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In the past few years, it has been discussed with increasing frequency, whether cube slip does occur in gamma' hardened nickel-base superalloys. Occurrence of cube slip has consequences for the modeling of orientation dependence of the CRSS. Until now, there are only few experimental investigations.
In principle, cube slip should be possible in primitive cubic lattices (e.g. L12 ordered gamma' phase) but not in face centered cubic ones (e.g. Ni solid solution). The most favourable specimen orientations are near [111], where the Schmid factors for this type of glide exceed those for octahedral systems.
There are two basic methods to detect cube slip: macroscopic slip trace analysis and Transmission electron microscopy (TEM) investigation of the dislocation structure. Few observations of cube slip by macroscopic slip traces are reported in the literature. But it is still uncertain under which test conditions cube slip occurs and what the dislocation mechanisms are. Cube slip was observed during tensile or compression tests of several first generation superalloys, but it seems not to occur during shear creep deformation (e.g. CMSX-4 at 980°C), and it is also lacking under conventional tensile or compression loading, if the gmma' particles are small. No observations were ever reported of dislocations gliding on {001} planes in matrix channels.
Cross-sectional transmission electron microscopy, in combination with energy dispersive X-ray spectroscopy and focused beam microdiffraction, was applied to study the solid-state reactions taking place during contact formation of the system Ge(115 nm)/Pd(50 nm)In0.53Ga0.47As. In order to get information about the sequence of the different processes, rapid thermal, annealing experiments in the range 225400 °C were performed. The following features were observed: at 225 °C Pd reacted with the substrate forming the quaternary phase PdxIn0.53Ga0.47As (x 4), and with the Ge-layer forming mainly PdGe and Pd2Ge. Between PdxIn0.53Ga0.47As and In0.53Ga0.47As, a 5 nm thick amorphous Pd-In-Ga-As layer remained, indicating that the first reaction step was solid-state amorphization. After annealing at 350 °C, PdxIn0.53Ga0.47As disappeared and regrowth of In0.53Ga0.47As occured. Finally, at 400 °C, residual Ge from the amorphous top layer diffused to the interface and grew epitaxially on the regrown In0.53Ga0.47As, thus separating the IIIV compound semiconductor from the Pd-Ge reaction products. The interface remained flat, while only about 10 nm of the active In0.53Ga0.47As layer had been modified during the annealing processes.
XTEM and TFXRD investigations of ohmic Ti/Al/Ti/Au/WSiN contacts on AlGaN/GaN HFET layer systems
(2002)
The microstructural features of the high-temperature-stable ohmic contact system Ti/Al/Ti/Au/WSiN on AlGaN/GaN were investigated using analytical transmission electron microscopy and thin film x-ray diffraction. For two typical rapid thermal annealing steps at 750 °C (non-ohmic behaviour) and 850 °C (ohmic behaviour) the intermetallic phases at the metal-semiconductor interface are presented. Increased annealing leads to the transformation of an Al2Au-AlAuTi phase mixture to a mixture of Al2Au-Al3Au8 phases and the formation of Ti-Al-nitride layers at the interfaces. In light of these results the electrical contact properties are discussed.
XTEM and TFXRD investigations of ohmic Ti/Al/Ti/Au/WSiN contacts on AlGaN/GaN HFET layer systems
(2002)
The microstructural features of the high-temperature-stable ohmic contact system Ti/Al/Ti/Au/WSiN on AlGaN/GaN were investigated using analytical transmission electron microscopy and thin film x-ray diffraction.
For two typical rapid thermal annealing steps at 750 ◦C (non-ohmic behaviour) and 850 ◦C (ohmic behaviour) the intermetallic phases at the metal–semiconductor interface are presented. Increased annealing leads to the transformation of an Al2Au-AlAuTi phase mixture to a mixture of Al2Au-Al3Au8 phases and the formation of Ti-Al-nitride layers at the interfaces. In light of these results the electrical contact properties are discussed.
X-ray photoelectron spectroscopy (XPS) and cross-sectional transmission electron microscopy (XTEM) were used to study the formation of AlN films by N+2 ion implantation of aluminium at energies of 3 keV and 100 keV. In both cases, a two-stage mechanism was found, comprising first the oriented precipitation of small particles of the hexagonal AlN-phase, followed by growth and coalescence finally forming a continuous AlN-layer while increasing the implantation dose from 1×1017 cm-2 to 2×1017 cm-2. The results of both methods are in excellent agreement and furthermore provide complementary information concerning chemical composition and binding energies as well as microstructural details.