Submicron Holes Research Articles

Relaxation of the trapped magnetic flux in a mesoscopic HTS with artificial pinning in the form of submicron holes

Vortex relaxation has been studied in a microsized HTS with various distributions of artificial pinning in the form of submicro-holes. It has been shown that, in some cases, for a superconductor with dimensions up to several micrometers, the time dependences of the trapped magnetic field do not correspond with the collective creep model. The dependences of the trapped-field relaxation rate and vortex activation energy on the magnetizing field (up to 0.5 T) and temperature (up to 50 K) have been obtained. It has been shown that the presence of submicro-holes slightly increases the relaxation rate, mainly due to the decrease in the number of random nanosized pinning centers.

Chitosan adhesives with sub-micron structures for photochemical tissue bonding

We describe a method for fabricating biocompatible chitosan-based adhesives with sub-micron structures to enhance tissue bonding. This procedure avoids coating and chemical modification of structures and requires a simple drop-casting step for the adhesive film formation. Chitosan thin films (27±3 μm) were fabricated with sub-micron pillars (rectangular cuboid with height ∼150 nm, square dimension ∼1 μm and pitch ∼2 μm) or holes (diameter ~500 nm or ~1 μm, depth ~100 or 400 nm, pitch of 1 or 2 μm). Polydimethylsiloxane moulds were used as negative templates for the adhesive solution that was cast and then allowed to dry to form thin films. These were applied on bisected rectangular strips of small sheep intestine and photochemically bonded by a green laser (λ= 532 nm, irradiance ∼110 J/cm2). The tissue repair was subsequently measured using a computer-interfaced tensiometer. The mould sub-micron structures were reproduced in the chitosan adhesive with high fidelity. The adhesive with pillars achieved the highest bonding strength (17.1±1.2 kPa) when compared to the adhesive with holes (13.0±1.3 kPa, p<0.0001, one-way ANOVA, n=15). The production of chitosan films with patterned pillars or holes in the sub-micron range was demonstrated, using a polydimethylsiloxane mould and a single drop-casting step. This technique is potentially scalable to produce adhesives of larger surface areas.

Characteristics of GaPO4-LTA: Unique phase transition into amorphous cubic particles by long-term soaking in water

The transformation of as-synthesized gallophosphate crystals with an LTA structure (GaPO4-LTA) into an amorphous phase was induced simply by soaking the crystals in water. The obtained amorphous gallophosphate (am-GaPO) particles maintained the characteristic initial cubic morphology of GaPO4-LTA but with no molecules of dipropylamine (DPA), which acts as an organic structure-directing agent for the crystal synthesis. Am-GaPO incorporates many water molecules in place of DPA. The removal of DPA enables the water molecules to contact the GaPO4-LTA framework, which degrades the crystallinity. Though am-GaPO was expected to be a porous material due to its many water molecules, the square-shaped submicron holes on the particle surface, and light scattering from the particle interior, only a small surface area of 6 m2/g was estimated by the Brunauer–Emmett–Teller method. The accessible holes were distributed mainly on the particle surface, and it was concluded that the incorporated water molecules were chemisorbed.

Micro-drilling of alkali-silicate glass with ultraviolet picosecond laser

The low efficiency of UV-laser ablation of transparent alkali-silicate glass has been increased by means of irradiation by 60Co γ-quanta to doses 104 −107 Gy to induce intensive UV-visible coloration. Varying the picosecond pulse energy of Nd:YAG laser at 4-harmonics 266 nm within 1−9 mJ and pulse number, arrays and grids of holes were drilled with diameters from 9 to 40 µm on area up to 1×1 cm2 . Shock waves of 4−5 µm were generated by expanding plasma around ablated holes at focused pulse energy density >108 J/m2 and nanoscale crystallization occurred there. Besides, a submicron hole was drilled aside the central micron hole due to generation of vacuum UV harmonics. The combined effect of γ-irradiation followed by UV laser drilling has resulted in decrease of silicon and oxygen contents, and generation of fluorine that may be caused by photonuclear reactions 28Si14→19F9+ 33Т1; 16O8→44He2; 16О8+3Т1→19F9. Because of glass viscosity and relaxation during 2 months at 300 K, the exit diameter of drilled holes has increased up to the entry one. Such micro-scale grids can be used for separating liquid mixtures or cleaning water.

Design of structural coloration for full-color high-definition computer-generated holograms.

This paper investigates the submicron scale color filter design in the high-definition computer-generated hologram (HD-CGH). It is addressed that single pixel structural coloration is essential for full-color wide-viewing angle HD-CGH because the conventional RGB color stripe filter degrades HD-CGH image quality due to low misalignment tolerance. Considering that a submicron scale slit or hole with metallic mirror sidewalls can operate as a single pixel color filter. We propose a design of single pixel RGB plasmonic color filter (PCF) and present the feasibility of applying the proposed single pixel RGB PCF to high-definition HD-CGHs. Based on the RGB PCF platform, a 1.1 µm × 1.1 µm RGB PCF is designed and the corresponding optical characteristics of the full-color HD-CGH are analyzed.

Towards Ultrafast Laser Micromachining of X-Ray Gratings and Creation of Sub-Micron Hole Patterns, Comparison of Results With Bessel and Gaussian Beams

We compare micromachining results with Gaussian and Bessel beams using an UV picosecond laser system and demonstrate feasibility to produce tungsten gratings for x-ray interferometry medical imaging, and sub-micrometer size hole patterns. The advantages of Bessel beams compared to Gaussian beams, are demonstrated for micromachining of rectangular shallow profile gratings with sharp edges. The high-aspect ratio grating (10 microns wide and 200 microns deep) from tungsten foil could only be obtained with the Gaussian beam and focusing with an F-Theta type lens. Bessel beams contain significant amount of energy in the side lobes in comparison with the central peak. The limited amount of the pulse energy in the central, 2-micron peak of the beam and destruction of the Bessel beam structure due to the narrow slit clipping the side lobes, prevented the Bessel beam deeper penetration. On the other hand, the axicon lens and the Bessel beam shape enable creation of shallow sub-micron size structures.

Magnetization of Ultraviolet-Reduced Graphene Oxide Flakes in Composites Based on Polystyrene.

This work presents our study results of the magnetization of multilayer UV-reduced graphene oxide (UV-rGO), polymer matrix (polystyrene), and a conjugated composite based on them. The mesoscopic structure of the composites synthesized in this work was studied by such methods as X-ray diffraction, SEM, as well as NMR-, IR- and Raman spectroscopy. The magnetization of the composites under investigation and their components was measured using a vibrating-sample magnetometer. It has been shown that the UV-reduction process leads to the formation of many submicron holes distributed inside rGO flakes, which can create edge defects, causing possibly magnetic order in the graphite samples under investigation on the mesoscopic level. This article provides an alternative explanation for the ferromagnetic hysteresis loop in UV-rGO on the base of superconductivity type-II.

Plasmon-induced efficient hot carrier generation in graphene on gold ultrathin film with periodic array of holes: Ultrafast pump-probe spectroscopy.

Using ultrafast pump-probe reflectivity with a 3.1 eV pump and coherent white light probe (1.1-2.6 eV), we show that graphene on gold nanostructures exhibits a strong coupling to the plasmonic resonances of the ordered lattice hole array, thus injecting a high density of hot carriers in graphene through plasmons. The system being studied is single-layer graphene on an ultrathin film of gold with periodic arrangements of holes showing anomalous transmission. A comparison is made with gold film with and without hole array. By selectively probing transient carrier dynamics in the spectral regions corresponding to plasmonic resonances, we show efficient plasmon induced hot carrier generation in graphene. We also show that due to high electromagnetic field intensities at the edge of the submicron holes, fast decay time (10-100 fs), and short decay length (1 nm) of plasmons, a highly confined density of hot carriers (very close to the edge of the holes) is generated by Landau damping of plasmons within the holey gold film. A contribution to transient decay dynamics due to the diffusion of the initial nonuniform distribution of hot carriers away from the hole edges is observed. Our results are important for future applications of novel hot carrier device concepts where hot carriers with tunable energy can be generated in different graphene regions connected seamlessly.

Interaction of electromagnetic waves with VO2 nanoparticles and films in optical and millimetre wave ranges: Prospective for nano-photonics, nano-antennas, and sensors

Recently great interest in the field of nano-optic is attracted to nano-antennas in both basic and applied research. Nano-antennas are represented by metallic nanoparticles and holes in thin films with arrays of the holes. The usual nano-antennas have fixed functionality, but it will be very interesting to get tunability of nano-antennas controlled by external field. Materials with phase transitions are candidates for the development of tuneable nanoantennas. In this report metal-dielectric phase transition in VO2 micro- and submicron particles, films and holes are studied experimentally and theoretically. The complex dielectric permittivity of VO2 is varied drastically with temperature due to structural phase transition, accompanying metal-insulator transition (MIT) at critical temperature (Tc = 340 K). In this work, VO2 film on glass substrate were prepared and investigated in MM wave range (27–37 GHz). Then submicron holes arrays were formed on VO2 films by FIB milling and their optical Raman spectra were studied. The MM wave response of nanosized VO2 films reveals strong anomalies near MIT. The holes and arrays show strong change of the Raman spectra at the wavelength 530 nm under heating by laser radiation. The optical and MM wave electromagnetic properties of homogeneous VO2 nanospheres embedded in the air are studied theoretically. Size effects on the optical properties of the VO2 nanosphere are investigated. In VO2 nanosphere, converting into metallic phase by heating leads to formation of a localized surface plasmon resonance (LSPR) which red shifts by increasing dimension.

High Speed Surface Illuminated Si Photodiode Using Microstructured Holes for Absorption Enhancements at 900–1000 nm Wavelength

A surface-illuminated silicon photodiode with both high speed and usable external quantum efficiency from 900 to 1000 nm wavelength is highly desirable for intra/inter data center Ethernet communications, high performance computing, and laser radar application. Such Si photodiodes have the potential for monolithic integration to CMOS integrated circuits which can significantly reduce the cost of data transmission per gigabit below one US dollar. To overcome silicon’s intrinsic weakness of absorption in these wavelengths, photon-trapping microstructured hole arrays are etched into the silicon surface, and the operational wavelengths of a high-speed silicon PIN photodiode are extended to 1000 nm. In this paper, the design and fabrication of such photon-trapping structures integrated into all-silicon photodiodes with significantly reduced absorption layer thicknesses to achieve high external quantum efficiency and fast response are presented. Different designs and geometries of the submicron holes on the sil...

ZnO Nanorod-Based Ultraviolet Photodetector Prepared on Patterned Sapphire Substrates

A patterned sapphire substrate with a submicron hole array structure was used to fabricate ZnO nanorod (NR) array by low-temperature hydrothermal method. A ZnO seed layer was spin-coated using sol-gel process and then etched to form separated seed islands. Different concentrations of zinc acetate in the hydrothermal solution were performed for ZnO NR synthesis to investigate ultraviolet (UV) photo-response properties. The ZnO NRs synthesized on the patterned substrates were oriented at various inclined angles. The diameter of the NRs increased and their surface-to-volume ratio decreased as the concentrations of zinc acetate increased from 0.01 to 0.04 M. X-ray diffraction and photoluminescence analyses showed that the NRs synthesized at a higher zinc acetate concentration had better crystal quality and fewer defects. The current–voltage characteristics of the ZnO NR-based metal-semiconductor-metal photodetectors exhibited a linear relationship, suggesting an Ohmic contact between NRs and Al electrodes. The UV response, defined by the resistance ratio (Rdark/RUV), of the photodetectors increased with the decreasing zinc acetate concentration from 0.04 to 0.01 M. Compared to traditional vertically aligned NR array on plain substrates, the proposed ZnO NR-based photodetector on the patterned substrates achieved improved UV responses, and the average increment for samples of 0.01–0.04 M was 145%.

Experimental and numerical study of tuneable supercontinuum generation in new kind of highly birefringent photonic crystal fiber

We report on a new kind of highly birefringent and highly nonlinear photonic crystal fiber with a row of sub-micron air hole in the fiber core. The diameters of air holes in fiber core and cladding are 0.2 μm and 6.6 μ$m respectively. The parameters of birefringence, nonlinear and dispersion coefficient of the fiber are simulated by finite element method. It is found that the birefringence of the fiber can exist at the wavelengths up to 1550 nm, which is one order of magnitude higher than that of the traditional polarization-maintaining fiber. The zero-dispersion wavelengths of the fast axis and slow axis are 1050 nm and 1080 nm respectively. This fiber has a clear advantage over conventional fiber in continuum generation. Firstly, the polarization state of the pulse traveling in the fiber can be sustained along the fiber length and the extinction ratio is more than 20 dB. In addition, the pulses travel at different group velocities along the two polarization directions, which provide a convenient way of tuning the properties of the generated supercontinuum. Using this fiber as a nonlinear medium, an efficient generation of a tunable supercontinuum is demonstrated by pumping with 15 ps pulses of 1040 nm laser radiation, which is located in the normal dispersion region. A half-wave plate is used to vary the input polarization of the light pulse launched into the fiber, and the polarization of output supercontinuum is adjusted by a Glan prism at the same time. It is experimentally found that the polarization of pulse has a significant influence on the generation of the supercontinuum. When the linear polarization of the input pulse matches with the direction of the main axis of the fiber, the supercontinuum can be broadened over wavelength range of 800-1500 nm, and the extinction ratio is 21.2 dB. The polarization direction of the output SC is found to coincide with the pump pulse. When the angle between the polarization of the input pulse and the fast axis is increased to 45 degrees, the output supercontinuum is circularly polarized and becomes narrowest, extending from 900 to 1300 nm. So we can realize the wide tuning of a supercontinuum by only changing the polarization direction of the incident pulse. Under the circumstances, the pulse in optical fiber can be broken into two components along the main axis respectively. If the input polarization direction is away from both principal axis directions, the power along the main axis and the contribution of cross phase modulation are reduced because of the walk-off effect, so the width of the supercontinuum will become narrower. It is suggested that this type of high birefringence photonic crystal fiber could be effectively applied to the generation of the tunable supercontinuum.

Fabrication of a W/CuxO/Cu memristor with sub-micron holes for passive sensing of oxygen

Memristive devices were fabricated and investigated for passive sensing of oxygen. The device design involved deposition of Cu bottom electrodes, oxygen-deficient copper oxide (CuxO) switching layers, and W top electrodes in a crossbar array structure. Two groups of holes that were 300nm and 700nm in diameter were etched in the top W electrodes to reveal the oxide surface. The devices were subjected to ambient air at 180°C to induce sensing in minutes. Measurements of atomic composition, which were determined via energy-dispersive X-ray spectroscopy (EDS), show an increase in oxygen atoms in the layer after exposure to ambient air. For the 300-nm holes, low and high resistance states demonstrated increased values (up to 25.0% and 74.8%, respectively) upon exposure to ambient air at 180°C. The larger 700-nm holes became capacitor-like after exposure. This work demonstrates a step towards the use of the memristor as a passive gas sensor, which we have named “memsensors”, by taking advantage of the device's ability to memorize (or record) historical information.

Droplet-induced dot, dot-in-hole, and hole structures in GaGe thin films grown by MOCVD on GaAs substrates

We report observations and origins of Ga-rich GaGe droplets and the localized etching of Ge-rich GaGe thin films grown on GaAs (100) substrates by metalorganic chemical vapor deposition. Micron and sub-micron dots, dot-in-holes, and holes have been fabricated by controlling the partial pressures of the Ga and Ge precursors as well as the substrate temperatures. The dot-in-hole features can also be converted to empty holes via post-growth sonication in hot deionized water due to the low melting point of the Ga-rich dots. Enhanced Raman scattering (ERS) of the Ge–Ge lattice vibrational mode has been observed at the wall of the concentric dot-in-hole structures as well as in the empty holes. To interpret the ERS mechanism, we have carried out finite-difference time-domain (FDTD) simulations, which reveal an enhanced electrical field for the obtained structures as a result of interference between the incident and reflected waves at the surface of the thin films that, in turn, results in the observed ERS. These findings greatly enrich the conventional droplet epitaxy and etching techniques and widen their applications.

Fabrication of high-brightness GaN-based light-emitting diodes via thermal nanoimprinting of ZnO-nanoparticle-dispersed resin

We fabricated high-brightness GaN-based light-emitting diodes (LEDs) with highly refractive patterned structures by using a thermal nanoimprint lithography (NIL). A highly refractive ZnO-nanoparticle-dispersed resin (ZNDR) was used in NIL, and a submicron hole, a submicron high-aspect-ratio pillar, and microconvex arrays were fabricated on the indium tin oxide (ITO) top electrode of GaN-based LED devices. We analyzed the light extraction mechanism for each of the three types of patterns by using a finite element method simulation, and found that the high-aspect-ratio pillar had a great ability to improve light extraction owing to its waveguide effect and prominent scattering effect. As a result, the light output power, which was measured in an integrating sphere, of the LED device was enhanced by up to 19.6% when the high-aspect-ratio pillar array was formed on the top ITO electrode of the device. Further, the electrical properties of none of the patterned LED devices fabricated using ZNDR degraded in comparison to those of bare LED devices.

The Effect of Inductively-Coupled-Plasma Reactive Ion Etching Power on the Etching Rate and the Surface Roughness of a Sapphire Substrate

In this study, patterned sapphire substrates are fabricated using nanosphere lithography (NSL) and inductively-coupled-plasma reactive ion etching (ICP-RIE). Polystyrene nanospheres of approximately 600 nm diameter are self-assembled on c-plane sapphire substrates by spin-coating. The diameter of the polystyrene nanospheres is modified to adjust the etching mask pitch cycle using oxygen plasma in the ICP-RIE system. A nickel thin film mask of 100 nm thickness is deposited by electron-beam evaporation on a substrate covered with treated nanospheres. The sapphire substrate is then etched in an inductively coupled plasma system using BCl3/Ar gas, to fabricate a structure with a periodic sub-micron hole array with different sidewall intervals. The DC bias voltage, the sapphire etching rate, the surface roughness, are studied as a function of the ICP and the RF power. Different sub-micron hole arrays with spacing cycles of 89 nm, 139 nm and 167 nm are successfully fabricated on the sapphire substrate, using suitable etching parameters.

A two-axis Lloyd's mirror interferometer for fabrication of two-dimensional diffraction gratings

A new two-axis Lloyd's mirror interferometer based on multi-beam interference is proposed. A square grating substrate with normal in the Z-axis is placed edge to edge with two rectangular mirrors with normals parallel to the XZ-plane (X-mirror) and the YZ-plane (Y-mirror), respectively. The angle between the substrate and each mirror is set to be larger than 90°, so that the beams reflected by the mirrors can be superimposed with the direct beam at the substrate to produce two-dimensional (2D) diffraction grating structures in a single exposure. Sub-micron pitched 2D hole grating structures were fabricated and evaluated.

Chip scale humidity sensing based on a microfluidic infiltrated photonic crystal

This work presents an optical on-a-chip humidity sensor based on the hydroscopic behavior of an infiltrated liquid into the sub-micron holes of a silicon photonic crystal. Direct measurements of the liquid refractive index in combination with numerical simulations show that the sensitivity of the device is due to changes of both the liquid's refractive index and volume. We report humidity sensing with a response time of 0.1 ms and study the stability and reversibility of the sensor. This demonstration highlights the sensitivity offered by optofluidics in photonic crystal circuits and the potential for realizing ultra-compact integrated humidity sensing components.

Rapid replication and facile modulation of subwavelength antireflective polymer film using injection nanomolding and optical property of multilayer coatings

A rapid, cost-effective and high-throughput process for nanotexturing subwavelength structures with high uniformity using the polycarbonate (PC) is realized via injection nanomolding. The process enables the precise control of nanohole array (NHA) surface topography (nanohole depth, diameter, and periodicity) over large areas thereby presenting a highly versatile platform for fabricating substrates with user-defined, functional performance. Specifically, the optical property of the PC substrates were systematically characterized and tuned through the modulation of the depths of NHA. The aspect ratio submicron holes can be easily modulated and experimentally proven by simply adjusting the molding temperature. The nanotextured depths were reliably fabricated in the range of 200 to 400 nm with a period of approximately 700 nm. The fabricated PC films can reduce the reflectivity from an original bare film of 10.2% and 8.9% to 1.4% and 2.1% with 400-nm depth of nanoholes at the wavelength of 400 and 550 nm, respectively. Compared with conventional moth-like nanostructures with nanopillar arrays with heights adjustable only by an etching process, this paper proposes a facile route with submicron holes to achieve a similar antireflective function, with a significantly reduced time and facile height modulation capability. Furthermore, the effects of multilayer coatings of dielectric and metallic layers on the nanomolded NHA have been performed and potential sensing application is explored.

Submicron-size patterning on the sapphire substrate prepared by nanosphere lithography and nanoimprint lithography techniques

In this paper, we demonstrate and compare the formation of ordered etching masks for submicron-size patterned sapphire substrates through use of the nanosphere lithography and nanoimprint lithography methods. The metal honeycomb network structure and the polymer pillar protrusion structure were obtained from these two methods. Subsequently, the inductively-coupled-plasma reactive ion etching technique was applied to etch the sapphire substrates, and the etchant mixture gases of boron trichloride and argon with the flow rate ratio of 1 to 6 were introduced into the etchant chamber. Two types of submicron -pattern structures were obtained on the sapphire substrate surface after the etching processes were completed. One type of sapphire substrate was the submicron hole array structure and another type was the submicron cone array structure. The working pressure had a considerable effect on the shape geometry and etching rate, and the possible mechanism is discussed.