From
atomic force microscopy (AFM) experiments, we report a new
phenomenon in which the dissolution rate of fused silica is enhanced
by more than 5 orders of magnitude by simply pressing a second, dissimilar
surface against it and oscillating the contact pressure at low kHz
frequencies in deionized water. The silica dissolution rate enhancement
was found to exhibit a strong dependence on the pressure oscillation
frequency consistent with a resonance effect. This harmonic enhancement
of the silica dissolution rate was only observed at asymmetric material
interfaces (e.g., diamond on silica) with no evidence of dissolution
rate enhancement observed at symmetric material interfaces (i.e.,
silica on silica) within the experimental time scales. The apparent
requirement for interface dissimilarity, the results of analogous
experiments performed in anhydrous dodecane, and the observation that
the silica “dissolution pits” continue to grow in size
under contact stresses well below the silica yield stress refute a
mechanical deformation or chemo-mechanical origin to the observed
phenomenon. Instead, the silica dissolution rate enhancement exhibits
characteristics consistent with a previously described ‘electrochemical
pressure solution’ mechanism, albeit, with greatly amplified
kinetics. Using a framework of electrochemical pressure solution,
an electrochemical model of mineral dissolution, and a recently proposed
“surface resonance” theory, we present an electro-chemo-mechanical
mechanism that explains how oscillating the contact pressure between
dissimilar surfaces in water can amplify surface dissolution rates
by many orders of magnitude. This reaction rate enhancement mechanism
has implications not only for dissolution but also for potentially
other reactions occurring at the solid–liquid interface, e.g.
catalysis.
Employing
high-voltage Ni-rich cathodes in Li metal batteries (LMBs)
requires stabilization of the electrode/electrolyte interfaces at
both electrodes. A stable solid–electrolyte interphase (SEI)
and suppression of active material pulverization remain the greatest
challenges to achieving efficient long-term cycling. Herein, studies
of NMC622 (1 mAh cm–2) cathodes were performed using
highly concentrated N-methyl-N-propylpyrrolidinium
bis(fluorosulfonyl)imide (C3mpyrFSI) 50 mol % lithium bis(fluorosulfonyl)imide
(LiFSI) ionic liquid electrolyte (ILE). The resulting SEI formed at
the cathode enabled promising cycling performance (98.13% capacity
retention after 100 cycles), and a low degree of ion mixing and lattice
expansion was observed, even at an elevated temperature of 50 °C.
Fitting of acquired impedance spectra indicated that the SEI resistivity
(R
SEI) had a low and stable contribution
to the internal resistivity of the system, whereas active material
pulverization and secondary grain isolation significantly increased
the charge transfer resistance (R
CT) throughout
cycling.
A new method of direct‐write nanolithography that is able to rapidly etch silica surfaces under a scanning atomic force microscopy (AFM) probe in tapping mode (TM) is reported. In this lithography technique, silica surfaces are etched using a recently described electro‐chemo‐mechanical phenomenon of frequency enhanced electrochemical pressure solution (FEEPS). In FEEPS, the tapping of the AFM tip generates oscillations of the Stern potential at the silica‐water interface that can accelerate the silica dissolution kinetics by more than 5–6 orders of magnitude when surface resonance states are achieved; i.e., when the oscillation frequency is in phase with the dynamics of interfacial chemical reaction steps. By scanning silica surfaces in TM, silica is selectively dissolved below the tapping tip as it is scanned. The FEEPS accelerated silica dissolution rates can generate etched features with depths of more than 60 nm in a single AFM tip pass. The rate of etching can be controlled easily by varying the scanning rate or by modulating the tapping frequency. This fine control over the silica etching process and because material is removed (dissolved) rather than displaced as with nanoscratching, the FEEPS process lends itself to gray‐scale nanolithography which is demonstrated.
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