Eliminating organic contamination on oxidized Si surfaces using atomic oxygen


Liz Strein, David Allred, Steven Turley


A “green” cleaning technique for Si/SiO2 ultrathin films is presented.  With the removal of adventitious carbon on the surface, Si/SiO2 ultrathin films can serve as calibration standards in vacuum ultraviolet reflectance characterization (the range from 8 to 60 nm).  We anticipate using these standards when making a mirror that will be sent to the moon and will be used to study the earth’s magnetic field.  Data are presented for the samples that demonstrate the effect of mild solvents in conjunction with the effect of varying an excimer lamp’s exposure time.  Data are determined by x-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry.   Additionally, we found that the antechamber of the XPS system deposits hydrocarbon onto the surface of samples.  We adapted a plasma cleaner so that it minimized the effects of this instrumental contamination.





Jacqualine Dee Jackson* and David D. Allred, Department of Physics and Astronomy, BYU, Provo, UT 84602 

* Now at the Department of Physics and Astronomy, University of Utah, SLC, UT 8411?


It is difficult to measure the reflectance of thin films accurately in the extreme ultraviolet due to lack of precision instrumentation in this range and the effects of surface roughness. However, this has little effect on transmittance measurements. Whereas the real part of the refractive index is dependant on both transmittance and reflectance, the imaginary part can be determined from transmittance data alone. It is possible to use Kramers-Kronig analysis to calculate the real part if the imaginary part is known over a sufficiently broad range. We show that the delta calculated from reflection and transmission data without taking into account roughness may underestimate the real part of the refractive index of scandium oxide by up to 40% near 270 eV.


Preparation and Characterization of Bilayer Reflectance Standards for the EUV


Zach Strother (Georgia Tech), David D. Allred and Nicole Brimhall (Physics and Astronomy, Brigham Young University)



Researchers would be benefited from stable, reliably, easy-to-prepare and characterize mirrors in the VUV/EUV (Vacuum/Extreme Ultraviolet) range (-8 to 80 nm). We are developing bilayers which exhibit strong interference fringes as a function of reflectance angle for large portions of the spectra. These show large interference fringes near the Brewster’s angle and acceptably large reflectance at near-normal incidence. One set of standards are thermally oxidized silicon wafers with 20-40 nm of SiO2 on Si. Reflectance vs. angle measurements exhibit large fringes in the ~8 to 30 nm range. Another class is sputtered Ru-Si bilayers which can exhibit strong interference fringes at 30.4 and acceptable performance at 58.4 nm. These wavelengths are of particular interest to us. They are important for space-based, magnetosphere-observing EUV observatories. We discuss preparation and characterization of the standards, their advantages and limitations. They are readily prepared even in small laboratories, easily characterized by a variety of techniques, and are sufficiently robust, stable and inert for long-term use.


Design and Fabrication of a Strain-Based Nano-Compass


Johnathan E. Goodsell,  Jonathon A.  Brame, Stephanie A. Getty and David Allred




A design for a single walled carbon nanotube (SWCNT) nanocompass is presented.  The operating principle seeks to exploit the sensitivity of SWCNT electrical conductivity to strain. The moment of an iron needle (like a compass) is transduced to an electronic readout to provide information about the magnetic field strength and direction.  The contemplated device consists of a suspended network of electrically contacted SWCNTs supporting a magnetically responsive, high aspect-ratio Fe needle.  During operation, torque on the Fe needle in a magnetic field should induce a strain on the suspended SWCNTs, which should be measurable as a change in the resistance across the electrodes.  An array of 4 test structures has successfully been fabricated.  Preliminary magnetic field measurements confirm that the electrode and needle geometry needs to be optimized and the nanotobe density needs to be decreased.