Spectroscopic nanometer resolution

Spectroscopic Imaging with Nanometer Resolution Using Near-Field Methods... 

One of the significant promises of NSOM is the development of chemical imaging based on vibrational spectroscopic data acquired with nanometer-scale spatial resolution. The advantages of apertureless (versus aperture-based212) methods become particularly important in imaging experiments performed in the... 

Various kinds of new spectroscopic methods will be applied to observe micro- and nanometer sized area in the liquid-liquid interface, and some inhomogeneity or localization of the interfacial compound will be observed. Especially, the optical chirality of the interfacial molecule and molecular aggregate will be very important and fundamental subject. The time-re-solved chiral spectrometry, chiral microscope, and imaging technique of interfacial chirality will be developed in very near future. Nonlinear chiral spectrometry is developed and will become more popular, because its high spatial resolution ability. 

Spectroscopic imaging with nanometer spatial resolution is a very attractive proposition. Having full spectroscopic information available at every pixel is also crucial for obtaining simultaneous chemical information for unknown, heterogeneous samples, or when following transient events. Detailed information from small frequency shifts (not available from fixed-frequency imaging) can also be obtained. 

Among the spectroscopic (EXAFS-like) methods of analysis of local atonuc structure, the SEFS method is a purely surface technique. The analyzed-layer depth in the SEFS method is determined by the mean free path of the secondary electrons and amounts to about 5-7 A. It is not feasible to obtain such a small depth of the analyzed layer by other EXAFS-like methods of surface structure analysis. It should be mentioned that from the standpoint of the physics of surfaces, information on the atonuc structure of superthin surface layers is of most interest, since it is precisely in these surface layers that one encounters the most considerable changes due to the presence of a free surface in a solid. The use of electron optics in the SEFS method makes it possible to obtain extrahigh resolution for the analyzed area (down to several nanometers), which presently is not attainable with X-ray optics used in the EXAFS method. 

Lateral resolution. When brilliant light sources like lasers or synchrotron radiation are used, the lateral resolution typically is diflractirMi limited in the range of a few micrometers for IR microscopy [2,11]. This can be improved by orders of magnitude with near-held IR microscopy [12], which enables resolution down to a few tens of nanometers, and spectroscopic studies by tuning of lasers [18] or use of a broadband synchrotron or laser source. IRSE biochip characterization with lateral resolution down to approximately 200 X 400 pm is possible. 

Having seen the power (and limitation) of nexafs spectroscopy in the preceding sections, one can readily envision the enhanced utility of nexafs spectroscopy as a characterization tool that would result from the addition of high spatial resolution capabilities. Since the spectroscopic sensitivity to specific moieties and functional groups can in many or even most cases be exceeded by ir, nmr, and Raman spectroscopies, nexafs microscopy will have to exceed the spatial resolution of these other spectroscopy techniques in order to be truly useful. To date, nexafs microscopy has surpassed a spatial resolution of 50 nm both in transmission to measure bulk properties (75-77) and in a reflection geometry to study surfaces (78,79). This level of spatial resolution is at least an order of magnitude better than what can be accomplished with complementary compositional analysis techniques. Future developments in nexafs microscopy might achieve a spatial resolution of a few nanometers (80,81). In addition, nexafs microscopy has exceptional surface sensitivity of about 10 nm, a sensitivity that could be improved to about 1 nm with photoemission electron microscopes (peem s) that incorporate a bandpass filter (80-82). 

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