W. RULAND AND H. TOMPA 99 size (and/or the perfection) of the graphitic layers and the orientation of the layer planes in the sense that the larger and more perfect layers tend to be more perfectly aligned parallel to the fiber axis. An investigation of this effect is facilitated by the use of approximations similar to equation (14) considering Jh to be a function of s and ~0. A detailed study of this effect is in progress.We are indebted to Mr J.P.Pauwels for technical assistance, to the staff of our Computer Centre for the numerical results, and to Dr R. Bacon for supplying the sample of carbon fibre. The dynamical theory of X-ray scattering of distorted crystals is applied to the case of silicon crystals in which boron has been diffused. Double spectrometer reflexion profiles can thus be theoretically computed. Agreement with the experimental profiles is good except that computed junction depths are higher than the values measured by metallographic methods. On the other hand, the present method leads to a reliable determination of the diffusion coefficient of boron in the case of relatively high concentrations. ReferencesOn sait que la pr6sence de bore diffus6 dans les cristaux de silicium cr6e une contraction du r6seau cristallin (Horn, 1955) variable avec la profondeur, modifie le profil des raies de diffraction X et le pouvoir r6flecteur des cristaux diffus6s (Burgeat, 1963(Burgeat, , 1965. Cette modification de la diffraction X se retrouve avec la diffusion du phosphore dans le silicium. L'6tude exp6rimentale des profils de raies sur les 6chantillons diffus6s est r6alis6e au diffractom&re double dans la disposition (n, -n) (James, 1948), le premier cristal &ant aussi parfait que possible. La diffusion du bore est r6alis6e dans des cristaux de silicium de type N (dop6s au phosphore) et la profondeur de p~n&ration de l'impuret6 diffus6e est rep6r6e par l'6paisseur de la couche invers6e ou profondeur de jonction.On admettra pour l'6tude th6orique du profil de raie obtenue (Burgeat, 1965), que l'impuret6 diffus6e (bore ou phosphore) provoque une contraction du r6seau cristallin ~t priori isotrope et proportionelle/t leur concentration (loi de V6gard). Dans le cas pr6sent ces impuret6s sont concentr6es au voisinage de la surface et tendent par cons6quent ~t donner ~t l'6chantillon une forme concave (Queisser, 1961). En pratique l'6paisseur de l'6chantillon est tr~s grande (1 ~t 2 ram) devant celle de la couche diffus6e et la raideur de l'ensemble est telle qu'aux temp6ratures de diffusion il y a cr6ation de dislocations parallbles ~t la surface (Prussin, 1961).Du point de vue des rayons X (nous sommes dans le cas de Bragg sym&rique -r6flexion 400) tout se passe comme si nous avions un cristal dont les plans (400) restent parall~les et plans, mais dont l'intervalle r6ti-culaire dHest fonction de la distance z h la surface.La propagation des rayons X (au voisinage de la condition de Bragg) dans un tel cristal a d6j& 6t6 6tudi6e (Taupin, 1964); elle est r6gie par le syst~me diff6rentiel suivant (11.6.3):
Single crystals belonging to a new modification of GeSe2 have been prepared by several methods. This new form appears orthorhombic with parameters a = 7.037 -+_ 0-30, b = 11.826 ± 0.010, c = 16.821 ± 0.040/~ and z= 16. The measured density is 4.35+ 0.040 g cm -3. The space group has not yet been determined because cutting thin X-ray samples from large as-grown crystals induces considerable cleavage.
A series of perfect single crystals of silicon have been irradiated with alpha particles from 210Po to a maximum dose of 20.1×1015 α/cm2. The convoluted profiles obtained by means of a double-crystal spectrometer in the (n, −n) arrangement, with a perfect unirradiated crystal on the first axis, exhibit a secondary peak on the low-angle side with half-width and peak intensity comparable to that of the main peak in most cases. The main peak does not seem to be much influenced by irradiation except for a slight depression and broadening. The dynamical theory as developed by Taupin for imperfect crystals has been applied to these results by assuming that the only effect of irradiation is to introduce a uniform change in the lattice constant of the crystal which is function only of depth normal to the crystal surface. The convoluted reflectivity of such an imperfect crystal is computed at the reflecting surface in the symmetrical Bragg case by using a profile for the damage as computed from the simple theory of collision based on Rutherford scattering and on the hard sphere model. A satisfactory agreement is found, on a qualitative basis, between computed and experimental profiles. The fact that the calculated profiles, within the limitations of the approximations involved, can reproduce the essential features of the experimental ones suggest that some coherence is preserved between the diffracted waves. The damaged region of the crystal, having a varying lattice parameter, gives rise to a secondary peak but exerts a negligible absorption effect on the main peak, which originates from the bulk.
We analyze in this paper the effect of thermal treatment on structural properties of GaAs/InGaAs strained-layer superlattices grown by molecular beam epitaxy. The superlattices are analyzed using double-crystal x-ray rocking curves. In order to model the satellites intensity variation as a function of the heat treatment time at a temperature of 850 °C, we have calculated the structure factors of the superlattices, taking into account both composition and lattice spacing modulation. The latter is found to be more influent in the calculation in this particular case. The deduced values of the diffusion coefficient, about 2×10−18 cm2/s, is discussed and compared to those determined on GaAs/AlAs structures.
InGaAs/GaAs strained layers superlattices have been grown by molecular beam epitaxy on GaAs. The best growth temperature was found to be 520–540 °C from photoluminescence measurements. Double x-ray diffraction was performed. It shows very good agreement with the kinematical theory. This technique proves to be of particular interest for such structures: a single profile leads to reliable and complete information on layer thickness and InGaAs composition.
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