# Engineering Grain Architecture in Epitaxial Aluminum on Miscut Substrates Toward Various Clean Limits and Giant Superconductivity Modulation

## TL;DR

This paper shows how using miscut substrates can control aluminum's grain structure and superconductivity, enabling significant modulation of its properties for advanced devices.

## Contribution

A novel method to engineer aluminum's grain architecture and superconductivity via substrate miscut without changing growth conditions.

## Key findings

- Miscut substrates enable 10-1000% modulation in superconducting properties of aluminum.
- Reducing grain boundaries lowers resistivity but increases strain-induced crystallinity deterioration.
- Substrate-induced strain can drive a transition from type-I to type-II-like superconducting behavior.

## Abstract

Aluminum (Al) has attracted considerable attention for uses in photonic, electronic, and quantum devices. Its grain architecture governs surface roughness, electron and light scattering, and quantum decoherence, all of which critically affect device performance. Enhancing crystalline domain size and refining granularity control remain an ongoing research focus for producing ultraclean nanofilms. This study investigates the crystallinity of epitaxial Al grown on miscut GaAs substrates and examines its influence on Al superconductivity. The introduction of a substrate miscut alters Al growth kinetics, enabling the formation of twinned grains, polycrystalline structures, and micrometer‐scale single crystal. Variations in grain architecture result in approximately 10%, 100%, and 1000% modulation of the superconducting critical temperature, current, and magnetic field, respectively, while maintaining constant channel geometries. Reducing macroscopic grain boundaries decreases the Al nanofilm resistivity but enhances strain‐induced crystallinity deterioration, driving a transition from type‐I to type‐II‐like superconducting behavior. We suggest that preparing Al nanofilms, which approach an ultraclean limit in terms of surface quality, crystallinity, and transport properties, requires careful control of substrate miscut as well as the grain architecture. These findings highlight a tunable approach to controlling Al granularity and superconductivity via miscut, lattice‐mismatched substrates.

The miscut substrate strategy offers a novel means to engineer aluminum surface roughness, grain architecture, crystallinity, and both normal and superconducting transport properties toward their clean limits by precisely tuning the miscut angle without altering growth conditions. Furthermore, the lattice mismatch strain induced by a substrate miscut can drive a transition from type‐I to type‐II‐like superconducting behavior.