bluuebunny/crossref_metadata_2025 huggingface dataset:
Low vision: a regional evaluation of service provision
Authors: Jackson A. J.
Published: July 2002

As we move rapidly towards the 21st century epidemiologists predict that within the western world, the number of individuals living into their 7th, 8th, and 9th decades will increase dramatically. The implications for those responsible for the provision of ophthalmic care will be a colossal increase in the incidents of age related degenerative pathology. Those specialising in low vision care will find that as the pool of persons requiring services expands, the financial resources available to provide materials will diminish. Targeting those most likely to benefit from low vision services can only be done when the population profile is fully understood and factors affecting success and failure are evaluated.

In this study records for three groups of 50 new low vision patients referred to a regional low vision clinic over a ten year period are evaluated (1 year, 5 years, 10 years). A total of 50 of those supplied with low vision aids were contacted by telephone and a questionnaire was used to determine whether low vision aids had been useful. Information was also gathered on patients' attitudes to the services provided at the clinic and the manor in which they were provided. A total of 52% of patients assessed were female (female 79/male 71). The average age of the population was 65 +/−22 (SD) years (range 15–98).

Thirty three percent of patients were registered as blind or partially sighted (blind 21%, partially sighted 11%). The proportion of clinic attendees who were registered increased by almost 12% over the ten year period. Of those attending, 48% had age related macular degeneration, 7% had diabetic retinopathy, 6% had myopic degeneration, 5% had glaucoma and 5% cataracts. A total of 39% of patients attending the clinic were seen within two years of having become visually impaired. The majority of these patients had been on a waiting list for between 4 and 9 months before having attended for a low vision assessment. This figure reflects the demands placed on an under funded regional service.

The most popular low vision aids supplied were stand magnifiers (52%) and (of which 77% were internally illuminated), 22% hand magnifiers, 12% were spectacle magnifiers and 4% were spectacle mounted telescopic devices. Only 6% of low vision aids were supplied for distant visual tasks. The majority of those supplied with low vision aids (92%) claimed to have benefited from attending the low vision clinic.
The quantitative evaluation of total internal reflection in keratoconus
Authors: Hood A. , Veen C. , Vaughan S. , Edwards M. P. , Simmons I. , Misson G.
Published: July 2002

Purpose: The phenomenon of apical total internal reflection in the cone of keratoconic patients has been described previously. This study was designed to assess the quantifiable nature of this sign and its ability to diagnose and monitor keratoconus.

Method: A sample of 30 patients with varying severity of keratoconus was compared with a series of sex and age matched normal controls and selected cases of spherically equivalent myopia. Each patient had a comprehensive corneal assessment including pachymetry, corneal topography, and standardised oblique slit lamp photography. The slit lamp photographs were digitally analysed to assess the area of total internal reflections. The severity of keratoconus was graded with a six stage ranking system based on the clinical appearance.

Results: The area of total internal reflection was compared to the ranking system of clinical grading. For moderate and marked cones, the area of total internal reflection correlates well with both the clinical appearance and corneal topography. For mild and borderline cases, the photographs show a less well defined area but this is nevertheless distinguishable from normals or spherically‐matched equivalents.

Conclusions: The area of total internal reflection visible in a keratoconic cornea correlates with the established techniques of grading keratoconus. Imaging this phenomenon may form the basis of a quantitative clinical for this condition.
Attendance of contact lens wearers at an ophthalmic Accident and Emergency unit
Authors: Radford C. F. , Gastaldo‐Brac V. , Hill A. R.
Published: July 2002

Contact lens (CL) complications account for 2.2–10.0% of patients attending ophthalmic Accident and Emergency (A&E) units. A survey was conducted to evaluate disease severity among CL wearers attending the Oxford Eye Hospital A&E Unit. CL wearers without a medical indication for CL wear completed a short questionnaire eliciting CL type and wear schedule. Subsequently, A&E Senior House Officers indicated the diagnosis and whether, in their opinion, the patient could have been managed by their optometrist or contact lens practitioner. Approximately half of the CL wearers (321/653, 49%) presented with CL related disorders, but only 16% (53/321) of these had potentially sight‐threatening disease. More than a third of these patients were deemed to be inappropriately attending (125/321, 39%), presenting with minor problems such as corneal abrasions, CL handling difficulties and CL solution ‘accidents’. Better patient instruction, together with encouragement to consult their optometrist or contact lens practitioner first if problems occur, would greatly reduce the burden of A&E attendance by CL wearers with minor complaints.
Rigid gas permeable contact lenses surface roughness examined by interferential shifting phase and scanning electron microscopies
Authors: Merindano M. D. , Canals M. , Saona C. , Costa J.
Published: July 2002

The anterior surface roughness of seven factory new rigid gas permeable (RGP) contact lenses has been studied by interferential shifting phase microscopy (ISPM) and scanning electron microscopy (SEM). Five lenses were fluorsilicone acrylate and two lenses were silicone acrylate. Their material Dk ranged from 14 to 210.

ISPM is shown to be a reliable and non‐destructive method to observe and measure the relief of the contact lens surface. Moreover, profile and contour data are easily stored for further quantitative studies.

ISPM contour patterns of the studied lenses are qualitatively compared with those obtained by SEM for the same lenses. Results point out that ISPM gives similar accuracy but it is non‐destructive and cheaper than SEM.

Moreover, the quantitative study of surface roughness suggests that there is a relationship between surface roughness and Dk of the lens material: surface roughness increases with Dk and allows to distinguish between lenses with low, medium and high Dk.
Fuchs' endothelial dystrophy: a fresh look at an aging disease
Authors: Bergmanson Jan P. G. , Sheldon Todd M. , Goosey John D.
Published: July 2002

The increasing number or corneal and intraocular surgeries performed together with longer life expectancy, elevates the risk for developing symptomatic Fuchs' endothelial dystrophy (FED). This article reviews the current understanding of FED, and, in addition, a case of early FED is presented clinically and histopathologically. Two FED corneas from one patient were examined histopathologically using an established histological protocol for light and electron microscopy. FED is an inherited autosomal dominant corneal endothelial disorder with incomplete penetrance that is up to 3 times less likely to develop in men. Treatment options are primarily palliative while surgical intervention routinely involves a penetrating keratoplasty. In this disease process the endothelium produces excessive amounts of basement membrane material of an abnormal composition resulting in the formation of a posterior collagenous layer. Extreme accumulations of this material created mushroom‐like formations, guttae, projecting into the anterior chamber. The endothelial cells were extremely thinned over the guttae, to the point where the cells may provide little more than barrier function. Despite a presumably compromised endothelial pump the corneas appeared relatively free of edema clinically and histopathologically. However, some edematous pockets deep in the basal epithelial layer were present suggesting that epithelial involvement occurs at an early stage in the disease. An early diagnosis of FED will help patients and surgeons to better elect optimal surgical timing and procedures. The current trend is to intervene surgically before the patient reaches the painful end‐stage. Interestingly, in the case examined, the endothelium presumably provided only a barrier function over large areas with an apparently reduced contribution from the endothelial fluid pump and yet the corneas remained relatively clear. Future research may confirm that decompensation occurs only when complete endothelial coverage is lost. If the endothelial barrier function is more important to corneal transparency than the endothelial pump function in FED, then the relative combination of these two functions in the normal cornea should also be reassessed.
The influence of interactions between accommodation and convergence on the lag of accommodation
Authors: Schor Clifton
Published: July 2002

Several models of myopia predict that growth of axial length is stimulated by blur. Accommodative lag has been suggested as an important source of blur in the development of myopia and this study has modeled how cross‐link interactions between accommodation and convergence might interact with uncorrected distance heterophoria and refractive error to influence accommodative lag.

Accommodative lag was simulated with two models of interactions between accommodation and convergence (one with and one without adaptable tonic elements). Simulations of both models indicate that both uncorrected hyperopia and esophoria increase the lag of accommodative and uncorrected myopia and exophoria decrease the lag or introduce a lead of accommodation in response to the near (40  cm) stimulus. These effects were increased when gain of either cross‐link, accommodative convergence (AC/A) or convergence accommodation (CA/C), was increased within a moderate range of values while the other was fixed at a normal value (clamped condition). These effects were exaggerated when both the AC/A and CA/C ratios were increased (covaried condition) and affects of cross‐link gain were negated when an increase of one cross‐link (e.g. AC/A) was accompanied by a reduction of the other cross‐link (e.g. CA/C) (reciprocal condition). The inclusion of tonic adaptation in the model reduced steady state errors of accommodation for all conditions except when the AC/A ratio was very high (2 MA/D).

Combinations of cross‐link interactions between accommodation and convergence that resemble either clamped or reciprocal patterns occur naturally in clinical populations. Simulations suggest that these two patterns of abnormal cross‐link interactions could affect the progression of myopia differently. Adaptable tonic accommodation and tonic vergence could potentially reduce the progression of myopia by reducing the lag of accommodation.
Developmental visual system anomalies and the limits of emmetropization
Authors: Smith Earl L. , Hung Li‐Fang , Harwerth Ronald S.
Published: July 2002

Optical defocus can within certain limits predictably alter ocular growth and refractive development in infant monkeys. However defocus, particularly unilateral defocus associated with anisometropia, can also promote abnormal sensory and motor development. We investigated the relationship between the effective operating range for emmetropization in infant monkeys and the refractive errors that produced amblyopia. Specifically, we examined the refractive‐error histories of monkeys that did not demonstrate compensating ocular growth for imposed refractive errors and used operant psychophysical methods to measure contrast sensitivity functions for 17 infant monkeys that were reared with varying degrees of optically imposed anisometropia. Imposed anisometropias that were within the operating range of the monkey’s emmetropization process were eliminated by differential interocular growth and did not produce amblyopia. On the other hand imposed anisometropias that failed to initiate compensating growth consistently produced amblyopia; the depth of the amblyopia varied directly with the magnitude of the imposed anisometropia. These results indicate that amblyopia and anisometropia are frequently associated because persistent anisometropia causes amblyopia. However, the failure of emmetropization in infants with refractive conditions that are known to promote sensory and motor anomalies indicates that factors other than optical defocus, presumably factors associated with the development of amblyopia and/or strabismus, can also influence early refractive development and in some cases cause anisometropia.
Effects of defocus and pupil size on human contrast sensitivity
Authors: Strang Niall C. , Atchison David A. , Woods Russell L.
Published: July 2002

Defocus lowers the contrast sensitivity function (CSF), producing a complex function with local dips and peaks. Previously, we were able to predict the shape of the CSF with large pupils from measured transverse aberrations with hypermetropic defocus but not with myopic defocus (Atchison et al., 1998c, J. Opt. Soc. Am. A.15, 2536). As there is no reason that myopic defocus should be more difficult to predict than hypermetropic defocus, we modified the procedure to try to improve CSF predictions with myopic defocus. Also, we extended the study to consider a range of pupil sizes. CSFs were measured for three subjects at three defocus levels (in‐focus, −2D and +2D) and three pupil sizes (2  mm, 4  mm and 6  mm). Using a diffraction optics model, transverse aberration measures and in‐focus CSF measures, we predicted the defocused CSFs. The predicted defocused CSFs were lower than the in‐focus CSF as expected, and had complex shapes that varied with defocus and pupil size and between subjects. While a few predictions were poor, generally, the overall magnitude and shape of the defocused CSFs were well predicted and similarly so for myopic and hypermetropic defocus. Some further improvements in technique are indicated.
Oral Care Reduces Pneumonia in Older Patients in Nursing Homes
Authors: Yoneyama Takeyoshi , Yoshida Mitsuyoshi , Ohrui Takashi , Mukaiyama Hideki , Okamoto Hiroshi , Hoshiba Kanji , Ihara Shinichi , Yanagisawa Shozo , Ariumi Shiro , Morita Tomonori , Mizuno Yasuro , Ohsawa Takayuki , Akagawa Yasumasa , Hashimoto Kenji , Sasaki Hidetada , Of The Oral Care Working Group Members
Published: July 2002

OBJECTIVES:

Aspiration of oral secretions and their bacteria is increasingly being recognized as an important factor in pneumonia. We investigated whether oral care lowers the frequency of pneumonia in institutionalized older people.

DESIGN:

Survey.

SETTING:

Eleven nursing homes in Japan.

PARTICIPANTS:

Four hundred seventeen patients randomly assigned to an oral care group or a no oral care group.

INTERVENTION:

Nurses or caregivers cleaned the patients' teeth by toothbrush after each meal. Swabbing with povidone iodine was additionally used in some cases. Dentists or dental hygienists provided professional care once a week.

MEASUREMENTS:

Pneumonia, febrile days, death from pneumonia, activities of daily living, and cognitive functions.

RESULTS:

During follow‐up, pneumonia, febrile days, and death from pneumonia decreased significantly in patients with oral care. Oral care was beneficial in edentate and dentate patients. Activities of daily living and cognitive functions showed a tendency to improve with oral care.

CONCLUSION:

We suggest that oral care may be useful in preventing pneumonia in older patients in nursing homes. J Am Geriatr Soc 50:430–433, 2002.
Excess Mortality or Institutionalization After Hip Fracture: Men Are at Greater Risk Than Women
Authors: Fransen Marlene , Woodward Mark , Norton Robyn , Robinson Elizabeth , Butler Meg , Campbell A. John
Published: July 2002

OBJECTIVES:

To assess 2‐year excess mortality or institutionalization risk associated with hip fracture in community‐dwelling people aged 60 and over.

DESIGN:

Cohort study.

SETTING:

Auckland, New Zealand, from July 1991 to February 1996.

PARTICIPANTS:

Five hundred sixty‐five community‐dwelling older people recently hospitalized with a hip fracture and 782 randomly selected controls, frequency matched for age and gender, living in the same catchment area as the cases.

MEASUREMENTS:

Two‐year mortality or institutionalization status.

RESULTS:

Over half (52.1%) of male hip fracture cases and 12.4% of male controls were dead or institutionalized, compared with 39.2% of female hip fracture cases and 19.7% of female controls. The odds ratio, adjusted for baseline demographic characteristics, medical status, and physical function, for death or institutionalization was 6.89 (95% confidence interval (CI) = 2.75–17.27) for men and 1.48 (95% CI = 1.02–2.19) for women.

CONCLUSIONS:

For both men and women who incur a hip fracture, the risks of dying or being institutionalized within 2 years are higher than for their peers. The independent effect of hip fracture on this outcome was significantly greater for men than women. The marked influences of prefracture health status, physical limitations, and gender on outcome have important implications for preventative strategies. J Am Geriatr Soc 50:685–690, 2002.
A Prospective Evaluation of the Charlson Comorbidity Index for Use in Long‐Term Care Patients
Authors: Bravo Gina , Dubois Marie‐France , Hébert Réjean , De Wals Philippe , Messier Lise
Published: July 2002

OBJECTIVES:

Because of the high prevalence of coexisting medical conditions in frail older adults, clinical investigators often need to adjust for comorbidity when assessing the effect of long‐term care (LTC) on patient outcomes. This study examined the prognostic value of the Charlson Comorbidity Index (CCI) in predicting 3‐year mortality and functional decline in the LTC setting and compared its prognostic value to that of two data‐derived comorbidity indices.

DESIGN:

Longitudinal cohort study.

SETTING:

Eighty‐eight residential care facilities from Quebec, Canada.

PARTICIPANTS:

Two hundred ninety‐one dependent older adults aged 65 and older.

MEASUREMENTS:

Subjects' functional abilities were assessed at baseline and 3 years later with the revised version of the Functional Autonomy Measurement System (SMAF). Comorbidity data and the exact date of death for those who had died were collected retrospectively from the subjects' medical files. Subjects were classified as functional decliners if they died or gained 5 points or more on the SMAF between the two assessments.

RESULTS:

Multivariate Cox and logistic regressions were used to derive two new comorbidity indices, one for predicting mortality and the other for identifying functional decliners. Although the CCI performed well in predicting these two outcomes, its performance was generally inferior to that of the two newly proposed indices.

CONCLUSIONS:

Findings suggest that the CCI can be improved upon when used to measure comorbidity in LTC patients. J Am Geriatr Soc 50:740–745, 2002.
H+ Fluxes at Plasmalemma Level: In Vivo Evidence for a Significant Contribution of the Ca2+‐ATPase and for the Involvement of its Activity in the Abscisic Acid‐Induced Changes in Egeria Densa Leaves
Authors: Beffagna N. , Romani G. , Sforza M. C.
Published: July 2002

Abstract: The features of Ca2+ fluxes, the importance of the Ca2+ pump‐mediated H+/Ca2+ exchanges at plasmalemma level, and the possible involvement of Ca2+‐ATPase activity in ABA‐induced changes of H+ fluxes were studied in Egeria densa leaves. The results presented show that, while in basal conditions no net Ca2+ flux was evident, a conspicuous Ca2+ influx (about 1.1 ìmol g−1 FW h−1) occurred. The concomitant efflux of Ca2+ was markedly reduced by treatment with 5 íM eosin Y (EY), a specific inhibitor of the Ca2+‐ATPase, that completely blocked the transport of Ca2+ after the first 20 ‐ 30 min. The decrease in Ca2+ efflux induced by EY was associated with a significant increase in net H+ extrusion (−ÄH+) and a small but significant cytoplasmic alkalinization. The shift of external [Ca2+] from 0.3 to 0.2 mM (reducing Ca2+ uptake by about 30 %) and the hindrance of Ca2+ influx by La3+ were accompanied by progressively higher −ÄH+ increases, in agreement with a gradual decrease in the activity of a mechanism counteracting the Ca2+ influx by an nH+/Ca2+ exchange. The ABA‐induced decreases in −ÄH+ and pHcyt were accompanied by a significant increase in Ca2+ efflux, all these effects being almost completely suppressed by EY, in line with the view that the ABA effects on H+ fluxes are due to activation of the plasmalemma Ca2+‐ATPase. These results substantially stress the high sensitivity and efficacy of the plasmalemma Ca2+ pump in removing from the cytoplasm the Ca2+ taken up, and the importance of the contribution of Ca2+ pump‐mediated H+/Ca2+ fluxes in bringing about global changes of H+ fluxes at plasmalemma level.
Phylogenetic Analyses of Aurantioideae (Rutaceae) Based on Non‐Coding Plastid DNA Sequences and Phytochemical Features
Authors: Samuel R. , Ehrendorfer F. , Chase M. W. , Greger H.
Published: July 2002

Abstract: Sequences of the plastid DNA atpB/rbcL intergenic spacer and rps16 intron from 23 genera and 47 species of Rutaceae were used to resolve phylogenetic relationships in subfamily Aurantioideae. According to these, the subfamily is monophyletic, but its classical subdivision into tribes Clauseneae and Citreae is only justified if the genus Murraya s.s. (exclusive of the species segregated as Bergera, e.g., Murraya koenigii and M. siamensis) and Merrillia are transferred to Citreae s.l. This conclusion is also well supported by phytochemistry, demonstrating accumulation of carbazoles in Bergera and Clausena, and of 8‐prenylated coumarins and polyoxygenated flavonoids in Murraya s.s. and Merrillia. Formation of both carbazoles, as well as 8‐prenylated coumarins, and polyoxygenated flavonoids in Micromelum suggests relationships between Clauseneae s.s. and Citreae s.l. The monophyly of several larger genera in both tribes is supported by relatively high bootstrap percentages and specific chemical profiles for e.g., Clausena, Micromelum, Glycosmis and Atalantia. In contrast, molecular, chemical, and other data show that none of the subtribes recognized within Aurantioideae reflect phylogenetic relationships. Only the clades with Clausena+Bergera, Murraya s.s. +Merrillia, and Citrus+Clymenia+Eremocitrus+Fortunella+Poncirus (“true Citrus fruit trees”) are well supported by such data. Among the outgroup genera, Zanthoxylum (Rutoideae) and Toddalia (Toddalioideae) are much closer to each other than to Ruta (Rutoideae).
GaAs photoconductive closing switches with high dark resistance and microsecond conductivity decay
Authors: Mazzola M. S. , Schoenbach K. H. , Lakdawala V. K. , Germer R. , Loubriel G. M. , Zutavern F. J.
Published: July 2002

Silicon-doped n-type gallium arsenide crystals, compensated with diffused copper, were studied with respect to their application as photoconductive, high-power closing switches. The attractive features of GaAs:Cu switches are their high dark resistivity, their efficient activation with Nd:YAG laser radiation, and their microsecond conductivity decay time constant. In our experiment, electric fields as high as 19 kV/cm were switched, and current densities of up to 10 kA/cm2 were conducted through a closely compensated crystal. At field strengths greater than approximately 10 kV/cm, a voltage ‘‘lock-on’’ effect was observed.
Defect reduction in strained InxGa1−xAs via growth on GaAs (100) substrates patterned to submicron dimensions
Authors: Guha S. , Madhukar A. , Chen Li
Published: July 2002

The misfit dislocation (MD) behavior of InxGa1−xAs (x≤0.15) grown via molecular beam epitaxy on GaAs(100) substrates containing parallel mesas of ultrasmall widths (0.6–1.3 μm) is examined via cross-sectional transmission electron microscope studies. A virtual absence of MDs running perpendicular to the mesa widths is found even though the film thicknesses are significantly larger than the so-called critical thickness for growth on nonpatterned substrates. In the nonpatterned regions of the substrate the mean separation of such MDs is ∼1500 Å and ∼940 Å for x=0.11 and x=0.15, respectively. The defect reduction observed is discussed in light of intrinsic effects relating to growth kinetics and strain relief at mesa edges and/or reduced dislocation multiplication occurring on the mesas.
Optical-beam-deflection atomic force microscopy: The NaCl (001) surface
Authors: Meyer Gerhard , Amer Nabil M.
Published: July 2002

We have imaged, in ultrahigh vacuum, the (001) surface of NaCl using an optical-beam-deflectin force microscope operating in the short-range repulsive regime. The design and performance characteristics of the microscope are given, and the observed atomic corrugations are compared with those deduced from He-atom scattering experiments.
Si-H and N-H vibrational properties in glow-discharge amorphous SiNx:H films (0<x<1.55)
Authors: Hasegawa Seiichi , Matsuda Masaaki , Kurata Yoshihiro
Published: July 2002

Amorphous SiNx:H films were prepared by rf glow discharge of SiH4-NH3 mixtures at 300 °C, and the SiH, NH, and SiN vibrational absorptions were investigated as a function of x. The stretching absorption profiles due to SiH and SiN bonds are reproduced by a superposition of two components at around 2000 and 2100 cm−1, and of three components at around 750, 840, and 960 cm−1, respectively. The dependence of these intensities on x was examined by means of a generation probability analysis on the basis of the random bonding model including SiH and NH bonds which play an important role in the film growth mechanism.
Transport properties of high-angle grain boundary weak links in YBa2Cu3O7 thin films
Authors: Lathrop D. K. , Moeckly B. H. , Russek S. E. , Buhrman R. A.
Published: July 2002

By patterning ∼1-μm-wide microbridges in laser ablated YBa2Cu3O7 films containing high-angle tilt boundaries, weak links have been isolated with critical currents low enough to avoid self-screening effects. The current-voltage characteristics of these high-angle tilt-boundary weak links are well described by the resistively shunted junction model, if noise rounding is included. The response of the supercurrent to magnetic field and temperature indicates that the weak links are spatially nonuniform, consisting of relatively small areas of high critical current density, Jc, separated by areas with very low or zero Jc. The response to rf power suggests that the current-phase relation is nonsinusoidal.
Photoemission studies of silicon on the Ru(001) surface
Authors: Lu Z. H. , Sham T. K. , Norton P. R. , Tan K. H.
Published: July 2002

Interactions of silicon atoms on a Ru(001) surface have been studied by synchrotron radiation photoemission spectroscopy and low-energy electron diffraction. A stable RuxSi1−x phase with high chemical uniformity was obtained by post-annealing the sample at 1370 °C. Upon interaction with silicon, the Ru d band was significantly narrowed (by about 1 eV), and shifted towards the Fermi level. The distributions of Si 3s,3p and Ru 4d in the occupied valence bands were clearly identified by using different photon energies. The chemical nature of Si-Ru interaction is discussed.
Giant anisotropies in the dielectric properties of quasi-epitaxial crystalline organic semiconductor thin films
Authors: Zang D. Y. , So F. F. , Forrest S. R.
Published: July 2002

We have measured the indices of refraction and dielectric constants along different directions in thin films of the crystalline organic semiconductor compound 3, 4, 9, 10 perylenetetracarboxylic dianhydride (PTCDA). The films were deposited via organic molecular beam deposition, resulting in single-crystalline, ‘‘quasi-epitaxial’’ films. Due to inherent asymmetries in the molecular crystal structure, film ordering results in giant anisotropies in their dielectric properties. For example, the index of refraction measured at a wavelength of λ=1.064 μm in the direction perpendicular to the substrate plane is n⊥ = 1.36 ± 0.01, whereas parallel to the plane, n∥=2.017±0.005, resulting in an index difference of Δn=0.66. Furthermore, the low-frequency dielectric constant of the films is ε⊥ = 1.9 ± 0.1 and ε∥ = 4.5 ± 0.2. To our knowledge, these are the largest anisotropies ever measured for thin films. We discuss a guided wave polarization-selective device which takes advantage of the large dielectric anisotropies characteristic of the thin organic films.
Quantum confinement effects in strained silicon-germanium alloy quantum wells
Authors: Xiao X. , Liu C. W. , Sturm J. C. , Lenchyshyn L. C. , Thewalt M. L. W. , Gregory R. B. , Fejes P.
Published: July 2002

We report the first detailed study of quantum confinement shifts of band-edge photoluminescence energies in Si/strained Si1−xGex/Si single quantum wells. A quantum confinement energy of up to 45 meV has been observed for quantum wells as small as 33 Å in width. The experimental results are in good agreement with a calculation of the hole confinement energies. The hole energy levels in quantum wells were obtained by numerically solving effective-mass equations with proper matching boundary conditions at interfaces using a 6×6 Luttinger–Kohn Hamiltonian. Both strain and spin-orbit interactions were included in the calculation.
Local poling of ferroelectric polymers by scanning force microscopy
Authors: Güthner P. , Dransfeld K.
Published: July 2002

We have demonstrated a new technique to polarize locally micron-sized areas of a ferroelectric vinylidene-fluoride trifluoroethylene (VDF-TrFE) copolymer film by locally applying a dc voltage between the tip of a scanning force microscope and the bottom electrode underneath the polymer film. To detect these polarized regions we have stimulated the film piezoelectrically by applying an ac electric field between tip and bottom electrode, and measuring locally amplitude and phase of the surface vibration. The size of the smallest region we could polarize so far was about 1 μm.
Al-O complex formation in ion implanted Czochralski and floating-zone Si substrates
Authors: La Ferla A. , Torrisi L. , Galvagno G. , Rimini E. , Ciavola G. , Carnera A. , Gasparotto A.
Published: July 2002

Aluminum ions at 100 MeV were implanted into floating-zone (FZ) and Czochralski (CZ) grown Si substrates. At this energy the influence of the surface on the subsequent thermal treatment is negligible. In FZ samples the electrical active dose, as measured by spreading resistance profilometry, is independent of the annealing time at 1200 °C. In the CZ samples instead it considerably decreases with time. Secondary ion mass spectrometry analysis in CZ samples have revealed the presence of a multipeak structure around the projected range region for both Al and O signals. In FZ the structure is just detectable. The results imply that the Al-O complex formation is enhanced by the presence of oxygen but that it is catalyzed by the damage created during the implant. The carrier profiles coincide in both CZ and FZ diffused substrates by predeposition of Al from a solid source, i.e., in damage-free samples.
Selective area oxidation of silicon with a scanning force microscope
Authors: Day H. C. , Allee D. R.
Published: July 2002

The use of a scanning force microscope with a metallized tip to do selective area oxidation of silicon is demonstrated. Sub-100 nm lines have been achieved. Removal of the oxide lines with buffered hydrofluoric acid reveals trenches in the silicon consistent with silicon consumption in SiO2 formation.
Segregation of Si δ doping in GaAs-AlGaAs quantum wells and the cause of the asymmetry in the current-voltage characteristics of intersubband infrared detectors
Authors: Liu H. C. , Wasilewski Z. R. , Buchanan M. , Chu Hanyou
Published: July 2002

Dopant segregation in the well region of a multiple quantum well intersubband photodetector can cause an asymmetry in the observed forward and reverse current-voltage characteristics. We compensate for the segregation by shifting the position of the Si δ doping in the well and model the effect with good agreement for a range of shift values. For samples grown at a substrate temperature of 605 °C, we find that the observed behavior is best described by assuming that the Si δ-doping profile smears in the growth direction resulting in an asymmetric broadening of about 27 Å.
Measurement of current voltage characteristics of single grain boundaries in melt textured bulk YBa2Cu3Ox
Authors: Sarma C. , Schindler G. , Haase D. G. , Koch C. C. , Saleh A. M. , Kingon A. I.
Published: July 2002

We have investigated the electrical properties of small parts of single grain boundaries in melt textured YBa2Cu3Ox. Similar measurements on grain boundary networks were also made to obtain composite properties. The results of Tc measurements and current-voltage characteristics in zero and small magnetic fields are presented. The R(T) characteristics suggest that there is second phase segregation in some parts of the grain boundary area. The current-voltage characteristics showed three different types of behavior: Resistive, Josephson-like, and flux flow. The Ic(B) data of Josephson junctions suggest that nonsuperconducting inclusions divide the grain boundaries into smaller single junctions.
Electrically switchable volume gratings in polymer-dispersed liquid crystals
Authors: Sutherland R. L. , Tondiglia V. P. , Natarajan L. V. , Bunning T. J. , Adams W. W.
Published: July 2002

We report electrical switching of the diffraction efficiency in volume Bragg gratings written holographically in polymer-dispersed liquid crystals (PDLCs). Scanning electron microscopy confirms the volume nature of the gratings and shows that they consist of periodic PDLC planes. The diffraction efficiency can be switched from a high value (∼50%) to a value near zero at fields ∼11 V/μm.
Creation of bulk, superlatticelike structure and giant magnetoresistance effect in a deformed Cu-Ni-Fe alloy
Authors: Chen L. H. , Jin S. , Tiefel T. H. , Ramesh R.
Published: July 2002

A spinodally decomposed Cu-20 Ni-20 Fe alloy containing ∼500 Å size ferromagnetic particles was uniaxially deformed to create a locally multilayered, superlatticelike structure with alternating ferromagnetic and nonmagnetic layers. When the size scale of each layer was made to be small, ∼15 Å thick, a dramatic improvement in room-temperature magnetoresistance ratio from ∼0.6 to ∼5% was obtained. An abnormal temperature dependence of magnetoresistance ratio, i.e., the room-temperature value being greater than that at 4.2 K, was found. The observed giant magnetoresistance behavior could be explained in terms of the field-induced decrease in electron scattering in a nearly superparamagnetic material although the spin-dependent scattering at the two-phase interface and in the ferromagnetic phase may also be a contributing factor.
Smooth polycrystalline ceramic substrates with enhanced metal adhesion by pulsed excimer laser processing
Authors: Lowndes Douglas H. , DeSilva M. , Godbole M. J. , Pedraza A. J. , Thundat T. , Warmack R. J.
Published: July 2002

Multishot pulsed XeCl (308 nm) excimer laser irradiation of commercial fine-grained polycrystalline alumina substrates is found to significantly improve their properties for metal film-bonding applications. A smoother surface finish is obtained, and the adhesion strength of subsequently deposited copper films to the laser-treated alumina surface is increased by a factor of 3–5 (200%–400%) under optimum laser conditions. Smoothing occurs when the alumina melts and undergoes molten flow before resolidifying. XPS measurements suggest that electrical activation of the near-surface region also may contribute to the enhanced copper adhesion.
Gap-state measurements on diamond-like carbon films
Authors: Mandel T. , Frischholz M. , Helbig R. , Hammerschmidt A.
Published: July 2002

A high frequency capacitance-voltage method is used to measure the electronic gap-state density in diamond-like carbon (DLC) films. The gap-state density is derived from the analysis of high frequency capacitance-voltage characteristics of DLC on crystalline silicon (c-Si) heterojunctions. Near the Fermi level the gap-state density in the DLC thin film is obtained of the order 1016 cm−3 eV−1. Furthermore, the energy-band diagram of a DLC/c-Si heterojunction is evaluated, and the work function of DLC is derived to be 3.6 eV.
Improved exchange coupling between ferromagnetic Ni-Fe and antiferromagnetic Ni-Mn-based films
Authors: Lin Tsann , Mauri Daniele , Staud Norbert , Hwang Cherngye , Howard J. Kent , Gorman Grace L.
Published: July 2002

Dc magnetron sputtered Ni-Mn and Ni-Mn-Cr films are demonstrated to exhibit strong and thermally stable antiferromagnetism, as well as high corrosion resistance. For a 25.2 nm thick 53.3 Ni-46.7 Mn (in atomic percent) film deposited on top of a 28.5 nm thick 81 Ni-19 Fe film, a unidirectional anisotropy field (HUA) of 120.6 Oe is obtained at room temperature after annealing in vacuum. The equivalent interfacial exchange coupling energy (JK) is 0.27 erg/cm2, three times higher than that of bilayer Ni-Fe/50Fe-50Mn films. This strong exchange coupling appears correlated with the presence of an antiferromagnetic θ (NiMn) phase with a CuAu-I-type ordered face-centered-tetragonal structure. The blocking temperature, at which the exchange coupling disappears, is higher than 400 °C. The Cr addition to the Ni-Mn film dilutes the exchange coupling, but the JK for the Cr content ≤10.7 at. %, is still higher than that of the Ni-Fe/Fe-Mn films. Both Ni-Mn and Ni-Mn-Cr films exhibit corrosion behaviors much better than the Fe-Mn film and comparable to the Ni-Fe film. The films are proposed as longitudinal bias layers for the stabilization of magnetoresistive read sensors.
Heteroepitaxial growth of ZnO films on diamond (111) plane by magnetron sputtering
Authors: Hachigo Akihiro , Nakahata Hideaki , Higaki Kenjiro , Fujii Satoshi , Shikata Shin-ichi
Published: July 2002

ZnO thin film has been epitaxially grown on the (111) plane of the diamond substrate by rf magnetron sputtering at substrate temperature as low as 260 °C. The crystallinity was examined by x-ray diffraction and reflection high-energy electron diffraction. It was found that the smallest standard deviation angle estimated from the x-ray rocking curve of the ZnO(0002) peak was 0.27° whereas the mismatch of the lattice parameter between film and substrate is 28.8%. The epitaxial relationship between ZnO film and the diamond is determined as [112̄0] ZnO//[1̄01] diamond.
γ-Al2O3 formation from pulsed-laser irradiated sapphire
Authors: Cao Siqi , Pedraza A. J. , Lowndes D. H. , Allard L. F.
Published: July 2002

High-resolution transmission electron microscopy was used to examine the effect of laser irradiation of sapphire (single crystalline α-Al2O3). It was observed that laser-melted material resolidified as γ-Al2O3 epitactically grown on the (0001) plane of α-Al2O3 having an orientation relationship (0001)α//(111)γ and [011̄0]α//[11̄0]γ. The interface between unmelted α-Al2O3 and resolidified γ-Al2O3 is atomically flat with steps of one to a few close-packed oxygen layers. The high thermal gradient in the α-Al2O3 did not produce any interfacial dislocations. However, pronounced lattice distortions existed in the resolidified γ-Al2O3. It is argued that the very rapid cooling rate present during solidification prevents the ordering of Al atoms that is required for the formation of the stable α-Al2O3 phase.
Imprint and oxygen deficiency in (Pb,La)(Zr,Ti)O3 thin-film capacitors with La-Sr-Co-O electrodes
Authors: Lee J. , Ramesh R. , Keramidas V. G. , Warren W. L. , Pike G. E. , Evans J. T.
Published: July 2002

La-Sr-Co-O/Pb-La-Zr-Ti-O/La-Sr-Co-O thin-film capacitors have been grown in various oxygen ambients by pulsed laser deposition. As the oxygen ambient became more reducing, the capacitors developed more voltage asymmetry in hysteresis loops and a more preferred polarization state directed towards the top electrode. PLZT capacitors cooled in a fully oxidizing atmosphere (i.e., 1 atm oxygen pressure) exhibited nominally symmetric hysteresis loops and also showed little imprint both with and without fully saturating bias fields. We find that ambient oxygen pressure is an important process parameter and the imprint behavior is closely related with ambient oxygen induced effects such as oxygen vacancies, its related defect-dipole complexes and trapping of free charges. The different imprint behavior under negative and positive bias also suggests that the dipolar-defect complexes tend to cause imprint in PLZT capacitors.
Piezoelectric tip-sample distance control for near field optical microscopes
Authors: Karrai Khaled , Grober Robert D.
Published: July 2002

An aluminum coated tapered optical fiber is rigidly attached to one of the prongs of a high Q piezoelectric tuning fork. The fork is mechanically dithered at its resonance frequency (33 kHz) so that the tip amplitude does not exceed 0.4 nm. A corresponding piezoelectric signal is measured on electrodes appropriately placed on the prongs. As the tip approaches within 20 nm above the sample surface a 0.1 nN drag force acting on the tip causes the signal to reduce. This signal is used to position the optical fiber tip to about 0 to 25 nm above the sample. Shear forces resulting from the tip-sample interaction can be quantitatively deduced.
Measurements of plasma fluctuations with a heavy-ion beam probe
Authors: Hallock G. A. , Schoch P. M. , Saadatmand K. , Hickok R. L. , Jennings W. C. , Connor K. A.
Published: July 2002

A heavy-ion beam probe can provide simultaneous, spatially resolved measurements of φ̃ and (ñσeff) in magnetically confined plasmas. Capabilities have been demonstrated on TMX, RENTOR, and ISX-B using single detector systems, which permit the evaluation of the frequency spectra out to several hundred kilohertz. The cross correlation and phase difference between ñ and φ̃ are also obtained by assuming T̃e fluctuations to be negligible. Present development effort is focused on the use of multiple detectors and multiple ion species. These should allow the determination of both the frequency and wave number spectra for ñ, φ̃, and T̃e. The resolution and limitation of these techniques and their application to studying fluctuation-induced transport will be discussed.
New technique for producing highly uniform droplet streams over an extended range of disturbance wavenumbers
Authors: Orme M. , Muntz E. P.
Published: July 2002

A recent discovery about a well-studied phenomenon leads to the formation of ultracoherent streams of liquid drops. A remarkably straightforward, although previously unreported, method of drop generation from capillary streams, which involves the imposition of an amplitude modulated sinusoidal carrier disturbance, is discussed. The amplitude-modulated disturbance results in the production of highly stable droplet streams over a previously unattainable range of wavenumbers. A decrease in the speed variation of the drops within the stream, which is a result of the amplitude modulation, is demonstrated over a range of nondimensional wavenumbers from 0.4 to 0.04. The nondimensional wavenumber is the ratio of stream circumference to disturbance wavelength. It is suggested that amplitude modulating the capillary stream’s disturbance may also decrease the diameter variation of the drops.
New method for time dependent x-ray absorption studies
Authors: Frahm R.
Published: July 2002

An absorption spectrum containing both the XANES and the EXAFS region can be recorded in several seconds if x-ray monochromators at synchrotron beamlines are scanned continuously. The experimental setups are described in detail. The accuracy of the method up to photon energies of 19 keV is demonstrated. Due to its advantages, the proposed approach may be used as an alternative to the energy dispersive EXAFS method, especially in the case of XANES spectroscopy.
Vibrating orifice droplet generator for precision optical studies
Authors: Lin H-B. , Eversole J. D. , Campillo A. J.
Published: July 2002

A special purpose vibrating orifice droplet generator is described possessing improved short-term monodispersity (instantaneous diameter fluctuations of 2×10−5 and a differential drift of 10−5/min.). We demonstrate that this is sufficient to allow cw laser excitation of specific morphology-dependent resonances (MDRs). Improved performance results from (1) the liquid sample being direct pressure fed to the vibrating orifice from a closed pressure reservoir rather than by a conventional gear driven syringe pump, and (2) the vibrating orifice is driven by a periodic square wave voltage source having a frequency which is four orders of magnitude more constant (1 part in 108 per day) than sources normally used. A novel variational size spectroscopy is also described that is made possible by programmed frequency ramping of the voltage source driving the vibrating orifice. By monitoring elastic scattering during ramped size changes we have been able to infer precise values of droplet index of refraction (to ±0.001) and size (to ±3 parts in 104) at any orifice operating frequency by comparison of the resulting experimental pattern to Lorentz–Mie calculations. This aerosol source permits the next generation of optical experiments (e.g., double resonance, fluorescence rate inhibition and enhancement, cw nonlinear optical, accurate chemical speciation, etc.) to be performed on droplets with diameters of 10–80 μm.
An automated apparatus for interfacial tension measurements by the sessile drop technique
Authors: Carlà M. , Cecchini R. , Bordi S.
Published: July 2002

A fully computer controlled apparatus for interfacial tension measurements at the mercury/solution or solution/solution interface is described. The apparatus is based on the drop-shape technique and employs a solid state video camera to take the drop profile; measurements can be accomplished as a function of interface polarization potential, temperature and solution concentration. Overall data reproducibility is better than 0.06%, with an acquisition time of about 45 s for each experimental data point.
Improved multilaser/multiparameter flow cytometer for analysis and sorting of cells and particles
Authors: Steinkamp John A. , Habbersett Robert C. , Hiebert Richard D.
Published: July 2002

An improved multilaser instrument has been developed for quantitative analysis and separation of biological cells and particles. Argon ion, krypton ion, and dye lasers are employed as excitation sources to sequentially illuminate cells labeled with multiple fluorochromes as they pass through an improved flow chamber that incorporates an electronic cell-volume sensor and an optical measurement region. Detectors located on the axis of each excitation beam are used to measure axial light loss and forward light scatter. Multicolor fluorescence is measured using a five-channel detector located orthogonal to the laser beam(s)-cell stream intersection(s). Sequential measurements are made on a cell-by-cell basis to provide pulse height, area, and width signals that are made coincident in time by analog delay modules to increase data throughput. Analog electronics are used to compute real-time ratios, sums, and differences of signals. Up to eight signals are acquired and displayed as single-parameter frequency distribution histograms and bivariate diagrams using a microcomputer. Processed signals also activate cell sorting according to computer-controlled preselected parametric criteria. The unique measurement capabilities and other new features designed into this instrument represent marked technological improvements over our previous system.
Chromatic aberration of three-cylinder electrostatic lenses
Authors: Olson D. , Szilagyi M.
Published: July 2002

Accurate calculations of the axial chromatic aberration coefficients of geometrically symmetric three-cylinder tripotential electrostatic lenses are presented for two different center electrode lengths. This is an extension of the first-order properties and the third-order spherical aberration coefficients published by Harting and Read.