Molecular materials containing tungsten polyoxometalates as the active elements embedded into polymer matrices are investigated as candidates for electronic device applications. The transport properties of these materials are investigated varying the interelectrode spacing and the polyoxometalate concentration. The I–V characteristics of planar devices reveal a conductivity peak at room temperature conditions for intermolecular distances less than 3 nm and electrode distances less than 100 nm. The transport characteristics are discussed in terms of tunneling mechanisms.

Tunneling transport in polyoxometalate based composite materials

Polyoxometalates are a class of well-defined metal oxygen clusters mostly known for their catalytic properties. However, their electronic and optical properties have been used in device applications such as electrochromic displays, dopants for conductive polymers, gas and chemical sensors, capacitors, and electrochemical cells. We fabricate nanodevices based on a composite poly(methyl methacrylate) H3SiW12O40 system and we investigate the effects of electrode material, electrode distance, and molecular concentration on the electronic transport characteristics. It is found that in the case of electrode distances smaller than 50 nm, tunneling effects appear, which are discussed using tunneling theory models. These effects are primarily dependent on the electrode distance and molecular concentration, and less on the electrode material.

Tungstate polyoxometalates as active components of molecular devices

In the last years, there has been an increasing interest in controlling the protein adsorption properties of surfaces because this control is crucial for the design of biomaterials. On the other hand, controlled immobilization of proteins is also important for their application as solid surfaces in immunodiagnostics and biosensors. Herein we report a new protein patterning method where regions of the substrate are covered by a hydrophilic film that minimizes protein adsorption. Particularly, poly(vinyl alcohol) (PVA) cross-linked structures created by an especially developed photolithographic process are proved to prevent protein physisorption and they are used as a guide for selective protein adsorption on the uncovered areas of a protein adsorbing substrate such as polystyrene. The PVA cross-linking is induced by photo-oxidation using, as a catalyst, polyoxometalate (H3PW12O40 or α-(NH4)6P2W18O62), which is removed using a methyl alcohol/water mixed solvent as the developer. We demonstrate that the poly...

Protein-resistant cross-linked poly(vinyl alcohol) micropatterns via photolithography using removable polyoxometalate photocatalyst.

Tunneling and negative resistance effects for composite materials containing polyoxometalate molecules

Transport properties of polyoxometalate containing polymeric materials

Tungsten nuclei, for the subsequent electroless deposition of nickel, were formed of a water-based tungsten-rich microlithographic resist consisting of phosphotungstic acid and polyvinyl alcohol (PVA). Spinning the aqueous resist solution at 4000 RPM yields a pinhole-free 10 3 A thick negative resist film, containing ∼60 weight percent (w/o) tungsten. Exposure (≤100 mJ cm -2 ) of the resists to 254 nm light, postbaking and developing in an aqueous developer produces 0.3 μm features

R. A. Srinivas

Papers

Micropatterned Films of Tungsten Nuclei for Subsequent Metallization Formed of a Phosphotungstic Acid‐Based Negative Resist