Resolution molecular-scale

Contact ratio, a, is defined as the real contact area divided by the nominal contact zone, where the real contact area is referred to as the sum of all areas where film thickness is below a certain criterion in molecular scale. The contact area was measured by the technique of Relative Optical Interference Intensity (ROII) with a resolution of 0.5 nm in the vertical direction and 1 /xm in the horizontal direction [69]. 

Ideally one would like to visualize the molecular-scale details at the edge of a droplet to obtain direct information about the molecular nature of wetting. This is not always possible, particularly when these details have dimensions below 300 A, the resolution limit of SPFM. However, the height and curvature of a droplet can usually be measured accurately. These parameters can then be used to obtain an effective contact angle, as defined in Eq. (10). We present here a few examples of this type of study. 

The already critical need for molecular-scale compositional mapping will increase as more complex structures are assembled. Currently, electron microscopy, scanning probe microscopy (SPM) and fluorescence resonance energy transfer (FRET) are the only methods that routinely provide nanometer resolution. 

Hua, E et al. 2004. Polymer imprint lithography with molecular-scale resolution. Nano Lett. 4 2467-2471. 

In liquids, the most commonly used methods are electrical conductivity (18, 19), light absorption, fluorescence (30) and chemical methods based on the color change of an indicator under the influence of an instantaneous reaction (21, 22). The spatial resolution of physical methods (optical, electrical microprobes) is about 100 ym (19) so that these are well suited to macromixing studies but cannot compete with chemical methods for the study of mixing at the molecular scale. An original method based on the continuous injection of radioactive tracers in an industrial mixer has also been proposed (23). In gases, concentration fluctuations have been measured using a catalytic wire (24). 

Little is known about the "molecular scale of time". Chemical research in the past has had its accent on highly varied spectroscopic methods, but these have been mainly for the study of spatial and frequency resolution. This spectrum of spectroscopies is incomplete without the inclusion of time. The availability of ultrashort pulses of energy and their application to molecular problems are therefore expected to form an important extension to the field of molecular spectroscopy. During the next decade the creation of new frontiers in chemistry through studies based on such techniques is inevitable. 

The innate complexity of practical catalytic systems has lead to trial and error procedures as the common approach for the design of new and more proficient catalysts. Unfortunately, this approach is far from being efficient and does not permit to reach a deep insight into the chemical nature of the catalytic processes. The consequence of this difficulty is a rather limited knowledge about the molecular mechanisms of heterogeneous catalysis. To provide information about catalysis on a molecular scale, surface science experiments on extremely well controlled conditions have been designed and resulted in a new research field in its own. However, even under these extremely controlled conditions it is still very difficult, almost impossible, to obtain precise information about the molecular mechanisms that underlie catalytic processes without an unbiased theoretical guide. The development of new and sophisticated experimental techniques that enable resolution at... 

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