Performance with various diffraction gratings:

Outline Drawing

Select Publications

Laboratory precision measurements of optical emissions from coronal iron

Abstract: Total solar eclipses, as the recent one seen across North America, are rare opportunities for optical spectroscopy of the corona. In view of the dearth of accurate rest-frame wavelength data, we measured 11 of the strongest optical coronal lines belonging to Fe X-XIV thereby proving the existence of the Fe XII line at 290.385(8) nm. Four lines, such as the green coronal line at 530.28113(13) nm, were measured with unprecedented precision, allowing in principle for absolute velocity determinations of plasmas with uncertainties of 0.08 km s−1. These results furthermore stringently benchmark the theory of complex open-3p-shell ions.

H. Bekker, C. Hensel, A. Daniel, A. Windberger, T. Pfeifer, and J. R. Crespo López-Urrutia

Contactless monitoring of Ge content and B concentration in ultrathin single and double layer Si1-xGex epitaxial films using multiwavelength micro-Raman spectroscopy

Abstract: Non-contact monitoring of Ge content and B concentration in single and double Si1-xGex epitaxial layers on Si(100) device wafers was attempted using high-resolution, multiwavelength micro-Raman spectroscopy. The Ge content and B concentration determined by secondary ion mass spectroscopy (SIMS) depth profiling showed very strong correlation with the position and full-width-at-half-maximum of the Si-Si peak from the Si1-xGex epitaxial layers as determined by Raman measurements. High resolution X-ray diffraction (HRXRD) characterization was done for all wafers to determine Ge and B sensitivity and form comparisons with Raman and SIMS analysis. The non-destructive, in-line monitoring of Ge content and B concentration of single and double Si1-xGex epitaxial layers with thickness ranging from 5 ~ 120 nm, on small area monitoring pads, was successfully demonstrated by multiwavelength micro-Raman spectroscopy during epitaxial process optimization, material property verification, and quality control applications.

Chun-Wei Chang, Min-Hao Hong, Wei-Fan Lee, Kuan-Ching Lee, Shiu-Ko Jang Jian, Yen Chuang, Yu-Ta Fan, Noriyuki Hasuike, Hiroshi Harima, Takeshi Ueda, Toshikazu Ishigaki, Kitaek Kang, and Woo Sik Yoo

Stress Characterization of Tungsten-Filled Through Silicon via Arrays Using Very High Resolution Multi-Wavelength Raman Spectroscopy

Abstract: Stress in Si adjacent to W-filled TSVs has been measured by multiwavelength Raman spectroscopy (probe depth ranging from 290 to 645 nm) and compared to finite element modeling. The stress in Si from the TSVs increases with TSV width and is almost constant at the different depths probed in this study. The Raman signal is mainly due to the sum of the Sx and Sy stress components, perpendicular and parallel to the TSV bars. The Sx component is tensile and the Sy component is compressive, with the Sy component dominant in between the TSVs. However, ~10 um from the edge of the TSV array, the two components are equal in magnitude so that the stress measured by Raman is zero, even though the individual Sx and Sy stresses are considerable. Hence, it is important to use finite element modeling in conjunction with Raman spectroscopy to characterize stresses in TSVs.

Jeff Gambino, Daniel Vanslette, Bucknell Webb, Cameron Luce, Takeshi Ueda, Toshikazu Ishigaki, Kitaek Kang, and Woo Sik Yoo

Stress evolution in surrounding silicon of Cu-filled through-silicon via undergoing thermal annealing by multiwavelength micro-Raman spectroscopy

Abstract: Three-dimensional stress development was observed in silicon surrounding the Cu-filled through-silicon via (TSV) structures undergoing the thermal annealing process. We show here, using a multiwavelength micro-Raman spectroscopy system, that the behavior of stress development in silicon after annealing step is dependent on the initial stress state as well as the geometry and directionality of the TSV array. The warping of stress curve for postannealed state with a reference of preannealed state is distinctively observed. Furthermore, the introduction of stress-free point is also attributed to the destructive stress interaction from different geometry and direction and initial stress state.

W. S. Kwon, D. T. Alastair, K. H. Teo, S. Gao, T. Ueda, T. Ishigaki, K. T. Kang, and W. S. Yoo

Pu-239/Pu-240 isotope emission spectroscopy in a laser-induced plasma

Abstract: Laser-induced breakdown spectroscopy (LIBS) has been applied for the determination of plutonium isotope ratios through direct observation of atomic emission from laser-induced plasmas at high resolution. The Pu-239/Pu-240 isotope shift of -0.355 cm-1 from the plutonium atomic line at 594.52202 nm (Blaise et al., The Atomic Spectrum of Plutonium, Argonne National Laboratory Report ANL-83-95, 1984) is clearly resolved in our plasma conditions. Atomic emission is dispersed through a 2-m spectrometer in double pass mode and collected on an electronically gated, intensified charge-coupled device (ICCD) camera. The integrated peak areas obtained from curve-fitting closely match the Pu-239/Pu-240 isotopic ratios obtained from standard methods of thermal ionization mass spectrometry and gamma spectrometry. The observed plutonium linewidths were 0.19 cm-1 (0.0067 nm). These linewidths are within the experimental error of the ideal instrument-limited linewidth, which is calculated to be 0.15 cm-1 (0.0052 nm) based upon the known modulation transfer function for the ICCD system. This linewidth should allow LIBS to be applicable for isotopic ratio measurements for all of the light actinides.

Coleman A. Smitha,, Max A. Martinezb, D.Kirk Veirsb and David A. Cremersc

Improvements in the determination of ISS Ca II K parameters

Abstract: Measurements of the ionized Ca II K line are one of the major resources for long-term studies of solar and stellar activity. They also play a critical role in many studies related to solar irradiance variability, particularly as a ground-based proxy to model the solar ultraviolet flux variation that may influence the Earth's climate. Full disk images of the Sun in Ca II K have been available from various observatories for more than 100 years and latter synoptic Sun-as-a-star observations in Ca II K began in the early 1970s. One of these instruments, the Integrated Sunlight Spectrometer (ISS) has been in operation at Kitt Peak (Arizona) since late 2006. The ISS takes daily observations of solar spectra in nine spectra bands, including the Ca II K and H line s. We describe recent improvements in data reduction of Ca II K observations, and present time variations of nine parameters derived from the profile of this spectral line

Luca Bertello, Alexei A. Pevtsov, Jack W. Harvey, Roberta M. Toussaint

SOLIS - A Modern Facility for Synoptic Solar Observations

Abstract: SOLIS (Synoptic Optical Long-term Investigations of the Sun) is a proposed suite of instruments that will modernize and greatly improve synoptic solar observations carried out by the National Solar Observatory on behalf the solar and solar-terrestrial physics communities. The primary scientific goal is to provide fundamental data necessary to understand the solar activity cycle, sudden energy releases in the solar atmosphere, and solar spectral irradiance changes. An operational goal is to produce real-time and near real-time data for forecasting space weather, and to augment the scientific yield from space mission such as SOHO and TRACE, and ground-based projects including RISE and GONG. State-of-the-art instrumentation and data collection techniques will be employed to enhance both the quality and quantity of data. A high degree of automation and remote control will provide faster user access to data and flexible interaction with the data-collection process. The instruments include a vector spectromagnetograph that will measure the magnetic field strength and direction over the full solar disk in 15 minutes, a full disk patrol delivering digital images in various spectral lines at a high cadence, a coronal emission line imager and photometer that will provide photometric and velocity images in at least five spectral lines, and a Sun-as-a-star precision spectrometer to measure changes in many spectral lines. The choice of sites for the instruments depends on potential partnerships with other observatories and the level of funding that can be obtained. The goal is to place the instruments at sites with large amounts of sunshine and coronal observing conditions as appropriate. The SOLIS proposal is currently under review by the National Science Foundation. 

Harvey, J.; Keller, C.; November, L.; NSO Staff

Aberration-corrected echelle spectrometer for measuring ultraviolet branching fractions of iron-group ions

Abstract: [Uses a three meter focal length Czerny Turner monochromator originally designed for VUV region] A high-resolution echelle spectrometer with broad wavelength coverage from the UV to the IR and high sensitivity to weak lines is described. Total instrument astigmatism is suppressed through rotation of the order separation system into an orthogonal plane. A suitable choice of mirror angles avoids increased coma. This spectrometer is used to record UV through IR spectra of Fe-group ions to measure improved branching fractions. These new results reduce transition probability uncertainties and yield more accurate derived stellar abundances. Instrument design and performance, including aberration compensation, are presented. 

Michael P. Wood and James E. Lawler

Luminescence signature of free exciton dissociation and liberated electron transfer across the junction of graphene/GaN hybrid structure

Abstract: [Large-area graphene grown on Cu foil with chemical vapor deposition was transferred onto intentionally undoped GaN epilayer to form a graphene/GaN Schottky junction. Optical spectroscopic techniques including steady-state and time-resolved photoluminescence (PL) were employed to investigate the electron transfer between graphene and n-type GaN at different temperatures. By comparing the near-band-edge excitonic emissions before and after the graphene covering, some structures in the excitonic PL spectra are found to show interesting changes. In particular, a distinct “dip” structure is found to develop at the center of the free exciton emission peak as the temperature goes up. A mechanism that the first dissociation of some freely moveable excitons at the interface was followed by transfer of liberated electrons over the junction barrier is proposed to interpret the appearance and development of the “dip” structure. The formation and evolution process of this “dip” structure can be well resolved from the measured time-resolved PL spectra. First-principles simulations provide clear evidence of finite electron transfer at the interface between graphene and GaN

Jun Wang, Changcheng Zheng, Jiqiang Ning, Lixia Zhang, Wei Li, Zhenhua Ni, Yan Chen, Jiannong Wang, Shijie Xu