Ying-Bing Jiang

An inorganic–organic proton exchange membrane for fuel cells with a controlled nanoscale pore structure

Proton exchange membrane fuel cells have the potential for applications in energy conversion and energy storage, but their development has been impeded by problems with the membrane electrode assembly. Here, we demonstrate that a silicon-based inorganic-organic membrane offers a number of advantages over Nafion--the membrane widely used as a proton exchange membrane in hydrogen fuel cells--including higher proton conductivity, a lack of volumetric size change, and membrane electrode assembly construction capabilities. Key to achieving these advantages is fabricating a silicon membrane with pores with diameters of approximately 5-7 nm, adding a self-assembled molecular monolayer on the pore surface, and then capping the pores with a layer of porous silica. The silica layer reduces the diameter of the pores and ensures their hydration, resulting in a proton conductivity that is two to three orders of magnitude higher than that of Nafion at low humidity. A membrane electrode assembly constructed with this proton exchange membrane delivered an order of magnitude higher power density than that achieved previously with a dry hydrogen feed and an air-breathing cathode.

Selective growth of Ge on Si(100) through vias of SiO2 nanotemplate using solid source molecular beam epitaxy

We demonstrate that Ge can be selectively grown on Si(100) through openings in a SiO2 nanotemplate by solid source molecular beam epitaxy. The selectivity relies on the thermal instability of GeO and SiO near 650 °C. Ge islands grow in the template windows and coalesce on top of the template, forming an epitaxial lateral overgrowth (ELO) layer. Cross-sectional transmission electron microscopy images show that the Ge seeds and the ELO layer are free of threading dislocations. Only stacking faults are generated but terminate within 70 nm of the Ge–Si interface, while twins along {111} planes are observed in the ELO layer. The threading-dislocation-free Ge seeds and ELO layer are attributed to epitaxial necking as well as Ge–Si intermixing at the interface.

Donor-acceptor biomorphs from the ionic self-assembly of porphyrins.

Microscale four-leaf clover-shaped structures are formed by self-assembly of anionic and cationic porphyrins. Depending on the metal complexed in the porphyrin macrocycle (Zn or Sn), the porphyrin cores are either electron donors or electron acceptors. All four combinations of these two metals in cationic tetra(N-ethanol-4-pyridinium)porphyrin and anionic tetra(sulfonatophenyl)porphyrin result in related cloverlike structures with similar crystalline packing indicated by X-ray diffraction patterns. The clover morphology transforms as the ionic strength and temperature of the self-assembly reaction are increased, but the structures maintain 4-fold symmetry. The ability to alter the electronic and photophysical properties of these solids (e.g., by altering the metals in the porphyrins) and to vary cooperative interactions between the porphyrin subunits raises the possibility of producing binary solids with tunable functionality. For example, we show that the clovers derived from anionic Zn porphyrins (electron donors) and cationic Sn porphyrins (electron acceptors) are photoconductors, but when the metals are reversed in the two porphyrins, the resulting clovers are insulators.

Formation trends in quantum dot growth using metalorganic chemical vapor deposition

We discuss the results of a growth matrix designed to produce high quantum dot (QD) density, defect-free QD ensembles, which emit at 1.3 μm using metalorganic chemical vapor deposition (MOCVD). In our study, we balance the nucleation rate and adatom surface migration to achieve high surface densities (1×1011 dots/cm2) and avoid QD coalescence or defects that commonly characterize MOCVD-grown QD ensembles designed for longer wavelength emission. Room-temperature photoluminescence (PL) spectra from corresponding surface QDs depend on QD size and density and show an emission wavelength up to 1600 nm. Ground-state PL from capped QDs is measured at 1.38 μm with a 40 meV linewidth. We demonstrate the ground-state 1.3 μm electroluminescence from a QD light-emitting diode structure grown on n-type GaAs.

Synthesis of Platinum Nanowheels Using a Bicellar Template

Disk-like surfactant bicelles provide a unique meso-structured reaction environment for templating the wet-chemical reduction of platinum(II) salt by ascorbic acid to produce platinum nanowheels. The Pt wheels are 496 +/-55 nm in diameter and possess thickened centers and radial dendritic nanosheets (about 2-nm in thickness) culminating in flared dendritic rims. The structural features of the platinum wheels arise from confined growth of platinum within the bilayer that is also limited at edges of the bicelles. The size of CTAB/FC7 bicelles is observed to evolve with the addition of Pt(II) complex and ascorbic acid. Synthetic control is demonstrated by varying the reaction parameters including metal salt concentration, temperature, and total surfactant concentration. This study opens up opportunities for the use of other inhomogeneous soft templates for synthesizing metals, metal alloys, and possibly semiconductors with complex nanostructures.

Heteroepitaxy of high-quality Ge on Si by nanoscale Ge seeds grown through a thin layer of SiO2

We demonstrate that high-quality Ge can be grown on Si covered with a thin layer of chemical SiO2. When the oxidized Si substrate is exposed to Ge molecular beam, 7-nm-wide seed pads form in the oxide layer and “touchdown” on the underlying Si. Upon continued exposure, Ge selectively grows on the seed pads rather than on SiO2, and the seeds coalesce to form an epitaxial lateral overgrowth (ELO) layer. The Ge ELO layer is characterized by transmission electron microscopy and etch-pit density (EPD). The Ge ELO layer is free of dislocation network, but stacking faults exist near the Ge-SiO2 interface. A fraction of these stacking faults propagate to the surface, resulting in EPD less than 2×106cm−2. The high quality Ge ELO layer is attributed to a high density of nanoscale Ge seed pads interspaced by 2–12-nm-wide SiO2 patches.

Tailoring Anisotropic Wetting Properties on Submicrometer-Scale Periodic Grooved Surfaces

The use of simple plasma treatments and polymer deposition to tailor the anisotropic wetting properties of one-dimensional (1D) submicrometer-scale grooved surfaces, fabricated using interferometric lithography in photoresist polymer films, is reported. Strongly anisotropic wetting phenomena are observed for as-prepared 1D grooved surfaces for both positive and negative photoresists. Low-pressure plasma treatments with different gas compositions (e.g., CHF(3), CF(4), O(2)) are employed to tailor the anisotropic wetting properties from strongly anisotropic and hydrophobic to hydrophobic with very high contact angle and superhydrophilic with a smaller degree of wetting anisotropy and without changing the structural anisotropy. The change of the surface wetting properties for these 1D patterned surfaces is attributed to a change in surface chemical composition, monitored using XPS. In addition, the initial anisotropic wetting properties on 1D patterned samples could be modified by coating plasma treated samples with a thin layer of polymer. We also demonstrated that the wetting properties of 1D grooved surfaces in a Si substrate could be tuned with similar plasma treatments. The ability to tailor anisotropic wetting on 1D patterned surfaces will find many applications in microfluidic devices, lab-on-a-chip systems, microreactors, and self-cleaning surfaces.

Strain-relieved, dislocation-free InxGa1−xAs∕GaAs(001) heterostructure by nanoscale-patterned growth

A strain-relieved, dislocation-free InxGa1−xAs layer is selectively grown on nanoscale SiO2-patterned GaAs(001) by molecular beam epitaxy. By localizing the epitaxial area to a periodic array of nanoscale circular holes opened in a SiO2 mask and allowing the InxGa1−xAs epilayers selectively grown on adjacent holes to coalesce over the SiO2 mask by lateral overgrowth, the strain of the resulting InxGa1−xAs layer (x=0.06) is relieved with a dramatically decreased generation of misfit dislocations. These experimental results qualitatively support the basic idea of the Luryi-Suhir proposal [Appl. Phys. Lett. 49, 140 (1986)].

Plasma torch production of macroscopic carbon nanotube structures

Abstract Analysis of the many studies of carbon nanotube formation in high-temperature ovens clearly indicates the key requirements of nanotube formation are an ‘atomic’ carbon source and a source of nanometal particles. We adapted this formulation to the high temperature (>3000 K) environment found in a low-power (

Ultra- Thin Conformal Pore-Sealing of Low-k Materials by Plasma-Assisted ALD

The implementation of porous ultralow k materials to the next generation of IC’s requires a practical pore-sealing technique, for which the deposition must be not only conformal to patterned features, but also nmthick so that the impact of this pore-sealing layer on the overall dielectric constant (k) is negligible. Atomic layer deposition (ALD) is the best choice to achieve these two points. However, regular ALD will penetrate into the internal porosity of a porous low k material, filling pores and drastically increasing the effective k value. Therefore, to seal the pores by ALD, internal deposition must be eliminated.