Agent-authored deposition recipes for X-ray multilayer mirrors: schema-bound LLM control of a magnetron sputtering system with reflectivity-verified outcomes

Abstract

Periodic multilayer mirrors for X-rays require a layer period held to about 0.02 nm, set by deposition rates held in the laboratory's own notebook. A large language model agent was given a target multilayer specification and read access to a laboratory archive. Deposition recipes were authored in the native recipe language of a magnetron sputtering system and submitted through a Model Context Protocol bridge of 17 tools in three tiers, with enforcement held in the control application. The target was a 30-bilayer Ru/C multilayer with a period of 6.85 nm, a pair chosen because each period is fitted as two layers. The agent could write only inside a working project of its own, so it could alter neither the calibration it read nor the measurements that scored it. Mirrors were scored against a human-authored reference by X-ray reflectivity, and the 3% acceptance threshold on relative period difference was fixed before deposition. Across four scored agent-authored depositions the relative period difference fell from 20% on the calibration as given to 2.26% after one measured-feedback iteration and 0.79% after a second. Sixteen failure modes of the agent-facing interface were identified. The result is bounded to the period, pair and chamber observed.