arXiv subjects

Riccardo Frisenda

Publications and source records attributed to Riccardo Frisenda.

At least 19 recordsLinked to original sources

arXiv2026

Modular and Cost-effective Scanning Photocurrent Microscopy System for Sub-micron characterization of 2D optoelectronic devices

Scanning photocurrent microscopy (SPCM) is a powerful technique for probing local optoelectronic phenomena in 2D semiconducting devices. However, commercial setups remain costly, complex and often lack flexibility and adaptability. In this work, we present a home-built SPCM platform built around the retrofitting of a conventional metallographic microscope by coupling it with different light sources (single-mode fiber-coupled lasers and multimode fiber-coupled high-power LEDs), a motorized XY stage, a digital camera and an electronic readout module. This system enables simultaneous acquisition of photocurrent and reflection intensity maps, requiring minimal modifications of the microscope. We reached sub-micron spatial resolution and high imaging fidelity by correlating photocurrent maps with reflection maps, optical micrographs and AFM topography data on different devices fabricated with different materials (InSe, MoS2, WSe2, Gr), on different substrates (Si/SiO2, compact disk). This work provides a reliable, accessible and reproducible high-performance SPCM platform that can be easily implemented in most laboratories for microscale optoelectronic characterization of 2D devices.

cond-mat.mtrl-sci↗

arXiv2025

Strain Engineering of Correlated Charge-Ordered Phases in 1T-TaS2

Strain engineering is a powerful strategy for controlling the structural and electronic properties of two-dimensional materials, particularly in systems hosting charge density wave (CDW) order. In this work, we apply uniaxial tensile and compressive strain to thin 1T-TaS2 flakes using a flexible, device-compatible platform, and systematically investigate the strain-dependent behavior of the nearly commensurate (NC) to incommensurate (IC) CDW phase transition. This transition is driven by Joule heating at room temperature. Electrical transport measurements reveal that both the switching threshold voltage and the resistance of the NC-CDW phase exhibit clear, reversible strain dependence. Furthermore, we identify a quadratic dependence between the strain-induced resistance change and the threshold voltage, confirming that piezoresistive modulation governs the strain-tunability of the phase transition. We demonstrate a room-temperature, electrically-readout strain and displacement sensor with threshold-like response in a programmable window. These results highlight the potential of 1T-TaS2 for on-chip sensing of strain and displacement.

cond-mat.mes-hall↗

arXiv2022

Strongly anisotropic strain-tunability of excitons in exfoliated ZrSe$_3$

We study the effect of uniaxial strain on the band structure of ZrSe$_3$, a semiconducting material with a marked in-plane structural anisotropy. By using a modified 3-point bending test apparatus, thin ZrSe$_3$ flakes were subjected to uniaxial strain along different crystalline orientations monitoring the effect of strain on their optical properties through micro-reflectance spectroscopy. The obtained spectra showed excitonic features that blueshift upon uniaxial tension. This shift is strongly dependent on the direction along which the strain is being applied. When the flakes are strained along the b-axis, the exciton peak shifts at ~ 60-95 meV/%, while along the a-axis, the shift only reaches ~ 0-15 meV/%. Ab initio calculations were conducted to study the influence of uniaxial strain, applied along different crystal directions, on the band structure and reflectance spectra of ZrSe$_3$, exhibiting a remarkable agreement with the experimental results.

cond-mat.mtrl-sci↗

arXiv2022

An automated system for strain engineering and straintronics of 2D materials

This work presents an automated three-point bending apparatus that can be used to study strain engineering and straintronics in two-dimensional materials. We benchmark the system by reporting reproducible strain tuned micro-reflectance, Raman, and photoluminescence spectra for monolayer molybdenum disulfide (MoS2). These results are in good agreement with reported literature using conventional bending apparatus. We further utilize the system to automate strain investigations of straintronic devices by measuring the piezoresistive effect and the strain effect on photoresponse in an MoS2 electrical device. The details of the construction of the straightforward system are given and we anticipate it can be easily implemented for study of strain engineering and straintronics in a wide variety of 2D material systems.

physics.app-ph↗

arXiv2022

Broadband-tunable spectral response of perovskite-on-paper photodetectors using halide mixing

Paper offers a low-cost and widely available substrate for electronics. It posses alternative characteristics to silicon, as it shows low density and high-flexibility, together with biodegradability. Solution processable materials, such as hybrid perovskites, also present light and flexible features, together with a huge tunability of the material composition with varying optical properties. In this study, we combine paper substrates with halide-mixed perovskites for the creation of low-cost and easy-to-fabricate perovskite-on-paper photodetectors with a broadband-tunable spectral response. From the bandgap tunability of halide-mixed perovskites we create photodetectors with a cut-off spectral onset that ranges from the NIR to the green, by increasing the bromide content on MAPb(I$_{1-x}$Br$_x$)$_3$ perovskite alloys. The devices show a fast and efficient response. The best performances are observed for the pure I and Br perovskite compositions, with a maximum responsivity of 376 mA/W on the MAPbBr$_3$ device. This study provides an example of the wide range of possibilities that the combination of solution processable materials with paper substrates offer for the development of low-cost, biodegradable and easy-to-fabricate devices.

physics.app-ph↗

arXiv2021

Integrating van der Waals materials on paper substrates for electrical and optical applications

Paper holds the promise to replace silicon substrates in applications like internet of things or disposable electronics that require ultra-low-cost electronic components and an environmentally friendly electronic waste management. In the last years, spurred by the abovementioned properties of paper as a substrate and the exceptional electronic, mechanical and optical properties of van der Waals (vdW) materials, many research groups have worked towards the integration of vdW materials-based devices on paper. Recently, a method to deposit a continuous film of densely packed interconnects of vdW materials on paper by simply rubbing the vdW crystals against the rough surface of paper has been presented. This method utilizes the weak interlayer vdW interactions and allows cleaving of the crystals into micro platelets through the abrasion against the paper. Here, we aim to illustrate the general character and the potential of this technique by fabricating films of 39 different vdW materials (including superconductors, semi-metals, semiconductors, and insulators) on standard copier paper. We have thoroughly characterized their optical properties showing their high optical quality: one can easily resolve the absorption band edge of semiconducting vdW materials and even the excitonic features present in some vdW materials with high exciton binding energy. We also measured the electrical resistivity for several vdW materials films on paper finding exceptionally low values, which are in some cases, orders of magnitude lower than those reported for analogous films produced by inkjet printing. We finally demonstrate the fabrication of field-effect devices with vdW materials on paper using the paper substrate as an ionic gate.

cond-mat.mtrl-sci↗

arXiv2021

Optical microscopy-based thickness estimation in thin GaSe flakes

We have implemented three different optical methods to quantitatively assess the thickness of thin GaSe flakes transferred on both transparent substrates, like Gel-Film, or SiO2/Si substrates. We show how their apparent color can be an efficient way to make a quick rough estimation of the thickness of the flakes. This method is more effective for SiO2/Si substrates as the thickness dependent color change is more pronounced on these substrates than on transparent substrates. On the other hand, for transparent substrates, the transmittance of the flakes in the blue region of the visible spectrum can be used to estimate the thickness. We find that the transmittance of flakes in the blue part of the spectrum decreases at a rate of 1.2%/nm. On SiO2/Si, the thickness of the flakes can be accurately determined by fitting optical contrast spectra to a Fresnel law-based model. Finally, we also show how the quantitative analysis of transmission mode optical microscopy images can be a powerful method to quickly probe the environmental degradation of GaSe flakes exposed to aging conditions.

physics.optics↗

arXiv2021

Biaxial versus uniaxial strain tuning of single-layer MoS$_2$

Strain engineering has arisen as a powerful technique to tune the electronic and optical properties of two-dimensional semiconductors like molybdenum disulfide (MoS2). Although several theoretical works predicted that biaxial strain would be more effective than uniaxial strain to tune the band structure of MoS2, a direct experimental verification is still missing in the literature. Here we implemented a simple experimental setup that allows to apply biaxial strain through the bending of a cruciform polymer substrate. We used the setup to study the effect of biaxial strain on the differential reflectance spectra of 12 single-layer MoS2 flakes finding a redshift of the excitonic features at a rate between -40 meV/% and -110 meV/% of biaxial tension. We also directly compare the effect of biaxial and uniaxial strain on the same single-layer MoS2 finding that the biaxial strain gauge factor is 2.3 times larger than the uniaxial strain one.

physics.app-ph↗

arXiv2021

In-plane anisotropic optical and mechanical properties of two-dimensional MoO$_3$

Molybdenum trioxide (MoO$_3$) in-plane anisotropy has increasingly attracted the attention of the scientific community in the last few years. Many of the observed in-plane anisotropic properties stem from the anisotropic refractive index and elastic constants of the material but a comprehensive analysis of these fundamental properties is still lacking. Here we employ Raman and micro-reflectance measurements, using polarized light, to determine the angular dependence of the refractive index of thin MoO$_3$ flakes and we study the directional dependence of the MoO$_3$ Young's modulus using the buckling metrology method. We found that MoO$_3$ displays one of the largest in-plane anisotropic mechanical properties reported for 2D materials so far.

cond-mat.mtrl-sci↗

arXiv2021

Integrating superconducting van der Waals materials on paper substrates

Paper has the potential to dramatically reduce the cost of electronic components. In fact, paper is 10 000 times cheaper than crystalline silicon, motivating the research to integrate electronic materials on paper substrates. Among the different electronic materials, van der Waals materials are attracting the interest of the scientific community working on paper-based electronics because of the combination of high electrical performance and mechanical flexibility. Up to now, different methods have been developed to pattern conducting, semiconducting and insulating van der Waals materials on paper but the integration of superconductors remains elusive. Here, the deposition of NbSe2, an illustrative van der Waals superconductor, on standard copy paper is demonstrated. The deposited NbSe2 films on paper display superconducting properties (e.g. observation of Meissner effect and resistance drop to zero-resistance state when cooled down below its critical temperature) similar to those of bulk NbSe2.

cond-mat.supr-con↗

arXiv2020

Naturally occurring van der Waals materials

The exfoliation of two naturally occurring van der Waals minerals, graphite and molybdenite, arouse an unprecedented level of interest by the scientific community and shaped a whole new field of research: 2D materials research. Several years later, the family of van der Waals materials that can be exfoliated to isolate 2D materials keeps growing, but most of them are synthetic. Interestingly, in nature plenty of naturally occurring van der Waals minerals can be found with a wide range of chemical compositions and crystal structures whose properties are mostly unexplored so far. This Perspective aims to provide an overview of different families of van der Waals minerals to stimulate their exploration in the 2D limit.

cond-mat.mtrl-sci↗

arXiv2020

Drawing WS2 thermal sensors on paper substrates

Paper based thermoresistive sensors are fabricated by rubbing WS2 powder against a piece of standard copier paper, like the way a pencil is used to write on paper. The abrasion between the layered material and the rough paper surface erodes the material, breaking the weak van der Waals interlayer bonds, yielding a film of interconnected platelets. The resistance of WS2 presents a strong temperature dependence, as expected for a semiconductor material in which charge transport is due to thermally activated carriers. This strong temperature dependence makes the paper supported WS2 devices extremely sensitive to small changes in temperature. This exquisite thermal sensitivity, and their fast response times to sudden temperature changes, is exploited thereby demonstrating the usability of a WS2-on-paper thermal sensor in a respiration monitoring device.

physics.app-ph↗

arXiv2020

Large birefringence and linear dichroism in TiS3 nanosheets

TiS3 nanosheets have proven to be promising candidates for ultrathin optoelectronic devices due to their direct narrow band-gap and the strong light-matter interaction. In addition, the marked in-plane anisotropy of TiS3 is appealing for the fabrication of polarization sensitive optoelectronic devices. Herein, we study the optical contrast of TiS3 nanosheets of variable thickness on SiO2/Si substrates, from which we obtain the complex refractive index in the visible spectrum. We find that TiS3 exhibits very large birefringence, larger than that of well-known strong birefringent materials like TiO2 or calcite, and linear dichroism. These findings are in qualitative agreement with ab initio calculations that suggest an excitonic origin for the birefringence and linear dichroism of the material.

cond-mat.mtrl-sci↗

arXiv2020

Polarization-sensitive and broadband photodetection based on a mixed-dimensionality TiS3/Si p-n junction

The capability to detect the polarization state of light is crucial in many day-life applications and scientific disciplines. Novel anisotropic two-dimensional materials such as TiS3 combine polarization sensitivity, given by the in-plane optical anisotropy, with excellent electrical properties. Here we demonstrate the fabrication of a monolithic polarization sensitive broadband photodetector based on a mixed-dimensionality TiS3/Si p-n junction. The fabricated devices show broadband responsivity up to 1050 nm, a strong sensitivity to linearly polarized illumination with difference between the two orthogonal polarization states up to 350 % and a good detectivity and fast response time. The discussed devices can be used as building blocks to fabricate more complex polarization sensitive systems such as polarimeters.

physics.app-ph↗

arXiv2020

Thickness identification of thin InSe by optical microscopy methods

Indium selenide (InSe), as a novel van der Waals layered semiconductor, has attracted a large research interest thanks to its excellent optical and electrical properties in the ultra-thin limit. Here, we discuss four different optical methods to quantitatively identify the thickness of thin InSe flakes on various substrates, such as SiO2/Si or transparent polymeric substrates. In the case of thin InSe deposited on a transparent substrate, the transmittance of the flake in the blue region of the visible spectrum can be used to estimate the thickness. For InSe supported by SiO2/Si, the thickness of the flakes can be estimated either by assessing their apparent colors or accurately analyzed using a Fresnel-law based fitting model of the optical contrast spectra. Finally, we also studied the thickness dependency of the InSe photoluminescence emission energy, which provides an additional tool to estimate the InSe thickness and it works both for InSe deposited on SiO2/Si and on a transparent polymeric substrate.

cond-mat.mtrl-sci↗

arXiv2020

Giant piezoresistive effect and strong band gap tunability in ultrathin InSe upon biaxial strain

The ultrathin nature and dangling bonds free surface of two-dimensional (2D) semiconductors allow for significant modifications of their band gap through strain engineering. Here, thin InSe photodetector devices are biaxially stretched, finding, a strong band gap tunability upon strain. The applied biaxial strain is controlled through the substrate expansion upon temperature increase and the effective strain transfer from the substrate to the thin InSe is confirmed by Raman spectroscopy. The band gap change upon biaxial strain is determined through photoluminescence measurements, finding a gauge factor of up to ~200 meV/%. We further characterize the effect of biaxial strain on the electrical properties of the InSe devices. In the dark state, a large increase of the current is observed upon applied strain which gives a piezoresistive gauge factor value of ~450-1000, ~5-12 times larger than that of other 2D materials and of state-of-the-art silicon strain gauges. Moreover, the biaxial strain tuning of the InSe band gap also translates in a strain-induced redshift of the spectral response of our InSe photodetectors with ΔEcut-off ~173 meV at a rate of ~360 meV/% of strain, indicating a strong strain tunability of the spectral bandwidth of the photodetectors.

cond-mat.mtrl-sci↗

arXiv2020

Superlattices based on van der Waals 2D materials

Two-dimensional (2D) materials exhibit a number of improved mechanical, optical, electronic properties compared to their bulk counterparts. The absence of dangling bonds in the cleaved surfaces of these materials allows combining different 2D materials into van der Waals heterostructures to fabricate p-n junctions, photodetectors, 2D-2D ohmic contacts that show unexpected performances. These intriguing results are regularly summarized in comprehensive reviews. A strategy to tailor their properties even further and to observe novel quantum phenomena consists in the fabrication of superlattices whose unit cell is formed either by two dissimilar 2D materials or by a 2D material subjected to a periodical perturbation, each component contributing with different characteristics. Furthermore, in a 2D materials-based superlattice, the interlayer interaction between the layers mediated by van der Waals forces constitutes a key parameter to tune the global properties of the superlattice. The above-mentioned factors reflect the potential to devise countless combinations of van der Waals 2D materials based superlattices. In the present feature article, we explain in detail the state-of-the-art of 2D materials-based superlattices and we describe the different methods to fabricate them, classified as vertical stacking, intercalation with atoms or molecules, moiré patterning, strain engineering and lithographic design. We also aim to highlight some of the specific applications for each type of superlattices.

cond-mat.mes-hall↗

arXiv2020

InSe Schottky diodes based on van der Waals contacts

Two-dimensional semiconductors are excellent candidates for next-generation electronics and optoelec-tronics thanks to their electrical properties and strong light-matter interaction. To fabricate devices with optimal electrical properties, it is crucial to have both high-quality semiconducting crystals and ideal con-tacts at metal-semiconductor interfaces. Thanks to the mechanical exfoliation of van der Waals crystals, atomically-thin high-quality single-crystals can easily be obtained in a laboratory. However, conventional metal deposition techniques can introduce chemical disorder and metal-induced mid-gap states that induce Fermi level pinning and can degrade the metal-semiconductor interfaces, resulting in poorly performing devices. In this article, we explore the electrical contact characteristics of Au-InSe and graphite-InSe van der Waals contacts, obtained by stacking mechanically exfoliated InSe flakes onto pre-patterned Au or graphite electrodes without the need of lithography or metal deposition. The high quality of the metal-semiconductor interfaces obtained by van der Waals contact allows to fabricate high-quality Schottky di-odes based on the Au-InSe Schottky barrier. Our experimental observation indicates that the contact barrier at the graphite-InSe interface is negligible due to the similar electron affinity of InSe and graphite, while the Au-InSe interfaces are dominated by a large Schottky barrier.

cond-mat.mes-hall↗