Semiconductor wafer bonding has increasingly become a technology of choice for materials integration in microelectronics, optoelectronics, and microelectromechanical systems. The present overview concentrates on some basic issues associated with wafer bonding such as the reactions at the bonding interface during hydrophobic and hydrophilic wafer bonding, as well as during ultrahigh vacuum bonding. Mechanisms of hydrogen-implantation induced layer splitting ͑''smart-cut'' and ''smarter-cut'' approaches͒ are also considered. Finally, recent developments in the area of so-called ''compliant universal substrates'' based on twist wafer bonding are discussed.

Chemical reactions at monolayers are usually carried out by exposing the solid surface to reactive species in the liquid or gas phase. Here is investigated interactions including chemical reactions between two monolayers that are immobilized on two opposing solid substrates, a phenomenon known as wafer bonding. Covalent S–S bonds were formed in a photochemical reaction between disulfide groups on organosilane solid films under mild conditions, and the resulting bonded wafer pairs were found to have better fracture surface energy than the thermally bonded wafer

modified with a custom-designed ultrasonic bath (Advanced Sonic Processing) was programmed to perform layer-by-layer assembly. For each sample, five preparatory bilayers of polyamine±PAA (where polyamine = PAH, BPEI, or LPEI) followed by ten bilayers of polyamine/Ru dye were deposited at pH values of 2.5, 4.8, and 7.0. The preparatory bilayers were formed by dipping first for 20 min in the polyamine solution, followed by 1 min in pH-adjusted Milli-Q water, a 20 min dip in PAA solution, a 1 min dip in another pH-adjusted Milli-Q water bath, a 4 min soak in the ultrasonic bath, and another dip in a pH-adjusted Milli-Q bath before returning to the polyamine solution. Ru dye multilayers were built up much the same way. The Ru dye dip directly replaced the PAA dip in the above cycle but with three pH-adjusted Milli-Q water baths following the substrate's immersion in the negatively charged dye. The pH was kept constant between all the solutions and water baths. All polyelectrolytes were mixed up as 10 mM solutions in Milli-Q water on a repeat unit basis. HCl and NaOH were used to adjust the pH to the appropriate value.