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This article presents an examination of well-controlled patterns created using a Ga+-based focused ion beam (FIB) on glass, while silicon substrates were used to evaluate the FIB performance by its achievable feature size versus time constraints. The pattern creation on glass was developed with the aim of studying potential surface-enhanced Raman spectroscopy (SERS) applications. Furthermore, the FIB was used to create dimer systems of periodically and randomly positioned dumbbell-shaped pits on the glass (each dimer occupies an area of 203 × 87 nm2). By following the bitmap pattern files, the FIB ensured there was 3000 dimer fabrication over a 20 × 20 μm2 large area, with a pit size and position variation below 10 nm. The article highlights that FIB can be used for precise large-area nano-fabrication. The gold nanoparticle dimers were formed on the prepatterned surface via capillary force-assisted deposition. The fabricated nanostructures were tested in SERS measurements. The enhancement factor for Rhodamine B molecule reached ~105, demonstrating the potential application of the method to create nanostructures in the sensor domain. [ABSTRACT FROM AUTHOR]

Carbon-based nanomaterials are viewed as preferred candidates as photothermal agents in tumor photothermal therapy due to their tailored structure and excellent biocompatibility. Herein, onion-like carbon (OLC) with controlled sp2/sp3-hybridized carbon ratios was explored as an effective photothermal reagent. The OLC was synthesized through thermal annealing of nanodiamonds, with an increase of the sp2 carbon content as the annealing temperature increased. The obtained OLC demonstrated high photothermal efficiency under 808 nm laser irradiation with a maximum value of 74.36% at an annealing temperature of 1400 °C. We suggest that a well-regulated amount of sp2 carbon in the OLC provided an abundance of conjugated π bonds, leading to enhanced light absorption and electron–phonon coupling. In addition, the OLC was conjugated with polyethylene glycol (PEG) and fluorescent molecules (FITC) to visualize the cellular uptake in HCT 116. In vivo tests demonstrated that the OLC-PEG-FITC exhibited good biocompatibility and achieved photothermal killing of cancer cells upon near-infrared laser irradiation. After treatment with the OLC-based photothermal agent, tumor tissues in tumor-bearing mice were effectively ablated. Taken together, these findings confirm the potential of the developed OLC as a photothermal agent for tumor therapy. [ABSTRACT FROM AUTHOR]

Gallium oxide (Ga2O3) is a promising material for high-power semiconductor applications due to its wide band gap and high breakdown voltage. However, the current methods for fabricating Ga2O3 nanostructures have several disadvantages, including their complex manufacturing processes and high costs. In this study, we report a novel approach for synthesizing β-Ga2O3 nanostructures on gallium phosphide (GaP) using ultra-short laser pulses for in situ nanostructure generation (ULPING). We varied the process parameters to optimize the nanostructure formation, finding that the ULPING method produces high-quality β-Ga2O3 nanostructures with a simpler and more cost-effective process when compared with existing methods. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were used to characterize the samples, which indicated the presence of phosphorous. X-ray photoelectron spectroscopy (XPS) confirmed the formation of gallium oxide, along with a minor amount of phosphorus-containing compounds. Structural analysis using X-ray diffraction (XRD) revealed the formation of a monoclinic β-polymorph of Ga2O3. We also measured the band gap of the materials using reflection electron energy loss spectroscopy (REELS), and found that the band gap increased with higher nanostructure formation, reaching 6.2 eV for the optimized sample. Furthermore, we observed a change in the heterojunction alignment, which we attribute to the change in the oxidation of the samples. Our results demonstrate the potential of ULPING as a novel, simple, and cost-effective method for fabricating Ga2O3 nanostructures with tunable optical properties. The ULPING method offers a green alternative to existing fabrication methods, making it a promising technology for future research in the field of Ga2O3 nanostructure fabrication. [ABSTRACT FROM AUTHOR]

The first report of deep eutectic solvents (DESs) was released in 2003 and was identified as a new member of ionic liquid (IL), involving innovative chemical and physical characteristics. Using green solvent technology concerning economical, practical, and environmental aspects, DESs open the window for sustainable development of nanomaterial fabrication. The DESs assist in different fabrication processes and design nanostructures with specific morphology and properties by tunable reaction conditions. Using DESs in synthesis reactions can reduce the required high temperature and pressure conditions for decreasing energy consumption and the risk of environmental contamination. This review paper provides the recent applications and advances in the design strategy of DESs for the green synthesis of nanomaterials. The strategy and application of DESs in wet-chemical processes, nanosize reticular material fabrication, electrodeposition/electrochemical synthesis of nanostructures, electroless deposition, DESs based nano-catalytic and nanofluidic systems are discussed and highlighted in this review. [ABSTRACT FROM AUTHOR]

One approach for the formation of structures with complex geometries at the nanoscale is the step-by-step assembly. In this case, it is necessary to be able to estimate the time required to establish orientational equilibrium for a preformed pair of particles. This process is statistical in nature and depends on the mechanism of interaction of the ensemble with the external field. The orientation of particles in an alternating field is associated with certain relaxation times, which depend on the viscosity and temperature of the medium, as well as on the geometric structure of the samples. This paper proposes an mathematical model of the process of establishing the distribution of nanoparticles pairs orientations taking into account the friction force, thermal motion, and the orienting laser field. A statistical orientation distribution was obtained for CdTe particles in the field of moderate laser radiation, and the average time for establishing orientational equilibrium was estimated.

Gallium oxide (Ga2O3) is a promising material for high-power semiconductor applications due to its wide band gap and high breakdown voltage. However, the current methods for fabricating Ga2O3 nanostructures have several disadvantages, including their complex manufacturing processes and high costs. In this study, we report a novel approach for synthesizing β-Ga2O3 nanostructures on gallium phosphide (GaP) using ultra-short laser pulses for in situ nanostructure generation (ULPING). We varied the process parameters to optimize the nanostructure formation, finding that the ULPING method produces high-quality β-Ga2O3 nanostructures with a simpler and more cost-effective process when compared with existing methods. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were used to characterize the samples, which indicated the presence of phosphorous. X-ray photoelectron spectroscopy (XPS) confirmed the formation of gallium oxide, along with a minor amount of phosphorus-containing compounds. Structural analysis using X-ray diffraction (XRD) revealed the formation of a monoclinic β-polymorph of Ga2O3. We also measured the band gap of the materials using reflection electron energy loss spectroscopy (REELS), and found that the band gap increased with higher nanostructure formation, reaching 6.2 eV for the optimized sample. Furthermore, we observed a change in the heterojunction alignment, which we attribute to the change in the oxidation of the samples. Our results demonstrate the potential of ULPING as a novel, simple, and cost-effective method for fabricating Ga2O3 nanostructures with tunable optical properties. The ULPING method offers a green alternative to existing fabrication methods, making it a promising technology for future research in the field of Ga2O3 nanostructure fabrication.

Diffraction limit has been the constraint of the nanostructure fabrication. Because the scanning near-field optical microscopy (SNOM) can work in the evanescent near-field region, its application in nano-processing has received extensive attention from researchers globally. In this paper, we combined nanosecond laser with cantilevered SNOM probe. Utilizing the high precision of the confinement and enhancement effect of probe tip and the high instantaneous energy of the laser, we realized nanostructure fabrication and in situ detection on Au nano-film. Feature sizes down to 47 nm full width at half maximum were fabricated. We investigated the laser propagation through the SNOM tip aperture and the light field intensity distribution on the surface of substrate theoretically. The calculation results demonstrate that the laser is highly restricted within the SNOM aperture and enhanced on the exit plane at the rim of aperture. After the transmission, the light field intensity distribution on the surface of the Au nano-film was enhanced due to the localized surface plasmon resonance. The thermal distribution on the surface of Au nano-film indicates that the peak of the temperature distribution appeared at the surface right underneath the center of the aperture. It is proved that the simulation results are consistent with the experimental results. [ABSTRACT FROM AUTHOR]

This paper reports on the formation of moth-eye nanopillar structures on surfaces of alkali-aluminosilicate Gorilla glass substrates using a self-masking plasma etching method. Surface and cross-section chemical compositions studies were carried out to study the formation of the nanostructures. CF x induced polymers were shown to be the self-masking material during plasma etching. The nanostructures enhance transmission at wavelengths over 525 nm may be utilized for fluid-induced switchable haze. Additional functionalities associated with nanostructures may be realized such as self-cleaning, anti-fogging, and stain-resistance. [ABSTRACT FROM AUTHOR]

Resonances in micrometer metal cavity structures are very important for the interactions between materials and light. Three similar cavities connected with waveguides are investigated through the finite difference time domain (FDTD) method and the coupled mode theory. Two fundamental surface resonance modes are demonstrated in the two simple cavities separately. Then two simple cavities are combined to form the third cavity. The fundamental resonant modes couple positively or oppositely to form coupled-mode resonances in the combined cavity. When the combined cavity structures are symmetric, the coupled-mode resonances lead to two transmission peaks. While the symmetry is broken with tens of nanometers displacements, the transmission peaks convert to dips. It is believed the Q value variation of coupled-mode resonances plays a key role in the conversion. When the structure is symmetric, the coupled-mode resonances in the upper and lower parts of the cavity have the same Q value and are degenerate. The superposition of them leads transmission peaks. While the symmetry is broken, the Q values of resonances in the upper and lower part of the cavity are different, leading to the degenerate coupled mode division. The superposition of the different Q-factor modes leads to the dips. The sensitive variation to the symmetry of structures can be used to control light-material interactions, optical switch, and improve the sensitivity of sensor devices. [ABSTRACT FROM AUTHOR]

Sub-10 nm nanostructures have received broad interest for their intriguing nano-optical phenomena, such as extreme field localization and enhancement, quantum tunneling effect, and strong coupling. The range of cutting-edge applications based on single-digit-nanometer scale structures has expanded with the development of nanofabrication technologies. However, challenges still remain in overcoming fabrication limits, such as scalability, controllability, and reproducibility for further practical applications of the sub-10 nm nanostructures. In this review, we discuss the recent advances in top-down nanofabrication methods towards single-digit-nanometer-sized structures. The well-known examples include electron beam lithography (EBL), focused ion beam (FIB) milling or lithography, atomic layer deposition (ALD), and other unconventional techniques to obtain sub-10 nm nanostructures or nanogaps. We discuss state-of-the-art applications for sub-10 nm nanophotonics such as optical trapping or sensing devices, imaging devices, and electronic devices. [ABSTRACT FROM AUTHOR]

Abstract Biocompatible-sensing materials hold an important role in biomedical applications where there is a need to translate biological responses into electrical signals. Increasing the biocompatibility of these sensing devices generally causes a reduction in the overall conductivity due to the processing techniques. Silicon is becoming a more feasible and available option for use in these applications due to its semiconductor properties and availability. When processed to be porous, it has shown promising biocompatibility; however, a reduction in its conductivity is caused by its oxidization. To overcome this, gold embedding through sputtering techniques are proposed in this research as a means of controlling and further imparting electrical properties to laser induced silicon oxide nanofibers. Single crystalline silicon wafers were laser processed using an Nd:YAG pulsed nanosecond laser system at different laser parameters before undergoing gold sputtering. Controlling the scanning parameters (e.g., smaller line spacings) was found to induce the formation of nanofibrous structures, whose diameters grew with increasing overlaps (number of laser beam scanning through the same path). At larger line spacings, nano and microparticle formation was observed. Overlap (OL) increases led to higher light absorbance’s by the wafers. The gold sputtered samples resulted in greater conductivities at higher gold concentrations, especially in samples with smaller fiber sizes. Overall, these findings show promising results for the future of silicon as a semiconductor and a biocompatible material for its use and development in the improvement of sensing applications.

Optical manipulation of various kinds of nanoparticles is vital in biomedical engineering. However, classical optical approaches demand higher laser power and are constrained by diffraction limits, necessitating tailored trapping schemes for specific nanoparticles. They lack a universal and biocompatible tool to manipulate nanoparticles of diverse sizes, charges, and materials. Through precise modulation of diffusiophoresis and thermo-osmotic flows in the boundary layer of an optothermal-responsive gold film, highly adaptable optothermal nanotweezers (HAONTs) capable of manipulating a single nanoparticle as small as sub-10 nm are designed. Additionally, a novel optothermal doughnut-shaped vortex (DSV) trapping strategy is introduced, enabling a new mode of physical interaction between cells and nanoparticles. Furthermore, this versatile approach allows for the manipulation of nanoparticles in organic, inorganic, and biological forms. It also offers versatile function modes such as trapping, sorting, and assembling of nanoparticles. It is believed that this approach holds the potential to be a valuable tool in fields such as synthetic biology, optofluidics, nanophotonics, and colloidal science., (© 2023 Wiley-VCH GmbH.)

With femtosecond (fs) laser pulse irradiation, a simple but efficient technique to fabricate bi- and quad-directional low spatial frequency laser-induced periodic surface structures (BD- and QD-LSFLs) is suggested on metals. By inserting a quartz wedge achromatic depolarizer prior to the focusing optics, we change the polarization of fs laser pulses periodically in one dimension within the laser spot, and find that this method leads to the creation of BD- and QD-LSFLs by simply raster scanning fs laser pulses on Ni. It is also demonstrated that the interval of orientation change of BD-LSFLs can be manipulated with defocus. • LSFLs with multiple orientations were fabricated on metals within a single raster scanline. • Interval of orientation change in bi-directional LSFLs was controlled with defocus. • Formation mechanism of BD- and QD-LSFLs was discussed with the superposition of two orthogonally polarized fs laser pulses. [ABSTRACT FROM AUTHOR]

An enhanced type of photonic crystal heterostructure microcavity obtained by tuning the radii of air holes close to the photonic crystal waveguide was designed and experimentally verified. The quality factor of the optimized cavity was about 1.73 × 105, which is greatly increased compared with that of the original heterostructure cavity. The main imperfections of the cavities were caused by the over-developing and over-etching of the side of the cavity structure. [ABSTRACT FROM AUTHOR]

Grayscale lithography is used to produce three-dimensional (3D) structures on micro- and nanoscale. During the last decade, micro-optics and other applications were actively pushing the market demand for such structures. Direct-write systems that use lasers and heated scanning probes can be used for high-precision grayscale micro- and nanolithography. They provide solutions for the most demanding applications in research and industrial manufacturing. At both the micro- and nanoscale, though, some challenges remain, mainly related to throughput. Ongoing R&D efforts and emerging new applications drive several companies to join forces in order to meet the market demands for grayscale lithography of today and in the future. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Chiral silver nanoneedles can be directly printed using "structured" laser pulses. • Chirality of the nanoneedles can be tuned by tailoring the spiral-shaped intensity pattern. • Optical angular momentum carried by the beam weakly affects the nanoneedles chirality. Abstract We report on fabrication of Ag nanoneedles with tailored chirality via direct ns-laser printing with "structured" laser beams, zero-optical-angular momentum spiral-shaped beams with variable intensity profiles as well as the perfect optical vortex (POV) beams having fixed donut-shaped intensity pattern and variable topological charge. The chirality of the laser-printed nanoneedles was found to be efficiently tailored via optimization of the corresponding intensity pattern of the zero-OAM spiral-shaped beam, while the increase of the topological charge of the POV beam was shown to weakly affect the nanoneedle geometry. Our comparative study reveals the key role of the initial surface intensity (temperature) distribution driving the helical movement of the transiently molten metal and directing formation of the nanoneedles with pronounced chirality on the surface of the noble-metal films. The obtained results pave the way toward realization of easy-to-implement scalable technology for the direct laser printing of plasmonic nanoneedles with pronounced and tailored chirality suited for various nanophotonic, chemical and biosensing applications. [ABSTRACT FROM AUTHOR]

Abstract Enhancement in fluorescence of samples in solution phase is very crucial for many practical applications. Herein, we report the fluorescence enhancement of a nanomolar solution using Ag core-silica shell nanostructures synthesized independently. Coumarin 6H dye solution has been taken as a case study. Three different Ag core – silica shell nanostructure solutions were prepared by varying the amount of reagent in Stöber method. The core-shell nanostructures were characterized by atomic force microscopy, dynamic light scattering, and UV–Visible spectrophotometry. The maximum values of fluorescence enhancement (η max) were found to be 2.5, 4.3, and 1.5 when respective solutions with average nanoshell thicknesses of 2.4, 16.7 and 28.3 nm were used individually. However, the value of η max increased by an order (η max ~13) when the mixture of the nanoshell solutions was used. The reason behind the improvement in η was ascribed to the optimization in the values of the distance (r) between nanoshell and dye molecules as well as the separation (d) between the nanoshells. This report, as we believe, will enable the scientific community in obtaining better enhancement in the fluorescence signal of labeled proteins and fluorescent molecules in aqueous media with ease. [ABSTRACT FROM AUTHOR]

Controlling the propagations of surface plasmon polaritons (SPPs) is important for many applications. Now, mainly structures for controlling SPPs are etched directly in the metal surface through experimental methods, such as focus ion beam lithography (FIB). In view of mature technology in processing dielectric products, we propose the metal-dielectric composite holography (MDCH) method to design dielectric structures for controlling the propagation of SPPs. The holographic groove structures are designed in dielectric film to control SPP propagation through the surface electromagnetic wave holography (SWH) method. The mutual coherence theory is applied to analyze the influence of the grooves in dielectric film on the phase of propagating SPPs, and the reconstruction condition is obtained. Based on the analysis results, two schemes are proposed to make MDCH structures satisfy the condition: reducing the width of the grooves or filling the grooves with another dielectric. The finite difference time domain (FDTD) method is applied to test the two schemes. Simulation results prove that two schemes are feasible when the width of the groove is smaller than 40 nm or the refractive index of the filling dielectric is limited to a certain range. The investigation verifies that the MDCH method is feasible and the SPP waves can be controlled with high efficiency. Based on the investigation, the mature hologram-fabricated methods and dielectric-processing methods may be used to fabricate structures for controlling SPP waves. The MDCH method may open up the possibility for mass production of plasmonic devices, avoiding the FIB experimental method. [ABSTRACT FROM AUTHOR]

Under femtosecond laser pulse irradiation, the selective control of structural periods of low spatial frequency laser-induced periodic surface structures (LSFLs) is investigated on metals at large incident beam angles. As increasing the number of irradiating pulses, we produce three types of LSFLs, small-, dual-, and large-scale LSFLs, and find two kinds of structural period variations, the sequential structural variations from small- to dual- to large-scale LSFLs and the nonsequential variation directly from small- to large-scale LSFLs by controlling the laser fluence. Using the efficacy factor with the help of the Maxwell-Garnett theory, our study also shows that all three types of LSFLs can be understood by the interference between the incident beam and surface plasmon polaritons at the air-nanostructure composite and metal interface rather than the air-metal interface. [ABSTRACT FROM AUTHOR]

We present the development of a label-free, highly sensitive fiber-optical biosensor for online detection and quantification of biomolecules. Here, the advantages of etched fiber Bragg gratings (eFBG) were used, since they induce a narrowband Bragg wavelength peak in the reflection operation mode. The gratings were fabricated point-by-point via a nonlinear absorption process of a highly focused femtosecond-pulsed laser, without the need of prior coating removal or specific fiber doping. The sensitivity of the Bragg wavelength peak to the surrounding refractive index (SRI), as needed for biochemical sensing, was realized by fiber cladding removal using hydrofluoric acid etching. For evaluation of biosensing capabilities, eFBG fibers were biofunctionalized with a single-stranded DNA aptamer specific for binding the C-reactive protein (CRP). Thus, the CRP-sensitive eFBG fiber-optical biosensor showed a very low limit of detection of 0.82 pg/L, with a dynamic range of CRP detection from approximately 0.8 pg/L to 1.2 µg/L. The biosensor showed a high specificity to CRP even in the presence of interfering substances. These results suggest that the proposed biosensor is capable for quantification of CRP from trace amounts of clinical samples. In addition, the adaption of this eFBG fiber-optical biosensor for detection of other relevant analytes can be easily realized. [ABSTRACT FROM AUTHOR]

This contribution concentrates on ion-induced bending phenomena which may serve as a versatile tool to manufacture nanostructured devices. In particular bending was studied in free standing Au cantilevers. The preparation and irradiation of the cantilevers were performed using a TESCAN LYRA dual beam system. Cantilevers with thicknesses ranging between 90 and 200 nm were irradiated with 30 keV Ga ions normal to the sample surface up to a maximum fluence of ∼3 × 10 20  Ga/m 2 . The bending of the cantilevers towards the incident beam is discussed in terms of local volume change due to accumulation of radiation-induced vacancies and substitutional Ga atoms in the Ga implantation layer, as well as due to accumulation of interstitial type clusters in the region beyond the Ga penetration range. A model is proposed to explain the observations, based on a set of rate equations for concentrations of point defects, i.e. vacancies, self-interstitials and implanted Ga atoms. The influence of preexisting defects is also discussed. The work shows that an in-depth understanding the ion-beam bending can play a predictive role in a quantitative control in for the micro- and nanofabrication of small-sized products. [ABSTRACT FROM AUTHOR]

The size of a plasmonic waveguide is not limited by the optical wavelength. This enables plasmonic waveguides on the order of several tens of nanometers in length, which is not possible with dielectric waveguides, and exceptionally strong light confinement and efficient interaction with nanomaterials that have various unique properties become possible. However, such waveguides are not easily introduced in optical integrated circuits, so a three-dimensional plasmonic mode converter is required. [ABSTRACT FROM AUTHOR]

In order to be compatible with CMOS processing, hybrid bonding of III-V materials on Silicon should be operated at 300 °C, which requires an interface layer. The thinnest layer could be obtained when surfaces are prepared oxide-free and activated. We have investigated several activation processes of de-oxidized surfaces and measured their activation efficiency by X-ray Photoelectron Spectroscopy. We report here on the high structural and optical quality of a hybrid III-V on Silicon interface obtained by bonding under vacuum at 300 °C de-oxidized surfaces activated by ozone. The resulting oxide interface layer is 1.2-nm thick the thinnest already reported. Structural characterization of this interface shows no defect in both crystalline lattices. Hybrid shallow ridge waveguides supporting an optical mode overlapping such an interface show 5 cm −1 propagation losses comparable to the value measured for monolithic InP-based waveguides or SOI waveguides produced with the same technology, evidencing the high optical quality of the hybrid interface. Such a thin layer is favorable for an accurate control of the optical performances within hybrid devices and offers a large versatility for their design. [ABSTRACT FROM AUTHOR]

This paper proposes guided-mode resonant GaN grating that are implemented on a GaN-on-silicon wafer structure. Numerical simulations based on rigorous coupled wave analysis (RCWA) are performed to model multiple resonances in thick GaN membranes. Back wafer etching of freestanding GaN membranes is used as a tuning mechanism to manipulate the optical performance in the visible wavelength range. Angular resolved micro reflectance measurements are conducted to characterize the fabricated GaN gratings and show the dependence of guided-mode resonances on the filling factor of the gratings, the membrane thickness, and the polarization of incident beam. The experimental results agree well with numerical simulations. This paper opens the way to fabricate guided-mode resonant GaN grating for many diverse applications.

Biocompatible-sensing materials hold an important role in biomedical applications where there is a need to translate biological responses into electrical signals. Increasing the biocompatibility of these sensing devices generally causes a reduction in the overall conductivity due to the processing techniques. Silicon is becoming a more feasible and available option for use in these applications due to its semiconductor properties and availability. When processed to be porous, it has shown promising biocompatibility; however, a reduction in its conductivity is caused by its oxidization. To overcome this, gold embedding through sputtering techniques are proposed in this research as a means of controlling and further imparting electrical properties to laser induced silicon oxide nanofibers. Single crystalline silicon wafers were laser processed using an Nd:YAG pulsed nanosecond laser system at different laser parameters before undergoing gold sputtering. Controlling the scanning parameters (e.g., smaller line spacings) was found to induce the formation of nanofibrous structures, whose diameters grew with increasing overlaps (number of laser beam scanning through the same path). At larger line spacings, nano and microparticle formation was observed. Overlap (OL) increases led to higher light absorbance's by the wafers. The gold sputtered samples resulted in greater conductivities at higher gold concentrations, especially in samples with smaller fiber sizes. Overall, these findings show promising results for the future of silicon as a semiconductor and a biocompatible material for its use and development in the improvement of sensing applications. [ABSTRACT FROM AUTHOR]

Surface enhanced Raman scattering has recently been proposed as a label free sensing method for diagnostic applications. Raman scattering is an excellent analysis tool because a wealth of information can be obtained using a single measurement, however the weak signal has made it unsuitable for detecting low concentrations of analytes. Using plasmonic nanostructures to create SERS substrates, the Raman signal can be amplified by several orders of magnitude, but SERS substrates have been complicated to fabricate. Here we report low-cost silicon substrates based on simple fabrication method of silver nanoparticles and silicon nanowires decorated with these nanoparticles for use as a convenient practical platform for SERS-active substrates. In addition, the placement of silver nanoparticles on silicon nanowires allowed the autoaligning of the hot spots such that low cost Raman systems with normal incident laser can be used. These substrates have the ability to detect wide range of concentrations of pyridine, as low as 10 –11 M. An enhancement factor of around 6 to 8 × 105 was observed for silver nanoparticles alone. By depositing the same nanoparticles on silicon nanowires, the enhancement factor jumped by orders of magnitude to 1011. [ABSTRACT FROM PUBLISHER]

Controlling surface plasmon polaritons (SPPs) propagation on metal surface is significant for wide applications. Simple and effective structures are needed for SPP propagation controlling. In this paper, the line holography method is proposed to design a simple structure to control SPP wave propagation. The designed structure is composed of only one metal line, rather than a number of grooves in the holograms designed by the common surface electromagnetic wave holography method (SWH). The holographic line structure can control SPPs propagation effectively. Through the line holography method, two holographic line structures are designed to focus aside a plane SPP wave to one or two points. The finite-difference time-domain (FDTD) method is used to simulate the control process. Results show that the holographic line can control the SPP wave propagation with efficiency of 55%, higher than that of the common SWH method (19%). [ABSTRACT FROM AUTHOR]

We present here a method to achieve an optical demultiplexer working in the visible range to achieve either a polarization beamsplitter (PBS) or the wavelength-division multiplexer (WDM), which is based on the integration of different periodic gratings using the suspended zero contrast grating (ZCG) structure. The proposed demultiplexer comprises two independent ZCG HfO 2 filters, which are very close to each other so that they can be illuminated and measured at the same time. By combining two independent HfO 2 ZCG filters with selectable functionalities in parallel and extending the waveguides on both sides, a PBS device or WDM device can be achieved. The finite difference time-domain (FDTD) method is used to simulate the coupling properties of the ZCG filters. The simulation results show that the proposed PBS device can effectively direct different polarized light with a wavelength of 650 nm into separate waveguides. The WDM device can also separate incoming 550 nm and 650 nm light beams into separate waveguides. The fabricated devices are characterized by the optical microscope and the atomic force microscope (AFM). [ABSTRACT FROM AUTHOR]

The evolution of the nanostructure induced on a titanium (Ti) surface with increasing irradiation pulse number by using a 400-nm femtosecond laser was examined by using scanning electron microscopy. High spatial frequency periodic structures of TiO 2 parallel to the laser polarization were initially observed because of the laser-induced oxidation of the Ti surface and the larger efficacy factor of TiO 2 in this direction. Periodically aligned TiO 2 nanowires with featured width as small as 20 nm were obtained. With increasing pulse number, however, low spatial frequency periodic structures of Ti perpendicular to the laser polarization became dominant because Ti possesses a larger efficacy factor in this direction. The competition between the high- and low-spatial frequency periodic structures is in good agreement with the prediction of the efficacy factor theory and it should also be observed in the femtosecond laser ablation of other metals which are easily oxidized in air. [ABSTRACT FROM AUTHOR]

The plasmonic integrated circuit, a potential application of surface plasmon polaritons (SPPs), can manipulate an SPP wave propagating on a metal surface in a way similar to electronic circuits. Here, we propose the concept of three-dimensional (3D) SPP wave manipulation: control of an SPP wave propagating in both the horizontal direction and the vertical direction. A hole set in the film can guide an SPP wave in the vertical direction. In the horizontal direction, two holographic groove patterns are used to focus an incident SPP wave on one surface of the film to the hole and control the divergent SPP waves transmitted from the hole on the other metal surface, respectively. The holographic groove patterns are designed via the methodology of surface electromagnetic wave holography. 3D finite-difference time-domain method simulations show a good performance of the 3D manipulation via these designed holographic groove patterns. [ABSTRACT FROM AUTHOR]

The rapid development of nanotechnologies and sciences has led to the great demand for novel lithography methods allowing large area, low cost and high resolution nano fabrications. Characterized by unique sub-diffraction optical features like propagation with an ultra-short wavelength and great field enhancement in subwavelength regions, surface plasmon polaritons (SPPs), including surface plasmon waves, bulk plasmon polaritons (BPPs) and localized surface plasmons (LSPs), have become potentially promising candidates for nano lithography. In this paper, investigations into plasmonic lithography in the manner of point-to-point writing, interference and imaging were reviewed in detail. Theoretical simulations and experiments have demonstrated plasmonic lithography resolution far beyond the conventional diffraction limit, even with ultraviolet light sources and single exposure performances. Half-pitch resolution as high as 22 nm (∼1/17 light wavelength) was observed in plasmonic lens imaging lithography. Moreover, not only the overview of state-of-the-art results, but also the physics behind them and future research suggestions are discussed as well. [ABSTRACT FROM AUTHOR]

Integrated photonics requires high gain optical materials in the telecom wavelength range for optical amplifiers and coherent light sources. Erbium (Er) containing materials are ideal candidates due to the 1.5 μm emission from Er ions. However, the Er density in typical Er-doped materials is less than 10 cm, thus limiting the maximum optical gain to a few dB/cm, too small to be useful for integrated photonic applications. Er compounds could potentially solve this problem since they contain much higher Er density. So far the existing Er compounds suffer from short lifetime and strong upconversion effects, mainly due to poor crystal qualities. Recently, we explore a new Er compound: erbium chloride silicate (ECS, Er(SiO)Cl) in the form of nanowire, which facilitates the growth of high quality single crystal with relatively large Er density (1.62 × 10 cm). Previous optical results show that the high crystal quality of ECS material leads to a long lifetime up to 1 ms. The Er lifetime-density product was found to be the largest among all the Er containing materials. Pump-probe experiments demonstrated a 644 dB/cm signal enhancement and 30 dB/cm net gain per unit length from a single ECS wire. As a result, such high-gain ECS nanowires can be potentially fabricated into ultra-compact lasers. Even though a single ECS nanowire naturally serves as good waveguide, additional feedback mechanism is needed to form an ultra-compact laser. In this work, we demonstrate the direct fabrication of 1D photonic crystal (PhC) air hole array structure on a single ECS nanowire using focused ion beam (FIB). Transmission measurement shows polarization-dependent stop-band behavior. For transverse electric (TE) polarization, we observed stop-band suppression as much as 12 dB with a 9 μm long airholed structure. Through numerical simulation, we showed that Q-factor as high as 11000 can be achieved at 1.53 μm for a 1D PhC micro-cavity on an ECS nanowire. Such a high Q cavity combined with the high material gain of ECS nanowires provides an attractive solution for ultra-compact lasers, an important goal of this research. [ABSTRACT FROM AUTHOR]

A high exposure depth nanolithography technology is presented. In the proposed scheme, the photoresist layer is used as a waveguide. With a subwavelength grating (SWG) coupling structure, the incident light is efficiently coupled into the photoresist waveguide, in which the single-mode-resonance (SMR) interference field is formed. Different from other interference lithography, the new scheme can realize high resolution and high exposure depth simultaneously. In this paper, the theoretical model of the SMR interference is established to analyze the light field distribution in the photoresist. The simulation result shows that interference pattern with period smaller than 140 nm and depth larger than 900 nm can be obtained in the photoresist, by using 441 nm incident light and 276 nm period grating coupling structure. [ABSTRACT FROM AUTHOR]

Vertically aligned 3D gallium nitride (GaN) nanowire arrays with sub-50 nm feature sizes were fabricated using a nanosphere lift-off lithography (NSLL) technique combined with hybrid top-down etching steps (i.e., inductively coupled plasma dry reactive ion etching (ICP-DRIE) and wet chemical etching). Owing to the well-controlled chemical surface treatment prior to the nanobead deposition and etching process, vertical GaN nanowire arrays with diameter of ~35 nm, pitch of ~350 nm, and aspect ratio of >10 could be realized using 500 nm polystyrene nanobead (PN) masks. This work has demonstrated a feasibility of using NSLL as an alternative for other sophisticated but expensive nanolithography methods to manufacture low-cost but highly ordered 3D GaN nanostructures.

The ability to deterministically fabricate nanoscale architectures with atomic precision is the central goal of nanotechnology, whereby highly localized changes in the atomic structure can be exploited to control device properties at their fundamental physical limit. Here, an automated, feedback-controlled atomic fabrication method is reported and the formation of 1D-2D heterostructures in MoS 2 is demonstrated through selective transformations along specific crystallographic orientations. The atomic-scale probe of an aberration-corrected scanning transmission electron microscope (STEM) is used, and the shape and symmetry of the scan pathway relative to the sample orientation are controlled. The focused and shaped electron beam is used to reliably create Mo 6 S 6 nanowire (MoS-NW) terminated metallic-semiconductor 1D-2D edge structures within a pristine MoS 2 monolayer with atomic precision. From these results, it is found that a triangular beam path aligned along the zig-zag sulfur terminated (ZZS) direction forms stable MoS-NW edge structures with the highest degree of fidelity without resulting in disordering of the surrounding MoS 2 monolayer. Density functional theory (DFT) calculations and ab initio molecular dynamic simulations (AIMD) are used to calculate the energetic barriers for the most stable atomic edge structures and atomic transformation pathways. These discoveries provide an automated method to improve understanding of atomic-scale transformations while opening a pathway toward more precise atomic-scale engineering of materials., (© 2023 Wiley-VCH GmbH.)

One kind of helium plasma-assisted approach has been presented to fabricate nanostructured tungsten. The morphology and properties evolution of tungsten under helium plasma exposure were investigated as a function of sample temperature, helium ion energy, helium ion dose and helium ion flux. The results show that high crystalline nanostructured tungsten was achieved at 1200 °C. Wavy, meshy and villiform tungsten can be expediently obtained via varying irradiation parameters. Appropriate helium ion energy and ion flux is beneficial to the formation of tungsten with stable nanostructure. The formed nanostructured tungsten was easily oxidized to stoichiometric tungsten trioxide. The as-prepared tungsten trioxide exhibits high light absorption and excellent photoelectrochemical activity. An anodic photocurrent of 3.93 mA/cm² was achieved at 1.6 V (vs. Ag/AgCl) under illumination of a 150 W Xe lamp in 0.5 M H2SO4 electrolyte. [ABSTRACT FROM AUTHOR]