Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 6 de 6
Mais filtros

Base de dados
Intervalo de ano de publicação
Nanoscale ; 11(41): 19462-19467, 2019 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-31528938


Conductance measurements in single-molecule junctions (SMJs) are on many occasions accompanied by inelastic spectroscopy and shot-noise measurements in order to obtain information about different vibration modes (or vibrons) and channels involved in the transport respectively. We have extended the single-molecule shot-noise measurements, which were previously performed at low bias, to high bias and we have studied the effects of these vibrons on the noise for a Deuterium (D2) molecule between Pt leads. We report here two important findings from these measurements. First, we find in our noise measurements that at the vibron energies of the molecule, a two-level fluctuation (TLF) is excited in the junction. Second, we show that in the presence of this TLF, a form of enhanced noise spectroscopy can be performed to detect inelastic electron-vibron interactions, by studying the third derivative of the noise (d3SI/dV3). This is possible because TLFs are insensitive to elastic scattering of electrons from defects, which nevertheless leave their signature in the usual inelastic electron tunnelling spectroscopy (IETS) measurements.

Beilstein J Nanotechnol ; 10: 337-348, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-30800573


A new way to control individual molecules and monoatomic chains is devised by preparing a human-machine augmented system in which the operator and the machine are connected by a real-time simulation. Here, a 3D motion control system is integrated with an ultra-high vacuum (UHV) low-temperature scanning tunnelling microscope (STM). Moreover, we coupled a real-time molecular dynamics (MD) simulation to the motion control system that provides a continuous visual feedback to the operator during atomic manipulation. This allows the operator to become a part of the experiment and to make any adaptable tip trajectory that could be useful for atomic manipulation in three dimensions. The strength of this system is demonstrated by preparing and lifting a monoatomic chain of gold atoms from a Au(111) surface in a well-controlled manner. We have demonstrated the existence of Fabry-Pérot-type electronic oscillations in such a monoatomic chain of gold atoms and determined its phase, which was difficult to ascertain previously. We also show here a new geometric procedure to infer the adatom positions and therefore information about the substrate atoms, which are not easily visible on clean metallic surfaces such as gold. This method enables a new controlled atom manipulation technique, which we will refer to as point contact pushing (PCP) technique.

Micromachines (Basel) ; 9(6)2018 May 29.
Artigo em Inglês | MEDLINE | ID: mdl-30424203


Molecular electronics saw its birth with the idea to build electronic circuitry with single molecules as individual components. Even though commercial applications are still modest, it has served an important part in the study of fundamental physics at the scale of single atoms and molecules. It is now a routine procedure in many research groups around the world to connect a single molecule between two metallic leads. What is unknown is the nature of this coupling between the molecule and the leads. We have demonstrated recently (Tewari, 2018, Ph.D. Thesis) our new setup based on a scanning tunneling microscope, which can be used to controllably manipulate single molecules and atomic chains. In this article, we will present the extension of our molecular dynamic simulator attached to this system for the manipulation of single molecules in real time using a graphics processing unit (GPU). This will not only aid in controlled lift-off of single molecules, but will also provide details about changes in the molecular conformations during the manipulation. This information could serve as important input for theoretical models and for bridging the gap between the theory and experiments.

Nano Lett ; 18(8): 5217-5223, 2018 08 08.
Artigo em Inglês | MEDLINE | ID: mdl-29957997


Since the work of Walter Schottky, it is known that the shot-noise power for a completely uncorrelated set of electrons increases linearly with the time-averaged current. At zero temperature and in the absence of inelastic scattering, the linearity relation between noise power and average current is quite robust, in many cases even for correlated electrons. Through high-bias shot-noise measurements on single Au atom point contacts, we find that the noise power in the high-bias regime shows highly nonlinear behavior even leading to a decrease in shot noise with voltage. We explain this nonlinearity using a model based on quantum interference of electron waves with varying path difference due to scattering from randomly distributed defect sites in the leads, which makes the transmission probability for these electrons both energy and voltage dependent.

Beilstein J Nanotechnol ; 8: 2389-2395, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-29234574


Scanning tunneling microscopes (STM) are used extensively for studying and manipulating matter at the atomic scale. In spite of the critical role of the STM tip, procedures for controlling the atomic-scale shape of STM tips have not been rigorously justified. Here, we present a method for preparing tips in situ while ensuring the crystalline structure and a reproducibly prepared tip structure up to the second atomic layer. We demonstrate a controlled evolution of such tips starting from undefined tip shapes.

Rev Sci Instrum ; 88(9): 093903, 2017 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-28964189


Shot noise measurements on atomic and molecular junctions provide rich information about the quantum transport properties of the junctions and on the inelastic scattering events taking place in the process. Dissipation at the nanoscale, a problem of central interest in nano-electronics, can be studied in its most explicit and simplified form. Here, we describe a measurement technique that permits extending previous noise measurements to a much higher frequency range, and to much higher bias voltage range, while maintaining a high accuracy in noise and conductance. We also demonstrate the advantages of having access to the spectral information for diagnostics.