Brood hiding test: a new bioassay for behavioral and neuroethological ant research

We describe a new bioassay for behavioral and neuroethological ant research, the brood hiding test. A group of adult ants is taken out of the nest, confined together with brood and exposed to strong light. Ants may interact with brood, and, in particular, transport it to the provided shadowed area. The brood hiding test may be accompanied by administration of neuroactive compounds and/or by measurements of their levels in the brain and/or in specific brain structures. During pilot tests with workers of Formica polyctena the values of the score quantifying ant behavior were positively correlated with the group size

Ferroelectricity and negative piezoelectric coefficient in orthorhombic phase pure ZrO2 thin films

A new approach for epitaxial stabilisation of ferroelectric orthorhombic (o-) ZrO2 films with negative piezoelectric coefficient in ∼ 8nm thick films grown by ion-beam sputtering is demonstrated. Films on (011)-Nb:SrTiO3 gave the oriented o-phase, as confirmed by transmission electron microscopy and electron backscatter diffraction mapping, grazing incidence x-ray diffraction and Raman spectroscopy. Scanning probe microscopy techniques and macroscopic polarization-electric field hysteresis loops show ferroelectric behavior, with saturation polarization of ∼14.3 µC/cm2, remnant polarization of ∼9.3 µC/cm2 and coercive field ∼1.2 MV/cm. In contrast to the o-films grown on (011)-Nb:SrTiO3, films grown on (001)-Nb:SrTiO3 showed mixed monoclinic (m-) and o-phases causing an inferior remnant polarization of ∼4.8 µC/cm2, over 50% lower than the one observed for the film grown on (011)-Nb:SrTiO3. Density functional theory (DFT) calculations of the SrTiO3/ZrO2 interfaces support the experimental findings of a stable polar o-phase for growth on (011) Nb:SrTiO3, and they also explain the negative piezoelectric coefficient.This work was supported by: (i) the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding Contract UIDB/04650/2020 and (ii) Project NECL - NORTE-01-0145-FEDER-022096 and Project UID/NAN/50024/2019. This work has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 958174 (M-ERA-NET3/0003/2021 - NanOx4EStor). This work was also developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, financed by national funds through the Portuguese Foundation for Science and Technology/MCTES. It is also funded by national funds (OE), through FCT – Fundação para a Ciência e a Tecnologia, I.P., in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of the article 23, of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19.The calculations were carried out at the OBLIVION Supercomputer (based at the High Performance Computing Center - University of Évora) funded by the ENGAGE SKA Research Infrastructure (reference POCI-01-0145-FEDER-022217 - COMPETE 2020 and the Foundation for Science and Technology, Portugal) and by the BigData@UE project (reference ALT20-03-0246-FEDER-000033 - FEDER and the Alentejo 2020 Regional Operational Program). Oblivion resources were accessed through the advanced computing projects CPCA/A2/5649/2020 and CPCA/A2/4628/2020, funded by FCT I.P. The authors gratefully acknowledge the HPC RIVR consortium (www.hpc-rivr.si) and EuroHPC JU (eurohpc-ju.europa.eu) for funding this research by providing computing resources of the HPC system Vega at the Institute of Information Science (www.izum.si)The calculations were carried out at the OBLIVION Supercomputer (based at the High Performance Computing Center - University of Évora) funded by the ENGAGE SKA Research Infrastructure (reference POCI-01-0145-FEDER-022217 - COMPETE 2020 and the Foundation for Science and Technology, Portugal) and by the BigData@UE project (reference ALT20-03-0246-FEDER-000033 - FEDER and the Alentejo 2020 Regional Operational Program). Oblivion resources were accessed through the advanced computing projects CPCA/A2/5649/2020 and CPCA/A2/4628/2020, funded by FCT I.P. The authors gratefully acknowledge the HPC RIVR consortium (www.hpc-rivr.si) and EuroHPC JU (eurohpc-ju.europa.eu) for funding this research by providing computing resources of the HPC system Vega at the Institute of Information Science (www.izum.si

Nanoscale device engineering and plasmon-enhanced light – matter interactions for the characterization of 2D materials

The PhD thesis introduces nanoscale tools for optoelectronic characterization of 2D materials, addressing limitations of existing techniques including destructiveness, imprecision, and vacuum requirements. Three novel characterization methods are proposed. They all employ gold nanoparticles as electrical contacts, offering both nano-sized electrodes and significant optical enhancement within the biased region, enabling the first precise, non invasive concurrent optical and electrical characterization of nanomaterials. The established methods are subsequently applied to evaluate the potential of 2D materials as nanoscale electrical switches by analysing the kinetics of their switching mechanism. First, the thesis presents a technique involving the drop-casting of gold nanoparticles onto 2D materials placed on gold substrates. Electrical contact is established by positioning an optically transparent and electrically conductive cantilever on a single nanoparticle. It is used to unveil morphological nano-processes occurring in MoS2 electrical nano-switches, known for their ultralow switching energies but poorly understood switching mechanism. Second, a novel scanning plasmonic microscopy technique is devised, utilizing a plasmonic nanoprobe with a single gold nanoparticle on an optically transparent and conductive cantilever. The nanoprobes enable precise electrode positioning on various material regions, offering user-friendliness, durability, reproducibility, and minimal material perturbation, as validated on WSe2 and MoS2 nanosheets, making them applicable to diverse materials. Third, the thesis introduces a configuration where a nanosheet is biased using patterned gold nano-discs located at the intersection of striped electrodes patterned using shadow masks. This layout eliminates the need for motorized cantilevers and the variability in the location of gold nanoparticles, as observed in the first approach. This configuration is employed to gain an understanding of the switching mechanism in nanoscale h-BN memristors, which are promising as foundational components for logic-in-memory computing systems. Therefore, this PhD thesis introduces nano-techniques for characterizing 2D materials, yielding insights into their electrical behaviour. These findings have implications for advancing and optimizing 2D electronic devices, opening new avenues for nanotechnology applications

Fully Optical in Operando Investigation of Ambient Condition Electrical Switching in MoS2 Nanodevices.

Funder: Winton Programme for the Physics of SustainabilityFunder: Cambridge Trust; Id: http://dx.doi.org/10.13039/501100003343MoS2 nanoswitches have shown superb ultralow switching energies without excessive leakage currents. However, the debate about the origin and volatility of electrical switching is unresolved due to the lack of adequate nanoimaging of devices in operando. Here, three optical techniques are combined to perform the first noninvasive in situ characterization of nanosized MoS2 devices. This study reveals volatile threshold resistive switching due to the intercalation of metallic atoms from electrodes directly between Mo and S atoms, without the assistance of sulfur vacancies. A "semi-memristive" effect driven by an organic adlayer adjacent to MoS2 is observed, which suggests that nonvolatility can be achieved by careful interface engineering. These findings provide a crucial understanding of nanoprocess in vertically biased MoS2 nanosheets, which opens new routes to conscious engineering and optimization of 2D electronics

Research Data supporting "Fully optical in operando investigation of ambient condition electrical switching in MoS2 nanodevices"

The research project the data originated from: MoS2 nanoswitches have shown superb ultra-low switching energies without excessive leakage currents. However, the debate about the origin and volatility of electrical switching is unresolved due to the lack of adequate nano-imaging of devices in operando. Here, we combine three optical techniques to perform the first non-invasive in situ characterization of nanosized MoS2 devices. Our study reveals volatile threshold resistive switching due to the intercalation of metallic atoms from electrodes directly between Mo and S atoms, without the assistance of sulfur vacancies. We observe a ‘semi-memristive’ effect driven by an organic adlayer adjacent to MoS2, which suggests that non-volatility can be achieved by careful interface engineering. Our findings provide a crucial understanding of nano-process in vertically biased MoS2 nanosheets, which opens new routes to conscious engineering and optimization of 2D electronics. $$\$$ The dataset usage instructions: Names of data files correspond to the names of Figures whose data they contain. Files: Figure_1f.002 and Figure_S3a.013_2 are rough AFM scans used for Figures 1f and S3a, respectively. To process the data, please download the Gwyddion software and follow the instructions from: http://gwyddion.net/. Optical and electrical data for Figures 1b-c, 2-3, 4a, 4d, 5a, S2a-b, S5 can be processed using any software for data analysis, such as Spyder (https://www.spyder-ide.org/). All optical data was pre-processed with background subtraction. Additionally, dark field scattering data (Fig. 1b, 4a, 4d, S2b) were reference normalized. Lorentzian curves were fitted to data (Fig. 1c, 2c, 3c) using Spyder software. Finally, Lorentzian fits of the photoluminescence response were subtracted to achieve clear Raman spectra (Fig. 1c, 3c insert). For all electrical data current was recalculated to current density by dividing measured current by electrode’s area (706.5 nm2). The outcome of FDTD simulations was exported to .txt format and provided in files for Figures 4b-c, S2c, and S4. It can be accessed by any software for data analysis, such as Spyder (https://www.spyder-ide.org/). $$\$$ The data collection methods: The optical and electrical data (files for Figures 1b-c, 2-3, 4a, 4d, 5a, S2a-b, S5) were collected using self-made setup as described in: https://doi.org/10.1002/adma.202209968, 5 Experimental Section -> Electrical Setup, Optical Setup. The setup was operated with self-written software in Python 3. FDTD simulations (files for Figures 4b-c, S2c, and S4) were performed as described in https://doi.org/10.1002/adma.202209968, 5 Experimental Section -> Electrical Setup, FDTD Simulations. Atomic force microscopy (AFM) scans (files for Figures 1f and S3) were collected with the AFM Multimode Nanoscope III. All data were collected at the University of Cambridge, Department of Materials Science & Metallurgy

Scanning Plasmon-Enhanced Microscopy for Simultaneous Optoelectrical Characterization

Scanning microscopy methods are crucial for the advancement of nanoelectronics. However, the vertical nano-probes in such techniques suffer limitations such as the fragility at the tip-sample interface, complex instrumentation, and the lack of in-operando functionality in several cases. Here, we introduce scanning plasmon-enhanced microscopy (SPEM) and demonstrate its capabilities on MoS2 and WSe2 nanosheets. SPEM combines a nanoparticle-on-mirror (NPoM) configuration with a portable conductive cantilever, enabling simultaneous optical and electrical characterization. This distinguishes it from other current techniques, which cannot provide both characterizations simultaneously. It offers a competitive optical resolution of 600 nm with local enhancement of optical signal up to 20,000 times. A single gold nanoparticle with a 15 nm radius forms pristine, non-damaging van der Waals contact, which allows observation of unexpected p-type behavior of MoS2 at the nanoscale. SPEM reconstructs the NPoM method by eliminating the need for extensive statistical analysis and offering excellent nanoscale mapping resolution of any selected region. It surpasses other scanning techniques in combining precise optical and electrical characterization, interactive simplicity, tip durability, and reproducibility, positioning it as the optimal tool for advancing nanoelectronics