Opaque Substrates Research Articles

(Cd,Zn,Mg)Te-based microcavity on MgTe sacrificial buffer: Growth, lift-off, and transmission studies of polaritons

Opaque substrates precluded, so far, transmission studies of II-VI semiconductor microcavities. This work presents the design and molecular beam epitaxy growth of semimagnetic (Cd,Zn,Mn)Te quantum wells embedded into a (Cd,Zn,Mg)Te-based microcavity, which can be easily separated from the GaAs substrate. Our lift-off process relies on the use of a MgTe sacrificial layer which stratifies in contact with water. This allowed us to achieve a II-VI microcavity prepared for transmission measurements. We evidence the strong light-matter coupling regime using photoluminescence, reflectivity, and transmission measurements at the same spot on the sample. By comparing a series of reflectance spectra before and after lift-off, we prove that the microcavity quality remains high. Thanks to Mn content in quantum wells we show the giant Zeeman splitting of semimagnetic exciton-polaritons in our transmitting structure.

Integrated structural color array enabled by ultrathin silver film via cavity-enhanced absorption

In this work, we experimentally demonstrate enhanced absorption resonance enabled by the deconstructive interference of the reflected light in a sandwiched nanostructures composing of the ultrathin silver layer, transparent SiO2 cavity, and the opaque metallic substrate (e.g., 300-nm Ag). Such cavity-enhanced absorption is tunable via modulating the thickness of the absorptive ultrathin silver layer or the embedded transparent SiO2 cavity, giving rise to tunable structural coloration. Through five deposition processes, a 32-channel colorful sample is successfully fabricated. We believe the concepts and results make it evident that such ultrathin absorptive film offers us unprecedented opportunities on developing various photonic applications such as labeling, visual arts, and optical filters.

Structural properties of CZTS thin films on glass and Mo coated glass substrates: a Rietveld refinement study

Due to the difficulty in analyzing a few properties of CZTS (Cu2ZnSnS4) films coated on opaque substrates, the process conditions are often optimized on normal soda lime glass substrates and then transfer the process to Mo coated soda lime glass (SLG) substrates for device fabrication. This study concentrates on the analysis of structural properties of CZTS films on normal glass and Mo coated SLG substrates. CZTS films were coated on these two substrates by spin coating followed by sulphurization in N2 + H2S atmosphere. Phase purity of the films was analyzed by GIXRD and Raman spectroscopy. W–H analysis was used for estimating crystallite size and lattice strain of the films on the two substrates. Detailed structural studies were carried out with Rietveld refinement technique using GSAS package. Kesterite model with space group I4 (SG No: 82) was chosen for the refinement. Formation of kesterite phase on both substrates was confirmed from the refined lattice constant values. Deviation in bond angle with respect to kesterite structure was also analyzed. Different structural parameters were observed for the films on these substrates. The study indicates that it is important to optimize the properties of CZTS film on Mo coated SLG substrate separately, without following the same preparation conditions used for coating film on glass substrates.

Simultaneous electrical and contractile monitoring of cardiomyocytes on silicon microelectrode arrays

Simultaneous electrical and contractile monitoring of cardiomyocytes on silicon microelectrode arrays

Reversible and repeatable phase transition at a negative temperature regime for doped and co-doped spin coated mixed valence vanadium oxide thin films.

Smooth, uniform mixed valance vanadium oxide (VO) thin films are grown on flexible, transparent Kapton and opaque Al6061 substrates by the spin coating technique at a constant rpm of 3000. Various elements e.g., F, Ti, Mo and W are utilized for doping and co-doping of VO. All the spin coated films are heat treated in a vacuum. Other than the doping elements the existence of only V4+ and V5+ species is noticed in the present films. Transmittance as a function of wavelength and the optical band gap are also investigated for doped and co-doped VO thin films grown on a Kapton substrate. The highest transparency (∼75%) is observed for the Ti, Mo and F (i.e., Ti–Mo–FVO) co-doped VO system while the lowest transparency (∼35%) is observed for the F (i.e., FVO) doped VO system. Thus, the highest optical band gap is estimated as 2.73 eV for Ti–Mo–FVO and the lowest optical band gap (i.e., 2.59 eV) is found for the FVO system. The temperature dependent phase transition characteristics of doped and co-doped VO films on both Kapton and Al6061 are studied by the differential scanning calorimetry (DSC) technique. Reversible and repeatable phase transition is noticed in the range of −24 to −26.3 °C.

Технология полихромного выделения градиентов электрического поля на электрополевых изображениях, сформированных частицами серебра

Shown for the first time the prospect of attracting polychrome conversion technology electro-filed images (EFI), for example, silver (AgHal) film Agfa, which is the optical isolation of various colors of the gradients of electric field effect on the photographic material and the possible visualization of the induced field of the charges of the interfacial (interlayer) polarization. In addition, with the use of strong reducing agents based on bivalent tin, conditions have been achieved that exclude the need to use optically opaque substrates when considering polychrome EFI in reflected light. For the used X-ray photographic material Agfa the most effective are double and triple conversion of monochrome (black and white) EFI to polychrome. As a result of which large Ag agglomerates of 4-5 to 0,5-2,0 microns in size and consisting of colloidal metal particles of 25 to 450 nm are formed. From the data of electron microscopy it follows that during the formation of polychrome EFI Ag-particles and their agglomerates with a complex geometric structure and nano-disperse composition are formed. This creates conditions for the complex nature of the interaction with them of electromagnetic radiation of the visible range of the spectrum, depending not only on the size of the particles, but also on their shape, mutual arrangement, as well as the presence of fractions of Ag particles of other sizes.

Organic solar cells on Al electroded opaque substrates: Assessing the need of ZnO as electron transport layer

Interfacial buffer layers such as electron and hole transporting layers are crucial in maximizing power conversion efficiencies of organic solar cell (OSC) devices. In this manuscript, we studied the role of solution processed ZnO as electron transport layer in devices with Aluminum (Al) cathode on opaque substrates in inverted device configuration where Al and Gold (Au) are used as cathode and anode, ZnO and MoO3 are used as electron and hole transport layers respectively whilst P3HT:PC60BM is used as active layer (ActL). The results show that a thin layer of Aluminum Oxide (Al2O3) present on thermally evaporated Al cathode acts as an electron transport layer (ETL) when ZnO is absent, with surface states present on Al2O3 layer aiding the electron transport to cathode. The presence of ZnO as ETL between Al and active layer leads to a decrease in the efficiency of solar cell from 2.9% to 1.9%, attributed to the trapping of electrons at Al/ZnO interface due to unfavourable band alignment created by the presence of composite Al2O3/ZnO layer, implying that an additional ETL is not required when Al is used as a bottom electrode and could be an added advantage due to reduced processing steps.

An Implantable Transparent Conductive Film with Water Resistance and Ultrabendability for Electronic Devices.

Recently, instead of indium tin oxide, the random mesh pattern of metallic nanowires for flexible transparent conducting electrodes (FTCEs) has received a great amount of interest due to its flexibility, low resistance, reasonable price, and compliant processes. Mostly, nanowires for FTCEs are fabricated by spray or mayer coating methods. However, the metallic nanowire layer of FTCEs, which is fabricated by these methods, has a spiked surface roughness and low junction contact between the nanowires that lead to their high sheet resistance value. Also, the nanowires on FTCEs are easy to peel-off through exterior forces such as bending, twisting, or contact. To solve these problems, we demonstrate novel methods through which silver nanowires (AgNWs) are deposited onto a nanosize porous nitrocellulose (NC) substrate by electrophoretic deposition (EPD) and an opaque and porous substrate. Respectively, through dimethyl sulfoxide treatment, AgNWs on NC (AgNW/NC) is changed to the transparent and nonporous FTCEs. This enhances the junction contact of the AgNWs by EPD and also allows a permanent attachment of AgNWs onto the substrate. To show the mechanical strength of the AgNWs on the transparent nitrocellulose (AgNW/TNC), it is tested by applying diverse mechanical stress, such as a binding test (3M peel-off), compressing, bending, twisting, and folding. Next, we demonstrate that AgNW/TNC can be effectively implanted onto normal newspapers and papers. As paper electronics, light-emitting diodes, which are laminated onto paper, are successfully operated through a basic AgNW/TNC strip circuit. Finally, it is demonstrated that AgNW/TNC and AgNW/TNC on paper are water resistant for 15 min due to the insulation properties of the nonporous substrate.

A novel wideband optical absorber based on all-metal 2D gradient nanostructures

Recently, all-metal nanostructures for perfect absorption of light have attracted much attention due to their excellent plasmonic and photonic properties, but only narrow absorption bands were obtained in previous studies. In this paper, a new kind of metallic metasurface with wideband absorption of visible light is designed, which consists only of a gold nanotriangle array on the opaque metal substrate. By combining different resonant modes in the gradual-changed triangular nanostructure, the wide absorption waveband in visible region from 378 to 626 nm is achieved with more than 90% absorptivity. We demonstrate that the absorption property of the nanostructure can be controlled by tuning the cell size and incident angle. In addition, a metallic trapezoidal grating structure is proposed which can also realize wideband light absorption. This research provides a novel strategy in designing wideband metamaterial absorbers for visible light based on all-metal nanostructures which have great potential applications in light energy harvesting and photoelectric conversion.

Reflective Small Angle Electron Scattering to Characterize Nanostructures on Opaque Substrates.

Features sizes in integrated circuits (ICs) are often at the scale of 10 nm and are ever shrinking. ICs appearing in today's computers and hand held devices are perhaps the most prominent examples. These smaller feature sizes demand equivalent advances in fast and accurate dimensional metrology for both development and manufacturing. Techniques in use and continuing to be developed include X-ray based techniques, optical scattering and of course the electron and scanning probe microscopy techniques. Each of these techniques have their advantages and limitations. Here the use of small angle electron beam scattering measurements in a reflection mode (RSAES) to characterize the dimensions and the shape of nanostructures on flat and opaque substrates is demonstrated using both experimental and theoretical evidence. In RSAES, focused electrons are scattered at angles smaller than 1° with the assistance of electron optics typically used in transmission electron microscopy. A proof-of-concept experiment is combined with rigorous electron reflection simulations to demonstrate the efficiency and accuracy of RSAES as a method of non-destructive measurement of shapes of features less than 10 nm in size on flat and opaque substrates.

Design of multiband selective near-perfect metamaterial absorbers with SiO2 cylinder/rectangle shell horizontally embedded in opaque silver substrate

In this paper, we presented two multiband selective near-perfect absorbers, respectively made of one-dimensional periodic SiO2 cylinder shell and SiO2 rectangle shell arrays horizontally embedded in silver substrate. The spectral-directional absorptivity of the proposed structures was numerically investigated with the finite element based Comsol Multiphysics software. Five near-perfect absorption bands in the wavenumber range from 2500 to 20,000cm−1 for TM-wave incidence were obtained for both absorbers. Physical mechanisms responsible for the multiband absorption were elucidated as due to resonance of magnetic polaritons and the effect of Wood’s anomaly. Furthermore, the effects of polarization angle and geometric parameters on the multiband selective absorption were explored. This work may provide new guidelines for designing high efficient multiband photodetectors or photon sorters.

Plasmonic lattice resonance-enhanced light emission from plastic scintillators by periodical Ag nanoparticle arrays

We have demonstrated that periodical arrays of silver nanoparticles can enhance the light emission from a plastic scintillator layer on the surface of a silicon substrate. The enhancement is attributed to surface lattice resonances with a photonic-plasmonic nature. Although the enhancement exhibits directional characteristics for individual wavelengths, the wavelength-integrated enhancement shows a monotonous increase with increasing emission angle. As a result, an overall 1.81-fold wavelength- and angle-integrated enhancement has been obtained. This observation is promising for fundamental and applied research into enhanced luminescent material layers on opaque substrates.

Measurement of the in-plane thermal conductivity by steady-state infrared thermography.

We demonstrate a simple and quick method for the measurement of the in-plane thermal conductance of thin films via steady-state IR thermography. The films are suspended above a hole in an opaque substrate and heated by a homogeneous visible light source. The temperature distribution of the thin films is captured via infrared microscopy and fitted to the analytical expression obtained for the specific hole geometry in order to obtain the in-plane thermal conductivity. For thin films of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate post-treated with ethylene glycol and of polyimide, we find conductivities of 1.0 W m-1 K-1 and 0.4 W m-1 K-1 at room temperature, respectively. These results are in very good agreement with literature values, validating the method developed.

Semiconductor meta-surface based perfect light absorber

We numerically proposed and demonstrated a semiconductor meta-surface light absorber, which consists of a silicon patches array on a silicon thin-film and an opaque silver substrate. The Mie resonances of the silicon patches and the fundamental cavity mode of the ultra-thin silicon film couple strongly to the incident optical field, leading to a multi-band perfect absorption. The maximal absorption is above 99.5% and the absorption is polarization-independent. Moreover, the absorption behavior is scalable in the frequency region via tuning the structural parameters. These features hold the absorber platform with wide applications in optoelectronics such as hot-electron excitation and photo-detection.

Multiband selective absorbers made of 1D periodic Ag/SiO2/Ag core/shell coaxial cylinders horizontally lying on a planar substrate.

In this paper, we present a one-dimensional periodic microstructure for multiband selective absorbers of thermal radiation. The microstructure is made of Ag/SiO2/Ag core/shell coaxial cylinders horizontally lying on top of a SiO2 dielectric spacer and an opaque silver substrate. The spectral-directional absorptivity of the proposed structure was numerically investigated with the finite element based Comsol Multiphysics software. Multiband selective absorption in the wavenumber range from 2500 to 20000 cm-1 for TM-wave incidence was obtained. Physical mechanisms responsible for the multiband selective absorption were elucidated due to the resonance of magnetic polaritons in the SiO2 spacer shell, excitation of surface plasmon polaritons at the SiO2/Ag interface, and the effect of Wood's anomaly. Furthermore, the effects of a silver core radius, spacer shell thickness, a confocal elliptical core/shell cylinder on the property of multiband absorption, and the absorptivity of the structure with one core/four shells coaxial cylinders were explored.

Vanadium dioxide based Fabry-Perot emitter for dynamic radiative cooling applications

An asymmetric Fabry-Perot emitter is proposed with a lossless dielectric spacer inserted between a vanadium dioxide (VO2) thin film and an opaque aluminum substrate. Switchable mid-infrared emittance has been achieved due to the insulator-to-metal transition of VO2. When VO2 is dielectric below 341K, the structure is highly reflective, thereby minimizing thermal radiation loss. Above 345K, the VO2 becomes metallic and forms a Fabry-Perot resonance cavity with high broadband emissivity around 10µm wavelength, providing a radiative cooling effect due to enhanced thermal emission. The radiative properties are calculated via a uniaxial transfer matrix method and Bruggeman effective medium theory. The physical mechanisms that provide the observed absorption enhancements are elucidated by examining the total phase shift in the multilayer structure and the phonon modes of VO2. When experiencing the VO2 phase transition, the radiative power of the proposed coating achieves a 6.5 fold enhancement for extraterrestrial spacecraft systems, and 7.3 fold enhancement for terrestrial systems such as buildings, making it a promising choice for dynamic radiative cooling applications in a variable environment. The findings here will facilitate research and development of novel coating materials for radiative cooling applications.

Addressing the electronic properties of III–V nanowires by photoluminescence excitation spectroscopy**This article belongs to the special issue: Emerging Leaders, which features invited work from the best early-career researchers working within the scope of J. Phys. D. This project is part of the Journal of Physics’ series 50th anniversary celebrations in 2017. Marta De Luca was selected by the Editorial Board

Semiconductor nanowires (NWs) have been attracting an increasing interest in the scientific community. This is due to their peculiar filamentary shape and nanoscale diameter, which renders them versatile and cost-effective components of novel technological devices and also makes them an ideal platform for the investigation of a variety of fascinating physical effects. Absorption spectroscopy is a powerful and non-destructive technique able to provide information on the physical properties of the NWs. However, standard absorption spectroscopy is hard to perform in NWs, because of their small volume and the presence of opaque substrates. Here, we demonstrate that absorption can be successfully replaced by photoluminescence excitation (PLE). First, the use of polarization-resolved PLE to address the complex and highly-debated electronic band structure of wurtzite GaAs and InP NWs is shown. Then, PLE is used as a statistically-relevant method to localize the presence of separate wurtzite and zincblende NWs in the same InP sample. Finally, a variety of resonant exotic effects in the density of states of InxGa1−xAs/GaAs core/shell NWs are highlighted by high-resolution PLE.

Depth-of-cure of Bulk-fill Composites Cured in Tooth or Opaque Substrate

ABSTRACT Purpose To determine the effect of substrate on the depth-of-cure determination when using hardness profiles in a covered-slot technique and to introduce a new covered-slot method that uses tooth substrates. Materials and methods Three bulk-fill composites and one conventional composite were tested: Tetric EvoCeram Bulk Fill, Venus Bulk Fill, Filtek Bulk Fill Flowable, Filtek Supreme Ultra. The composites were light-cured in rectangular slots (2 mm deep, 2 mm wide) made in a plaster mold or an extracted tooth. The slots were covered with an orange glass plate during curing, leaving one end exposed for light-curing. After curing, the glass plate was removed and the sample was stored in the dark for 24 hours before Vickers hardness was measured as a function of depth at 0.5-mm intervals. Results were analyzed using two-way analysis of variance (ANOVA) and pairwise comparisons (significance level 0.05). Results The hardness of composites cured in covered-slot molds decreased with increasing depth (p < 0.001). Bulk-filled composites cured in plaster molds had a slightly lower depth-of-cure than those cured in natural tooth substrates. Differences between the tooth and plaster substrates were significant at all depths in the “packable” bulk-fill composite (Tetric EvoCeram Bulk Fill), and were significant at ≥2.5 and ≥3.5 mm in the flowable bulk-fill composites (Filtek Bulk Fill Flowable and Venus Bulk Fill) respectively. Conclusion Using natural tooth substrates in the covered-slot method increased the depth-of-cure of bulk-filled composites in comparison to opaque plaster molds. How to cite this article Church BW, Tantbirojn D, Do T, Wells MH, Versluis A. Depth-of-cure of Bulk-fill Composites Cured in Tooth or Opaque Substrate. Int J Experiment Dent Sci 2017;6(2):68-73.

Metallic Metasurfaces for Light Absorbers

Multi-band light perfect absorption by all-metal resonant structure is of particular interest for applications in a wide variety of technologies. Here, we propose and demonstrate a new strategy for achieving multi-band light absorber based on the metallic sub-wavelength structure, which consists of a hexagonally packed nanoring-nanodisk composite array on an opaque metal substrate. By introducing asymmetry to the nanoring-nanodisk hybrid system, new absorption bands emerge. The optical properties are enabled by strong plasmon resonances of the metallic resonators and their near-field coupling effects. Designing such nanostructures is a promising route for all-metal multi-band light absorption platform, which can be used as absorption filters, photo-thermal therapy, multispectral thermal emitters, and plasmonic biosensors.

Simulation of perfect absorber at visible frequencies using TiN-based refractory plasmonic metamaterials

Refractory titanium nitride (TiN) nanoellipsoid was proposed as unit component for metamaterial perfect absorber in visible frequencies. Combining both the intrinsic loss of the TiN material in short wavelength ( 500 nm), the metamaterial perfect absorber based TiN nanoellipsoid array can be a broadband perfect absorber in whole visible region. An average absorbance of 98.5 % over the whole visible spectrum was obtained with a total thickness of only 200 nm. The structure is directly applicable to all kinds of opaque substrates with no need for metallic bottom.