Resolution optical microscopy

One interesting new field in the area of optical spectroscopy is near-field scaiming optical microscopy, a teclmique that allows for the imaging of surfaces down to sub-micron resolution and for the detection and characterization of single molecules [, M]- Wlien applied to the study of surfaces, this approach is capable of identifying individual adsorbates, as in the case of oxazine molecules dispersed on a polymer film, illustrated in figure Bl.22,11 [82], Absorption and emission spectra of individual molecules can be obtamed with this teclmique as well, and time-dependent measurements can be used to follow the dynamics of surface processes. 

Figure Bl.22.11. Near-field scanning optical microscopy fluorescence image of oxazine molecules dispersed on a PMMA film surface. Each protuberance in this three-dimensional plot corresponds to the detection of a single molecule, the different intensities of those features being due to different orientations of the molecules. Sub-diffraction resolution, in this case on the order of a fraction of a micron, can be achieved by the near-field scaiming arrangement. Spectroscopic characterization of each molecule is also possible. (Reprinted with pennission from [82]. Copyright 1996 American Chemical Society.)...

Hamann H F, Gallagher A and Nesbitt D J 1999 Enhanced sensitivity near-field scanning optical microscopy at high spatial resolution Appl. Phys. Lett. 75 1469-71... 

Microscopy is one of the most direct physical methods for determining surface roughness. The resolution can go from macroscopic to atomic size, depending on the technique. Thus the order of magnitude of the range of observation is the millimeter for optical microscopy, the micrometer for... 

Barry, Clinton Wilson (1979) examined the structure of cements prepared from a glass powder from which very fine particles had been removed to improve resolution. The microstructure of the set cement is clearly revealed by Nomarski reflectance optical microscopy (Figure 5.14). Glass particles are distinguished from the matrix by the presence of etched circular areas at the site of the phase-separated droplets. The micrograph... 

The compensation birefringence measurement is very easily coupled to optical microscopy in the transmission and reflection modes, thus allowing characterizing orientation with a spatial resolution of a few hundreds of nanometers [14]. Polarizing microscopes are widely available and are often used for birefringence studies even if spatial resolution is not required. Objectives specifically designed for cross-polarized microscopy are necessary to avoid artifacts. 

The resolution or "resolving power" of a light microscope is usually specified as the minimum distance between two lines or points in the imaged object, at which they will be perceived as separated by the observer. The Rayleigh criterion [42] is extensively used in optical microscopy for determining the resolution of light microscopes. It imposes a resolution limit. The criterion is satisfied, when the centre of the Airy disc for the first object occurs at the first minimum of the Airy disc of the second. This minimum distance r can then be calculated by Equation (3). 

The analytical performance of CL microscopy imaging in terms of detectability, precision, accuracy, and spatial resolution was previously reported by us [25], The system allowed for the detection of 400 amol of enzymes such as F1RP or AP, with a spatial resolution as low as 1 pm and very low background. CL coupled with optical microscopy thus represents a useful tool for enzyme, antigen,... 

Seeing the surface of a catalyst, preferably in atomic detail, is the ideal of every catalytic chemist. Unfortunately, optical microscopy is of no use for achieving this, simply because the rather long wavelength of visible light (a few hundred nanometers) does not enable features smaller than about one micrometer to be detected. Electron beams offer better opportunities. Development over the past 40 years has resulted in electron microscopes which routinely achieve magnifications on the order of one million times and reveal details with a resolution of about 0.1 nm [1], The technique has become very popular in catalysis, and several reviews offer a good overview of what electron microscopy and related techniques tell us about a catalyst 12-6],... 

Transmission electron microscopy (TEM) is a powerful and mature microstructural characterization technique. The principles and applications of TEM have been described in many books [16 20]. The image formation in TEM is similar to that in optical microscopy, but the resolution of TEM is far superior to that of an optical microscope due to the enormous differences in the wavelengths of the sources used in these two microscopes. Today, most TEMs can be routinely operated at a resolution better than 0.2 nm, which provides the desired microstructural information about ultrathin layers and their interfaces in OLEDs. Electron beams can be focused to nanometer size, so nanochemical analysis of materials can be performed [21]. These unique abilities to provide structural and chemical information down to atomic-nanometer dimensions make it an indispensable technique in OLED development. However, TEM specimens need to be very thin to make them transparent to electrons. This is one of the most formidable obstacles in using TEM in this field. Current versions of OLEDs are composed of hard glass substrates, soft organic materials, and metal layers. Conventional TEM sample preparation techniques are no longer suitable for these samples [22-24], Recently, these difficulties have been overcome by using the advanced dual beam (DB) microscopy technique, which will be discussed later. 

Although electron microscopy is approached in this chapter as an analytical technique (a variant of XRF), it is essential to state at the outset that electron microscopy is far more versatile than this. Many standard descriptions of electron microscopy approach the subject from the microscopy end, regarding it as a higher resolution version of optical microscopy. Several texts, such as Goodhew et al. (2001), Reed (1993) and Joy et al. (1986), are devoted to the broad spectrum of analytical electron microscopy, but the emphasis here on the analytical capacity is justified in the context of a book on archaeological chemistry. 

The resolution of a conventional microcope is limited by the classical phenomena of interference and diffraction. The limit is approximately X/2, X being the wavelength. This limit can be overcome by using a sub-wavelength light source and by placing the sample very close to this source (i.e. in the near field). The relevant domain is near-field optics (as opposed to far-field conventional optics), which has been applied to microscopy, spectroscopy and optical sensors. In particular, nearfield scanning optical microscopy (N SOM) has proved to be a powerful tool in physical, chemical and life sciences (Dunn, 1999). 

During investigations we were analyzing samples by methods of X-ray diffraction, electron scanning microscopy, microprobe analysis, atomic force microscopy, high-resolution transmission electron microscopy with preliminary attracting of the another methods including optical microscopy, Raman spectroscopy, thermal analysis and some of others. 

The Sccmning Electron Microscope (SEM) is a standard imaging technique based on electron back-scattering from the sample surface. It analyses the surfaces of solid objects, producing images with the resolution which is about order of magnitude better than that of optical microscopy (typically 10 nm). The SEM avoids the problem of thin samples (TEM) but the SEM observation requires the deposition of a thin conductive metal film on the sample surface to prevent sample charging. 

---