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Noble metal nanostructures have been widely explored as an effective method to increase photon absorption and charge separation in plasmonic photocatalysis. In this study, we integrated two differe...

In this project, crystalline silver nanowires (AgNWs) are successfully grown using a continuous segmented flow process. The robust relationship among the structural, electrical and optical properties of the AgNWs in the function of the polyvinylpyrrolidone (PVP) chain length is elaborated. A concise carrier transport and a density mechanism are also discussed using a localized conductive atomic force microscopy analysis. The obtained results proved that the AgNWs synthesized using PVP with a chain length of 1.3 M exhibit excellent electrical and optical properties in the form of flexible transparent film with a sheet resistance of 90% at various bending angles. These findings present an alternative approach for production of AgNWs and fabrication of a high flexible transparent electrode.

The ability of band offsets at multiferroic/metal and multiferroic/electrolyte interfaces in controlling charge transfer and thus altering the photoactivity performance has sparked significant attention in solar energy conversion applications. Here, we demonstrate that the band offsets of the two interfaces play the key role in determining charge transport direction in a downward self-polarized BFO film. Electrons tend to move to BFO/electrolyte interface for water reduction. Our experimental and first-principle calculations reveal that the presence of neodymium (Nd) dopants in BFO enhances the photoelectrochemical performance by reduction of the local electron–hole pair recombination sites and modulation of the band gap to improve the visible light absorption. This opens a promising route to the heterostructure design by modulating the band gap to promote efficient charge transfer.

Charge transport dynamics in ZnO based inverted organic solar cell (IOSC) has been characterized with transient photocurrent spectroscopy and localised photocurrent mapping-atomic force microscopy. The value of maximum exciton generation rate was found to vary from 2.6 × 1027 m−3s−1 (Jsat = 79.7 A m−2) to 2.9 × 1027 m−3s−1 (Jsat = 90.8 A m−2) for devices with power conversion efficiency ranging from 2.03 to 2.51%. These results suggest that nanorods served as an excellent electron transporting layer that provides efficient charge transport and enhances IOSC device performance. The photovoltaic performance of OSCs with various growth times of ZnO nanorods have been analysed for a comparison between AM1.5G spectrum and local solar spectrum. The simulated PCE of all devices operating under local spectrum exhibited extensive improvement with the gain of 13.3–13.7% in which the ZnO nanorods grown at 15 min possess the highest PCE under local solar with the value of 2.82%.

This thesis examines the fabrication process of noble metal bimetallic Au/Ag nanoparticles via solid-state thermal dewetting under different annealing temperature and composition ratio of bimetallic nanoparticles. Also, this thesis delivers a general approach to understand the plasmon-induced charge interaction, hence photochemistry of Au/Ag bimetallic nanoparticles/semiconductor photoanode by determining the optimal composition ratio of 0.25 Au/Ag bimetallic nanoparticles which is capable of exploiting the enhanced electrical conduction and localized surface plasmon resonance effect for photoelectrochemical water splitting.

This present work demonstrates the integration of oxygen atoms into the graphene matrix to develop graphene oxide (GO) with tailored oxidation degrees which render them as photoactive materials for hydrogen (H2) evolution. GO photocatalysts derived from the modified Hummer’s method can endow tunable optical and electronic properties by varying the oxidation level into three increasing degrees GO-0.33, GO-0.47 and GO-0.53. Absorption spectroscopy revealed the increasing band gap of GO with respect to increasing oxygen contents and XRD, Raman and AFM studies revealed transformation in properties with increasing degree of oxygenated graphene. As opposed to graphite or graphene which is not photoresponsive, all GO samples exhibited photocatalytic activity towards H2 generation in sacrificial systems containing 0.1 M Na2S/Na2SO3. Among the studied samples, GO with intermediate O/C ratio of 0.47 (GO-0.47) exhibited the highest H2 photoactivity of 1104.3 μmolg−1h−1 after of light irradiation, owing to the presence of optimal oxygen loading content in GO. The study reveals that mere chemical modification by oxygen groups on the graphene can confer photocatalytic properties whose activity is further adjustable by modification in the oxygen level.

Samarium (5%Sm) and manganese (0.5%Mn) co-doped BiFeO 3 (B5SF0.5MO) polycrystalline multiferroic ceramics were prepared by solid-state-reaction to study the morphology, local polarization switching and piezoresponse, using atomic force microscopy (AFM) and piezoresponse force microscopy (PFM). Room temperature x-ray diffraction (XRD) and micro-Raman spectra reveal that samarium and manganese co-doping retains the parental rhombohedral R 3 c structure of BiFeO 3 (BFO). The out-of-plane (OP) PFM phase images show domains with oppositely oriented polarizations which are distinguished as domains with downward and upward polarizations with respect to the cantilever direction. Polarization switching occurs in the poled sample by locally poling the sample at negative and positive biases. Following the domain switching mechanism in BFO, it was found that 109° domain switching occurred besides the growth of 180° domains upon application of an electric field. The clockwise phase hysteresis implies the Debye model of piezoelectric relaxation effect due to defects that are both elastic and electric dipoles. The negative self-polarization in these samples is supposed to be the result of built-in internal bias field generated from excess electrons and charge defects like oxygen vacancies. The Saturated localized in-field hysteresis phase and amplitude loops from 180° domains suggest the existence of well-defined polarization along the field direction and suggests that Sm and Mn co-doped BFO can be a potential material for nanoscale piezoelectric applications.

The ability of band offsets at multiferroic/metal and multiferroic/electrolyte interfaces in controlling charge transfer and thus altering the photoactivity performance has sparked significant attention in solar energy conversion applications. Here, we demonstrate that the band offsets of the two interfaces play the key role in determining charge transport direction in a downward self-polarized BFO film. Electrons tend to move to BFO/electrolyte interface for water reduction. Our experimental and first-principle calculations reveal that the presence of neodymium (Nd) dopants in BFO enhances the photoelectrochemical performance by reduction of the local electron-hole pair recombination sites and modulation of the band gap to improve the visible light absorption. This opens a promising route to the heterostructure design by modulating the band gap to promote efficient charge transfer.

Indirect nanosecond-pulsed laser ablation of Au film of 10 nm–600 nm has been performed to investigate the ablated surface morphology of Au film as compared to direct pulsed laser ablation. This work shows that both the direct and indirect ablations give similar trend of ablation threshold fluence for film thickness equal or less than 170 nm. In this region, the ablation mechanism is driven by melting and vaporization. However, for film thickness greater than 170 nm, indirect ablation exhibits superior film quality with 3.0–3.6 factors less applied laser fluence compared to direct ablation and thus has no heat-affected zone and no recast material. As a result, the ablation mechanism for indirect ablation is driven by photomechanical process. This work highlighted the significant role of irradiation orientation (direct and indirect) as well as the correlation of heat penetration depth with different Au film thickness in influencing the ablation mechanism of Au film on glass substrate.

Observation of visible light trapping in zinc oxide (ZnO) nanorods (NRs) correlated to the optical and photoelectrochemical properties is reported. In this study, ZnO NR diameter and c-axis length respond primarily at two different regions, UV and visible light, respectively. ZnO NR diameter exhibits UV absorption where large ZnO NR diameter area increases light absorption ability leading to high efficient electron-hole pair separation. On the other hand, ZnO NR c-axis length has a dominant effect in visible light resulting from a multiphoton absorption mechanism due to light reflection and trapping behavior in the free space between adjacent ZnO NRs. Furthermore, oxygen vacancies and defects in ZnO NRs are associated with the broad visible emission band of different energy levels also highlighting the possibility of the multiphoton absorption mechanism. It is demonstrated that the minimum average of ZnO NR c-axis length must satisfy the linear regression model of Z p,min = 6.31d to initiate the multiphoton absorption mechanism under visible light. This work indicates the broadening of absorption spectrum from UV to visible light region by incorporating a controllable diameter and c-axis length on vertically aligned ZnO NRs, which is important in optimizing the design and functionality of electronic devices based on light absorption mechanism.