Advances in submicron infrared vibrational band chemical imaging

The technique of infrared near-field microscopy with submicron resolution i s an important addition to the chemical sciences arsenal in the last few ye ars. Although related to highly successful scanning optical probe microscop ies in the visible, infrared near-field microscopy had to overcome several obstacles, which slowed its development. This review illustrates the histor y as well as the state of the art of this new field, its limitations and pe rspectives. At present, two main experimental approaches have been successf ul: the apertureless metal tip approach and the fibre tip aperture approach . The two variants are compared from the point of view of resolution, ease of implementation in the laboratory and image formation mechanisms. The tec hniques using chemically specific vibrational absorption contrast are empha sized here, in the general context of chemical microscopy, which includes o ther methods such as chemical force,]Raman and fluorescence microscopies. T he phenomenon of surface-enhanced infrared absorption is also mentioned in relation to near-field infrared microscopy, with regard to important aspect s of image formation and possible improvements. The main advantages of spat ial resolution, chemical sensitivity; non-intrusiveness, minute amounts of specimen and the possibility of quantitative analytical measurements make i nfrared near-field microscopy a powerful tool. We also examine here possibl e future applications that go beyond the limits of classical vibrational mi crospectroscopy, as well as directions for additional advances.