Influence of phase stability on the in situ growth stresses in Cu/Nb multilayered films

Abstract

As the length scale of individual layers were reduced in a Cu/Nb multilayer, a face centered cubic (fcc)-to-body centered cubic (bcc) and bcc-to-fcc transformations were noted for Cu and Nb respectively. In addition, at equal fractions of Cu/Nb and at a very thin thickness, the layers vitrified. These phase transformations have been modeled using a thermodynamic phase diagram where strain, interfacial, and volumetric energy considerations were used to determine the phase as a function of the bilayer thickness and volume fraction in the multilayer. Using HRTEM, the evolution of the interface from semicoherent-to-coherent was observed as a function of phase and bilayer spacing and is discussed in terms of the interfacial energy contributions towards phase stability. The vitrification has been rationalized by the positive enthalpy of mixing with clustering quantified by atom probe tomography between these two species. All of these phase transformations have been related to real-time, intrinsic growth stress measurements. Upon phase transforming, a reduction in the compressive stress within all of the multilayers were noted. The stabilization of bcc Cu appeared to have a dramatic effect on the growth stresses of Nb that contributed to the compressive stress relaxation. This relaxation was captured in a molecular dynamics simulation of the multilayers and is contributed to the change in interfacial stress and stress distributions within the Cu layer. This demonstrates that phase

Maskless Patterning of Metal Outflow in Alternating Metal/Ceramic Multiple Nanolayers by Femtosecond Laser Irradiation

“…For a highly coherent interface and strong chemical interaction between the metal and ceramic layers, the interfacial mobility of metal atoms can be suppressed, resulting in a superheating of the confined metal . It is generally acknowledged that the atomic mobility and associated thermal stability may be greatly affected by the growth stresses and thermally induced stresses in the metal layer. − Notably, fast diffusion of metal atoms along incoherent and weakly bonded metal–ceramic interfaces can be surprisingly fast due to the relatively low activation energies of vacancy formation and migration in the metal . Hence, depending on the nature of the metal–ceramic interface and the residual stress state, the microstructural response of metal nanolayers upon thermal/mechanical post-treatment can be distinctly different between confined and nonconfined metal–ceramic nanolaminates.…”

Nanomaterials by design: a review of nanoscale metallic multilayers

“…One of the most common methods is reflection high-energy electron diffraction, which is used to monitor the growth progress during material synthesis by PVD [6]. Growth stresses are another commonly studied property that may be monitored during deposition, and provide insight into the microstructure of the final NMMs [239]. In addition, in situ XRD tests have been used to study the evolution of the microstructure of NMMs upon exposure to ion irradiation [200,240] and to determine their deformation behavior upon heating/cooling [36,194].…”

Solute distributions in tantalum‐containing zirconium diboride ceramics

“…Specimens for APT were prepared by a focused ion beam (FIB; Scientific Quanta Dual Beam FIB/ Lyra Tescan FIB, Thermo Fisher Scientific) lift‐out procedure near and at grain boundaries of ZB and ZTB compositions similar to the method reported by Guo et al Excised tips were sharpened though annular milling with a Ga ion beam at 30 keV followed by a 5‐keV cleaning step to remove surface damage resulting from the sharpening process. Prepared specimens were maintained at 40 K and field‐evaporated in a Local Electrode Atom Probe 5000XS (CAMECA) assisted by a 355‐nm‐wavelength ultraviolet laser pulsing at 400 pJ with a dynamic pulse frequency between 300 and 600 kHz.…”