Self-driving laboratory for accelerated discovery of thin-film materials.

Discovering and optimizing commercially viable materials for clean energy applications typically takes more than a decade. Self-driving laboratories that iteratively design, execute, and learn from materials science experiments in a fully autonomous loop present an opportunity to accelerate this research process. We report here a modular robotic platform driven by a model-based optimization algorithm capable of autonomously optimizing the optical and electronic properties of thin-film materials by modifying the film composition and processing conditions. We demonstrate the power of this platform by using it to maximize the hole mobility of organic hole transport materials commonly used in perovskite solar cells and consumer electronics. This demonstration highlights the possibilities of using autonomous laboratories to discover organic and inorganic materials relevant to materials sciences and clean energy technologies.

Evidence for superconductivity in Li-decorated monolayer graphene.

Monolayer graphene exhibits many spectacular electronic properties, with superconductivity being arguably the most notable exception. It was theoretically proposed that superconductivity might be induced by enhancing the electron-phonon coupling through the decoration of graphene with an alkali adatom superlattice [Profeta G, Calandra M, Mauri F (2012) Nat Phys 8(2):131-134]. Although experiments have shown an adatom-induced enhancement of the electron-phonon coupling, superconductivity has never been observed. Using angle-resolved photoemission spectroscopy (ARPES), we show that lithium deposited on graphene at low temperature strongly modifies the phonon density of states, leading to an enhancement of the electron-phonon coupling of up to λ ≃ 0.58. On part of the graphene-derived π*-band Fermi surface, we then observe the opening of a Δ ≃ 0.9-meV temperature-dependent pairing gap. This result suggests for the first time, to our knowledge, that Li-decorated monolayer graphene is indeed superconducting, with Tc ≃ 5.9 K.

Aminoacyl-tRNA conformation. Information from steroid and oligonucleotide probes.

The conformations of aminoacyl- and deacylated tRNA Phe (yeast) have been compared by using the steroid progesterone and the tetranucleotides U-C-C-C and C-G-A-A as probes of transfer RNA ordered structure. U-C-C-C is complementary to G18-G19-G20-A21 in the dihydrouridine loop and C-G-A-A is complementary to T54-psi55-C56-G57 in the ribosylthymine loop. None of the probes bound to deacylated tRNA Phe but all three bound to phenylalanyl-tRNA Phe, with molar association constants of the order of 10(4) M-1. The oligonucleotide binding data imply that the tertiary hydrogen bonds between G18 and psi55, G19 and C56, T54 and m1A58, and A21 and the ribose of U8 (Quigley, G. J., Wang, A. H. J., Seeman, N. C., Suddath, F. L., Rich, A., Sussman, J. L., and Kim, S. H., (1975) Proc. Natl. Acad. Sci. U.S.A. 72, 4866-4870) are destabilized or broken on aminoacylation, unmasking the sequence T-psi-C-G thought to be involved in ribosome binding of aminoacyl-tRNA. The presumed progesterone binding site is G18-G19-G20, which is part of the binding site for U-C-C-C. Competition was not, however, observed between these two probes; model building has shown that they could, theoretically, bind simultaneously. Since progesterone bound to N-acetyl-Phe-tRNA Phe, the introduction of the additional positive charge on aminoacylation is not sufficient per se to explain the conformational change. The association of progesterone with peptidyl-tRNA Phe was similar to that with aminoacyl-tRNA Phe, implying that no further conformational change takes place in the region of the steroid binding site on formation of a peptide bond.