Biomedical subjects

G Kostorz

Publications and source records attributed to G Kostorz.

14 recordsLinked to original sources

PubMed2006

TEM and HREM study of Al3Zr precipitates in an Al-Mg-Si-Zr alloy.

The structure of Al(3)Zr precipitates in Al-1.0Mg-0.6Si-0.5Zr (in wt.%) alloy was investigated using conventional transmission electron microscopy (TEM) and high-resolution TEM (HREM). After annealing of the alloy in the temperature range 450-540 degrees C, spherical precipitates of metastable L1(2)-Al(3)Zr phase appeared nearly homogeneously within the matrix, and elongated particles were found at grain boundaries. L1(2)-structured Al(3)Zr were about 20-30 nm in diameter and coherent with the matrix. Inside some of them, planar faults parallel to {100} planes were revealed by use of HREM. Most probably, these faults are an indication of the transition stage of transformation to the stable D0(23)-type Al(3)Zr phase. The elongated precipitates (about 100 nm) were identified as D0(22)-type Al(3)Zr. Energy-dispersive X-ray analysis showed that they contain, apart from Al, mainly Zr with small amounts of Si. The substitution of Al by Si increased the stability of the D0(22)-Al(3)Zr as compared with D0(23)-Al(3)Zr.

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PubMed2004

Bulk interfaces in a Ni-rich Ni-Au alloy investigated by high-resolution Z-contrast imaging.

Interfaces between Au-rich precipitates and the Ni-rich matrix in a decomposed Ni-10 at.% Au alloy were investigated by low-magnification and high-resolution Z-contrast imaging. During aging at 923 K, the originally single crystalline sample decomposed and recrystallized resulting in a microstructure consisting of subgrains separated by small-angle grain boundaries. These small-angle grain boundaries are decorated by Au-rich precipitates. The interfaces between the Au-rich precipitates and the Ni-rich matrix were characterized with respect to the orientation relationship between precipitates and matrix, misfit dislocations and concentration gradients. Two transformation modes were identified that are involved in the decomposition of bulk Ni-rich Ni-Au alloys. While in the first mode the interface is semi-coherent, in the second mode the interface corresponds to an incoherent twin boundary. It is further shown that strain fields around misfit dislocations can result in systematic errors in the determination of the concentration gradients across interfaces between precipitates and matrix.

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PubMed2003

Self-assembled semiconductor quantum dots with nearly uniform sizes.

Self-assembled PbSe quantum dots on PbTe quasisubstrates, where the quasisubstrate layer is grown on Si(111), show a size distribution as low as 2%, below any other reported size distribution. The result is explained by nonoverlapping diffusion radii for most of the dots and their nucleation occurring mainly at defects (glide steps of the quasisubstrate), conditions which are not met by self-assembled quantum-dot structures in other material systems.

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PubMed2002

The asymptotic leading term of anisotropic small-angle scattering intensities. II. Non-convex particles.

For anisotropic particulate samples with scattering contrast (delta n)(2), the leading asymptotic term of the scattering intensity, along a direction q (q/q) of reciprocal space, is [4 pi(2)(delta n)(2)/q(4)]sigmaj [1/kappaG.j(+/-q)]. Here, kappaG.j(+/-q)denotes the Gaussian curvature value at the points (labelled by j) of the interphase surface where the normal is either parallel or antiparallel to q. If the Gaussian curvature vanishes at, say, the jth of these points, the corresponding contribution takes the form Cj/qalpha with 2< or = alphaj<4, Cj and alphaj being determined by the local behaviour of the surface. However, the intensity detected by a counter pixel, with opening solid angle deltaomega(q0) along (mean) direction q0, asymptotically still behaves as 4pi(2) (delta n)(2)(deltaomega(q0))/q(4), where S(deltaomega(q0)) is the area of that part of the interface that has its normals inside deltaomega(q0).

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PubMed2000

Bloch waves and weak-beam imaging of crystals

The influence of the number of diffracted beams on weak-beam contrast simulations of thickness contour lines and dislocation images is investigated. For large deviation parameters s(g)-->thickness contour lines from two-beam simulations are similar to those from many-beam simulations. In many-beam simulations of wedge-shaped bent samples extra thickness contour lines appear at locations with ((g)-->, 3(g)-->). These extra lines occur between the imaging condition ((g)-->, -(g)-->) and ((g)-->, 3(g)-->). Therefore, in the case of a more symmetrical imaging condition many-beam simulations are mandatory. In bent samples the contributions of different Bloch waves to weak-beam images change as a function of the imaging conditions ((g)-->, x(g)-->). Near ((g)-->, 3.5(g)-->) two Bloch waves dominate. In the case of x <3 two other Bloch waves with different wavelengths are most important for the image contrast. The 'classical' ((g)-->, 3(g)-->) weak-beam condition is not suitable to determine signs and magnitudes of Burgers vectors from terminating thickness contour lines. Higher deviation parameters s(g)--> are necessary, especially for dense dislocation arrangements.

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PubMed1994