Uwe Arp

SURF III - an improved storage ring for radiometry

The National Institute of Standards and Technology (NIST) operates the newly upgraded Synchrotron Ultraviolet Radiation Facility (SURF III) mainly as a light source for radiometry. SURF III provides continuum radiation from the far-infrared to the soft X-ray spectral range and has its peak output in the extreme ultraviolet. SURF III is a circular-orbit, weak-focusing (single dipole magnet) storage ring, a feature which is advantageous if the synchrotron radiation output is calculated. We report the improvements achieved during a recent upgrade from SURF II to SURF III and our strategy to accurately determine the magnetic flux density, radio frequency (RF), beam current, and beam size, which are the parameters necessary to characterize the source completely.

Ultraviolet radiometry with synchrotron radiation and cryogenic radiometry

The combination of a cryogenic radiometer and synchrotron radiation enables detector scale realization in spectral regions that are otherwise difficult to access. Cryogenic radiometry is the most accurate primary detector-based standard available to date, and synchrotron radiation gives a unique broadband and continuous spectrum that extends from x ray to far IR. We describe a new cryogenic radiometer-based UV radiometry facility at the Synchrotron Ultraviolet Radiation Facility II at the National Institute of Standards and Technology. The facility is designed to perform a variety of detector and optical materials characterizations. The facility combines a high-throughput, normal incidence monochromator with an absolute cryogenic radiometer optimized for UV measurements to provide absolute radiometric measurements in the spectral range from 125 nm to approximately 320 nm. We discuss results on photodetector characterizations, including absolute spectroradiometric calibration, spatial responsivity mapping, spectroreflectance, and internal quantum efficiency. In addition, such characterizations are used to study UV radiation damage in photodetectors that can shed light on the mechanism of the damage process. Examples are also given for UV optical materials characterization.

Uniform and enhanced field emission from chromium oxide coated carbon nanosheets

Carbon nanosheets, a two-dimensional carbon nanostructure, are promising electron cathode materials for applications in vacuum microelectronic devices. This letter demonstrates a simple approach to improve the spatial emission uniformity of carbon nanosheets by coating them with a chromium oxide thin film. Photoelectron emission microscopy observations and in situ field emission tests revealed that chromium oxide coated carbon nanosheets not only have spatial uniformity but also have coating thickness dependent field emission properties. For example, a coating thickness of ∼1.5nm gave a substantially greater field emission than as-grown nanosheets or other thickness coatings.

Absolute pulse energy measurements of soft x-rays at the Linac Coherent Light Source

This paper reports novel measurements of x-ray optical radiation on an absolute scale from the intense and ultra-short radiation generated in the soft x-ray regime of a free electron laser. We give a brief description of the detection principle for radiation measurements which was specifically adapted for this photon energy range. We present data characterizing the soft x-ray instrument at the Linac Coherent Light Source (LCLS) with respect to the radiant power output and transmission by using an absolute detector temporarily placed at the downstream end of the instrument. This provides an estimation of the reflectivity of all x-ray optical elements in the beamline and provides the absolute photon number per bandwidth per pulse. This parameter is important for many experiments that need to understand the trade-offs between high energy resolution and high flux, such as experiments focused on studying materials via resonant processes. Furthermore, the results are compared with the LCLS diagnostic gas detectors to test the limits of linearity, and observations are reported on radiation contamination from spontaneous undulator radiation and higher harmonic content.

Tomography of integrated circuit interconnect with an electromigration void

An integrated circuit interconnect was subject to accelerated-life test conditions to induce an electromigration void. The silicon substrate was removed, leaving only the interconnect test structure encased in silica. We imaged the sample with 1750 eV photons using the 2-ID-B scanning transmission x-ray microscope at the Advanced Photon Source, a third-generation synchrotron facility. Fourteen views through the sample were obtained over a 170° range of angles (with a 40° gap) about a single rotation axis. Two sampled regions were selected for three-dimensional reconstruction: one of the ragged end of a wire depleted by the void, the other of the adjacent interlevel connection (or “via”). We applied two reconstruction techniques: the simultaneous iterative reconstruction technique and a Bayesian reconstruction technique, the generalized Gaussian Markov random field method. The stated uncertainties are total, with one standard deviation, which resolved the sample to 200±70 and 140±30 nm, respectively. The t...

Synchrotron radiation-based irradiance calibration from 200 to 400 nm at the Synchrotron Ultraviolet Radiation Facility III

A new facility for measuring irradiance in the UV was commissioned recently at the National Institute of Standards and Technology (NIST). The facility uses the calculable radiation from the Synchrotron Ultraviolet Radiation Facility as the primary standard. To measure the irradiance from a source under test, an integrating sphere spectrometer-detector system measures both the source under test and the synchrotron radiation sequentially, and the irradiance from the source under test can be determined. In particular, we discuss the calibration of deuterium lamps using this facility from 200 to 400 nm. This facility improves the current NIST UV irradiance scale to a relative measurement uncertainty of 1.2% (k=2).

Characterization of the response of chromium-doped alumina screens in the vacuum ultraviolet using synchrotron radiation

We have measured the response of chromium-doped alumina screens to vacuum ultraviolet radiation and derived quantum efficiency curves for the energy range from 30 to 300 eV. A model is presented to explain the structure in this curve. In addition, the radiation hardness of such screens, which have found application as narrow-band radiation detectors for a hot fusion plasma diagnostic, is reported here for MeV electrons. Finally, a simple model is constructed to obtain the carrier diffusion length and the bulk efficiency of this material.

New ultraviolet radiometry beamline at the Synchrotron Ultraviolet Radiation Facility at NIST

We have constructed a new ultraviolet (UV) radiometry facility at the Synchrotron Ultraviolet Radiation Facility (SURF II) at the National Institute of Standards and Technology (NIST). The facility combines a high-throughput normal-incidence monochromator with an absolute cryogenic radiometer (ACR) optimized for UV measurements to provide absolute detector-based radiometric calibrations in the spectral range 125 nm to approximately 320 nm. The system can be configured for spectroradiometric calibration of photodetectors with completely automated mapping of detector spatial and angular responsivity. The facility can easily be adapted for other spectroradiometric measurements including transmittance and reflectance and the spectral range can be extended to about 50 nm.

Total photoion yield of atomic chromium at the 2p threshold

The total photoion yield spectrum of atomic chromium has been determined in the range of the 2p thresholds. The experimental data are compared to Hartree-Fock calculations, which include the interaction between three configurations, and to a previously published electron energy loss spectrum of solid chromium.

Ultraviolet characterization of integrating spheres

We have studied the performance of polytetrafluoroethylene integrating spheres in the ultraviolet (UV) region with wavelengths as short as 200 nm. Two techniques were used for this study; first, the spectral throughput of an integrating sphere irradiated by a deuterium lamp was analyzed by a monochromator. Second, a UV laser beam was directed into an integrating sphere, and spectrally dispersed laser induced fluorescence was studied. Significant absorption and fluorescence features were observed in the UV region and attributed to the contamination in the integrating sphere. We demonstrate that integrating spheres are easily contaminated by environmental pollutants such as polycyclic aromatic hydrocarbons emitted from engine exhaust. Baking of the contaminated integrating sphere can reverse some but not all of the effects caused by contaminants. The implications for using integrating spheres for UV measurement are discussed.