Quantum dots are often called artificial atoms because, like real atoms, they confine electrons to quantized states with discrete energies. However, although real atoms are identical, most quantum dots comprise hundreds or thousands of atoms, with inevitable variations in size and shape and, consequently, unavoidable variability in their wavefunctions and energies. Electrostatic gates can be used to mitigate these variations by adjusting the electron energy levels, but the more ambitious goal of creating quantum dots with intrinsically digital fidelity by eliminating statistical variations in their size, shape and arrangement remains elusive. We used a scanning tunnelling microscope to create quantum dots with identical, deterministic sizes. By using the lattice of a reconstructed semiconductor surface to fix the position of each atom, we controlled the shape and location of the dots with effectively zero error. This allowed us to construct quantum dot molecules whose coupling has no intrinsic variation but could nonetheless be tuned with arbitrary precision over a wide range. Digital fidelity opens the door to quantum dot architectures free of intrinsic broadening-an important goal for technologies from nanophotonics to quantum information processing as well as for fundamental studies of confined electrons.

We presented an extensible multidimensional sensor with conjugated nonspecific dye-labeled DNA sequences absorbed onto gold nanoparticles (DNA-AuNPs) as receptors. At the presence of target protein, DNA was removed from the surface of AuNPs due to the competitive binding, which resulted in a red-to-blue color change along with salt-induced aggregation of AuNPs for colorimetric analysis and fluorescent "turn-on" signal of the labeled dye for fluorescence analysis. The orthogonal and complementary fluorescent and colorimetric signals obtained from each protein were applied to distinguish different proteins. By simply changing the DNA sequences, more dual-channel sensing elements could be easily obtained and added into this multidimensional sensor. This enhanced its discriminating power to the proteins. With three sensing elements, our extensible multidimensional sensing platform exhibited excellent discrimination ability. Eleven proteins at the concentration of 50 nM had been classified with accuracies of 100% by using linear discriminant analysis (LDA). Remarkably, two similar proteins [bovine serum albumin (BSA) and human serum albumin (HSA)] at various concentrations and the mixture of these two proteins with different molar ratios had been successfully discriminated in one LDA plot as well. Furthermore, in the presence of human urine sample, 10 proteins at 1.0 μM could also be well-discriminated. The accuracy of discrimination of unknown samples was all 100% for these experiments. This strategy is a complement of the multidimensional sensing system and traditional sensor platform, offering a new way to develop sensitive array sensing systems.

The vertical manipulation of native adatoms on a III-V semiconductor surface was achieved in a scanning tunneling microscope at 5 K. Reversible repositioning of individual In atoms on InAs(111)A allows us to construct one-atom-wide In chains. Tunneling spectroscopy reveals that these chains host quantum states deriving from an adatom-induced electronic state and substantial substrate-mediated coupling. Our results show that the combined approach of atom manipulation and local spectroscopy is capable to explore atomic-scale quantum structures on semiconductor platform.

Abstract. The performances of the new ScientaOmicron LT-UHV 4-STM microscope have been certified by a series of state-of-art STM experiments on an Au(1 1 1) surface at 4.3 K. During the STM operation of the 4 STM scanners (independently or in parallel with an inter tip apex front to front distance down to a few tens of nanometers), a ΔZ stability of about 2 pm per STM was demonstrated. With this LT-UHV 4-STM stability, single Au atom manipulation experiments were performed on Au(1 1 1) by recording the pulling, sliding and pushing manipulation signals per scanner. Jump to contact experiments lead to perfectly linear low voltage I-V characteristics on a contacted single Au ad-atom with no need of averaging successive I-V's. Our results show how this new instrument is exactly 4 times a very precise single tip LT-UHV-STM. Two tips surface conductance measurements were performed on Au(1 1 1) using a lock-in technique in a floating sample mode of operation to capture the Au(1 1 1) surface states via two STM tips dI/dV characteristics.

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On a native graphite surface, 15 nm-thick solid-state nanogears are nanofabricated with a 30 nm outer diameter and six teeth. The nanogears are manipulated one at a time by the tip of an atomic force microscope using the sample stage displacements for the manipulation and recording of the corresponding manipulation signals. For step heights below 3.0 nm, nanogears are manipulated up and down native graphite surface step edges. In the absence of a central shaft per nanogear, gearing between nanogears is limited to a few 1/12 turns for six teeth. When the graphite step is higher than 3 nm, a rack-and-pinion mechanism was constructed along the edge with a 90 nm nanogear pinion.