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Microwave impedance microscopy : from acoustics to photovoltaics

This thesis details my efforts to expand the capabilities of microwave impedance microscopy (MIM), and apply those capabilities to variety of systems of technological relevance. MIM is a sensitive microwave measurement of the change in impedance of a scanned, nanoscale probe. By measuring this impedance, properties of the sample under study, including conductivity and permittivity, can be obtained at nanoscale resolution without direct electrical contact. How this tip impedance relates to the quantities of interest can depend on many details of the measurement and measured device, however. In this thesis I explore some of those details. Chapter 1 includes the standard interpretation of MIM as a qualitative measurement of local permittivity and conductivity, in addition to background on related scanning probe methods. This understanding is largely sufficient for many systems, including the phase change materials (e.g. Ge2Sb2Te5) studied in Chapter 5. Such materials have dramatically different conductivities between their amorphous and crystalline states, making MIM an ideal tool for studying various types of phase change devices. Chapter 2 explores a number of measurement techniques and principles which can expand the capabilities of MIM and address some of its limitations, including quantitative measurement. A class of such techniques, those involving modulated optical illumination of the tip-sample interface during MIM measurement, is explored in detail in Chapter 4. These include MIM measurement of photoconductivity, band-gap, and carrier lifetime. Finally, chapter 3 covers the application of MIM to ferroelectric domains and domain walls. The primary topic of this chapter is the radically different measurement mechanism possible in piezoelectric materials, in which MIM can be used to measure the transduction of electrical energy to acoustic waves.

Gap junction protocols

Presenting state-of-the-art protocols to study gap junctions, this detailed book first focuses on the use of methods and tools to investigate the different aspects of connexin expression and gap junction regulation. The second part of the volume describes several methods to probe gap junction functionality as such. Written in the highly successful Methods in Molecular Biology series format, chapters include introductions to their respective topics, lists of the necessary materials and reagents, step-by-step and readily reproducible laboratory protocols, and key tips on troubleshooting and avoiding known pitfalls. Authoritative and practical, Gap Junction Protocols is intended for basic and applied researchers in the area of biomedical and life sciences, both in academic and industrial settings.

Online SpringerLink

Guest-induced emergent properties in Metal–Organic Frameworks [electronic resource].

Metal–Organic frameworks (MOFs) are crystalline nanoporous materials comprised of organic electron donors linked to metal ions by strong coordination bonds. Applications such as gas storage and separations are currently receiving considerable attention, but if the unique properties of MOFs could be extended to electronics, magnetics, and photonics, the impact on material science would greatly increase. Recently, we obtained “emergent properties, ” such as electronic conductivity and energy transfer, by infiltrating MOF pores with “guest” molecules that interact with the framework electronic structure. In this Perspective, we define a path to emergent properties based on the Guest@MOF concept, using zinc-carboxylate and copper-paddlewheel MOFs for illustration. Energy transfer and light harvesting are discussed for zinc carboxylate frameworks infiltrated with triplet-scavenging organometallic compounds and thiophene- and fullerene-infiltrated MOF-177. In addition, we discuss the mechanism of charge transport in TCNQ-infiltrated HKUST-1, the first MOF with electrical conductivity approaching conducting organic polymers. Lastly, these examples show that guest molecules in MOF pores should be considered not merely as impurities or analytes to be sensed but also as an important aspect of rational design.

Online OSTI