Nanoglasses: a trail towards uncharted regions of vitreous materials and their properties?

Nanoglasses are a class of non-crystalline materials composed of nanoscale glass regions separated by glass-glass interfaces that possess distinct structural and thermodynamic characteristics. These internal interface regions with finite width of the order of several nanometres introduce excess free volume, altered short- and medium-range order, including the distribution of chemical constituents, and modified energetic states compared with conventional homogeneous glasses, giving rise to unique structural and functional properties. Additionally, the interfaces between the glass cores and the glass-glass interfaces need to be considered, as the specific interface areas are large. In this perspective paper, we discuss the structure, thermodynamics, and stability of glass-glass interfaces and examine their implications for the design and properties of nanoglasses, highlighting that this approach represents a novel pathway for modifying amorphous materials more broadly. Particular attention is given to columnar thin-film nanoglasses, where vertically aligned glassy columns create a high density of internal interfaces. We outline how interfacial excess energy, configurational entropy, and relaxation processes influence the metastability and properties of these materials. Furthermore, we discuss perspectives on how the control of interface density and chemistry may enable tailoring of mechanical, diffusion, and functional properties, including enhanced plasticity, altered transport behaviour, and tuneable optical or electronic responses. Finally, open questions regarding interfacial structure, thermodynamic driving forces, and stability are identified, emphasizing opportunities for integrating nanoglasses into advanced functional thin-film systems.