Seed layer method

Overlayer (also Two Layer and Seed Layer) Method this method (several variants have been developed by different research groups) is a combination of the crushed crystal and fast evaporation methods. Fast solvent evaporation is used to form the first layer of small matrix-only crystals, followed by deposition of a solution of matrix plus analyte on top of the crystal layer. The difference between the fast evaporation and the overlayer methods is in the second layer solution, where the addition of matrix to the latter is believed to provide improved results particularly for mixtures. The method has several convenient features that make it a popular approach. It inherits all the advantages of the fast evaporation method and avoids some of its limitations, while providing enhanced sensitivity and better spot-to-spot reproducibility. 

The most successful approach to control membrane formation involves segregation of the processes of crystal nucleation and growth [24]. The so-called ex situ or secondary (seeded) growth methods, unlike the direct synthesis procedures just discussed, include a first step in which a closely packed layer of colloidal zeolite crystals, synthesized homogenously, is deposited onto... 

Bimetallic particles with layered structures have opened fascinating prospects for the design of new catalysts. Schmid et al. [10m] have applied the classical seed-growth method [20] to synthesize layered bimetallic Au/Pd and Pd/Au colloids in the size range of 20-56 nm. The sequential reduction of gold salts and palladium salts with sodium citrate allows the gold core to be coated with Pd. This layered bimetallic colloid is stabilized by trisulfonated triphenylphosphane and sodium sulfanilate. More than 90% metal can be isolated in the solid state and is redispersable in water in high concentrations. 

Some work has been reported on deposition of hydroxyapatite under hydrothermal conditions, that is much above 100 °C. This includes a study by Liu, Savino and Yates (2011) who coated hydroxyapatite on titanium, stainless steel, aluminium and copper substrates by a seeded hydrothermal deposition method. The deposition strategy included an electrochemical reaction to form quickly a thin layer of HAp seed crystals. Subsequent hydrothermal crystal growth from the seed layer resulted in dense and durable HAp films. In a typical hydrothermal synthesis, a solution of Na2EDTA (0.20 M) and Ca(NOs)2 (0.20 M) was prepared in 15 ml water and a solution of (NH4)2HP04 (0.12 M) in 15 ml water was prepared in a second container. The two source solutions were mixed together after the pH of each solution was raised to 10.0 with ammonium hydroxide. The resulting combined solution was stirred at room temperature for about 20 min and then transferred to a Teflon-lined stainless steel pressure vessel of 40 ml internal volume. 

One possible interpretation of the prediction that as characteristic size decreases deposition becomes conformal is that smaller features are easier to fill. This conclusion is not consistent with industrial experience. Bearing in mind that a wafer contains many features, a predicted conformal deposition rate may not be acceptable due to a random spatial variation in deposition rate. Such variations may result from, among other things, a nonuniform seed layer. Below we discuss a possible method that accounts for such imperfections. 

Copper interconnection via electrochemical means has received increasing attention. Currently the most acceptable method is based on electrodeposition of copper on top of a copper seed layer which has previously been deposited by CVD or sputtering method 1 . 

All the above mentioned high perm-selectivity of zeolite membranes can be attributed to the selective sorption into the membranes. Satisfactory performance can be obtained by defective zeolite membranes. Xylene isomers separation by zeolite membranes compared with polymeric membranes are summarized in Table 15.4. As shown, zeolite membranes showed much higher isomer separation performances than that of polymeric membranes. Specially, Lai et al. [41] prepared b-oriented silicalite-1 zeolite membrane by a secondary growth method with a b-oriented seed layer and use of trimer-TPA as a template in the secondary growth step. The membrane offers p-xylene permeance of 34.3 x 10 kg/m. h with p- to o-xylene separation factor of up to 500. Recently, Yuan et al. [42] prepared siUcalite-1 zeolite membrane by a template-free secondary growth method. The synthesized membrane showed excellent performance for pervaporation separation of xylene isomers at low temperature (50°C). 

There are two reincarnations of this method, schematically illustrated in Fig. 2. The first method uses a silicon or glass wafer as a substrate material, while the second method uses a nickel Plate. A silicon or glass wafer is coated by evaporation or sputtering with a conductive seed layer ( 100 nm) such as Ni or Cu or Au. A thin layer ( 50 nm) of Ti or Cr is used to enhance adhesion of the conducting layer to the silicon substrate. The wafer is then coated with a layer of photoresist, which is subsequently exposed to UV light and developed so that the... 

Mechanical polishing of the wafer In this technique, nanometre sized diamond powder is sprinkled on the sihcon wafer and the wafer is mechanically scratched. By this, the diamond powder is spread uniformly throughout the wafer and this acts as a seeding layer in the CVD system. Seeding [28] through this method results in a nucleation density of Wicaf. 

A method used to ensure the complete filling of vias is electroless plating of nickel. Electroless plating is a process to plate metal without electrical current involved. As a result, it eliminates the seed layer needed in electroplating. To plate nickel on copper, the copper surface must first be activated in a palladium chloride solution. This activation treatment allows palladium to bond to copper at certain sites so that the subsequent nickel plating can nucleate. 

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