As femtosecond (fs) laser machining advances from micro/nanoscale to macroscale, approaches capable of machining macroscale geometries that sustain micro/nanoscale precisions are in great demand. In this research, an fs laser sharp shaping approach was developed to address two key challenges in macroscale machining (i.e. defects on edges and tapered sidewalls). The evolution of edge sharpness (edge transition width) and sidewall tapers were systematically investigated through which the dilemma of simultaneously achieving sharp edges and vertical sidewalls were addressed. Through decreasing the angle of incidence (AOI) from 0° to −5°, the edge transition width could be reduced to below 10 µm but at the cost of increased sidewall tapers. Furthermore, by analyzing lateral and vertical ablation behaviors, a parameter-compensation strategy was developed by gradually decreasing the scanning diameters along depth and using optimal laser powers to produce non-tapered sidewalls. The fs laser ablation behaviors were precisely controlled and coordinated to optimize the parameter compensations in general manufacturing applications. The AOI control together with the parameter compensation provides a versatile solution to simultaneously achieve vertical sidewalls as well as sharp edges of entrances and exits for geometries of different shapes and dimensions. Both mm-scale diameters and depths were realized with dimensional precisions below 10 µm and surface roughness below 1 µm. This research establishes a novel strategy to finely control the fs laser machining process, enabling the fs laser applications in macroscale machining with micro/nanoscale precisions.

The increase in both power and packing densities in power electronic devices has led to an increase in the market demand for effective heat-dissipating materials with a high thermal conductivity and thermal expansion coefficient compatible with chip materials while still ensuring the reliability of the power modules. Metal matrix composites, especially copper matrix composites, containing carbon fibers, carbon nanofibers, or diamond are considered very promising as the next generation of thermal-management materials in power electronic packages. These composites exhibit enhanced thermal properties, as compared to pure copper, combined with lower density. This paper presents powder metallurgy and hot uniaxial pressing fabrication techniques for copper/carbon composite materials which promise to be efficient heat-dissipation materials for power electronic modules. Thermal analyses clearly indicate that interfacial treatments are required in these composites to achieve high thermal and thermomechanical properties. Control of interfaces (through a novel reinforcement surface treatment, the addition of a carbide-forming element inside the copper powders, and processing methods), when selected carefully and processed properly, will form the right chemical/mechanical bonding between copper and carbon, enhancing all of the desired thermal and thermomechanical properties while minimizing the deleterious effects. This paper outlines a variety of methods and interfacial materials that achieve these goals.

Three-dimensional (3D) electrically conductive micro/nanostructures are now a key component in a broad range of research and industry fields. In this work, a novel method is developed to realize metallic 3D micro/nanostructures with silver-thiol-acrylate composites via two-photon polymerization followed by femtosecond laser nanojoining. Complex 3D micro/nanoscale conductive structures have been successfully fabricated with ~200 nm resolution. The loading of silver nanowires (AgNWs) and joining of junctions successfully enhance the electrical conductivity of the composites from insulating to 92.9 S m⁻¹ at room temperature. Moreover, for the first time, a reversible switching to a higher conductivity is observed, up to ~10⁵ S m⁻¹ at 523 K. The temperature-dependent conductivity of the composite is analyzed following the variable range hopping and thermal activation models. The nanomaterial assembly and joining method demonstrated in this study pave a way towards a wide range of device applications, including 3D electronics, sensors, memristors, micro/nanoelectromechanical systems, and biomedical devices, etc.