Progress in spectroscopic ellipsometry: Applications from vacuum ultraviolet to infrared

Spectroscopic ellipsometry (SE) is a noncontact and nondestructive optical technique for thin film characterization. In the past 10 yr, it has migrated from the research laboratory into the semiconductor, data storage, display, communication, and optical coating industries. The wide acceptance of SE is a result of its flexibility to measure most material types: dielectrics, semiconductors, metals, superconductors, polymers, biological coatings, and even multilayers of these materials. Measurement of anisotropic materials has also made huge strides in recent years. Traditional SE measurements cover the ultraviolet, visible, and near infrared wavelengths. This spectral range is now acquired within seconds with high accuracy due to innovative optical configurations and charge coupled device detection. In addition, commercial SE has expanded into both the vacuum ultraviolet (VUV) and midinfrared (IR). This wide spectral coverage was achieved by utilizing new optical elements and detection systems, along with UV or Fourier transform IR light sources. Modern instrumentation is now available with unprecedented flexibility promoting a new range of possible applications. For example, the VUV spectral region is capable of characterizing lithographic materials for 157 nm photolithography. The VUV also provides increased sensitivity for thin layers (e.g., gate oxides or self-assembled monolayers) and allows investigation of high-energy electronic transitions. The infrared spectral region contains information about semiconductor doping concentration, phonon absorption, and molecular bond vibrational absorptions. In this work, we review the latest progress in SE wavelength coverage. Areas of significant application in both research and industrial fields will be surveyed, with emphasis on wavelength-specific information content

Doubts about How the Middle Horizon Collapsed (ca. A.D. 1000) and Other Insights from the Looted Cemeteries of the Lower Ica Valley, South Coast of Peru

This paper presents new information from funerary contexts in the lower Ica Valley, south coast of Peru, spanning two millennia from the end of the Early Horizon to the Late Intermediate Period. Although severely looted, these sites can still yield valuable information. We discuss their architecture and material culture in the context of radiocarbon dates. Among other findings, these cast new light on the poorly understood transition from the Middle Horizon to the Late Intermediate Period, for which a paucity of archaeological data from c. A.D. 1000 to 1250 has long been taken as evidence of an environmentally or socially-induced demographic collapse. Yet the data we present here suggests that the basins of the lower Ica Valley were likely occupied continuously over this period, and that the echoes of Wari influence here may have lasted longer than previously thought.We thank the Ministerio de Cultural del Perú for granting permission for the fieldwork (No. 0028-2010-VMPCIC-MC) and analysis of samples for dating (No. 369-2011-VMPCIC-MC); Alberto Benavides Ganoza and the people of Samaca for facilitating fieldwork, all participants of the Proyecto de investigación arqueológica Samaca and Viviana Siveroni and Ruben Garcia for their useful thoughts and suggestions. This work was funded by the Arts and Humanities Research Council