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.

Pore collapse and regrowth in silicon electrodes for rechargeable batteries.

Structure and composition of an 11 nm thick amorphous silicon (a-Si) thin film anode, capped with 4 nm of alumina are measured, in operando, by neutron reflectivity (NR) and electrochemical impedance spectroscopy in a lithium half-cell. NR data are analyzed to quantify the a-Si thickness and composition at various states of charge over six cycles. The a-Si anode expands and contracts upon lithiation and delithiation, respectively, while maintaining its integrity and low interfacial roughness (≤1.6 nm) throughout the cycling. The apparently non-linear expansion of the a-Si layer volume versus lithium content agrees with previous thin-film a-Si anode studies. However, a proposed pore collapse and regrowth (PCRG) mechanism establishes that the solid domains in the porous LixSi film expand linearly with Li content at 8.48 cm(3) mol(-1) Li, similar to crystalline Si. In the PCRG model, porosity is first consumed by expansion of solid domains upon lithiation, after which the film as a whole expands. Porosity is reestablished at 5-28% upon delithiation. Data show that the alumina protective layer on the a-Si film functions as an effective artificial solid electrolyte interphase (SEI), maintaining its structural integrity, low interfacial roughness, and relatively small transport resistance. No additional spontaneously-formed SEI is observed in this study.

MOF-based electronic and opto-electronic devices.

Metal-organic frameworks (MOFs) are a class of hybrid materials with unique optical and electronic properties arising from rational self-assembly of the organic linkers and metal ions/clusters, yielding myriads of possible structural motifs. The combination of order and chemical tunability, coupled with good environmental stability of MOFs, are prompting many research groups to explore the possibility of incorporating these materials as active components in devices such as solar cells, photodetectors, radiation detectors, and chemical sensors. Although this field is only in its incipiency, many new fundamental insights relevant to integrating MOFs with such devices have already been gained. In this review, we focus our attention on the basic requirements and structural elements needed to fabricate MOF-based devices and summarize the current state of MOF research in the area of electronic, opto-electronic and sensor devices. We summarize various approaches to designing active MOFs, creation of hybrid material systems combining MOFs with other materials, and assembly and integration of MOFs with device hardware. Critical directions of future research are identified, with emphasis on achieving the desired MOF functionality in a device and establishing the structure-property relationships to identify and rationalize the factors that impact device performance.

Effect of critical dimension variation on SAW correlator energy.

The effect of critical dimension (CD) variation and metallization ratio on the efficiency of energy conversion of a surface acoustic wave (SAW) correlator is examined. We find that a 10% variation in the width of finger electrodes predicts only a 1% decrease in the efficiency of energy conversion. Furthermore, our model predicts that a metallization ratio of 0.74 represents an optimum value for energy extraction from the SAW by the interdigitated transducer (IDT).

Silver growth on micropatterned DNA chips: effect of growth conditions and morphology on I-V behavior.

An approach to the design of DNA-based electronics is presented, in which standard microfabrication processes are integrated with lithographic patterning of single-stranded oligonucleotides followed by hybridization to gold-labeled, complementary oligonucleotides and subsequent silver enhancement for signal amplification. The resulting bioinorganic devices demonstrate micron-sized geometric features, very little non-specific silver growth, a distinct silver morphology in the patterned region, and a 10(9)-fold increase in conductivity across an electrode gap when compared with control devices. This approach may prove useful for the fabrication of high fidelity, high-density arrays for DNA-based biosensing applications.