Search

Dielectrics featuring a high relative permittivity, i.e., high-k dielectrics, have become the standard insulators in gate architectures, enhancing the electrical performance of both room temperature and cryogenic electronics. This study delves into the cryogenic (3 K) performance of high-k dielectrics commonly used as gate insulators. We fabricated Al2O3 and HfO2 layers via atomic layer deposition (ALD) and extrapolated relative permittivity (k) and dielectric strength (EBD) from AC (100 Hz–100 kHz) and DC measurements on metal–insulator–metal capacitors. Our findings reveal a strong dependence of HfO2 cryogenic performance on ALD growth temperature, while the latter shows a negligible impact on Al2O3. We estimated ∼9% and ∼14% reductions in the relative permittivities of HfO2 and Al2O3, respectively, at temperatures from 300 to 3 K. Additionally, we designed and fabricated Al2O3/HfO2 bilayers and checked their properties at cryogenic temperatures. The study also investigates the impact of the patterning method, namely, UV or electron-beam lithography (acceleration voltage of 10, 20, or 30 kV), on the high-k dielectric properties. [ABSTRACT FROM AUTHOR]

Back-action refers to a response that retro-acts on a system to tailor its properties with respect to an external stimulus. This effect is at the heart of many electronic devices such as amplifiers, oscillators, and sensors. Here, we demonstrate that back-action can be exploited to achieve non-reciprocal transport in superconducting circuits. In our devices, dissipationless current flows in one direction whereas dissipative transport occurs in the opposite direction. Supercurrent diodes presented so far rely on magnetic elements or vortices to mediate charge transport or external magnetic fields to break time-reversal symmetry. Back-action solely turns a conventional reciprocal superconducting weak link with no asymmetry between the current bias directions into a rectifier, where the critical current amplitude depends on the bias sign. The self-interaction of the supercurrent stems from the gate tunability of the critical current in metallic and semiconducting systems, which promotes nearly ideal magnetic field-free rectification with selectable polarity. The superconducting diode effect has the potential to advance the design of non-dissipative circuit components yet there are many practical aspects to overcome before reaching the application stage. Here, the authors investigate the non-reciprocal current-voltage relationship in gate-controlled metallic nanowires, demonstrating the realisation of the superconducting diode effect without the need to break time-reversal symmetry using an applied magnetic field. [ABSTRACT FROM AUTHOR]

In the past decades, bone tissue engineering developed and exploited many typologies of bioreactors, which, besides providing proper culture conditions, aimed at integrating those bio‐physical stimulations that cells experience in vivo, to promote osteogenic differentiation. Nevertheless, the highly challenging combination and deployment of many stimulation systems into a single bioreactor led to the generation of several unimodal bioreactors, investigating one or at mostly two of the required biophysical stimuli. These systems miss the physiological mimicry of bone cells environment, and often produced contrasting results, thus making the knowledge of bone mechanotransduction fragmented and often inconsistent. To overcome this issue, in this study we developed a perfusion and electroactive‐vibrational reconfigurable stimulation bioreactor to investigate the differentiation of SaOS‐2 bone‐derived cells, hosting a piezoelectric nanocomposite membrane as cell culture substrate. This multimodal perfusion bioreactor is designed based on a numerical (finite element) model aimed at assessing the possibility to induce membrane nano‐scaled vibrations (with ~12 nm amplitude at a frequency of 939 kHz) during perfusion (featuring 1.46 dyn cm−2 wall shear stress), large enough for inducing a physiologically‐relevant electric output (in the order of 10 mV on average) on the membrane surface. This study explored the effects of different stimuli individually, enabling to switch on one stimulation at a time, and then to combine them to induce a faster bone matrix deposition rate. Biological results demonstrate that the multimodal configuration is the most effective in inducing SaOS‐2 cell differentiation, leading to 20‐fold higher collagen deposition compared to static cultures, and to 1.6‐ and 1.2‐fold higher deposition than the perfused‐ or vibrated‐only cultures. These promising results can provide tissue engineering scientists with a comprehensive and biomimetic stimulation platform for a better understanding of mechanotransduction phenomena beyond cells differentiation. [ABSTRACT FROM AUTHOR]

Superconducting circuits based on hybrid InAs Josephson Junctions (JJs) play a starring role in the design of fast and ultra‐low power consumption solid‐state quantum electronics and exploring novel physical phenomena. Conventionally, 3D substrates, 2D quantum wells (QWs), and 1D nanowires (NWs) made of InAs are employed to create superconducting circuits with hybrid JJs. Each platform has its advantages and disadvantages. Here, the InAs‐on‐insulator (InAsOI) is proposed as a groundbreaking platform for developing superconducting electronics. An epilayer of semiconducting InAs with different electron densities is grown onto an InAlAs metamorphic buffer, efficiently used as a cryogenic insulator to decouple adjacent devices electrically. JJs with various lengths and widths are fabricated employing Al as a superconductor and InAs with different electron densities. A switching current density of 7.3 µA µm−1, a critical voltage of 50‐to‐80 µV, and a critical temperature equal to that of the superconductor used are achieved. For all the JJs, the switching current follows a Fraunhofer‐like pattern with the out‐of‐plane magnetic field. These achievements enable the use of InAsOI to design and fabricate surface‐exposed Josephson Field Effect Transistors with high critical current densities and superior gating properties. [ABSTRACT FROM AUTHOR]

Abstract Piezoelectric films of poly(vinylidenedifluoride-trifluoroethylene) (P(VDF-TrFE)) and of P(VDF-TrFE)/boron nitride nanotubes (BNNTs) were prepared by cast-annealing and used for SaOS-2 osteoblast-like cell culture. Films were characterized in terms of surface and bulk features, and composite films demonstrated enhanced piezoresponse compared to plain polymeric films (d 31 increased by ~80%). Osteogenic differentiation was evaluated in terms of calcium deposition, collagen I secretion, and transcriptional levels of marker genes (Alpl , Col1a1 , Ibsp , and Sparc) in cells either exposed or not to ultrasounds (US); finally, a numerical model suggested that the induced voltage (~20-60 mV) is suitable for cell stimulation. Although preliminary, our results are extremely promising and encourage the use of piezoelectric P(VDF-TrFE)/BNNT films in bone tissue regeneration. Graphical Abstract Piezoelectric nanocomposite P(VDF-TrFE)/BNNTs films promote differentiation of SaOS-2 osteoblast- like cells upon ultrasounds stimulation. Image 1 [ABSTRACT FROM AUTHOR]

We present a planar laser diode based on a simple fabrication scheme compatible with virtually any geometry accessible by standard semiconductor lithography technique. We show that our lasers exhibit ∼1 GHz -3 dB-modulation-bandwidth already in this prototypical implementation. Directions for a significant speed increase are discussed. [ABSTRACT FROM AUTHOR]

We demonstrate anti-bunched emission from a lateral-light emitting diode. Sub-Poissonian emission statistic, with a g(2)(0) = 0.7, is achieved at cryogenic temperature in the pulsed low-current regime, by exploiting electron injection through shallow impurities located in the diode depletion region. Thanks to its simple fabrication scheme and to its modulation bandwidth in the gigahertz range, we believe our devices are an appealing substitute for highly attenuated lasers in existing quantum-key-distribution systems. Our devices outperform strongly attenuated lasers in terms of multi-photon emission events and can therefore lead to a significant security improvement in existing quantum key distribution systems. [ABSTRACT FROM AUTHOR]

A surface-acoustic-wave (SAW) driven light-emitting-diode structure that can implement a single-photon source for quantum-cryptography applications is demonstrated. Our lateral n-i-p junction is realized starting from an undoped GaAs/AlGaAs quantum well by gating. It incorporates interdigitated transducers for SAW generation and lateral gates for current control. We demonstrate acoustoelectric transport and SAW-driven electroluminescence. The acoustoelectric current can be controlled down to complete pinch-off by means of the lateral gates. [ABSTRACT FROM AUTHOR]

The possibility to tune, through the application of a control gate voltage, the superconducting properties of mesoscopic devices based on Bardeen–Cooper–Schrieffer metals was recently demonstrated. Despite the extensive experimental evidence obtained on different materials and geometries, a description of the microscopic mechanism at the basis of such an unconventional effect has not been provided yet. This work discusses the technological potential of gate control of superconductivity in metallic superconductors and revises the experimental results, which provide information regarding a possible thermal origin of the effect: first, we review experiments performed on high-critical-temperature elemental superconductors (niobium and vanadium) and show how devices based on these materials can be exploited to realize basic electronic tools, such as a half-wave rectifier. Second, we discuss the origin of the gating effect by showing gate-driven suppression of the supercurrent in a suspended titanium wire and by providing a comparison between thermal and electric switching current probability distributions. Furthermore, we discuss the cold field-emission of electrons from the gate employing finite element simulations and compare the results with experimental data. In our view, the presented data provide a strong indication regarding the unlikelihood of the thermal origin of the gating effect. [ABSTRACT FROM AUTHOR]

We present an unconventional scheme for acoustic charge transport devices based on a n-i-n lateral junction as electron injector. We show that surface acoustic waves (SAWs) are able to pick up electrons from a current flowing through the n-i-n junction and steer them towards the Ohmic output contact. Acoustic charge transport was studied at various temperatures, as a function of injector current, voltage bias, and SAW power. The possibility to modulate the acoustoelectric current by means of lateral in-plane gates is also discussed. The main advantage of our approach relies on the possibility to drive the n-i-n injector by means of both voltage and current sources, thus allowing to sample and process voltage and current signals. [ABSTRACT FROM AUTHOR]

Electroluminescence emission controlled by means of surface acoustic waves (SAWs) in planar light-emitting diodes (pLEDs) is demonstrated. Interdigital transducers for SAW generation were integrated onto pLEDs fabricated following the scheme which we have recently developed [Cecchini et al., Appl. Phys. Lett. 82, 636 (2003)]. Current-voltage, light-voltage, and photoluminescence characteristics are presented at cryogenic temperatures. We argue that this scheme represents a valuable building block for advanced optoelectronic architectures. [ABSTRACT FROM AUTHOR]

Piezoelectric films of poly(vinylidenedifluoride-trifluoroethylene) (P(VDF-TrFE)) and of P(VDF-TrFE)/boron nitride nanotubes (BNNTs) were prepared by cast-annealing and used for SaOS-2 osteoblast-like cell culture. Films were characterized in terms of surface and bulk features, and composite films demonstrated enhanced piezoresponse compared to plain polymeric films (d 31 increased by ~80%). Osteogenic differentiation was evaluated in terms of calcium deposition, collagen I secretion, and transcriptional levels of marker genes (Alpl, Col1a1, Ibsp, and Sparc) in cells either exposed or not to ultrasounds (US); finally, a numerical model suggested that the induced voltage (~20-60 mV) is suitable for cell stimulation. Although preliminary, our results are extremely promising and encourage the use of piezoelectric P(VDF-TrFE)/BNNT films in bone tissue regeneration., (Copyright © 2017 Elsevier Inc. All rights reserved.)

By exploiting the resonant coupling between a travelling wave and the stationary modes of a cavity, we present the first scheme for integrated automatic interaction-free surface acoustic wave routing of fluids. Our scheme opens the way to the implementation of logic gates based on instantaneous liquid distribution.