Ultrathin

From Section 24.2.3, it became evident that films with a very low thickness are required. Such films have been described as nanofilms [8], but most commonly they are designated as ultrathin films. As there is no strict definition of the thickness range that is considered, it can be quite broad below 100 nm [9]. However, in view of the applications mentioned, a film thickness of around 20-30 nm or less is the main target for this chapter. 

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A. Schmidt, L. K. Chau, A. Back, and N. R. Armstrong, Epitaxial Phthalocyanine Ultrathin Films Grown by Organic Molecular Beam Epitaxy (OMBE), in Phthalo-cyanines, Vol. 4, C. Leznof and A. P. B. Lever, eds., VCH Publications, 1996. 

A. Ulman, An Introduction to Ultrathin Organic Films From Langmuir-Blodgett to Self-Assembly, Academic, New York, 1991. 

Madey T E, Guan J, Nien C-H, Dong C-Z, Tao H-S and Campbell R A 1996 Faceting induced by ultrathin metal films on W(111) and Mo(111) structure, reactivity, and electronic properties Surf. Rev. Lett. 3 1315... 

Marrian C R K, Perkins F K, Brandow S L, Koloski T S, Dobisz E A and Calvert J M 1994 Low voltage electron beam lithography in self-assembled ultrathin films with the scanning tunneling microscope Appi. Rhys. Lett. 64 390... 

Wu M-C, Estrada C A, Corneille J S and Goodman D W 1996 Model surface studies of metal oxides adsorption of water and methanol on ultrathin MgO films on Mo(IOO) J. Chem. Phys. 96 3892... 

Xu X and Goodman D W 1992 New approach to the preparation of ultrathin silicon dioxide films at low temperature Appl. Phys. Lett. 61 774... 

Rasing Th 1998 Nonlinear magneto-optical studies of ultrathin films and multilayers Noniinear Optios in Metais ed... 

Vollmer R 1998 Magnetization-induced second harmonic generation from surfaces and ultrathin films Nonlinear Optics in Metals e6 K H Bennemann (Oxford Clarendon) pp 42-131... 

Ulman A 1991 Ultrathin Organic Films (London Academic)... 

Guokenberger R, Fleim M, Cevo G, Knapp FI F, Wiegrabe W and Flillebrand A 1994 Soanning tunnelling miorosoopy of insulators and biologioal speoimens based on lateral oonduotivity of ultrathin water films Science 266 1538... 

Peachey J, van Alsten J and Granick S 1991 Design of an apparatus to measure the shear response of ultrathin liquid films Rev. Sci. Instrum. 62 463-73... 

One fiirther method for obtaining surface sensitivity in diffraction relies on the presence of two-dimensional superlattices on the surface. As we shall see fiirtlrer below, these correspond to periodicities that are different from those present in the bulk material. As a result, additional diffracted beams occur (often called fractional-order beams), which are uniquely created by and therefore sensitive to this kind of surface structure. XRD, in particular, makes frequent use of this property [4]. Transmission electron diffraction (TED) also has used this property, in conjunction with ultrathin samples to minimize bulk contributions [9]. 

The examples described above are only a small selection out of a tremendous number of investigations of LB films aird SAMs. This number is still increasing aird it is expected tlrat ultrathin orgairic films will play a central role in botlr fundamental aird applied sciences in tire future. 

Ulman A 1992 Ultrathin Organic Films (Boston Aoademio) p 123... 

Barraud A, Rosilio C and Ruaudel-Teixier A 1980 Polymerized monomolecular layers a new class of ultrathin resins for microlithography Thin Soiid Fiims 68 91-8... 

Orthmann E and Wegner G 1986 Preparation of ultrathin layers of molecularly controlled architecture from polymeric phthalocyanines by the Langmuir-Blodgett-technique 1986 Angew. Chem. Int. Edn. Engl. 25 1105-7... 

Sun F, Castner D G and Grainger D W Ultrathin 1993 Self-assembled polymeric films on solid-surfaces. 2. Formation of 11-(n-pentyldithio)undecanoate-bearing polyacrylate monolayers on gold Langmuirs 3200-7... 

Steiner U B, Cased W R, Suter U W, Rehahn M and Schmitz L 1993 Ultrathin layers of low and high-molecular-weight imides on gold and copper Langmuir 6 3245-54... 

The disks are assumed to lie in the same plane. While this picture is implausible for bulk crystallization, it makes sense for crystals grown in ultrathin films, adjacent to surfaces, and in stretched samples. A similar mathematical formalism can be developed for spherical growth and the disk can be regarded as a cross section of this. 

Considerable research and development effort is being placed on a chlorine-resistant membrane that wiU maintain permeabUity and selectivity over considerable time periods (years). This polymer activity is not limited to hoUow fibers, but the thick assymetric skin of hoUow-fiber constmction might offer an advantage in resolving the end use need as opposed to the ultrathin dat-sheet composite membranes. 

Gate oxide dielectrics are a cmcial element in the down-scaling of n- and -channel metal-oxide semiconductor field-effect transistors (MOSEETs) in CMOS technology. Ultrathin dielectric films are required, and the 12.0-nm thick layers are expected to shrink to 6.0 nm by the year 2000 (2). Gate dielectrics have been made by growing thermal oxides, whereas development has turned to the use of oxide/nitride/oxide (ONO) sandwich stmctures, or to oxynitrides, SiO N. Oxynitrides are formed by growing thermal oxides in the presence of a nitrogen source such as ammonia or nitrous oxide, N2O. Oxidation and nitridation are also performed in rapid thermal processors (RTP), which reduce the temperature exposure of a substrate. 

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