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Ionizing radiation-induced paramagnetic defects in calcified tissues like tooth enamel are indicators of irradiation dose. Hydroxyapatite (HA), the principal constituent in these materials, incorporates a variety of anions (CO

Electron paramagnetic resonance (EPR) spectroscopy characterizes the magnetic properties of paramagnetic materials at the atomic and molecular levels. Resonators are an enabling technology of EPR spectroscopy. Microresonators, which are miniaturized versions of resonators, have advanced inductive-detection EPR spectroscopy of mass-limited samples. Here, we provide our perspective of the benefits and challenges associated with microresonator use for EPR spectroscopy. To begin, we classify the application space for microresonators and present the conceptual foundation for analysis of resonator sensitivity. We summarize previous work and provide insight into the design and fabrication of microresonators as well as detail the requirements and challenges that arise in incorporating microresonators into EPR spectrometer systems. Finally, we provide our perspective on current challenges and prospective fruitful directions.

We report a strategy for realizing tunable electrical conductivity in metal-organic frameworks (MOFs) in which the nanopores are infiltrated with redox-active, conjugated guest molecules. This approach is demonstrated using thin-film devices of the MOF Cu3(BTC)2 (also known as HKUST-1; BTC, benzene-1,3,5-tricarboxylic acid) infiltrated with the molecule 7,7,8,8-tetracyanoquinododimethane (TCNQ). Tunable, air-stable electrical conductivity over six orders of magnitude is achieved, with values as high as 7 siemens per meter. Spectroscopic data and first-principles modeling suggest that the conductivity arises from TCNQ guest molecules bridging the binuclear copper paddlewheels in the framework, leading to strong electronic coupling between the dimeric Cu subunits. These ohmically conducting porous MOFs could have applications in conformal electronic devices, reconfigurable electronics, and sensors.

Ever since the invention of the scanning probe and electron microscope, a goal has been to image liquid specimens as easily as in a light microscope, and to measure liquid processes with a good resolution in both spatial and temporal. Direct observation of electrochemical processes is essential to develop electrochemical models, optimize nanostructures, and understand reaction mechanisms. We have developed and improved some in-situtechniques and tested them on electrochemical processes. In an attempt to have improved topography and surface reactivity information, we have designed and fabricated nanometer sized scanning probe tips for combined atomic force microscopy (AFM) and scanning electrochemical microscopy (SECM). We report here the characterization of these tips using an in-house fabricated calibration sample and a model anode. In another approach we have used scanning near-field microwave microscopy (sMIM) for imaging in liquids using ultrathin molecular impermeable membranes separating scanning probes from samples enclosed in environmental cells. We imaged a process of dendritic growth during model electroplating reaction. Due to very small energy of few gigahertz microwaves we demonstrate the advantages of this microscopy for non-destructive artifact-free imaging compared to electron microscopy [1]. Different to TEM in liquids which has been used successfully to study the electrochemical processes very little research has been performed using liquid SEM [2]. We explore this imaging modality and describe here a novel chip [3,4] and cell designs enabling us to study Ag electrodeposition in real time using SEM in liquids. All these techniques are complementary and well suited for in situelectrochemistry. These examples demonstrate the versatility of these techniques and can be extended to other applications such as corrosion, battery and bio-medical research. References: [1] A. Tselev, J. Velmurugan, A. Ievlev, S. Kalinin,and A. Kolmakov ACS Nano, 10 (3),3562, 2016 [2] E. Jensen, C. Kobler, P. S. Jensen and K. Molhave, Ultramicroscopy, 129, 63, 2013 [3] F. Yi, W. Osborn, J. Betz, J and D.A. LaVan Microelectromechanical Systems, 24, 1185, 2015 [4] M. D. Grapes, T. LaGrange, L.H. Friedman, B. W. Reed, G. H. Campbell, T. P. Weihs and D. A. LaVan Review of Scientific Instruments, 85, 084902, 2014