Mohamad Rusop Mahmood

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.

Growth of High-Density Zinc Oxide Nanorods on Porous Silicon by Thermal Evaporation

The formation of high-density zinc oxide (ZnO) nanorods on porous silicon (PS) substrates at growth temperatures of 600–1000 °C by a simple thermal evaporation of zinc (Zn) powder in the presence of oxygen (O2) gas was systematically investigated. The high-density growth of ZnO nanorods with (0002) orientation over a large area was attributed to the rough surface of PS, which provides appropriate planes to promote deposition of Zn or ZnOx seeds as nucleation sites for the subsequent growth of ZnO nanorods. The geometrical morphologies of ZnO nanorods are determined by the ZnOx seed structures, i.e., cluster or layer structures. The flower-like hexagonal-faceted ZnO nanorods grown at 600 °C seem to be generated from the sparsely distributed ZnOx nanoclusters. Vertically aligned hexagonal-faceted ZnO nanorods grown at 800 °C may be inferred from the formation of dense arrays of ZnOx clusters. The formation of disordered ZnO nanorods formed at 1000 °C may due to the formation of a ZnOx seed layer. The growth mechanism involved has been described by a combination of self-catalyzed vapor-liquid-solid (VLS) and vapor-solid (VS) mechanism. The results suggest that for a more precise study on the growth of ZnO nanostructures involving the introduction of seeds, the initial seed structures must be taken into account given their significant effects.

Seed/catalyst-free vertical growth of high-density electrodeposited zinc oxide nanostructures on a single-layer graphene

We report the seed/catalyst-free vertical growth of high-density electrodeposited ZnO nanostructures on a single-layer graphene. The absence of hexamethylenetetramine (HMTA) and heat has resulted in the formation of nanoflake-like ZnO structure. The results show that HMTA and heat are needed to promote the formation of hexagonal ZnO nanostructures. The applied current density plays important role in inducing the growth of ZnO on graphene as well as in controlling the shape, size, and density of ZnO nanostructures. High density of vertically aligned ZnO nanorods comparable to other methods was obtained. The quality of the ZnO nanostructures also depended strongly on the applied current density. The growth mechanism was proposed. According to the growth timing chart, the growth seems to involve two stages which are the formation of ZnO nucleation and the enhancement of the vertical growth of nanorods. ZnO/graphene hybrid structure provides several potential applications in electronics and optoelectronics such as photovoltaic devices, sensing devices, optical devices, and photodetectors.

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.

Seed/catalyst-free growth of zinc oxide nanostructures on multilayer graphene by thermal evaporation

We report the seed/catalyst-free growth of ZnO on multilayer graphene by thermal evaporation of Zn in the presence of O2 gas. The effects of substrate temperatures were studied. The changes of morphologies were very significant where the grown ZnO structures show three different structures, i.e., nanoclusters, nanorods, and thin films at 600°C, 800°C, and 1,000°C, respectively. High-density vertically aligned ZnO nanorods comparable to other methods were obtained. A growth mechanism was proposed based on the obtained results. The ZnO/graphene hybrid structure provides several potential applications in electronics and optoelectronics.

Performance of an Ultraviolet Photoconductive Sensor Using Well-Aligned Aluminium-Doped Zinc-Oxide Nanorod Arrays Annealed in an Air and Oxygen Environment

Ultraviolet (UV) photoconductive sensors were fabricated using an aluminium (Al)-doped zinc-oxide (ZnO) nanorod array with a diameter between 40 and 150 nm and thickness of approximately 1.1 µm. The nanorod arrays were prepared using a sonicated sol–gel immersion and annealed at 500 °C under different ambient conditions of air and oxygen. The annealing process induced the formation of nanoholes on the nanorod surfaces, which increased the nanorod surface area. The nanoholes existed in larger quantities on the nanorod surfaces annealed in air compared with the nanorods annealed in an oxygen environment. This condition reduced the rise and decay time constants of the air-annealed UV sensor. However, the sample annealed in an oxygen ambient shows the highest responsivity of 1.55 A/W for UV light (365 nm, 5 mW/cm2) under a 10 V bias mainly due to defect reduction and improvement in stoichiometric properties. To the best of our knowledge, a UV photoconductive sensor using this ZnO nanostructure has not yet been reported.

Effects of annealing environments on the solution-grown, aligned aluminium-doped zinc oxide nanorod-array-based ultraviolet photoconductive sensor

We have fabricated metal-semiconductor-metal- (MSM-) type ultraviolet (UV) photoconductive sensors using aluminium- (Al-) doped zinc oxide (ZnO) nanorod arrays that were annealed in different environments: air, oxygen, or a vacuum. The Al-doped ZnO nanorods had an average diameter of 60 nm with a thickness of approximately 600nm that included the seed layer (with thickness ∼200 nm). Our results show that the vacuum-annealed nanorod-array-based UV photoconductive sensor has the highest photocurrent value of 2.43 × 10-4 A. The high photocurrent is due to the high concentration of zinc (Zn) interstitials in the vacuum-annealed nanorod arrays. In contrast, the oxygen-annealing process applied to the Al-doped ZnO nanorod arrays produced highly sensitive UV photoconductive sensors, in which the sensitivity reached 55.6, due to the surface properties of the oxygen-annealed nanorods, which have a higher affinity for oxygen adsorption than the other samples and were thereby capable of reducing the sensors dark current. In addition, the sensor fabricated using the oxygen-annealed nanorod arrays had the lowest rise and decay time constants. Our result shows that the annealing environment greatly affects the surface condition and properties of the Al-doped ZnO nanorod arrays, which influences the performance of the UV photoconductive sensors.

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.

Controllable Growth of Vertically Aligned Aluminum-Doped Zinc Oxide Nanorod Arrays by Sonicated Sol--Gel Immersion Method depending on Precursor Solution Volumes

Aluminium (Al)-doped zinc-oxide (ZnO) nanorod arrays have been successfully prepared using a novel and low-temperature sonicated sol–gel immersion method. The photoluminescence (PL) spectrum reveals the appearance of two emission peaks from the nanorod that are centred at 381 and 590 nm. The nanorod has a hexagonal structure with a flat-end facet, as observed using field-emission electron microscopy (FESEM). Interestingly, all samples have similar surface morphologies and diameter sizes of 40 to 150 nm after immersion in different precursor-solution volumes. The thickness-measurement results show that the thicknesses of the samples increase after immersion in higher precursor-solution volumes. We show for the first time that the growth of nanorod arrays along the c-axis can be controlled using different precursor volumes, and its growth mechanism is discussed. X-ray diffraction (XRD) spectra indicate that the prepared nanorods are ZnO with a hexagonal wurtzite structure that grows preferentially along the c-axis.

High electron mobility and low carrier concentration of hydrothermally grown ZnO thin films on seeded a-plane sapphire at low temperature

Hydrothermal zinc oxide (ZnO) thick films were successfully grown on the chemical vapor deposition (CVD)-grown thick ZnO seed layers on a-plane sapphire substrates using the aqueous solution of zinc nitrate dehydrate (Zn(NO3)2). The use of the CVD ZnO seed layers with the flat surfaces seems to be a key technique for obtaining thick films instead of vertically aligned nanostructures as reported in many literatures. All the hydrothermal ZnO layers showed the large grains with hexagonal end facets and were highly oriented towards the c-axis direction. Photoluminescence (PL) spectra of the hydrothermal layers were composed of the ultraviolet (UV) emission (370 to 380 nm) and the visible emission (481 to 491 nm), and the intensity ratio of the former emission (IUV) to the latter emission (IVIS) changed, depending on both the molarity of the solution and temperature. It is surprising that all the Hall mobilities for the hydrothermal ZnO layers were significantly larger than those for their corresponding CVD seed films. It was also found that, for the hydrothermal films grown at 70°C to 90°C, the molarity dependences of IUV/IVIS resembled those of mobilities, implying that the mobility in the film is affected by the structural defects. The highest mobility of 166 cm2/Vs was achieved on the hydrothermal film with the carrier concentration of 1.65 × 1017 cm−3 grown from the aqueous solution of 40 mM at 70°C.