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Scanning Optical Microscopy at λ/10 Resolution Using Near‐Field Imaging Methods a
Author(s) -
ISAACSON M.,
BETZIG E.,
HAROOTUNIAN A.,
LEWIS A.
Publication year - 1986
Publication title -
annals of the new york academy of sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.712
H-Index - 248
eISSN - 1749-6632
pISSN - 0077-8923
DOI - 10.1111/j.1749-6632.1986.tb34555.x
Subject(s) - engineering physics , library science , engineering , art history , physics , computer science , art
Throughout this conference we have been discussing various aspects of the spatial and spectral imaging of components of biological systems. In fact, most of the imaging or microcharacterization methods discussed in this symposium and presently in use are fundamentally limited by the wavelength of the exciting radiation used. Furthermore, as nature would have it, in general, the smaller the wavelength of the radiation probe, the greater the structural damage to the sample under study. For example, optical microscopy (and spectroscopy) can be reasonably nondestructive if visible wavelengths are used, but the spatial resolution achievable is only of the order of one-half micron or so. Even with the new confocal scanning methods recently developed (e.g. REFERENCE 1) the resolution is only about 2,500 A, and that using near UV radiation. Thus, for this method to achieve higher spatial resolution, more destructive, shorter wavelength UV radiation needs to be used. Of course, there are proponents at this symposium who circumvent that resolution limit by using high-energy electrons. There, using conventional electron microscopes of 100 kV to 300 kV accelerating voltages, electron wavelengths of ,037 to .0197 A are achievable. The aberrations of the lenses used limit the spatial resolution to about 100 times the wavelength (a few A or so), but that is still significantly better than that achievable with conventional light microscopy. The problem is that electrons of such high energies are extremely destructive (e.g. REFERENCE 2) and the sample preparation required to view the object in vacuo requires extreme care. There are other proponents who would use soft X rays rather than electrons for their imaging (see REFERENCE 3), but again radiation damage to the sample can play a deleterious role. An alternative way around this wavelength limit to resolution is that described by 0. H. Griffith (e.g. REFERENCES 4, 5) using photoelectron microscopy. In this case, light is incident on the sample, but one images the resultant photoelectrons. Thus, the resolution achievable is ultimately limited by the photoelectron wavelength and not the incident light. Since the wavelength of an electron is less than that of a photon of the same energy ( X, , , , , , = (150/E)'/' whereas Xphoton = 12,399/E where E is the energy of the photon or electron), this method can achieve resolutions almost two orders of