A 1 eV neutral atomic fluorine beam has been shown to produce etch rates in silicon as high as 1 μm/min. Using a CaF2 resist layer we fabricated 120 μm deep by 1 μm wide trenches (aspect ratio 120:1) in silicon with little sidewall taper (slopes of about 1000:1) or aspect-ratio dependent etching effects. Achieving such anisotropic etching suggests that the scattered species do not contribute significantly to sidewall etching under the conditions of this experiment. We estimate that the ultimate depth attainable for a 1 μm wide trench is about 250 μm and that the critical parameter for attaining a trench of a certain depth is the aspect ratio. Our observations and analysis suggest that this etching technique can be used to fabricate trenches on a nanoscale level while maintaining high aspect ratios of 100 or greater.

Angular distributions are measured for individually resolved ν′, j′ states of HF produced by F + H 2 f HF(ν′ ) 1, j′) + H and F + H 2 f HF(ν′)2, j′) + H reactive collisions in a crossed-beams scattering apparatus. Simultaneous resolution of the HF vibrational and rotational states is achieved spectroscopically for the first time, using laser excitation in conjunction with bolometric detection. The technique is sensitive to population differences between ν′ ) 1, j′ and ν′ ) 2, j′ -1 states optically coupled by specific P 2 (j′) lines of a vibrotational chemical laser. The measurements are greatly facilitated by the development of a new high-temperature atomic fluorine beam source, which exhibits excellent stability, very high intensity, and narrow velocity distributions. Features common to individual product rotational states are as follows: strong backward scattering into ν′ ) 2, j′; weaker backward scattering into ν′ ) 1, j′; and heretofore unobserved scattering into ν′ ) 1, j′ in the forward hemisphere. These angular distributions agree qualitatively with predictions from fully three-dimensional exact quantum reactive scattering calculations (Castillo et al., J. Chem. Phys. 1996, 104, 6531) that were conducted on an accurate potential energy surface (Stark and Werner, J. Chem. Phys. 1996, 104, 6515). However, quasi-classical calculations conducted on the same potential energy surface do not produce any substantial forward-scattered HF in ν′ ) 1 (Aoiz et al., Chem. Phys. Lett. 1994, 223, 215), suggesting that its appearance in the forward hemisphere may be a quantum effect. The quantum theoretical cross-sections also suggest that the forward ν′ ) 1 products arise almost entirely from H 2 reactants initially in j ) 1.

Angular distributions for individually resolved ν, j states from the F+H2→HF(ν,j)+H chemical reaction are measured for the first time. Vibrational and rotational resolution is achieved simultaneously by applying laser+bolometer detection techniques to crossed-beam reactive scattering. In addition to backward-scattering HF(ν=1, j=6) and HF(ν=2, j=5), we also observe HF(ν=1, j=6) products scattered into the forward hemisphere. The results are in qualitative agreement with fully three-dimensional exact quantum reactive scattering calculations [Castillo et al., J. Chem. Phys. 104, 6531 (1996)] which were conducted on an accurate potential-energy surface [Stark and Werner, J. Chem. Phys. 104, 6515 (1996)]. However, the forward-scattered HF(ν=1, j=6) observed in this experiment is not reproduced by quasi-classical calculations [Aoiz et al., Chem. Phys. Lett. 223, 215 (1994)] on the same potential-energy surface.

Both phase I and III in Na2SO4 have been stabilized at room temperature by substitution with the sulfate salts of the aliovalent cations Y3+, La3+, Dy3+, Ce4+, and Ca2+. Phase stabilization has been studied using laser Raman spectroscopy to measure the internal optic modes of the sulfate anion. Phase III is stabilized by a few tenths of a mole percent of the substituent, while phase I is stabilized by roughly ten times that concentration. Stabilization of both phase I and phase III does not appear to depend significantly on the charge of the guest ion. The enthalpy and entropy of the phase III to phase I transition was found to decrease markedly with increasing substituent cation concentration.

Results of Raman, x-ray diffraction, and differential scanning calorimetry studies of lithium sodium sulfate (LiNaSO4) doped with Cd2+ are presented. The x-ray diffraction and differential scanning calorimetry data show that there is no significant change in the room temperature structure over the substitutional range studied. Raman spectra of Cd2+ substituted lithium sodium sulfate are compared with the temperature dependent spectra of pure LiNaSO4 and found to be qualitatively similar, reflecting the increasing breakdown of factor group correlated SO2−4 vibrations with increasing Cd2+ concentration.