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Solar-based water sanitation is an environmentally friendly process for obtaining clean water that requires efficient light-to-heat-to-vapour generation. Solar-driven interfacial evaporation has potential, but the inability to control interfacial evaporators for solar tracking limits efficiency at large solar zenith angles and when using optical concentration. Furthermore, clogging affects the efficiency of the device. Here, we create a super-wicking and super-light-absorbing (SWSA) aluminium surface for efficient solar-based water sanitation. The measured evaporation rate exceeds that of an ideal device operating at 100% efficiency, which we hypothesize resulted from a reduced enthalpy of vaporization within the microcapillaries. Limited solar absorber–water contact for water transport minimizes heat losses to bulk water and maximizes heat localization at the SWSA surface. The device can be mounted at any angle on a floating platform to optimize incident solar irradiance and can readily be integrated with commercial solar-thermal systems. With a design that is analogous to bifacial photovoltaic solar panels, we show a 150% increase in efficiency compared with a single-sided SWSA. Given the open capillary channels, the device surface can be easily cleaned and reused. Using the SWSA surface to purify contaminated water, we show a decrease in the level of contaminants to well below the WHO and EPA standards for drinkable water. Solar-driven interfacial evaporation can be a sustainable process to obtain clean water but device efficiency and simplicity need improving. This study presents a super-wicking and super-light-absorbing aluminium surface with increased efficiency, a simple structure and strong performance.

Water-repellent superhydrophobic (SH) surfaces promise a wide range of applications, from increased buoyancy to drag reduction, but their practical use is limited. This comes from the fact that an SH surface will start to lose its efficiency once it is forced into water or damaged by mechanical abrasion. Here, we circumvent these two most challenging obstacles and demonstrate a highly floatable multifaced SH metallic assembly inspired by the diving bell spiders and fire ant assemblies. We study and optimize, both theoretically and experimentally, the floating properties of the design. The assembly shows an unprecedented floating ability; it can float back to the surface even after being forced to submerge under water for months. More strikingly, the assembly maintains its floating ability even after severe damage and piercing in stark contrast to conventional watercrafts and aquatic devices. The potential use of the SH floating metallic assembly ranges from floating devices and electronic equipment protection to highly floatable ships and vessels.

A femtosecond (fs)-laser-processed surface that repels liquid polymer in water is reported in this paper. We define this phenomenon as the "superpolymphobicity". Three-level microstructures (including microgrooves, micromountains/microholes between the microgrooves, and nanoripples on the whole surface) were directly created on the stainless steel surface via fs laser processing. A liquid polydimethylsiloxane (PDMS) droplet on the textured surface had the contact angle of 156 ± 3° and contact angle hysteresis less than 4° in water, indicating excellent underwater superpolymphobicity of the fs-laser-induced hierarchical microstructures. The contact between the resultant superhydrophilic hierarchical microstructures and the submerged liquid PDMS droplet is verified at the underwater Cassie state. The underwater superpolymphobicity enables to design the shape of cured PDMS and selectively avoid the adhesion at the PDMS/substrate interface, different from the previously reported superwettabilities. As the examples, the microlens array and microfluidics system were prepared based on the laser-induced underwater superpolymphobic microstructures.

Hierarchical micro/nanostructured TiO2/Ag substrates for surface-enhanced Raman scattering (SERS) application are fabricated by depositing Ag nanoparticles on the surface of TiO2 hierarchical micro/nanostructures, which are formed by combining femtosecond laser structuring with scalable hydrothermal treatment. Our results show that the morphology of hierarchical micro/nano TiO2/Ag architectures can significantly influence SERS performance. Compare with one-dimensional TiO2/Ag nanostructures hydrothermally fabricated on laser untreated Ti surface, a four-fold enhancement is shown in the SERS signal with excellent reproducibility. Most importantly, enhancement is significantly stronger in the valleys of our microstructures than on the hills due to geometrical orientation of nanostructures on the surface of the microstructure. The site predictability for SERS enhancement is one of the major roadblock for SERS applications. Present study provides an effective way to enhance the site predictability for optimal SERS in addition to a significant enhancement in signal strength.

Femtosecond (fs) laser processing can significantly alter the optical, thermal, mechanical, and electrical properties of materials. Here, we show that fs-laser processing transforms aluminum (Al) to a highly efficient and multipronged heat exchanger. By optimizing the formed surface nano- and microstructures, we increase the Al emissivity and surface area by 700% and 300%, respectively. Accordingly, we show that fs-laser treated Al (fs-Al) increases the radiative and convective cooling power of fs-Al by 2100% and 300%, respectively, at 200 °C. As a direct application, we use fs-Al as a heat sink for a thermoelectric generator (TEG) and demonstrate a 280% increase in the TEG output power compared to a TEG with an untreated Al heat exchanger at 200 °C. The multipronged enhancement in fs-Al heat exchange properties lead to an increase in the TEG output power over a wide temperature (T) range (T>50°C). Conversely, a simple radiative cooling heat exchanger increases the TEG output power within a limited temperature range (T>150°C). We investigate the laser processing parameters necessary to maximize the spectral emissivity and surface area of fs-Al. Fs-Al promises to be a widely used and compact heat exchanger for passive cooling of computers and data centers as well as to increase the efficiency of TEGs incorporated in sensors and handheld electronics., Graphical abstract Image 1, Highlights • We produced a novel heat-exchanger by creating nano/micro surface structures on Al via femtosecond laser processing. • We increased the Al emissivity, surface area, radiative and convective cooling by 700%, 300%, 2100% and 300% respectively. • We demonstrated a 280% increase in the TEG output power compared with an untreated Al heat exchanger at 200 °C.

[Image: see text] In this work, the surfaces that repel liquid polydimethylsiloxane (PDMS) droplets in water were created by femtosecond laser treatment. We define this superwetting phenomenon as underwater “superpolymphobicity”. The resultant underwater superpolymphobic silicon surface shows a contact angle of 159 ± 1° and a sliding angle of 1.5 ± 0.5° to liquid PDMS droplets in water. This underwater superpolymphobicity can be achieved on a wide range of hydrophilic materials, including semiconductors, glass, and metals. The adhesion between the liquid polymer and a solid substrate is effectively prevented by the underwater superpolymphobic microstructures. The underwater superpolymphobicity will have a great significance in designing the adhesion between the polymer and a solid substrate, controlling the shape of the cured polymer materials, as well as nearly all the applications based on the polymer materials.

In this paper, we demonstrate a simple yet effective hybrid method to fabricate lab-on-a-chip devices on aluminum (Al) foil. Instead of using conventional photoresists and lithography methods, an array of square units is first produced by femtosecond laser direct writing, followed by generating highly ordered anodized aluminum oxide (AAO) nanoporous structures within each unit. The AAO treated area becomes hydrophilic. Next, we functionalize the surrounding area outside the square units to superhydrophobic by electrochemical deposition and further chemical modification. This hydrophilic and hydrophobic pattern allows us to confine the liquid samples to be detected within the hydrophilic AAO detection area. We use rhodamine 6G (R6G) as a probe, and obtain a fluorescence intensity enhancement from R6G by 70 times over a flat surface. This leads to the detection sensitivity of R6G molecules to a concentration as low as 10−17 mol L−1. By mixing R6G with RhB molecules, the fluorescence emission bands shift significantly due to the addition of RhB molecules, showing a significantly improved spectral resolution compared to traditional fluorescence spectrometers for liquid samples. This phenomenon can be attributed to the energy transfer between R6G and RhB under laser excitation, which was enhanced by the AAO nanostructures. The array-based LOC device demonstrated in this paper is simple and convenient to fabricate, has low sample consumption and dramatically enhances the fluorescence yield with improved spectral resolution.

A strategy is proposed here to fabricate microfluidic channels based on underwater superpolymphobic microgrooves with nanoscale rough surface structure on glass surface produced by femtosecond (fs) laser processing. The fs laser-induced micro/nanostructure on glass surface can repel liquid polydimethylsiloxane (PDMS) underwater, with the contact angle (CA) of 155.5 ± 2.5° and CA hysteresis of 2.7 ± 1.5° to a liquid PDMS droplet. Such a phenomenon is defined as the underwater "superpolymphobicity". Microchannels as well as microfluidic systems are easily prepared and formed between the underwater superpolymphobic microgroove-textured glass substrate and the cured PDMS layer. Because the tracks of the laser scanning lines are programmable, arbitrary-shaped microchannels and complex microfluidic systems can be potentially designed and prepared through fs laser direct writing technology. The concept of "underwater superpolymphobicity" presented here offers us a new strategy for selectively avoiding the adhesion at the polymer/substrate interface and controlling the shape of cured polymers; none of these applications can find analogues in previously reported superwetting materials.

A grooved hydrophobic structure is one of the most commonly adopted surface structures inspired by nature, such as rice leaves and butterfly wings, to achieve anisotropic wetting/dewetting. The retraction dynamics of a liquid droplet after impact on a solid surface is less explored than its counterpart, the spreading dynamics, even though it is equally crucial for determining the performance in actual applications. Therefore, in this study, the effects of groove orientation, impact velocity, and surface temperature on the retraction dynamics of a water droplet were investigated through high-speed imaging. The impact velocity and surface temperature were systematically changed while keeping the size of the grooved structures the same. As the impact velocity of the droplet was increased, the enhanced spreading along the groove structures delayed the initiation of droplet retraction. This resulted in anisotropic shapes of the droplet during retraction. During the early stage of droplet retraction, the retraction rate of the droplet was found to be independent of both the groove orientation and impact velocity. The anisotropic retraction of the droplet was also observed by increasing the surface temperature. At a high surface temperature (250°C), there was significant reduction in the retraction rate (~20%) in the direction perpendicular to the grooves, resulting in the formation of an ellipsoidal droplet. It is proposed that the oscillating vapour flow underneath the droplet caused by the groove structures is responsible for the temperature-induced anisotropic retraction.

Wastewater recycling could be part of an environmentally feasible solution to an increasing global water crisis. In a recent work, we made a push toward that end, introducing a super-wicking, super-light-absorbing solar trackable panel for water sanitation.

In this work, we demonstrate an enhanced thermoelectric output power using nanoporous alumina grown on aluminum (Al) surfaces. The improved power is due to enhanced thermal emissivity and passive radiative cooling associated with nanoporous alumina. We show that a careful balance between conduction, convection, and radiation heat transfer processes leads to optimal passive cooling for 30–40 μm thick alumina layers, while the nanopore size has a negligible effect. By growing a conformal alumina layer on an Al heatsink surface, the output power of a commercial thermoelectric generator (TEG) showed about 55%–70% increase for temperature range of 150 − 250 °C compared to using an untreated Al heatsink. With minimal footprint and no additional energy input, our passive cooling optimization method is a simple and facile way to enhance the TEG output power and can be extended to other applications that utilize Al heatsinks, e.g., computers, cell-phones, and refrigerators.

Ordered nanostructure arrays have attracted intensive attention because of their various applications. However, it is still a great challenge to achieve ordered nanostructure patterning over a large area (such as wafer-scale) by a technique that allows high throughput, large pattern area and low equipment costs. Here, through a unique design of the fabrication and transferring processes, we achieve a facile transferring of wafer-scale ultrathin alumina membranes (UTAMs) onto substrates without any twisting, folding, cracking and contamination. The most important in our method is fixing the UTAM onto the wafer-scale substrate before removing the backside Al and alumina barrier layer. It is also demonstrated that the thickness and surface smoothing of UTAMs play crucial roles in this transferring process. By using these perfectly transferred UTAMs as masks, various nanostructure patterning including nanoparticle, nanopore (nanomesh) and nanowire arrays are fabricated on wafer-scale substrates with tunable and uniform dimension. Because there are no requirements for UTAMs, substrates and materials to be deposited, the method presented here shall provide a cost-effective platform for the fabrication of ordered nanostructures on large substrates for various applications in nanotechnology.

Perfectly ordered nanoparticle arrays are fabricated on large-area substrates (cm(2)) via a cost-effective nonlithographic route. Different surface plasmon resonance (SPR) modes focus consequently on their own positions due to the identical shape and uniform size and distance of these plasmonic metallic nanoparticles (Ag and Au). On the basis of this and FDTD (finite-difference time-domain) simulation, this work reveals the variation of all SPR parameters (position, intensity, width, and mode) with nanoparticle heights, which demonstrates that the effect of heights are different in various stages. On increasing the heights, the major dipole SPR mode precisely blue-shifts from the near-infrared to the visible region with intensity strengthening, a peak narrowing effect, and multipole modes excitation in the UV-vis range. The intensity of multipole modes can be manipulated to be equal to or even greater than the major dipole SPR mode. After coating conformal TiO2 shells on these nanoparticle arrays by atomic layer deposition, the strengthening of the SPR modes with increasing the heights results in the multiplying of the photocurrent (from ∼2.5 to a maximum 90 μA cm(-2)) in this plasmonic-metal-semiconductor-incorporated system. This simple but effective adjustment for all SPR parameters provides guidance for the future design of plasmonic metallic nanostructures, which is significant for SPR applications.

Zinc oxide, a wide band-gap semiconductor, has shown extensive potential applications in high-efficiency semiconductor photoelectronic devices, semiconductor photocatalysis, and diluted magnetic semiconductors. Due to the undisputed lattice integrity, ZnO single crystals are essential for the fabrication of high-quality ZnO-based photoelectronic devices, and also believed to be ideal research subjects for understanding the underlying mechanisms of semiconductor photocatalysis and diluted magnetic semiconductors. This review, which is organized in two main parts, introduces the recent progress in growth, basic characterization, and device development of ZnO single crystals, and some related works in our group. The first part begins from the growth of ZnO single crystal, and summarizes the fundamental and applied investigations based on ZnO single crystals. These works are composed of the fabrication of homoepitaxial ZnO-based photoelectronic devices, the research on the photocatalysis mechanism, and dilute magnetic mechanism. The second part describes the fabrication of highly thermostable n-type ZnO with high mobility and high electron concentration through intentional doping. More importantly, in this part, a conceptual approach for fabricating highly thermostable p-type ZnO materials with high mobility through an integrated three-step treatment is proposed on the basis of the preliminary research.

In this study, we present a facile method to enhance the transmittance of soda lime glasses through hydrothermal processing. By adjusting the treated parameters, we obtain two types of glass with enhanced transmission: one frosted glass and one clear glass. Our results show that after surface modification with ammonium hydroxide solution, the transmittance of the frosted glass reach more than 95%. Scanning electron microscopy studies reveal that the treated surface is covered with irregular micro-craters. On the other hand, the treated clear glass is covered with extensive nanoflakes structure. We achieve a maximum of 5.4% transmittance enhancement for the clear glass over a wide wavelength range, to 96.7% for normal incidence.

Controllable nanofabrication is at the very foundation of nano-science and nano-technology. Today, ultrafast laser writing has been broadly adopted for micro-fabrication because of its ability to make precise and rapid processing of almost all types of materials in an ambient environment. However, direct laser writing is typically unsuitable for high-quality 2D nano-patterning. In this work, we introduce a maskless laser nano-lithographic technique that allows us to create regular 2D periodic nanopatterns on glass. Glass is a particularly challenging material since it does not absorb light readily. Our strategy starts with a glass sample being coated with a thin layer of metal, and then irradiated with a series of pulse bursts at progressively increasing fluence levels. This process allows us to sequentially activate a series of tailored physical processes that lead to the formation of regular 2D periodic nanopatterns on glass. The formation mechanism of this nano-patterning is also simulated numerically and further corroborated by a series of control experiments. We also show controllability in forming various shapes and sizes of nanopatterns through tailored fluence doses. Our technique provides a high-speed and low-cost method for glass nanofabrication.

The spatial distribution of localized surface plasmon resonance (LSPR) plays a key role in many plasmonic applications. Based on the thermal stability of alumina templates, this work reports a novel approach to manipulate the distribution of LSPR and exhibits its significance for an important plasmonic application, the surface-enhanced Raman spectroscopy (SERS). A suitable thermal annealing sharpens the edges in top surfaces (far from the substrates) of Ag nanoparticles, which significantly strengthens the distal mode (DM) with the LSPR excited on the top surfaces. Because the top surface is the major place to adsorb probe molecules, this manipulation greatly improves the detection sensitivity of SERS. Our research provides a new way to improve the sensitivity of SERS, which also indicates that great care has to be taken on special LSPR mode which is largely responsible for a certain plasmonic application (e.g., the DM for SERS although it is not the major mode).

Two kinds of nanoscale TiO2 films were prepared by magnetron sputtering and screen printing methods, respectively. Results show that both phase composition and specific surface area of the film affect the photocatalytic bactericidal efficiency. Time-series in situ atomic force microscopy (AFM) observation were further used to characterize the cellular responses of Escherichia coli (E. coli) in photocatalytic process. Some nanosized patches were found on the bacterial surface in the forepart of photocatalytic reaction. It suggested that the photocatalytic attack induced the self-protection of bacteria at first. Subsequently, some cracks on the surface and the enlargement of cell body indicated that the cell wall was damaged and lost its structure supporting function, and it eventually led to the death of bacteria.

Ideal Al-doped ZnO (AZO) thin films should have high carrier mobility and carrier concentration, as well as high thermal and chemical stability. To achieve these properties, ZnO should be heavily doped with Al and perfectly crystallized. Through analyzing the possible valence state of the elements and local lattice structures of AZO films during the gas-phase deposition process, we find that the current gas-phase deposition method may encounter an intrinsic obstacle that heavy doping of Al, high thermal stability, and high mobility (perfect crystallinity) cannot be achieved simultaneously. However, based on the understanding that an AZO thin film prepared in oxidizing atmosphere is actually accompanied with a high concentration of zinc vacancy, we propose a strategy to obtain an AZO film with ideal characteristics. Under an oxidizing atmosphere, a heavily doped AZO film with a high concentration of zinc vacancy is prepared using a gas-phase deposition method. Then a zinc vapor annealing treatment is emplo...

The subsolidus phase relations of the ZnO–P 2 O 5 –WO 3 ternary system were investigated by means of X-ray diffraction (XRD). No ternary compound was found in this ternary system, while five binary compounds were obtained and six compatibility triangles were determined. The phase diagram of pseudobinary system Zn 3 (PO 4 ) 2 –ZnWO 4 was also constructed through XRD and differential thermal analysis (DTA) methods, which forms eutectic system with eutectic temperature about 990 °C. The corresponding eutectic component is 30 mol% ZnWO 4 and 70 mol% Zn 3 (PO 4 ) 2 .

The subsolidus phase relations of the ternary system ZnO–V 2 O 5 –WO 3 was investigated by means of X-ray diffraction (XRD) analysis. The phase relations had been constructed. Five binary compounds, five tie lines and six three-phase regions were determined in this system. The possible component regions for ZnO single crystal flux growth were discussed. The phase diagram of Zn 4 V 2 O 9 –ZnWO 4 pseudo-binary system from 740 °C to 1300 °C was also determined through XRD and differential thermal analysis (DTA) methods. DTA results indicated this system was a eutectic system, and the eutectic temperature was 880 °C and eutectic point component was 78 mol% Zn 4 V 2 O 9 and 22 mol% ZnWO 4 . The compounds composed of 78 mol% Zn 4 V 2 O 9 and 22 mol% ZnWO 4 might be suitable flux for ZnO crystal growth.

Applicable surface enhanced Raman scattering (SERS) active substrates require high enhancement factor (EF), excellent spatial reproducibility, and low-cost fabrication method on a large area. Although several SERS substrates with high EF and relative standard deviation (RSD) of signal less than 5% were reported, reliable fabrication for large area SERS substrates with both high sensitivity and high reproducibility via low-cost routes remains a challenge. Here, we report a facile and cost-effective fabrication process for large-scale SERS substrate with Ag inter-nanoparticle (NP) gaps of 5 nm based on ultrathin alumina mask (UTAM) surface pattern technique. Such closely packed Ag NP arrays with high density of electromagnetic field enhancement ("hot spots") on large area exhibit high SERS activity and excellent reproducibility, simultaneously. Rhodamine 6G molecules with concentration of 1 × 10(-7) M are used to determine the SERS performance, and an EF of ∼10(9) is obtained. It should be noted that we obtain RSDs about 2% from 10 random spots on an area of 1 cm(2), which implies the highly reproducible signals. Finite-difference time-domain simulations further suggest that the enhanced electric field originates from the narrow gap, which agrees well with the experimental results. The low value of RSD and the high EF of SERS signals indicate that the as-prepared substrate may be promising for highly sensitive and uniform SERS detection.

This work reports a nonlithographic nanopatterning approach to fabricate perfectly ordered nanoparticle arrays with tunable and uniform dimensions from about 30 to 80 nm and strict periods of 100 nm in a square lattice on large-area substrates by combining nanoimprinting with ultrathin alumina membrane technique. There is no requirement of any organic layer to support an ultrathin membrane in our novel route, which totally addressed the problems of nonuniform pores in prepatterned alumina templates and contamination during sample preparation, and thus is indispensable for our fabrication of ideally regular nanoparticle arrays on various kinds of substrates (such as flexible plastic). The effect of imprinted pressure on the prepatterning of Al foil was also studied in order to ensure the reusability of the precious imprinting stamps. This simple but efficient method provides a cost-effective platform for the fabrication of perfectly ordered nanostructures on substrates for various applications in nanotechnology.

Two kinds of nanoscale TiO2 films were prepared by magnetron sputtering and screen printing methods, respectively. Results show that both phase composition and specific surface area of the film affect the photocatalytic bactericidal efficiency. Time-series in situ atomic force microscopy (AFM) observation were further used to characterize the cellular responses of Escherichia coli (E. coli) in photocatalytic process. Some nanosized patches were found on the bacterial surface in the forepart of photocatalytic reaction. It suggested that the photocatalytic attack induced the self-protection of bacteria at first. Subsequently, some cracks on the surface and the enlargement of cell body indicated that the cell wall was damaged and lost its structure supporting function, and it eventually led to the death of bacteria.

The subsolidus phase relations of the ternary system ZnO–V 2 O 5 –WO 3 was investigated by means of X-ray diffraction (XRD) analysis. The phase relations had been constructed. Five binary compounds, five tie lines and six three-phase regions were determined in this system. The possible component regions for ZnO single crystal flux growth were discussed. The phase diagram of Zn 4 V 2 O 9 –ZnWO 4 pseudo-binary system from 740 °C to 1300 °C was also determined through XRD and differential thermal analysis (DTA) methods. DTA results indicated this system was a eutectic system, and the eutectic temperature was 880 °C and eutectic point component was 78 mol% Zn 4 V 2 O 9 and 22 mol% ZnWO 4 . The compounds composed of 78 mol% Zn 4 V 2 O 9 and 22 mol% ZnWO 4 might be suitable flux for ZnO crystal growth.