Low Optical Reflectivity Research Articles

Experimental study of the organic light emitting diode with a p-type silicon anode

We have fabricated and studied an organic light emitting diode (OLED) with a p-type silicon anode and a SiO 2 buffer layer between the anode and the organic layers which emits light from a semitransparent top Yb/Au cathode. The luminance of the OLED is up to 5600 cd/m 2 at 17 V and 1800 mA/cm 2, the current efficiency is 0.31 cd/A. Both its luminance and current efficiency are much higher than those of the OLEDs with silicon as the anodes reported previously. The enhancement of the luminance and efficiency can be attributed to an improved balance between the hole- and electron-injection through two efficient ways: 1) restraining the hole-injection by inserting an ultra-thin SiO 2 buffer layer between the Si anode and the organic layers; and 2) enhancing the electron-injection by using a low work function, low optical reflectance and absorption semitransparent Yb/Au cathode.

Optical Coherence Tomography Findings in Valsalva Retinopathy

To demonstrate the plane of premacular hemorrhage in Valsalva retinopathy with optical coherence tomography Observational case report Two young men with Valsalva stress-related premacular hemorrhage were evaluated by OCT scans, taken just above the level of sedimented blood. In both cases, OCT demonstrated two distinct membranes: a highly reflective band immediately above the premacular hemorrhage, corresponding to the internal limiting membrane, and an overlying patchy membrane with low optical reflectivity consistent with posterior hyaloid. OCT supported the clinical impression that the plane of premacular hemorrhage in Valsalva retinopathy is probably under ILM. Larger case studies are required to confirm this finding.

Interfacial chemistry of Sm with Alq 3 and its implication to organic light-emitting devices

Interfacial chemistry of samarium (Sm) with tris-(8-hydroxyquinoline) aluminum (Alq 3) has been investigated. Photoelectron analysis revealed strong interactions at the Sm–Alq 3 interface and limited Sm diffusion into Alq 3. The lowest unoccupied molecular orbital of Alq 3 was found to be 0.28 eV below the Fermi level of Sm at the Sm–Alq 3 contact, implying lacking a barrier to electron-injection from the Sm to Alq 3. Replacing Sm for MgAg as a cathode in organic electroluminescent devices considerably improved current–voltage characteristics, while the device efficiency was found to decrease by 40%. The reduction in efficiency is attributed to low optical reflectance at the Sm–Alq 3 interface.

Energy band bowing parameter in AlxGa1−xN alloys

Molecular-beam epitaxy grown AlxGa1−xN alloys covering the entire range of alloy compositions, 0⩽x⩽1, have been used to determine the alloy band gap dependence on its composition. The Al chemical composition was deduced from secondary ion mass spectroscopy and Rutherford backscattering. The composition was also inferred from x-ray diffraction. The band gap of the alloy was extracted from low temperature optical reflectance measurements which are relatively more accurate than photoluminescence. Fitting of the band gap data resulted in a bowing parameter of b=1.0 eV over the entire composition range. The improved accuracy of the composition and band gap determination and the largest range of the Al composition over which our study has been conducted increase our confidence in this bowing parameter.

AHubble Space TelescopeSnapshot Survey of Proto–Planetary Nebula Candidates: Two Types of Axisymmetric Reflection Nebulosities

We report the results from an optical imaging survey of proto-planetary nebula candidates using the Hubble Space Telescope (HST). The goals of the survey were to image low surface brightness optical reflection nebulosities around proto-planetary nebulae and to investigate the distribution of the circumstellar dust, which scatters the star light from the central post-asymptotic giant branch star and creates the optical reflection nebulosities. We exploited the high resolving power and wide dynamic range of HST and detected nebulosities in 21 of 27 sources. The reduced and deconvolved images are presented along with photometric and geometric measurements. All detected reflection nebulosities show elongation, and the nebula morphology bifurcates depending on the degree of the central star obscuration. The star-obvious low-level-elongated (SOLE) nebulae show a bright central star embedded in a faint, extended nebulosity, whereas the dust-prominent longitudinally extended (DUPLEX) nebulae have remarkable bipolar structure with a completely or partially obscured central star. The intrinsic axisymmetry of these proto-planetary nebula reflection nebulosities demonstrates that the axisymmetry frequently found in planetary nebulae predates the proto-planetary nebula phase, confirming previous independent results. We suggest that axisymmetry in proto-planetary nebulae is created by an equatorially enhanced superwind at the end of the asymptotic giant branch phase. We discuss that the apparent morphological dichotomy is caused by a difference in the optical thickness of the circumstellar dust/gas shell with a differing equator-to-pole density contrast. Moreover, we show that SOLE and DUPLEX nebulae are physically distinct types of proto-planetary nebulae, with a suggestion that higher mass progenitor AGB stars are more likely to become DUPLEX proto-planetary nebulae.

Chemistry and kinetics of chemical vapor infiltration of pyrocarbon – VI. Mechanical and structural properties of infiltrated carbon fiber felt

The mechanical and structural properties of carbon fiber felts infiltrated with pyrolytic carbon at a temperature of 1100°C and pressures of 20 and 30 kPa using methane and a methane/hydrogen-mixture were investigated. Flexural strength, modulus, strain-to-failure, pore size distribution, crystallite parameters, and microstructural properties, using scanning electron microscopy and polarized-light microscopy, have been determined and analyzed, respectively. These properties were correlated with deposition chemistry and kinetics. The individual fibers are coated with a smooth laminar carbon layer showing low optical reflectivity, followed by another smooth laminar carbon layer showing medium reflectivity, and a rough laminar carbon sheath showing high reflectivity. These changes of carbon structure with progressive infiltration are discussed on the basis of a parameter [ A S/ V R] describing the ratio of internal surface area A S and pore volume V R of the felt. This parameter continuously increases with progressive infiltration whereby the deposition chemistry is changed from polynuclear aromatic to mononuclear aromatic and finally to light, linear hydrocarbons as the major carbon forming species. An autocatalytic mechanism is proposed to explain sharp transitions between the various carbon structures.

Effect of Aging on Polymerization of a Low Refractive Index Epoxy, Daikin Optodyne UV-1100

Thermal analysis for a UV light-curable epoxy adhesive material recently commercialized by Daikin for assembly of optical fiber devices with a low optical reflection was performed. This epoxy was used in the assembly of LiNbO3 waveguide devices; previous reliability tests measuring mechanical and optical characteristics confirm the stability of this epoxy for the fiber connection. However, due to an intrinsic characteristic of the material, polymerization by a curing process on the device assembly line was incomplete, and additional polymerization was expected to occur after assembly. Here, the duration necessary for complete polymerization of this adhesive material is estimated experimentally to be 1.8 years at 80°C. Further, the activation energy for such additional polymerization is derived to be 0.38 eV (~0.4 eV, considering measurement errors).

Optical detection of leaky-Rayleigh waves at air–solid interfaces

Due to the difficulties associated with ultrasonic generation and detection in air in the megahertz region, air-coupled nondestructive evaluation has only recently been explored. In this work, a shear transducer is mounted directly over the edge of a solid specimen so that it can generate a bulk mode in the interior of the solid as well as a Rayleigh wave along the surface. A recently developed optical heterodyne interferometer proved to be sensitive to the leaky-Rayleigh wave in air more than a centimeter away from the solid surface. Results of velocity and attenuation measurements of leaky-Rayleigh waves for several solids will be presented. The technique can also be applied to plates to measure leaky-Lamb velocity and attenuation in air. This method can be used for low optical reflectivity solid surfaces: Thus it can be extended for noncontact nondestructive evaluation applications.

Leaky-Rayleigh wave detection at air–solid interfaces by optical heterodyne interferometry

Recent developments have proven optical heterodyne interferometry to be a sensitive detector for ultrasonic amplitude and phase measurements in transparent materials. In this letter it is shown that this optical technique is sensitive enough to detect leaky-Rayleigh as well as leaky-Lamb waves in air reradiated from solids in the megaHertz region. Probing the leaky wave field at several positions parallel to the solid surface can yield the Rayleigh wave velocity of both transparent and opaque solids. This method can be used for low optical reflectivity solid surfaces: thus it can be extended for noncontact nondestructive evaluation applications.

Dual beam spectrometer for optical studies of spread monolayers at the air-water interface

An optical spectrometer for the study of low level optical absorption and reflection of spread monolayers at the air-water interface is described. This spectrometer is suitable for measurements at wavelengths from ∼350 to 800 nm and has a precision of ∼2×10−5 in terms of effective optical density. It employs a dual beam design utilizing fiber optic bundles to guide light and a multichannel photodiode array detection system. Instrumental control and data gathering are designed within Labwindows software. Representative spectral absorption data from chlorophyll a degradation kinetics are presented by way of illustration. Comparison of chlorophyll a reflection and absorption is also given.

High contrast, submilliwatt power InGaAs/GaAs strained-layer multiple-quantum-well asymmetric reflection modulator

A high contrast, low power optical reflection modulator with an InGaAs/GaAs strained-layer multiple quantum well (MQW) nonlinear spacer is demonstrated. Taking advantage of large absorptive and dispersive nonlinearities near the exciton peak, on/off contrast ratios exceeding 29 dB are achieved with submilliwatt pump powers at room temperature.

Internal stress in ion beam sputtered molybdenum films

Stress in molybdenum films deposited by ion beam sputtering has been studied as a function of deposition parameters, such as accelerating voltage, incident angle, and chamber pressure. It has been found that the physical properties of deposited molybdenum films controlled primarily by the ion beam accelerating voltage and substrate orientation with respect to the ion beam. For films deposited at near normal incidence, measured stresses are highly compressive (2–5 GPa) and increase almost linearly with the accelerating voltage (600–1500 V). Under these conditions, deposited molybdenum films exhibit low resistivity and high optical reflectance. As the substrates are rotated to near grazing incidence, measured stress is either negligible or slightly tensile and are almost independent of accelerating voltage. The extremely high resistivity and low reflectance measured indicates the poor quality of the deposited film at grazing incidence. No significant effect was observed when the chamber pressure was varied between 7×10−5 and 5×10−4 Torr. The observations are interpreted by ‘‘structure zone model’’ and ‘‘atomic peening mechanism’’ (forward sputtering and recoil damage to the depositing films) previously proposed for films prepared by conventional sputtering and evaporation.

Direct Observation of the Phase Separated Microstructure of a Sodium Borosilicate Glass and Its Development During Heat Treatment

By treating Corning code 7740 sodium borosilicate glass (composition by weight 80.5% SiO2, 13% B2O3, 3.8% Na2O, 2.2% Al2O3, 0.4% K2O) with a process consisting of heat treatment within the immiscibility region followed by a chemical etch, it is possible to produce a thin surface layer on the glass giving a low total optical reflectivity over the entire visual spectrum. In the course of a full investigation into this phenomenon, an attempt has been made to fully characterize the nature and development of the two-phase structure produced by the heat treatment.Coupons of glass 3 x 3 x 0.125 inches, as received from Corning Glass Works, were heated for times ranging between 1-1/2 and 1000 hours at 600°C (well below the phase transition temperature, about 650°C for this glass). It is known that a three-hour heat treatment maximizes the antireflective property. Electron microscope specimens were conventionally prepared by mechanical grinding and ion thinning. However, after ion thinning, specimens were chemically etched by floating them on a drop of 0.1 wt% NH4.HF in 1.6N HNO3 solution, for typically 2 to 5 minutes. Specimens were rinsed by repeated flushing with distilled water, dried, and then carbon coated to prevent charging effects.

The reflectance of dendritic-tungsten surfaces

The relatively low total optical reflectance measured from the surface of dendritic tungsten is quantitatively explained in terms of multiple reflections from the surface structure. A geometrical optical model is found to adequately describe the multiple reflections from dendrites which have an average spacing of about 5 μm. Coefficients representing the fraction of light reflected a given number of times are determined by analysis of the total reflectance of the dendritic surface on which an antireflective coating has been formed by anodization. At most wavelengths, second-order reflection (or light twice reflected) is found to dominate the reflectance of the dendritic surface for angles of incident light up to about 60° from normal, beyond which the first-order reflection becomes dominant. Based on the model, the reflectance of a geometrically characterized dendritic surface can be predicted for any type and thickness of antireflective coating.

Responses of the a3 component of cytochrome c oxidase to substrate and ligand addition

We have previously described a transient high spin ferric heme species in cytochrome c oxidase (EC 1.9.3.1) which represents a 3+ 3 (Beinert, H. and Shaw, R.W. (1977) Biochim. Biophys. Acta 462, 121–130), and can be detected and quantitatively determined by EPR. We have now used our ability to generate this species to study reactions of a 3+ 3 with substrates and ligands and also responses to pH changes. This was accomplished by multiple rapid mixing and freezing techniques in conjunction with low temperature EPR and optical reflectance spectroscopies. The substrates used were O 2 and ferrocytochrome c and the ligands cyanide, sulfide, azide and carbon monoxide. Contrary to the oxidized, resting form of the enzyme, the transient high spin species of a 3+ 3 reacts within <10 ms stoichiometrically with cyanide and sulfide and at a slower rate with azide. The transient a 3+ 3 species responds to O 2 and CO by changes in signal size or shape, although no oxidoreduction is involved, indicating that a 3+ 3 registers the presence of these gases. The high spin signal of the transient species is readily abolished by ferrocytochrome c or on raising the pH. Decreasing the pH induces a shift from the rhombic towards the axial component of the signal. Since the responses to CO and pH are analogous for the rhombic transient species to those observed with the rhombic high spin ferric heme species produced on partial reduction, it is suggested that the rhombic signals represent a 3+ 3 in either case. In all these experiments, in which EPR detectable a 3+ 3 was observed in large yield, no extra signals for copper or correspondingly increased intensity in the copper signal at g = 2 were seen. The relationship is discussed of the obviously reactive transient species of a 3+ 3 to other ‘activated’ species that have been reported and to the oxidized resting form of the enzyme, which is known to react only slowly with ligands and to respond sluggishly to substrate.

Reflectance and structure of evaporated chromium and molybdenum films

Chromium and molybdenum films deposited in a high vacuum at room temperature are shown to have anomalously low optical reflectance throughout the 0.2–2.5-μm wavelength range. Deposition at about 700°C for chromium and 1000°C for molybdenum, or postdeposition annealing, gives films with bulk reflectance. X-ray diffraction and transmission electron microscopy show the films deposited at room temperature to be very fine grained (80–100-Å grain size). Electrical resistivity of the fine grained films is high (3–5 times bulk). High-temperature deposition or annealing gives larger grains (≳400 Å) and lower resistivity. A simple model accounts for the resistivity behavior.

Abstract: Thermal-spray coatings for computer components

The technology of plasma flame spraying is being used extensively by IBM to combat wear and prolong the life of computer components. The wear environments which cause the most severe problems are abrasive in nature—card stock, paper documents, and magnetic tape. Currently, IBM is using plasma‐deposited tungsten carbide, chromium oxide, aluminum oxide, and alumina/titania coatings on over 50 component parts which must function in these severe wear areas. Traditionally, wear resistance has been the prime application area for flame‐spray‐deposited coatings; however, during the past few years many other applications have been developed which should be cited.A plasms may be formed from a diatomic gas by first dissociating the molecules into atoms and then ionizing the atoms. To accomplish the dissociation, energy must be put into the system. The energy is produced by a constant high‐potential discharge across the electrodes in a confined space under high pressure. The process is accomplished by a large tempera...