Thermal Dewetting Process Research Articles

Multi-Functional Applications of H-Glass Embedded with Stable Plasmonic Gold Nanoislands.

Metal nanoparticles (MNPs) are synthesized using various techniques on diverse substrates that significantly impact their properties. However, among the substrate materials investigated, the major challenge is the stability of MNPs due to their poor adhesion to the substrate. Herein,it isdemonstrated how a newly developed H-glass can concurrently stabilize plasmonic gold nanoislands (GNIs) and offer multifunctional applications. The GNIs on the H-glassaresynthesized using a simple yet, robust thermal dewetting process. The H-glass embedded with GNIs demonstrates versatility in its applications, such as i) acting as a room temperature chemiresistive gas sensor (70% response for NO2 gas); ii) serving as substrates for surface-enhanced Raman spectroscopy for the identifications of Nile blue (dye) and picric acid (explosive) analytes down to nanomolar concentrations with enhancement factors of 4.8 × 106 and 6.1 × 105 , respectively; and iii) functioning as a nonlinear optical saturable absorber with a saturation intensity of 18.36 × 1015 Wm-2 at 600nm, and the performance characteristics are on par with those of materials reported in the existing literature. This work establishes a facile strategy to develop advanced materials by depositing metal nanoislands on glass for various functional applications.

Silver Nanoparticle Arrays onto Glass Substrates Obtained by Solid-State Thermal Dewetting: A Morphological, Structural and Surface Chemical Study.

Silver nanoparticles (NPs) on glass substrates were obtained by a solid-state thermal dewetting (SSD) process using vacuum-evaporated-silver precursor layers. An exhaustive investigation of the morphological, structural, and surface chemistry properties by systematically controlling the precursor film thickness, annealing temperature, and time was conducted. Thin silver films with thicknesses of 40 and 80 nm were deposited and annealed in air by applying a combined heat-up+constant temperature–time program. Temperatures from 300 to 500 °C and times from 0 to 50 min were assayed. SSD promoted the morphological modification of the films, leading to the Ag NPs having a discrete structure. The size, shape, surface density, and inter-nanoparticle distance of the nanoparticles depended on the initial film thickness, annealing temperature, and time, exhibiting a cubic silver structure with a (111) preferred crystallographic orientation. The prepared NPs were found to be highly enriched in the Ag{111}/Ag{110}/Ag{100} equilibrium facets. SSD not only promotes NP formation but also promotes the partial oxidation from Ag to AgO at the surface level. AgO was detected on the surface around the nanoparticles synthesized at 500 °C. Overall, a broad framework has been established that connects process factors to distinguish resultant Ag NP features in order to develop unique silver nanoparticles for specific applications.

Controlling Equilibrium Morphologies of Bimetallic Nanostructures Using Thermal Dewetting via Phase-Field Modeling.

Herein, we report a computational model for the morphological evolution of bimetallic nanostructures in a thermal dewetting process, with a phase-field framework and superior optical, physical, and chemical properties compared to those of conventional nanostructures. The quantitative analysis of the simulation results revealed nano-cap, nano-ring, and nano-island equilibrium morphologies of the deposited material in thermal dewetting, and the morphologies depended on the gap between the spherical patterns on the substrate, size of the substrate, and deposition thickness. We studied the variations in the equilibrium morphologies of the nanostructures with the changes in the shape of the substrate pattern and the thickness of the deposited material. The method described herein can be used to control the properties of bimetallic nanostructures by altering their equilibrium morphologies using thermal dewetting.

Solid-state thermal dewetted silver nanoparticles onto electrochemically grown self-standing vertically aligned ZnO nanorods for three-dimensional plasmonic nanostructures

Three dimensional (3D) plasmonic nanostructures composed of silver nanoparticles decorated ZnO NRs arrays, have been fabricated by a process combining the electrochemical growth of ZnO NRs and further formation of Ag nanoparticles by the solid-state thermal dewetting (SSD) process. The effect of SSD parameters on the morphological, structural and optical properties of the Ag NPs decorated ZnO NRs arrays has been investigated. It is possible to tune the bandgap of the Ag NPs@ZnO nanorods array 3D plasmonic nanostructure by tailoring the Ag nanoparticle sizes, allowing light manipulation at the nanoscale. The silver nanoparticles attached to the ZnO NRs arrays experienced surface plasmonic coupling effect, causing enhancement in the room temperature photoluminescence (PL) UV emission and quenching the corresponding visible light one. An enhancement in the near band edge emission PL intensity of ZnO to the deep level emission PL intensity ratio after Ag NPs decoration of the ZnO nanostructures corresponding to ca. 11 folds has been observed, indicating that the defect emission is obviously suppressed.

InGaP Nano-pattern Structure Realized by Thermally Dewetted Au Nanoparticles and Anisotropic Dry Etching

Background:: Optical reflection loss can be reduced more than 30% when multilayers ARC are deposited on the optoelectronic devices surface. Besides that, sub-wavelength structures, which have a period sufficiently smaller than the wavelength of light, have been introduced as an antireflection layer to offer a new possibility to suppress the Fresnel reflection. Normally, e-bean and nano-imprint lithography techniques are used to create nano-scale etch mask patterns. Metallic nanoparticles, which can be formed by a thermal dewetting process of metal thin film without any nanolithography techniques, can be utilized as an etch mask for the nano structure fabrications. The nano-patterned structures were fabricated on a silicon nitride passivation layer of a GaInP/GaAs/Ge triple-junction solar cell and showed an enhancement of its performance due to improved optical transmission and current matching. Objective:: Investigate the influences of InGaP nano-pattern structures on the optical characteristics and applied for compound solar cells. Method:: In this report, disordered InGaP nano-pattern structures were formed by thermally dewetted Au nanoparticles and anisotropic dry etching processes. The effects of the InGaP nano-patterned structure on the optical reflection characteristics were investigated. Results:: The result indicated that the InGaP nano-patterned structure can reduce the optical reflection in a wide range of wavelengths and, thus, can work as an antireflection layer. The InGaP nanostructure can improve up to 14.8% in the short circuit current density compared to that of the planar cell. Conclusion:: The InGaP nano structures have been successfully fabricated by thermal dewetted Au nanoparticles and anisotropic dry etching methods. The fabricated Au nanoparticles pattern was found to be the best when annealing temperature is 400°C for 30 minutes with the 5nm thick of Au film. By controlling dry etching time, the height of InGaP nanostructures can be varied from 95 nm to 150 nm. With the increasing of the height, the optical reflectance can be down to 22%. The InGaP nanostructure with the height of 150 nm was also introduced to the window layer of a single junction GaAs soar cell. The result indicated that the InGaP nanostructure only affects on the short circuit current density.

Dewetting Metal Nanofilms-Effect of Substrate on Refractive Index Sensitivity of Nanoplasmonic Gold.

The localized surface plasmon resonance (LSPR) sensitivity of metal nanostructures is strongly dependent on the interaction between the supporting substrate and the metal nanostructure, which may cause a change in the local refractive index of the metal nanostructure. Among various techniques used for the development of LSPR chip preparation, solid-state dewetting of nanofilms offers fast and cost effective methods to fabricate large areas of nanostructures on a given substrate. Most of the previous studies have focused on the effect of the size, shape, and inter-particle distance of the metal nanostructures on the LSPR sensitivity. In this work, we reveal that the silicon-based supporting substrate influences the LSPR associated refractive index sensitivity of gold (Au) nanostructures designed for sensing applications. Specifically, we develop Au nanostructures on four different silicon-based ceramic substrates (Si, SiO2, Si3N4, SiC) by thermal dewetting process and demonstrate that the dielectric properties of these ceramic substrates play a key role in the LSPR-based refractive index (RI) sensitivity of the Au nanostructures. Among these Si-supported Au plasmonic refractive index (RI) sensors, the Au nanostructures on the SiC substrates display the highest average RI sensitivity of 247.80 nm/RIU, for hemispherical Au nanostructures of similar shapes and sizes. Apart from the significance of this work towards RI sensing applications, our results can be advantageous for a wide range of applications where sensitive plasmonic substrates need to be incorporated in silicon based optoelectronic devices.

Study the Effect of Chemical Treatment on Substrate Surface on the Formation Nanodots Array and its Optical Properties

In this research, an effective method to fabricate various metallic nanoand micro structure patterns is developed by combination of chemical stamping and selective peeling off technique. The feasibility of the process is experimentally studied and demonstrated. In this paper, the authors present the effects of the chemical treatment on the substrate surface on the formation of the nanodots array and its absorbance property. The results show that the chemical treatment by dropping Acetone solution on the quartz glass substrate strongly affects the morphology and absorbance property of the nanodots array. With the Acetone treatment on the substrate, the nanodots become smaller and more uniform in size through thermal dewetting process. Simultaneously, it results in blue shifted of the absorbance peak and enhancement of the absorbance peak intensity. The improvement of the optical property of the nanodots array is useful for plasmonic solarcell and bio sensing applications.

Novel Optimized Hybrid Terahertz Photoconductive Antennas

We demonstrate the results of on THz emission from hybrid THz photoconductive antenna loaded with silver nanoantenna. The results of experimental investigations are in a good agreement with numerical simulations presented in our recent work. The conversion efficiency reveals over 5-fold improvement at certain frequencies, if compared with similar photoconductive antenna without silver nanoparticles, while previous results for this type of antenna barely exceeded 2-fold conversion efficiency gain. We propose a cost-effective fabrication procedure to realize such hybrid THz antennas with optimized plasmonic nanostructures via thermal dewetting process, which does not require any post processing and makes the proposed solution very attractive for applications.

Boosting Terahertz Photoconductive Antenna Performance with Optimised Plasmonic Nanostructures.

Advanced nanophotonics penetrates into other areas of science and technology, ranging from applied physics to biology, which results in many fascinating cross-disciplinary applications. It has been recently demonstrated that suitably engineered light-matter interactions at the nanoscale can overcome the limitations of today’s terahertz (THz) photoconductive antennas, making them one step closer to many practical implications. Here, we push forward this concept by comprehensive numerical optimization and experimental investigation of a log-periodic THz photoconductive antenna coupled to a silver nanoantenna array. We shed light on the operation principles of the resulting hybrid THz antenna, providing an approach to boost its performance. By tailoring the size of silver nanoantennas and their arrangement, we obtain an enhancement of optical-to-THz conversion efficiency 2-fold larger compared with previously reported results for similar structures, and the strongest enhancement is around 1 THz, a frequency range barely achievable by other compact THz sources. We also propose a cost-effective fabrication procedure to realize such hybrid THz antennas with optimized plasmonic nanostructures via thermal dewetting process, which does not require any post processing and makes the proposed solution very attractive for applications.

Periodically Patterned Au-TiO2 Heterostructures for Photoelectrochemical Sensor.

Periodically patterned Au nanorods in TiO2 nanocavities (Au NRs@TiO2) were fabricated via magnetron sputtering followed by a thermal dewetting process. This innovative Au NRs@TiO2 heterostructure was used as a plasmonic sensing platform for photoelectrochemical detection of glucose and lactose. This Au NRs@TiO2 patterned heterostructure possesses superior sensing properties to other Au nanoparticle-based sensors because (i) localized surface plasmon resonance (LSPR) generated at Au/TiO2 interfaces enhanced sensitivity of glucose (lactose) amperometric detection; (ii) periodic Au nanocrystals in TiO2 nanocavities accelerated charge separation and transfer rate, especially under monochromatic blue light irradiation; (iii) discrete planar architectures comprising Au NRs immobilized on TiO2 substrates significantly improved stability and reusability of the sensors. A low detection limit of 1 μM (10 μM) and a high sensitivity of 812 μA mM-1 cm-2 (270 μA mM-1 cm-2) were achieved on the Au NRs@TiO2 heterostructures for glucose (lactose) detection without the addition of enzymes. Good selectivity and superb stability over more than 8 weeks was also demonstrated using these Au NRs@TiO2 heterostructures for glucose (lactose) detection. Additionally, this cost-efficient technique can be easily extended to other photoelectrochemical sensing systems when considering the combination of sensing and visible or infrared light source enhancement.

Fabrication of Metallic Nanodot Arrays Using Nano-Chemical Stamping Technique with a Polymer Stamp

The aim of this study is to develop metallic nanodot arrays with controlled morphology and alignment. To produce gold nanodot arrays with high throughput, the authors propose a new efficient fabrication process based on the templated thermal dewetting method, using a nano-chemical stamping technique with a polymer mold. This process comprises four steps: sputter etching on a quartz glass substrate, patterning of micrometer size by printing with acetone on the substrate by stamping with a polymer film stamp, deposition of a thin Au film on the substrate, and self-organization of the metal nanodot arrays by thermal dewetting. A new method, using a cyclo-olefin polymer film mold for chemical patterning by nano-chemical stamping, was examined. Since the acetone stamped on the substrate reduces the surface energy and affects the contact angle of the gold nanodots, the gold nanodots are distributed along the stamped pattern. It is found that the pattern stamped with acetone on the substrate works as a template for the thermal dewetting process. The nano-chemical stamping technique is useful in controlling the size and distribution of the nanodots.

Versatile Micropatterning of Plasmonic Nanostructures by Visible Light Induced Electroless Silver Plating on Gold Nanoseeds.

A versatile fabrication technique for plasmonic silver (Ag) nanostructures that uses visible light exposure for micropatterning and plasmon resonance tuning is presented. The surface of a glass substrate modified with gold (Au) nanoseeds by a thermal dewetting process was used as a Ag plating platform. When a solution containing silver nitrate and sodium citrate was dropped on the Au nanoseeds under visible light exposure, the plasmon-mediated reduction of Ag ions was induced on the Au nanoseeds to form Ag nanostructures. The plasmon resonance spectra of Ag nanostructures were examined by an absorption spectral measurement and a finite-difference time-domain (FDTD) simulation. Some examples of Ag nanostructure patterning were demonstrated by means of light exposure through a photomask, direct writing with a focused laser beam, and the interference between two laser beams. Surface enhanced Raman spectroscopy (SERS) of 4-aminothiophenol (4-ATP) was conducted with fabricated Ag nanostructures.

Efficient Fabrication Process of Metal Nanodot Arrays Using Direct Nanoimprinting Method with a Polymer Mold

A new fabrication process of metal nanodot arrays using the thermal dewetting method was developed in this study. This process was comprised of three steps: thin Au film deposition on a quartz glass substrate, groove patterning by direct nanoimprinting, and self-organization of metal nanodot arrays by thermal dewetting. A new idea to utilize a polymer film mold for groove patterning by direct nanoimprinting was examined. The polymer film mold was prepared by hot-embossing groove patterns of a mother mold on a cyclo olefin polymer (COP) film. The mother mold was prepared from a silicon wafer. The polymer film mold was used for direct nanoimprinting on a metal film deposited on a quartz substrate. The experimental results revealed that the COP film mold can effectively form a micro groove pattern on the Au film despite the COP film mold being softer than the Au film. The micro groove on the Au film was also found to be effective in aligning the nanodots in lines. The micro groove patterning using the COP film mold was also confirmed to be useful in controlling the dot size and alignment during the thermal dewetting process.

Scattering analysis for random antireflective structures on fused silica in the ultraviolet.

Random antireflective structures are fabricated on fused silica by the thermal dewetting process and reactive ion etching, which shows a broadband antireflective effect over the whole visible wavelength. However, the transmittance in the ultraviolet is limited by the scattering from the etched structures. A graded refractive index model ignoring the scattering in the visible range is applied to extract the etched profile. Then the Lubachevsky-Stillinger algorithm is used to reconstruct the random antireflective structures with the extracted profile. Bidirectional scattering distribution for the reconstructed structures is simulated with the finite-difference time-domain method, which indicates the importance of transmissive scattering the scattering directivity. The scattering directivity is explained well with an effective grating model. The period of the effective grating can guide the prepared technique in the ultraviolet.

Fabrication of Disordered Subwavelength Structures on Curved Surfaces by Using a Thermal Dewetting Process

We present disordered moth eye structures on curved surfaces fabricated by dry etching of thermally dewetted metal nanoparticles. This lithography-free fabrication allows the formation of subwavelength scale nanostructures on the strongly inclined surfaces such as ball lens as well as on the microlens arrays with low curvature. In particular, we found that the size and average distance of nanostructures are closely related to the inclined angle of the surface. Experimental results on oblique angle deposition of metal thin films followed by thermal dewetting also support these effects.

Gold nanoparticle integrated with nanostructured carbon and quantum dots: synthesis and optical properties

Multilayer graphene shell encapsulated gold nanoparticle—quantum dot hybrids were derived by combining wet-chemical, thermal, and covalent chemistry approaches. Uniformly patterned gold nanoparticles on a silicon substrate were obtained via gold film deposition in an electroless method followed by a thermal dewetting process. The resulting gold nanoparticles were further surface oxidized and utilized as catalysts for the chemical vapor deposition growth of multilayer graphene shell encapsulated on the gold nanoparticles (referred as “multilayer graphene shell encapsulated Au nanoparticle” or graphene nanoparticles (GNPs)). As a next step, the surface of GNPs was modified to result in carboxylic (−COOH) functionalities, which enabled carbodiimide-based covalent linking of amine-terminated CdS x Se1-x @ZnS quantum dots (QDs) on the GNP surface. The GNPs and GNP-QD heterostructures were characterized using scanning and transmission electron microscopy for size, morphology, spatial distribution, and crystal structure evaluation. In addition, UV-vis, fluorescence spectroscopy, and discrete dipole approximation (DDA) modeling were utilized for understanding the band gap energies, fluorescence quenching, and light-matter interactions of the derived hybrids/heterostructures.

2503 Fabrication of nanodot arrays by the templated thermal dewetting method using nano chemical stamp technique

The authors propose a new efficient fabrication process by the templated thermal dewetting method in this paper. This process comprises 4 steps. Firstly, sputter etching on a quartz glass substrate. Secondly, line and space pattern of micrometer size is printed with acetone on the substrate by means of stamping with a polymer film stamp. Thirdly, an Au film is deposited on the substrate. Finally, the substrate is annealed. It is revealed that the line and space pattern stamped with acetone on the substrate works as a template of the thermal dewetting process. Nano chemical stamping technique is useful to control the distribution of nanodots size.

Fabrication of an ordered nanodot array by thermal dewetting on a patterned substrate

Abstract A new process to fabricate an ordered gold nanodot array by thermal dewetting on a patterned substrate is proposed in this paper. Its feasibility was demonstrated through the experiments. The process comprises three steps; fabrication of a square nano-grooves grid on a substrate by nano-plastic forming, deposition of a thin gold film on the patterned substrate, and annealing the metal coated substrate to form an ordered nanodot array. The effects of the thickness of the deposited metal film on the morphology of nanodot array are studied. It is found that a nanodot array of good uniformity and regularity is obtained by optimizing the gold film thickness. It is verified that patterning of groove grid on a substrate is effective to improve the uniformity and regularity of the nanodot array in the thermal dewetting process.

22am2-A7 テンプレーテッド熱デウェッティングのためのプラスチックモールドを用いた金薄膜層への直接ナノインプリント法

A new fabrication process of a metal nano-dot array by the templated thermal dewetting process is developed in this paper. This process comprises 3 steps; the thin Au film deposition on a quartz glass substrate, the nano imprint by using the plastic mold on the Au film, and self-organization of a nano dot array by the thermal dewetting process. In this propose, self-organization of nano dot array on a groove patterned substrate is investigated. Effect of groove patterned on the dot morphology and arrangement are studied experimentally. The results show that the polymer film mold transfer grooves pattern on the surface of workpieces and it is show that grooves by this process is effective to control nano dot array generation in its thermal annealing process. It is confirmed that a nano dot array of good arrangement can be fabricated by the templated thermal dewetting method.

Templated Thermal Dewetting Process by Utilizing Nano Plastic Forming Technology

A new nano manufacturing method to fabricate minute metal elements on a quartz substrate is reported in this paper. Such minute metal elements are useful to develop optical metamaterials, which have artificial optical properties that have not existed in nature. Proposed fabrication method in this paper is a kind of templated thermal dewetting, in which the Nano Plastic Forming technique is employed to fabricate templated patterns. Firstly, gold thin film is deposited on a quartz glass substrate by using a spatter coater. Then, an adequate groove pattern is fabricated using specially designed diamond tools. Finally, the substrate is annealed in an electric furnace to induce thermal dewetting. In this experiment, effects of annealing conditions and thickness of gold thin film on morphology of the aggregated gold film are studied. In addition, physical modeling of gold separation by thermal dewetting is studied. Through the experiments, possibility of Nano Plastic Forming technique on fabrication of nano metal element is discussed.