Hierarchically Structured Materials

We show that Raman spectral lines from H-2, D-2, T-2, HD, HT and DT are readily resolved, permitting an effective means to analyze isotopic hydrogen mixtures used in muon-catalyzed fusion experiments. We propose a Raman spectrographic system to allow for real-time analysis of targets involving all three isotopes of hydrogen.

A constrained non-linear deconvolution method was used to analyse the Raman spectrum of amorphous carbon. The method was tested by applying it to a model spectrum. Before the deconvolution the observed Raman spectrum was smoothed by a least-squares convoluting procedure. The proper width of the spread function used in the deconvolution was determined by examining the reversibility of the deconvolution process. The deconvolution result for the Raman spectrum of amorphous carbon has a form very similar to the phonon density of states of graphite. This is taken to be additional evidence for Shuker and Gamon's model for Raman spectra of amorphous materials. Potentially, the deconvolution method can also be used for other aspects of Raman spectrum analysis of amorphous materials, such as finding the relative intensity of each peak of study the structure of the material.

Measurements of the circular polarization of Balmer-α radiation emitted by excited hydrogen atoms, following the transmission of (20-50)-keV protons through thin, tilted amorphous carbon foils, exhibit markedly unexpected behavior asa function of exposure of the foil to the proton beam. Specifically, the circular polarization changes from an initially well understood tilt-angle dependence to a behavior which, for low tilt angles, gives the opposite handedness of circular polarization from that predicted. In addition, the degree of alignment, indicated by the linear Stokes parameter M/I, is enhanced also as a function of dose. These changes in the tilt-angle dependence of the Stokes parameters have been systematically correlated with beam-induced graphitization of the foil, which is observed to occur from Raman measurements.

The cutting of cross‐linked glasses such as silica and Corning 7059 can be difficult. We conducted an experimental study to determine the feasibility of using a high‐speed waterjet to cut thin Corning 7059 glass. Cutting using either pure de‐ionized high pressure water at 380 MPa (55 000 psi) or de‐ionized water with entrained garnet abrasive was studied. The roughness of the cut surfaces was measured and compared. Photomicrographs were taken of glass examples cut at different traversing rates with pure water and with the abrasive entrained waterjet. Comparative studies of cutting with and without the entrained abrasive material showed that a cutting rate of 127 mm/min with abrasive could achieve a smoothness of about 9 μm rms. The abrasive waterjet can cut Corning 7059 glass into any desired shape. The process is safe, inexpensive, fast, and amenable to computer operation.

We have fabricated arrays of siliconfield emitters using semiconductorlithography techniques. The density of the tips was 105/cm2. The maximum current that can be extracted from each emitter is limited by resistive heating. We have investigated how the electron current emitted changes under constant applied voltage. We found that the current is very sensitive to the vacuum conditions. We attribute this to sputtering of the emitters due to ionized residual gas molecules. The poorer the vacuum, the higher the instability in the current. We studied this phenomenon at 10−6 and 10−8 Torr. The model of two concentric spherical shells is used to obtain the ion energy distribution. This is then used to calculate the rate of ion bombardment and the rate of atoms sputtered. A lifetime of the tip can be deduced from these calculations.  

We have used Raman spectroscopy, large‐ and small‐angle x‐ray diffraction spectroscopy of sputter‐deposited, vacuum‐annealed, soft x‐ray Mo/Si thin‐film multilayers to study the physics of silicide formation. Two sets of multilayer samples with d‐spacing 8.4 and 2.0 nm have been studied. Annealing at temperatures above 800 °C causes a gradual formation of amorphous MoSi2 interfaces between the Si and Mo layers. The transition from amorphous to crystalline MoSi2 is abrupt. The experimental results indicate that nucleation is the dominant process for the early stage and crystallization is the dominant process after nucleation is well advanced. In the thicker multilayer, a portion of the siliconcrystallizes during annealing and a strong Raman signal is observed. An advantage of Raman spectroscopy is that the Raman signal of the silicide is observed even before the presence of MoSi2 can be seen using x‐ray diffraction. This study indicates that Raman spectroscopy is an effective technique for characterizing the formation of crystalline silicides.