Energy storage science calls for techniques to elucidate ion transport over a range of conditions and scales. We introduce a new technique, pascalammetry, in which stress is applied to a solid-state electrochemical device and induced faradaic current transients are measured and analyzed. Stress-step pascalammetry measurements are performed on operando microbattery probes (Li2O/Li/W) and Si cathodes, revealing stress-assisted Li+ diffusion. We show how non-Cottrellian lithium diffusional kinetics indicates stress, a prelude to battery degradation. An analytical solution to a diffusion/activation equation describes this stress signature, with spatiotemporal characteristics distinct from Cottrell's classic solution for unstressed systems. These findings create an unprecedented opportunity for quantitative detection of stress in solid-state batteries through the current signature. Generally, pascalammetry offers a powerful new approach to study stress-related phenomena in any solid-state electrochemical system.

The interaction of solvent molecules with metallic surfaces impacts many interfacial chemical processes: We investigate the chemical and structure evolution that follows adsorption of the polar solvent dimethylformamide (DIM) on Ag(111). An Ag(DMF)(2) coordination complex forms spontaneously by DMF etching of Ag(111), yielding Allied films of the complexes and DMF. Utilizing ultrahigh vacuum scanning tunneling microscopy (UHV-STM), in combination with X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) computations, we map monolayer phases from the 2-D gas regime, consisting of a binary mixture of DMF and Ag(DMF)(2), through the saturation monolayer limit, in which these two chemical species phase separate into ordered islands. Structural models for the near-square DMF phase and the chain-like Ag(DMF)(2) phase are presented and supported by DFT computation. Interface evolution is summarized in a surface pressure-composition phase diagram, which allows structure prediction over arbitrary experimental conditions. This work reveals new surface coordination chemistry for an important electrolyte electrode system and illustrates how surface pressure can be used to tune monolayer phases.

The recently discovered large nonsaturating magnetoresistance in semimetal $\mathrm{WT}{\mathrm{e}}_{2}$ may result from near-perfect electron-hole compensation, however recent reports question whether the compensation is adequate to explain the observations. Experiments on significantly uncompensated $\mathrm{WT}{\mathrm{e}}_{2}$ are needed. We measure magnetoresistance ${\ensuremath{\rho}}_{xx}(H)$, Hall effect ${\ensuremath{\rho}}_{xy}(H)$, and an electrolyte gating effect in thin (100 nm) exfoliated $\mathrm{WT}{\mathrm{e}}_{2}$. We observe ${\ensuremath{\rho}}_{xy}(H)$ linear in $H$ at low $H$ consistent with near-perfect compensation, however ${\ensuremath{\rho}}_{xy}(H)$ becomes nonlinear and changes sign with increasing $H$, implying a breakdown of compensation. We break compensation more significantly by using an electrolytic gate for highly electron-doped $\mathrm{WT}{\mathrm{e}}_{2}$ with Li. In gated $\mathrm{WT}{\mathrm{e}}_{2}$ the nonsaturating ${\ensuremath{\rho}}_{xx}(H)$ persists to $H=14\phantom{\rule{0.16em}{0ex}}\mathrm{T}$, even with significant deviation from perfect electron-hole compensation $(p/n=0.84)$ where the two-band model predicts a saturating ${\ensuremath{\rho}}_{xx}(H)$. Our results indicate electron-hole compensation is not the mechanism for extremely large magnetoresistance in $\mathrm{WT}{\mathrm{e}}_{2}$; alternative explanations are needed.

Graphene decorated with 5d transitional metal atoms is predicted to exhibit many intriguing properties; for example iridium adatoms are proposed to induce a substantial topological gap in graphene. We extensively investigated the conductivity of single-layer graphene decorated with iridium deposited in ultra-high vacuum at low temperature (7 K) as a function of Ir concentration, carrier density, temperature, and annealing conditions. Our results are consistent with the formation of Ir clusters of ~100 atoms at low temperature, with each cluster donating a single electronic charge to graphene. Annealing graphene increases the cluster size, reducing the doping and increasing the mobility. We do not observe any sign of an energy gap induced by spin-orbit coupling, possibly due to the clustering of Ir.

Serpentine chain C60 phases were observed in scanning tunneling microscopy (STM) images of C60 layers on zinc phthalocyanine (ZnPc) or pentacene covered Ag(111) and Au(111) surfaces. This low-density, quasi-one-dimensional organization contrasts starkly with the close-packed hexagonal phases observed for C60 layers on bare metal substrates. STM was employed to perform a detailed investigation of these chain structures for C60/ZnPc/Ag(111) heterolayers. Motivated by the similarity of these chain phases, and the chain and stripe organization occurring in dipole-fluid systems, we investigated a model based on competing van der Waals attractions and electrostatic repulsions between C60 molecules as an explanation for the driving force behind these monolayer phases. Density functional theory (DFT) calculations revealed significant charge transfer to C60 from the Ag(111) substrate, through the intervening ZnPc layer, inducing electrostatic interactions between C60 molecules. Molecular dynamics simulations performed with attractive van der Waals interactions plus repulsive dipole-dipole interactions reproduced the C60 chain phases with dipole magnitudes consistent with DFT calculations.

We present a detailed study of magnetoresistance h̊o̊xx(H), Hall effect h̊o̊xy(H), and electrolyte gating effect in thin (<100 nm) exfoliated crystals of WTe2. We observe quantum oscillations in H of both h̊o̊xx(H) and h̊o̊xy(H), and identify four oscillation frequencies consistent with previous reports in thick crystals. h̊o̊xy(H) is linear in H at low H consistent with near-perfect electron-hole compensation, however becomes nonlinear and changes sign with increasing H, implying a breakdown of compensation. A field-dependent ratio of carrier concentrations p/n can consistently explain h̊o̊xx(H) and h̊o̊xy(H) within a two-fluid model. We also employ an electrolytic gate to highly electron-dope WTe2 with Li. The non-saturating h̊o̊xx(H) persists to H = 14 T with magnetoresistance ratio exceeding 2 x 104 deviation from perfect electron-hole compensation (p/n = 0.84), where the two-fluid model predicts a saturating h̊o̊xx(H). Our results suggest electron-hole compensation is not the mechanism for extremely large magnetoresistance in WTe2, other alternative explanations need to be considered.

A carbon-nanotube-enabling scanning probe technique/nanotechnology for manipulating and measuring lithium at the nano/mesoscale is introduced. Scanning Li-nanopipette and probe microscopy (SLi-NPM) is based on a conductive atomic force microscope (AFM) cantilever with an open-ended multi-walled carbon nanotube (MWCNT) affixed to its apex. SLi-NPM operation is demonstrated with a model system consisting of a Li thin film on a Si(111) substrate. By control of bias, separation distance, and contact time, attograms of Li can be controllably pipetted to or from the MWCNT tip. Patterned surface Li features are then directly probed via noncontact AFM measurements with the MWCNT tip. The subsequent decay of Li features is simulated with a mesoscale continuum model, developed here. The Li surface diffusion coefficient for a four (two) Li layer thick film is measured as D=8(±1.2)×10(-15) cm(2) s(-1) (D=1.75(±0.15)×10(-15) cm(2) s(-1)). Dual-Li pipetting/measuring with SLi-NPM enables a broad range of time-dependent Li and nanoelectrode characterization studies of fundamental importance to energy-storage research.

A non-local Hall bar geometry is used to detect neutral-current Hall effects in graphene on silicon dioxide. Disorder is tuned by the addition of Au or Ir adatoms in ultra-high vacuum. A reproducible neutral-current Hall effect is found in both as-fabricated and adatom-decorated graphene. The Hall angle exhibits a complex but reproducible dependence on gate voltage and disorder, and notably breaks electron-hole symmetry. An exponential dependence on length between Hall and inverse-Hall probes indicates a neutral current relaxation length of approximately 300 nm. The short relaxation length and lack of precession in parallel magnetic field suggest that the neutral currents are valley currents. The near lack of temperature dependence from 7-300 K is unprecedented and promising for using controlled disorder for room temperature neutral-current electronics.

The desorption and interactions of ethylene carbonate (EC) and dimethyl carbonate (DMC) with clean and lithiated graphite substrates were measured by temperature-programmed desorption (TPD) and reaction (TPR) methods under UHV conditions. Both EC and DMC interact weakly with the clean C(0001) surface with adsorption energies of 0.60 +/- 0.06 and 0.64 +/- 0.05 eV, respectively. Addition of Li+ to the C(0001) substrate significantly increases the binding energies of molecular carbonates, and the range of measured values is indicative of EC solvation of lithium ions. EC undergoes complete decomposition on metallic Li films. Organolithium products were quantified by TPR, and the amount of lithium carbonate product was determined by detailed mass balance analysis. Decomposition of 1.5 L of EC resulted in the formation of 0.64 +/- 0.12 L of lithium ethylene dicarbonate, 0.40 +/- 0.05 L of lithium ethylene glycolate, and 0.5 +/- 0.2 L of lithium carbonate. The branching ratio at the immediate EC-metallic lithium interface was determined as 70.% organolithium products vs 30% inorganic lithium product.

We report an ultrahigh vacuum scanning tunneling microscopy study of thermally driven interface rearrangement in binary films of [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) and zinc phthalocyanine (ZnPc), a model electron acceptor electron donor system for organic solar cells. Neat PCBM films have been previously shown to undergo a transition from a disordered (glassy) phase to a crystalline hexagonal close-packed (hcp) arrangement above a critical packing density of 0.9 molecules/nm(2). We now show how local PCBM density has a critical impact on binary film structure evolution. Bilayer films of PCBM and ZnPc undergo a spontaneous vertical phase separation to PCBM/ZnPc/Au(111) stacking at lower (<0.9 molecules/nm(2)) PCBM densities. This vertical phase separation is shown to be electrostatically preferred, with the PCBM/ZnPc/Au(111) dimer stacking lower in energy by 0.16 eV/pair relative to ZnPc/PCBM/Au(111) stacking. At higher local PCBM densities, sufficient to nucleate hcp PCBM domains, ZnPc molecules do not displace PCBM to the second layer. PCBM density variations in binary films thus give rise to heterogeneous interface structures.

The molecular organization of a polar phthalocyanine, titanyl phthalocyanine (TiOPc), on the Ag(110) surface was studied with scanning tunneling microscopy (STM). in addition to the intermolecular hydrogen bonding and electrostatic interactions that guide structure for nonpolar Pc's, we find evidence for the impact of dipole interactions on layer organization for TiOPc/Ag(110). TiOPc molecules adsorb on Ag(110) with a tilted orientation that contrasts with the flat-lying orientation typically observed for nonpolar phthalocyanines. At the highest TiOPc coverages, the layer consists of neighboring TiOPc molecules with opposing molecular tilts. Close inspection reveals a higher level organization, consisting of "zigzag" TiOPc molecular chains with molecular spacings along the chain that are smaller than the average within the layer. We suggest an explanation for this behavior based on the dipole-dipole interactions within the chain. At reduced coverage, variable densities of molecular vacancies form, depending on the coverage. The vacancies align to form rows that order into well-organized superstructures. Finally, TiOPc surface structures on Ag(110) are compared and contrasted with those on Ag(111). The different adlayer arrangements on these two surfaces created by molecule-molecule interactions and molecule-substrate interactions lead to a change from a "ferroelectric" orientation for the TiOPc molecular tilts (and in-plane dipole components) on Ag(111) to an "antiferroelectric" arrangement on Ag(110). We show that this change agrees with theoretical predictions of the influence of lattice symmetry on dipole lattice arrangements, providing additional evidence for the impact of dipole-dipole interactions on the TiOPc surface layer organization.

The temperature-dependent conductivity of bilayer graphene with adsorbed layers of the halocarbon molecule CF3Cl was studied under ultra high vacuum conditions. Upon warming CF3Cl sub-monolayer from 25 K, the electrical conductivity drops abruptly at 47 K and exhibits additional inflection points at 60 K and 69 K. CF3Cl multi-layers exhibit an abrupt conductivity gain at 54 K. These conductivity features correspond to known temperature-coverage phase boundaries for CF3Cl films measured on graphite. The changes in conductivity reflect changes in dielectric screening and disorder potential of the CF3Cl adlayer. The chemical specificity of phase transitions presents a basis for sensor selectivity.

U. Maryland Sandia National Labs U. California, Irvine Gary Rubloff Director John Sullivan CA Phil Collins SB Lee-Deputy Director Alec Talin CA Reginald Penner Reza Ghodssi Katie Jungjohann Zuzanna Siwy John Cumings Tom Harris UCLA Chunsheng Wang Kevin Leung Bruce Dunn YuHuang Wang U. Florida Michigan State U. Liangbing Hu Charles Martin Yue Qi Janice Reutt-Robey U. Utah Past members Bryan Eichhorn Henry White Ellen Williams Assoc. Dir. for Programs Yale University Michael Fuhrer Elizabeth Lathrop Mark Reed Tom Picraux Ext. Advisory Board... Affiliates... Ashley Predith Mission: To reveal scientific insights and design principles that enable a next-generation electrical energy storage technology based on dense mesoscale architectures of multifunctional nanostructures. NEES (2009-2018)

Molecular interfaces have been prepared in titanyl phthalocyanine (TiOPc)-C-60 monolayer films on Ag(111) and characterized with ultra high vacuum-scanning tunneling microscopy. Two distinct TiOPc monolayer phases, namely, a hexagonal phase and a honeycomb phase, were first generated as molecular-film substrates for C-60 growth. Both TiOPc monolayer structures rearrange upon C-60 adsorption, yielding films with nanophase-separated TiOPc and C-60 domains and a new cocrystalline TiOPc2(C-60)(1) honeycomb network. Kinetic access to the cocrystalline network is most facile from the hexagonal TiOPc monolayer, producing extended domains. Detailed models for emergent structural phases and molecular interfaces are presented. Mechanisms for C-60-induced rearrangements are developed from coverage-dependent measurements.