Temperature dependence of surface roughening during homoepitaxial growth on Cu(001)

URL:http://link.aps.org/doi/10.1103/PhysRevB.64.125427 DOI:10.1103/PhysRevB.64.125427X-ray scattering has been used to study the roughening of the Cu(001) surface during homoepitaxial growth, as a function of temperature. Between 370 and 160 K, the mean-square roughness σ2, obtained from specular reflectivity data, was found to increase as a power law σ2=Θ2β for coverages Θ, ranging from 3 to 96 ML. The roughening exponent β was observed to depend on the temperature of the substrate: it monotonically increases with decreasing temperature from β≈1/3 at T=370K to β≈1/2, at T=200K. At 110 K a smoother growth re-enters in the presence of a large vacancy concentration in the deposited film.Support is acknowledged from the National Science Foundation under contracts ~P.W.S.! DMR-9202528 and~P.F.M. and C.E.B.! DMR-9623827 and the Midwest Superconductivity Consortium ~MISCON! under DOE Grant No. DH-FG02-90ER45427. The SUNY X3 beamline was supported by the DOE, under Contract No. DE-FG02-86ER45231, and the NSLS was supported by the DOE, Division of Material Sciences, and Division of Chemical Sciences. We thank Ian Robinson for the Cu crystal and for valuable discussions

Temperature-dependent vacancy formation during the growth of Cu on Cu(001)

URL:http://link.aps.org/doi/10.1103/PhysRevB.66.195413 DOI:10.1103/PhysRevB.66.195413X-ray diffraction measurements show that a large number of vacancies are incorporated in thin Cu films grown on Cu(001) at low temperatures. At any given deposition temperature between 110 and 160 K, the vacancy concentration cv, obtained from reflectivity data, does not change with the coverage Θ, for 2.5ML<~Θ<~20ML. However, cv is temperature dependent: for 15-ML-thick films, grown at different temperatures, it monotonically decreases with increasing T from cv≈2% at 110 K to zero at T=160K. A different “cv vs T” dependence is observed for films grown at 110 K and then annealed at progressively higher temperatures. Here cv≈2% persists over a broad temperature interval (between 110 and 200 K) and cv exhibits a slower decrease upon heating, reaching zero at 300 K.Support is acknowledged from the National Science Foundation under Contract Nos. ~P.W.S.! DMR-9202528 and ~P.F.M., C.E.B.! DMR-9623827 and the Midwest Superconductivity Consortium ~MISCON! under DOE Grant No. DEFG02-90ER45427. The SUNY X3 beamline is supported by the DOE, under Contract No. DE-FG02-86ER45231 and the NSLS is supported by the DOE, Division of Material Sciences and Division of Chemical Sciences

Vacancy formation in homoepitaxially grown Ag films and its effect on surface morphology

URL:http://link.aps.org/doi/10.1103/PhysRevB.66.075418 DOI:10.1103/PhysRevB.66.075418Synchrotron x-ray diffraction was used to investigate the low-temperature homoepitaxial growth on Ag(001) and Ag(111) surfaces. For both orientations, the Ag films deposited at T=100K were observed to exhibit a 1% surface-normal compressive strain, indicating that an appreciable vacancy concentration (∼2%) is incorporated in the growing film. Concomitantly with the incorporation of vacancies, the growth on Ag(111) leads to the formation of pyramidlike structures with a non-Gaussian distribution of heights, whereas a similar effect was not observed for Ag(001).Support is acknowledged from the National Science Foundation under Contract ~P.W.S.! No. DMR-9202528 and ~P.F.M., C.E.B., W.C.E.! No. DMR-9623827 and the Midwest Superconductivity Consortium ~MISCON! under DOE Grant No. DE-FG02-90ER45427. The SUNY X3 beam line is supported by the DOE, under Contract No. DE-FG02-86ER45231, and the NSLS is supported by the DOE, Division of Material Sciences and Division of Chemical Sciences

Thermal expansion of the Ag(111) surface measured by x-ray scattering

URL:http://link.aps.org/doi/10.1103/PhysRevB.63.113404 DOI:10.1103/PhysRevB.63.113404We have investigated the structure of the Ag(111) surface, for temperatures between 300 and 1100 K (90% of the bulk melting point), using synchrotron x-ray diffraction. Our data show no evidence of the anomalously large surface thermal expansion previously reported by medium-energy ion-scattering [Phys. Rev. Lett. 72, 3574 (1994)]. At all temperatures we find that the interlayer separations at the surface differ from their bulk counterparts by less than 1%, indicating that the surface expands similarly to the underlying bulk crystal. This behavior is in good agreement with results from molecular dynamics simulations.Support is acknowledged from the National Science Foundation under Contract Nos. ~PWS! DMR-9202528 and ~PFM, CEB, WCE! DMR-9623827 and the Midwest Superconductivity Consortium ~MISCON! under DOE Grant No. DE-FG02-90ER45427. The SUNY X3 beam line is supported by the DOE, under Contract No. DE-FG02-86ER45231, and the NSLS was supported by the DOE, Division of Material Sciences and Division of Chemical Sciences

Vacancy trapping and annealing in noble-metal films grown at low temperature

doi:10.1063/1.1527988We have used synchrotron x-ray diffraction to study the homoepitaxial growth on Cu(001), Ag(001), and Ag(111), at temperatures between 300 and 65 K. The growth on all of these surfaces exhibits a consistent trend towards a large compressive strain that is attributed to the incorporation of vacancies into the growing film below 160 K. In each case, the vacancy concentration is ∼ 2% at 110 K and we have measured the temperature dependence for incorporation on the (001) surfaces as well as the annealing behavior for Cu(001). These results, which suggest new kinetic mechanisms, have important implications for understanding epitaxial crystal growth.Support is acknowledged from the NSF under Contract Nos. ~P.W.S! DMR-9202528 and ~P.F.M!, ~C.E.B! DMR-9623827, MISCON under DOE Grant No. DE-FG02-90ER45427, and the University of Missouri Research Board. The SUNY X3 beam line is supported by the DOE, under Contract No. DE-FG02-86ER45231 and the NSLS is supported by the DOE, Division of Material Sciences and Division of Chemical Sciences. The Advanced Photon Source is supported by DOE Contract No. W-31-109-Eng-38, and the mCAT beam line is supported through the Ames Laboratory Contract No. DOE W-7405-Eng-82

Aging-related tau astrogliopathy (ARTAG):harmonized evaluation strategy

Pathological accumulation of abnormally phosphorylated tau protein in astrocytes is a frequent, but poorly characterized feature of the aging brain. Its etiology is uncertain, but its presence is sufficiently ubiquitous to merit further characterization and classification, which may stimulate clinicopathological studies and research into its pathobiology. This paper aims to harmonize evaluation and nomenclature of aging-related tau astrogliopathy (ARTAG), a term that refers to a morphological spectrum of astroglial pathology detected by tau immunohistochemistry, especially with phosphorylation-dependent and 4R isoform-specific antibodies. ARTAG occurs mainly, but not exclusively, in individuals over 60 years of age. Tau-immunoreactive astrocytes in ARTAG include thorn-shaped astrocytes at the glia limitans and in white matter, as well as solitary or clustered astrocytes with perinuclear cytoplasmic tau immunoreactivity that extends into the astroglial processes as fine fibrillar or granular immunopositivity, typically in gray matter. Various forms of ARTAG may coexist in the same brain and might reflect different pathogenic processes. Based on morphology and anatomical distribution, ARTAG can be distinguished from primary tauopathies, but may be concurrent with primary tauopathies or other disorders. We recommend four steps for evaluation of ARTAG: (1) identification of five types based on the location of either morphologies of tau astrogliopathy: subpial, subependymal, perivascular, white matter, gray matter; (2) documentation of the regional involvement: medial temporal lobe, lobar (frontal, parietal, occipital, lateral temporal), subcortical, brainstem; (3) documentation of the severity of tau astrogliopathy; and (4) description of subregional involvement. Some types of ARTAG may underlie neurological symptoms; however, the clinical significance of ARTAG is currently uncertain and awaits further studies. The goal of this proposal is to raise awareness of astroglial tau pathology in the aged brain, facilitating communication among neuropathologists and researchers, and informing interpretation of clinical biomarkers and imaging studies that focus on tau-related indicators

Concurrent Alzheimer's disease-related pathology lowers the threshold for developing dementia in argyrophilic grain disease

Background: Argyrophilic grain disease (AGD) constitutes a neurodegenerative disorder that occurs in the brains of the elderly and affects 5% of all patients with dementia, tan-protein-containing lesions known as argyrophilic grains in neuronal processes and coiled bodies in oligodendrocytes characterize this disease. Dementia is encountered in only a subset of cases that display the morphological pattern of AGD at autopsy. Objective: To determine the role of concurrent Alzheimer's disease (AD)-related pathology for the development of dementia in AGD patients. Methods: Autopsy brains from 30 demented and 49 non-demented AGD patients, from 46 AD patients and from 86 non-demented controls without AGD were staged for the distribution of AD-related neurofibrillary changes and amyloid 13-protein (AI3) deposits. To identify differences in the distribution of AD-related pathology between demented and non-demented AGD cases, and to differentiate the pattern of AD-related changes in AGD cases from that seen in AD and non-demented controls, we compared the distribution of AI3-deposits and neurofibrillary changes among these groups of cases. Differences in the stages of the distribution of neurofibrillary changes and A[3-deposits among these groups were analyzed statistically. Conclusions: Demented AGD patients exhibited significantly higher stages of AD-related AI3-deposition and neurnfibrillary tangle pathology as compared to non-demented AGD cases, but significantly lower stages of both lesions compared to AD without AGD. In conclusion, AGD is a clinically relevant neurodegenerative entity that significantly lowers the threshold for developing dementia when it is associated with AD-related pathology