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Random nanowire networks (NWNs) are promising synthetic architectures for non-volatile memory devices and hardware-based neuromorphic applications due to their history-dependent responses, recurrent connectivity, and neurosynaptic-like behaviors. Such brain-like functions occur due to emergent resistive switching phenomena taking place in the interwire junctions which are viewed as memristive systems; they operate as smart analogue switches whose resistance depends on the history of the input voltage/current. We successfully demonstrated that NWNs made with a particular class of memristive junctions can exhibit a highly-selective conduction mechanism which uses the lowest-energy connectivity path in the network identified as the "winner-takes-all" state. However, these complex networks do not always behave in the same fashion; in the limit of sufficiently low input currents (preceding this selective conduction regime), the system behaves as a leakage capacitive network and its electrical activation is driven by cascades of breakdown-based activation events involving binary capacitive transitions. Understanding these two regimes is crucial to establish the potential of these materials for neuromorphics, and for this, we present two computational modelling schemes designed to describe the capacitive and memristive responses of NWNs interrogated adiabatically by voltage/current sources. Our results are corroborated by experimental evidence that reveal the fine electrical properties of NWN materials in their respective formation (capacitive) and conducting (memristive) stages. [ABSTRACT FROM AUTHOR]

We investigate the charging state of an isolated single dangling bond formed on an unpassivated Si(100) surface with c(4 χ 2) reconstruction, by comparing scanning tunneling microscopy and spectroscopy analysis with density functional theory calculations. The dangling bond is created by placing a single hydrogen atom on the bare surface with the tip of a scanning tunneling microscope. The Η atom passivates one of the dimer dangling bonds responsible for the surface one-dimensional electronic structure. This leaves a second dangling at the reacted surface dimer which breaks the surface periodicity. We consider two possible Η adsorption configurations for both the neutral and the doped situation (n- and p-type). In the case of n-doping we find that the single dangling bond state is doubly occupied and the most stable configuration is that with Η bonded to the bottom Si atom of the surface dimer In the case of p-doping the dangling bond is instead empty and the configuration with the Η attached to the top atom of the dimer is the most stable. Importandy the two configurations have different scattering properties and phase shift fingerprints. This might open up interesting perspectives for fabricating a switching device by tuning the doping level or by locally charging the single dangling bond state. [ABSTRACT FROM AUTHOR]

Halogen etching of Si(100) surfaces has long been considered to involve the selective removal of atoms from an essentially static surface. Here we show that vacancy sites produced by etching are mobile at elevated temperature and rearrange to form features that were considered to be the direct products of etching. We demonstrate that the etch features observed at different temperatures are not due to different mechanisms. Rather, kinetic etch products formed at low temperatures are transformed into thermodynamically more stable features at higher temperatures.

A chemically induced dimer configuration was prepared on the silicon (Si) (100) surface and was characterized by scanning tunneling microscopy (STM) and spectroscopy (STS). These prepared dimers, which are essentially untilted and differ both electronically and structurally from the dynamically tilting dimers normally found on this surface, are more reactive than normal dimers. For molecular hydrogen (H2) adsorption, the enhancement is about 10(9) at room temperature. There is no appreciable barrier for the H2 reaction at prepared sites, indicating the prepared configuration closely approximates the actual dimer structure in the transition state. This previously unknown ability to prepare specific surface configurations has important implications for understanding and controlling reaction dynamics on semiconductor surfaces.

Chlorine atoms strongly chemisorbed at dangling bond sites on the Si(100)-(2 x 1) surface are observed by scanning tunneling microscopy (STM) to hop between adjacent sites. The origin of this behavior is suggested to be an interaction between the field of the probe tip and the dipole moment of the silicon-chlorine bond. Chlorine atom migration is shown to be facilitated by the presence of a metastable chlorine bridge-bonded minimum. The STM probe was used to excite single chlorine atoms into this bridging configuration, resulting in a local population inversion. Selective application of voltage pulses between the probe tip and the surface rearranged the local bonding and induced transformations between different types of chlorine sites. In this manner, adsorbed species can be dissected and their composition and structure directly probed.

The various products from the reaction of chlorine (Cl) with the adatom layer of the Si(111)-(7x7) surface have been identified with scanning tunneling microscopy (STM). Initially, a single Cl atom reacts with the adatom dangling bond. At higher surface coverage, additional Cl atoms insert themselves into the Si-Si backbonds between the adatom and rest-atom layers, producing adatoms that have reacted with two or three Cl atoms. These products are characterized by different registries with respect to the underlying rest layer and appear in STM images as adatoms of different sizes, consistent with the breaking of Si-Si backbonds and the formation ofnew Si-Cl bonds.