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Dark hollow beams (DHBs) possess great potential for material processing, holography, and vortex beams, and thus designing a high-Q DHB cavity is significant for these applications. In this Letter, a method of designing and optimizing a high-Q DHB cavity based on a one-dimensional topological photonic crystal (TPhC) is proposed. Furthermore, how the structural parameters control the performance of the cavity is analyzed with the help of finite-element-method (FEM) simulation. According to the simulation results, the Q factor of the designed cavity can reach the order of 105 with only 19 periods of layers. It is critical to mention that, although increasing the layers can improve the average Q of the cavity, it will cause serious fluctuation of both the Q factor and the divergence angle of the output beam. The design method proposed in this Letter may not only help designers of future DHB lasers but also promote the applications of DHBs in various fields.

A ring focus reflector is proposed for transmitting a perfect vortex (PV) beam, and the transmission characteristics of the PV beam with different topological charges in free space after passing through the reflector are studied. The reflector parameters can be determined by fitting the structural formula, and PV beams of different orders transmit with small spot sizes at the same time. The transmission trajectory calculated by the diffraction formula is consistent with the ray tracing results. The research results show that the reflector can achieve a high level of transmission efficiency of beams with different topological charges, which is conducive to the multiplexing of PV beams.

The chemical vapor deposition technique was used to prepare the Ag doped ZnO microrods, which were located on Si substrates at two different positions. The scanning electron microscopy revealed that the samples have a clear hexagonal shape. X-ray diffraction provided information about the preferential orientation along the c-axis. The Raman analysis revealed that a new Raman mode appears at 492 cm-1 due to Ag doping. As this mode has not been reported early, it could be used as a characteristic mode of Ag doping in Raman spectrum. The red shift of the E2 (high) mode proves the existence of tensile stress in the samples. DOI: http://dx.doi.org/10.5755/j01.ms.25.3.19130

This paper reports on two experimental psychology studies on influence of the color and logo position in the field of HNB product, which used to measure the user experience. Based on the eye tracking method, we conducted two experimental studies. The independent variables were the different colors and logo position of HNB products. The dependent variables include first fixation time, first fixation duration, total fixation duration, second fixation time and subjective evaluation. A total of 68 people participated in the experiment. The main findings of this study were as follows: (1) In terms of HNB color preference, black and white were the most acceptable colors. (2) In the selection of logo position, the lower right and upper right position were more popular with users. (3) The first fixation time and the second fixation time can reflect the most real inner experience. In addition, this study provides a method for reference value with consumer decision-making for the industrial design optimization in relate consumer electronic product fields.

In this paper, we demonstrate a newly designed hybridized triboelectric nanogenerator (TENG) fabric incorporating multiple working modes, which can effectively harvest ambient mechanical energy for conversion into electric power by working in a hybridization of a contact-separation mode, a sliding mode and a freestanding triboelectric layer mode. The power generation of each mode of the TENG fabric was systematically investigated and compared along different directions, under different frequencies and at different locations. Owing to the advanced structural design, the as-fabricated TENG fabric could be switched between multiple working modes according to its real working situation. High output voltage and current of about 140 V and 0.6 μA, respectively, were obtained from a larger size of TENG fabric, which could be used to light up 120 LEDs in series. Compared to the previously reported TENGs, such a hybridized TENG fabric based on hybridized modes has much better adaptability for harvesting energy (such as human walking, running, and other human motion) in different directions. This work presents the promising potential of hybridized TENG fabric for power generation and self-powered wearable devices.

In this study, a novel Pb(II) ion-imprinted polymer based on magnetic laminar graphene oxide composite materials (MnFe2O4@SiO2/GO-IIP) was synthesized by surface ion-imprinted technique for the selective removal of lead ions from aqueous solutions. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and magnetic measurement system were used to characterize the structure and property of as-prepared adsorbents. The adsorption experiments exhibited the MnFe2O4@SiO2/GO-IIP possessed a good adsorption performance and the maximum adsorption capacity of Pb (II) ions reached 58.82 mg g-1. The adsorption could be accomplished within 30 min and the adsorbents could be separated quickly by a permanent magnet. The Langmuir adsorption isotherm and pseudo-second-order kinetic models were used to describe the adsorption procedure appropriately and the result proved that the chemisorption was the rate-limiting step. The selectivity coefficient of Pb (II)/Ni(II), Pb (II)/Zn(II), Pb (II)/Cd(II), Pb (II)/Co(II) were 25.37, 19.71, 33.07 and 45.7, respectively. In addition, the regeneration experiments confirmed the high stability and reproducibility of adsorbents. Lastly, X-ray photoelectron spectroscopy (XPS) proved the bonding mechanisms of the material and Pb(II) ions with a coordination N‒Pb bond.

The broadband and self-powered photodetectors have attracted significant attention due to the versatility and without extra energy. In this work, we fabricate a self-powered and broadband photodetector based on Si/ZnO/CdO three-component heterojunctions. The photodetector has a fast response time (shorter than 0.45 s) to the ultraviolet and visible illumination at 0 V bias. CdO film is used as the transparent electrode because of the superior electrical characterization and the appropriate band structure of ZnO/CdO, which facilitates electrons transferring from ZnO nanorods to the CdO electrode and reflects holes back into the ZnO, thus reducing recombination at the ZnO/CdO interface and enhancing photocurrent. Moreover the performance of the photodetector is optimized and significantly enhanced by the piezo-phototronic effect of ZnO nanorods. This work may provide a potential approach to enhance the performance of self-powered and broadband photodetectors.

Because of the different melting point, it is difficult to doped Ag element in ZnO film. Ag dopant can adjust the properties of ZnO materials. In this paper, we deposited Ag doped ZnO film using two step vapour evaporation method on c-plane sapphire substrate. The SEM image shows that the doped film was composed of small grain which compact in order and the Ag microwires was dispersed on the surface. The EDX graph proves that the Ag was indeed in the film. The XRD pattern reveals that the doped film has prefer orientation along the c-axis with wurtzite structure and the dopants have not effect the crystal quality.

In this work, we fabricate a ZnO/NiO/Si heterojunction photodetector, which successfully realizes selective detection of UV or visible light in a single photodetector. In addition, the pyro-phototronic effect has been confirmed as an effective approach for enhancing the performance of photodetectors based on ZnO. The pyro-phototronic effect is carefully studied by comparing with a ZnO/Si heterojunction photodetector under UV and visible illumination at different bias voltages. To enhance the photodetector's wavelength selectivity, the parameters and structure are further optimized for the ZnO/NiO/SiO2/Si heterojunction photodetector. The newly designed photodetector may be used to selectively detect and distinguish UV and visible illumination in a single photodetector.

In this work, we study the field emission properties of a single vertical carbon nanotube with cathode radius changing. The carbon nanotube is considered as purely perfect conductor, and the anode and cathode are modeled as discs. The radius of anode is kept as 24m, then the radius of cathode is changed from 24 m to 1 m. The emitter of that CNT consists of a hemispherical cap of 4 nm radius (r) on top of a cylinder height of 2 m (h). The distance from anode to cathode is w=h+20m. The overall surface area of the CNT and cathode are all grounded, and the anode plate has a constant potential value of 100 V. The distribution of potential and electric field, field emission current are obtained by simulating with the help of COMSOL Multiphysics 4.3b electrostatics module. We find that with cathode radius decrease, the electric field strength over the surface of carbon nanotube (CNT) strengthening and field emission current increase.

A room temperature ethanol sensor based on Au-modified zinc oxide microwires (Au/ZnO MWs) is demonstrated. Au nanoparticles (Au NPs) were immobilized via ion sputtering onto the surface of CVD-fabricated ZnO microwires (ZnO MWs) to serve as sensitizers. Au modification was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and photoluminescence. Gas-sensing tests indicated that the modified microwires exhibited an enhanced performance relative to the unmodified ZnO microwires over a wide gas concentration range, with very stable repeatability, fast recovery time and high sensing response and selectivity. A sensing mechanism is described in terms of localized surface plasmon resonance (LSPR) effect of Au NPs. The superior sensing characteristics indicate the device's potential applications as room-temperature gas sensor, and a straightforward and economical fabrication also makes it very attractive for more widespread use.

Piezotronic pressure sensors have drawn a lot of attention since the piezotronic theory was established. In this work, a piezotronic pressure sensor based on ZnO/NiO core/shell nanorods array is fabricated by a simple and low-cost method. From the I – V characteristics, we can know that a reliable barrier layer is formed at the ZnO/NiO interface. When the ZnO/NiO nanorods are compressed by the pressure, the piezopotential in ZnO changes the NiO barrier height and then modulate the carrier distribution and transportation. Furthermore, the piezo-phototronic effect is a three-way coupling effect of semiconductor, piezoelectric-polarization and photon-excitation properties, which may be a feasible approach to enhance the performance of pressure sensors by tuning the generation, separation and recombination of photo-generated electron–hole pairs during optoelectronic processes in piezoelectric-semiconductor materials. Here, the performance of the pressure sensors is optimized and significantly enhanced by coupling of the piezoelectric effect and photo-excitation of ZnO nanorods. Under a UV (365 nm) illumination, the enhancement in switch ratio and sensitivity of the pressure sensor is about 353% and 445%, respectively. The enhancement is attributed to weakening the influence of bulk resistance. Thus, ZnO/NiO interface plays a crucial role in determining the electrical transport property. Particularly, the created electrons by photons moved towards and accumulated at the interface, which results that more electrons can tunnel through the barrier layer than that without UV illumination under loading. These results indicate the capability of the piezo-phototronic effect to effectively enhance/optimize the performances of pressure sensors.

In this work, a UV photodetector based on a ZnO/NiO core/shell nanorods array is fabricated by hydrothermal growth processes and thermal oxidation. Compressive strain is applied to enhance the Ilight and sensitivity of the UV photodetectors. Under a 1 N compressive strain at −3.5 V, the enhancement in Ilight and sensitivity of the UV photodetector is about 74% and 78.7%, respectively. The possible working principle is that the negative piezo-polarization at the ZnO/NiO interface shifts the depletion region to the ZnO side leading to an increase of the photon-absorption volume. This work may provide a potential approach to enhance the performance of the ZnO/NiO UV photodetector.

An ultraviolet photodetector based on p-NiO/n-ZnO heterojunction was fabricated using thermal oxidation and hydrothermal growth processes. The properties of the UV photoresponse under various strains were investigated. The results showed that the magnitude and the sign of the strain (tension/compression) have a great influence on the decay time by coupling piezoelectric and surface oxygen adsorption/desorption effects. These results demonstrate an effective approach for designing and fabricating strain modulated fast reset UV photodetectors.

In this study, we fabricate a nanogenerator device based on a composite structure formed by ZnO nanorods array/BaTiO3 coating layer for harvesting mechanical energy from environment. The whole device is composed of a Si substrate, a ZnO nanorods array, a BaTiO3 coating layer and a top Cu foil electrode. The ZnO nanorods were grown by a hydrothermal synthesis technique and the BaTiO3 thin layer was coated on the surface of the ZnO nanorods by rf magnetron sputtering process. It is a simple and low-cost growth method to make the ZnO nanorods array act as a template to increase the area of the subsequently deposited BaTiO3 layer. The device produced an enhanced average current of 105 nA, which was 7 times larger than the devices with only piezoelectric ZnO nanorods array and 3.5 times larger than the devices with only piezoelectric BaTiO3 thin film, respectively. The possible reasons contributing to the enhancement of the output current were discussed.

In this research work, a p-NiO/n-ZnO heterostructure was fabricated using thermal oxidation and hydrothermal growth processes. The p-NiO films were oxidized at different temperatures. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and UV–visible spectral analysis were used to characterize the p-NiO/n-ZnO heterostructure. The results indicated that the NiO films oxidized at higher temperature have wider optical band gap and lower defect density. In particular, by comparing the photoresponse properties of the UV photodetectors oxidized at different temperatures we suggest that the oxidation temperatures have a great influence on the photoresponse time. The defect density of NiO film decreases with increasing oxidation temperature. And the defect density affects the photoresponse characteristics that the decay time decreases with the decreasing of defect density as the NiO oxidation temperature increases. This work could serve as a valuable guideline for designing and improving the p-NiO/n-ZnO UV photodetectors in a low-cost and large-scale way.

A p-CuO/n-ZnO heterostructure was synthesized on an indium tin oxide coated flexible substrate (polyethylene terephthalate) by a simple and low-cost hydrothermal method. Scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction were used to characterize the as-synthesized heterostructure. The results indicated that flower-like CuO nanostructure conformably formed on the ZnO nanorods. Furthermore, a nanogenerator based on the p-CuO/n-ZnO heterostructure was fabricated for harvesting energy from environment, and the output performance of the device was investigated. A larger output current of ~100 nA was obtained in comparison with ZnO based nanogenerator, which could be ascribed to the formation of p–n heterojunctions in the CuO/ZnO composites, reducing the screening effect of excessive electrons. This strategy may provide a highly promising platform for realizing a high-performance flexible piezoelectric energy harvester by new composite piezoelectric material.

This paper proposes a novel electrode pair (EP) layout method to obtain the exact electrical parameters in metal/semiconductor Ohmic contact, with focus on obtaining the specific contact resistance and the effective electrode width for IC design. The deduction process in extracting the contact parameters has been modelled, analyzed by TCAD simulations, and verified by the experimental data. The sheet resistance variance underneath the contact and outside the contact can be distinguished and obtained exactly by the proposed model. The work provides a distinct perspective to understand and quantify the electrical characteristics in a greater variety of semiconductor Ohmic contacts, and it can also assist engineers for a better electrode layout design.

In this work, an ultraviolet (UV) photodetector based on a ZnO nanowires (NWs) array with metal-semiconductor-metal Schottky junction structure was successfully fabricated on a flexible polyester fibre substrate by a low-temperature hydrothermal method. Subjected to a 0.2% tensile strain at -1 V, the

Enhancing the output power of a nanogenerator is essential in applications as a sustainable power source for wireless sensors and personal electronic devices. As one possible solution, NiO–ZnO heterojunction is used for piezoelectric performance enhancement via both suppressing the screening effect in the ZnO film and forming a reliable p–n junction at the interfaces instead of the Schottky barriers. From pristine ZnO nanogenerators, alternating current (AC)-type output signal was observed, while from NiO–ZnO nanogenerators, direct current (DC)-type output signal was surprisingly obtained under the same vertical compressive force. By forming a NiO–ZnO heterostructure, the DC output voltage was up to 430 mV and the maximum output current density was of 40 nA cm −2 , which are approximately 21-fold higher voltage and 13 times larger current density by comparison to the pristine ZnO nanogenerators. The results provide a simple, low-cost and effective approach for enhancing the piezoelectric performance.

ZnO microwires of two different cross-sectional profiles were synthesized by chemical vapor deposition, and their morphologies were characterized by scanning electron microscopy. Their cross-sectional hexagonal profile could be tuned from straight to curved sides, by regulating the ZnO:graphite powder ratio used during synthesis. The ZnO microwires had hexagonal profiles with curved sides at a higher graphite ratio, and hexagonal profiles with straight sides at a lower graphite ratio. The higher graphite ratio was speculated to lower the growth rate from center to hexagonal sides, relative to the corners. The ZnO microwires were fabricated into gas sensors, and their sensing characteristics towards ethanol gas were investigated. The sensor based on a ZnO microwire with curved sides exhibited superior ethanol sensing performance than that based on a microwire with straight sides, which was attributed to the higher surface-to-volume ratio of the curved-side microwire. The sensor based on a ZnO microwire with curved sides was stable, and exhibited rapid response and recovery times. The straight-forward and economical fabrication of the gas sensor at room temperature makes it attractive for practical application.

In this paper, branched ZnO nanotrees (NTs) have been synthesized on flexible fiber-paper substrates by introducing a multistep hydrothermal approach for realizing high-performance piezoelectric nanogenerators. With this method, a significant enhancement in output voltage of the NGs ranging from 14 mV to 0.1 V was achieved, with a nearly 20 times enhanced power density compared to the vertically grown ZnO NWs. This is the first demonstration of fabricating branched ZnO NTs-coated fiber paper for energy harvesting devices, which may provide guidelines for designing high-performance piezoelectric energy harvesting.

In this study, a nanogenerator based on Cu2O–ZnO p–n junction has been fabricated on Cu wire substrates for harvesting mechanical energy from the environment. The flexible nanogenerator is composed of a Cu substrate, a Cu2O layer, ZnO nanorods and an outer Au-coated paper electrode; the Cu2O layer was obtained by oxidizing Cu wires directly and the ZnO nanorods were grown on the Cu2O layer using a low-temperature hydrothermal method. The existence of the Cu2O–ZnO p–n junction makes a contribution towards reducing the number of excess electrons in the ZnO, which facilitates in improving the output signal and also overcomes short circuits. An Au-coated paper electrode can involve more nanorods in the power generation process. The DC output voltage was up to 42 mV and the maximum output current density was 400 nA, which are approximately a 13-fold higher voltage and a one order of magnitude larger current in comparison to devices without a Cu2O layer, respectively. This study may provide important insight into a facile fabrication method for low-cost and high-performance energy harvesting devices.

Piezoelectric nanogenerators have been intensively developed in terms of their materials and applications; however, only modest structural progress has been made due to limitations in the growth mechanisms of nano-materials. In this work, a piezoelectric nanogenerator based on ZnO micro-thornyballs (ZMTBs) was introduced. ZMTBs were synthesized by chemical vapor deposition method without the presence of any seed layers or substrates. Electrical characterization was subsequently performed to reveal the characteristics of the contacts formed between the ZnO micro-thornyballs and the copper electrode. The electric output ability of the ZNTTs nanogenerators has been studied in reference to the experiment and the numerically calculation.

Quaic-nanotetrapods ZnO nanostructure were fabricated by a simple chemical vapour deposition method. The morphologies, crystalline qualities and optical characteristics of the quaic-nanotetrapods ZnO nanotetrapods were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL) analytic technology, respectively. A piezoelectric nanogenerator based on the ZnO nanotetrapods was fabricated by a simple technique. And the energy harvesting ability is studied by experimental characterization methods and theoretical calculations.

In this work the piezoelectric effect of one-dimensional ZnO gear-shaped microwires (GMWs) is studied by the finite element method. By calculating the piezopotential of substrate-bound gear-shaped ZnO microwires oriented along the c-axis with gear groove depth of 0–5 μm, we demonstrate that the GMW has more advantage for piezoelectric nanogenerators than the common hexagonal microwire (HMW). To understand the anisotropic electricity generation, the calculated piezopotential distribution in the bent ZnO GMW and HMW has been analyzed under an external force with the different directions. Moreover, the calculation also indicates that the effect of geometric size on piezopotential for the GMW is similar to the HMW. Our results will be a guidance for the design of high-efficiency energy harvesting devices.

A simple and effective method of synthesizing nanorods (NRs) and the ability to control the size and aspect ratio of them are crucial for fabricating nanodevices. In this paper, we present a systematic study of the growth of ZnO NRs on common paper substrates using a hydrothermal approach by adjusting the growth conditions. By a slight variation of the solution concentration and the growth time, significant changes in morphology and size (aspect ratio) of the obtained ZnO NRs have been controlled. Moreover, the piezoelectric power generation from ZnO-paper nanogenerators grown with different precursor concentration and growth time are also investigated. It is found that the morphology and aspect ratio of NRs have significant influence on the piezoelectric behavior. This type of flexible piezoelectric nanogenerator will have potential applications in implantable biosensors and wearable self-powered electronic devices.

Hexagonal single-crystal graphene domains were grown on copper (Cu) foil via chemical vapor deposition and were etched with hydrogen at 950 °C from 7 to 60 min at atmospheric pressure. Numerous trenches were observed on the initial graphene domains after etching, and the trench patterns were closely associated with the Cu crystal orientation. No trenches were found if the etching process was conducted before cooling down. Thus, the etching trenches were bound up with the wrinkles formed during the cooling down process. Then, the process of etching on the wrinkles was examined. This simple hydrogen etching technology proved that wrinkles and point defects existed even in hexagonal single-crystal graphene domains. This method could be a convenient way to detect the distribution and morphology of wrinkles in graphene.

Large-area highly ordered silicon nanohole (SiNH) arrays on Si substrate have been fabricated by the combination of nanosphere lithography and metal assisted electroless etching. The diameter, length of nanoholes, and the center-to-center distance of adjacent nanoholes, can be accurately controlled by nanosphere lithography and metal assisted electroless etching conditions. The sub-wavelength structure of SiNH arrays had excellent antireflection property with a low reflectance of 3.5% within the wavelength range of 300–1000 nm. Compared to the planar Si, the SiNH samples exhibited a higher photoelectrochemical hydrogen generation performance. The improved performance was attributed to SiNH arrays providing an effective light-trapping and a higher semiconductor/electrolyte interface areas which reduce the overpotential required for photoelectrochemical hydrogen reaction. Furthermore, decorating the SiNH arrays with platinum nanoparticles (PtNPs) yielded a significantly high photovoltage of 0.12 V. The photoconversion efficiency of Pt-decorated SiNH (Pt/SiNH) arrays was 22% under the illumination of 100 mW/cm2, higher than that of SiNH arrays (15.5%) and the planar Si (8.1%).

A novel feed network based on the microstrip/slotline transition is proposed in this paper. This feed network not only has ultra-wide impedance bandwidth but also can improve space utilization and make the design of antenna array easier. Then an ultra-wideband (UWB) antenna array with four elements fed by the network is designed. The antenna array is simulated, manufactured and measured. The results show that the impedance bandwidth with return loss under i10dB is 88.76%, from 2.35GHz to 6.1GHz. Within the impedance bandwidth, the radiation performance is satisfactory, and the gain of the array is 2.1{7.1dB, higher than that of the element. The cross-polarization level of the array is lower than i20dB, just as the element. A reasonable agreement of results is achieved between simulation and measurement.

One-dimensional (1D) ZnO microwires were successfully synthesized by chemical vapor deposition and their structural and morphological properties were analyzed by X-ray diffraction and scanning electron microscopy, demonstrating that the microwires were single crystalline with perfect hexagonal structure and smooth surface. Using these 1D microstructures, we fabricated a novel ZnO-based ethanol gas sensor. Operating at room temperature, the sensor was found to have good sensing characteristics. The reliability and stability of the sensor could be improved by connecting multiple 1-wire devices (1-WD) in parallel into a multi-wires device. In interior natural lighting environment and under 3 V bias, the response and recovery time of the 1-WD to 200 ppm ethanol gas were

Wafer-scale high density aligned p-type silicon nanowire (SiNW) arrays decorated with discrete platinum nanoparticles (PtNPs) have been fabricated by metal assisted electroless etching followed by an electroless platinum deposition process, and systematic investigations of photoelectrochemical behavior of Pt/SiNW were also reported in this study. Coating of PtNPs on SiNW sidewalls yielded a more positive onset potential (Vos), which enhances the photoelectrochemical hydrogen generation performance of the photoelectrodes, though excessive PtNPs deposition leads to a decreased photocurrent. Additionally, we have demonstrated that the photoelectrode consisting of longer SiNWs yielded a higher limiting current. However, when the length of SiNWs was increased further to >4 μm, the limiting current dramatically reduced, which is presumably because an increased interface recombination and scattering resulting from the increased surface area of SiNWs begin to play a dominant role. The results demonstrate Pt/SiNW to be a promising hybrid system for photoelectrochemical water splitting, and device performance may be further improved via optimal conditions of PtNPs deposition time and SiNWs length.

Si/ZnO core/shell nanowire (NW) arrays were fabricated using atomic layer deposition of ZnO shell on n-Si NW arrays prepared by metal assisted electroless etching method. Scanning electron microscopy, transmission electron microscopy and X-ray diffraction were utilized to characterize the core/shell structures. Water splitting performance of the core/shell structures was preliminarily studied. The Si/ZnO core/shell NW arrays yielded significantly higher photocurrent density than the planar Si/ZnO structure due to their low reflectance and high surface area. The photoelectrochemical efficiency was found to be 0.035 and 0.002 % for 10 μm-long Si/ZnO NW array and planar Si/ZnO sample, respectively. These results suggested that core/shell structure is superior to planar heterojunction for PEC electrode design. We demonstrated the dependence of photocurrent density on the length of the core/shell array, and analyzed the reasons why longer NW arrays could produce higher photocurrent density. The relationship between the thickness of ZnO shell and the photoconversion efficiency of Si/ZnO NW arrays was also discussed. By applying the core/shell structure in electrode design, one may be able to improve the photoelectrochemical efficiency and photovoltaic device performance.