It has long been anticipated that the ultimate in miniature circuitry will be crafted of single atoms. Despite many advances made in scanned probe microscopy studies of molecules and atoms on surfaces, challenges with patterning and limited thermal stability have remained.Here we make progress toward those challenges and demonstrate rudimentary circuit elements through the patterning of dangling bonds on a hydrogen-terminated silicon surface. Dangling bonds sequester electrons both spatially and energetically in the bulk band gap, circumventing short-circuiting by the substrate. We deploy paired dangling bonds occupied by one moveable electron to form a binary electronic building block.Inspired by earlier quantum dot-based approaches, binary information is encoded in the electron position allowing demonstration of a "binary wire" and an OR gate.The prospect of atom scale computing was initially indicated by "molecular cascades"where sequentially toppling molecules were arranged in precise configurations to achieve binary logic functions 1 . Many notable approaches toward molecular electronics 2-7 , atomic electronics 8,9 , and quantum-dot-based electronics 10-15 have also been explored.The quantum dot based approaches [16][17][18][19][20] are particularly attractive, as they provide a low power yet fast basis 21 to go beyond today's CMOS technology 22 . These approaches, however, require cryogenic temperatures to minimize the population of thermally-excited states and achieve the desired functionality. Variability among quantum dots and sensitivity to uncontrolled fields are

Photoredox catalysis provides many green opportunities for radical-mediated synthetic transformations. However, the determination of the underlying mechanisms has been challenging due to lack of quantitative methods that can be easily implemented in synthetic labs, where this research tends to be centered. We report here on the development, characterization and calibration of a novel actinometer based on the photocatalyst tris(2,2′-bipyridyl)ruthenium(II) chloride (Ru(bpy)3Cl2). By using the same molecule as the photocatalyst and the actinometer, we eliminate problems associated with matching sample spectral distribution, lamp-sample spectral overlap and other problems intrinsic to doing quantitative photochemistry in a laboratory that has little expertise in this area. In order to validate our actinometer system in determining the quantum yield of a Ru(bpy)3Cl2 photosensitized reaction, we test the Ru(bpy)3Cl2 catalyzed oxidation of benzhydrol to benzophenone as a model chain reaction. We also revive the rotating sector method by updating the technique for modern LED technologies and demonstrate how intermittent illumination on the timescale of milliseconds to seconds can help probe a chain reaction, using the benzhydrol to benzophenone oxidation to validate the technique. We envision these methods to have great implications in the field of photoredox catalysis, providing researchers with valuable research tools.

This paper introduces SiQAD, a computer-aided design tool enabling the rapid design and simulation of atomic silicon dangling bond quantum dot patterns capable of computational logic. Several simulation tools are included, each able to inform the designer on various aspects of their designs: a ground-state electron configuration finder, a non-equilibrium electron dynamics simulator, and an electric potential landscape solver with clocking electrode support. Simulations have been compared against past experimental results to inform the electron population estimation and dynamic behavior. New logic gates suitable for this platform have been designed and simulated, and a clocked wire has been demonstrated. This work paves the way for the exploration of the vast and fertile design space of atomic silicon dangling bond quantum dot circuits.

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Using a non-contact atomic force microscope we track and manipulate the position of single electrons confined to atomic structures engineered from silicon dangling bonds (DBs) on the hydrogen terminated silicon surface. By varying the probe-sample separation we mechanically manipulate the equilibrium position of individual surface silicon atoms and use this to directly switch the charge state of individual DBs. Because this mechanism is based on short range interactions and can be performed without applied bias voltage, we maintain both site-specific selectivity and single-electron control. We extract the short range forces involved with this mechanism by subtracting the long range forces acquired on a dimer vacancy site. As a result of relaxation of the silicon lattice to accommodate negatively charged DBs we observe charge configurations of DB structures that remain stable for many seconds at 4.5 K. Subsequently we use charge manipulation to directly prepare the ground state and metastable charge configurations of DB structures composed of up to six atoms.