Rapid evolution of the Photosystem II electronic structure during water splitting

Photosynthetic water oxidation is a fundamental process that sustains the biosphere. A Mn4Ca cluster embedded in the photosystem II protein environment is responsible for the production of atmospheric oxygen. Here, time-resolved x-ray emission spectroscopy (XES) was used to observe the process of oxygen formation in real time. These experiments reveal that the oxygen evolution step, initiated by three sequential laser flashes, is accompanied by rapid (within 50 μs) changes to the Mn Kβ XES spectrum. However, no oxidation of the Mn4Ca core above the all MnIV state was detected to precede O-O bond formation, and the observed changes were therefore assigned to O-O bond formation dynamics. We propose that O-O bond formation occurs prior to the transfer of the final (4th) electron from the Mn4Ca cluster to the oxidized tyrosine YZ residue. This model resolves the kinetic limitations associated with O-O bond formation, and suggests an evolutionary adaptation to avoid releasing of harmful peroxide species.

An automated approach to detecting signals in electroantennogram data

Coupled gas chromatography/electroantennographic detection (GC-EAD) is a widely used method for identifying insect olfactory stimulants present in mixtures of volatiles, and it can greatly accelerate the identification of insect semiochemicals. In GC-EAD, voltage changes across an insect's antenna are measured while the antenna is exposed to compounds eluting from a gas chromatograph. The antenna thus serves as a selective GC detector whose output can be compared to that of a "general" GC detector, commonly a flame ionization detector. Appropriate interpretation of GC-EAD results requires that olfaction-related voltage changes in the antenna be distinguishable from background noise that arises inevitably from antennal preparations and the GC-EAD-associated hardware. In this paper, we describe and compare mathematical algorithms for discriminating olfaction-generated signals in an EAD trace from background noise. The algorithms amplify signals by recognizing their characteristic shape and wavelength while suppressing unstructured noise. We have found these algorithms to be both powerful and highly discriminatory even when applied to noisy traces where the signals would be difficult to discriminate by eye. This new methodology removes operator bias as a factor in signal identification, can improve realized sensitivity of the EAD system, and reduces the number of runs required to confirm the identity of an olfactory stimulant.

Volatiles associated with preferred and nonpreferred hosts of the Nantucket pine tip moth, Rhyacionia frustrana

Ovipositing female Nantucket pine tip moth, Rhyacionia frustrana, prefer loblolly pine, Pinus taeda L., to slash pine, Pinus elliottii Engelm, except during the first spring following planting of seedlings. Host discrimination by R. frustrana increases as seedlings develop, suggesting that changes in the chemical composition of seedlings may mediate the moth's host preferences. Volatile compounds from slash and loblolly pine seedlings were collected using solid-phase microextraction (SPME) during the first year following planting. Four collection periods coincided with adult emergence and oviposition during each of four annual generations of R. frustrana in the Georgia Coastal Plain. Infestation of slash pine peaked during the second tip moth generation and was similar to the loblolly pine infestation level. By the fourth tip moth generation, slash pine infestation levels had declined and diverged considerably from those of loblolly pine. Significant differences in relative quantities of beta-pinene, alpha-phellandrene, limonene, beta-phellandrene, bornyl acetate, beta-caryophyllene, and an unidentified sesquiterpene occurred between slash and loblolly pine during the fourth generation. However, no strong correlation was observed between any individual compound and host damage that could readily explain the temporal changes in R. frustrana host preference. Gas chromatographic-electroantennographic detection (GC-EAD) analyses of standards identified 19 different seedling-associated compounds that elicited antennal responses from R. frustrana females, indicating that a blend of terpenoids may mediate host discrimination.

High-rate automated deposition system for the manufacture of complex multilayer coatings

A previously described automated thin-film deposition system based on rf-magnetron sputtering could deposit quite complex optical multilayer systems with good precision and with no one in attendance [Sullivan and Dobrowolski, Appl. Opt. 32, 2351-2360 (1993)]. However, the deposition rate was slow, and the uniform area on the substrate was limited. We describe an ac-magnetron sputtering process in which the same deposition accuracy has been combined with significantly better film uniformity and a fivefold or sevenfold increase in the deposition rate. This makes the equipment of commercial interest. Experimental results are presented for several difficult coating problems.

Influence of small inhomogeneities on the spectral characteristics of single thin films

It is well known that the spectral transmittance and reflectance of a thin film can be influenced by even small inhomogeneities or variations in its complex refractive-index profile. Formulas are derived that describe the theoretical variation of the spectral characteristics for small changes in the refractive index and the extinction coefficient of a homogeneous thin film. These formulas, accurate to the first order in the change in the complex refractive index, are compared with exact calculations for a number of different types of inhomogeneities. It is shown that specific qualitative features in the refractive-index profile of a nearly homogeneous thin film frequently can be determined from an examination of the change in the spectral transmittance and reflectance at normal incidence.

Broadband high-reflection multilayer coatings at oblique angles of incidence

The angular properties of various wideband high reflectors are investigated. The theory is developed for the design of high reflectors based on contiguous quarter-wave stacks for use at one oblique angle or for a range of angles of incidence. Numerical results are presented for several high reflectors designed to have a high reflectance in the 0.4-0.8-mum spectral region for use at 50 degrees and with angles of incidence ranging between 0 degrees and 50 degrees . A random error perturbation analysis shows that such layer systems can be produced experimentally.

Implementation of a numerical needle method for thin-film design

A variant of the powerful thin-film needle design technique, which was first described by Tikhonravov and his co-workers, is described. In this method thin layers are introduced at optimum positions within the refractive-index profile of a given multilayer system. In the original method the optimum locations for the layer insertions are calculated analytically, whereas in this variant of the method they are determined numerically. This approach, although somewhat slower, is very flexible. With the numerical needle method it is easy to define a merit function that consists of quite complex spectral quantities, such as Commission Internationale de l'Eclairage color coordinates or custom spectral properties that are defined at run time. In the program described, three different absorbing or nonabsorbing materials can be used for the needle layers and one or more needles can be inserted into the system at any given time. Multilayer solutions can also be sought in which the system is defined in terms of repeating groups of layers. It is also possible to calculate automatically a series of solutions to a particular problem with increasing overall thicknesses or to perform simultaneous calculations on several different systems. Examples are given that illustrate these various points.

Survey of Ti-, B-, and Y-based soft x-ray-extreme ultraviolet multilayer mirrors for the 2- to 12-nm wavelength region

We have performed an experimental investigation of Ti-, B(4)C-, B-, and Y-based multilayer mirrors for the soft x-ray¿extreme ultraviolet (XUV) wavelength region between 2.0 and 12.0 nm. Eleven different material pairs were studied: Ti/Ni, Ti/Co, Ti/Cu, Ti/W, B(4)C/Pd, B/Mo, Y/Pd, Y/Ag, Y/Mo, Y/Nb, and Y/C. The multilayers were sputter deposited and were characterized with a number of techniques, including low-angle x-ray diffraction and normal incidence XUV reflectometry. Among the Ti-based multilayers the best results were obtained with Ti/W, with peak reflectances up to 5.2% at 2.79 nm at 61° from normal incidence. The B(4)C/Pd and B/Mo multilayer mirrors had near-normal incidence (5°) peak reflectances of 11.5% at 8.46 nm and 9.4% at 6.67 nm, respectively, whereas a Y/Mo multilayer mirror had a maximum peak reflectance of 25.6% at 11.30 nm at the same angle. The factors limiting the peak reflectance of these different multilayer mirrors are discussed.

Universal antireflection coatings for substrates for the visible spectral region

It is possible to design normal-incidence antireflection coatings that reduce the reflectance of any substrate with a refractive index that lies in the range of 1.48 to 1.75. The performance of such coatings depends on the width of the spectral region over which the reflectance is to be suppressed, on the coating materials used for their construction, and on the overall optical thickness of the layer system. For example, the calculated average spectral reflectance of a set of six different substrates with refractive indices 1.48, 1.55, 1.60, 1.65, 1.70, and 1.75, when coated with a 0.56-μm-thick, eight-layer antireflection coating designed for the 0.40-0.80-μm spectral region, was 0.34%. This is higher than the average reflectance that is attainable with a conventional antireflection coating of similar optical thicknesses designed for a particular refractive index. However, it is an acceptable value for most applications. With the universal type of antireflection coating described, it is thus possible to coat a number of different refractive-index substrates in one deposition run, and this can result in considerable cost and time savings.

Optimal single-band normal-incidence antireflection coatings

Mathematical and computational evidence that strongly suggests that optimal solutions exist to single-band, normal-incidence antireflection coating problems is presented. It is shown that efficient synthesis and refinement techniques can quickly and accurately find such solutions. Several visible and infrared antireflection coating examples are presented to support this claim. Graphs that show the expected optimal performance for different representative substrates, refractive-index ratios, wavelength ranges, and overall optical thickness combinations are given. Typical designs exhibit a pronounced semiperiodic clustering of layers, which has also been observed in the past. Explanations of this phenomenon are proposed.

Metal/dielectric transmission interference filters with low reflectance. 2. Experimental results

The successful fabrication of metal/dielectric multilayer filters requires not only accurate control of the individual layer thicknesses, but also a good knowledge of the optical constants of the materials used in the filters. In the case of metal films, it is also essential to know whether any transition layers are formed at the interfaces and, if so, how their thicknesses and optical constants depend on the deposition conditions. An automatic, real-time process control, magnetron sputtering deposition system was modified to permit the manufacture of metal/dielectric filters using optical monitoring techniques. To illustrate the performance of this system, two bandpass filters, a short-wavelength pass filter, and a neutral density filter were produced, all having a low reflectance for light incident on one side. The metal layers used in these filters consisted of either Ni or Ag. TheAg films could be protected from the O(2) plasma using thin Ni or Si films. Good agreement was obtained between the calculated and measured spectral transmittance and reflectance curves.

In situ reflectance measurements of soft-x-ray/extreme-ultraviolet Mo/Y multilayer mirrors

With a new ultrahigh-vacuum deposition/ref lectometer system, Mo/Y multilayer mirrors were deposited by dc-magnetron sputtering and characterized in situ with synchrotron radiation. The Mo/Y multilayer mirrors, measured before exposure to air, had near-normal-incidence reflectances as high as 46% at wavelengths near 11.4 nm. After several days of exposure these samples typically had a relative reflectance loss of ~10% as a result of oxidation of the top Mo layer. The best Mo/Y multilayers were fabricated with base pressures below the low 10(-9) Torr range and after a bakeout to reduce water vapor in the chamber.

Mo/Y multilayer mirrors for the 8-12-nm wavelength region

Mo/Y multilayer mirrors were deposited by dc magnetron sputtering under different deposition conditions. They were characterized by reflectance measurements at normal and grazing angles of incidence, by transmission electron microscopy, and by Auger depth profiling. Normal-incidence peak reflectances of 34% and 22% were measured at wavelengths of 11.5 and 8.1 nm, respectively. Interface roughness and contamination of the layers during deposition limit the peak reflectance of these Mo/Y mirrors.

Mo/Y multilayer mirrors for the 8-12-nm wavelength region

Mo/Y multilayer mirrors were deposited by dc magnetron sputtering under different deposition conditions. They were characterized by reflectance measurements at normal and grazing angles of incidence, by transmission electron microscopy, and by Auger depth profiling. Normal-incidence peak reflectances of 34% and 22% were measured at wavelengths of 11.5 and 8.1 nm, respectively. Interface roughness and contamination of the layers during deposition limit the peak reflectance of these Mo/Y mirrors.

Extreme-ultraviolet Mo/Si multilayer mirrors deposited by radio-frequency-magnetron sputtering

Mo/Si multilayer mirrors with a high reflectance at normal incidence in the 130-135-Å spectral region have been deposited by rf magnetron sputtering. A new and quick technique was used to calibrate the deposition rates. Characterization by transmission electron microscopy (TEM) and grazing-incidence x-ray diffraction (XRD) indicated good thickness control of the deposition process and low interface roughness. However, the TEM and, indirectly, the XRD reflectance measurements, indicated that the interfaces are asymmetric. A brief review discussing the origin of the modulation of the Bragg peak intensities in the XRD reflectance is given. An analytical formula was derived for periodic multilayers that describes the effect of asymmetric interfaces on the amplitude of the Bragg peak modulation. Theoretically, in XRD reflectance measurements, any asymmetry in the interdiffusion of the Mo-Si interfaces results in a decrease of the usual amplitude modulation of the Bragg peaks. Extreme-ultraviolet (XUV) reflectance measurements were also made with synchrotron radiation on a new high-resolution reflectometer. The near-normal-incidence peak reflectances measured at λ = 134 Å were ~ 59% for the best multilayer mirrors. Good fits to both XRD and XUV reflectance measurements have been obtained with a model that allows for interface asymmetry.

Optical coatings deposited by reactive ion plating

The effect of different reactive ion-plating process parameters on the transmittance and the reflectance of single layers of HfO(2), Ta(2)O(5), and SiO(2) are investigated. The optical constants obtained for these three as-deposited materials are presented. Laser-damage threshold trends are examined on single- and double-layer coatings at 1064 nm and on high-reflectance coatings for 248 nm. Single- and double-cavity filters are constructed for the UV (< 1-nm bandwidth) and near-infrared (50-nm bandwidth) regions, respectively. After the filters are postannealed in air at 375 °C for several hours, a shift in the peak wavelengths is observed along with a substantial increase in the peak transmittance. As expected, no significant wavelength shifts result from changes in the humidity of the ambient atmosphere.

Deposition error compensation for optical multilayer coatings. II. Experimental results-sputtering system

A fully automated magnetron-sputtering system for the deposition of complicated optical multilayer structures is described. The process control includes the real-time determination of the deposited layer thicknesses and adjustment of the remaining layer thicknesses to reoptimize the final performance of the multilayer system. With this deposition system it should be possible to produce almost any all-dielectric filter that can be designed, subject only to limitations imposed by time, cost, and mechanical stability of the coatings. To demonstrate the performance of the deposition system, five complex multilayer systems were fabricated. The theoretical and measured spectral transmittance curves of these multilayer systems closely agree with one another over broad spectral regions. The equipment is capable of unattended operation over periods of 24 h or more.

Optical interference, contrast-enhanced electroluminescent device

A contrast enhancement for electroluminescent displays that uses optical interference is described. The reflection of ambient light from a display can be greatly reduced through the addition of thin-film optical components. In particular, a black layer system consisting of a dielectric layer and a thin absorbing layer is able to reduce the luminous reflectance from 75% to 3% when deposited next to the aluminum counterelectrode. Furthermore, with the addition of several other thin-film optical layers, the luminous reflectance can be decreased to 0.4% while also decreasing the sensitivity of the reflectance to the thicknesses of the electro-optic layers. Theoretical examples of different layer systems with and without optical components are provided. A prototype display that incorporates a black layer system was built, and a luminous reflectance of 3% was achieved.

Deposition error compensation for optical multilayer coatings. I. Theoretical description

The manufacture of complicated optical coatings consisting of many layers of different thicknesses can be a challenge, especially if the deposition technique does not produce dense layers. Deposition errors in a layer can affect not only the desired performance of a multilayer, but can also lead to a complete breakdown of the monitoring and control of subsequent layers. The best chance to achieve the desired optical performance of a multilayer involves deposition error compensation. In this process, the construction parameters of a completed layer are evaluated to determine if any deposition errors have occurred and then the remaining layers of the multilayer system are reoptimized to compensate for any errors made. This paper describes a versatile deposition error compensation program developed at the National Research Council of Canada for the simulation and real-time control of the manufacture of multilayers composed of dielectric or absorbing films. To model porous layers, an effective medium theory approach is used to relate the optical constants of the layer in vacuum and air to the microstructure of the layer. In the simulation mode, random errors are applied to the thickness and porosity of the layers and measurement errors are also included. The best monitoring strategy for the manufacture of a given multilayer is established on the basis of statistical information obtained from a number of these simulations. In this paper the results of calculations on the effectiveness of various monitoring strategies are presented for a sharp edge filter produced by three different physical vapor deposition methods. An extensive list of references to previous papers dealing with sources of errors during deposition is also provided.

Practical magnetron sputtering system for the deposition of optical multilayer coatings

A magnetron sputtering system is described in which, at any one time, as many as four different 15-cm x 46-cm rectangular planar magnetron targets can be mounted vertically in the deposition chamber. These can be attached to either dc or rf power supplies for direct or reactive deposition of metal, metal oxide, or nitride films. Typical target materials include Ag, Al, C, Mo, Nb, Ni, Si, W, and Zr. Good uniformity can be obtained on stationary substrates, although better results are possible with oscillating substrates. The refractive indices are given for several useful oxide materials. The materials and thicknesses of the individual layers that comprise an optical multilayer system are entered into a computer that subsequently controls the deposition parameters, the substrate motion, and the deposition time. After a relatively simple calibration process, coatings that consist of between 20 and 60 layers can be produced to within an accuracy of 1% or 2%. A wideband optical monitor is available for checking the performance of the multilayer system during its deposition. Several examples of multilayer coatings that were prepared on this equipment are given.

High performance optical wavelength multiplexer-demultiplexer

The principle of an optical wavelength multiplexer-demultiplexer is described in which the signals undergo repeated reflections from special filter elements that can be designed for a wide range of cross-talk ratios. The insertion losses of these units can be quite small and they can be implemented to provide simultaneous multichannel two-way transmission. In a preliminary investigation of an experimental prototype an insertion loss of 0.5 dB and a cross talk of -35 dB were demonstrated. The multiplexer-demultiplexer is expected to have a long life and high reliability.

Magnetic resonance imaging of traumatized ligaments of the ankle

The clinical examination of acute soft tissue injuries of the ankle does not necessarily help to delineate the extent of injury. Ankle stress radiographs and arthrography have been applied for a more accurate assessment of the actual degree of ligamentous damage. However, these studies do not define the level of the ligament tear of the relationship of torn ligament ends to one another. This information would seem to be valuable in deciding whether a conservative or surgical approach would be advisable. The following study evaluated the possible role of magnetic resonance imaging in assessment of these injuries. The ability to assess ankle ligaments was first undertaken. Once this was successfully performed, magnetic resonance imaging was used to assess the degree of ligament damage in 15 patients. Magnetic resonance imaging proved to be comparable to arthrography. It also provided additional valuable information.

Extreme-ultraviolet optical constant determination near an absorption edge

The determination of optical constants from the reflectance versus angle of incidence data in the extreme ultraviolet region near an absorption edge may be affected by instrument spectral resolution.

Use of the Reese osteotomy guide system for fusion of the first metatarsophalangeal joint

This manuscript presents a new use for the Reese Osteotomy Guide. The technical aspect of this procedure is discussed in detail. Advantages and disadvantages of its use are reviewed.

Optical properties of palladium in the visible and near UV spectral regions

The dielectric function data, epsilon = epsilon(1) -/+ iepsilon(2), of palladium thin films prepared by dc magnetron sputtering are given for the spectral range 1.6-5.5 eV. A comparison is made between these results and those obtained for Pd films and bulk specimens over the past twenty years. While a number of measurements show good agreement in epsilon(1), there is a considerable variation in the epsilon(2) data among the different groups. Some of these differences can be explained either by the sample preparation, which affects the morphology of the films, or else by uncertainties related to film thickness.

Interevaluator variability in the measurement of proximal articular set angle

The proximal articular set angle (PASA) is used in the evaluation of hallux abducto valgus, as well as a criterial parameter for the selection or rejection of various hallux abducto valgus corrective procedures. The authors casually observed variability in the measurement of PASA in clinical situations, stimulating the development of the presented study to determine if, in fact, the measurement of PASA varies excessively from one physician to another. The results clearly indicate that the interevaluator measurement of PASA is excessive (p less than 0.001 in seven of eight x-ray series and p less than 0.01 in one of eight x-ray series). The authors discuss the clinical implications of the findings. Furthermore, the shortcomings of the study are discussed, specifically the inability to conclude about intraevaluator variability.

Use of the 4 x 4 matrix method in the optics of multilayer magnetooptic recording media

The new 4x4 matrix method described by Lin-Chung and Teitler [P. J. Lin-Chung and S. Teitler, J. Opt. Soc. Am. A 1, 703 (1984)] is used to study the optics of multilayer magnetooptic recording media. It is demonstrated that the method is capable of handling very complicated optical multilayer structures. For a quodrilayer magnetooptic recording system consisting of an overcoat layer, a magnetic layer, an intermediate dielectric layer, and a reflector, the readout of the system is optimized against the thickness of the overcoat and intermediate layers. As well, cases of oblique angle of incidence, anisotropy in the nonmagnetic part of the dielectric constants, and misalignment of the magnetization are treated.