Friday, November 27, 2009

New Process for the Application of Spin Transition Molecular Materials In Thin Layers

Centre National De La Recherche Scientifique (C.N.R.S.) (Paris, FR) and Universitat De Valencia (Valencia, ES) investigators developed  a new process for the application of thin layers of substantially pure spin transition molecular materials while maintaining the hysteresis properties of the material. The process makes it possible to obtain a dense uniform surface with very low roughness.  By "thin layer" deposition is meant the application onto a silicon substrate of a layer of material whose thickness lies between 1 nm and 10 micrometers.

According to inventors Azzedine Bousseksou (Toulouse, FR); Gabor Molnar (Toulouse, FR), Saioa Cobo (Castanet Tolosan, FR), Lionel Salmon (Carcassonne, FR), Jose Antonio Real Cabezos (Valencia, ES) and Christophe Vieu (Auzeville Tolosane, FR),  there is at the present time no other method through which a thin layer of spin transition complexes can be deposited as a thin layer while maintaining the properties of spin transition, hysteresis and a surface condition of acceptable quality. It is therefore particularly desirable to provide a process for the deposition of spin transition complexes as thin layers which will fulfill these requirements.

The research team discovered a new process of thin layer application which fulfils these requirements. In particular the process makes it possible to maintain properties such as the hysteresis, transition temperature, etc., of the massive material when it is deposited as a thin layer. In addition to this the thin layer comprises only the spin transition compound, so it is not necessary to use a mixture, as is the case in spin coating, where a binding polymer/material mixture is required

The process, detailed in U.S. Patent Application 20090291328, also makes it possible to control the thickness of the deposited layers over a very wide range--from a few nanometers to a few micrometers. Furthermore the thin layers obtained are dense, uniform, of very small roughness, generally between 1 and 20 nm. Finally, micro- and nano-structuring of the deposits is possible. The process makes it possible to produce perfectly localized deposits.

The inventors have prepared a bistable thin layer comprising a substantially pure spin transition material for the first time. This layer can be subsequently micro/nano-structured.  .

The substrate may be micro- or nano-structured, using conventional techniques. Micro- or nano-structures of thin layers of spin transition compounds may be manufactured using a microtechnology technique known as "lift-off". One important condition for the use of this process is that the thin layer should be insoluble in the solvent used to lift the resin (for example acetone). This condition is fulfilled by three-dimensional systems, in particular those described below, which are very poorly soluble in common solvents. In the case of deposits made using the layer-by-layer technique an additional condition must be fulfilled--the resin used to mask the surface must be insoluble in the solvent used for deposition. This problem does not arise in the case of the process of deposition by evaporation.

In order to manufacture micro/nano-structured molecular deposits the substrate is first coated with a photosensitive resin and then different resin patterns are obtained by standard photolithography or electronic lithography. The spin transition compound is then deposited layer-by-layer or by thermal evaporation. In the last (lift-off) step the patterns of resin (negative image) are dissolved in acetone, leaving patterns comprising the molecular complex (positive image) which are insoluble in acetone on the substrate.

This method makes it possible to deposit the compound as small elements of controlled size (of micron and nanometer dimensions) having a very favorable morphology (dense with little roughness) for various envisaged applications using spin transition molecular compounds.

FIG. 9: Diagrammatical presentation of the process for the microstructuring of thin layers of the spin transition complex Fe[HB(pz).sub.3].sub.2 by photolithography and thermal evaporation.

FIG. 10: Photographs of microstructures of the compound Fe[(HB(pz).sub.3].sub.2. The metal areas not coated with the product correspond to areas protected by the photolithographic resin.

FIG. 11: Diagrammatical presentation of the process for microstructuring thin layers of the spin transition complex Fe(pyrazine)[Pt(CN).sub.4] by electronic lithography and layer-by-layer deposition and lift-off.

FIG. 12: Images obtained by SEM of a layer according to the invention having different structures obtained following fifteen deposition cycles (a, b: 2 .mu.m; c: 500 nm; d, e: 200 nm; f: 30 nm). The bars on the scale are 30 .mu.m (a), 5 .mu.m (b, c, d) and 500 nm (e, f) respectively.

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