Preface on laser material interactions: from basic science to industrial applications (LaserMaterInter2020)

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A review on photothermal conversion of solar energy with nanomaterials and nanostructures: from fundamentals to applications

Solar energy is a green, sustainable, and de facto inexhaustible energy source for mankind. The conversion of solar energy into other forms of energy has attracted extensive research interest due to climate change and the energy crisis. Among all the solar energy conversion technologies, photothermal conversion of solar energy exhibits unique advantages when applied for water purification, desalination, high-temperature heterogeneous catalysis, anti-bacterial treatments, and deicing. In this review, the various photothermal conversion mechanisms based on different forms of heat release are summarized and some of the latest examples are presented. In addition, the necessary prerequisites for solar-driven photothermal materials toward their practical applications are also discussed. Further, the latest advances in photothermal conversion of solar energy are discussed, focusing on different types of photothermal applications. Finally, a summary is given and the challenges and opportunities in the photothermal conversion of solar energy are presented. This review aims to give a comprehensive understanding of emerging solar energy conversion technologies based on the photothermal effect, especially by using nanomaterials and nanostructures

Direct Laser Synthesis of Functional Coatings by FEL Treatments

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Deformation behavior of gold/copper multilayer systems

Two sets of Au/Cu multilayers with a total thickness of 2 µm were deposited with magnetron sputtering onto Si/SiO2 with an individual layer thickness of 250 nm and 25 nm. Subsets of the samples were treated with rapid thermal annealing (RTA) at temperatures of 300°C and 400°C for 60 s each to allow inter-diffusion and alloying at the Au/Cu interfaces. The mechanical behavior was evaluated by nanoindentation with a Vickers indenter at maximum loads of 20 mN to 500 mN. Cross sections of the nanoindentations were prepared by focused ion beam technique to investigate the deformation phenomena of the multilayer structure by scanning electron microscopy. In comparison of both, the 25 nm and the 250 nm structure, respectiveley, the latter shows a delamination near the indenter edge normal vector to the substrate surface, whereas the thin layers show buckling and shear banding as deformation mechanisms and no delamination occurs. The Martens hardness HM determined at a depth of 10 % of the total multilayer thickness increases from 1.8 GPa to 2.2 GPa with the annealing at 300°C for the 250 nm layers and to 2.9 GPa with the reduction of the layer thickness to 25 nm. X-ray diffraction patterns reveal a strong texture in \u3c111\u3e direction normal to the substrate surface and the formation of a Au-Cu solid solution phase during annealing. The decrease in individual layer thickness leads to a classic increase of the Martens hardness due to dislocation pile-up and a significant change in deformation behavior from dislocation plasticity to shear banding, which Li et al. [1] describe as buckling-assisted grain boundary sliding. After annealing, a notable increase of the hardness is observed for the 250 nm layers, while for the 25 nm layers it does not change significantly. Subsequent TEM investigations shall provide information on the processes in the layers and at the layer interfaces. Please click Additional Files below to see the full abstract

Effect of SiO2 interlayer thickness in Au/SiO2/Si multilayer systems on Si sources and the formation of Au-based nanostructures

Si sources involved in the growth of Au-SiOx nanostructures are investigated through the rapid thermal annealing of gold thin films on SiO2/Si substrates with various SiO2 layer thicknesses (3, 25, 100, 500 nm) in a reducing atmosphere. This method reveals three Si sources whose involvement depends on the thickness of the SiO2 layers, i.e., Si diffusion from the substrate, and SiO from SiO2 decomposition and from Si active oxidation. Increasing thicknesses of the SiO2 layer hampers the Si diffusion and the decomposition of regions of the SiO2 layer, which decreases the concentrations of discovered regions weakening the Si active oxidation. These discovered regions appear in systems with a SiO2 layer of 25 or 100 nm, while they are absent for a 500 nm layer. Furthermore, Au-SiOx nanostructures of different shapes form in each system. Both behaviors indicate that the influence and transport mechanisms of the different Si sources are largely dependent on the thicknesses of the SiO2 layers and that they control the evolution of the Au-SiOx nanostructures. A clear understanding of the relationship between these thicknesses and the possible Si sources and their roles in the evolution of the nanostructures makes the tailored fabrication of nanostructures possible

Formation and evolution of Au-SiOx heterostructures: from nanoflowers to nanosprouts

This work reports the formation of circular cavities and Au-SiOx nanoflowers after annealing of thin Au film deposited on SiO2/Si substrates, and the transformation of nanoflowers to nanosprouts with increasing the annealing time. Two reference experiments indicate that both H2 and Si are indispensable for the above structures. The formation of cavities can be attributed to the SiO2 layer decomposition and the product, volatile SiO, provides a Si source for the formation of nanoflowers at the early stage. A model is proposed to indicate that SiO gas produced at the Si/SiO2 interface can diffuse to the surface assisted by the defects in the SiO2 layer before the decomposed cavities are exposed. Then the exposing of those cavities introduces another volatile SiO from the active oxidation of Si substrate, provoking a change in the direction of the main Si source, which in turn makes the one nanoparticle of the nanoflower split in two and finally form the nanosprout. The model about the escape of SiO further details SiO2 decomposition process, and the transformation mechanism from nanoflowers to nanosprout sheds light on a feasible nanofabrication method to design tunable size and shape of nanoparticles

Controllable Si oxidation mediated by annealing temperature and atmosphere

The morphology evolution by thermal annealing induced dewetting of gold (Au) thin films on silicon (Si) substrates with a native oxide layer and its dependences on annealing temperature and atmosphere are investigated. Both dewetting degree of thin film and Au/Si interdiffusion extent are enhanced with the annealing temperature. Au/Si interdiffusion can be observed beyond 800 °C and Au-Si droplets form in both argon and oxygen (Ar + O2) and argon and hydrogen (Ar + H2) environments. In Ar + O2 case, the passive oxidation (Si + O2 → SiO2) of diffused Si happens and thick silicon oxide (SiOx) covering layers are formed. A high temperature of 1050 °C can even activate the outward growth of free-standing SiOx nanowires from droplets. Similarly, annealing at 800 °C under Ar + H2 situation also enables the slight Si passive oxidation, resulting in the formation of stripe-like SiOx areas. However, higher temperatures of 950-1050 °C in Ar + H2 environment initiate both the SiOx decomposition and the Si active oxidation (2Si + O2 → 2SiO(g)), and the formation of solid SiOx is absent, leading to the only formation of isolated Au-Si droplets at elevated temperatures and droplets evolve to particles presenting two contrasts due to the Au/Si phase separation upon cooling

High-efficiency photothermal water evaporation using broadband solar energy harvesting by ultrablack silicon structures

Development of broadband absorption materials for solar energy harvesting is an important strategy to address global energy issues. Herein, it is demonstrated that an ultrablack silicon structure with abundant surface texturing can absorb about 98.7% solar light within the wavelength range of 300 to 2500 nm, i.e., a very large range and amount. Under 1 sun irradiation, the ultrablack silicon sample's surface temperature can increase from 21.2 to 51.2 °C in 15 min. During the photothermal water evaporation process, the ultrablack silicon sample's surface temperature can still reach a highest temperature of 43.2 °C. The average photothermal conversion efficiency (PTCE) can be as high as 72.96%. The excellent photothermal performance to the excellent light-trapping ability of the pyramidal surface nanostructures during solar illumination, which leads to extremely efficient absorption of light, is attributed. In addition, the large water contact area also enables fast vapor transport. The stability of the photothermal converter is also examined, presenting excellent structure and performance stabilities over 10 cycles. This indicates that the ultrablack Si absorber can be a promising photothermal conversion material for seawater desalination, water purification, photothermal therapy, and more

Morphological and compositional mapping of supersaturated AuNi alloy nanoparticles fabricated by solid state dewetting

The solid state dewetting (SSD) of metallic bilayers is a straightforward method for the fabrication of alloy nanoparticles. In particular, alloys that present a gap of miscibility offer a rich phenomenology regarding not only the particle formation but also the composition of their phases. In the present work, AuNi precursor bilayers have been annealed at different temperatures and times to produce AuNi alloy nanoparticles. The evolution of the shape, size, and interparticle distance as well as the composition of the different phases formed in the nanoparticles, allow to unravel the role of the annealing temperatures and times for the fabrication of AuNi supersaturated alloys. Furthermore, the results offer a morphological and compositional map for the fabrication of AuNi alloys nanoparticles of different shapes, sizes, and compositions. Therefore, this map is a useful tool for the tailored design of supersaturated or decomposed nanoparticles by SSD

Hydrogenated TiO2 nanoparticles loaded with Au nanoclusters demonstrating largely enhanced performance for electrochemical reduction of nitrogen to ammonia

Pristine TiO2/Au (P-TiO2/Au) is modified by hydrogen plasma (H-TiO2/Au) or hydrogen and oxygen plasma (H-O-TiO2/Au) treatment, and then used as electrochemical catalysts for nitrogen reduction reaction (NRR). H-TiO2/Au shows enhanced performance for the NRR process compared with both P-TiO2/Au and H-O-TiO2/Au. After hydrogenation treatment, some disordered regions on the surface of TiO2 nanoparticles are formed, and a large number of oxygen vacancies are incorporated into the TiO2 crystalline structures. When the samples are used as catalysts for electrochemical NRR, the yield of NH3 of H-TiO2/Au is about ten times compared to that of P-TiO2/Au and about three times that of H-O-TiO2/Au, while the highest Faradaic efficiency of 2.7% is also obtained at the potential of -0.1 V for the H-TiO2/Au catalyst. The density functional theory (DFT) calculation results confirm that H-TiO2/Au with oxygen vacancies and the disordered surface layer is much preferred energetically for the NRR process. It proves that enhanced adsorption of N2 molecules on the catalyst and reduced reaction barriers due to the presence of defects play an important role in improving catalysts’ performances. The results show that the plasma hydrogenation technique can be used as an efficient method to modify catalysts for electrochemical NRR processes