Comparative analysis of resonant phonon THz quantum cascade lasers

We present a comparative analysis of a set of GaAs-based THz quantum cascade lasers, based on longitudinal-optical phonon scattering depopulation, by using an ensemble Monte Carlo simulation, including both carrier-carrier and carrier-phonon scattering. The simulation shows that the parasitic injection into the states below the upper laser level limits the injection efficiency and thus the device performance at the lasing threshold. Additional detrimental effects playing an important role are identified. The simulation results are in reasonable agreement with the experimental findings.Comment: 3 pages, 3 figure

Sensing Dynamically Evolved Short‐Range Nanomechanical Forces in Fast‐Mutating Single Viral Spike Proteins

Understanding changes in the mechanical features of a single protein from a mutated virus while establishing its relation to the point mutations is critical in developing new inhibitory routes to tackle the uncontrollable spread of the virus. Addressing this, herein, the chemomechanical features of a single spike protein are quantified from alpha, beta, and gamma variants of SARS-CoV-2. Integrated amplitude-modulation atomic force microscopy is used with dynamic force–distance curve (FDC) spectroscopy, in combination with theoretical models, to quantify Young's modulus, stiffness, adhesion forces, van der Waals forces, and the dissipative energy of single spike proteins. These obtained nanomechanical properties can be correlated with mutations in the individual proteins. Therefore, this work opens new possibilities to understand how the mechanical properties of a single spike protein relate to the viral functions. Additionally, single-protein nanomechanical experiments enable a variety of applications that, collectively, may build up a new portfolio of understanding protein biochemistry during the evolution of viruses

Versatile Multimodality Imaging System Based on Detectorless and Scanless Optical Feedback Interferometry-A Retrospective Overview for A Prospective Vision

In this retrospective compendium, we attempt to draw a "fil rouge" along fifteen years of our research in the field of optical feedback interferometry aimed at guiding the readers to the verge of new developments in the field. The general reader will be moved at appreciating the versatility and the still largely uncovered potential of the optical feedback interferometry, for both sensing and imaging applications. By discovering the broad range of available wavelengths (0.4-120 μm), the different types of suitable semiconductor lasers (Fabry-Perot, distributed feedback, vertical-cavity, quantum-cascade), and a number of unconventional tenders in multi-axis displacement, ablation front progression, self-referenced measurements, multispectral, structured light feedback imaging and compressive sensing, the specialist also could find inspirational suggestions to expand his field of research

Terahertz near-field nanoscopy based on detectorless laser feedback interferometry under different feedback regimes

Near-field imaging techniques, at terahertz frequencies (1–10 THz), conventionally rely on bulky laser sources and detectors. Here, we employ a semiconductor heterostructure laser as a THz source and, simultaneously, as a phase-sensitive detector, exploiting optical feedback interferometry combined with scattering near-field nanoscopy. We analyze the amplitude and phase sensitivity of the proposed technique as a function of the laser driving current and of the feedback attenuation, discussing the operational conditions ideal to optimize the nano-imaging contrast and the phase sensitivity. As a targeted nanomaterial, we exploit a thin (39 nm) flake of Bi2Te2.2Se0.8, a topological insulator having infrared active optical phonon modes. The self-mixing interference fringes are analyzed within the Lang–Kobayashi formalism to rationalize the observed variations as a function of Acket's parameter C in the full range of weak feedback (C < 1)

Optical Anisotropy in Single Light-Emitting Polymer Nanofibers

We investigate the optical anisotropy of single nanofibers realized by electrospinning a conjugated polymer. Polarized infrared and micro-Raman measurements evidence a higher degree of molecular orientation in fibers processed from tetrahydrofuran solutions, with respect to samples spun from mixture with dimethyl sulfoxide. The fraction of ordered molecules is correlated to the fibers morphology. Polarized photoluminescence highlights a larger red shift (60 meV) for spectra from fibers processed from tetrahydrofuran, confirming the higher achieved molecular order resulting in reduced interchain separation and hence excitonic emission with lower transition energies compared to that from randomly aligned molecules. Conjugated polymer fibers are obtained, emitting light with polarization ratios up to 5, usable as polarized photonic nanosources

Surface composition of mixed self-assembled monolayers on Au by infrared attenuated total reflection spectroscopy

Abstract Self-assembled monolayers (SAMs) of N-(2-hydroxyethyl)-3-mercaptopropanamide (NMPA) were synthesized directly on the surface of electron-beam evaporated Au films, starting from 3-mercaptopropionic acid (3MPA) via ethyl-3-(3-dimethylamino-propyl)carbodiimide/N-hydroxysulfosuccinimide sodium salt (EDC/NHSS) coupling with ethanolamine hydrochloride. The influence on the reaction yield of the acidity of EDC/NHSS solutions (pH = 5.6 or 4.8) was assessed by exploiting the high surface sensitivity of infrared attenuated total reflection spectroscopy. The light-matter interaction was modeled in the framework of a matrix formalism considering the complete multi-layer sample structure. A comparison between the relative intensity of the main absorption bands, associated with amide I and carbonyl stretching of carboxylic acid or amide II vibrations, with a calibration curve obtained from the measurement of mixed 3MPA/NMPA SAMs, show that the more acid solution is 16% more efficient. This is mostly due to the higher protonation of the 3MPA

Quantum Cascade Laser-Based Photoacoustic Sensor for Trace Detection of Formaldehyde Gas

We report on the development of a photoacoustic sensor for the detection of formaldehyde (CH2O) using a thermoelectrically cooled distributed-feedback quantum cascade laser operating in pulsed mode at 5.6 μm. A resonant photoacoustic cell, equipped with four electret microphones, is excited in its first longitudinal mode at 1,380 Hz. The absorption line at 1,778.9 cm−1 is selected for CH2O detection. A detection limit of 150 parts per billion in volume in nitrogen is achieved using a 10 seconds time constant and 4 mW laser power. Measurements in ambient air will require water vapour filters

About the amplification factors in organic bioelectronic sensors

A systematic comparison between electrochemical and organic bioelectronic sensors reveals a unified rational description for a transistor amplified detection

Correction: Printed, cost-effective and stable poly(3-hexylthiophene) electrolyte-gated field-effect transistors

Correction for 'Printed, cost-effective and stable poly(3-hexylthiophene) electrolyte-gated field-effect transistors' by Davide Blasi et al., J. Mater. Chem. C, 2020, DOI: 10.1039/d0tc03342a