Full-scale quantum computers require the integration of millions of qubits, and the potential of using industrial semiconductor manufacturing to meet this need has driven the development of quantum computing in silicon quantum dots. However, fabrication has so far relied on electron-beam lithography and, with a few exceptions, conventional lift-off processes that suffer from low yield and poor uniformity. Here we report quantum dots that are hosted at a 28Si/28SiO2 interface and fabricated in a 300 mm semiconductor manufacturing facility using all-optical lithography and fully industrial processing. With this approach, we achieve nanoscale gate patterns with excellent yield. In the multi-electron regime, the quantum dots allow good tunnel barrier control—a crucial feature for fault-tolerant two-qubit gates. Single-spin qubit operation using magnetic resonance in the few-electron regime reveals relaxation times of over 1 s at 1 T and coherence times of over 3 ms.

Bulk phase transformation kinetics were not well understood before Davenport and Bain developed time-temperature-transformation (TTT) diagrams for steel alloys in the 1930s. These powerful diagrams revolutionized the heat treatment of steel and other alloys. Grain boundaries and internal interfaces are now known to behave in a phase-like manner, referred to as 'complexions', and their transitions can be represented on TTT diagrams. We present experimental grain boundary complexion TTT diagrams for polycrystalline Al2O3 and Y2O3. Grain boundary mobility discontinuities in Y2O3 occur at different temperatures for different annealing times, an unusual pattern that becomes understandable when viewed on a complexion TTT diagram. Similarly, the anisotropy of Al2O3 complexion kinetics can be visualized with these diagrams. Complexion TTT diagrams are a graphical tool to control interface-related phenomena such as diffusion, creep, oxidation, and microstructure evolution. They could explain why two-step sintering produces dense nanocrystalline ceramics and offer insight into other processes as well.

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Grain-boundary character distributions (GBCDs) were determined for spark plasma sintered Y-and La-doped aluminas prepared at temperatures between 1450°C and 1600°C. La doping leads to grain boundaries that adopt (0001) orientations 3.7 times more frequently than expected in a random distribution, whereas the Y-doped microstructures are more equiaxed. At 1500°C, some of the boundaries in the Y-doped samples transform to a higher mobility complexion; in this microstructure, the f0112g grain-boundary plane is 1.3 times more likely to occur than expected in a random distribution. After the fastgrowing grains impinge, the dominant plane becomes f1120g and these boundaries have areas that are 1.2 times more likely to occur than expected in a random distribution. The grainboundary planes in the Y-and La-codoped samples preferred (0001) and f0112g orientations, combining the characteristics of the singly doped samples. Grain boundaries with a 60°m isorientation about [0001] were up to six times more common than random in the Y-doped samples. The preference for (0001) oriented grain-boundary planes in the La-doped sample persisted at all specific misorientations.H. Chan-contributing editor Manuscript No. 33558.