Seth Thomas Taylor

Self-assembly of an organic–inorganic block copolymer for nano-ordered ceramics

Self-assembly is a promising approach for achieving controlled nanoscale architectures in ceramics. The addition of ceramic-forming precursors to templating agents such as self-assembled surfactants or organic block copolymers (BCPs) has thus far been the primary route to forming ordered nanoporous oxides1,2,3,4,5 and nanostructured non-oxide ceramics6,7,8,9. In spite of its viability, however, this approach has several intrinsic shortcomings, including: (1) stringent requirements for amphiphilicity between template and precursor, lack of which may lead to macro-phase separation and loss of nano-scale order; (2) morphologies that can change uncontrollably with varying amounts of added ceramic precursor. Here we report a novel single-source ceramic precursor, based on a hybrid organic–inorganic BCP of polynorbornene–decaborane, that enables the formation of ordered ceramic nanostructures with tunable morphology and composition. In particular, we describe the synthesis of nanostructured boron carbonitride and mesoporous boron nitride, the latter of which exhibits the highest reported surface area for this material to date.

Strain dependent facet stabilization in selective-area heteroepitaxial growth of GaN nanostructures

We report on the selective-area heteroepitaxy and facet evolution of submicron GaN islands on GaN-sapphire, AlN-sapphire, and bare sapphire substrates. It is shown that strain due to the lattice mismatch between GaN and the underlying substrate has a significant influence on the final morphology and faceting of submicron islands. Under identical metalorganic chemical vapor deposition growth parameters, islands with low or no mismatch strain exhibit pyramidal morphologies, while highly strained islands evolve into prismatic shapes. Furthermore, islands grown with relatively low compressive mismatch strain yield more uniform arrays of pyramids as compared to the nonstrained, homoepitaxially grown crystals. It is proposed that the strain dependency of Ehrlich-Schwoebel barriers across different crystallographic planes could potentially account for the observed morphologies during selective area growth of GaN islands.

Epitaxial growth of 20 nm InAs and GaAs quantum dots on GaAs through block copolymer templated SiO2 masks

We report on selective area growth of InAs and GaAs quantum dots (QDs) on GaAs through ∼20 nm SiO2 windows prepared by block copolymer lithography. We discuss the mechanisms of growth through these masks, highlighting the variation of the resulting morphology (dot size, spacing, uniformity, and areal density) as a function of growth parameters. We have obtained highly uniform arrays of InAs and GaAs QDs with mean diameters and areal densities of 20.6 nm and 1×1011 cm−2, respectively. We have also investigated the optical characteristics of these QDs as a function of temperature and drawn correlations between the optical response and their crystalline quality.

Infrared p-i-n photodiodes based on InAs quantum dots grown on 20 nm patterned GaAs

We report on selective area growth of InAs quantum dots on GaAs substrates patterned with a hexagonal array of 20 nm pores using block copolymer lithography. We discuss the mechanisms of growth, highlighting the variation in the resulting morphology as a function of nucleation enhancing AlGaAs layers. We also evaluate the optoelectronic performance of p-i-n photodiodes based on single layer nanopatterned grown InAs quantum dot devices. At low to moderate reverse biases, we observe room temperature photoresponse in both near- and mid-IR regimes. At high biases, we observe strong avalanche effects in the mid-IR range with a gain factor of ∼4000.

Heterogeneous integration of semiconducting and carbide nanowires on Si substrates

Integration of nanowires onto foreign substrates, and in functional devices, is widely recognized as a significant hurdle to further development of nanosystems based on quasi-one dimensional nanostructures. We describe methods for directly integrating relevant nanostructures on technologically relevant Si substrates using vapor phase synthesis of the nanowires. It is shown that ZnO nanowires may be directly integrated onto Si substrates containing patterned metal lines. Preferential growth from the edge of the metal lines has been achieved. We also show that growth of refractory transition metal carbides is also possible using catalytic growth. The electrical properties of such systems are also discussed. Finally, methods of integrating nanowires vertically on a Si substrate are also described.