Low-Temperature Preparation of High-Temperature Nickel Germanides Using Multilayer Reactants

Abstract

Nickel germanide thin films were prepared using nickel−germanium multilayers as reactive precursors. Over the composition range x Ni = 0.24−0.42, high-temperature germanides (δ-Ni5Ge2, ε-Ni5Ge3, and Ni3Ge2) form under conditions where the phases are thermodynamically unstable. δ-Ni5Ge2 forms over a broader range of composition than has been observed previously. The three high-temperature phases accessible by this synthetic route are observed to share related structure types, which are related to the structure of amorphous nickel germanium alloys with similar composition. The ability to selectively prepare metastable phases under mild conditions has important implications with respect to the search for new materials for use in integrated devices.

Phase formation in intermixed Ni–Ge thin films: Influence of Ge content and low-temperature nucleation of hexagonal nickel germanides

“…A similar behavior has been observed previously by Ellner et al in the bulk system [3] and by Jensen et al in multilayer Ni-Ge films [8]. Since the structure of this HEX phase can be regarded as intermediate between the two prototype structures of Ni 2 In and NiAs, the monotonic decrease of the lattice parameters can be explained by a systematic incorporation of extra vacancies on the Ni sites as more Ge is added to the mixture [13,8]. The observation of this metastable HEX phase and its behavior as a function of Ge content is very similar to what has been observed recently for the h-phase in the Ni-Si system [11].…”

“…6, which shows a systematic contraction of the lattice with increasing Ge content. A similar behavior has been observed previously by Ellner et al in the bulk system [3] and by Jensen et al in multilayer Ni-Ge films [8]. Since the structure of this HEX phase can be regarded as intermediate between the two prototype structures of Ni 2 In and NiAs, the monotonic decrease of the lattice parameters can be explained by a systematic incorporation of extra vacancies on the Ni sites as more Ge is added to the mixture [13,8].…”

“…However, the existence of other Ni-germanides in this intermediate region could not be ruled out due to overlapping peak positions of different Nirich germanides [6]. Interestingly, Jensen et al [8] reported on the metastable nucleation of the high temperature -Ni 5 Ge 3 when annealing ratio-controlled Ni-Ge multilayers on an inert SiO 2 substrate.…”

Spontaneous Growth and Phase Transformation of Highly Conductive Nickel Germanide Nanowires

“…Given sufficient reaction time to reach equilibrium, the final phases depend on the identity and amount of the limiting reactant species. Thermal annealing leads to Ni enrichment and hence NW phase transformation to ε-Ni 5 Ge 3 . , However, the formation of the metastable hexagonal ε-Ni 5 Ge 3 phase instead of the stable monoclinic ε′-Ni 5 Ge 3 phase likely occurred due to the particular annealing conditions used, namely heating above the phase transition between the equilibrium phase and the metastable phases, annealing for the particular period, and relatively fast quenching. The observation of the metastable ε-Ni 5 Ge 3 phase suggests that kinetic factors play important roles during phase transformation.…”

Nucleation and growth kinetics of co-deposited copper and selenium precursors to form metastable copper selenides

“…Providing energy into the system to overcome the smaller activation energy, E a,1 , for the metastable phase but not sufficient to overcome the larger activation energy, E a,2 , required to form the thermodynamic product traps the metastable product. In the 70s this concept was capitalized on by metallurgists seeking novel metallic glasses [2][3][4] and more recently metastable films precursors have been used to systematically prepare new compounds, understand nucleation barriers to compound formation and to better understand the energy landscapes made accessible by deposited films [5][6][7][8][9][10][11][12][13][14][15][16][17].…”