation of XPEEM to probe electrified graphene–liquid interfaces using electrolyte-filled microchannel arrays as a new sample platform. We demonstrate the important methodological advantage of these multi-sample arrays: they combine the wide field of view hyperspectral imaging capabilities from XPEEM with the use of powerful data mining algorithms to reveal spectroscopic and temporal behaviors at the level of the individual microsample or the entire array ensemble
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
Interfacial Electrochemistry in Liquids Probed with Photoemission Electron Microscopy
Studies of the electrified solid–liquid interfaces are crucial for understanding biological and electrochemical systems. Until recently, use of photoemission electron microscopy (PEEM) for such purposes has been hampered by incompatibility of the liquid samples with ultrahigh vacuum environment of the electron optics and detector. Here we demonstrate that the use of ultrathin electron transparent graphene membranes, which can sustain large pressure differentials and act as a working electrode, makes it possible to probe electrochemical reactions in operando in liquid environments with PEEM