Calibration procedure for gel permeation chromatography

A novel procedure is presented for calibrating a gel permeation chromatograph by using broad polymer fractions. The limit in accuracy is set by the accuracy of number-average and weight-average molecular weight measurements and the reproducibility of the chromatograph. In the particular calibration for linear polyethylene described here, low molecular weight fractions were prepared by nitric acid oxidation of annealed single crystals. The calibration is then of particular value in morphological studies of polyethylene. The influence in the calibration of polar endgroups on the polymer, as produced in these oxidized samples is discussed.     

DC plasma etching of silicon by sulfur hexafluoride. Mass spectrometric study of the discharge products

Polycrystalline silicon wafers were etched in dc discharges of SF₆. SF_x species were extracted from the discharges and measured with a mass spectrometer. A systematic procedure was used to measure the SF _x ⁺ signals such that they are indicators of events in the discharge close to the sample undergoing etching. The picture that emerges is remarkably simple and shows the relative stability of several SF_x species including SF₆, SF₄, SF₂, and SF which are shown to be extracted from the discharge both in the presence and absence of the silicon sample. When silicon is being etched on the cathode of the discharge cell, the only significant additional products are SiF₄ and S₂F₂. A comparison of blank and sample data for opposite substrate polarities shows that there is only a small cation-assisted etching effect and suggests that ions do not play an important role in the etching of silicon by SF₆ discharges.     

Comparison of calorimetric and IR-spectroscopic data for alcohols and alcoholic solutions

The heats of solution of alcohols in hexane can be considered as the energy necessary to break hydrogen bonds (H-bond). The amount of non H-bonded OH groups estimated from caloric data, are in good agreement with IR-spectroscopic data. Comparison of calorimetric and IR-spectroscopically determined H-bond energies permit the separation of intermolecular van der Waals effects from H-bond interactions. This separation shows that van der Waals interactions of alcohols or water should not be underestimated.     

Loss of continuum Lorentz invariance in gauge theories on a triangular lattice

On a triangular lattice, a weakly chiral lagrangian of interacting bosons and fermions is constructed to be naturally invariant under the triangular symmetry. The continuum limit of the resulting field theory is not Lorentz invariant. We explicitly show this for the propagator of the massive Schwinger model.     

A new paraelectric center in lithium-doped KBr

We report paraelectric resonance measurements for KBr:Li⁺⁷ and KBr:Li⁺⁶. The observed zero-field splittings are large - 62, 65, and 141.5 GHz ± 1 GHz in KBr:Li⁺⁷, and 88 and 118 GHz ± in KBr:Li⁺⁶ — giving an isotope shift of 40% for the lower lines. The uncorrected dipole moment is p = 0.98 ± 0.05 eA. The presence of OH^- seems to suppress the Li⁺ signal.