Theoretical and Experimental Analysis of Surface Roughness and Adhesion Forces of MEMS Surfaces Using a Novel Method for Making a Compound Sputtering Target

Achieving a compound thin film with uniform thickness and high purity has always been a challenge in the applications concerning micro electro mechanical systems (MEMS). Controlling the adhesion force in micro/nanoscale is also critical. In the present study, a novel method for making a sputtering compound target is proposed for coating Ag–Au thin films with thicknesses of 120 and 500 nm on silicon substrates. The surface topography and adhesion forces of the samples were obtained using atomic force microscope (AFM). Rabinovich and Rumpf models were utilized to measure the adhesion force and compare the results with the obtained experimental values. It was found that the layer with a thickness of 500 nm has a lower adhesion force than the one with 120 nm thickness. The results further indicated that due to surface asperity radius, the adhesion achieved from the Rabinovich model was closer to the experimental values. This novel method for making a compound sputtering target has led to a lower adhesion force which can be useful for coating microgripper surfaces.

Electronic structures and optical characteristics of fluorescent pyrazinoquinoxaline assemblies and Au interfaces

Understanding the excitonic processes at the interfaces of fluorescent π-conjugated molecules and metal electrodes is important for both fundamental studies and emerging applications. Adsorption configurations of molecules on metal surfaces significantly affect the physical characteristics of junctions as well as molecules. Here, the electronic structures and optical properties of molecular assemblies/Au interfaces were investigated using scanning probe and photoluminescence microscopy techniques. Scanning tunneling microscopy images and tunneling conductance spectra suggested that the self-assembled molecules were physisorbed on the Au surface. Visible-range photoluminescence studies showed that Au thin films modified the emission spectra and reduced the lifetime of excitons. Surface potential maps, obtained by Kelvin probe force microscopy, could visualize electron transfer from the molecules to Au under illumination, which could explain the decreased lifetime of excitons at the molecule/Au interface.

Electron Irradiation Effects in Au thin Flms

Room temperature 200 keV electron irradiation effects on the area retraction behavior presented by 6.75 nm thick Au thin films deposited over a self-standing SiO 2 / silicon nitride membrane are investigated as a function of the irradiation fluence Φ. The as-deposited films already contain void discontinuities. The void growth behavior is investigated considering irradiation and thermally-induced surface atoms’ migration. The film’s coverage area A(Φ) and void perimeter P(Φ), obtained via Transmission Electron Microscopy observations, allow for calculating the atomic displacement causing the area retraction. This data is compared with model calculations of irradiation and thermally-induced atomic fluxes. The results demonstrate that the balance between the thermal and irradiation processes strongly depends on the choice of the surface thermal diffusivity values, which present large discrepancies in the literature. Our results suggest that irradiation-induced atomic displacements follow the same thermodynamic driving forces acting in thermal processes. The work also discloses a new method to investigate surface atoms’ behavior and promote microstructural modifications at room or lower temperatures.