SCANNING TUNNELING MICROSCOPY STUDIES OF GROWTH MEDIUM & TEMPERATURE DEPENDENT STRUCTURAL PHASES OF ALKANETHIOL SELF-ASSEMBLED MONOLAYERS, REACTIVE SELF-ASSEMBLED MONOLAYERS, & FLAT GOLD NANOPARTICLE/INDIUM TIN OXIDE SUBSTRATES AND A SCANNING SURFAC

Abstract

Self-assembled monolayers (SAMs) of alkanethiolates on Au(111) represent promising platforms to study the molecular surfaces and interfaces for applications ranging from molecular electronics, nanophotonics to biology. Understanding the effect of growth conditions on SAMs particularly on their structural features is important from both fundamental and applied points of view. Knowledge of SAM structural features and structural phase transitions provides important insights into molecular packing for the control of the molecular self-assembly.

We compared SAMs grown from different media, from 1 mM C10 solution in decalin, hexadecane and triethylene glycol and from C10 vapor. We present a molecularly-resolved scanning tunneling microscopy study showing the dependence of the SAM structure on the growth conditions. We have established conditions for making samples almost vacancy islands (VI) free with very large SAM domains of (2√3 × 3)rect. superstructure and (√3 × 4√3)R30° striped phase and investigated the orientation of low-index step edges of Au(111) for normal and striped-phase SAMs. We showed that the striped phase is stable to converting to (2√3 × 3)rect. below 40 °C.

We demonstrate that flat gold nanoparticles (FGNPs) supported on indium tin oxide glass (ITO) are excellent substrates for molecularly-resolved STM imaging of alkanethiol SAMs. Nanoparticles were characterized using STM, TEM, and SEM techniques. Surface treatment techniques, Ar/O2 and H2 plasma treatments, dry thermal annealing and exposures to UV/O3, were used to prepare the surfaces of FGNPs supported on ITO and Au/mica substrates for high-resolution STM imaging of alkanethiol SAMs.

We developed a convergent approach to functionalize SAM surfaces. Ordered mixed monolayers comprised of alkanethiols and azidoalkanethiols islands are formed and subsequent IMesCulBr catalyzed [3+2] "click" cycloaddition reaction with substituted alkyne introduced dilute substituent onto the ordered surface.

Mechanical stress is one of the major factors in current design and manufacture of very large scale integrated (VLSI) devices. Mechanical stress in deep sub-micron silicon technologies can drastically alter carrier mobility (e.g., approximately 25% dependent on device geometry). This affects the device performance. Current in-line production stress metrology is conducted only at a wafer monitor level. The available stress measurement techniques such as micro-Raman spectroscopy, nano beam diffraction (NBD), converging electron beam diffraction (CEBD) either do not have required resolution or they require complex data interpretation. We present a method for measuring mechanical stress in deep sub-micron silicon devices with high spatial resolution using scanning Kelvin probe force microscopy and scanning surface photovoltage (SSPVM) techniques.