Xiaozhu Zhou

Electrochemical deposition of ZnO nanorods on transparent reduced graphene oxide electrodes for hybrid solar cells

Monocrystalline ZnO nanorods (NRs) with high donor concentration are electrochemically deposited on highly conductive reduced graphene oxide (rGO) films on quartz. The film thickness, optical transmittance, sheet resistance, and roughness of rGO films are systematically studied. The obtained ZnO NRs on rGO films are characterized by X-ray diffraction, transmission electron microscopy, photoluminescence, and Raman spectra. As a proof-of-concept application, the obtained ZnO NRs on rGO are used to fabricate inorganic-organic hybrid solar cells with layered structure of quartz/rGO/ZnO NR/poly(3-hexylthiophene)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (P3HT/PEDOT:PSS)/Au. The observed power conversion efficiency (PCE, eta), approximately 0.31%, is higher than that reported in previous solar cells by using graphene films as electrodes. These results clearly demonstrate that rGO films with a higher conductivity have a smaller work function and show a better performance in the fabricated solar cells.

Synthesis of hexagonal close-packed gold nanostructures

Solid gold is usually most stable as a face-centred cubic (fcc) structure. To date, no one has synthesized a colloidal form of Au that is exclusively hexagonal close-packed (hcp) and stable under ambient conditions. Here we report the first in situ synthesis of dispersible hcp Au square sheets on graphene oxide sheets, which exhibit an edge length of 200-500 nm and a thickness of ~ 2.4 nm (~ 16 Au atomic layers). Interestingly, the Au square sheet transforms from hcp to a fcc structure on exposure to an electron beam during transmission electron microscopy analysis. In addition, as the square sheet grows thicker (from ~ 2.4 to 6 nm), fcc segments begin to appear. A detailed experimental analysis of these structures shows that for structures with ultrasmall dimensions (for example, <~ 6 nm thickness for the square sheets), the previously unobserved pure hcp structure becomes stable and isolable.

Interfacing live cells with nanocarbon substrates.

Nanocarbon materials, including single-walled carbon nanotubes (SWCNTs) and graphene, promise various novel biomedical applications (e.g., nanoelectronic biosensing). In this Letter, we study the ability of SWCNT networks and reduced graphene oxide (rGO) films in interfacing several types of cells, such as neuroendocrine PC12 cells, oligodendroglia cells, and osteoblasts. It was found that rGO is biocompatible with all these cell types, whereas the SWCNT network is inhibitory to the proliferation, viability, and neuritegenesis of PC12 cells, and the proliferation of osteoblasts. These observations could be attributed to the distinct nanotopographic features of these two kinds of nanocarbon substrates.

Conjugated-Polyelectrolyte-Functionalized Reduced Graphene Oxide with Excellent Solubility and Stability in Polar Solvents

Conjugated-polyelectrolyte (CPE)-functionalized reduced graphene oxide (rGO) sheets are synthesized for the first time by taking advantage of a specially designed CPE, PFVSO(3), with a planar backbone and charged sulfonate and oligo(ethylene glycol) side chains to assist the hydrazine-mediated reduction of graphene oxide (GO) in aqueous solution. The resulting CPE-functionalized rGO (PFVSO(3)-rGO) shows excellent solubility and stability in a variety of polar solvents, including water, ethanol, methanol, dimethyl sulfoxide, and dimethyl formamide. The morphology of PFVSO(3)-rGO is studied by atomic force microscopy, X-ray diffraction, and transmission electron microscopy, which reveal a sandwich-like nanostructure. Within this nanostructure, the backbones of PFVSO(3) stack onto the basal plane of rGO sheets via strong pi-pi interactions, while the charged hydrophilic side chains of PFVSO(3) prevent the rGO sheets from aggregating via electrostatic and steric repulsions, thus leading to the solubility and stability of PFVSO(3)-rGO in polar solvents. Optoelectronic studies show that the presence of PFVSO(3) within rGO induces photoinduced charge transfer and p-doping of rGO. As a result, the electrical conductivity of PFVSO(3)-rGO is not only much better than that of GO, but also than that of the unmodified rGO.

Label-free, electrochemical detection of methicillin-resistant staphylococcus aureus DNA with reduced graphene oxide-modified electrodes

Reduced graphene oxide (rGO)-modified glassy carbon electrode is used to detect the methicillin-resistant Staphylococcus aureus (MRSA) DNA by using electrochemical impedance spectroscopy. Our experiments confirm that ssDNA, before and after hybridization with target DNA, are successfully anchored on the rGO surface. After the probe DNA, pre-adsorbed on rGO electrode, hybridizes with target DNA, the measured impedance increases dramatically. It provides a new method to detect DNA with high sensitivity (10(-13)M, i.e., 100 fM) and selectivity.

Reduced graphene oxide films used as matrix of MALDI-TOF-MS for detection of octachlorodibenzo-p-dioxin.

A reduced graphene oxide (rGO) film was used as the matrix in the matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF-MS) for the detection of octachlorodibenzo-p-dioxin (OCDD) with a detection weight as low as 500 pg.

Chemically Functionalized Surface Patterning

Patterning substrates with versatile chemical functionalities from micro- to nanometer scale is a long-standing and interesting topic. This review provides an overview of a range of techniques commonly used for surface patterning. The first section briefly introduces conventional micropatterning tools, such as photolithography and microcontact printing. The second section focuses on the currently used nanolithographic techniques, for example, scanning probe lithography (SPL), and their applications in surface patterning. Their advantages and disadvantages are also demonstrated. In the last section, dip-pen nanolithography (DPN) is emphatically illustrated, with a particular stress on the patterning and applications of biomolecules.

Electrochemical deposition of Cl-doped n-type Cu2O on reduced graphene oxide electrodes

Reduced graphene oxide (rGO) electrodes can be applied for the electrochemical deposition of various semiconductor oxides. In this study, we demonstrate the electrochemical deposition of Cl-doped n-type Cu2O (Cl–Cu2O) on rGO electrodes. The structure and properties of the deposited Cl–Cu2O have been investigated extensively. Moreover, the effect of Cl doping on the carrier concentration and photocurrent of Cl–Cu2O has also been investigated. Our study shows significant implications in tailoring the properties of materials deposited on rGO electrodes by using electrochemical methods.

Shape-Selective Deposition and Assembly of Anisotropic Nanoparticles

We report the large-area assembly of anisotropic gold nanoparticles into lithographically defined templates with control over their angular position using a capillary force-based approach. We elucidate the role of the geometry of the templates in the assembly of anisotropic nanoparticles consisting of different shapes and sizes. These insights allow us to design templates that immobilize individual triangular nanoprisms and concave nanocubes in a shape-selective manner and filter undesired impurity particles from a mixture of triangular prisms and other polyhedra. Furthermore, by studying the assembly of two particles in the same template, we elucidate the importance of interparticle forces in this method. These advances allow for the construction of face-to-face and edge-to-edge nanocube dimers as well as triangular nanoprism bowtie antennas. As an example of the fundamental studies enabled by this assembly method, we investigate the surface-enhanced Raman scattering (SERS) of face-to-face concave cube dimers both experimentally and computationally and reveal a strong polarization dependence of the local field enhancement.

Capillary force-driven, large-area alignment of multi-segmented nanowires.

We report the large-area alignment of multi-segmented nanowires in nanoscale trenches facilitated by capillary forces. Electrochemically synthesized nanowires between 120 and 250 nm in length are aligned and then etched selectively to remove one segment, resulting in arrays of nanowires with precisely controlled gaps varying between 2 and 30 nm. Crucial to this alignment process is the dispersibility of the nanowires in solution which is achieved by chemically modifying them with hexadecyltrimethylammonium bromide. We found that, even without the formation of an ordered crystalline phase at the droplet edges, the nanowires can be aligned in high yield. To illustrate the versatility of this approach as a nanofabrication technique, the aligned nanowires were used for the fabrication of arrays of gapped graphene nanoribbons and SERS substrates.