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Zinc oxide, as an inexpensive anode material, has attracted less attention than other metal oxides due to its poor cycling stability. A rational design of ZnO nanostructures with well-controlled particle sizes and microstructures is essential in order to improve their stability and performance as electrodes for lithium ion batteries (LIBs). Here, we demonstrate a simple approach via atomic layer deposition (ALD) to synthesize ZnO quantum dots (QDs) on graphene layers, in which the size of the ZnO QDs can be controlled from 2 to 7 nm by ALD cycles. A strong relationship between size and electrochemical performance is observed, in which smaller sized QDs on graphene display enhanced electrochemical performance. A high reversible specific capacity of 960 mA h g−1 is achieved at a current density of 100 mA g−1 for 2 nm ZnO QDs, approaching to the theoretical value of ZnO as the LIB anode. The greatly enhanced cycling stability and rate performance of the ALD ZnO QD/graphene composite electrode can be attributed to the well-maintained structural integrity without pulverization upon electrochemical charge/discharge for ZnO QDs with the grain size below a critical value.

Amorphous SnO2 (a-SnO2) thin films were conformally coated onto the surface of reduced graphene oxide (G) using atomic layer deposition (ALD). The electrochemical characteristics of the a-SnO2/G nanocomposites were then determined using cyclic voltammetry and galvanostatic charge/discharge curves. Because the SnO2 ALD films were ultrathin and amorphous, the impact of the large volume expansion of SnO2 upon cycling was greatly reduced. With as few as five formation cycles best reported in the literature, a-SnO2/G nanocomposites reached stable capacities of 800 mAh g(-1) at 100 mA g(-1) and 450 mAh g(-1) at 1000 mA g(-1). The capacity from a-SnO2 is higher than the bulk theoretical values. The extra capacity is attributed to additional interfacial charge storage resulting from the high surface area of the a-SnO2/G nanocomposites. These results demonstrate that metal oxide ALD on high surface area conducting carbon substrates can be used to fabricate high power and high capacity electrode materials for lithium-ion batteries.

We present results on patterning microstructures using laser-guidance deposition of nanoparticles from particle-in-solvent suspensions. A laser beam axially confines and propels the particles inside a hollow optical fiber towards a substrate. Confining is provided by the gradient forces arising from light refraction or electrical forces on polarizable particles. The driving force results from the momentum conservation of photons scattered on particles. Polystyrene particles (100 and 400 nm in diameter) and gold particles (from 8 to 50 nm) with different surface organic functionality serve as a constructive material for fabrication of microstrips. In the experiments, the laser power varies from 0.1 to 1.6 W. The microstrips produced under different deposition conditions are studied using optical microscopy and atomic force microscopy. It was found that deposited polystyrene and gold particles form nanoclusters consisting of at least several particles. If deposited at an appropriate rate, such nanoclusters form multilayer microstrips of high particle density. The typical width of the microstrips ranges from less than 10 microns to 100 microns. This technique allows us to fabricate parallel arrays made of colloidal particles with different surface functionality, which seems to be an especially attractive approach for developing novel chemical and biological microsensors.

Uniform amorphous vanadium oxide films were coated on graphene via atomic layer deposition and the nano-composite displays an exceptional capacity of ~900 mA h g(-1) at 200 mAg(-1) with an excellent capacity retention at 1 A g(-1) after 200 cycles. The capacity contribution (1161 mA h g(-1)) from vanadium oxide only almost reaches its theoretical value.

Two laser-based direct-write techniques to guide particles from a mist source to a target substrate by laser beams were recently developed at Michigan Tech. The laser-guided direct-write (LGDW) technique uses a hollow optical fiber, while the laser-guided microsensor patterning (LGMP) technique uses a micrometer-sized aperture. The techniques are suggested to be utilized for patterning microstructures made of nanoparticles that are either crystallized from liquid precursors or directly deposited from nanoparticle-in-liquid suspensions. The computational results based on the paraxial Fraunhofer approximation of a Gaussian beam diffracted by a circular aperture and experimental measurements of corresponding deposition rate under different conditions suggest several factors for setup optimization of LGMP. The results indicate that among the most important factors are the aperture size relative to the laser beam-waist size and the divergence of the beam near the aperture. Examples of gold-thiolate, protein-coated polystyrene, and carbon-polymer composites deposition are presented.