Quantum Graphene Asymmetric Devices for Harvesting Electromagnetic Energy.

We present here the fabrication at the wafer level and the electrical performance of two types of graphene diodes: ballistic trapezoidal-shaped graphene diodes and lateral tunneling graphene diodes. In the case of the ballistic trapezoidal-shaped graphene diode, we observe a large DC current of 200 µA at a DC bias voltage of ±2 V and a large voltage responsivity of 2000 /, while in the case of the lateral tunneling graphene diodes, we obtain a DC current of 1.5 mA at a DC bias voltage of ±2 V, with a voltage responsivity of 3000 .

Subthreshold slope below 60 mV/decade in graphene transistors induced by channel geometry at the wafer-scale.

In this paper, we demonstrate experimentally that field-effect transistors with nanoconstricted graphene monolayer channels have a subthreshold swing (SS) below 60 mV/dec, which is slightly dependent on temperature. Two shapes of nanoconstricted graphene monolayers are considered: (i) a bow-tie shape, representative for a symmetric channel, and (ii) a trapezoidal shape, which illustrates an asymmetric channel. While both types of nonuniform channels are opening a bandgap in graphene, thus showing an on/off ratio of 10, the SS in the graphene bow-tie channel is below 60 mV/dec in the temperature range 25 °C-44 °C.

Tuning the infrared resonance of thermal emission from metasurfaces working in near-infrared.

We simulated numerically and demonstrated experimentally that the thermal emittance of a metasurface consisting of an array of rectangular metallic meta-atoms patterned on a layered periodic dielectric structure grown on top of a metallic layer can be tuned by changing several parameters. The resonance frequency, designed to be in the near-infrared spectral region, can be tuned by modifying the number of dielectric periods, and the polarization and incidence angle of the incoming radiation. In addition, the absorbance/emittance value at the resonant wavelength can be tuned by modifying the orientation of meta-atoms with respect to the illumination direction.

Nanomaterials for Energy Harvesting.

Energy harvesting is no longer simply an academic issue; it has grown into a problem with real industrial and even social significance [...

Harvesting microwave energy using pyroelectricity of nanostructured graphene/zirconium-doped hafnium oxide ferroelectric heterostructures.

In this work, we present the design, atomistic/circuit/electromagnetic simulations, and the experimental results for graphene monolayer/zirconium-doped hafnium oxide (HfZrO) ultra-thin ferroelectric-based field effect transistors fabricated at the wafer scale, regarding the pyroelectricity generation directly from microwave signals, at room temperature and below it, namely at 218 K and at 100 K. The transistors work like energy harvesters, i.e.

Nanomaterials and Devices for Harvesting Ambient Electromagnetic Waves.

This manuscript presents an overview of the implications of nanomaterials in harvesting ambient electromagnetic waves. We show that the most advanced electromagnetic harvesting devices are based on oxides with a thickness of few nanometers, carbon nanotubes, graphene, and molybdenum disulfide thanks to their unique physical properties. These tiny objects can produce in the years to come a revolution in the harvesting of energy originating from the Sun, heat, or the Earth itself.

Ultralow voltage (1V) electrical switching of SnS thin films driven by a vertical electric field.

In this paper, we show in a series of experiments on 10 nm thick SnS thin film-based back-gate transistors that in the absence of the gate voltage, the drain current versus drain voltage (-) dependence is characterized by a weak drain current and by an ambipolar transport mechanism. When we apply a gate voltage as low as 1V, the current increases by several orders of magnitude and the-dependence changes drastically, with the SnS behaving as a-type semiconductor. This happens because the current flows from the source (S) to the drain (D) electrode through a discontinuous superficial region of the SnS film when no gate voltage is applied.

Ultrathin tin sulfide field-effect transistors with subthreshold slope below 60 mV/decade.

In this paper, we present for the first time a field-effect-transistor (FET) having a 10 nm thick tin sulfide (SnS) channel fabricated at the wafer scale with high reproducibility. SnS-based FETs are in on-state for increasing positive back-gate voltages up to 6 V, whereas the off-state is attained for negative back-gate voltages not exceeding -6 V, the on/off ratio being in the range 10-10depending on FET dimensions. The SnS FETs show a subthreshold slope (SS) below 60 mV/decade thanks to the in-plane ferroelectricity of SnS and attaining a minimum value SS = 21 mV/decade.

The microwave properties of tin sulfide thin films prepared by RF magnetron sputtering techniques.

In this paper we present the microwave properties of tin sulfide (SnS) thin films with the thickness of just 10 nm, grown by RF magnetron sputtering techniques on a 4 inch silicon dioxide/high-resistivity silicon wafer. In this respect, interdigitated capacitors in coplanar waveguide technology were fabricated directly on the SnS film to be used as both phase shifters and detectors, depending on the ferroelectric or semiconductor behaviour of the SnS material. The ferroelectricity of the semiconducting thin layer manifests itself in a strong dependence of the electrical permittivity on the applied DC bias voltage, which induces a phase shift of 30 degrees mmat 1 GHz and of 8 degrees mmat 10 GHz, whereas the transmission losses are less than 2 dB in the frequency range 2-20 GHz.

Graphene Nanopore Arrays for Electron Focusing and Antifocusing.

We have shown, via numerical simulations, that a symmetric array of nanopores with appropriately designed shapes and sizes arranged along an arc of a circle in a graphene nanoribbon can focus or antifocus an incident ballistic electron wavefunction. The position of the focal/antifocal region depends on the electron energy. This effect, which takes place in the energy interval of one-transverse-mode propagation in the nanoribbon, highlights the similarities with plasmonic focusing by an array of holes in a metallic sheet, while emphasizing the differences between the propagation and excitation of electrons and electromagnetic fields.

Graphene/Ferroelectric (Ge-Doped HfO) Adaptable Transistors Acting as Reconfigurable Logic Gates.

We present an array of 225 field-effect transistors (FETs), where each of them has a graphene monolayer channel grown on a 3-layer deposited stack of 22 nm control HfO/5 nm Ge-HfO intermediate layer/8 nm tunnel HfO/-Si substrate. The intermediate layer is ferroelectric and acts as a floating gate. All transistors have two top gates, while the -Si substrate is acting as a back gate.

Characterization of Monochromatic Aberrated Metalenses in Terms of Intensity-Based Moments.

Consistent with wave-optics simulations of metasurfaces, aberrations of metalenses should also be described in terms of wave optics and not ray tracing. In this respect, we have shown, through extensive numerical simulations, that intensity-based moments and the associated parameters defined in terms of them (average position, spatial extent, skewness and kurtosis) adequately capture changes in beam shapes induced by aberrations of a metalens with a hyperbolic phase profile. We have studied axial illumination, in which phase-discretization induced aberrations exist, as well as non-axial illumination, when coma could also appear.

Bloch oscillations at room temperature in graphene/h-BN electrostatic superlattices.

In this manuscript, we report the fabrication and the measurements of Bloch oscillations at room temperature in electrostatic graphene/h-BN superlattices. The electrostatic superlattice consists of an array of tilted metallic electrodes deposited over graphene monolayer/h-BN monolayer grown on 2 inch wafers of doped Si/SiO. We show the formation of minibands at room temperature, negative differential resistance and the evidence of Bloch oscillations.

Perspectives on Atomic-Scale Switches for High-Frequency Applications Based on Nanomaterials.

Nanomaterials science is becoming the foundation stone of high-frequency applications. The downscaling of electronic devices and components allows shrinking chip's dimensions at a more-than-Moore rate. Many theoretical limits and manufacturing constraints are yet to be taken into account.

Reduced Graphene Oxide Sheets as Inhibitors of the Photochemical Reactions of α-Lipoic Acid in the Presence of Ag and Au Nanoparticles.

The influence of Ag and Au nanoparticles and reduced graphene oxide (RGO) sheets on the photodegradation of α-lipoic acid (ALA) was determined by UV-VIS spectroscopy. The ALA photodegradation was explained by considering the affinity of thiol groups for the metallic nanoparticles synthesized in the presence of trisodium citrate. The presence of excipients did not induce further changes when ALA interacts with Ag and Au nanoparticles with sizes of 5 and 10 nm by exposure to UV light.

Wafer-scale graphene-ferroelectric HfO/Ge-HfO/HfO transistors acting as three-terminal memristors.

In this paper we report a set of experiments at the wafer level regarding field-effect transistors with a graphene monolayer channel transferred on the ferroelectric HfO/Ge-HfO/HfO three-layer structure. This kind of transistor has a switching ratio of 10 between on and off states due to the bandgap in graphene induced by the ferroelectric structure. Both top and back gates effectively control the carriers' charge flow in graphene.

Memtransistors Based on Nanopatterned Graphene Ferroelectric Field-Effect Transistors.

The ultimate memristor, which acts as resistive memory and an artificial neural synapse, is made from a single atomic layer. In this manuscript, we present experimental evidence of the memristive properties of a nanopatterned ferroelectric graphene field-effect transistor (FET). The graphene FET has, as a channel, a graphene monolayer transferred onto an HfO-based ferroelectric material, the channel being nanopatterned with an array of holes with a diameter of 20 nm.

Graphene bandgap induced by ferroelectric HfO doped with Zr (HfZrO).

Motivated by the need to open a bandgap in graphene, we show experimentally that the CMOS-compatible ferroelectric HfZrO substrate induces a bandgap of 0.18 eV in graphene monolayer, which allows top-gate graphene/HfZrO/SiO/Si field-effect transistors to have high on/off current ratio, of about 10, at small drain voltages, of 0.5 V, and for gate voltage spans of only 3.

Reconfigurable horizontal-vertical carrier transport in graphene/HfZrO field-effect transistors.

We have fabricated at wafer level field-effect-transistors (FETs) having as channel graphene monolayers transferred on a HfZrO ferroelectric, grown by atomic layer deposition on a doped Si (100) substrate. These FETs display either horizontal or vertical carrier transport behavior, depending on the applied gate polarity. In one polarity, the FETs behave as a graphene FET where the transport is horizontal between two contacts (drain and grounded source) and is modulated by a back-gate.

Graphene bandgap induced by ferroelectric Pca2 HfO substrates: a first-principles study.

The electronic properties of graphene on top of ferroelectric HfO2 substrates in an orthorhombic phase with space group Pca21 are investigated using density functional theory calculations. The space group Pca21 was recently identified as one of the two potential candidates for ferroelectricity in hafnia, with the polarization direction oriented along the [001] direction. Our results indicate the appearance of sizable energy gaps in graphene induced by the HfO2 substrate, as a consequence of orbital hybridization and the locally deformed graphene structure.

Electromagnetic energy harvesting based on HfZrO tunneling junctions.

HfZrO ferroelectrics with a thickness of 6 nm were grown directly on Si using atomic layer deposition, top and bottom metallic electrodes being subsequently deposited by electron-beam metallization techniques. Depending on the polarity of the ±10 V poling voltages, the current-voltage dependence of these tunneling diodes shows a rectifying behavior for different polarizations, the ON-OFF ratio being about 10. Because the currents are at mA level, the HfZrO tunneling diodes coupled to an antenna array can harvest electromagnetic energy at 26 GHz (a bandwidth designated for internet of things), with a responsivity of 63 V W and a NEP of 4 nW/Hz.

Wafer-scale very large memory windows in graphene monolayer/HfZrO ferroelectric capacitors.

We have fabricated and electrically characterized at the wafer scale tens of metal-ferroelectric (HfZrO)-semiconductor capacitors and metal-graphene monolayer-ferroelectric (HfZrO)-semiconductor capacitors with the same top electrode dimensions. We have found that the memory windows of the capacitors containing graphene are 3-4 times larger than the ferroelectric capacitors without graphene, and increase even more after annealing. This physical effect can be attributed to the additional electric field exerted by the graphene monolayer on the HfZrO ferroelectric semiconductor capacitor, and to the negative thermal extension coefficient of graphene, respectively.

Tunable fractional Fourier transform implementation of electronic wave functions in atomically thin materials.

A tunable fractional Fourier transform of the quantum wave function of electrons satisfying either the Schrödinger or the Dirac equation can be implemented in an atomically thin material by a parabolic potential distribution applied on a direction transverse to that of electron propagation. The difference between the propagation lengths necessary to obtain a fractional Fourier transform of a given order in these two cases could be seen as a manifestation of the Berry phase. The Fourier transform of the electron wave function is a particular case of the fractional Fourier transform.

Ballistic transport in graphene Y-junctions in transverse electric field.

We investigate the prospects for current modulation in single layer graphene Y-junctions in the ballistic regime, under an external electric field. Overcoming the inability of inducing field effect in graphene nanoribbons by a stacked gate, the proposed in-plane electric field setup enables a controlled current transfer between the branches of the Y-junction. This behavior is further confirmed by changing the angular incidence of the electric field.