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  • 1
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5910-5915 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The surface layer of crystalline silicon implanted with 1.5 MeV Si ions with doses ranging from 1×1011 to 1×1015 Si+/cm2 has been studied by Raman scattering. Raman line intensities, shapes and shifts have been used to investigate the defects in the near-surface layer. Above doses of 1×1013 Si+/cm2, Raman provides evidence for the presence of amorphous silicon islands within the crystalline structure. The phonon-confinement model (PCM) which is based on the breakdown in wavevector selection rules due to scattering from finite domain sizes has been used to estimate the effective average distance between defects. The PCM has also been modified by introducing a term attributable to residual stress in the near-surface layer. By fitting experimental Raman spectra with the modified PCM, the Raman line shifts due to stress effects are decoupled from those due to phonon confinement. The mechanisms for the stress creation are also discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 3228-3237 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Defect structures were investigated by transmission electron microscopy for GaN/Al2O3 (0001) epilayers grown by metal-organic chemical vapor deposition using a two-step process. The defect structures, including threading dislocations, partial dislocation bounding stacking faults, and inversion domains, were analyzed by diffraction contrast, high-resolution imaging, and convergent beam diffraction. GaN film growth was initiated at 600 °C with a nominal 20 nm nucleation layer. This was followed by high-temperature growth at 1080 °C. The near-interfacial region of the films consists of a mixture of cubic and hexagonal GaN, which is characterized by a high density of stacking faults bounded by Shockley and Frank partial dislocations. The near-interfacial region shows a high density of inversion domains. Above ∼0.5 μm thickness, the film consists of isolated threading dislocations of either pure edge, mixed, or pure screw character with a total density of ∼7×108 cm−2. The threading dislocation reduction in these films is associated with cubic to hexagonal transformation of the nucleation layer region during high temperature growth. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic domain structure and microscopic magnetization reversal processes in epitaxial Fe/GaAs(001) films with cubic anisotropy and in-plane easy axes have been investigated by a Lorentz microscope equipped with a magnetizing stage. For the films of a few hundred angstroms thickness we observe the single domain remanent state predicted for a two-dimensional film but find that domains play a crucial role in the magnetic reversal process. For reversal along the in-plane 〈110〉 directions (hard axes), magnetization reversal proceeds via a combination of coherent rotation and displacements of weakly pinned 90° domain walls at critical fields. For magnetization reversal along the in-plane 〈100〉 directions (easy axes), an irregular checkerboard domain structure develops at the critical field and both 180° and 90° domain walls coexist. The reversal of the domains with magnetization vector opposite to the applied field direction takes place by a combination of two 90° reorientations. We discuss how these processes are related to the magnetic anisotropies present in the film and the macroscopic M-H hysteresis curves.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6501-6503 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An electron-microscopy-based technique of electron-energy-loss spectroscopy (EELS) has been used to characterize electronic and magnetic properties of ultrathin Fe films grown on GaAs(100) surface, as a function of the film thickness. Large-area electron transparent membranes for microscopic analysis are prepared by ion-beam thinning or chemical etching from the substrate side, and the top surface of the ultrathin Fe film is protected by a thin Cr layer. Analysis of the Fe 2p, Cr 2p, and O 1s absorption spectra confirms that only the Cr layer is oxidized. The local magnetic moments of the ultrathin Fe films are deduced from the "white line'' branching ratio in the Fe 2p absorption spectra. For Fe films as thin as 150 A(ring), the magnetic moment is not different from that found in bulk α-Fe. For a 70-A(ring) Fe film, the local magnetic moment is enhanced although the average magnetization is reduced. As doping is suspected to be the cause for the departure from bulk α-Fe properties. In the case where the 50-A(ring) film is polycrystalline and discontinuous, spatially resolved EELS has been used to distinguish small island clusters from large crystalline particles. The large particles are α-Fe crystallites and the islands are probably also heavily affected by As doping.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 49-51 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: InAs quantum dots inserted at the middle of a GaAs quantum well structure have been investigated by transmission electron microscopy and scanning transmission electron microscopy. We find that the growth condition of the overlayer on the InAs dots can lead to drastic changes in the structure of the dots. We attribute the changes to a combination of factors such as preferential growth of the overlayer above the wetting layers because of the strained surfaces and to the thermal instability of the InAs dots at elevated temperature. The result suggests that controlled sublimation, through suitable manipulation of the overlayer growth conditions, can be an effective tool to improve the structure of the self-organized quantum dots and can help tailor their physical properties to any specific requirements of the device applications. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2468-2470 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a study of the transport properties of two-dimensional electron gases formed in GaAs/AlGaAs heterostructures in which InAs self-assembled quantum dots have been inserted in the center of a GaAs quantum well. We observed that, while maintaining a constant carrier density, the mobility increased as the InAs dot density was reduced. The ratio of the transport to the quantum lifetime was measured to be approximately five with the dominant scattering mechanism attributed to short-range scattering from the inserted InAs dots. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1520-5002
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Community dentistry and oral epidemiology 22 (1994), S. 0 
    ISSN: 1600-0528
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract – The United States and Norway have approximately the same per capita Gross Domestic Product (GDP) and average personal income, but their per capita health spending patterns are quite different. In 1982, the US spent 6.5% of its total health expenditures on dental services while Norway spent 5.4%. A higher percentage of Norwegian adults see a dentist annually as compared to US adults. In 1984, the mean net income of dentists in private practice was $66940 in the US and 27 125 in Norway; this is respectively 5 and 1 3/4 times the average per capita income in those countries. The American publicly-employed dentist earned approximately two-thirds of what the American private practitioner made, while still earning approximately 50% more than his Norwegian counterpart. Some basic information concerning the ratios of dentists, specialists, and dental hygienists to the population is given. The relative proportion of women dentists in the two countries is contrasted. Finally, data on graduates from the dental schools, enrollment cuts, and estimated dentist to population ratios by the year 2000 are described to compare future manpower that will be available to the two countries. Several dissimilarities in the political and social systems are described and discussed. It is emphasized that caution should be used when interpreting and comparing data about countries with different dental delivery, political, and social systems.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of public health dentistry 55 (1995), S. 0 
    ISSN: 1752-7325
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: This paper reviews recent changes in the epidemiology of dental caries and assesses their potential impact on the diagnosis and management of the disease and the planning and operation of sealant programs. These changes, such as the decline in caries and slowing of the rate of progression of the disease, have important implications for diagnosing and treating incipient lesions, predicting caries risk, and conducting effective disease preventive programs. Traditional paradigms for restoring carious lesions are being replaced by newer strategies that emphasize disease prevention and conservation of tooth structure. The search continues for the identification of practical models for predicting caries risk at the individual level. This paper describes a method useful for targeting resources in sealant placement programs by enabling one to determine the relative effectiveness of sealing alternative tooth surfaces in the oral cavity. One guide serves as a widely adopted manual for those who use or intend to use dental sealants in caries prevention programs. This paper provides a brief review of that document, “Preventing Pit and Fissure Caries: A Guide to Sealant Use,” as well as guidelines for sealant utilization provided by the American Dental Association, and information regarding dental sealant programs under Medicaid. The final portion of the paper provides a synthesis of the epidemiology reviewed and summarizes the implications of findings for sealant programs.
    Type of Medium: Electronic Resource
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