Search for: All records

This perspective highlights recent advances in super-resolution, mid-infrared imaging and spectroscopy. It provides an overview of the different near field microscopy techniques developed to address the problem of chemically imaging specimens in the mid-infrared “fingerprint” region of the spectrum with high spatial resolution. We focus on a recently developed far-field optical technique, called infrared photothermal heterodyne imaging (IR-PHI), and discusses the technique in detail. Its practical implementation in terms of equipment used, optical geometries employed, and underlying contrast mechanism are described. Milestones where IR-PHI has led to notable advances in bioscience and materials science are summarized. The perspective concludes with a future outlook for robust and readily accessible high spatial resolution, mid-infrared imaging and spectroscopy techniques. 

Infrared photothermal heterodyne imaging (IR-PHI) represents a convenient table top approach for conducting superresolution imaging and spectroscopy throughout the all-important mid infrared (MIR) spectral region. Although IR-PHI provides label-free, superresolution MIR absorption information, it is not quantitative. In this study, we establish quantitative relationships between observed IR-PHI signals and relevant photothermal parameters of investigated specimens. Specifically, we conduct a size series analysis of different radii polystyrene (PS) beads so as to quantitatively link IR-PHI signal contrast to specimen heat capacity, MIR peak absorption cross-section, and scattering cross-section at IR-PHI’s probe wavelength. 

Limited approaches exist for imaging and recording spectra of individual nanostructures in the midinfrared region. Here we use infrared photothermal heterodyne imaging (IR-PHI) to interrogate single, high aspect ratio Au nanowires (NWs). Spectra recorded between 2,800 and 4,000 cm⁻¹for 2.5–3.9-μm-long NWs reveal a series of resonances due to the Fabry–Pérot modes of the NWs. Crucially, IR-PHI images show structure that reflects the spatial distribution of the NW absorption, and allow the resonances to be assigned to them= 3 andm= 4 Fabry–Pérot modes. This far-field optical measurement has been used to image the mode structure of plasmon resonances in metal nanostructures, and is made possible by the superresolution capabilities of IR-PHI. The linewidths in the NW spectra range from 35 to 75 meV and, in several cases, are significantly below the limiting values predicted by the bulk Au Drude damping parameter. These linewidths imply long dephasing times, and are attributed to reduction in both radiation damping and resistive heating effects in the NWs. Compared to previous imaging studies of NW Fabry–Pérot modes using electron microscopy or near-field optical scanning techniques, IR-PHI experiments are performed under ambient conditions, enabling detailed studies of how the environment affects mid-IR plasmons.

 

In the title compound, C 12 H 13 NO 2 , the five-membered ring has an envelope conformation; the disubstituted C atom lies out of the mean plane through the four other ring atoms (r.m.s. deviation = 0.0038 Å) by 0.1877 (18) Å. The plane of the phenyl substituent is practically perpendicular to that of the planar part of the five-membered ring, with a dihedral angle of 87.01 (5)°. In the crystal, molecules are linked by weak C—H...O hydrogen bonds, forming inversion dimers. The dimers are linked by further C—H...O hydrogen bonds, as well as carbonyl–carbonyl attractive interactions [O...C = 3.2879 (19) Å], forming a three-dimensional framework structure.