Indirect-deposition approach

Fabrication by inkjet/piezoelectric methods (indirect-deposition approach)... 

DNA arrays are fabricated by immobilizing the complementary DNA (cDNA) onto a solid substrate such as silicon, nylon or glass. This can be achieved by robotic printing of polymerase chain reaction (PCR) products (also known as direct-deposition approach), photolithographical synthesis of complementary oligonucleotides or piezoelectric inkjet printing of PCR products (also known as indirect-deposition approach). 

However, UPD method cannot be used to prepare Pt monolayer on other metals readily because of the mismatched redox potentials. Adzic and coworkers developed a method to deposit Pt monolayer on metal substrates indirectly [59c]. In this approach, a sacrificial copper monolayer is first deposited on a selected metal using the UPD method, followed by a galvanic replacement reaction by Pt ions (Fig. 2.13) [60]. This approach successfully broadens the possible metal elements that can be directly or indirectly deposited by this technique. 

As shown in Fig. 13.1, a CMP step is required in the STI process. There are two possible approaches to implementing the CMP step STI—direct and indirect. In a direct STI process, the CMP process is applied directly on a wafer right after the trench oxide deposition (Fig. 13.1). The CMP process removes the overburden oxide as well as the topography created during trench oxide deposition over the features with various pattern densities across the dies and the wafer. For some slurries, especially the conventional oxide slurries, these topographies are a challenge. To overcome this difficulty, a pre-CMP step is sometimes implemented in which a reverse mask is applied onto the film and the oxide in the raised area is preferentially etched. After the etching step, the... 

The various tunable properties of zeolites have inspired a great variety of concepts in electrochemistry with zeolite-modified electrodes. For example, silver ions inside the zeolite pore system arc not electrochemically active in amperometric detection. Flowever, indirect analyte detection can occur when the analyte causes the removal of silver ions into the solution where they are electrochemically detected.[94] This indirect approach was extended to different copper-exchanged zeolites and demonstrated for the detection of several non-elcctroactive ions including alkali metal, ammonium and calcium.[95] A zeolite-modified electrode (ZME) with high selectivity towards Pb over Cd in cyclic voltammetry was prepared via electrophoretic deposition of zeolite Y, coated with Nafion.[96]... 

By no means does the nomenclature imply advantages or disadvantages of the approaches. Direct is not necessarily better than indirect (or vice versa), and negative is not necessarily worse than positive (or vice versa). The various approaches have their advantages and should be carefully chosen in the context of the desired patterns, the substrates, reactants, and deposition materials involved. 

Both reactions generate OH ions that increase the interfacial pH in the vicinity of the cathode, which catalyzes the sol-gel process facilitating the film formation. The process is illustrated in Figure 12.2. van Ooij and coworkers [10] showed the enhancement in forming an interfacial layer of —Si—O—metal covalent bond by electrodeposition of silane on aluminum alloys. There are three major advantages of the electrodeposition approach, as clearly pointed out by Mandler and coworkers in their first publication [2] (1) the pH varies only close to the cathode, so the stability of the bulk solution is not affected (2) the deposition process is controllable by electrochemical parameters and (3) the film deposition is restricted to the conducting part of the surface and is controlled by the kinetics of the electrochemical process. Note that some reports refer this approach as electro-assisted deposition, since it is an indirect electrodeposition process where the sol monomer is not directly involved in the electrochemical reactions [15,19,28,29]. 

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