Direct-deposition

A unique but widely studied polymeric LB system are the polyglutamates or hairy rod polymers. These polymers have a hydrophilic rod of helical polyglutamate with hydrophobic alkyl side chains. Their rigidity and amphiphilic-ity imparts order (lyotropic and thermotropic) in LB films and they take on a F-type stmcture such as that illustrated in Fig. XV-16 [182]. These LB films are useful for waveguides, photoresists, and chemical sensors. LB films of these polymers are very thermally stable, as was indicated by the lack of interdiffusion up to 414 K shown by neutron reflectivity of alternating hydrogenated and deuterated layers [183]. AFM measurements have shown that these films take on different stmctures if directly deposited onto silicon or onto LB films of cadmium arachidate [184]. 

In the spunbond process, the fiber is spun similarly to conventional melt spinning, but the fibers are attenuated by air drag appHed at a distance from the spinneret. This allows a reasonably high level of filament orientation to be developed. The fibers are directly deposited onto a moving conveyor belt as a web of continuous randomly oriented filaments. As with meltblown webs, the fibers are usually thermal bonded or needled (53). 

These three functions involve the movement of O2, CO2, and HjO through the epidermal layers of the leaf. The analogy to human inhalation is obvious. With the diffusion of gases into and out of the leaf, pollutant gases have a direct pathway to the cellular system of the leaf structure. Direct deposition of particulate matter also occurs on the outer surfaces of the leaves. 

Feed residue coke is the small portion of the (non-residue) feed that is directly deposited on the catalyst. This coke comes from the very heavy fraction of the feed and its yield is predicted by the Conradson or Ramsbottom carbon tests. 

Experimental applications include the direct deposition of patterns as small as 0.5 im in semiconductor applications using holographic methods, and the production of rods and coreless boron and silicon carbide fibers (see Ch. 19). 

These compounds generally decompose into two stable primary species the methyl radical (CH3) and acetylene (C2H2).P 1 The methyl radical is considered the dominant compound in generating the growth of CVD diamond.P2][23] Direct deposition from acetylene, although difficult experimentally, has been accomplished, with a marked increase in the crystallinity of the diamond deposit.P" ... 

The deposition temperature is above 1200°C and the deposit usually consists of an outer layer of MoSi2 and an intermediate layer of MoSi.PlP l Such reactions are difficult to control and often result in mechanical stresses and voids at the interface, which may cause adhesion failure. The direct deposition of the silicide is often preferred. This is accomplished by reacting a gaseous silicon compound with a gaseous metal compound, as shown in the following sections. 

Figure 4. Simplified schematic of an optical/infrared focal plane array. The detector is a thin wafer of light sensitive material that is connected to a thin layer of solid state electronics - the connection is made either by direct deposition (CCD) or bump bonding (IR detector). The solid state electronics amplify and read out the charge produced by the incident light.

Humans may also be indirectly affected through exposure to increased levels of toxic metals in drinking water and food. Increased levels of toxic metal are a consequence of direct deposition of pollutants into water sources, increased leaching of metal from soils and lake sediments, and increased corrosion of water pipes. 

The flux of particles in the other direction, deposition on the ocean surface, occurs intermittently in precipitation (wet deposition) and more continuously as a direct uptake by the surface (dry deposition). These flux densities may be represented by a product of the concen-... 

These processes are very rapid and allow the preparation of inorganic supports in one step. This technique allows large-scale manufacturing of supports such as titania, fumed silica, and aluminas. Sometimes the properties of the material differ from the conventional preparation routes and make this approach unique. Multicomponent systems can be also prepared, either by multimetallic solutions or by using a two-nozzle system fed with monometallic solutions [22]. The as-prepared powder can be directly deposited onto substrates, and the process is termed combustion chemical vapor deposition [23]. 

Direct Chemical or Electrochemical Deposition of the Disperse Catalyst This method of direct deposition from a solution of its salt on a suitable conducting substrate is simpler and more practical than the preparation of electrodes from the hnished powders. It has the merit of being able to provide better contact between the catalyst and substrate, and multicomponent metal catalysts can be deposited from a solution containing a mixture of salts of several metals. 

This method is especially valid for the preparation of gold NPs mixed with activated carbon, which are active and stable for the selective oxidation of hydrocarbons and alcohols in water. Over activated carbon gold could not be directly deposited as NPs by using the techniques described above, such as DP and even by GG. Gold colloids with mean diameters from 2.5 to lOnm stabilized by poly vinyl alcohol or poly vinyl p5rrolidone are used. 

Figure 7. Gold NPs directly deposited on PVC microbeads by deposition-reduction method.

Unless complexes are adsorbed on surfaces, the successive reduction will not occur so that nanoclusters might not be grown on the surface. The third one is the direct deposition of metal from solution by the reduction of the reducing agent, as shown in Figure 2. 

Figure 2. Direct deposition mechanism for particle growth compared with aggregation of adsorbed species.

Figure 3. Direct deposition mechanism leading to highly dispersed and nanosized particle formation, compared with reaction between adsorbed species.

DP-MS suffers from system saturation sample loads of a few ig are to be used. DP-ToFMS equipped with El and FI sources is a thermal separation technique for solids which allows exact mass determination (Section 6.3.3). In order to detect and characterise polymer fragments of higher molecular weight, techniques such as DCI, in which the sample is thermally desorbed by the filament on which it is directly deposited, and laser desorption... 

The success of spectral identification depends on the appropriate reference spectra for comparison. IR measurement of eluates that are at slightly subambient temperature is advantageous considering that the large databases of condensed-state spectra may be searched. Spectra measured by matrix-isolation GC-FTIR have characteristically narrow bandwidths compared with the spectra of samples in the condensed phase near ambient temperature or in the gas phase. In addition, the relative intensities of bands in the spectra of matrix-isolated samples often change compared with either gas- or condensed-phase spectra [195]. GC-FTIR spectra obtained by direct deposition match well with the corresponding reference spectra in standard phase... 

Consequently, the major experimental options for the analyst are packed or capillary SFC, mobile phase with/without modifier and off-line or on-line mode, namely direct deposition (DD-SFC-FUR) vs. flowcell. Both small-bore packed columns and narrow-bore open-tubular columns have been used for SFC-FTIR analysis using a pressure-stable, thermostated, flow-cell or solvent elimination interfaces. 

SFC-TLC is largely unexplored. Stahl [927] developed a device for supercritical fluid extraction with deposition of the fluid extracts on a moving TLC plate. Wunsche et al. [928] have described an automated apparatus for direct pSFC-TLC coupling. Compared to collecting the effluent from the SFC in decompression vessels, the direct deposition of the effluent on the TLC plate leads to significant losses of analytes. Multidimensional SFC has been reviewed [929]. 

DD (1) Dipole-dipole interactions (2) Decoupling/double resonance (high power 1H decoupling) (3) Direct deposition... 

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