Patterning Of Nanorods Research Articles

Anisotropic Stick-Slip Frictional Surfaces via Titania Nanorod Patterning.

Nanoscale or microscale surface texturing is an effective technique to tailor the tribological properties between two surfaces that are rubbed against each other. In order to achieve the desired frictional properties by a patterned surface, one needs an in-depth understanding of the underlying mechanisms. Here, we demonstrate anisotropic stick-slip friction achieved via a nanotextured surface of tilted titania nanorods (TiNRs). The surface was developed by using the glancing angle deposition (GLAD) technique, and exhibited load-dependent variations in stick-slip friction as well as frictional anisotropy in different sliding directions. For studying the frictional properties of the newly developed surface, lateral force microscopy (LFM) was performed in three different reciprocal orientations (0° rotated, 45° rotated, 90° rotated) using a custom-made colloidal alumina atomic force microscopy (AFM) probe. The frictional behavior was found to vary significantly with the orientation. At 0° rotated position) a prominent "stick-slip" was observed when scanning opposite to the tilt direction, whereas the phenomenon reduced significantly when the nanotextured surface was scanned along the tilt direction or rotated to different angles (45 and 90°) with respect to the sliding direction of the AFM cantilever supporting the probe. The experimental findings were interpreted based on the classical solution for large deflections of tilted elastic rods. Overall, the textured surface, LFM-based frictional measurement, and the quantitative analysis presented here provide a fundamental understanding of how friction can be significantly varied on a surface patterned with tilted TiNRs at a length scale of about 1 μm, which can be comprehensively applied to nanorod patterns of other materials on different substrates.

Biosynthesis of Ag-doped ZnO nanorods using template Bacillus sp. and polyethylene glycol via sol-gel-hydrothermal methods for antifungal application

Synthesis of Ag-ZnO nanorods (Ag-ZnO NR) utilizing biological materials, specifically the extracellular enzymes of Bacillus sp. Combined with polyethylene glycol (PEG) as a nanorod pattern template has been proposed. Polyethylene glycol (PEG) of varying relative molecular mass (Mr): 6000, 8000, and 10000 was used. Characterization of Ag-ZnO NR with ultraviolet spectroscopy (UV–vis) revealed absorption at (λmax) = 300 - 330 nm, a blue shift region that was identical to the growth of the Ag-ZnO crystal nucleus. Infrared spectroscopy (FT-IR) profile of Bacillus sp. revealed high intensity at wave number 1600 -1650 cm−1, indicating the amine NH strain in the extracellular enzyme Bacillus sp.; 1430 – 1387 cm−1, indicating -CH3 strain, and 1050 cm−1 indicating CO in PEG. X-ray diffraction (XRD) showed high intensity at 2θ: 31.75°; 34.41°; 36.25° indicates hexagonal wurtzite ZnO (ICDS-ZnO 2017). In contrast, Ag-doped ZnO exhibited high intensity at 2θ: 38. 07°; 44.28°; 66.35° (ICDS-Ag) with crystallite size of 21.85 nm. Scanning electron microscope (SEM) revealed nanorod and spherical particles of 198.96 nm of Ag-ZnO NR PEG-10000. The antifungal effectiveness that was measured based on the number of free radicals •O2 and •OH in the photocatalytic reaction using a p-benzoquinone scavenger reached 85±0.7 %. The highest antifungal activity was detected with an inhibition zone of 3.65-3.04 mm. This finding is very promising for the green synthesis of ZnO and its application as future antifungal application in textile industries.

Directed Assembly of Gold Nanorods by Microwrinkles

Gold nanorod patterns made with microwrinkle substrate were investigated. The wide range and uniform patterning of gold nanorods are useful for the various applications. By changing the width of th...

Helicoidal Patterning of Gold Nanorods by Phase Separation in Mixed Polymer Brushes.

The spatial distribution of polymer ligands on the surface of nanoparticles (NPs) is of great importance because it determines their interactions with each other and with the surrounding environment. Phase separation in mixtures of polymer brushes has been studied for spherical NPs; however, the role of local surface curvature of nonspherical NPs in the surface phase separation of end-grafted polymer ligands remains an open question. Here, we examined phase separation in mixed monolayers of incompatible polystyrene and poly(ethylene glycol) brushes end-capping the surface of gold nanorods in a good solvent. By varying the molar ratio between these polymers, we generated a range of surface patterns, including uniform and nonuniform polystyrene shells, randomly distributed polystyrene surface patches, and, most interestingly, a helicoidal pattern of polystyrene patches wrapping around the nanorods. The helicoidally patterned nanorods exhibited long-term colloidal stability in a good solvent. The helicoidal wrapping of the nanorods was achieved for the mixtures of polymers with different molecular weights and preserved when the quality of the solvent for the polymers was reduced. The helicoidal organization of polymer patches on the surface of nanorods can be used for templating the synthesis or self-assembly of helicoidal multicomponent nanomaterials.

Helicoidal Patterning of Nanorods with Polymer Ligands.

Chiral packing of ligands on the surface of nanoparticles (NPs) is of fundamental and practical importance, as it determines how NPs interact with each other and with the molecular world. Herein, for gold nanorods (NRs) capped with end-grafted nonchiral polymer ligands, we show a new mechanism of chiral surface patterning. Under poor solvency conditions, a smooth polymer layer segregates into helicoidally organized surface-pinned micelles (patches). The helicoidal morphology is dictated by the polymer grafting density and the ratio of the polymer ligand length to nanorod radius. Outside this specific parameter space, a range of polymer surface structures was observed, including random, shish-kebab, and hybrid patches, as well as a smooth polymer layer. We characterize polymer surface morphology by theoretical and experimental state diagrams. The helicoidally organized polymer patches on the NR surface can be used as a template for the helicoidal organization of other NPs, masked synthesis on the NR surface, as well as the exploration of new NP self-assembly modes.

Helicoidal Patterning of Nanorods with Polymer Ligands

AbstractChiral packing of ligands on the surface of nanoparticles (NPs) is of fundamental and practical importance, as it determines how NPs interact with each other and with the molecular world. Herein, for gold nanorods (NRs) capped with end‐grafted nonchiral polymer ligands, we show a new mechanism of chiral surface patterning. Under poor solvency conditions, a smooth polymer layer segregates into helicoidally organized surface‐pinned micelles (patches). The helicoidal morphology is dictated by the polymer grafting density and the ratio of the polymer ligand length to nanorod radius. Outside this specific parameter space, a range of polymer surface structures was observed, including random, shish‐kebab, and hybrid patches, as well as a smooth polymer layer. We characterize polymer surface morphology by theoretical and experimental state diagrams. The helicoidally organized polymer patches on the NR surface can be used as a template for the helicoidal organization of other NPs, masked synthesis on the NR surface, as well as the exploration of new NP self‐assembly modes.

Rapid Large-Scale Assembly and Pattern Transfer of One-Dimensional Gold Nanorod Superstructures

The utility of gold nanorods for plasmonic applications largely depends on the relative orientation and proximity of the nanorods. Though side-by-side or chainlike nanorod morphologies have been previously demonstrated, a simple reliable method to obtain high-yield oriented gold nanorod assemblies remains a significant challenge. We present a facile, scalable approach which exploits meniscus drag, evaporative self-assembly, and van der Waals interactions to precisely position and orient gold nanorods over macroscopic areas of 1D nanostructured substrates. By adjusting the ratio of the nanorod diameter to the width of the nanochannels, we demonstrate the formation of two highly desired translationally ordered nanorod patterns. We further demonstrate a method to transfer the aligned nanorods into a polymer matrix which exhibits anisotropic optical properties, allowing for rapid fabrication and deployment of flexible optical and electronic materials in future nanoscale devices.

Inkjet-printed gold nanorods using biocompatible polyelectrolyte layer-by-layer coating for patterned photothermal applications.

Photothermal effect using biocompatible nanoparticles with near infrared wavelength light is a versatile tool in biomedical applications due to the temperature sensitivity of cells and good penetrability of the light through many biological systems. However, precise patterning of the nanoparticles on biochips to control the location and intensity of the photothermal effect requires suitable fabrication methods. In this report, we show that inkjet printing of aqueous nanoparticle solution on polyelectrolyte layer-by-layer coated substrates enables micron-scale patterning of gold nanorods, and thus application of photothermal effect with good control.

Photoinduced Micropattern Alignment of Semiconductor Nanorods with Polarized Emission in a Liquid Crystal Polymer Matrix.

Photoalignment technology provides high alignment quality with an exceptional control over the local director of liquid crystals. Because of the reorientation ability of sulfonic azo dye molecules, they offer high azimuthal and polar anchoring energy with a low pretilt angle for the orientation of liquid crystals and liquid crystal composites. In this work, we make use of this approach to align thin film composites of light-emitting semiconductor nanorods dispersed in a liquid crystal polymer into both one-dimensional and two-dimensional microscale patterns. After unidirectional alignment, the patterns are fabricated by a second irradiation with different polarization azimuth and the employment of a photomask. Fluorescence micrographs reveal the nanorod pattern alignment in domain sizes down to 2 μm. Apart from demonstrating the possibility of controlling the orientation of anisotropic nanocrystals with strongly polarized emission on microscopic scale, our results are promising for the fabrication of complex nanostructures for photonic applications.

Structural and Morphological Analysis of Nanocomposite SnO<sub>2</sub>-Graphene Synthesized by Sol-Gel Method

Gas sensor performance is strongly influenced by the crystal structure, composition and morphology of the material used. In this paper, structural and morphological analysis of nanocomposite SnO2-Graphene synthesized by Sol-Gel method with the composition of 1:1, 1:2, 1:3 will be described. Analysis of the morphology and structure of nanocomposite SnO2-Graphene is investigated using XRD, SEM and TEM with the purpose of obtaining the crystal structure, morphology, composition and size of the resulting particles. The XRD results showed that the formation of the crystalline phase can be recorded at 2θ = 26.64; 34.2; 51.92, where the results of SEM show that the nanomaterial SnO2 has tetragonal structure while the graphene has hexagonal structure. The nanocomposite SnO2-Graphene has nanorod pattern. Furthermore, the surface analysis using TEM of nanocomposite SnO2-Graphene shows that the surface has the rod diameter in the range of 5-8 nm. The unique nanopattern of SnO2-Graphene will have potential applicability as the sensing material for CO gas sensor.

Influence of seed layer thickness on well-aligned ZnO nanorods via hydrothermal method

Zinc oxide (ZnO) nanorods (NRs) were fabricated via the hydrothermal method at 90°C for 6 hour on the substrates with the ZnO seed layers. The ZnO seed layers had previously prepared at the different thickness, whose effects on the ZnO NRs were investigated. On the prepared ZnO samples, the morphologies and the crystal structures were examined by field-emission scanning electron microscopy and X-ray diffraction, respectively. The results show that the thickness of the seed layers directly affected on their crystallinity, the surface roughness and the ZnO NRs structures. From the hydrothermal process, the ZnO NRs grown on the seed layers with the smooth surface showed the well-aligned nanorod patterns. In addition, the growth rate of the ZnO NRs was also greatly affected by the seed layer thickness because of the corresponding surface energy. Finally, the optimizations of the uniformity and high aspect ratios of the ZnO NRs were carefully investigated and discussed.

Self-assisted optothermal trapping of gold nanorods under two-photon excitation

We report a self-assisted optothermal trapping and patterning of gold nanorods (GNRs) on glass surfaces with a femtosecond laser. We show that GNRs are not only the trapping targets, but also can enhance the optothermal trapping of other particles. This trapping phenomenon is the net result of thermophoresis and a convective flow caused by localized heating. The heating is due to the conversion of absorbed photons into heat at GNR’s longitudinal surface plasmon resonance (LSPR) wavelength. First, we investigated the optothermal trapping of GNRs at their LSPR wavelength on the glass surface with as low as 0.5 mW laser power. The trapping range was observed to be larger than a typical field of view, e.g. 210 µm × 210 µm here. Second, by adjusting the distance between the laser focus and the glass surface, ring patterns of GNRs on the glass surface were obtained. These patterns could be controlled by the laser power and the numerical aperture of the microscope objective. Moreover, we examined the spectral emission of GNRs under different trapping conditions using the spectral phasor approach to reveal the temperature and association status of GNRs. Our study will help understanding manipulation of flows in solution and in biological systems that can be applied in future investigations of GNR-induced heating and flows.

Self-Assisted Optothermal Trapping of Gold Nanorods Under Two-Photon Excitation

We report self-assisted optothermal trapping and patterning of gold nanorods (GNRs) on glass surfaces with a femtosecond laser. We show that GNRs are not only the trapping targets, but also can induce convective flows that drive more particles toward the trap. The trapping phenomenon is the net result of thermophoresis and convective flow caused by localized heating, which is due to the conversion of absorbed photons into heat at GNR's longitudinal surface plasmon resonance wavelength. We investigated the optothermal trapping of GNRs at the glass surface which can be obtained with laser power as low as 0.5 mW at 840 nm. The attraction of particles toward the central hot spot can be larger than the typical field of view, e.g. attraction toward the trap was observed from a range of 210 µm × 210 µm. By moving the laser focus away from the glass surface, at certain distances, ring patterns of GNRs on the glass surface can be obtained visualizing the regions of flow. These patterns could be controlled by the laser power and the numerical aperture of the microscope objective. Moreover, we examined the spectral emission of GNRs under different trapping conditions using the spectral phasor approach to reveal the temperature and association status of GNRs. Our study will help understanding manipulation of flows in solution and in biological systems which could arise in future applications of GNRs induced heating and flows. Work done in part with funds from NIH P41-GM103540 and NIH P50-GM076516.

Combining surface plasmonic and light extraction enhancement on InGaN quantum-well light-emitters.

Surface plasmon coupling with light-emitters and surface nano-patterning have widely been used separately to improve low efficiency InGaN light-emitting diodes. We demonstrate a method where dielectric nano-patterning and Ag nanoparticles (NPs) are combined to provide both light extraction and internal quantum efficiency enhancement for InGaN/GaN quantum-well light-emitters. By fabricating dielectric nano-rod pattern on the GaN surface, an optical coating that improves the light extraction is obtained, and furthermore has a low refractive index which blue-shifts the plasmonic resonance of Ag NPs towards the emission wavelength. We investigate emission components from both the GaN and sapphire surface of the semiconductor crystal and show that Ag NPs on dielectric nano-pattern compared to a planar surface, result in a stronger enhancement.

Multiplex serum cytokine immunoassay using nanoplasmonic biosensor microarrays.

Precise monitoring of the rapidly changing immune status during the course of a disease requires multiplex analysis of cytokines from frequently sampled human blood. However, the current lack of rapid, multiplex, and low volume assays makes immune monitoring for clinical decision-making (e.g., critically ill patients) impractical. Without such assays, immune monitoring is even virtually impossible for infants and neonates with infectious diseases and/or immune mediated disorders as access to their blood in large quantities is prohibited. Localized surface plasmon resonance (LSPR)-based microfluidic optical biosensing is a promising approach to fill this technical gap as it could potentially permit real-time refractometric detection of biomolecular binding on a metallic nanoparticle surface and sensor miniaturization, both leading to rapid and sample-sparing analyte analysis. Despite this promise, practical implementation of such a microfluidic assay for cytokine biomarker detection in serum samples has not been established primarily due to the limited sensitivity of LSPR biosensing. Here, we developed a high-throughput, label-free, multiarrayed LSPR optical biosensor device with 480 nanoplasmonic sensing spots in microfluidic channel arrays and demonstrated parallel multiplex immunoassays of six cytokines in a complex serum matrix on a single device chip while overcoming technical limitations. The device was fabricated using easy-to-implement, one-step microfluidic patterning and antibody conjugation of gold nanorods (AuNRs). When scanning the scattering light intensity across the microarrays of AuNR ensembles with dark-field imaging optics, our LSPR biosensing technique allowed for high-sensitivity quantitative cytokine measurements at concentrations down to 5-20 pg/mL from a 1 μL serum sample. Using the nanoplasmonic biosensor microarray device, we demonstrated the ability to monitor the inflammatory responses of infants following cardiopulmonary bypass (CPB) surgery through tracking the time-course variations of their serum cytokines. The whole parallel on-chip assays, which involved the loading, incubation, and washing of samples and reagents, and 10-fold replicated multianalyte detection for each sample using the entire biosensor arrays, were completed within 40 min.

Patterned growth of zinc oxide nanorods using poly(vinyl alcohol)-N-methyl-4(4′-formylstyryl)pyridinium methosulfate acetal and zinc acetate mixture as a seed layer

This paper reports a new method for fabricating two-dimensional ZnO nanorod patterns. A water soluble mixture of poly(vinyl alcohol)-N-methyl-4(4′-formylstyryl)pyridinium methosulfate acetal (PVA-Sbq) and zinc acetate (ZnA) was used as a negative photoresist to produce the desired patterns using conventional photolithography. Hydrothermally-grown ZnO nanorods were grown selectively on the calcined PVA-Sbq/ZnA patterns. The appropriate concentration of PVA-Sbq and ZnA that can produce the desirable seed layer pattern was determined experimentally. Furthermore, the effects of the calcination time on the morphology and vertical alignment of ZnO nanorods were investigated. The vertically-aligned ZnO nanorods were generated by sufficient calcination of the patterned seed layer. On the other hand, the aspect ratio of ZnO nanorods decreased slightly with increasing calcination time. This new approach provides a simple and cost-effective method for fabricating ZnO nanorod patterns which can be beneficial in various solid-state devices and optoelectronic applications.

Fabrication of two-dimensional zinc oxide nanorod patterns and their application for optical diffraction grating effect

We present a novel method for fabricating two-dimensional arrays of zinc oxide (ZnO) nanorod patterns. Vertically aligned ZnO nanostructure patterns were synthesized by hydrothermal growth on a two-dimensional seed layer pattern formed by atomic layer deposition. Various characteristics of ZnO seed films were experimentally studied in order to optimize the fabrication of ZnO rod structures in terms of their uniformity and vertical alignment on the two-dimensional-patterned surfaces. Using these ZnO structures as hierarchical electrodes, we demonstrate that localized electric fields in the proximity of ZnO rod patterns can be used for periodic alignment of liquid crystal molecules, resulting in the optical diffraction grating effect. Process conditions for creating ZnO rod patterns that best enhance diffraction efficiency are further discussed. The current study is the first demonstration of hierarchical ZnO rod patterns as electrodes for optical modulation of a medium. We believe this will be beneficial for future optical applications.

Growth and morphological evolution of Co3-x Mn x O4 (x = 1, 2) thin films

We grew epitaxial CoMn2O4 and Co2MnO4 thin films on Nbdoped (0.1 wt.%) SrTiO3(100) singlecrystal substrates by using pulsed laser deposition and studied how the growth temperature affected their crystal structures and surface morphologies. For Co2MnO4, increasing the growth temperature induced no significant changes except for an enlarged grain size. In contrast for CoMn2O4, increasing the growth temperature caused its surface morphology to evolve from spherical grains to rectangular nanorods; additionally, X-ray diffraction showed that these rectangular nanorod grains scattered to domains with different crystal orientations. We attribute this rectangular nanorod pattern to self-assembled domains originating from Jahn-Teller distortions and film-substrate lattice mismatch

Enhanced Device Efficiency of Bilayered Inverted Organic Solar Cells Based on Photocurable P3HTs with a Light‐Harvesting ZnO Nanorod Array

Periodically patterned zinc oxide nanorod (P‐ZnO NR) layers are directly prepared from a pre‐patterned ZnO seed layer using a polydimethylsiloxane (PDMS) elastomeric stamp and then applied in inverted organic photovoltaic devices (IOPVs). The IOPV is assembled with a hydrothermally grown zinc oxide nanorod patterns with a (100) preferential crystal orientation as an electron transport buffer layer (ETBL) and photoactive bilayer consisting of methacylate end‐functionalized poly(3‐hexylthiophene) (P3HT‐MA), phenyl‐C60‐butyric acid methyl ester (PC60BM) and indene‐C60 bis‐adduct (IC60BA). In te IOPVs, the P‐ZnO NR is found to induce efficient light harvesting and the photocrosslinkable P3HTs afford solution‐processed bilayer architecture in IOPVs to show improved device stability and performance (PCEmax= 5.95%), as the bilayered structure allowed direct exciton splitting, thus reducing the charge recombination.

Electronic Nose Based on Multipatterns of ZnO Nanorods on a Quartz Resonator with Remote Electrodes

An electrodeless monolithic multichannel quartz crystal microbalance (MQCM) sensor was developed via the direct growth of ZnO nanorod patterns of various sizes onto an electrodeless quartz crystal plate. The patterned ZnO nanorods acted as independent resonators with different frequencies upon exposure to an electric field. The added mass of ZnO nanostructures was found to significantly enhance the quality factor (QF) of the resonator in electrodeless QCM configuration. The QF increased with the length of the ZnO nanorods; ZnO nanorods 5 μm in length yielded a 7-fold higher QF compared to the QF of a quartz plate without ZnO nanorods. In addition, the ZnO nanorods offered enhanced sensitivity due to the enlarged sensing area. The developed sensor was used as an electronic nose for detection of vapor mixtures with impurities.