Monolayers substrate choice

Plasmonic nanostructures that are materials consisting of noble metal nanoparticles with sizes of 1-100 nm are known as specific substrates for surface enhanced Raman scattering and luminescence enhancement [1-4]. These effects are stimulated by the localized surface plasmon absorption (LSPA) and may be controlled by the change of metal nanoparticle sizes, their concentration and a substrate choice [5]. New opportunities for surface-enhanced effect realization and optimization are now discussed in connection with bimetallic nanostructures [6]. At the technological aspect one of the simplest types of a binary nanostructure is a stratified system made of two different monolayers, each is consisted of definite metal nanoparticles. The LSPA properties of these binary close-packed planar nanostructures are the subject of the paper. 

A well researched and popular class of monolayers is based on the strong adsorption of thiols (R - SH), disulfides (R - S - S - R) and sulfides (R - S - R) onto metal surfaces. Although thiols, disulfides, and sulfides strongly align with a number of different metals Hke gold, silver, platinum, or copper, gold is usually the substrate of choice because of its inert properties and the formation of a well-defined crystal structure. 

In contrast to the mixed monolayer, a single monolayer could be used provided that the initiator was not very efficient. AIBN is an excellent choice due to its low molar absorptivity and a long half-life therefore, the initiator will still be present after an initial period of irradiation when the first brush is deposited. The substrate could then be cleaned and reintroduced to a new monomer solution to yield a mixed brush. Both thermal and photochemi-... 

A way to stretch or compress metal surface atoms in a controlled way is to deposit them on top of a substrate with similar crystal symmetry, yet with different atomic diameter and lattice constant. Such a single monolayer of a metal supported on another is called an overlayer. Metal overlayers strive to approach the lattice constant of their substrate without fully attaining it hence, they are strained compared to their own bulk state [24, 25]. The choice of suitable metal substrates enables tuning of the strain in the overlayer and of the chemisorption energy of adsorbates. A Pt monolayer on a Cu substrate, for instance, was shown to bind adsorbates much weaker than bulk platinum due to compressive strain induced by the lattice mismatch between Pt and Cu, with Cu being smaller [26]. 

In addition, the patterning method presented here is not restricted only to glass substrates unlike the use of patterned SAMs (self-assembled monolayers), where the choice of substrates is limited. In general this method would allow for the photogeneration of patterns of CaCOj on a variety of substrates, including e.g. conducting polymers, which would be beneficial for electrical stimulation of cells to enhance their proliferation and differentiation. 

The reasons behind the specific choice of apparatus geometry can best be shown by a brief review of prior work. The earliest canal type surface viscometer was introduced by Dervician and Joly (8). In this apparatus, an insoluble monolayer is floated on a substrate fluid in a straight channel. The film is forced to flow through the channel by movement of a floating barrier. This motion is resisted principally by surface viscosity. Thus, the small force required to propel the film at a given speed may be measured and used to determine the surface viscosity of the film. A relatively complete theoretical treatment has been provided by Harkins and Kirkwood (5) for insoluble films with Newtonian surface viscosity in deep channels. Actual measurements are typically made in shallow channels, however, which are formed by floating the channel boundaries on the liquid surface. This method is not applicable to soluble surface films, which tend to diffuse through the substrate fluid and pass behind the barrier. Nevertheless, the most accurate values of surface viscosity available have been produced by this approach. 

SAMs allows us to tune the properties of surfaces at the molecular level, but due to the nature of SAMs (tightly packed, movements of molecules within monolayers restricted) the choice of reaction is important. One must consider that steric effects are likely to be exacerbated for certain surface reactions, leading to an energy barrier higher than would be expected in solution chemistry. To successfully functionalize a SAM, reaction conditions must not cause destruction of the monolayer or damage the underlying substrate. 

Successful IR spectroscopy of ultrathin films is very sensitive to the choice of the method and the optical geometry of the experimental set-up, maximizing spectral contrast and the amount of information obtained about the film. These choices should be made on the basis of a comparison of band intensities in film spectra calculated for different experimental conditions. In this section, this approach will be demonstrated using a 1-nm weakly absorbing hypothetical layer that models an isotropic organic monolayer with optical constants 2 = 1-3 and 2 = 0.1 in the region of the vCH vibrations (v = 2800 cm ). The layer is assumed to be located on a Ge or A1 substrate. The spectra were calculated for /7-polarized reflection IRRAS and ATR and single transmission. 

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