Characterization of MHz pulse repetition rate femtosecond laser-irradiated gold-coated silicon surfaces

Merging of Bi-Modality of Ultrafast Laser Processing: Heating of Si/Au Nanocomposite Solutions with Controlled Chemical Content

Ultrafast laser processing possesses unique outlooks for the synthesis of novel nanoarchitectures and their further applications in the field of life science. It allows not only the formation of multi-element nanostructures with tuneable performance but also provides various non-invasive laser-stimulated modalities. In this work, we employed ultrafast laser processing for the manufacturing of silicon-gold nanocomposites (Si/Au NCs) with the Au mass fraction variable from 15% (0.5 min ablation time) to 79% (10 min) which increased their plasmonic efficiency by six times and narrowed the bandgap from 1.55 eV to 1.23 eV. These nanostructures demonstrated a considerable fs laser-stimulated hyperthermia with a Au-dependent heating efficiency (~10-20 °C). The prepared surfactant-free colloidal solutions showed good chemical stability with a decrease (i) of zeta (ξ) potential (from -46 mV to -30 mV) and (ii) of the hydrodynamic size of the nanoparticles (from 104 nm to 52 nm) due to the increase in the laser ablation time from 0.5 min to 10 min. The electrical conductivity of NCs revealed a minimum value (~1.53 µS/cm) at 2 min ablation time while their increasing concentration was saturated (~1012 NPs/mL) at 7 min ablation duration. The formed NCs demonstrated a polycrystalline Au nature regardless of the laser ablation time accompanied with the coexistence of oxidized Au and oxidized Si as well as gold silicide phases at a shorter laser ablation time (<1 min) and the formation of a pristine Au at a longer irradiation. Our findings demonstrate the merged employment of ultrafast laser processing for the design of multi-element NCs with tuneable properties reveal efficient composition-sensitive photo-thermal therapy modality.

Drastic Gas Sensing Selectivity in 2-Dimensional MoS2 Nanoflakes by Noble Metal Decoration

Noble metal nanoparticle decoration is a representative strategy to enhance selectivity for fabricating chemical sensor arrays based on the 2-dimensional (2D) semiconductor material, represented by molybdenum disulfide (MoS₂). However, the mechanism of selectivity tuning by noble metal decoration on 2D materials has not been fully elucidated. Here, we successfully decorated noble metal nanoparticles on MoS₂ flakes by the solution process without using reducing agents. The MoS₂ flakes showed drastic selectivity changes after surface decoration and distinguished ammonia, hydrogen, and ethanol gases clearly, which were not observed in general 3D metal oxide nanostructures. The role of noble metal nanoparticle decoration on the selectivity change is investigated by first-principles density functional theory (DFT) calculations. While the H₂ sensitivity shows a similar tendency with the calculated binding energy, that of NH₃ is strongly related to the binding site deactivation due to preferred noble metal particle decoration at the MoS₂ edge. This finding is a specific phenomenon which originates from the distinguished structure of the 2D material, with highly active edge sites. We believe that our study will provide the fundamental comprehension for the strategy to devise the highly efficient sensor array based on 2D materials.

Environmentally Friendly Improvement of Plasmonic Nanostructure Functionality towards Magnetic Resonance Applications

Plasmonic nanostructures have attracted a broad research interest due to their application perspectives in various fields such as biosensing, catalysis, photovoltaics, and biomedicine. Their synthesis by pulsed laser ablation in pure water enables eliminating various side effects originating from chemical contamination. Another advantage of pulsed laser ablation in liquids (PLAL) is the possibility to controllably produce plasmonic nanoparticles (NPs) in combination with other plasmonic or magnetic materials, thus enhancing their functionality. However, the PLAL technique is still challenging in respect of merging metallic and semiconductor specific features in nanosized objects that could significantly broaden application areas of plasmonic nanostructures. In this work, we performed synthesis of hybrid AuSi NPs with novel modalities by ultrashort laser ablation of bulk gold in water containing silicon NPs. The Au/Si atomic ratio in the nanohybrids was finely varied from 0.5 to 3.5 when changing the initial Si NPs concentration in water from 70 µg/mL to 10 µg/mL, respectively, without requiring any complex chemical procedures. It has been found that the laser-fluence-insensitive silicon content depends on the mass of nanohybrids. A high concentration of paramagnetic defects (2.2·× 10¹⁸ spin/g) in polycrystalline plasmonic NPs has been achieved. Our findings can open further prospects for plasmonic nanostructures as contrast agents in optical and magnetic resonance imaging techniques, biosensing, and cancer theranostics.

Facile Synthesis of Multifunctional Magnetoplasmonic Au-MnO Hybrid Nanocomposites for Cancer Theranostics

Significant attention is paid to the design of magnetoplasmonic nanohybrids, which exploit synergistic properties for biomedical applications. Here, a facile method was employed to prepare plasmonic magnetic Au-MnO heterostructured hybrid nanoparticles for imaging-guided photothermal therapy of cancers in vitro, with the view to reducing the serious drawbacks of chemotherapy and gadolinium-based contrast agents. The biocompatibility of the prepared Au-MnO nanocomposites was further enhanced by Food and Drug Administration (FDA)-approved triblock copolymers Pluronic^® F-127 and chitosan oligosaccharide (COS), with complementary support to enhance the absorption in the near-infrared (NIR) region. In addition, synthesized COS-PF127@Au-MnO nanocomposites exhibited promising contrast enhancement in T₁ MR imaging with a good r₁ relaxivity value (1.2 mM^-1 s^-1), demonstrating a capable substitute to Gd-based toxic contrast agents. In addition, prepared COS-PF127@Au-MnO hybrid nanoparticles (HNPs) produced sufficient heat (62 °C at 200 μg/mL) to ablate cancerous cells upon 808 nm laser irradiation, inducing cell toxicity, and apoptosis. The promising diagnostic and photothermal therapeutic performance demonstrated the appropriateness of the COS-PF127@Au-MnO HNPs as a potential theranostic agent.

Carbon nanotube synthesis and spinning as macroscopic fibers assisted by the ceramic reactor tube

Macroscopic fibers of carbon nanotubes (CNT) have emerged as an ideal architecture to exploit the exceptional properties of CNT building blocks in applications ranging from energy storage to reinforcement in structural composites. Controlled synthesis and scalability are amongst the most pressing challenges to further materialize the potential of CNT fibers. This work shows that under floating catalyst chemical vapor conditions in the direct spinning method, used both in research and industry, the ceramic reactor tube plays an unsuspected active role in CNT growth, leading for example to doubling of reaction yield when mullite (Al_4+2xSi_2−2xO_10−x(x ≈ 0:4)) is used instead of alumina (Al₂O₃), but without affecting CNT morphology in terms of number of layers, purity or degree of graphitization. This behaviour is confirmed for different carbon sources and when growing either predominantly single-walled or multi-walled CNTs by adjusting promotor concentration. Analysis of large Si-based impurities occasionally found in CNT fiber fabric samples, attributed to reactor tube fragments that end up trapped in the porous fibers, indicate that the role of the reactor tube is in catalyzing the thermal decomposition of hydrocarbons, which subsequently react with floating Fe catalyst nanoparticles and produce extrusion of the CNTs and formation of an aerogel. Reactor gas analysis confirms that extensive thermal decomposition of the carbon source occurs in the absence of Fe catalyst particles, and that the concentration of different carbon species (e.g. carbon dioxide and ethylene) is sensitive to the reactor tube type. These finding open new avenues for controlled synthesis of CNT fibers by decoupling precursor decomposition from CNT extrusion at the catalyst particle.

Nucleic acid functionalized fiber optic probes for sensing in evanescent wave: optimization and application

Nucleic acid functionalized evanescent wave fiber optic (EWFO) biosensors have attracted much attention due to their remarkable advantages in both device configuration and sensing performance. One critical technique in EWFO biosensor fabrication is its surface modification, which requires (1) minimal nonspecific adsorption and (2) high-quality DNA immobilization to guarantee satisfactory sensing performances. Focusing on these two requirements, a series of optimizations have been conducted in this work to develop reliable DNA-functionalized EWFO probes. Firstly, the surface planeness of EWFO probes were found to be greatly improved by a novel HF/HNO₃ mixture etching solution. Both atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were conducted to investigate the morphological structures and surface chemical compositions. Besides, EWFO sensing performances adopting moderate immobilization of irrelevant DNA were investigated for optimization purposes. Furthermore, a split aptamer based sandwich-type EWFO sensor was developed using adenosine (Ade) as the model target (LOD = 25 μM). To the best of our knowledge, this study is the first case to focus on the optimization of etching solution compositions in the fabrication of combination tapered fibers, which provides experimental basis for the understanding of the silica-etching mechanism using HF/HNO₃ mixture solution and may further inspire related researches.

Reliable DNA-functionalized optic probes for sensing in evanescent wave have been developed based a series of optimizations on the etching solution and immobilization chemistry.

Economic and High Performance Phosphorus-Carbon Composite for Lithium and Sodium Storage

Porous carbon derived from rice hulls has potential for application in phosphorus-carbon composites as high capacity anode materials for lithium-ion and sodium-ion batteries. The native composition of rice husks produces a porous carbon with a unique doped structure, as well as an efficient pore and channel structure, which may facilitate high and stable lithium storage. After cycling for over 100 cycles, the composite delivered a capacity of about 1293 mAh g^-1, as well as a coulombic efficiency of nearly 99% at the current density of 130 mA g^-1 with a capacity density of 1.43 mAh cm^-2. High specific discharge capacities were maintained at different current densities (∼2224, ∼1895, ∼1642, and ∼1187 mAh g^-1 _composite at 130, 260, 520, and 1300 mA g^-1, respectively). This study may offer a golden opportunity to change the humble fate of rice hulls, and also pave the way toward successful battery application for phosphorus-carbon composite anode materials.

SERS Active Nanobiosensor Functionalized by Self-Assembled 3D Nickel Nanonetworks for Glutathione Detection

We introduce a "non-noble metal" based SERS active nanobiosensor using a self-assembled 3D hybrid nickel nanonetwork. A tunable biomolecule detector fabricated by a bottom-up approach was functionalized using a multiphoton ionization energy mechanism to create a self-assembled 3D hybrid nickel nanonetwork. The nanonetwork was tested for SERS detection of crystal violet (CV) and glutathione (GSH) at two excitation wavelengths, 532 and 785 nm. The results reveal indiscernible peaks with a limit of detection (LOD) of 1 picomolar (pM) concentration. An enhancement factor (EF) of 9.3 × 10⁸ was achieved for the chemical molecule CV and 1.8 × 10⁹ for the biomolecule GSH, which are the highest reported values so far. The two results, one being the CV molecule proved that nickel nanonetwork is indeed SERS active and the second being the GSH biomolecule detection at both 532 and 785 nm, confirm that the nanonetwork is a biosensor which has potential for both in vivo and in vitro sensing. In addition, the selectivity and versatility of this biosensor is examined with biomolecules such as l-Cysteine, l-Methionine, and sensing GSH in cell culture medium which mimics the complex biological environment. The functionalized self-assembled 3D hybrid nickel nanonetwork exhibits electromagnetic and charge transfer based SERS activation mechanisms.

Electroassisted codeposition of sol-gel derived silica nanocomposite directs the fabrication of coral-like nanostructured porous gold

Herein, we report on a one-step coelectrodeposition method to form gold-silica nanocomposite materials from which high surface area nanostructured gold electrodes can be produced. The as-prepared Au-SiO2 films possess an interconnected three-dimensional porous framework with different silica-gold ratios depending on the deposition solutions and parameters. Chemical etching of the nanocomposite films using hydrofluoric acid resulted in the formation of nanostructured porous gold films with coral-like structures and pores in the nanometer range. The cross-linkage of the gold coral branches resulted in the generation of a porous framework. X-ray photoelectron spectroscopy confirms the complete removal of silica. Well-controlled surface area enhancement, film thickness, and morphology were achieved by manipulating the deposition parameters, such as potential, time, and gold ion and sol-gel monomer concentrations in the deposition solution. An enhancement in the surface area of the electrode up to 57 times relative to the geometric area has been achieved. The thickness of the as-prepared Au-SiO2 nanocomposite films is relatively high and varied from 8 to 15 μm by varying the applied deposition potential while the thickness of the coral-like nanostructured porous gold films ranged from 0.22 to 2.25 μm. A critical sol-gel monomer concentration (CSGC) was determined at which the deposited silica around the gold coral was able to stabilize the coral-like gold nanostructures, while below the CSGC, the coral-like gold nanostructures were unstable and the surface area of the nanostructured porous gold electrodes decreased.

Interface interaction induced ultra-dense nanoparticles assemblies

We demonstrate a simple and clean physical methodology for fabricating such nanoparticle assemblies (dense arrays and/or dendrites) related to the interfacial interaction between the constructed materials and the anodized aluminum oxide (AAO) porous templates. The interfacial interaction can be regulated by the surface tension of the constructed materials and the AAO membrane, and the AAO-template structure, such as pore size, membrane thickness and surface morphologies. Depending on the interfacial interaction between the constructed materials and the AAO templates, NP arrays with mean particle diameters from 3.8 ± 1.0 nm to 12.5 ± 2.9 nm, mean inter-edge spacings from 3.5 ± 1.4 nm to 7.9 ± 3.4 nm and areal densities from 5.6 × 10(11) NPs per cm(2) to 1.5 × 10(12) NPs per cm(2) are fabricated over large areas (currently ~2 cm × 3 cm). The fabrication process includes firstly thermal evaporation of metal layers no more than 10 nm thick on the pre-coated Si wafer by AAO templates with a thickness of less than 150 nm and mean pore sizes no more than 12 nm, and then removal of the AAO templates. The NP arrays can be stable for hours at a temperature slightly below the melting point of the constructed materials (e.g., ~800 °C for Au NPs for 4 hours) with little change in size and inter-particle separation. Using one of them (e.g., 11.8 nm Au NPs) as growth-oriented catalysts, ultra-thin (12.1 ± 2.3 nm) dense nanowires can be conveniently obtained. Furthermore, dendrite superstructures can be generated easily from eutectic alloy NPs with diameters of ~10 nm pre-formed by thermal evaporation of metal layers more than 20 nm thick on surface-patterned thick AAO templates (e.g., 500 nm). The resulting dendrites, dense arrays and other superstructures (i.e., nanorods and nanowires) formed using NP arrays as catalysts, should have broad applications in catalysis, information technology, photovoltaics and biomedical engineering.

Novel approach to the fabrication of Au/silica core-shell nanostructures based on nanosecond laser irradiation of thin Au films on Si

We demonstrate the possibility of producing Au/SiO(2) core-shell nanoparticles by nanosecond laser irradiation of thin (5 and 20 nm) Au films on Si. The Au/Si eutectic reaction and dewetting process caused by the fast melting and solidification dynamics induced by the nanosecond laser irradiations are investigated as the origin of the formation of core-shell nanoparticles. Using several microscopic techniques (Rutherford backscattering spectrometry, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, and energy filtered transmission electron microscopy) the formation and evolution of the core-shell structures are investigated as a function of the laser fluence in the 500-1500 mJ cm(-2) range for both film thicknesses. In particular, the mean height and diameter and surface density evolution of the core-shell structures are quantified and correlated to the laser fluence and Au film thickness.