Resolution aspects

In this chapter, the motivations to adopt MLR systems for optical e-beam, x-ray, and ion-beam lithographic systems will be given, followed by a survey of published MLR systems. Specific practical considerations such as planarization, pinhole and additive defects, interfacial layer, etch residue, film stress, interference effects, spectral transmission, inspection and resist stripping will be discussed. The MLR systems will be compared in terms of resolution, aspect ratio, sensitivity, process complexity and cost. 

To clarify the selection of a particular MLR system (ILR, 2LR, or 3LR system) a comparison in terms of process complexity, resolution, aspect ratio, linewidth tolerance, sensitivity and effort required for research and development will be given. Then a comparison between deep-UV and RIE PCM systems in terms of resolution, aspect ratio, substrate patterning processes allowed, temperature stability, resist removal at the alignment sites, tool-controlling parameters, and tool cost will be included. 

Resolution Aspect Ratio Limited by Resist Performance Resist Performance Enhanced Resist Performance Enhanced... 

Sensitivity Potential Limited, Depending on Resolution Aspect Ratio Requirements Less Limited than ILRs, Depending on Special Resist Combinations Most Unlimited, Only Limited by AvailABLE Resist Sensitivity... 

Intensive signals behave in a nonadditive manner, as is true for pressure and temperature. When the size of a system is increased, the signal value remains constant and does not scale with system dimensions. Intensive signals can therefore be measured within small parts of a system - but only when it is at (local) thermodynamic equilibrium - and so miniaturization is limited only by resolution aspects and by mounting requirements. 

Depending on the situation, there are several unknowns in Equation (10.4). In its most general case the unknowns are a, a2, bi, b2, c2ji and c2j2. The standard Xi has pseudorank one (see Chapter 2, Section 6), and, hence, can be decomposed in its contributions ai and bi. Note that there is still intensity ambiguity because aibl equals aiQ Q 1b y, for any nonzero a. The quantification of the analyte requires the estimation c2,i and sometimes it is also convenient to obtain estimates of ai, a2, bi and b2 for diagnostics purposes. This is the curve resolution aspect of second-order calibration. 

Having demonstrated the achievement of high-resolution sohd state NMR capability, the authors describe experiments that combine the high-resolution aspect of MAS NMR with methods that retain the structure and/or dynamic information inherent in the anisotropic interactions. Rotational-echo double resonance (REDOR) allows the determination of D between isolated heteronuclear spin pairs. D is related simply and without approximation to intemuclear separation. Hence, REDOR makes possible the unambiguous direct determination of intemuclear distance between the labeled spin pair, independent of pair orientation, i. e., in amorphous and /or microaystaUine solids, and extends our abihty to quantitatively explore complex materials. It is also possible to extract intemuclear distance from homonuclear dipolar coupled spin pairs, and these experiments are also reviewed. 

Compared witii other direct force measurement teclmiques, a unique aspect of the surface forces apparatus (SFA) is to allow quantitative measurement of surface forces and intermolecular potentials. This is made possible by essentially tliree measures (i) well defined contact geometry, (ii) high-resolution interferometric distance measurement and (iii) precise mechanics to control the separation between the surfaces. 

Apart from tliese mainstream metliods enabling one to gain a comprehensive and detailed stmctural picture of proteins, which may or may not be in tlieir native state, tliere is a wide variety of otlier metliods capable of yielding detailed infonnation on one particular stmctural aspect, or comprehensive but lower resolution infonnation while keeping tlie protein in its native environment. One of tlie earliest of such metliods, which has recently undergone a notable renaissance, is analytical ultracentrifugation [24], which can yield infonnation on molecular mass and hence subunit composition and their association/dissociation equilibria (via sedimentation equilibrium experiments), and on molecular shape (via sedimentation velocity experiments), albeit only at solution concentrations of at least a few tentlis of a gram per litre. 

From a map at low resolution (5 A or higher) one can obtain the shape of the molecule and sometimes identify a-helical regions as rods of electron density. At medium resolution (around 3 A) it is usually possible to trace the path of the polypeptide chain and to fit a known amino acid sequence into the map. At this resolution it should be possible to distinguish the density of an alanine side chain from that of a leucine, whereas at 4 A resolution there is little side chain detail. Gross features of functionally important aspects of a structure usually can be deduced at 3 A resolution, including the identification of active-site residues. At 2 A resolution details are sufficiently well resolved in the map to decide between a leucine and an isoleucine side chain, and at 1 A resolution one sees atoms as discrete balls of density. However, the structures of only a few small proteins have been determined to such high resolution. 

Direct sampling of solids may be carried out using laser ablation. In this technique a high-power laser, usually a pulsed Nd-YAG laser, is used to vaporize the solid, which is then swept into the plasma for ionization. Besides not requiring dissolution or other chemistry to be performed on the sample, laser ablation ICPMS (LA-ICPMS) allows spatial resolution of 20-50 pm. Depth resolution is 1-10 pm per pulse. This aspect gives LA-ICPMS unique dit nostic capabilities for geologic samples, surface features, and other inhomogeneous samples. In addition minimal, or no, sample preparation is required. 

Recalling that a separation is achieved by moving the solute bands apart in the column and, at the same time, constraining their dispersion so that they are eluted discretely, it follows that the resolution of a pair of solutes is not successfully accomplished by merely selective retention. In addition, the column must be carefully designed to minimize solute band dispersion. Selective retention will be determined by the interactive nature of the two phases, but band dispersion is determined by the physical properties of the column and the manner in which it is constructed. It is, therefore, necessary to identify those properties that influence peak width and how they are related to other properties of the chromatographic system. This aspect of chromatography theory will be discussed in detail in Part 2 of this book. At this time, the theoretical development will be limited to obtaining a measure of the peak width, so that eventually the width can then be related both theoretically and experimentally to the pertinent column parameters. 

F. Munari and K. Grob, Automated on-line HPLC-HRGC instnimental aspects and application for the determination of heroin metabolites in urine , J. High. Resolut. Chromatogr. Chromatogr. Commun. 11 172-176(1988). 

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