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.

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.

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.

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.

Conservation of artists' acrylic emulsion paints: XPS, NEXAFS and ATR-FTIR studies of wet cleaning methods.

Works of art prepared with acrylic emulsion paints became commercially available in the 1960s. It is increasingly necessary to undertake and optimise cleaning and preventative conservation treatments to ensure their longevity. Model artists' acrylic paint films covered with artificial soiling were thus prepared on a canvas support and exposed to a variety of wet cleaning treatments based on aqueous or hydrocarbon solvent systems. This included some with additives such as chelating agents and/or surfactants, and microemulsion systems made specifically for conservation practice. The impact of cleaning (soiling removal) on the paint film surface was examined visually and correlated with results of attenuated total reflection Fourier transform infrared, XPS and near-edge X-ray absorption fine structure analyses - three spectroscopic techniques with increasing surface sensitivity ranging from approximately - 1000, 10 and 5 nm, respectively. Visual analysis established the relative cleaning efficacy of the wet cleaning treatments in line with previous results. X-ray spectroscopy analysis provided significant additional findings, including evidence for (i) surfactant extraction following aqueous swabbing, (ii) modifications to pigment following cleaning and (iii) cleaning system residues. © 2014 The Authors. Surface and Interface Analysis published by John Wiley & Sons, Ltd.

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.

Determination of the electron escape depth for NEXAFS spectroscopy.

A novel method was developed to determine carbon atom density as a function of depth by analyzing the postedge signal in near-edge X-ray absorption fine structure (NEXAFS) spectra. We show that the common assumption in the analysis of NEXAFS data from polymer films, namely, that the carbon atom density is constant as a function of depth, is not valid. This analysis method is then used to calculate the electron escape depth (EED) for NEXAFS in a model bilayer system that contains a perfluorinated polyether (PFPE) on top of a highly oriented pyrolitic graphite (HOPG) sample. Because the carbon atom densitites of both layers are known, in addition to the PFPE surface layer thickness, the EED is determined to be 1.95 nm. This EED is then used to measure the thickness of the perfluorinated surface layer of poly(4-(1H,1H,2H,2H-perfluorodecyl)oxymethylstyrene) (PFPS).

A direct comparison of surface and bulk chain-relaxation in polystyrene.

Near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy was used to measure simultaneously the relaxation rates of polystyrene (PS) molecules at the free surface and in the bulk. The samples were uniaxially stretched and annealed at temperatures below the bulk glass transition temperature of PS. The surface and bulk chain relaxation was monitored by measuring the partial-electron and the fluorescence NEXAFS yields, respectively, both parallel and perpendicular to the stretching direction. The decay of the optical birefringence was also measured to provide an independent measure of the bulk relaxation. Relaxation of PS chains was found to occur faster on the surface relative to the bulk. The magnitude of the surface glass transition temperature suppression over the bulk was estimated based on the information on the temperature dependence of the rates.

Unraveling the symmetry of the hole states near the Fermi level in the MgB2 superconductor.

We use x-ray absorption spectroscopy (XAS) and electron energy loss spectroscopy (EELS) to study the fine structure at the K edge of boron in MgB(2). We observe in XAS a peak of width 0.7 eV at the edge threshold, signaling a narrow energy region with empty boron p states near the Fermi level. The changes in the near edge structure observed in EELS with direction of the momentum transfer imply that these states have p(x)p(y) symmetry. Our observations are consistent with electronic structure calculations indicating a narrow energy window of empty p(x)p(y) states that falls to zero at 0.8 eV above the Fermi level. The disappearance of the p(x)p(y) feature in EELS at grain boundaries suggests that this signature may become powerful in probing superconductivity at nanoscale.

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.

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.

Home based rehabilitation for anterior cruciate ligament reconstruction.

Fifty-four patients who underwent arthroscopically assisted anterior cruciate ligament reconstruction with bone-patellar tendon-bone autograft or allograft were studied prospectively to compare a postoperative home based rehabilitation program with a clinic based program. Fifty-four patients (mean age, 30 years) were assigned randomly to the home based program (27 patients) or the clinic based program (27 patients). The home based schedule featured six physical therapy visits during a 6-month postoperative study period, whereas the clinic based schedule specified 24 physical therapy visits during those 6 months. All patients entered in the study met strict selection criteria: age older than 15 years, no previous ligament repair or reconstruction, no complicating medical conditions, no collegiate or professional athletes, reconstruction at least 6 weeks after injury, and informed consent. At the 6-month followup, no significant statistical differences were found between the two groups in range of motion, thigh atrophy, anterior drawer compliance, hopping tests, Lysholm scores, or subjective health status scores. Thus, the authors conclude that in a selected group of patients who have undergone anterior cruciate ligament reconstruction, a home based postoperative rehabilitation program is feasible, safe, and effective.

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.

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.

Occult osseous lesions associated with anterior cruciate ligament tears.

Occult osseous lesions occurring with anterior cruciate ligament tears have been described only recently. Twenty patients with complete anterior cruciate ligament disruptions and evidence of occult osseous lesions on their preoperative magnetic resonance (MR) images were evaluated retrospectively at 24- to 73-months' followup to document the natural history and long-term effects of the lesions. Thirty-seven initial osseous signal abnormalities were documented on the MR images of 20 patients. All 20 patients had lesions in the posterolateral tibial plateau, and 13 had additional lesions in the lateral femoral condyle. Twenty-four of the 37 osseous lesions appeared resolved on followup MR images, and 13 had become sclerotic. Lesions of the lateral tibial plateau were especially likely to be sclerotic at followup. This study reaffirms the specificity of bone signal abnormalities of the posterolateral tibial plateau and lateral femoral condyle in association with complete anterior cruciate ligament tears. The data indicate that a proportion of anterior cruciate ligament patients will incur progressive articular cartilage abnormalities, although case-by-case predictions based on initial MR images would be unreliable.

Arthroscopic posteromedial visualization of the knee.

Arthroscopic visualization of the posteromedial compartment of the knee via an anterolateral portal is not commonly practiced, yet it is relatively simple, has low morbidity, and is of diagnostic and therapeutic value. This prospective study evaluates posteromedial visualization of the knee joint in a series of 117 consecutive patients who underwent arthroscopy for diagnosis or treatment, or both, of 209 pathologic conditions. The technique was deemed simple to perform in 78% of patients. It was found to be more difficult in knees with degenerative joint disease. Posteromedial visualization was found to be essential for diagnosis or treatment in 4% of the diagnosed conditions, and helpful in an additional 13%. The technique was most useful for tears of the posterior horn of the medial meniscus, some of which were not detected by visualization from the anteromedial compartment alone. Visualization of the posteromedial compartment was deemed adequate in 89% of the patients, and there was no morbidity.

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.

MRI findings of acute turf toe. A case report and review of anatomy.

Normal anatomy of the metatarsophalangeal joint of the hallux has been well described. However, the pathologic anatomy of turf toe, a common injury among football and rugby players, has not been documented in detail. Magnetic resonance images (MRI) of a classic case of turf toe were examined and the findings were compared with MRI of a normal specimen and correlated with known features of gross anatomy. MRI findings confirmed that turf toe involves a sprain or tear of the plantar metatarsophalangeal joint capsule.