Film preparation drawbacks

Three major drawbacks currently plague LB resists. First, application time is too long (in the order of a few minutes to a few hours), because many coats, each only a few nanometers thick, are required to ensure defect-free etching protection. Second, etching resistance must be improved for adequate resist performance. Third, the substrate and the film preparation bath must be scrupulously clean. Because LB resist technology is still in its infancy, ongoing research may yet provide solutions to these problems. 

Thin film deposition by means of sputtering is a fairly well known method and has been employed for more than a century. An inherent drawback of the method is the tendency of the metal films to become contaminated with the inert gas atoms present as a medium. There is furthermore a multitude of process parameters to be considered. For these reasons the method has not received much attention in the past. Nowadays the ability to prepare amorphous thin films by means of sputtering is employed on a wide scale since it has been shown on different occasions that the films prepared by this method possess properties that compare favourably with those obtained by other methods. 

The most convenient (and thus the most common) configuration of an electrochromic electrode is in the form of a thin-layer, compact film, prepared by direct sputtering or evaporation on indium tin oxide (ITO)-coated glass substrates. Other preparation methods include sol-gel, chemical vapour deposition and anodic oxidation. The various preparation procedures and the related advantages and drawbacks are described in a series of recent reviews [8-12] to which the reader is referred for details. 

Starch is an attractive biosynthesized and biodegradable alternative suitable for film preparation and foaming. Unfortunately, starch presents some disadvantages. It is highly hygroscopic, brittle without plasticizer and its mechanical properties are very sensitive to moisture content [51]. Still, these drawbacks can be avoided by, for example, blending the starch with an appropriate biodegradable polymer. On the market... 

Sol-gel-based biosensors have attracted an enormous scientific attention is the last decades [171-179], Despite the volume of the published work, inherent drawbacks associated with the nature and the synthetic routes followed for the preparation of such gels still exist. These include cracking of the films, high concentration of methanol/ ethanol in the resulted sol, and the most important point regarding the development of amperometric-based biosensors, the lack of conductivity. 

Saha et al. [109] have proposed an improved ion deposition methodology based on a dual ion-beam assisted deposition (dual IBAD) method. Dual IBAD combines physical vapor deposition (PVD) with ion-beam bombardment. The unique feature of dual IBAD is that the ion bombardment can impart substantial energy to the coating and coating/substrate interface, which could be employed to control film properties such as uniformity, density, and morphology. Using the dual lABD method, an ultralow, pure Ft-based catalyst layer (0.04-0.12 mg Ft/cm ) can be prepared on the surface of a GDL substrate, with film thicknesses in the range of 250-750 A. The main drawback is that the fuel cell performance of such a CL is much lower than that of conventional ink-based catalyst layers. Further improvement... 

A different aspect of preparation of an organized nanoparticles on a fluid is called as the rheotaxy technique. It is a well-established one to fabricate a well-crystallized film. Mobility of the atoms on the surface of the liquid substrate favors the aggregation of atoms in the growing films (41). In order to avoid a drawback of the rheotaxy, i.e., the negative effect of high surface tension of the substrate, a modification has been made by Romeo et al. (42,43), where they used substrates of elevated temperature close to but below their melting points. They prepared, e.g., ZnS Mn thin films on some low-melting metals such as Pb, Bi or Bi-Sb alloy. 

One of the major drawbacks of liposomes is related to their preparation methods [3,4]. Liposomes for topical delivery are prepared by the same classic methods widely described in the literature for preparation of these vesicles. The majority of the liposome preparation methods are complicated multistep processes. These methods include hydration of a dry lipid film, emulsification, reverse phase evaporation, freeze thaw processes, and solvent injection. Liposome preparation is followed by homogenization and separation of unentrapped drug by centrifugation, gel filtration, or dialysis. These techniques suffer from one or more drawbacks such as the use of solvents (sometimes pharmaceutically unacceptable), an additional sizing process to control the size distribution of final products (sonication, extrusion), multiple-step entrapment procedure for preparing drug-containing liposomes, and the need for special equipment. 

The spin coating technique has attracted interest, since it maintains many aspects of technical catalysts prepared by pore volume or incipient wetness impregnation, and simultaneously allows the interpretation and analysis in a similar way as the more well-defined model systems discussed above [30]. Here, a solution of the desired catalyst precursor is dropped onto a wafer covered with an oxide film, which is spun on a rotor to create a liquid layer of uniform thickness in order to mimic traditional wet impregnation preparation of catalysts. Control of the catalyst loading and particle size is to some degree achieved by varying the rotation speed, concentration, and vapor pressure of the solute. Still the method suffers, however, from many of the drawbacks associated with wet-impregnated model catalysts, which imparts detailed mechanistic studies. 

Liposomes are formed by rehydration of a lipid film at temperatures below 4°C. The substances to be entrapped are added to the aqneons solntion consequently, formation of vesicles and entrapment occur simultaneously. After this preparation period, inhibitor molecules are added to the external medium that block all enzymes that have not been entrapped, before the suspension is extruded through filters with appropriate pore sizes. One main drawback of this strategy is that it can only be applied with lipids that have their main transition temperature below 0°C. This technique has basically been applied for the synthesis of poly(Phe) in liposomes. ... 

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