Effect of surface oxidation on the electronic transport properties of phosphorene gas sensors: a computational study

The potential for phosphorene-based devices has been compromised by the material's fast degradation under ambient conditions. Its tendency to fully oxidize under O₂-rich and humid environments, leads to the loss of its appealing semiconducting properties. However, partially-oxidized phosphorene (po-phosphorene), has been demonstrated to remain stable over significantly longer periods of time, thereby enabling its use in sensing applications. Here, we present a computational study of po-phosphorene-based gas sensors, using the Density-Functional-based Tight Binding (DFTB) method. We show that DFTB accurately predicts the bandgap for the pristine material and po-phosphorene, the electronic transport properties of po-phosphorene at different surface oxygen concentrations, and the appropriate trends in Density-of-States (DOS) contributions caused by adsorbed gas molecules, to demonstrate its potential application in the development of gas sensors. Results are compared against the more traditional and expensive Density Functional Theory (DFT) method using generalized gradient approximation (GGA) exchange–correlation functionals, which significantly underestimates the material's bandgap

Cluster Amplitudes and Their Interplay with Self-Consistency in Density Functional Methods

Density functional theory (DFT) provides convenient electronic structure methods for the study of molecular systems and materials. Regular Kohn-Sham DFT calculations rely on unitary transformations to determine the ground-state electronic density, ground state energy, and related properties. However, for dissociation of molecular systems into open-shell fragments, due to the self-interaction error present in a large number of density functional approximations, the self-consistent procedure based on the this type of transformation gives rise to the well-known charge delocalization problem. To avoid this issue, we showed previously that the cluster operator of coupled-cluster theory can be utilized within the context of DFT to solve in an alternative and approximate fashion the ground-state self-consistent problem. This work further examines the application of the singles cluster operator to molecular ground state calculations. Two approximations are derived and explored: i), A linearized scheme of the quadratic equation used to determine the cluster amplitudes, and, ii), the effect of carrying the calculations in a non-self-consistent field fashion. These approaches are found to be capable of improving the energy and density of the system and are quite stable in either case. The theoretical framework discussed in this work could be used to describe, with an added flexibility, quantum systems that display challenging features and require expanded theoretical methods.Comment: 17 pages, 5 figures, 1 table, submitted to ChemPhysChe

Creating a three dimensional intrinsic electric dipole on rotated CrI3_3 bilayers

Two-dimensional (2D) materials are being explored as a novel multiferroic platform. One of the most studied magnetoelectric multiferroic 2D materials are antiferromagnetically-coupled (AFM) CrI$_3$ bilayers. Neglecting magnetism, those bilayers possess a crystalline point of inversion, which is only removed by the antiparallel spin configuration among its two constituent monolayers. The resultant intrinsic electric dipole on those bilayers has a magnitude no larger than 0.04 pC/m, it points out-of-plane, and it reverts direction when the--Ising-like--cromium spins are flipped (toward opposite layers {\em versus} away from opposite layers). The combined presence of antiferromagnetism and a weak intrinsic electric dipole makes this material a two-dimensional magnetoelectric multiferroic. Here, we remove the crystalline center of inversion of the bilayer by a relative $60^{\circ}$ rotation of its constituent monolayers. This process {\em enhances} the out-of-plane intrinsic electric dipole tenfold with respect to its magnitude in the non-rotated AFM bilayer and also creates an even stronger and switchable in-plane intrinsic electric dipole. The ability to create a three-dimensional electric dipole is important, because it enhances the magnetoelectric coupling on this experimentally accessible 2D material, which is explicitly calculated here as well.Comment: Accepted at PRB on May 1, 202

All-Armchair Graphene Nanoribbon Field Effect Uridine Diphosphate Glucose Sensor: First-Principles In-Silico Design and Characterization

Label-free sensors capable of detecting low concentrations of significant biomolecular substances without inducing immune response would simplify experiments, minimize errors, improve real-time observations, and reduce costs in probing living organisms. This paper presents a first-principles, in-silico derived, all-armchair graphene nanoribbon field-effect transistor (g-FET) device for the detection and measurement of low-concentration (pM-nM) uridine diphosphate glucose, UDP-glucose. UDP-glucose is an intermediate reactant in the synthesis of sucrose in a plant cell’s cytoplasm and an extracellular signaling molecule capable of activating downstream defense mechanisms. The unique g-FET configuration for the semiconducting channel and electrodes favors the fabrication of high-density nanoarray sensors. Optimal device electronic transport and switching properties are predicted by screening configurations with different widths, to control bandgap, and lengths, to control thermionic versus tunneling transport across the semiconducting junction. A self-assembled monolayer (SAM) of pyrene derivatives, 1-pyrenebutyric acid, is used to noncovalently functionalize the graphene surface on one end and to covalently ligate the target analyte on the other while providing mechanical, chemical, and electronic signal sensing stability. We find that the device offers a predicted limit of detection (LOD) of 0.997 n mM/L (where n is the number of sensor units in an array), with high transconductance sensitivity, 0.75– 1.5μS for 1–3 UDP-glucose molecules, at low input (V_G=0.9 V) and output voltages V_(DS)=0.1 V. Thus, a 1000×1000 nanoarray sensor would yield an LOD = 0.997 nM/L. This low-power, all-armchair g-FET sensor with SAM ligands that may be chosen to bind different biomarkers provides a unique opportunity for high throughput, real-time, low-cost, high-mobility, and minimal-calibration sensing applications

Partially-oxidized phosphorene sensor for the detection of sub-nano molar concentrations of nitric oxide: a first-principles study

The development of new techniques or instruments for detecting and accurately measuring biomarker concentrations in living organisms is essential for early diagnosis of diseases, and for tracking the effectiveness of treatments. In chronic diseases, such as asthma, precise phenotyping can help predict the response of patients to treatments and reduce the risk of complications. Fractional exhaled nitric oxide (Fe_(NO)) is a positive biomarker for eosinophilic asthma in humans, and it can be directly detected in the respiratory tract, at very low and volatile concentrations, which makes real-time measurement a challenge. This work describes the first-principles design and characterization of a molecular- and back-gated electronic field-effect transistor device for the detection and measurement of ultra-low Fe_(NO) concentrations (pM–nM) from a person' s exhaled breath, as a cost-efficient alternative to the slower and more expensive techniques based on off-line sputum characterization via mass spectrometry. The proposed device uses a partially oxidized phosphorene semiconducting channel material for Fe_(NO) detection, allowing nM L^(−1) concentration measurements of this analyte in an array configuration with an effective sensing surface area of 8.775 μm^2, which results in a predicted limit of detection (LOD) of 19 nM L^(−1). In spite of the limited stability of phosphorene in oxygen-rich and humid environments, the proposed device would be practical for mobile applications with disposable sensors

All-Armchair Graphene Nanoribbon Field Effect Uridine Diphosphate Glucose Sensor: First-Principles In-Silico Design and Characterization

Label-free sensors capable of detecting low concentrations of significant biomolecular substances without inducing immune response would simplify experiments, minimize errors, improve real-time observations, and reduce costs in probing living organisms. This paper presents a first-principles, in-silico derived, all-armchair graphene nanoribbon field-effect transistor (g-FET) device for the detection and measurement of low-concentration (pM-nM) uridine diphosphate glucose, UDP-glucose. UDP-glucose is an intermediate reactant in the synthesis of sucrose in a plant cell’s cytoplasm and an extracellular signaling molecule capable of activating downstream defense mechanisms. The unique g-FET configuration for the semiconducting channel and electrodes favors the fabrication of high-density nanoarray sensors. Optimal device electronic transport and switching properties are predicted by screening configurations with different widths, to control bandgap, and lengths, to control thermionic versus tunneling transport across the semiconducting junction. A self-assembled monolayer (SAM) of pyrene derivatives, 1-pyrenebutyric acid, is used to noncovalently functionalize the graphene surface on one end and to covalently ligate the target analyte on the other while providing mechanical, chemical, and electronic signal sensing stability. We find that the device offers a predicted limit of detection (LOD) of 0.997 n mM/L (where n is the number of sensor units in an array), with high transconductance sensitivity, 0.75– 1.5μS for 1–3 UDP-glucose molecules, at low input (V_G=0.9 V) and output voltages V_(DS)=0.1 V. Thus, a 1000×1000 nanoarray sensor would yield an LOD = 0.997 nM/L. This low-power, all-armchair g-FET sensor with SAM ligands that may be chosen to bind different biomarkers provides a unique opportunity for high throughput, real-time, low-cost, high-mobility, and minimal-calibration sensing applications

Anomalous Temperature and Polarization Dependences of Photoluminescence of Metal-Organic Chemical Vapor Deposition-Grown GeSe2

Germanium diselenide (GeSe2) is a 2D semiconductor with air stability, a wide bandgap, and anisotropic optical properties. The absorption and photoluminescence (PL) of single-crystalline 2D GeSe2 grown by metal-organic chemical vapor deposition and their dependence on temperature and polarization are studied. The PL spectra exhibit peaks at 2.5 eV (peak A) and 1.8 eV (peak B); peak A displays a strongly polarized emission along the short axis of the crystal, and peak B displays a weak polarization perpendicular to that of peak A. With increasing temperature, peak B shows anomalous behaviors, i.e., an increasing PL energy and intensity. The excitation energy-dependent PL, time-resolved PL, and density functional theory calculations suggest that peak A corresponds to the band-edge transition, whereas peak B originates from the inter-band mid-gap states caused by selenium vacancies passivated by oxygen atoms. The comprehensive study on the PL of single-crystalline GeSe2 sheds light on the origins of light emission in terms of the band structure of anisotropic GeSe2, making it beneficial for the corresponding optoelectronic applications