Linewidth limitations

Optical Lithography. Optical Hthography uses visible or ultraviolet light as the exposure media, and is the dominant Hthographic process used for patterning IC wafers. The linewidth limit is near 0.4 p.m, although some narrower features may be possible (34). The masks typically are made from patterned, opaque chromium films on glass. 

The natural linewidth is the smallest contribution to the line profile of a transition and is only rarely seen as limiting within the laboratory. For an electronic transition with a lifetime of 10000 ps the linewidth is of order 0.00053 cm-1 but for a rotational transition the lifetime linewidth 5.3 x 10-15 cm-1. The best microwave spectra recorded in the laboratory have a linewidth of a few Hz or 10-12 cm-1, which is close (but not very) to the natural linewidth limit. 

Muller, J.G., U. Lemmer, G. Raschke, M. Anni, U. Scherf, J.M. Lupton, and J. Feldmann. 2003. Linewidth-limited energy transfer in single conjugated polymer molecules. Phys Rev Lett 91 267403. 

The most ftmdamental limitation on sharpness of spectral lines is the so-called natural linewidth. Because an... 

Light sources can either be broadband, such as a Globar, a Nemst glower, an incandescent wire or mercury arc lamp or they can be tunable, such as a laser or optical parametric oscillator (OPO). In the fomier case, a monocln-omator is needed to achieve spectral resolution. In the case of a tunable light source, the spectral resolution is detemiined by the linewidth of the source itself In either case, the spectral coverage of the light source imposes limits on the vibrational frequencies that can be measured. Of course, limitations on the dispersing element and detector also affect the overall spectral response of the spectrometer. 

Finally, instmmental broadening results from resolution limitations of the equipment. Resolution is often expressed as resolving power, v/Av, where Av is the probe linewidth or instmmental bandpass at frequency V. Unless Av is significantly smaller than the spectral width of the transition, the observed line is broadened, and its shape is the convolution of the instrumental line shape (apparatus function) and the tme transition profile. 

The potential of a tunable dye laser should not be overlooked. A tunable dye laser, employing an organic dye as lasing material allows one to choose any suitable excitation line within a particular region. This is in contrast to the case of a gas ion laser which has a limited number of emission lines at fixed wavelength. Nevertheless, a tunable dye laser has significant drawbacks such as poor resolution imposed by the dye laser linewidth (1.2 cm-1) and a continuous background spectrum which requires the use of a tunable filter 15-18). 

It is also clear from Eq. (2.5.1) that the linewidth of the observed NMR resonance, limited by 1/T2, is significantly broadened at high flow rates. The NMR line not only broadens as the flow rate increases, but its intrinsic shape also changes. Whereas for stopped-flow the line shape is ideally a pure Lorentzian, as the flow rate increases the line shape is best described by a Voigt function, defined as the convolution of Gaussian and Lorentzian functions. Quantitative NMR measurements under flow conditions must take into account these line shape modifications. 

FIGURE 2.2 Resolution may increase with increasing frequency. A two-line EPR absorption spectrum is given at three different microwave frequencies. The line splitting (and also the line position) is caused by an interaction that is linear in the frequency the linewidth is independent of the frequency. This is a theoretical limit of maximal resolution enhancement by frequency increase. In practical cases the enhancement is usually less in some cases there is no enhancement at all. 

INPUT g-values git linewidth r, frequency v, field limits INPUT stepwidth in solid angle dcosB, dip spectral points n NULL absorption-array... 

Its capability to titrate sites on heterogeneous surfaces makes photoemission of adsorbed xenon in principle a particularly attractive technique for investigating the surfaces of catalysts. Unfortunately, the technique has its limitations, because the Xe 5p /2 peak has a finite linewidth of about 0.4 eV. If a surface possesses more than three to four different adsorption sites, the spectra may become too... 

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