Jalal Rouhi

Physical properties of fish gelatin-based bio-nanocomposite films incorporated with ZnO nanorods

Well-dispersed fish gelatin-based nanocomposites were prepared by adding ZnO nanorods (NRs) as fillers to aqueous gelatin. The effects of ZnO NR fillers on the mechanical, optical, and electrical properties of fish gelatin bio-nanocomposite films were investigated. Results showed an increase in Youngs modulus and tensile strength of 42% and 25% for nanocomposites incorporated with 5% ZnO NRs, respectively, compared with unfilled gelatin-based films. UV transmission decreased to zero with the addition of a small amount of ZnO NRs in the biopolymer matrix. X-ray diffraction showed an increase in the intensity of the crystal facets of (10ī1) and (0002) with the addition of ZnO NRs in the biocomposite matrix. The surface topography of the fish gelatin films indicated an increase in surface roughness with increasing ZnO NR concentrations. The conductivity of the films also significantly increased with the addition of ZnO NRs. These results indicated that bio-nanocomposites based on ZnO NRs had great potentials for applications in packaging technology, food preservation, and UV-shielding systems.

Fast synthesis of multilayer carbon nanotubes from camphor oil as an energy storage material

Among the wide range of renewable energy sources, the ever-increasing demand for electricity storage represents an emerging challenge. Utilizing carbon nanotubes (CNTs) for energy storage is closely being scrutinized due to the promising performance on top of their extraordinary features. In this work, well-aligned multilayer carbon nanotubes were successfully synthesized on a porous silicon (PSi) substrate in a fast process using renewable natural essential oil via chemical vapor deposition (CVD). Considering the influx of vaporized multilayer vertical carbon nanotubes (MVCNTs) to the PSi, the diameter distribution increased as the flow rate decreased in the reactor. Raman spectroscopy results indicated that the crystalline quality of the carbon nanotubes structure exhibits no major variation despite changes in the flow rate. Fourier transform infrared (FT-IR) spectra confirmed the hexagonal structure of the carbon nanotubes because of the presence of a peak corresponding to the carbon double bond. Field emission scanning electron microscopy (FESEM) images showed multilayer nanotubes, each with different diameters with long and straight multiwall tubes. Moreover, the temperature programmed desorption (TPD) method has been used to analyze the hydrogen storage properties of MVCNTs, which indicates that hydrogen adsorption sites exist on the synthesized multilayer CNTs.

High-performance dye-sensitized solar cells based on morphology-controllable synthesis of ZnO-ZnS heterostructure nanocone photoanodes.

High-density and well-aligned ZnO–ZnS core–shell nanocone arrays were synthesized on fluorine-doped tin oxide glass substrate using a facile and cost-effective two-step approach. In this synthetic process, the ZnO nanocones act as the template and provide Zn2+ ions for the ZnS shell formation. The photoluminescence spectrum indicates remarkably enhanced luminescence intensity and a small redshift in the UV region, which can be associated with the strain caused by the lattice mismatch between ZnO and ZnS. The obtained diffuse reflectance spectra show that the nanocone-based heterostructure reduces the light reflection in a broad spectral range and is much more effective than the bare ZnO nanocone and nanorod structures. Dye-sensitized solar cells based on the heterostructure ZnO–ZnS nanocones are assembled, and high conversion efficiency (η) of approximately 4.07% is obtained. The η improvement can be attributed primarily to the morphology effect of ZnO nanocones on light-trapping and effectively passivating the interface surface recombination sites of ZnO nanocones by coating with a ZnS shell layer.

Annealing Heat Treatment of ZnO Nanoparticles Grown on Porous Si Substrate Using Spin-Coating Method

ZnO nanoparticles were successfully deposited on porous silicon (PSi) substrate using spin-coating method. In order to prepare PSi, electrochemical etching was employed to modify the Si surface. Zinc acetate dihydrate was used as a starting material in ZnO sol-gel solution preparation. The postannealing treatments were investigated on morphologies and photoluminescence (PL) properties of the ZnO thin films. Field emission scanning electron microscopy (FESEM) results indicate that the thin films composed by ZnO nanoparticles were distributed uniformly on PSi. The average sizes of ZnO nanoparticle increase with increasing annealing temperature. Atomic force microscopic (AFM) analysis reveals that ZnO thin films annealed at 500°C had the smoothest surface. PL spectra show two peaks that completely correspond to nanostructured ZnO and PSi. These findings indicate that the ZnO nanostructures grown on PSi are promising for application as light emitting devices.

Fabrication of nanogap electrodes via nano-oxidation mask by scanning probe microscopy nanolithography

In this study, a simple technique was introduced for the fabrication of nanogap electrodes by using nano-oxidation scanning probe microscopy lithography with a Cr/Pt coated silicon tip. Silicon electrodes with a gap of sub-31 nm were fabricated successfully by this technique. The current-voltage measurements (I-V) of the electrodes demonstrated excellent insulating characteristics. This technique is simple, controllable, inexpensive, and faster than common methods. The results showed that silicon electrodes have a great potential for the fabrication of single molecule transistors, single electron transistors, and other nanoelectronic devices.

Controlling the shape and gap width of silicon electrodes using local anodic oxidation and anisotropic TMAH wet etching

A simple method for fabricating silicon electrodes with various shapes and gap widths was designed using the special properties of anisotropic tetramethylammonium hydroxide (TMAH) wet etching and local anodic oxidation (LAO). A statistical system was used for the optimization of the parameters of the LAO process to facilitate a better understanding and precise analysis of the process. Analyses of the interaction effects among the significant factors of LAO showed that the relative humidity and applied voltage were interdependent. They had the strongest interaction effect on the dimensions of the oxide mask. TMAH with a concentration of 25% was used as an etchant solution in (1 0 0) silicon with a rectangular oxide mask. The observed undercutting at convex corners, tip shape of emitters and gap widths of electrodes were exactly consistent with theoretical studies. Combination of the LAO method and anisotropic TMAH wet etching was successfully used to fabricate Si nano-gap electrodes. This fabrication method of sharp and round tip emitters was simple, controllable and faster than common techniques. These results indicate that the method can be a new approach for studying the electrical properties of nano-gap electrodes.

Growth of Vertically Aligned ZnO Nanorods Arrays by Hydrothermal Method

Well-aligned ZnO nanorod arrays with different average diameters were grown on silicon (100) substrates by hydrothermal method via the precursors of zinc nitrate hexahydrate (Zn (NO3)2 .6H2O) and Hexamethylenetetramine (C6 H12N4) with equal molar concentration at 0.025 mol/l and 0.05 mol/l. The ZnO nanorods were characterized by X-ray diffraction (XRD) and field emission Scanning electron microscopy (FE-SEM). XRD results indicated that all the ZnO nanorods were preferentially grown along [000 direction (c-axis). field emission Scanning electron microscopy images showed that the well-faceted hexagonal ZnO nanorods were grown vertically from the silicon (100) substrates.

Synthesis of needle-shape ZnO-ZnS core-shell heterostructures and their optical and field emission properties

Well-aligned ZnO-ZnS core-shell nano-needle arrays were synthesized using a simple aqueous solution approach to investigate the optical and field emission properties of heterostructure materials. The photoluminescence of the core-shell nano-needles exhibits a distinct enhancement compared with that of uncoated ZnO nano-needles. The UV-vis spectra show that the ZnS shell layer enhances the optical absorption of ZnO nano-needles by decreasing the interface band gap, which indicates the potential application of heterostructures in photovoltaic and solar cells. The core-shell nano-needles exhibit a remarkably high field enhancement factor of 3.74 × 103, a low turn-on field of 2.31 V/μm, and a high time stability. These findings show that the construction of core-shell heterostructure can efficiently improve the field emission performance of ZnO nano-needles, which is a promising route for the development of novel nanoemitters with controllable morphology and as suitable shell materials for heterostructures.

Developing high-sensitivity ethanol liquid sensors based on ZnO/porous Si nanostructure surfaces using an electrochemical impedance technique

ZnO nanostructures were synthesized on porous Si (PSi) substrates using the thermal catalytic-free immersion method. Crack-like ZnO nanostructures were formed on the bare, sponge-like PSi structures. An approach to fabricate chemical sensors based on the ZnO/PSi nanostructure arrays that uses an electrochemical impedance technique is reported. Sensor performance was evaluated for ethanol solutions by the morphology and defect structures of the ZnO nanostructure layer. Results indicate that the ZnO/PSi nanostructure chemical sensor exhibits rapid and high response to ethanol compared with a PSi nanostructure sensor because of its small particle size and an oxide layer acting as a capacitive layer on the PSi nanostructure surface.

Boron-doped amorphous carbon film grown by bias assisted pyrolysis chemical vapor deposition

Boron-doped amorphous carbon (a-C:B) films were successfully synthesized via a bias-assisted pyrolysis-chemical vapor deposition (CVD). The effect of substrate bias on the thickness, surface morphology, electrical properties of a-C:B film were investigated. The AFM measurements and conductivity result show the surface roughness and resistivity of a-C:B films decreases with increasing substrate bias from 0 to −20V. The fabricated films were evaluated for use in photovoltaic solar cells. The fabricated solar cell with the configuration of Au/p-C:B/n-Si/Au achieved conversion efficiency (η) of 1.431% at applied bias voltage of −20V. This result showed the successful interstitial doping of boron in the amorphous carbon films deposited by this method.