Monolayer crystal field

Takeya, J. et al.. Effects of polarized organosilane self-assembled monolayers on organic single-crystal field-effect transistors, Appl. Phys. Lett., 85, 5078, 2004. 

Figure 3.7 Dark-field electron micrograph of a monolayer crystal of poly(4-methylpentene-l) grown from a 0.1% solution in equivolume xylene and amyl acetate solution at 90°C. Each of the four sectors has a 100 growth face contrast is described in the text. From Khoury and Barnes [7] contribution of the National Institute of Standards and Technology.

The rapid rise in computer speed over recent years has led to atom-based simulations of liquid crystals becoming an important new area of research. Molecular mechanics and Monte Carlo studies of isolated liquid crystal molecules are now routine. However, care must be taken to model properly the influence of a nematic mean field if information about molecular structure in a mesophase is required. The current state-of-the-art consists of studies of (in the order of) 100 molecules in the bulk, in contact with a surface, or in a bilayer in contact with a solvent. Current simulation times can extend to around 10 ns and are sufficient to observe the growth of mesophases from an isotropic liquid. The results from a number of studies look very promising, and a wealth of structural and dynamic data now exists for bulk phases, monolayers and bilayers. Continued development of force fields for liquid crystals will be particularly important in the next few years, and particular emphasis must be placed on the development of all-atom force fields that are able to reproduce liquid phase densities for small molecules. Without these it will be difficult to obtain accurate phase transition temperatures. It will also be necessary to extend atomistic models to several thousand molecules to remove major system size effects which are present in all current work. This will be greatly facilitated by modern parallel simulation methods that allow molecular dynamics simulations to be carried out in parallel on multi-processor systems [115]. 

As the analytical, synthetic, and physical characterization techniques of the chemical sciences have advanced, the scale of material control moves to smaller sizes. Nanoscience is the examination of objects—particles, liquid droplets, crystals, fibers—with sizes that are larger than molecules but smaller than structures commonly prepared by photolithographic microfabrication. The definition of nanomaterials is neither sharp nor easy, nor need it be. Single molecules can be considered components of nanosystems (and are considered as such in fields such as molecular electronics and molecular motors). So can objects that have dimensions of >100 nm, even though such objects can be fabricated—albeit with substantial technical difficulty—by photolithography. We will define (somewhat arbitrarily) nanoscience as the study of the preparation, characterization, and use of substances having dimensions in the range of 1 to 100 nm. Many types of chemical systems, such as self-assembled monolayers (with only one dimension small) or carbon nanotubes (buckytubes) (with two dimensions small), are considered nanosystems. 

Many investigations with surfaces have been carried out in this and other laboratories using the ion-bombardment method of cleaning. These include (1) structure investigations of the surface plane on clean surfaces, (2) work-function determinations, (3) adsorption measurements, (4) catalysis, (5) surface recombination velocity, (6) surface conductivity, and (7) field effect. One of the significant finds indicates that the relative positions of the atoms in the clean 100 surface planes of germanium and silicon are not the same as those of similar planes in the bulk crystals, but that these relative positions are the same when a monolayer of oxygen is adsorbed on these surfaces (9). 

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