arXiv subjects

Peter Grutter

Publications and source records attributed to Peter Grutter.

21 records · Page 2Linked to original sources

arXiv2009

Energy levels of few electron quantum dots imaged and characterized by atomic force microscopy

Strong confinement of charges in few electron systems such as in atoms, molecules and quantum dots leads to a spectrum of discrete energy levels that are often shared by several degenerate quantum states. Since the electronic structure is key to understanding their chemical properties, methods that probe these energy levels in situ are important. We show how electrostatic force detection using atomic force microscopy reveals the electronic structure of individual and coupled self-assembled quantum dots. An electron addition spectrum in the Coulomb blockade regime, resulting from a change in cantilever resonance frequency and dissipation during tunneling events, shows one by one electron charging of a dot. The spectra show clear level degeneracies in isolated quantum dots, supported by the first observation of predicted temperature-dependent shifts of Coulomb blockade peaks. Further, by scanning the surface we observe that several quantum dots may reside on what topologically appears to be just one. These images of grouped weakly and strongly coupled dots allow us to estimate their relative coupling strengths.

cond-mat.mes-hall↗

arXiv2005

Detection of Single Electron Charging in an Individual InAs Quantum Dot by Noncontact Atomic Force Microscopy

Single electron charging in an individual InAs quantum dot was observed by electrostatic force measurements with an atomic force microscope (AFM). The resonant frequency shift and the dissipated energy of an oscillating AFM cantilever were measured as a function of the tip-back electrode voltage and the resulting spectra show distinct jumps when the tip was positioned above the dot. The observed jumps in the frequency shift, with corresponding peaks in dissipation, are attributed to a single electron tunneling between the dot and the back electrode governed by Coulomb blockade effect, and are consistent with a model based on the free energy of the system. The observed phenomenon may be regarded as the ``force version'' of the Coulomb blockade effect.

cond-mat.mtrl-sci↗

arXiv2001

I-V characteristics and differential conductance fluctuations of Au nanowires

Electronic transport properties of Au nano-structure are investigated using both experimental and theoretical analysis. Experimentally, stable Au nanowires were created using mechanically controllable break junction in air, and simultaneous current-voltage (I-V) and differential conductance $δI/δV$ data were measured. The atomic device scale structures are mechanically very stable up to bias voltage $V_b\sim0.6V$ and have a life time of a few $minutes$. Facilitated by a shape function data analysis technique which finger-prints electronic properties of the atomic device, our data show clearly differential conductance fluctuations with an amplitude $>1%$ at room temperature, and a nonlinear I-V characteristics. To understand the transport features of these atomic scale conductors, we carried out {\it ab initio} calculations on various Au atomic wires. The theoretical results demonstrate that transport properties of these systems crucially depend on the electronic properties of the scattering region, the leads, and most importantly the interaction of the scattering region with the leads. For ideal, clean Au contacts, the theoretical results indicate a linear I-V behavior for bias voltage $V_b<0.5V$. When sulfur impurities exist at the contact junction, nonlinear I-V curves emerge due to a tunnelling barrier established in the presence of the S atom. The most striking observation is that even a single S atom can cause a qualitative change of the I-V curve from linear to nonlinear. A quantitatively favorable comparison between experimental data and theoretical results is obtained. We also report other results concerning quantum transport through Au atomic contacts.

physics.comp-ph↗