Increase In Optical Contrast Research Articles

Enhanced Optical Contrast and Switching in Near‐Infrared Electrochromic Devices by Optimizing Conjugated Polymer Oligo(Ethylene Glycol) Sidechain Content and Gel Electrolyte Composition

AbstractA detailed investigation addressing the effects of functionalizing conjugated polymers with oligo(ethylene glycol) (EGn) sidechains on the performance and polymer‐electrolyte compatibility of electrochromic devices (ECDs) is reported. The electrochemistry for a series of donor‐acceptor copolymers having near‐infrared (NIR)‐optical absorption, where the donor fragment is 3,4‐ethylenedioxythiophene (EDOT) or an EGn functionalized bithiophene (g2T) and the acceptor fragment is diketopyrrolopyrrole (DPP) functionalized with branched alkyl or EGn sidechains, is extensively probed. ECDs are next fabricated and it is found that EGn sidechain incorporation must be finely balanced to promote polymer‐electrolyte compatibility and provide efficient ion exchange. Proper electrolyte‐cation pairing and polymer structural tuning affords a 2x increase in optical contrast (from 12% to 24%) and >60x reduction in switching time (from 20 to 0.3 s). Atomic force microscopy (AFM)/grazing incidence wide‐angle X‐ray scattering (GIWAXS) characterization of the polymer film morphology/microstructure reveals that an over‐abundance of EGn sidechains generates large polymer crystallites, which can suppress ion exchange. Lastly, time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) indicates sidechain/electrolyte identity does not influence the electrolyte penetration depth into the films, and EGn sidechain inclusion increases electrolyte cation uptake. The material structural design insight and guidelines regarding the polymer‐electrolyte ion insertion/expulsion dynamics reported here should be of significant utility for developing next‐generation mixed ionic‐electronic conducting materials.

Implementing 0.1 nm B4C barriers in ultrashort period 1.0 nm W/Si multilayers for increased soft x-ray reflectance

Ultrashort period 1.0 nm W/Si multilayers have potential as dispersive Bragg reflectors in high-resolution x-ray fluorescence. However, formation of WSix leads to poor optical performance. To address this, we introduce ultrathin 0.1 nm B4C diffusion barriers in sputter-deposited 1.0 nm W/Si, inhibiting W–Si interaction. We demonstrate that the peak reflectance at a wavelength of 0.834 nm increased with a factor of 3.4 compared to W/Si. Diffuse scattering measurements reveal no change in interfacial roughness when applying B4C barriers compared to W/Si. X-ray reflectivity analysis shows a substantial increase in optical contrast between Si and W as well as sharper transitions between the layers. Chemical analysis suggests that the B4C barrier reduces formation of WSix through partial substitution of W-silicide bonds with W-carbide/boride bonds, leading to an increase in optical contrast. The resulting structure of W/Si with B4C barriers offers a compelling alternative to the more established W/B4C multilayer at the ultrashort scale due to its superior soft- and hard x-ray reflectance.

Novel approach for improving electrochromic and mechanical properties of NiO film: Experiment and molecular dynamics simulation

In this paper, we systematically studied the effect of substrate surface roughness on the electrochromic and mechanical properties of NiO films deposited on FTO conductive glass by magnetron sputtering. Results showed that increasing substrate surface roughness led to an increase in optical contrast of the film and decreased response time. The NiO film deposited on FTO (Ra 20 nm) had the largest optical contrast (54.7 % at 600 nm) and fastest response time (7.0 s and 1.7 s). Moreover, SEM, XPS, and EDS analyses revealed that the resultant increase in nanoporosity with increasing surface roughness was the main reason for this occurrence. The growth process of the NiO film was simulated by molecular dynamics, and the mechanism of the nanoporous structure was explained theoretically. The mechanical test showed that the composite hardness of FRa20 was 4.2 GPa, while the elastic modulus of the NiO film deposited on it was 74.9 GPa, which was better than all the other films. Thus, this study provides a novel and convenient approach for improving the electrochromic and mechanical properties of NiO films.

A study on the crystallization behavior of Sn-doped amorphous Ge2Sb2Te5 by ultraviolet laser radiation

In this paper, the influence of Sn doping (0%, 8% and 14%) on the crystallization of Ge2Sb2Te5 was studied with the aid of an ultraviolet laser. The XRD analyses revealed that the addition of Sn maintained the NaCl-type structure of Ge2Sb2Te5 after crystallization but expanded the lattice parameter due to the smaller atomic radii of Ge replaced by Sn. Raman peaks (123, 150 and 110cm−1) moved towards lower wavenumbers (118, 137 and 104cm−1), which can be explained by the remarkable decrease of the binding energy from Ge–Te to Sn–Te. A remarkable increase in optical contrast from 15% to 40% was observed in the Sn-doped Ge2Sb2Te5 film after crystallization with both the isothermal annealing and laser radiance. While the optical contrast changed little for a fixed volume fraction of Sn-doped sample with the variation of laser fluence which is attributed to the crystallization mechanism induced by laser under different fluences is the same.

Multimodal imaging of heterogeneous polymers at the nanoscale by AFM and scanning near-field ellipsometric microscopy

Scanning near field ellipsometric microscopy (SNEM) was used to simultaneously obtain optical images and tapping mode topography images of the microphase separated morphology of PS-b-P2VP block copolymer thin films. Optical images revealed a spatial resolution well below the diffraction limit. The SNEM setup used consisted of an AFM and an ellipsometer that were commercially available and that did not require major changes in their design to build the hybrid microscope. The observed increase in optical contrast for gold coated tips compared to silicon AFM probe tips was in qualitative agreement with the calculated increase in scattering amplitude according to the point dipole model for a gold AFM probe tip compared to a bare silicon AFM probe tip of the same size. The dielectric constant difference between the two blocks of the diblock copolymer was increased by selectively staining the P2VP block with iodine vapor. This resulted in an increase in the optical contrast between the PS and P2VP domains. Furthermore, the decrease in optical contrast as a function of increasing tip-sample separation was studied. It was observed that at 50nm tip sample separation the optical contrast was significantly reduced. The non-linear decay of the near-field amplitude signal as a function of the tip-sample separation calculated with the point dipole model supported this experimental result. The use of tapping mode in SNEM opens novel opportunities to study soft matter down to the macromolecular level.

Electrical, optical, and thermal properties of Sn-doped phase change material Ge2Sb2Te5

In this article, effect of Sn on the electrical, optical, and thermal properties of Ge2Sb2Te5 is studied. Ge2Sb2Te5, Ge1.55Sb2Te5Sn0.45, and Ge1.1Sb2Te5Sn0.9 alloys are prepared by melt quenching technique and their thin films are prepared by thermal evaporation on glass substrates. These materials are then characterized by differential scanning calorimetry, X-ray diffraction, optical method, and impedance measurements. Doping with Sn maintains the NaCl-type crystalline structure of Ge2Sb2Te5. Activation energy (Ea) for crystallization is calculated by Kissinger’s method. Ea decreases slightly from 2.56 eV for Ge2Sb2Te5 to 2.24 eV for Ge1.1Sb2Te5Sn0.9. The distinct change in extinction coefficient (k) of Ge2Sb2Te5 and Sn-doped amorphous films is found in the visible region. A large increase in optical contrast (C) is observed in the Sn-doped phase change materials. The phase change transition is studied using impedance measurements as a function of temperature. Impedance measurements show the appearance of nucleation centers in samples heated at temperatures below crystallization temperature (Tc) and above glass transition temperature (Tg).

Computer enhanced digital angiography.

A new computer image enhancement technique was employed on cardiac images of 10 dogs and 7 patients to demonstrate the feasibility of an on-line automatic delineation of the left ventricular endocardial silhouette with a peripheral venous injection of contrast material while simultaneously reducing the x-ray dosage. This technique employs a very fast analog-to-digital conversion system capable of digitizing on-line video frames. By storing and continuously updating the first 30 video frames and then subtracting each incoming frame from this memory, most of the background is eliminated leaving only the contrast filled ventricle. Using calibrated densitometric measurements, we found that iodine concentrations in the human left ventricle following venous injection of 40 ml Renografin-76 (25 ml/s), peaked at 4.3 +/- 0.3 mg/ml (mean +/- SD) compared to 14.8 +/- 0.8 mg/ml following direct injection of 40 ml at 13 ml/s (p less than 0.001). The computer enhanced venous-injected images had an optical contrast 14 times greater than that of the unenhanced direct left ventriculogram. This increase in optical contrast provided unambiguous subjective definition of the endocardial borders. This technique is applicable to both central and peripheral contrast injection whereby high quality images can be obtained at approximately 98% reduction in radiation (5 mA, 65-85 kV), allowing performance of serial studies.

Behavior of skew-bubbles in orthoferrites

Optical and magnetic properties of orthoferrite platelets with the optical axis normal to the surface have been investigated. A simple calculation has been performed indicating that a considerable increase of optical contrast between domains magnetized in opposite directions can be expected in such platelets when compared to the contrast obtainable in platelets with the crystalline c axis perpendicular to the surface. A numerical calculation has also beem performed for the stability range of a skew-bubble occuring in an orthoferrite platelet in which the magnetization is not perpendicular to the surface. It was found that this range is smaller and shifted to the lower bias fields than that for a normal bubble, amd that the ellipticity of a skew-bubble is larger. Experiments confirmed the theoretical prediction. On the basis of experimental results it was concluded that the shape of the skew-bubble wall is rather complex in thin platelet. This hypothesis has been confirmed to a certain degree by experiments performed on platelets with different thicknesses.