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The crystal structures of tetramethylene glycol dibenzoate (1). tetramethylene glycol di-para-chlorobenzoate (2), and tetramethylene glycol di-para-nitrobenzoate (3) have been solved by direct methods in order to establish the possible conformations of the methylenic sequence in poly(tetramethy1ene t$rephthalate), poly(4GT). Compound 1 has a triclinic unit cell of dimensions a = 7.870(3), b = 8.574(3), c = 12.993(4) A; a = 83.76(3), p = 89.92(3), y = 64.68(3)"; Z = 2, space group P I . For 2 the unit cell is also triclinic and has dimensigns a = 5.916(3), b = 7.599(2), c = 10.404(2) A; a = 67.81(2), p = 77.47(2), 7 = 81.63(3)'; Z = 1, space group P1. The unit cell dimensions of 3 are a = 6.086(1), b = 1 I .475(3), c = 13.162(3) A and p = 101.93(2)", Z = 2. The space group is P 2 , l c . The structures were solved by direct methods using 2682, 969, and 781 observed reflections for 1, 2, and 3, respectively. The refinements were concluded when R reached the values of 0.042, 0.046, and 0.045, respectively. The conformation of the methylenic sequence varies depending on the substituent on the benzoate group. The conformation observed in 1 is t g -t t t , it is t t t t t for 2, and t g -t g t for 3 (t = trans, g = gauche). Although the equivalent fiber repeat of 3 coincides with the observed fiber repeat for a-poly(4GT), this does not imply that 3 and a-poly(4GT) have the same conformation. Compound 2 allows for the modelling of the p-form of poly(4GT). However, this does not lead to a clear choice between the two structures reported for this form. The two distinct conformations proposed for the p-form of poly(4GT) are distinguished on the basis of their ir and Raman spectra. The comparison of the spectra of the model compounds reveals that, in ir, for an all-trans conformation there is no absorption band at 1383 cm-' but one is present at 1395 cm-I. This situation that is observed in the ir spectra of p-poly(4GT) led us to propose that this form has the all-trans conformation as proposed by Hall and Pass. This choice is further supported by the presence of three bands at 1047, 1347, and 1405 c m ' in the Raman spectra of p-poly(4GT). These three bands are only observed in the model compounds having the all-trans conformation.ALLAN PALMER, SUZIE POULIN-DANDURAND et F R A N~O I S BRISSE. Can. J. Chem. 63, 3079 (1985). Les structures cristallines des bis(benzoate) (I), bisbara-chlorobenzoate) (2) et bis@ara-nitrobenzoate (3) du tetram6thylene glycol ont ttC rCsolues dans le but d'etablir les conformations possibles des sequences mjthyltniques du poly-(terephtalate de tetramkthylene), poly(4TG). Le composC 1 appartient au groupe d'espace triclinique P 1, avec a benzoate. On a observe les conformations suivantes: t g -t t r pour le compose 1, t t r i t pour le composC 2 et t g -t g t pour le compose 3 (t = trans, g = gauche). Le fait que la pCriode de fibre Cquivalente du composC 3 coincide avec la pCriode de fibre observie pour I'a-poly(4TG), n'implique pas necessairement que ces deux composCs ont la mCme conformation. ...

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Plasma silicon nitride (P-SiN) films were prepared from SiH4/NH3 mixtures in a large volume microwave plasma (LMP) apparatus, at substrate temperatures T2 ranging from ambient to 250°C.Under otherwise nominally identical fabrication conditions, deposition rates were 10 to 25 times greater than those reported by others for radio- or audio-frequency plasmas.Based on film compositions, determined by elastic recoil detection (ERD), and measurements of such properties as density, refractive index, etch rate in dilute HF, and moisture permeation coefficient, our best P-SiN films (produced at T2 ≥ 200°C) are very similar to those reported in the literature.

We report here on the further development of a new technique for doping plasma-deposited amorphous silicon by thermal evaporation of metal into the plasma from which the film is grown. We show that the de bias applied to the substrate has an important effect on the incorporation of the metal into the film, and on the doping efficiency. We also report on our efforts to monitor and control the evaporation by mass spectroscopy.