Zinc Phosphide Nanowires Exhibit Evolving Cross Sections, Triangular, Pseudo-pentagonal, and Hexagonal, Grown from Earth-abundant Components

The pursuit of sustainable and flexible solar energy technologies demands new materials based on readily available elements, and researchers are now exploring zinc phosphide for this purpose. Simon Escobar Steinvall, Hampus Thulin, and Nico Kawashima, alongside colleagues at their institutions, demonstrate a method for growing zinc phosphide nanowires using only earth-abundant components. Their work reveals that these nanowires exhibit a remarkable ability to change shape, forming triangular, pseudo-pentagonal, and hexagonal cross-sections depending on growth conditions. This control over nanowire geometry represents a significant advance, paving the way for sustainable solar energy harvesting and offering a novel approach to creating nanoscale structures within the wires themselves through the formation of heterotwins.

Zinc Phosphide Nanowire Growth Parameter Exploration

Scientists meticulously investigated the growth of zinc phosphide nanowires, focusing on how temperature and precursor gas composition influence their structure. The study combined experimental observations with computational modelling to understand the nucleation and growth mechanisms, aiming to optimize synthesis. Results reveal that specific conditions favour the formation of particular cross-sections, such as triangular or pseudo-pentagonal shapes. Computational modelling, employing density functional theory, determined the surface energies of different crystal facets of zinc phosphide. Slab models were relaxed to obtain accurate energy values, used in a Wulff construction to predict the equilibrium shape of the nanocrystals, identifying the most stable facets.

Calculations of the Gibbs free energy of nucleation revealed that the pseudo-pentagonal cross-section requires less energy to form compared to the triangular shape, suggesting it is thermodynamically more favourable under the studied conditions. The team calculated the critical radius for nucleation, determining the minimum size a nucleus must reach to become stable and grow. By carefully analysing the geometry-dependent terms and calculating the critical base length, scientists determined the minimum free energy required for nucleation, demonstrating that the pseudo-pentagonal cross-section is easier to nucleate, offering a pathway to more efficient nanowire growth.

Tin-Catalyzed Growth of Zinc Phosphide Nanowires

Researchers developed a sustainable method for growing zinc phosphide nanowires, utilizing earth-abundant materials and precise control over their structure. The study pioneered a vapor-liquid-solid growth technique using tin as a catalyst deposited on silicon substrates, avoiding scarce elements. Liquid metal catalyst particles were deposited by introducing a tin-containing precursor at elevated temperatures, resulting in a high density of particles with controlled size, crucial for subsequent nanowire growth. By systematically varying growth temperature and the ratio of precursor gases, scientists observed three distinct nanowire morphologies: triangular, pseudo-pentagonal, and twin plane superlattice. Detailed analysis using scanning electron microscopy revealed a strong correlation between growth conditions and the resulting nanowire morphology. Radial overgrowth of the nanowire side facets also depended on both temperature and the precursor ratio, with higher ratios promoting increased overgrowth rates at intermediate temperatures, attributed to the surface diffusion of zinc atoms.

Earth-Abundant Zinc Phosphide Nanowire Growth Demonstrated

Scientists achieved the epitaxial growth of zinc phosphide nanowires using exclusively earth-abundant materials, representing a significant step towards sustainable solar cell technology. The team successfully employed tin as the catalyst and silicon as the substrate, enabling fabrication through metalorganic chemical vapour deposition. Experiments revealed a remarkable ability to control nanowire morphology by tuning both temperature and the ratio of precursor gases during growth. At temperatures exceeding 356°C and high precursor ratios, the nanowires exhibited a twin plane superlattice structure.

However, by lowering the temperature and adjusting the precursor ratio, scientists observed the formation of distinct cross-sectional shapes, including irregular five-faceted pseudo-pentagonal structures and triangular nanowires. Detailed analysis of catalyst particle size showed that tin nanoparticles deposited at 630°C yielded average diameters of 45nm ±14nm. The team mapped the growth parameter space, demonstrating that pseudo-pentagonal nanowires emerged at intermediate temperatures, while triangular nanowires formed at the lowest temperatures explored. These findings demonstrate a clear pathway to produce metastable crystal morphologies and enable more sustainable manufacturing routes for emerging semiconductor materials.

Zn3P2 Nanowires Grown From Earth Abundant Materials

This research demonstrates the successful epitaxial growth of zinc phosphide nanowires using exclusively earth-abundant materials, a significant step towards sustainable solar energy technologies. By employing tin as a catalyst and silicon as the substrate, the team achieved controlled growth of nanowires exhibiting distinct cross-sectional morphologies, including triangular, pseudo-pentagonal, and twin plane superlattice structures, directly linked to precise control of growth temperature and the ratio of precursor gases. The team attributes these structural variations to metastable facet formation constrained by the underlying substrate, confirmed through a combination of experimental observation and theoretical modelling. Notably, the formation of the twin plane superlattice structure, achieved at higher temperatures and phosphine concentrations, introduces the possibility of creating internal wells within the nanowires, potentially enhancing their functionality.

This work establishes nanoscale epitaxy as a viable method for producing metastable crystal structures in emerging semiconductor compounds, opening new avenues for materials design. Future work could focus on optimizing the nanowire growth process for improved efficiency and exploring the potential of these structures in photovoltaic devices. The team also suggests that this method could be extended to other earth-abundant semiconductor materials, paving the way for a new generation of sustainable energy technologies.