A multi-technique approach to understanding delithiation damage in LiCoO2 thin films.

We report on the delithiation of LiCoO2 thin films using oxalic acid (C2H2O4) with the goal of understanding the structural degradation of an insertion oxide associated with Li chemical extraction. Using a multi-technique approach that includes synchrotron radiation X-ray diffraction, scanning electron microscopy, micro Raman spectroscopy, photoelectron spectroscopy and conductive atomic force microscopy we reveal the balance between selective Li extraction and structural damage. We identify three different delithiation regimes, related to surface processes, bulk delithiation and damage generation. We find that only a fraction of the grains is affected by the delithiation process, which may create local inhomogeneities. However, the bulk delithiation regime is effective to delithiate the LCO film. All experimental evidence collected indicates that the delithiation process in this regime mimics the behavior of LCO upon electrochemical delithiation. We discard the formation of Co oxalate during the chemical extraction process. In conclusion, the chemical route to Li extraction provides additional opportunities to investigate delithiation while avoiding the complications associated with electrolyte breakdown and simplifying in-situ measurements.

Crystalline Structure and Vacancy Ordering across a Surface Phase Transition in Sn/Cu(001).

We report a surface X-ray diffraction study of the crystalline structure changes and critical behavior across the (3√2 × âˆš2)R45° → (√2 × âˆš2)R45° surface phase transition at 360 K for 0.5 monolayers of Sn on Cu(100). The phase transition is of the order-disorder type and is due to the disordering of the Cu atomic vacancies present in the low temperature phase. Two different atomic sites for Sn atoms, characterized by two different heights, are maintained across the surface phase transition.

Electronic structure of Sn/Cu(100)-[Formula: see text].

We present measurements of the Fermi surface and underlying band structure of Sn/Cu(100)-[Formula: see text]. This phase is observed for a coverage of 0.60-0.65 monolayers. Its electronic structure is characterized by a free-electron-like surface band folded with the reconstruction periodicity. At variance with other surface phases of Sn on Cu(100), no temperature-induced phase transition is observed for this phase from 100 K up to the desorption of Sn.

Surface x-ray diffraction analysis using a genetic algorithm: the case of Sn/Cu(100)-[Formula: see text].

The application of genetic algorithms to the analysis of surface x-ray diffraction data is discussed and the implementation of a genetic algorithm of evolutionary type is described in detail. The structure of Sn/Cu(100)-[Formula: see text] is determined on the basis of surface x-ray diffraction data analysed using this algorithm. The results are compared to previous findings using other techniques.

Surface electronic structure of Pb/Cu(100): surface band filling and folding.

We report an investigation into the surface electronic structure of Pb/Cu(100) in the submonolayer coverage range. A prominent surface band is detected in the whole coverage range analysed. The band is gradually filled as Pb coverage increases. For a Pb coverage of 0.375 ML, corresponding to the c(4 × 4) phase, a strong c(4 × 4) folding of this state is observed in the valence band. The origin of these results and the nature of the surface electronic structure of Pb/Cu(100)- c(4 × 4) are discussed.

Structural origin of the Sn 4d core level line shape in Sn/Ge(111)-(3x3).

High-resolution photoemission of the Sn 4d core level of Sn/Ge(111)-(3x3) resolves three main components in the line shape, which are assigned to each of the three Sn atoms that form the unit cell. The line shape found is in agreement with an initial state picture and supports that the two down atoms are inequivalent. In full agreement with these results, scanning tunnel microscopy images directly show that the two down atoms are at slightly different heights in most of the surface, giving rise to an inequivalent-down-atoms (3x3) structure. These results solve a long-standing controversy on the interpretation of the Sn 4d core-level line shape and the structure of Sn/Ge(111)-(3x3).

Interaction of atomic hydrogen with the beta-SiC(100) 3 x 2 surface and subsurface.

We investigate clean and atomic hydrogen exposed beta-SiC(100) 3 x 2 surfaces by synchrotron radiation-based Si 2p core-level photoemission spectroscopy. The clean 3 x 2 surface reconstruction exhibits three surface and subsurface components. Upon hydrogen exposures, those surface and subsurface components are shifted to lower binding energies by large values, indicating significant charge transfer to the surface and subsurface regions, in excellent agreement with the recently discovered H-induced beta-SiC(100) 3 x 2 surface metallization. In addition, the interaction of hydrogen results in a large reactive component at Si 2p supporting an asymmetric charge transfer in the third plane below the surface, in agreement with previous experimental investigations. However, the results are inconsistent with recent ab initio theoretical "frozen" calculations predicting H atom to be in a bridge-bond position.

Observation of a Mott insulating ground state for Sn/Ge(111) at low temperature.

We report an investigation on the properties of 0.33 ML of Sn on Ge(111) at temperatures down to 5 K. Low-energy electron diffraction and scanning tunneling microscopy show that the (3x3) phase formed at approximately 200 K, reverts to a new ((square root 3)x(square root 3))R30 degrees phase below 30 K. The vertical distortion characteristic of the (3x3) phase is lost across the phase transition, which is fully reversible. Angle-resolved photoemission experiments show that, concomitantly with the structural phase transition, a metal-insulator phase transition takes place. The ((square root 3)x(square root 3))R30 degrees ground state is interpreted as the formation of a Mott insulator for a narrow half-filled band in a two-dimensional triangular lattice.

[Formula: see text] ↔ (3 × 3) phase transition in Pb/Ge(111) and Sn/Ge(111): a phenomenological study on the phase transition anomalies and the role of defects.

A phenomenological study of the [Formula: see text] phase transitions occurring in the adsorption systems Pb/Ge(111) and Sn/Ge(111) is presented. The starting point of such a study is the Landau theory. The critical behaviour expected theoretically for the two interfaces, and the corresponding influence of defects, are discussed in detail. Symmetry arguments show that, contrary to general belief, the critical behaviours of Pb/Ge(111) and Sn/Ge(111) are essentially different. The Landau-like approach employed to study the influence of defects provides a consistent and general manner to interpret the existing experimental data. Special attention is paid to the influence of hopping defects in Sn/Ge(111).

Tuning the surface state dimensionality of Cu nanostripes.

Stepped Cu nanostripes with varying terrace widths are self-assembled during Ag-induced periodic faceting of vicinal Cu(111). By changing Ag coverage the average terrace size within individual Cu stripes is readily tuned, making it possible to select the one-dimensional or two-dimensional character of surface states. Furthermore, the average terrace size can be smoothly switched from 10 to 30 A, thereby tracking the transition from step-lattice, quasi-two-dimensional umklapp bands to terrace-confined one-dimensional quantum well states.

Phonon softening, chaotic motion, and order-disorder transition in Sn/Ge(111).

The phonon dynamics of the Sn/Ge(111) interface is studied using high-resolution helium atom scattering and first-principles calculations. At room temperature we observe a phonon softening at the Kmacr; point in the (sqrt[3]xsqrt[3])R30 degrees phase, associated with the stabilization of a (3x3) phase at low temperature. That phonon band is split into three branches in the (3x3) phase. We analyze the character of these phonons and find out that the low- and room-temperature modes are connected via a chaotic motion of the Sn atoms. The system is shown to present an order-disorder transition.

Electron wave function at a vicinal surface: switch from terrace to step modulation.

The Cu(111) surface state has been mapped for vicinal surfaces with variable step densities by angle-resolved photoemission. Using tunable synchrotron radiation to vary the k dependence perpendicular to the surface, as well as the (k) dependence, we find a switch between two qualitatively different regimes at a miscut of 7 degrees (17 A terrace width). For larger miscut angles the step modulation of the wave function dominates, and for smaller miscut angles the terrace modulation dominates. These observations resolve an apparent inconsistency between prior photoemission and STM results.