Iujin Blagidze

In this study, we electroplate Cu electrode on Si substrate to realize a large-area vacuum nanogap for electron tunneling. We used cathode coating, cathode rotation, asymmetric current regime, and electrolyte temperature stabilization to obtain the regular geometry of the Cu electrode and reduce its internal tension. Subsequently, internal tension was altered to achieve the predefined surface curvature (concave or convex). For 12-mm diameter Ag/Cu electrode, we achieve the curvature of 40 nm/mm from the Ag side. Reduction of the electrode diameter to 3 mm allowed curvature as low as of 2.5 nm/mm. It also allowed fabrication of two conformal electrodes having a nanogap of less than 5 nm wide, over the area of 7 mm2 . Such electrodes can be used for efficient energy conversion and cooling in the mixed thermionic and thermotunneling regime.

In this study, we regulate adhesion between thin metal films to produce a large-area vacuum nanogap for electron tunneling. Multilayer structures comprising thin metal films with adjustable adhesion were fabricated. The Cu/Ag/Ti/Si structures were grown on Si substrates and include thin Ti and Ag films and a thick Cu layer. The Ag and Ti films were deposited on the Si substrate under vacuum, and a thick Cu layer was subsequently electroplated onto the Ag surface. Later, the sandwich was separated and a vacuum nanogap was opened to produce two Ag/Cu and Ti/Si conformal electrodes. The adhesion strength between the Ti and Ag films was precisely adjusted by exposing the structures to dry O2 after Ti growth but before Ag growth. The resulting adhesion needed to be sufficiently high to allow electroplating of Cu and sufficiently low to allow subsequent separation. Either heating or cooling was used to separate the sandwiches. The structures separated as a result of the different thermal expansion parameters of the Si and Cu electrodes and the low adhesion between the Ti and Ag layers. After separation, the Ag and Ti surfaces were analyzed optically using a Michelson interferometer. Adhesion regulation and optimization of the electroplating regime allowed fabrication of two conformal electrodes with a nanogap smaller than 5 nm and an area larger than 7 mm2. Such electrodes can be used for efficient energy conversion and cooling in the mixed thermionic and thermotunneling regime.

We report measurements of dynamic (a.c.) electrical conductivity in borosilicate glasses doped with cadmium sulfoselenide and copper and silver iodides in a wide temperature range below the glass transition temperature Tg and at different frequencies. The concentration of the mobile dopant ions is governed by specific heat treatment conditions of the glass samples leading to a creation of the CdSSe, AgI and CuI semiconductor nanocrystals. Investigations include different cases from a full solution of the dopant ions coming from a dissociation of the dopants during the glass preparation to their almost complete incorporation into the nanocrystals in the glass matrix. At temperatures higher than 150 °C–200 °C the a.c. conductivity in all the examined glasses exhibits the Arrhenius behavior. In this temperature range the mixed mobile ion effect is detected: the doped glasses have the low values of the conductivity compared to the undoped ones. In the low temperature range only weak temperature dependence is detected for all the samples. The mixed mobile ion effect is still presented for the CdSSe-doped glasses, whereas the AgI- and CuI-doped glasses exhibit the classical MMIE which is essentially absent at low temperatures.