NANOENGINEERING

Professors Chang, Cohen, Christofides, Hicks, Monbouquette, Orkoulas and Nobe

Polymerized membranes or vesicles find applications in the fields of separation, chromatography, and sensing.  The Cohen group works in the area of macromolecular and nano-surface engineering of polymer and inorganic surfaces. Research on surface chemistry and physics is the foundation of Dr. Cohen's quest to develop more efficient and selective membranes and sorption resins, design new molecular chemical sensors, biocompatible surfaces, and manipulate heterogeneous surface crystallization processes. 

AFM Image of silicon wafer surface modified by graft polymerization of poly(vinyl acetate). Image area: 300 x 300 nm; Vertical height scale: 10 nm 

Molecular modeling and experimental investigations are geared towards understanding the structure of silylated and graft-polymerized surfaces (e.g., topology, conformation and distribution) and devising physical and chemical methods (e.g., graft polymerization and self-assembly) to control surface properties.  A recent major accomplishment of Dr. Cohen's group is a patented ceramic-polymer composite membrane.  This membrane, with a nano-structured separation layer, has proven effective in protein ultrafiltration and pervaporation separation of organic-organic and organic-aqueous mixtures. 

 Membrane Separation Technology

Professors Friedlander and Christofides are collaborating on basic studies of the synthesis of nanoparticles and their aggregates by gas-phase (aerosol) processes.  Aerosol processes are widely used in industry to manufacture additives and fillers incorporated in polymers and rubber.  Currently there is much interest in the synthesis of metal oxide nanoparticles for advanced materials such as superplastic ceramics and photocatalysts.  At UCLA we have discovered that chain aggregates of nanoparticles are elastic under certain conditions.  This property may explain the remarkable effects that nanoparticle additives such as fumed silica and carbon black have on the properties of conventional polymers such as rubber, and it may also be of value in the fabrication of flexible coatings.  Multiscale models are developed to explain experimental discoveries and to optimize the operation of industrial-scale nanoparticle systems.

Professor Nobe also focuses on investigating physical properties of electrodeposited quantum dots, nanomagnets, nanowires (10 to 400 nm diam. with aspect ratios up to 18,000), nanostructured multilayers, and metal oxide and conducting polymer supercapacitors.  The figure shows an example of an electrochemical nano system (ENS) where cobalt nanowires were electrodeposited from anodized alumina templates. 

Electrodeposited cobalt nanowires (200 nm diam., 60 mm long) from anodized alumina.

Molecular engineering of innovative systems that mimic biological systems is researched to solve technological problems.  Since the direct manipulation of individual molecules presents obvious technological difficulties, much of the research has focused on self-assembling systems.  For example, Professor Monbouquette's group has borrowed an approach that magnetobacteria use to produce the magnetite particles needed for magnetotaxis in the synthesis of semiconductor nanoparticles.  Size monodisperse, 100-nm-diameter phospholipid vesicles serve as compartments for synthesis of <10-nm-diameter II-VI semiconductor nanocrystals of tightly controlled size and composition.  These nanoparticles exhibit size-dependent physical properties due to quantum confinement of electrons.  Size and surface-engineered particles may find applications in lasers, flat-panel displays, and quantum computing.  Monbouquette's group is also pursuing the use of quantum dots in creating surfaces with a feature size of 2-3 nm.

Electrophoretically mobile, photocatalytic CdS 2dots "draw" trails of reacted ligands on an atomically smooth substrate.

Professor Chang's group is working on atomic layer deposition (ALD) to engineer nanometer thin films and nanolaminates with atomic resolution and controllability.   Atomic layer deposition is typically referred to a binary chemical reaction sequence where the surface reaction of each chemical precursor is self-terminating.  In each half reaction, a gas phase chemical precursor reacts with a surface functional group and the reaction proceeds until all the surface functional groups have been replaced with the other functional group.  Since these half reactions are self-limiting, growth of thin film beyond one monolayer is not possible once all surface functional groups are reacted.  Films are deposited by repetitive application of a single layer deposition sequence. Highly uniform, conformal, and stoichiometric films can be easily synthesized, for example, nanolaminates can be formed through the use of multiple chemical precursors in alternating reaction sequences.  ALD has been used to deposit metals, metal oxides, metal nitrides, semiconductors, transparent conductive oxides, and ferroelectric materials, with potential applications in microelectronics, membrane, sensor, bioceramic, and catalysis. 

Atomic Layer Deposition Yielding Atomically Smooth Nanometer Thin Films.   

Professor Hicks' group has developed a method of simulating reactions on compound semiconductor surfaces using molecular cluster calculations with density functional theory.  Using this method, a cluster model for a gallium arsenide surface has been developed, which identified all the reaction sites on the surface as being an arsenic dimer and two second-layer gallium atoms.  Each arsenic dangling bond is filled with a pair of electrons, while each gallium dangling bond is empty, in excellent agreement with experimental observations.  The most exciting result from this work is the prediction of the vibrational frequencies of the optimized clusters and their excellent comparison with infrared data.  This unique capability allows a definitive assignment of the observed vibrational bands to specific adsorption sites.  This method is currently being applied to the study of surface reaction mechanisms for organometallic precursors.