Electron spin resonance microcopy (ESRM) is an imaging method aimed at the observation of paramagnetic species in small samples with micron-scale spatial resolution. At present, this technique is pursued mainly for biological applications at room temperature and in relatively low static magnetic fields. This work is focused on the use of ESRM for the measurement of solid samples. First, a brief comparison of various electron spin resonance (ESR) detection techniques is provided, with an emphasis on conventional "induction detection". Following that, some methodological details are provided along with experimental examples carried out at room temperature and in a static field of approximately 0.5 T. These examples show for the first time the imaging of solid samples measured by "induction detection" ESR with a resolution better than 1 mum. Based on these experimental examples and capabilities, an outlook for the future prospects of this methodology in terms of spin sensitivity and resolution is provided. It is estimated that single-spin sensitivity could be achieved for some samples at liquid-helium temperatures and static fields of approximately 2 T. Furthermore, under these conditions, spatial resolution could reach the nanometer scale. Finally, a description of possible applications of this new methodology is provided.
A pulsed electron spin resonance (ESR) microimaging system operating at the Q-band frequency range is presented. The system includes a pulsed ESR spectrometer, gradient drivers, and a unique high-sensitivity imaging probe. The pulsed gradient drivers are capable of producing peak currents ranging from ∼9 A for short 150 ns pulses up to more than 94 A for long 1400 ns gradient pulses. Under optimal conditions, the imaging probe provides spin sensitivity of ∼1.6 × 10(8) spins∕√Hz or ∼2.7 × 10(6) spins for 1 h of acquisition. This combination of high gradients and high spin sensitivity enables the acquisition of ESR images with a resolution down to ∼440 nm for a high spin concentration solid sample (∼10(8) spins∕μm(3)) and ∼6.7 μm for a low spin concentration liquid sample (∼6 × 10(5) spins/μm(3)). Potential applications of this system range from the imaging of point defects in crystals and semiconductors to measurements of oxygen concentration in biological samples.
Diffusion in porous media is a general subject that involves many fields of research, such as chemistry (e.g. porous catalytic pallets), biology (e.g. porous cellular organelles), and materials science (e.g. porous polymer matrixes for controlled-release and gas-storage materials). Pulsed-gradient spin-echo nuclear magnetic resonance (PGSE NMR) is a powerful technique that is often employed to characterize complex diffusion patterns inside porous media. Typically it measures the motion of at least approximately 10(15) molecules occurring in the milliseconds-to-seconds time scale, which can be used to characterize diffusion in porous media with features of approximately 2-3 mum and above (in common aqueous environments). Electron Spin Resonance (ESR), which operates in the nanoseconds-to-microseconds time scale with much better spin sensitivity, can in principle be employed to measure complex diffusion patterns in porous media with much finer features (down to approximately 10 nm). However, up to now, severe technical constraints precluded the adaptation of PGSE ESR to porous media research. In this work we demonstrate for the first time the use of PGSE ESR in the characterization of molecular restricted diffusion in common liquid solutions embedded in a model system for porous media made of sub-micron glass spheres. A unique ESR resonator, efficient gradient coils and fast gradient current drivers enable these measurements. This work can be further extended in the future to many applications that involve dynamical processes occurring in porous media with features in the deep sub-micron range down to true nanometric length scales.
A system for the generation of short, powerful, and agile pulses of current drive is described. The system is made of several submodules, most of them ' 'homemade' ' and is capable of producing current pulses ranging from 9 A for 150 ns pulses to 94 A for 1400 ns pulse duration, when connected to a nominal 0.6 V/2.75 lH coil. The amplitude of successive current pulses can be updated in the ls time scale. Such capabilities are very useful in the field of electron spin resonance microimaging and for the measurements of diffusion by electron spin resonance. A variant of the system can also be used for the nuclear magnetic resonance imaging of samples located in grossly inhomogeneous magnetic field or for solid-state nuclear magnetic resonance imaging. Details of the system electronic design as well as some representative experimental results are provided.
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