J. F. MacKay

Comparison of surface roughness of polished silicon wafers measured by light scattering topography, soft‐x‐ray scattering, and atomic‐force microscopy

The surface roughness of silicon wafers after different stages of chemomechanical polishing was investigated by light scattering topography, soft‐x‐ray scattering, and atomic‐force microscopy. Quantitative values of the rms roughness, the lateral correlation length, and the roughness exponent are extracted. The results suggest deviations from the ‘‘ideal’’ polishing process at large length scales.

Synchrotron-Produced Ultrasoft X Rays: Equivalent Cell Survival at the Isoattenuating Energies 273 eV and 860 eV

In this paper we report on survival of Chinese hamster V79 and mouse C3H 10T1/2 cells after irradiation with synchrotron-produced 273 eV and 860 eV ultrasoft X rays. These two energies, which are available by multilayer monochromatization of the synchrotron output spectrum, exhibit equal attenuation within living cells. Such an isoattenuating energy pair allows the direct examination of how biological effectiveness varies with the energy of the ultrasoft X rays. In comparing survival results, we find similar biological effectiveness of these two energies for both the C3H 10T1/2 and the V79 cells. These results are not consistent with previous findings of increasing RBE with decreasing ultrasoft X-ray energies. In addition, after correcting for mean nuclear dose based on measurements of cell thickness obtained with confocal microscopy, we find no significant differences in survival between the two ultrasoft X-ray energies and 250 kVp X rays. These results suggest that RBE does not increase with decreasing energy of ultrasoft X rays between 860 eV and 273 eV. The possible impact of our results on past results for ultrasoft X rays is discussed.

Determination of interfacial roughness correlation in W/C multilayer films: Comparison using soft and hard x‐ray diffraction

Interfacial roughness correlation in W/C multilayer films with periods of 23, 30, and 37 A is examined with x‐ray diffraction using λ in the 10–13 A range and λ=1.54 A. Transverse scans through multilayer Bragg reflections are analyzed to determine the magnitude and lateral correlation length of the component of interfacial roughness that is perfectly correlated through the multilayer stack. The results are independent of wavelength, even though hard x rays sample much more deeply into the film, indicating that interfacial roughness is not changing through these films.

A comparison of cytotoxicity after whole- or partial-cell irradiation with synchrotron-produced ultrasoft X rays.

We introduce a method which allows partial-volume irradiation of live cells using synchrotron-produced ultrasoft X rays and micro-fabricated irradiation masks. The masks were made by X-ray lithography at the University of Wisconsin Synchrotron Radiation Center, and they consist of 1.85-microm-wide stripes of gold 1.35 microm apart plated onto thin silicon nitride membranes. When placed adjacent to Mylar on which live cells are plated, these masks allow cells to be irradiated in a striped pattern with dimensions much smaller than the cell nuclei. Using 1340 eV synchrotron-produced X rays, we compare the survival of cells subjected to uniform irradiation and cells subjected to partial-volume irradiation. Our results show that, at equal mean dose to the nucleus (i.e. equal total energies deposited), survival is not statistically different for the two treatments over a wide range of doses. Thus imparting equal energies to smaller intranuclear volumes does not appear to enhance cell killing.

A double mirror W/C multilayer monochromator for radiation biology applications

A double-mirror multilayer monochromator was developed for the purpose of irradiating live cell cultures at the Synchrotron Radiation Center, University of Wisconsin-Madison. The monochromator is designed for the soft x-ray region with photon energies between 270 and 2400 eV. Multilayer mirrors with 55 bilayers of W/C and a bilayer spacing of d = 3.0 nm are sputter deposited on Si substrates. By proper masking of the sputtering sources, variation in the bilayer spacing over the area of the mirror is minimized. The uniformity of the bilayer spacing was measured to be delta d/d < 1%, over the 75 mm x 25 mm area of the mirrors. The reflectivity was measured as a function of energy to determine the integrated reflectivity and evaluate the contribution of the specular reflection and higher orders to the monochromatic beam. The use of suitable filters with a Si(Li) detector allows determination of the spectral output of the monochromator. The output power of the monochromator between 270 and 2400 eV is measured. The resolution of the monochromator is delta lambda/lambda = 0.04. Applications of the monochromator to radiation biology are discussed.

Direct observation of interface roughness dependence of interfacial magnetism using diffuse x-ray resonant magnetic scattering (abstract)

Interfacial roughness plays an important role in the magnetoresistance of magnetic multilayers, yet the relationship between roughness and the magnetic properties at interfaces is not well understood. In recent years, x-ray resonant magnetic scattering (XRMS) has been developed to investigate the interaction of polarized x rays and magnetic materials. By combining XRMS in azimuthal transverse scans, the diffuse intensity scattered from the roughness of the boundary between magnetic and nonmagnetic layers can be probed to yield information on the relationship between magnetism and interfacial roughness that cannot be obtained by any other method. Using synchrotron produced circularly polarized x rays tuned to the L2 edge of Co, x-ray diffuse intensity scans for a fixed angle of incidence are made for sputter deposited Co films and Co/Cu/Co sandwiches. For smooth films, the ratio of the XRMS diffuse intensity to the XRMS specular intensity is smaller than the ratio of the average specular intensity to the a...

Response of calcium fluoride to 275–2550 eV photons

Abstract CaF2:Dy (TLD-200) chips were irradiated with monoenergetic photon beams of synchroton radiation of 275, 400, 500, 600, 730, 900, 1200, 1500 and 2550 eV energy. The phosphor response as a function of total energy delivered is reported. Glow curves for He- and air-annealed dosimeters are presented, showing the adverse effect of air anneal. Supralinearity factors based on the integrated TL response and on the height of the 200°C peak were determined and are reported.

Connection between Structure and Electronic Properties in Epitaxial Magnetic Layers

This study explores the consequences of structure on the electronic properties of magnetic multilayers. Epitaxial layers of Co and Cu are grown on Cu(100) in a new deposition system that couples sputter-deposition with MBE and contains a wide range of characterization tools, including RHEED, LEED, and Kerr effect. This system can be coupled in situ to spin-polarized, angle-resolved photoemission and to resonant, magnetic X-ray scattering, both employing synchrotron radiation. The interface structure turns out to be critical in determining the coercivity and the presence of quantum well states, which determine oscillatory magnetic coupling.

Determination of interfacial roughness correlation in W/C multilayer films: comparison using soft and hard x-ray diffraction

Interfacial roughness correlation in W/C multilayer films with periods of 23 angstroms, 30 angstroms, and 37 angstroms is examined with x-ray diffraction using (lambda) in the 10 angstroms to 13 angstroms range and (lambda) equals 1.54 angstroms. Transverse scans through multilayer Bragg reflections are analyzed to determine the magnitude and lateral correlation length of the component of interfacial roughness that is perfectly correlated through the multilayer stack. The results are independent of wavelength, even though hard x rays sample match more deeply into the film, indicating that interfacial roughness is not changing through these films.

Transmission maps of the ACIS UV/optical blocking filters

The AXAF CCD imaging spectrometer (ACIS) consists of ten CCDs arranged in two arrays, one for imaging astronomical fields and one to be used in conjunction with transmission gratings for spectroscopy of astrophysical sources. ACIS uses Lexan/aluminum meshless films placed above these two CCD arrays to filter by mapping their soft x-ray transmission on fine spatial scales, so that the filter response can be removed from the CCD data and a more accurate estimate of the true sky recovered. We measured engineering and flight versions of these filters at the University of Wisconsin Synchrotron Radiation Center between June 1995 and April 1996. For all data, better than one percent accuracy in transmission as a function of energy was maintained over the entire filter area. The resulting transmission maps reveal spatial non-uniformities in the filters of about 0.5 percent to 2 percent. These transmission maps provide the finest spatial calibration ever achieved on such filters.