Strain and Bond Length Dynamics upon Growth and Transfer of Graphene by NEXAFS Spectroscopy from First-Principles and Experiment.

As the quest toward novel materials proceeds, improved characterization technologies are needed. In particular, the atomic thickness in graphene and other 2D materials renders some conventional technologies obsolete. Characterization technologies at wafer level are needed with enough sensitivity to detect strain in order to inform fabrication. In this work, NEXAFS spectroscopy was combined with simulations to predict lattice parameters of graphene grown on copper and further transferred to a variety of substrates. The strains associated with the predicted lattice parameters are in agreement with experimental findings. The approach presented here holds promise to effectively measure strain in graphene and other 2D systems at wafer levels to inform manufacturing environments.

High-resolution X-ray emission spectroscopy with transition-edge sensors: present performance and future potential.

X-ray emission spectroscopy (XES) is a powerful element-selective tool to analyze the oxidation states of atoms in complex compounds, determine their electronic configuration, and identify unknown compounds in challenging environments. Until now the low efficiency of wavelength-dispersive X-ray spectrometer technology has limited the use of XES, especially in combination with weaker laboratory X-ray sources. More efficient energy-dispersive detectors have either insufficient energy resolution because of the statistical limits described by Fano or too low counting rates to be of practical use. This paper updates an approach to high-resolution X-ray emission spectroscopy that uses a microcalorimeter detector array of superconducting transition-edge sensors (TESs). TES arrays are discussed and compared with conventional methods, and shown under which circumstances they are superior. It is also shown that a TES array can be integrated into a table-top time-resolved X-ray source and a soft X-ray synchrotron beamline to perform emission spectroscopy with good chemical sensitivity over a very wide range of energies.

Nature of the metal insulator transition in ultrathin epitaxial vanadium dioxide.

We have combined hard X-ray photoelectron spectroscopy with angular dependent O K-edge and V L-edge X-ray absorption spectroscopy to study the electronic structure of metallic and insulating end point phases in 4.1 nm thick (14 units cells along the c-axis of VO2) films on TiO2(001) substrates, each displaying an abrupt MIT centered at ~300 K with width <20 K and a resistance change of ΔR/R > 10(3). The dimensions, quality of the films, and stoichiometry were confirmed by a combination of scanning transmission electron microscopy with electron energy loss spectroscopy, X-ray spectroscopy, and resistivity measurements. The measured end point phases agree with their bulk counterparts. This clearly shows that, apart from the strain induced change in transition temperature, the underlying mechanism of the MIT for technologically relevant dimensions must be the same as the bulk for this orientation.

Performance of a four-element Si drift detector for X-ray absorption fine-structure spectroscopy: resolution, maximum count rate, and dead-time correction with incorporation into the ATHENA data analysis software.

The performance of a four-element Si drift detector for energy-dispersive fluorescence-yield X-ray absorption fine-structure measurements is reported, operating at the National Institute of Standards and Technology beamline X23A2 at the National Synchrotron Light Source. The detector can acquire X-ray absorption fine-structure spectra with a throughput exceeding 4 x 10(5) counts per second per detector element (>1.6 x 10(6) total counts per second summed over all four channels). At this count rate the resolution at 6 keV is approximately 220 eV, which adequately resolves the Mn Kalpha and Kbeta fluorescence lines. Accurate dead-time correction is demonstrated, and it has been incorporated into the ATHENA data analysis program. To maintain counting efficiency and high signal to background, it is suggested that the incoming count rate should not exceed approximately 70% of the maximum throughput.

Charge-transfer satellites and chemical bonding in photoemission and x-ray absorption of SrTiO3 and rutile TiO2: Experiment and first-principles theory with general application to spectroscopic analysis.

First-principles, real-time-cumulant, and Bethe-Salpeter-equation calculations fully capture the detailed satellite structure that occurs in response to the sudden creation of the core hole in both photoemission and x-ray absorption spectra of the transition-metal compounds SrTiO3 and rutile TiO2. Analysis of the excited-state, real-space charge-density fluctuations betrays the physical nature of these many electron excitations that are shown to reflect the materials' solid-state electronic structure and chemical bonding. This first-principles development of the cumulant-based core hole spectral function is generally applicable to other systems and should become a standard tool for all similar spectroscopic analysis going beyond the quasiparticle physics of the photoelectric effect.

A practical superconducting-microcalorimeter X-ray spectrometer for beamline and laboratory science.

We describe a series of microcalorimeter X-ray spectrometers designed for a broad suite of measurement applications. The chief advantage of this type of spectrometer is that it can be orders of magnitude more efficient at collecting X-rays than more traditional high-resolution spectrometers that rely on wavelength-dispersive techniques. This advantage is most useful in applications that are traditionally photon-starved and/or involve radiation-sensitive samples. Each energy-dispersive spectrometer is built around an array of several hundred transition-edge sensors (TESs). TESs are superconducting thin films that are biased into their superconducting-to-normal-metal transitions. The spectrometers share a common readout architecture and many design elements, such as a compact, 65 mK detector package, 8-column time-division-multiplexed superconducting quantum-interference device readout, and a liquid-cryogen-free cryogenic system that is a two-stage adiabatic-demagnetization refrigerator backed by a pulse-tube cryocooler. We have adapted this flexible architecture to mate to a variety of sample chambers and measurement systems that encompass a range of observing geometries. There are two different types of TES pixels employed. The first, designed for X-ray energies below 10 keV, has a best demonstrated energy resolution of 2.1 eV (full-width-at-half-maximum or FWHM) at 5.9 keV. The second, designed for X-ray energies below 2 keV, has a best demonstrated resolution of 1.0 eV (FWHM) at 500 eV. Our team has now deployed seven of these X-ray spectrometers to a variety of light sources, accelerator facilities, and laboratory-scale experiments; these seven spectrometers have already performed measurements related to their applications. Another five of these spectrometers will come online in the near future. We have applied our TES spectrometers to the following measurement applications: synchrotron-based absorption and emission spectroscopy and energy-resolved scattering; accelerator-based spectroscopy of hadronic atoms and particle-induced-emission spectroscopy; laboratory-based time-resolved absorption and emission spectroscopy with a tabletop, broadband source; and laboratory-based metrology of X-ray-emission lines. Here, we discuss the design, construction, and operation of our TES spectrometers and show first-light measurements from the various systems. Finally, because X-ray-TES technology continues to mature, we discuss improvements to array size, energy resolution, and counting speed that we anticipate in our next generation of TES-X-ray spectrometers and beyond.

Isotropic thin PTCDA films on GaN(0 0 0 1).

The growth of 3, 4, 9, 10-perylene tetracarboxylic dianhydride (PTCDA) on the Ga-polar GaN(0 0 0 1) surface has been studied by x-ray photoelectron spectroscopy (XPS), spot profile analysis low-energy electron diffraction (SPA-LEED), near edge x-ray absorption fine structure (NEXAFS), and scanning tunneling microscopy (STM). The stoichiometric ratios derived from XPS indicate that the molecules remain intact upon adsorption on the surface. Furthermore, no chemical shifts can be observed in the C 1s and O 1s core levels with progressing deposition of PTCDA, suggesting none or only weak interactions between the molecules and the substrate. NEXAFS data indicate the PTCDA molecules being oriented with their molecular plane parallel to the surface. High-resolution STM shows PTCDA islands of irregular shape on the sub-micron scale, and together with corresponding SPA-LEED data reveals a lateral ordering of the molecules that is compatible with the presence of (1 0 2) oriented PTCDA nano-crystals. SPA-LEED moreover clearly shows the presence of homogeneously distributed rotational domains of two-dimensionally isotropic PTCDA.

Feasibility of home care for certain respiratory-dependent restrictive or obstructive lung disease patients.

Some patients requiring long-term intermittent or continuous mechanical ventilation can be safely treated at home with less cost and greater patient and family satisfaction. This is supported by experience with restrictive or obstructive respiratiroy disease patients in a respirator home care program from 1973 through 1979; some were followed for over four years. Moreover, risk is low as judged by few medical complications and no deaths attributed to home care. When compared with their need for hospitalization in the preceding 12 months, patients in the home care program required fewer days in the hospital (restrictive, 88 percent; obstructive, 37 percent). Given proper organization and resources, home care can be a useful alternative to continued hospitalization for certain respirator-dependent patients.

Decline in respiratory function and experience with long-term assisted ventilation in advanced Duchenne's muscular dystrophy.

We present 17 patients with advanced DMD who required long-term assisted ventilation. Eleven patients used part-time assisted ventilation. Five of the patients received BV and/or M-IPPV or N-IPPV between two and nine years before requiring full-time T-IPPV, while six others initially used part-time T-IPPV. One patient used all three modes before requiring full-time T-IPPV. Mean (+/- SD) FVC and rebreathe PCO2 at the outset of assisted ventilation were 0.62 +/- 0.20 L and 47.4 +/- 7.5 mm Hg, respectively. Clinical features were divided between symptoms suggesting respiratory muscle fatigue and sleep-related disordered breathing. We found that, while useful in early respiratory insufficiency, BV is associated with recurrent aspiration. In our experience, N-IPPV offers the safest and most convenient form of noninvasive ventilation. When the VC has decreased to about 300 ml, most patients will require full-time ventilation; T-IPPV is advised to provide airway access to suction secretions.

Syndesmotic ankle sprains.

In this study we reviewed ankle sprains in a professional football team over a 6 year period. Fifteen players who sustained syndesmotic ankle sprains were compared with 28 players who sustained significant lateral ankle sprains. Players with syndesmotic sprains missed significantly more games and practices and they received substantially more treatments than players with lateral ankle sprains. Physical examination findings, results of radiographic evaluations, and etiologic factors are discussed. The external rotation stress test, a clinical method for diagnosis of this type of sprain at the time of injury, is described. Results of this study clearly demonstrate a prolonged recovery time for syndesmotic ankle sprains. Physicians and trainers who are aware of this injury can differentially diagnose these two types of sprains in the early postinjury period by the method described.

Lunate and perilunate dislocations in professional football players. A five-year retrospective analysis.

The purpose of this retrospective study was to review the treatment and prognosis of lunate and perilunate carpal dislocations in professional football players in the National Football League over a 5-year period. There were 7 lunate and 3 perilunate dislocations in 10 players. The mechanism of injury was hyperextension in 9 of 10 players. Five players were subsequently treated by closed reduction and percutaneous pinning; the others were treated by open reduction and K-wire fixation. No player was treated by cast immobilization alone. Intraoperative techniques, postoperative immobilization and protection, return to play, final follow-up physical examination, radiographic evaluation, and complications were reviewed. Results of this study clearly demonstrate that lunate and perilunate carpal dislocations do not mean the end of a career in professional football, although a minimum of 4 weeks of playing time is lost. Treatments varied with respect to open or closed reductions, placement of pins, casts, and time of immobilization. None of the variations was clearly superior or detrimental, although four of the five players who returned to play in the same season were treated by closed reduction with percutaneous pinning.

Refracture of proximal fifth metatarsal (Jones) fracture after intramedullary screw fixation in athletes.

This study details six instances of refracture of clinically and radiographically healed fractures of the base of the fifth metatarsal after intramedullary screw fixation. Four professional football players, one college basketball player, and one recreational athlete underwent intramedullary screw fixation of fifth metatarsal fractures. The athletes were released to full activities an average of 8.5 weeks (range, 5.5 to 12) after fixation, when healing was clinically and radiographically documented. Three football players developed refracture within 1 day of return to full activity. The other three athletes refractured at 2.5, 4, and 4.5 months after return to activity. Two football players underwent repeat fixation with larger screws and returned to play in the same season. The college basketball player underwent bone grafting and returned to play in subsequent seasons. The other three athletes underwent nonoperative management and healed uneventfully over 6 to 8 weeks. On the basis of this series, we recommend that 1) screw fixation using a large-diameter screw should be given careful consideration for patients with large body mass for whom early return to activity is important; 2) functional bracing, shoe modification, or an orthosis should be considered for return to play; 3) if refracture occurs, exchange to a larger screw may allow return to play in the same season; and 4) alternative imaging should be considered to help document complete healing.

Achilles tendon allograft reconstruction of the anterior cruciate ligament-deficient knee.

Thirty-five patients had reconstruction of the anterior cruciate ligament with intraarticular fresh-frozen Achilles tendon allograft and extraarticular tibial band tenodesis. Patients were followed 2 to 4 years (mean, 2.5). Evaluation included clinical and functional examinations, measurement of tibiofemoral displacement, and anteroposterior and lateral radiographs. Clinical results were considered satisfactory in 85% of the patients; 16 had arthroscopic examination after the allograft; allograft biopsies in 9 at this time showed cellular and vascular tissue without evidence of immune reaction. Clinical, arthroscopic, and biopsy results were favorable, but radiologic results were not. In most patients there was a significant size increase in femoral and tibial bone tunnels, as measured from radiographs. In the 6 most extreme cases, bone tunnels measured 20 mm or more in diameter, twice the initial size. Etiology and clinical significance of these bone tunnel changes remain unknown. Enlargement appears to occur early after operation; it stabilizes within 2 years. No statistical correlation was seen between tunnel enlargement and results of clinical and functional examinations; nevertheless, unexplained tunnel enlargement is cause for concern, and allograft replacement of the anterior cruciate ligament with fresh-frozen Achilles tendon allograft should be considered a salvage procedure.

Comparison of arthroscopic and open reconstruction of the anterior cruciate ligament. Early results.

The purpose of this study was to determine in a prospective, randomized, blinded design whether arthroscopically assisted anterior cruciate ligament reconstruction offered any significant immediate or short-term advantages over traditional open reconstruction through a limited arthrotomy. Patients with a diagnosis of deficiency of the anterior cruciate ligament were randomly assigned to one of two treatment groups: the open group (limited open reconstruction) or the arthroscopic group (fully arthroscopic reconstruction). Postoperatively, both groups were treated identically. Intra- and postoperative observations included length of surgery, duration of hospitalization, and amount of pain medication. Follow-up evaluations were performed at 1, 6, 12, 16, 20, and 24 weeks to record crepitus, swelling, range of motion, ligament laxity, and thigh atrophy. Lysholm scores were obtained at the 16 and 24 week follow-ups. At 24 weeks, 86% of the open group and 89% of the arthroscopic group had good-to-excellent results. Intraoperative, postoperative, and follow-up findings indicated no statistically significant differences or relationships between the two groups in any of the variables measured, except that operative time was 13 minutes longer in the arthroscopic group (P < 0.001). The results do not substantiate a clinical advantage for either technique.

Lumbar transverse process fractures in professional football players.

In the general population, fractures of the transverse processes of lumbar vertebrae occur in cases of high-energy blunt trauma, often in motor vehicle accidents. Football players may incur the same fractures, but the circumstances and outcomes are different in this specific subgroup. A review of 29 cases among National Football League players reveals that associated visceral injuries are rare, and the time lost from sports is only an average of 3.5 weeks.

Anterior cruciate ligament reconstruction as an outpatient procedure.

During a 27-month period, 222 patients with 227 anterior cruciate ligament-deficient knees underwent arthroscopically assisted reconstructions as outpatient procedures. Bone-tendon-bone autografts were used for 169 of these reconstructions; the other 58 were done with bone-tendon-bone allografts. Additional procedures were performed on 180 of the patients. The interval from injury to reconstruction averaged 29 months. The protocol developed at our clinic employs a general anesthetic administered with the intent of same-day discharge, infiltration of the skin and joint with bupivacaine, a cold compressive dressing, and the use of both ketorolac tromethamine and a Schedule III narcotic (acetaminophen with codeine or with propoxyphene) for postoperative pain control. At an average followup of 10 months, no readmissions in the immediate postoperative period had been required and no short- or long-term postoperative complications could be attributed to the protocol. This safe and effective technique offers the patient the advantage of anterior cruciate ligament reconstruction as a same-day procedure and allows the surgeon to implement its use in any outpatient setting without additional discharge planning.

Lower extremity lengthening by Wagner's method and by callus distraction.

Fifty-three patients underwent 64 lengthenings of the femur or tibia by the Wagner technique or by the callus distraction method. Thirty-six femoral and 28 tibial segments were lengthened. Simultaneous lengthening of the femur and tibia was performed in seven limbs. Three segments underwent repeat lengthenings. The average length gained by the Wagner method was 5.1 cm in the femur and 5.4 cm in the tibia. Length gains by callus distraction were 4.9 cm in the femur and 4.5 cm in the tibia. Complication rates were fewer and less severe with callus distraction. The number of operations, days of hospitalization, and length of total treatment were less in patients operated on with the callus distraction method than in those who underwent the Wagner technique.

High-pass photocathode x-ray ionization chamber for surface EXAFS.

An x-ray detector that collects electrons emitted from a cathode plate and amplifies them through field intensified ionization in helium gas is described. The sensitivity of the detector to the photon frequency increases by nearly an order of magnitude as the photon energy exceeds the absorption edge of the photocathode. The detector current as a function of the x-ray frequency is shown to yield the extended x-ray absorption fine structure (EXAFS) of layers of copper as thin as 30 A in a few minutes.

National Institute of Standards and Technology Synchrotron Radiation Facilities for Materials Science.

Synchrotron Radiation Facilities, supported by the Materials Science and Engineering Laboratory of the National Institute of Standards and Technology, include beam stations at the National Synchrotron Light Source at Brookhaven National Laboratory and at the Advanced Photon Source at Argonne National Laboratory. The emphasis is on materials characterization at the microstructural and at the atomic and molecular levels, where NIST scientists, and researchers from industry, universities and government laboratories perform state-of-the-art x-ray measurements on a broad range of materials.

External skeletal fixation. Secondary indications.

In addition to open tibial fractures, external fixation has many other applications to the leg. By keeping the method in mind, the surgeon will find the occasional application in which external fixation may serve as a convenient, safe, and comfortable alternative method of treatment.