Nanohole Research Articles

Kinetic calculation analysis of Ga deposition on the morphology evolution of GaAs quantum ring

GaAs Quantum Ring (QR) was gained on GaAs (001) by Droplet Epitaxy (DE), and the microscopic morphology of the GaAs samples was observed by Scanning Tunnel Microscope (STM). The kinetic model of Local Droplet Etching (LDE) was mainly used to study the influence of Ga deposition on the morphology evolution from Ga droplets to GaAs QR. Comparing experimental data with the theoretical value, it can be seen that the increase of Ga deposition will cause the reduction of surface density of Ga droplets, but the volume, height and diameter of Ga droplets will increase. Geometric dimension of GaAs QR increased also with the increase of Ga deposition. In addition, it found that the rate at which the substrate was etched was affected by Ga deposition and As pressure from experiment. The more Ga deposition, the deeper GaAs nano hole. However, GaAs nano hole became shallower under high As pressure. These results are consistent with theoretical calculation analysis. Under high substrate temperature, GaAs double rings finally evolved into a single ring. Above all results have certain guiding significance for the preparation of patterned GaAs substrates and the controlled growth of GaAs QR morphology.

Enhanced photocatalytic performance of ammonia self-etched holely g-C3N4 decorated with anatase nanoflakes by a facile synthesis process

Graphitic carbon nitride (g-C3N4) nanosheets have attracted extensive attention in the field of photocatalysis due to their superior properties. However, the photocatalytic performance of g-C3N4 is still restricted by the limited active sites and high combination rate of photo-generated carriers. To confront these drawbacks, a facile NH3 self-etching and TiO2 decorating method is employed in this work. The self-released NH3 with high concentration in thermal condensation process etches and exfoliates g-C3N4 into less aggregated nanosheets with abundant nano holes (~2.7 nm). The specific surface area is up to 224 m2·g−1, which is higher than the previous reported samples prepared by template-free methods. The formed holes endow g-C3N4 nanosheets with more exposed active edges that greatly accelerate mass exchange and photo-generated carriers transfer. After decorating anatase TiO2 nanoflakes, the composite photocatalyst exhibits a Z-scheme heterojunction behavior and enhances spatial separation efficiency of photo-generated carriers greatly. As a result, the photocatalytic performance is significantly enhanced: the photodegradation rate on rodamine B reaches 99.2% within 8 min and the hydrogen evolution rate reaches as high as 1764 μmol·g−1·h−1. This work provides a facile and low-cost processing method to prepare high active and stable photocatalysts, and show the importance in rational designing the nano-materials by well-directed preparation process and energy band engineering.

Opposite Polarity Surface Photovoltage of MoS2 Monolayers on Au Nanodot versus Nanohole Arrays.

We prepared MoS2 monolayers on Au nanodot (ND) and nanohole (NH) arrays. Both these sample arrays exhibited enhanced photoluminescence intensity compared with that of a bare SiO2/Si substrate. The reflectance spectra of MoS2/ND and MoS2/NH had clear features originating from excitation of localized surface plasmon and propagating surface plasmon polaritons. Notably, the surface photovoltages (SPV) of these hybrid plasmonic nanostructures had opposite polarities, indicating negative and positive charging at MoS2/ND and MoS2/NH, respectively. Surface potential maps, obtained by Kelvin probe force microscopy, suggested that the potential gradient led to a distinct spatial distribution of photo-generated charges in these two samples under illumination. Furthermore, the local density of photo-generated excitons, as predicted from optical simulations, explained the SPV spectra of MoS2/ND and MoS2/NH. We show that the geometric configuration of the plasmonic nanostructures modified the polarity of photo-generated excess charges in MoS2. These findings point to a useful means of optimizing optoelectronic characteristics and improving the performance of MoS2-based plasmonic devices.

A Sensor Based on Nanoantennas

At the end of the XX century, a new phenomenon was discovered by Ebbesen, the extraordinary optical transmission. He reported that metallic arrays composed of nano holes, also called nanoantennas, can support resonant optical transmissions responsible by the amplification and concentration of electromagnetic radiation. Classical diffraction theories do not predict this extraordinary phenomenon. This article shows the timeline of theories that try to model the interaction between light and metal planes with slits, holes, grooves or apertures. The comparison between theories is done. Furthermore, as the optical response of these nanoantennas is dependent on the complex dielectric function, there is a high probability of successfully using these structures as sensors. This article aimed to verify how the structure parameters (periodicity, hole diameter, nanoantenna thickness and substrate thickness) can influence the optical response in order to tune the spectrum. Using a Finite Element Tool, several 3D simulations aim to conclude about the parameters influence on air–gold–quartz and air–aluminum–quartz structures, being the nanoantenna made with gold and aluminum. Moreover, all the simulations allow us to verify a resonant spectral response and the existence of great values of amplification near the metal surface. This is a clear evidence of a energy exchange due to the generation and propagation of surface plasmon polaritons. Based on the spectra taken from the parameter analysis, a specific structure was chosen to test two different sensors. A temperature sensor and a tissue detection sensor were tested and the simulations are presented. It is concluded that a nanostructure based on a nanoantenna can be used as a sensor for several applications.

Processing of a Large‐Scale Microporous Group on Copper Foil Current Collectors for Lithium Batteries Using Femtosecond Laser

Due to the thin thickness (≈8 μm) and soft nature of copper foil current collectors, it is extremely difficult to process large‐scale micro–nano holes on their surface. In this study, trepanning drilling of a copper foil current collector with a 1030 nm femtosecond laser system is investigated with emphasis on developing the processing technology of copper foil current collectors with different entry and exit sizes while maintaining good hole quality. The effects of laser parameters on the processing quality of copper foil current collectors are comprehensively studied. The relationship between geometric morphology and processing parameters as well as the formation mechanism is fully discussed. The smallest hole taper is found at a defocusing amount of −1.8 mm. Consequently, a group of holes with 250 000 micropores is obtained on a (2 cm × 2 cm) current collector, demonstrating the high efficiency and high quality of femtosecond laser‐based processing. Half‐cells with a modified current collector operate with a more stable response than half‐cells with unmodified copper foil at cycle performance and rate performance.

Arrays of Plasmonic Nanostructures for Absorption Enhancement in Perovskite Thin Films.

We report optical characterization and theoretical simulation of plasmon enhanced methylammonium lead iodide (MAPbI) thin-film perovskite solar cells. Specifically, various nanohole (NH) and nanodisk (ND) arrays are fabricated on gold/MAPbI interfaces. Significant absorption enhancement is observed experimentally in 75 nm and 110 nm-thick perovskite films. As a result of increased light scattering by plasmonic concentrators, the original Fabry–Pérot thin-film cavity effects are suppressed in specific structures. However, thanks to field enhancement caused by plasmonic resonances and in-plane interference of propagating surface plasmon polaritons, the calculated overall power conversion efficiency (PCE) of the solar cell is expected to increase by up to 45.5%, compared to its flat counterpart. The role of different geometry parameters of the nanostructure arrays is further investigated using three dimensional (3D) finite-difference time-domain (FDTD) simulations, which makes it possible to identify the physical origin of the absorption enhancement as a function of wavelength and design parameters. These findings demonstrate the potential of plasmonic nanostructures in further enhancing the performance of photovoltaic devices based on thin-film perovskites.

Enhanced photoluminescence of MoS2–Au nanostructures: Nanotriangle and nanohole arrays

We investigated the photoluminescence (PL) characteristics of MoS2–Au hybrid nanostructures, fabricated by nanosphere lithography and wet-transfer techniques. Two kinds of Au nanostructures - such as nanotriangles (NTs) and nanoholes (NHs) - were fabricated for comparison. MoS2 monolayers on both NT and NH arrays exhibited enhanced PL intensity, compared with those on SiO2/Si substrates and flat Au thin films. Numerical simulations revealed clear distinction in the electric field intensity distributions in the NT and NH arrays at the PL excitation wavelength. Such difference could be attributed to the excitation of localized and propagating surface plasmon in the NT and NH arrays. This work helps us to understand how the plasmonic NT and NH arrays affect the physical properties of the MoS2 monolayers on them.

Nanopillar and nanohole fabrication via mixed lithography

We report a fabrication method for the production of nanopillar (NP) or nanohole (NH) arrays together with a micrometer-sized structure within a single layer. On a 200 mm silicon wafer, we produced 200–400 nm NP or NH arrays using electron beam lithography (EBL). The EBL patterns on a positive-tone EB resist—either a poly(methyl methacrylate) or chemically semi-amplified resist—were transferred to a hard mask oxide (HMO) layer using reactive-ion etching (RIE), as the first etching step. We used the HMO as an intermediate layer to connect the EB patterns to photolithography patterns. On the EB-patterned HMO layer, large-scale photolithography patterns were produced on a photoresist (PR), and transferred to the HMO layer using the second RIE step. After removing the PR, the mixed EB and photolithography patterns in the HMO layer were transferred to the target layer in the third RIE step. Our method offers an efficient way to combine nanometer-sized EBL patterns with high-throughput photolithography patterns in a single layer.

Large-scale highly ordered periodic Au nano-discs/graphene and graphene/Au nanoholes plasmonic substrates for surface-enhanced Raman scattering

In this paper, the study of using masks to directly generate large area, highly ordered and periodical nanostructure has been exhibited. Periodic Au nano-discs(NDs) arrays have been fabricated on top of graphene by using holey Si3N4 mask which is directly fixed on top of graphene and Au metal is deposited through the holes in mask by thermal evaporation method under vacuum condition. This fabrication method provides an easy, fast and cost efficiency way to generate periodical nanostructure. Also, Au nanoholes(NHs) structure has been studied by using holey Si3N4 as a template. The surface-enhanced Raman scattering (SERS) sensitivities of periodical Au NDs/graphene and graphene/Au NHs hybrid structures have been systematically studied. The internal mechanisms could be explained by chemical mechanism effect of graphene and electromagnetic mechanism effect of metallic nano-structures. The enhancement factors have been systematically investigated by varying the diameter and the thickness of Au discs and Au NHs. Raman mappings of Au NDs with 2.5 μm diameter illustrate that the larger SERS enhancements exist in the rim of NDs which has good agreement with the electric field simulation result. The SERE enhancement factors of fluorescein obtained from Au NDs/graphene substrates shows an improvement factor of 500% in comparison of graphene substrate. The calculated SERS enhancement factors of graphene/Au NHs achieve 1,200% in comparison of graphene/planar Au film substrate.

Flattened zero dispersion Photonic crystal fibers with embedded nano holes and ultra low confinement loss for supercontinuum generation

In this paper unique photonic crystal fiber (PCF) structure with nanoholes embedded have been studied. Embedded nanoholes have been filled with different materials of alcoholic groups like butanol, ethanol, methanol and propanol. Investigations of these structure shows flattened zero dispersion in visible range to far infrared regions. Simulated PCF structure reports ultra-low confinement loss of the order of 10-8 dB/km. Designed PCF promises to give large nonlinear coefficient of 3000 W-1Km-1 at 1335nm wavelengths. Numerical simulation of the fiber for the generation of supercontinuum generation (SCG) has been performed. Low power pump pulses of 50fs duration have been used. With a fiber of length of 15cm and pulses of 1kW, 2kW, 5kW and 10kW peak power, supercontinuum broadening of about 607nm, 908nm, 1987nm and 2405nm respectively.

Influence of surface microstructure on bonding strength of modified polypropylene/aluminum alloy direct adhesion

Abstract Microstructures and bonding strength between the treated aluminum alloy and modified polypropylene (PP) were systemically investigated in this study. The results show that an increase in the surface energy of PP by grafting maleic anhydride(MAH) will result in better wetting of the resin on the aluminum alloy layer. The porous microstructures were produced by polishing and anodizing. The interfacial bonding strength of specimens was increased rapidly after anodizing, and the maximum tensile shear strength and work of fracture of P/P-AlP specimen reach up to 10.05 MPa and 14.82 KJ/m2, respectively. The great increase in bonding strength was attributed to porous microstructures and large roughness on the aluminum alloy surface which resulted in resin melt flew into nano holes to from micro mechanical interlocking.

Ultrafast Tunable Near-Field Radiative Thermal Modulator Made of Ge3Sb2Te6

We show numerically the phase change material Ge3Sb2Te6 (GST) with special configuration as a heat modulator in the regime of near-field radiative heat transfer (NFRHT). The ability of GST to allow ultrafast reversible switch between two phases endows it great potential in practical modulation application. By designing silicon carbide (SiC) nanoholes (NHs) filled with GST, this configuration could achieve a considerable modulation effect and large near-field radiative heat flux. The underlying mechanism can be explained by the observation that the entire configuration supports either hyperbolic modes or surface phonon polaritons (SPhPs) resonance modes and even the combination of both modes, thereby resulting in the remarkable modulation effect. In addition, the effects of the volume filling factor and graphene coverage are also investigated at the vacuum gap distance of 100 nm. With graphene coverage, the modulation factor can be further improved to as high as 0.72 achieved at the volume filling factor of 0.6 with temperature difference of 20 K. The proposed configuration has the potential to effectively modulate heat in the near-field regime for designing heat modulation applications in the future.

Long- and Short-Range Ordered Gold Nanoholes as Large-Area Optical Transducers in Sensing Applications

Unconventional lithography (such as nanosphere lithography (NSL) and colloidal lithography (CL)) is an attractive alternative to sequential and very expensive conventional lithography for the low-cost fabrication of large-area nano-optical devices. Among these, nanohole (NH) arrays are widely studied in nanoplasmonics as transducers for sensing applications. In this work, both NSL and CL are implemented to fabricate two-dimensional distributions of gold NHs. In the case of NSL, highly ordered arrays of gold NHs distributed in a hexagonal lattice onto glass substrates were fabricated by a simple and reproducible approach based on the self-assembling of close-packed 500 nm diameter polystyrene particles at an air/water interface. After the transfer onto a solid substrate, the colloidal masks were processed to reduce the colloidal size in a controllable way. In parallel, CL was implemented with short-range ordered gold NH arrays onto glass substrates that were fabricated by electrostatically-driven self-assembly of negatively charged colloids onto a polydiallyldimethylammonium (PDDA) monolayer. These distributions were optimized as a function of the colloidal adsorption time. For both approaches, controllable and reproducible procedures are presented and discussed. The optical responses of the NH structures are related to the short-range ordering level, and their good performances as refractive index transducers are demonstrated.

Study on integrally molded PA6/304 stainless steel by micro-nano pressing technology

With application of micro-nano pressing technology (MNPT) polyamide 6 (PA6) and 304 stainless steel were integrally molded, and the mechanical properties and structure on the interface of plastic and metal were investigated in the study. The micro structures on the stainless steel specimen surface were achieved by physical and/or chemical surface treatment techniques including polishing and etching methods, respectively. The tensile shear strength and work of fracture for the integrally molded specimen were influenced greatly by the surface treatment on stainless steel. The maximal tensile shear strength and the fracture work for the MNPT molded sample reached up to ca. 11 MPa and 17 KJ/m2, respectively. In addition, the interface fractography of the MNPT molded specimen was characterized by scanning electron microscope (SEM) and atomic force microscope (AFM). These results indicated PA6 melt flew into the micro and/or nano holes on the chemical etched metal surface during hot press molding to form micro mechanical interlock structure to prepare strong MNPT molded samples.

Beneficial effect of reducing symmetry on the enhancement of optical absorption of nanohole arrays

Nanostructure plays an important role in improving the absorption efficiency of thin film solar cells. In this paper, we have studied the dependence of the absorption efficiency of nanohole (NH) array on the shape and rotation angle of the NH. Results show that, in a large NH size range, the ultimate efficiency of a tilted elliptical NH array is higher than that of any vertical circular NH array. The ultimate efficiency of the elliptical NH array with its NH tilted at the angle when the array yields the maximum efficiency is 9.7% higher than the maximum efficiency that any vertical circular NH array can offer. Rotating the elliptical NHs around the axes perpendicular to the bottom of the NHs for an appropriate angle, the ultimate efficiency of the array enhances further and is 16.2% higher than that of the optimal vertical circular NH array. Compared with vertical NH arrays, the tilted and rotated NH structures present greater mode density of state, which can couple with the incident light. The reduction of symmetry is the main reason that leads to more resonance modes and greater absorption efficiency in the structure.

Neutral, charged excitons and biexcitons in strain-free and asymmetric GaAs quantum dots fabricated by local droplet etching

We present an experimental and theoretical study of the optical properties of asymmetric strain-free GaAs quantum dots (QDs) fabricated by filling of self-organized nanoholes (NHs) created by local droplet etching. The energy levels are calculated within the effective mass approximation using as input a model anisotropic QD shape with C2v symmetry based on atomic force microscopy (AFM) profiles of NHs. The influence of the QD height and shape anisotropy on the exciton emission energy and the s-px and s-py energy splittings is studied theoretically. The experimentally observed bound nature of excitonic states is well reproduced by our theoretical approach which includes direct Coulomb energies and correlation effects. We investigate the fine-structure splitting (FSS) of the neutral exciton as a function of dot size. Theoretical calculations of the long-range electron-hole (e-h) exchange interaction predict an increase of the FSS with decreasing QD height, which describes well the experimental trend.

Selective Separation of Lead Ions Using New Nano-Adsorbent GH-92

One of the main sources of environment pollution is the industrial wastewater which contains heavy metals and can be found in many industries. If these heavy metals enter in the human body, would cause many health problems. On the other hand, different researches around the world show that nanotechnology is an effective way to remove pollutants. In this research, for the first time in the world, a type of natural sponge of Persian Gulf that has Nano holes has been used to remove the lead ion selectively from calcium, magnesium and cobalt ions in aqueous solution. The present study identified a sample belonging to the sponge of Demospongiae class. The aggregation of absorption in the sponge, contact time, particle size and by measuring environment`s pH were measured. The results show this type of sponge, GH-92, is able to absorb different amounts of mentioned metal ions. Adsorption amount of calcium, magnesium and cobalt by this type of sponge was very small. The highest adsorption capacity belonged to lead ion in pH= 4.5 to 5 with mesh 230 which was 79.19 mg per gram of adsorbent. This is the highest adsorption capacity of lead comparison with reported articles for selective separation of lead ion.

The Time Dependency of Nano Hole Form for Al Nanoimprinting

The Time Dependency of Nano Hole Form for Al Nanoimprinting

An InGaN/GaN MQWs Solar Cell Improved By a Surficial GaN Nanostructure as Light Traps

The InGaN/GaN multi-quantum-wells (MQWs) solar cells employing the surficial GaN nanostructure as light traps were investigated. The performance of the InGaN/GaN MQWs solar cell with nano holes surface shows an obvious advantage over that with nano poles, much less than the planar one. From the measurements of EQE and photoluminescence spectra, the enhancement of photoelectric response contributes to the device performances. Because the effective light absorption is increased, the conversion efficiency significantly improves from 1.02% (planar surface) up to 2.235% (nano holes surface). Although the performance is still low, it is exactly an effective method to enhance the conversion efficiency via introducing nanostructures on the surface of the InGaN/GaN MQWs cells.

Depolarized haze of nano-porous AAO film via porosity and aspect control

Multiple scattering induced haze and depolarization effects of nano-porous AAO films controlled by detuning the porosity and aspect ratio of the nano holes are investigated. The nano-porous AAO film with its porosity increasing from 12.6% to 19.3% enhances the scattering of the incident laser beam with its maximal scattering angle enlarged from 5° to 8° under TM-mode incidence and from 6° to 10° under TE-mode incidence. Because of multiple scattering within the porous holes of the AAO, the depolarization on the reflected beam by transferring its electric field from horizontal to the vertical such that the polarization ratio is degraded with a randomized haze. The porosity of AAO surface broadens from 12.6% to 19.3% when increasing the bias voltage from 40 to 60 V during the second-step of the electro-chemical anodization process, which essentially adjusts the polarization ratio under TM-mode and TE-mode incidences raise from 0.31 to 0.35 and from 0.32 to 0.48, respectively. The depolarized haze of the nano-porous AAO film is correlated with its porosity and aspect ratio controlled by the pore size and etched depth of the AAO. Under TM-mode incidence, the simulated polarization ratio increases from 0.35 to 0.38, which correlates well with experimental results. In contrast, the experiment result slightly deviates from the theoretical prediction as the TE-mode field interacts more surface area than the TM-mode field does. Such a nano-porous AAO exhibits tunable depolarized haze via the control porosity and aspect ratio, which is particularly suitable to serve as the catalytic buffer for synthesizing the hydrophobic and hazed solar energy converters.