arXiv subjects

Andrea Zappe

Publications and source records attributed to Andrea Zappe.

8 recordsLinked to original sources

arXiv2021

Three-dimensional imaging of integrated-circuit activity using quantum defects in diamond

The continuous scaling of semiconductor-based technologies to micron and sub-micron regimes has resulted in higher device density and lower power dissipation. Many physical phenomena such as self-heating or current leakage become significant at such scales, and mapping current densities to reveal these features is decisive for the development of modern electronics. However, advanced non-invasive technologies either offer low sensitivity or poor spatial resolution and are limited to two-dimensional spatial mapping. Here we use near-surface nitrogen-vacancy centres in diamond to probe Oersted fields created by current flowing within a multi-layered integrated circuit in pre-development. We show the reconstruction of the three-dimensional components of the current density with a magnitude down to about $\approx 10 \,\rm \mu A / \mu m^2$ and sub-micron spatial resolution at room temperature. We also report the localisation of currents in different layers and observe anomalous current flow in an electronic chip. Our method provides, therefore a decisive step toward three-dimensional current mapping in technologically relevant nanoscale electronics chips.

physics.app-ph↗

arXiv2021

Lateral diffusion of phospholipids in artificial cell membranes measured by single shallow NV centers

We measure diffusion of organic molecules located a few nanometers from the diamond surface. To study molecular diffusion, we perform local detection of nuclear magnetic resonance, based on single shallow Nitrogen-Vacancy (NV) centers in diamond. Specifically, we demonstrate measurements of translational diffusion coefficient of phospholipids in an artificial cell membrane by employing correlation spectroscopy. An analysis of correlation decay curves using different diffusion models shows, that a simple 2D diffusion model gives satisfactory diffusion coefficients, although the choice of the model affects the extracted numbers. We find significant differences among the diffusion coefficients measured by different single NV centers, which we attribute to local heterogeneities of the lipid layers, likely caused by the supporting diamond substrate.

cond-mat.mes-hall↗

arXiv2018

Robust and efficient control of spin probes in a complex (biological) environment. Towards sensing of fast temperature fluctuations

We present an optimized scheme for nanoscale measurements of temperature in a complex environment using the nitrogen-vacancy center in nanodiamonds. To this end we combine a Ramsey measurement utilized to temperature determination with advanced optimal control theory. We test our new design on single nitrogen-vacancy centers in bulk diamond and fixed nanodiamonds, achieving better readout signal than with common soft or hard microwave control pulses. We demonstrate temperature readout using rotating nanodiamonds in an agarose matrix. Our method opens the way to measure temperature fluctuations in complex biological environment. The used principle however, is universal and not restricted to temperature sensing.

cond-mat.mes-hall↗

arXiv2017

Quantum light in curved low dimensional hexagonal boron nitride systems

Low-dimensional wide bandgap semiconductors open a new playing field in quantum optics using sub-bandgap excitation. In this field, hexagonal boron nitride (h-BN) has been reported to host single quantum emitters (QEs), linking QE density to perimeters. Furthermore, curvature/perimeters in transition metal dichalcogenides (TMDCs) have demonstrated a key role in QE formation. We investigate a curvature-abundant BN system - quasi one-dimensional BN nanotubes (BNNTs) fabricated via a catalyst-free method. We find that non-treated BNNT is an abundant source of stable QEs and analyze their emission features down to single nanotubes, comparing dispersed/suspended material. Combining high spatial resolution of a scanning electron microscope, we categorize and pin-point emission origin to a scale of less than 20 nm, giving us a one-to-one validation of emission source with dimensions smaller than the laser excitation wavelength, elucidating nano-antenna effects. Two emission origins emerge: hybrid/entwined BNNT. By artificially curving h-BN flakes, similar QE spectral features are observed. The impact on emission of solvents used in commercial products and curved regions is also demonstrated. The 'out of the box' availability of QEs in BNNT, lacking processing contamination, is a milestone for unraveling their atomic features. These findings open possibilities for precision engineering of QEs, puts h-BN under a similar 'umbrella' of TMDC's QEs and provides a model explaining QEs spatial localization/formation using electron/ion irradiation and chemical etching.

cond-mat.mes-hall↗

arXiv2017

Molecular quantum spin network controlled by a single qubit

Scalable quantum technologies will require an unprecedented combination of precision and complexity for designing stable structures of well-controllable quantum systems. It is a challenging task to find a suitable elementary building block, of which a quantum network can be comprised in a scalable way. Here we present the working principle of such a basic unit, engineered using molecular chemistry, whose control and readout are executed using a nitrogen vacancy (NV) center in diamond. The basic unit we investigate is a synthetic polyproline with electron spins localized on attached molecular sidegroups separated by a few nanometers. We demonstrate the readout and coherent manipulation of very few ($\leq 6 $) of these $S=1/2$ electronic spin systems and access their direct dipolar coupling tensor. Our results show, that it is feasible to use spin-labeled peptides as a resource for a molecular-qubit based network, while at the same time providing simple optical readout of single quantum states through NV-magnetometry. This work lays the foundation for building arbitrary quantum networks using well-established chemistry methods, which has many applications ranging from mapping distances in single molecules to quantum information processing.

cond-mat.mes-hall↗

arXiv2015

Relaxometry and dephasing imaging of superparamagnetic magnetite nanoparticles using a single qubit

To study the magnetic dynamics of superparamagnetic nanoparticles we use scanning probe relaxometry and dephasing of the nitrogen-vacancy (NV) center in diamond, characterizing the spin-noise of a single 10-nm magnetite particle. Additionally, we show the anisotropy of the NV sensitivity's dependence on the applied decoherence measurement method. By comparing the change in relaxation (T 1 ) and dephasing (T 2 ) time in the NV center when scanning a nanoparticle over it, we are able to extract the nanoparticle's diameter and distance from the NV center using an Ornstein-Uhlenbeck model for the nanoparticle's fluctuations. This scanning-probe technique can be used in the future to characterize different spin label substitutes for both medical applications and basic magnetic nanoparticle behavior.

cond-mat.mes-hall↗

arXiv2013

Subunit rotation in single FRET-labeled F1-ATPase hold in solution by an anti-Brownian electrokinetic trap

FoF1-ATP synthase catalyzes the synthesis of adenosine triphosphate (ATP). The F1 portion can be stripped from the membrane-embedded Fo portion of the enzyme. F1 acts as an ATP hydrolyzing enzyme, and ATP hydrolysis is associated with stepwise rotation of the gamma and epsilon subunits of F1. This rotary motion was studied in great detail for the last 15 years using single F1 parts attached to surfaces. Subunit rotation of gamma was monitored by videomicroscopy of bound fluorescent actin filaments, nanobeads or nanorods, or single fluorophores. Alternatively, we applied single-molecule Förster resonance energy transfer (FRET) to monitor subunit rotation in the holoenzyme FoF1-ATP synthase which was reconstituted in liposomes. Now we aim to extend the observation times of single FRET-labeled F1 in solution using a modified version of the anti-Brownian electrokinetic trap (ABELtrap) invented by A. E. Cohen and W. E. Moerner. We used Monte Carlo simulations to reveal that stepwise FRET efficiency changes can be analyzed by Hidden Markov Models even at the limit of a low signal-to-background ratio that was expected due to high background count rates caused by the microfluidics of the ABELtrap.

q-bio.BM↗

arXiv2012

Step size of the rotary proton motor in single FoF1-ATP synthase from a thermoalkaliphilic bacterium by DCO-ALEX FRET

Thermophilic enzymes can operate at higher temperatures but show reduced activities at room temperature. They are in general more stable during preparation and, accordingly, are considered to be more rigid in structure. Crystallization is often easier compared to proteins from bacteria growing at ambient temperatures, especially for membrane proteins. The ATP-producing enzyme FoF1-ATP synthase from thermoalkaliphilic Caldalkalibacillus thermarum strain TA2.A1 is driven by a Fo motor consisting of a ring of 13 c-subunits. We applied a single-molecule Förster resonance energy transfer (FRET) approach using duty cycle-optimized alternating laser excitation (DCO-ALEX) to monitor the expected 13-stepped rotary Fo motor at work. New FRET transition histograms were developed to identify the smaller step sizes compared to the 10-stepped Fo motor of the Escherichia coli enzyme. Dwell time analysis revealed the temperature and the LDAO dependence of the Fo motor activity on the single molecule level. Back-and-forth stepping of the Fo motor occurs fast indicating a high flexibility in the membrane part of this thermophilic enzyme.

q-bio.BM↗