The amount of electronic waste (e-waste) globally has doubled in just five years, from approximately 20 million tons to 40 million tons of e-waste generated per year. In 2016, the global amount of e-waste reached an all-time high of 44.7 million tons. E-waste is an invaluable unconventional resource due to its high metal content, as nearly 40% of e-waste is comprised of metals. Unfortunately, the rapid growth of e-waste is alarming due to severe environmental impacts and challenges associated with complex resource recovery that has led to the use of toxic chemicals. Furthermore, there is a very unfortunate ethical issue related to the flow of e-wastes from developed countries to developing countries. At this time, e-waste is often open pit burned and toxic chemicals are used without adequate regulations to recover metals such as copper. The recovered metals are eventually exported back to the developed countries. Thus, the current global circular economy of e-waste is not sustainable in terms of environmental impact as well as creation of ethical dilemmas. Although traditional metallurgical processes can be extended to e-waste treatment technologies, that is not enough. The complexity of e-waste requires the development of a new generation of metallurgical processes that can separate and extract metals from unconventional components such as polymers and a wide range of metals. This review focuses on the science and engineering of both conventional and innovative separation and recovery technologies for e-wastes with special attention being given to the overall sustainability. Physical separation processes, including disassembly, density separation, and magnetic separation, as well as thermal treatment of the polymeric component, such as pyrolysis, are discussed for the separation of metals and non-metals from e-wastes. The subsequent metal recovery processes through pyrometallurgy, hydrometallurgy, and biometallurgy are also discussed in depth. Finally, insights on future research towards sustainable treatment and recovery of e-waste are presented including the use of supercritical CO₂.

The microstructure and the room-temperature hysteretic magnetic properties of sputtered, 10 nm thin films of equiatomic binary alloys of CoPt and FePt were characterized using transmission electron microscopy (TEM) and a superconducting quantum interference device (SQUID) magnetometer. A transformation from an atomically disordered, face-centered-cubic structure to the ${\text{L1}}_0$ ordered structure occurred during postdeposition annealing and was characterized using digital analysis of dark-field TEM images. The transformation was observed to follow first-order nucleation and growth kinetics, and the ordered volume fraction transformed was quantified at numerous points during the transformation. The ordered volume fraction was then compared to the magnetic coercivity data obtained from the SQUID magnetometer. In contrast to the relationship most commonly described in the literature, that the highest coercivity corresponds to a two phase ordered/disordered mixture, the maximum value for coercivity in this study was found to correspond to the fully ordered state. Furthermore, in samples that were less than fully ordered, a direct relationship between ordered volume fraction and coercivity was observed for both CoPt and FePt. The proposed mechanism for the high coercivity in these films is an increasing density of magnetic domain wall pinning sites concurrent with an increasing fraction of ordered phase.

We report a quantitative analysis of both surface and grain-boundary scattering in Cu thin films with independent variation in film thickness (27 to 158 nm) and grain size (35 to 425 nm) in samples prepared by subambient temperature film deposition followed by annealing. Film resistivities of carefully characterized samples were measured at both room temperature and at 4.2 K and were compared with physical models that include the effects of surface and grain-boundary scattering. Grain-boundary scattering is found to provide the strongest contribution to the resistivity increase. However, a weaker, but significant, role is observed for surface scattering. We find that the data are best fit when the Mayadas and Shatzkes’ model of grain-boundary scattering and the Fuchs and Sondheimer’s model of surface scattering resistivity contributions are combined using Matthiessen’s rule (simple addition of resistivities). This finding implies that grain-boundary scattering preserves the component of electron momentum parallel to the grain-boundary plane. Using Matthiessen’s rule, we find our data are well described by a grain-boundary reflection coefficient of 0.43 and a surface specularity coefficient of 0.52. This analysis finds a significantly lower contribution from surface scattering than has been reported in previous works and we attribute this difference to the careful quantitative microstructural characterization performed on our samples. The effects of surface roughness, impurities, voids, and interactions between surface and grain-boundary scattering are also examined and their importance is evaluated.

Two series of epitaxial CoPt and FePt films, with nominal thicknesses of 42 or 50 nm, were prepared by sputtering onto single-crystal MgO(001) substrates in order to investigate the chemical ordering and the resultant magnetic properties as a function of alloy composition. In the first series, the film composition was kept constant, while the substrate temperature was increased from 144 to 704 °C. In the second series the substrate temperature was kept constant at 704 °C for CoPt and 620 °C for FePt, while the alloy stoichiometry was varied in the nominal range of 40–60-at. % Co(Fe). Film compositions and thicknesses were measured via Rutherford backscattering spectrometry. The lattice and long-range order parameter for the $L{1}_0$ phase were obtained for both sets of films using x-ray diffraction. The room-temperature magnetocrystalline anisotropy constants were determined for a subset of the films using torque magnetometry. The order parameter was found to increase with increasing temperature, with ordering occurring more readily in FePt when compared with CoPt. A perpendicular anisotropy developed in CoPt for substrate temperatures above 534 °C and in FePt above 321 °C. The structure and width of the magnetic domains in CoPt and FePt, as seen by magnetic force microscopy, also demonstrated an increase in magnetic anisotropy with increasing temperature. For the films deposited at the highest temperatures (704 °C for CoPt and 620 °C for FePt), the order parameter reached a maximum near the equiatomic composition, whereas the magnetocrystalline anisotropy increased as the concentration of Co or Fe was increased from below to slightly above the equiatomic composition. It is concluded that nonstoichiometric $L{1}_0$ CoPt and FePt, with a slight excess of Co or Fe, are preferable for applications requiring the highest anisotropies.