Optical Sheet Research Articles

The Electro-Optical Performance of Silver Nanowire Networks

Networks of metallic nanowires have the potential to meet the needs of next-generation device technologies that require flexible transparent conductors. At present, there does not exist a first principles model capable of predicting the electro-optical performance of a nanowire network. Here we combine an electrical model derived from fundamental material properties and electrical equations with an optical model based on Mie theory scattering of light by small particles. This approach enables the generation of analogues for any nanowire network and then accurately predicts, without the use of fitting factors, the optical transmittance and sheet resistance of the transparent electrode. Predictions are validated using experimental data from the literature of networks comprised of a wide range of aspect ratios (nanowire length/diameter). The separation of the contributions of the material resistance and the junction resistance allows the effectiveness of post-deposition processing methods to be evaluated and provides a benchmark for the minimum attainable sheet resistance. The predictive power of this model enables a material-by-design approach, whereby suitable systems can be prescribed for targeted technology applications.

Correlation between the morphology and the opto-electronic and electrical properties of organometallic halide perovskite (CH3NH3MH3) thin films

Organometallic halide perovskites are emerging as a promising class of materials for optoelectronic applications. Crystal morphology is important for improving the organic-inorganic lead halide perovskite semiconductor property in optoelectronic, electrical and photovoltaic devices. It is thus important to investigate how the changes in crystal morphology affect the semiconductor behavior. This work presents a study that was carried out to assess the relationship between different deposition methodologies and the opto-electronic and electrical properties of the resultant organometallic halide perovskite thin films. Herein, single step solution deposition method and two step solution deposition methods have been used to deposit perovskite thin films. The structure and morphology of perovskite was controlled by changing concentration, annealing temperatures and dip coating times. From the study, prepared films showed different morphologies as the concentration, annealing temperatures and dip coating times were varied. Optical band gap energies of 2.23 eV, 2.13 eV and 2.09 eV were obtained for samples prepared by single step solution deposition method and 1.57 eV, 1.55 eV and 1.52 eV for two step solution deposition method. The sheet resistance values decreased with an increase in concentration, annealing temperatures and dip coating times. The decrease in optical band gap energy and sheet resistances are excellent properties for high performance photovoltaic devices.

A comparison of non-invasive versus invasive measures of intracranial pressure in hypoxic ischaemic brain injury after cardiac arrest

AimIncreased intracranial pressure (ICP) in hypoxic ischaemic brain injury (HIBI) can cause secondary ischaemic brain injury and culminate in brain death. Invasive ICP monitoring is limited by associated risks in HIBI patients. We sought to evaluate the agreement between invasive ICP measurements and non-invasive estimators of ICP (nICP) in HIBI patients. MethodsEligible consecutive adult (age>18) cardiac arrest patients with HIBI were included as part of a single centre prospective interventional study. Invasive ICP monitoring and nICP measurements were undertaken using: a) transcranial Doppler ultrasonography (TCD), b) optic nerve sheet diameter ultrasound (ONSD) and c) jugular venous bulb pressure (JVP). Multiple measurements applied in linear mixed-effects models were considered to obtain the correlation coefficient between ICP and nICP as well as their predictive abilities to detect intracranial hypertension (ICP≥20mm Hg). ResultsEleven patients were included (median age of 47 [range 20–71], 8 males and 3 females). There was a linear relationship between ICP and nICP with ONSD (R=0.53 [p<0.0001]), JVP (R=0.38 [p<0.001]) and TCD (R=0.30 [p<0.01]). The ability to predict intracranial hypertension was highest for ONSD and TCD (area under the receiver operating curve (AUC)=0.96 [95% CI: 0.90–1.00] and AUC=0.91 [95% CI: 0.83–1.00], respectively). JVP presented the weakest prediction ability (AUC=0.75 [95% CI: 0.56–0.94]). ConclusionsONSD and TCD methods demonstrated agreement with invasively-monitored ICP, suggesting their potential roles in the detection of intracranial hypertension in HIBI after cardiac arrest.

БЕСКОНТАКТНОЕ ИЗМЕРЕНИЕ ТОЛЩИНЫ СТЕКЛА

This article describes an optical non-contact sheet glass thickness meter, whose principle of operation is based on the comparison of optical signals obtained by three photodiodes from the same sources. In this case, two light beams pass through the glass, one of which falls on the controlled sample at an angle, the second is directed perpendicular to the surface of the glass. The third beam does not pass through the sample. The device will allow carry in out operational quality control of glass in the process of its manufacture. Using of the reference channel in the scheme will provide the reliable data, taking into account the influence of various external factors.

Device Characteristics of Top-Emitting Organic Light-Emitting Diodes Depending on Anode Materials for CMOS-Based OLED Microdisplays

We investigated the optical reflectance, surface roughness, and sheet resistance of aluminum (Al)/titanium nitride (TiN), titanium (Ti), and tungsten (W) layers on Si substrates, which are available in the CMOS foundry, for organic light-emitting diode (OLED) microdisplays. The devices with different metal anode layers exhibited different hole-injection properties and OLED performances, owing to the different optical and electrical properties of metal anode layers. Based on the OLED characteristics, the Al/TiN layer was selected as an anode layer for OLED microdisplays. A green monochromatic OLED microdisplay panel was designed and implemented using the 0.11-μm CMOS process. The density of pixels was ∼2 351 pixels per inch and the panel's active area was 0.7 in in diagonal. The resolution of the panel was 1 280 × 3 × 1 024, corresponding to SXGA. The panel was successfully operated, and the maximal luminance was ∼460 cd/m2.

Effects of different annealing processes on optoelectronic and bending fatigue properties of AgZr and ITO/AgZr thin film metallic glass

Transparent conducting oxide (TCO) films are widely used throughout the optoelectronics industry. The present study explores the optoelectronic responses of AgZr (AZ) and ITO/AgZr (IAZ) thin film metallic glasses (TFMGs) with different Ag and Zr compositions and processed by two different annealing methods, namely furnace annealing (FA) and laser annealing (LA). Among the various as-deposited AZ and IAZ films, the ITO/Ag66Zr34 (IA6Z) film has the highest optical transmittance (55.7%) and the lowest sheet resistance (145.8 Ω/□) For the FA samples, an annealing temperature of 300 °C results in the optimal optoelectronic properties, namely a transmittance of 68.4% and a sheet resistance of 47.2 Ω/□. For the LA samples, the optimal processing conditions (a pulse energy of 2.5 μJ and a repetition rate of 150 kHz) yield optical transmittance and sheet resistance values of 64.0% and 17.8 Ω/□ respectively. The optimal LA processing conditions increase the Haacke figure of merit of the IA6Z sample from 2.0 × 10−5 in the as-deposited condition to 6.5 × 10−4 Ω−1 under the annealed condition; corresponding to a 32.5-fold improvement. Finally, the relative change in resistivity (ΔR/R0, where R0 is the initial resistivity, Ri is the measured resistivity after a certain number of cycles, and ΔR is Ri− R0) of the as-deposited IA6Z sample following fatigue testing (10,000 cycles) with a bend radius of 7 mm (ΔR/R0=0.49) is significantly lower than that of a pure ITO film of roughly equivalent thickness (ΔR/R0=0.93).

Optimization of Mo/Cr bilayer back contacts for thin-film solar cells.

Molybdenum (Mo) is the most commonly used material as back contact in thin-film solar cells. Adhesion of Mo film to soda–lime glass (SLG) substrate is crucial to the performance of solar cells. In this study, an optimized bilayer structure made of a thin layer of Mo on an ultra-thin chromium (Cr) adhesion layer is used as the back contact for a copper zinc tin sulfide (CZTS) thin-film solar cell on a SLG substrate. DC magnetron sputtering is used for deposition of Mo and Cr films. The conductivity of Mo/Cr bilayer films, their microstructure and surface morphology are studied at different deposition powers and working pressures. Good adhesion to the SLG substrate has been achieved by means of an ultra-thin Cr layer under the Mo layer. By optimizing the deposition conditions we achieved low surface roughness, high optical reflectance and low sheet resistivity while we could decrease the back contact thickness to 600 nm. That is two thirds to half of the thickness that is currently being used for bilayer and single layer back contact for thin-film solar cells. We demonstrate the excellent properties of Mo/Cr bilayer as back contact of a CZTS solar cell.

Relationship between wire orientation and optical and electrical anisotropy in silver nanowire/polymer composite films

Silver nanowire (AgNW)/polymer composite films fabricated by roll-to-roll slot die-coating exhibit optical and electrical anisotropy. To evaluate the dependence of the film’s optical and electrical properties on the AgNW orientation, we quantify their polarized optical extinction and sheet resistance. Applying image analysis tools to microscope images, we show structural anisotropy due to a slightly preferential AgNW orientation. Optical anisotropy due to longitudinal- and transverse-mode surface plasmons resonances is predominantly observed in the lengthwise and crosswise direction of the composite films, respectively. Electrical anisotropy also depends on the measurement direction: sheet resistance is small in the lengthwise direction. These data indicate that the distribution of AgNWs is not fully isotropic, with their long axis preferentially oriented along the lengthwise direction of the composite films. Furthermore, although optical and electrical anisotropies are of comparable magnitude, both are smaller than the structural anisotropy. Optical anisotropy is still observed even when the amount of AgNWs increases, indicating that their orientation remains relatively constant. Electrical anisotropy is also preserved, indicating that junction resistance prevails in such composite films. The relationship between polarized transmittance and sheet resistance at a given measurement angle is consistent with a figure-of-merit equation often used for randomly-oriented AgNWs.

Integrating fluorescence computed tomography with optical sheet illumination for imaging of live single cells.

We present a new approach for three-dimensional (3D) live single-cell imaging with isotropic sub-micron spatial resolution using fluorescence computed tomography (fCT). A thin, highly inclined and laminated optical (HILO) sheet of light is used for fluorescence excitation in live single cells that are rotated around an axis perpendicular to the optical axis. During a full rotation, 400-500 two-dimensional (2D) projection images of the cell are acquired from multiple viewing perspectives by rapidly scanning the HILO light sheet along the optical axis. We report technical characteristics of the HILO approach and the results of a quantitative comparison with conventional epi fCT, demonstrating that HILO fCT offers significantly (about 17 times) reduced photobleaching and a two-fold improvement in 3D imaging contrast. We discuss potential application areas of the method for cell structure studies in live single cells with isotropic 3D spatial resolution.

Bifacial CdS/CdTe thin-film solar cells with copper nanowires as a transparent back contact.

A bifacial CdS/CdTe thin-film solar cell with a superstrate configuration was demonstrated by using copper nanowire (CuNW)/indium tin oxide (ITO) back contacts as a transparent and conductive electrode (TCE). CdS and CdTe were deposited by chemical bath deposition and close-spaced sublimation techniques, respectively. The CuNWs acted both as an acceptor dopant and TCE for the p-CdTe, improving the total cell efficiency compared to a copper-free back contact. CuNW/ITO back contacts with high optical transmittance (72.3% at 550 nm) and low sheet resistance (47.1 Ω/sq.) were obtained. The average cell efficiency of the bifacial CdS/CdTe thin-film cells with the optimized CuNW/ITO back contact was 10.0% (front-side illumination) and 0.55% (rear-side illumination). The quantum efficiencies under front-side and rear-side illumination were studied. The prepared bifacial cell can facilitate full usage of incoming sunlight (direct or diffused), enhancing the output power under cloudy conditions.

Extended field-of-view single-molecule imaging by highly inclined swept illumination

Single-molecule imaging inside cells is a valuable tool to study subcellular structures, gene expression, and the dynamics of biomolecules. Here, we present highly inclined swept tile illumination microscopy. By sweeping a thin highly inclined and laminated optical sheet (HILO) with confocal slit detection, our method provides a twofold thinner illumination and greater than fortyfold larger imaging area than conventional HILO microscopy, enabling 3D single-molecule imaging with a high signal-to-background ratio. We demonstrate single-molecule mRNA imaging with a few probes or a single probe in cultured cells and mouse brain tissues, and video-rate live-cell imaging.

Meters-long propagation of diffraction-free space-time light-sheets.

Space-time (ST) wave packets are pulsed beams in which the spatial frequencies and wavelengths are tightly correlated. Proper design of the functional form of these correlations results in diffraction-free and dispersion-free axial propagation; that is, propagation invariance in free space. To date, observed propagation distances of such ST wave packets has been on the order of a few centimeters. Here we synthesize an ST wave packet in the form of a pulsed optical sheet of transverse spatial width ∼200 μm and spectral bandwidth of ∼2 nm, and observe its diffraction-free propagation for approximately 6 meters. For such ST wave packets, we identify the spectral uncertainty - the precision in associating the spatial and temporal frequencies - as a critical parameter in determining the propagation-invariant distance. We present a design strategy and an experimental methodology that enables further increase in the diffraction-free length.

Evolution and decay of gravity wavefields in weak-rotating environments: a laboratory study

Gravity waves are prominent physical features that play a fundamental role in transport processes of stratified aquatic ecosystems. In a two-layer stratified basin, the equations of motion for the first vertical mode are equivalent to the linearised shallow water equations for a homogeneous fluid. We adopted this framework to examine the spatiotemporal structure of gravity wavefields weakly affected by the background rotation of a single-layer system of equivalent thickness $$h_{\ell }$$ , via laboratory experiments performed in a cylindrical basin mounted on a turntable. The wavefield was generated by the release of a diametral linear tilt of the air–water interface, $$\eta _{\ell }$$ , inducing a basin-scale perturbation that evolved in response to the horizontal pressure gradient and the rotation-induced acceleration. The basin-scale wave response was controlled by an initial perturbation parameter, $${\mathcal{A}}_{*} = \eta _{0}/h_{\ell }$$ , where $$\eta _{0}$$ was the initial displacement of the air–water interface, and by the strength of the background rotation controlled by the Burger number, $${\mathcal{S}}$$ . We set the experiments to explore a transitional regime from moderate- to weak-rotational environments, $$0.65\le {\mathcal{S}} \le 2$$ , for a wide range of initial perturbations, $$0.05\le {\mathcal{A}}_{*}\le 1.0$$ . The evolution of $$\eta _{\ell }$$ was registered over a diametral plane by recording a laser-induced optical fluorescence sheet and using a capacitive sensor located near the lateral boundary. The evolution of the gravity wavefields showed substantial variability as a function of the rotational regimes and the radial position. The results demonstrate that the strength of rotation and nonlinearities control the bulk decay rate of the basin-scale gravity waves. The ratio between the experimentally estimated damping timescale, $$T_{d}$$ , and the seiche period of the basin, $$T_{g}$$ , has a median value of $$T_{d}/T_{g}\approx 11$$ , a maximum value of $$T_{d}/T_{g}\approx 10^{3}$$ and a minimum value of $$T_{d}/T_{g}\approx 5$$ . The results of this study are significant for the understanding the dynamics of gravity waves in waterbodies weakly affected by Coriolis acceleration, such as mid- to small-size lakes.

Parametric analysis of thin multifunctional elastomeric optical sheets

Abstract Flexible optical sheets are thin large-area polymer light guide structures that can be used to create innovative passive light-harvesting and illumination systems. The optically transparent micro-patterned polymer sheet is designed to be draped over arbitrary surfaces or hung like a curtain. The light guidance sheet is fabricated by bonding two or more micro-patterned layers with different indices of optical refraction. By imprinting micro-optical elements on the constituent layers, it is possible to have portions of the optical sheet act as a light concentrator, near ‘lossless’ transmitter, or diffuser. However, the performance and efficiency of the flexible optical sheet depends on the overall curvature (κ) of the optical sheet and the relative orientation of incident light source. To illustrate this concept, the impact of key design parameters on the controlled guidance of light through a two-layer polydimethylsiloxane (PDMS) concentrator-transmitter-diffuser optical sheet is investigated using ray tracing simulation software. The analysis initially considers a flat (κ=0) PDMS optical sheet exposed to a collimated light source. The impact of sheet curvature (κ&gt;0) on both system efficiency and illumination uniformity is then briefly explored. Critical design guidelines for creating multifunctional monolithic optical sheets are also summarized.

Reverse-mode thermoresponsive light attenuators produced by optical anisotropic composites of nematic liquid crystals and reactive mesogens

Polymer network liquid crystals (PNLCs) whose optical transmittance state switches between transparence at low temperatures and haze at high temperatures were fabricated from mixtures of nematic liquid crystals (LCs) and reactive mesogens (RMs). This PNLC structure is simple but effective, namely, consists of micro-scale domains of orientation-ordered LCs and anisotropically polymerized RMs. The domains form through photopolymerization induced phase separation with inhomogeneous irradiation projected by laser speckling techniques. This irradiation method enables you to control the size and shape of phase-separation domains, and these PNLCs can be applied to novel thermoresponsive optical devices; optical isolators, thermometric sheets, and smart windows.

Direct growth of graphene on vertically standing glass by a metal-free chemical vapor deposition method

A new method to directly grow graphene on quartz glass substrate by atmospheric-pressure chemical vapor deposition (CVD) without using any catalyst was developed. The prime feature of this method is to build a vertical-glass model in the quartz tube to significantly increase the collision probability of the carbon precursors and reactive fragments between each other with the glass surface. The growth rate of high-quality graphene on glass remarkably increases compared with the conventional gas flow CVD technique. The optical transmittance and sheet resistance of the graphene glass can be readily adjusted by regulating growth time. When growth time is 35 min, the graphene glass presents an intriguing sheet resistance of about 1.48 kΩ sq−1 at a transmittance of 93.08% and exhibits an excellent hydrophobic performance. The method is simple and scalable, and might stimulate various potential applications of transparent and conductive graphene glass in practical fields.

Spectroscopic ellipsometry investigation of the optical properties of graphene oxide dip-coated on magnetron sputtered gold thin films

Despite intensive investigations on graphene oxide-gold nanocomposites, the interaction of graphene oxide sheets with magnetron sputtered gold thin films has not been studied yet. The optical constants of graphene oxide thin films dip-coated on magnetron sputtered gold thin films were determined by spectroscopic ellipsometry in the [300–1000] wavelength range. Moreover, the morphologic properties of the samples were investigated by SEM analysis. Graphene oxide absorbs mainly in the ultraviolet region, but when it is dip-coated on magnetron sputtered gold thin films, its optical constants show dramatic changes, becoming absorbing in the visible region, with a peak of the extinction coefficient at 3.1 eV. Using magnetron sputtered gold thin films as a substrate for graphene oxide thin films could therefore be the key to enhance graphene oxide optical sheets' properties for several technological applications, preserving their oxygen content and avoiding the reduction process.

Optimization of Highly Inclined Optical Sheet Illumination for Super-Resolution Microscopy

Optimization of Highly Inclined Optical Sheet Illumination for Super-Resolution Microscopy

Free-standing paper-like heat spreading films based on graphene oxide-aromatic molecule composites

Graphene has recently attracted great attention as a heat spreading material due to its unique thermal transfer property. Structural defects introduced into graphene unavoidably during graphene growth or processing are significantly affect its thermal transfer property. In this study, we choose four aromatic molecules (naphthalene, anthracene, tetracene and perylene) as “molecular patches” to heal structural defects in graphene, and free-standing paper-like heat spreading films based on graphene oxide (GO)-aromatic molecule composites have been fabricated via a synchronous reduction and assembly procedure, showing tunable optical transmittance and low sheet resistance. The Raman and X-ray diffraction characterizations of the as-prepared films indicate that the aromatic molecules have been adsorbed successfully by the GO and have partially restored the intrinsic quality of graphene. Preliminary studies on heat spreading materials using GO-aromatic molecule composite films demonstrate that the films can lead to obvious reduction in temperature of the hot source, indicating that these films are promising heat spreading materials for commercial portable electronics.

Diffraction-free space–time light sheets

Diffraction-free optical beams propagate freely without change in shape and scale. Monochromatic beams that avoid diffractive spreading require two-dimensional transverse profiles, and there are no corresponding solutions for profiles restricted to one transverse dimension. Here, we demonstrate that the temporal degree of freedom can be exploited to efficiently synthesize one-dimensional pulsed optical sheets that propagate self-similarly in free space. By introducing programmable conical (hyperbolic, parabolic, or elliptical) spectral correlations between the beam's spatio-temporal degrees of freedom, a continuum of families of axially invariant pulsed localized beams is generated. The spectral loci of such beams are the reduced-dimensionality trajectories at the intersection of the light-cone with spatio-temporal spectral planes. Far from being exceptional, self-similar axial propagation is a generic feature of fields whose spatial and temporal degrees of freedom are tightly correlated. These one-dimensional `space-time' beams can be useful in optical sheet microscopy, nonlinear spectroscopy, and non-contact measurements.