The use of extremely accurate, simple-to-use, flexible, and biocompatible wearable electronics for temperature monitoring is of great clinical demand for COVID-19 cases, postoperative recovery, monitoring chronobiology, and disease prediction. To address these issues, we report the fabrication of wearable three-dimensional (3D) Polydopamine titanium dioxide copper nanocluster (PDA-TiO2@Cu-NCs) sensor based on cost effective copper nanoclusters (Cu-NCs). The results reveal that the developed multi-functional strain sensor demonstrated biocompatibility, environmental stability, flexible thermistor with ultra-sensitivity. The sensor was used to detect wide human physiological activities with superior sensitivity of 177 % for finger bending angle 0 degrees to 90 degrees and 1770 % for compressed by human leg with higher stability and fast recovery 20 ms. The smart sensor monitored human respiration patterns and could identify people by facial recognition and handwriting sensory device. Additionally, the proposed thermistors sensor can detect wide temperature range changes in two different rang with a temperature coefficient of resistance (TCR) value of -0.143 degrees C-1 at 0 degrees C to 60 degrees C with high resolution of 2 degrees C. This research provides a new high-performance multifunctional sensor design for potential applications as flexible electronics, human body temperature sensors, thermistors, photodetector, anti-counterfeiting, and medical diagnostics related applications.

The role of the exact Hartree-Fock (HF) exchange in determining the band gap and other properties of defects in crystalline solids is investigated. Two defects in diamond, VHd1 and VHq1 (one first neighbour of the vacancy is saturated with hydrogen, and the three unpaired electrons combine to give a quadruplet, 3 spin up, or a doublet, two spin up and one down), are used as test cases. The results obtained with a gradient corrected functional, PBE, one range separate hybrid, HSE06, two full range hybrids, B3LYP and PBE0, and the Hartree-Fock Hamiltonian are compared. The crucial role of the exact HF exchange emerging from this comparison is confirmed by a set of calculations with a variable functional, PBE(X), in which X is the percentage of HF exchange, which is varied from 0 to 100, where PBE(0) coincides with PBE, and PBE(25) with PBE0.

The (Z)-4-methyl-2-(((3-nitrophenyl)imino)methyl)phenol (C15H14N2O3) (MNIMP) was prepared by condensation of 2-hydroxy-5-methyl-benzaldehyde and 2-methyl-4-nitro-phenylamine in ethanol and characterized by NMR (1H and 13C), IR and UV-Visible spectroscopy. The molecular crystal packing has been quantitatively explored via Hirshfeld surface analysis, where the intramolecular C−H⋯O bonding represents the principle contribution that stabilizes the crystal packing, with an overall 27.5% for O⋯H interactions. The outcomes of a theoretical investigation conducted at the B3LYP/6-311++G(d,p) level using the DFT approach are in strong agreement with the results of the experiment. The experimental outcome is compatible with the optimized structure. Z)-4-methyl-2-(((3-nitrophenyl)imino)methyl)phenol vibrational spectrum is calculated at the same theoretical level (DFT/ B3LYP/6-311++G(d,p)), and it is discovered that the theoretically estimated vibrational frequencies and assignments accord well with experimental FT-IR values.

Nanoscale devices developed from low-dimensional materials (one and two-dimensional systems) have recently attracted great attention due to their critical applications in micro/nano electromechanics. However, the practical fabrication of 2D systems is often more challenging than that of their 1D counterparts. In the current investigation, the convergence of 1D nanotube properties toward the 2D slab limit has been verified and confirmed. In this regard, a variety of geometrical, electronic, and response (mechanical and piezoelectric) properties are computed for both zigzag (n,0) metal oxide MO (M = Be, Mg, Ca, Zn, Cd) nanotubes and MO 2D surfaces. The variation of such properties as a function of the tube index n (ranging from 6 to 48, corresponding to 24 to 192 atoms per cell, respectively) is highlighted. Additionally, the electronic and nuclear contributions to all aforementioned response properties have been discussed and analyzed. Interestingly, CdO (48,0) nanotube introduces considerable direct and converse piezoelectric constants: e11 = 6.04 |e|×bohr and d11 = 22.88 pm/V. These electromechanical coefficients converge well to the values of the 2D surface, while the response is entirely dominated by the ionic contribution, confirming the flexibility and softness. Such findings make these MO nanotubes good candidates for nanoscale energy conversion piezoelectric applications.

Piezoelectricity is pivotal for applications in micro/nanoelectromechanical (MEMS/NEMS) systems. Inducing such property into the two-dimensional Sc2CTT′ MXenes (where T and T′ are the functionalization atoms) via homogeneous and heterogeneous surface functionalization is explored. The functionalization atoms T and T′ located at the upper and lower surfaces, respectively, are identical in the case of homogeneous functionalization, while they differ in the case of heterogeneous functionalization. Upon T and T′ exchange, an additional reverse heterogeneous configuration is generated. The heterogeneous functionalization of Sc2CT2 induces an extraordinary in-plane and out-of-plane piezoelectric effect owing to symmetry breaking. Interestingly, both heterogeneous and its reverse configuration show approximately identical geometrical, energetic, and even elastic properties, but rather different piezoelectric coefficients. The obtained piezoelectric effect is more than ten times larger than the experimentally measured piezoelectricity of MoS2-monolayer. Our study suggests a way toward more efficient nanoscale piezoelectric devices based on Sc2C MXenes.

Piezoelectricity is pivotal for applications in micro/nanoelectromechanical(MEMS/NEMS) systems. Inducing such a property into the two-dimensionalSc(2)CTT & PRIME; MXenes (where T and T & PRIME; are the functionalizationatoms) via homogeneous and heterogeneous surface functionalizationis explored. The functionalization atoms T and T & PRIME; located atthe upper and lower surfaces, respectively, are identical in the caseof homogeneous functionalization, while they differ in the case ofheterogeneous functionalization. Upon T and T & PRIME; exchange, anadditional reverse heterogeneous configuration is generated. The heterogeneousfunctionalization of Sc2CT2 induces extraordinaryin-plane and out-of-plane piezoelectric effects owing to symmetrybreaking. Interestingly, both heterogeneous and its reverse configurationsshow approximately identical geometrical, energetic, and even elasticproperties, but rather different piezoelectric coefficients. The obtainedpiezoelectric effect is more than ten times larger than the experimentallymeasured piezoelectricity of a MoS2-monolayer. Our studysuggests a way toward more efficient nanoscale piezoelectric devicesbased on the Sc2C MXenes for energy conversion and storage.

This work uses ab-initio CBS-QB3 and density functional theory (B3LYP) to analyze the structure, stability, and aromaticity of all isosteric nitrogen-boron pyrroles. The mono-NB unit substituted group of the isosteric NB pyrrole has four isosteres, whereas the multi-NB unit substituted group has two isosteres. These two groups make up all isosteric NB pyrrole. For structural, energetic, magnetic, and electron delocalization criteria, the results highlight the predominance of the PN3B2 isostere and its greater stability over other conformers. In addition, the global reactivity indices, ESP, HOMO-LUMO, and NBO charges have all been estimated to forecast the active side's electron donation and acceptance. These isosteres are categorized as weak electrophiles and marginal nucleophiles. NB-isosteres have poorer stability, HOMO-LUMO gap, and aromaticity than the parent (pyrrole). In general, NB compounds with more ring sharing are less aromatic than NB molecules with less ring sharing. The current study is anticipated to help in understanding of the chemistry of NB substituted molecules and their experimental identification and characterization.

Recently, flexible, stretchable, and wearable sensors have received breakthrough due to wide applications in next generation portable electronics. Despite the use of many nanostructured hydrogels to construct stretchable devices, the integrated excellent optical and mechanical properties as well as intended functionality and satisfactory sensing performance are difficult to achieve with flexible/stretchable devices. Herein, we developed a multifunctional poly dopamine-titanium dioxide/silver quantum dots@ MXene organo-hydrogel (PDA-TiO2/ AgQDs@MXene organo-hydrogel) as an optoelectronic wearable strain sensor with superior mechanical properties. The results reveal a promising sensor capability of monitoring and tracking human activities, vital signs, sign language, vocal cords vibrations during vocalization, touch, temperature, and photodetection of visible light. The developed sensor demonstrated superior anti-freezing point of - 45 degrees C, results in high performance capability at sub-zero temperatures. Additionally, it exhibited self-healing after 5 min with a healing efficiency (HE) 57% and an electrical healing efficiency (EHE) 70%. The water retention behavior (maintain 94.12% of the initial weight after 102 days) and excellent mechanical properties (570 kPa at strain 455%) were introduced. The sensor exhibited ultra-sensitivity (810%) during stretching to 400%, response time (19 ms), and also operated in other harsh circumstances such as bending, twisting, and compression with high reliability. The results provide a new path for future applications of the developed sensor in smart wearable electronics, soft robotics, artificial throat, optoelectronics, and smart healthcare monitoring and diagnosis.

The relative stability of various phases of five AVF3 compounds (A = Li, Na, K, Rb and Cs) is investigated starting from the cubic (C) Pm3̄m (221) prototype structure, with five atoms (one formula unit) in the primitive cell. To the authors' knowledge, only three of these compounds have been investigated experimentally (Na, K and Rb), and they are reported as being cubic. The picture emerging from the present simulation is quite different: CsVF3 and RbVF3 are dynamically stable in the cubic structure, KVF3 is tetragonal, with space group (SG) I4/mcm (no. 140) and 10 atoms in the unit cell; note, however, that an orthorhombic Pnma (62) phase (four formula units) exists, which is not a subgroup of I4/mcm (140), and is very close in energy to the tetragonal phase. Further symmetry lowering is observed in the Na and Li compounds that are orthorhombic. The energy gain and volume reduction with respect to the cubic aristotype increase along the series K, Na and Li, and is very large for the last two compounds. Both FM and AFM solutions have been explored, and they show a very similar path along the SG modifications. The present scheme for determining the lowest energy SG is general, and can be applied to any perovskite. The B3LYP full range hybrid functional and the Hartree-Fock (HF) Hamiltonian, an all-electron Gaussian type basis set and the CRYSTAL code have been used.

Piezoelectricity is pivotal for applications in micro/nanoelectromechanical systems(MEMS/NEMS).Inducing such a property in 2D systems via the reduction of the dimensionality of their corresponding 3D bulk is here explored.Based on DFT theory and Gaussian-type-localized basis sets,the structural,elec-tronic,mechanical,and piezoelectric properties of both 3D and 2D rare earth monochalcogenides RmX(Rm=Tm,Yb,Lu,and X=S,Se,Te)are investigated using the CRYSTAL code.Most intriguingly,the 2D LuX compounds display a buckled structure,where the Lu and X atoms protrude from the monolayer surface leading to an additional out-of-plane piezoelectric effect;(e31=2104.84,1770.28,1 689.79 pC/m,and d31=56.37,49.76,and 147.90 pm/V for LuS,LuSe,and LuTe,respectively).Such piezoelectric response is two orders of magnitude larger than the one of recently reported 2D ferroelectric MXenes,and is nearly thirty times larger than the commonly used AlN and GaN bulk structures.Furthermore,the reduced elastic constants obtained,when compared to other 2D materials,confirm the flexibility and softness of the considered 2D systems.

Stretchable multi-functional electronic skin devices capable of interface with parts of human body and/or internal organs to diagnose the anterior cruciate ligament (ACL) injuries and rehabilitation of human joint motion are attractive candidates for next-generation wearables biomedical devices, soft robots, and the Internet of Things (IoT). Such devices need to be of excellent mechanical property, anti-freezing, antibacterial, biocompatible to be comfortable to wear for long term usage and accommodate strains from repeated movement and prevent skin irritation. To address this need, we introduced conductive organo-hydrogels based on silver quantum dots (COH@AgQDs) as multi-functional stretchable sensor with outstanding high-performance diagnostic capabilities. We demonstrated a prototype from the developed sensors integrated into a wirelessly Arduino board and a smartphone was selected to transmit data which offers promising wireless system for rehabilitation after surgeries. Additionally, the developed device has ability to differentiate between ACL injury and healthy knee with different pattern shapes and high sensitivity. Moreover, the flexible sensor can inhibit the growth of bacteria (Escherichia coli (E-coli)) and Staphylococcus aureus (S. aureus) and protect human health for long-term use. It exhibited outstanding anti-freezing property (-53 degrees C), antibacterial, self-healing, robust mechanical property (strain 420% at stress 96 kPa), and high linearity.

The linear and nonlinear optical (NLO) properties of fullerene and fullerene-like structures, including crystallogen and pnictogen elements, are computed quantum mechanically. The tensors of optical polarizability, α, and second hyperpolarizability, γ, for a series of buckyball fullerene analogues, namely, Si60, Ge60, Sn60, Pb60, P60, As60, Sb60, and Bi60, are reported and analyzed. The eight considered nanocages are here classified into four categories: nanocages stabilized in the X60 form, including C60, As60, Sb60, and Bi60; nanocages that are not stabilized in the X60 form but are found to be stable in a distorted buckled b-X60 form, with X = Si and Ge; nanocages stabilized only in an exohedral decorated X60-Y60 form, X = Sn, Y = H or F; and finally nanocages that are not stable in either distorted or decorated form; however, their corresponding tabular nanotubes are found to be stable; such group includes P and Pb elements. A suggested nomenclature for the above-mentioned fullerenes is given for the first time, where many geometrical, energetic, and optical parameters are discussed extensively. These systems are energetically stable. The cohesive energies of Bi60 and Sn60-F60 range from -1.2 to -4.8 eV/atom and can be compared to -2.4 and -3.3 eV/atom from the corresponding 2D bismuthene and stanene monolayers, respectively. While bismuthellene, Bi60, shows vigorous optical responses compared to standard fullerene, the (9, 0) phosphorus nanotube gives not only enhanced polarizability and second hyperpolarizability but also an inducing first hyperpolarizability, β, which was null by symmetry in the case of spherical fullerenes. The proposed models are expected to be promising materials for optoelectronic and NLO applications.

The effect of the charge of a point defect on the infrared spectrum and the hyperfine coupling constants is discussed with reference to the VO defect in silicon. Five charge states have been considered, from +2e to -2e. Calculations are performed by using a local Gaussian type basis set and the B3LYP hybrid functional. The dominant peak in the IR spectrum increases linearly from 708 cm(-1) (+2 charge), to 904 cm(-1) (-2 charge). The intensity decreases from 4073 to 1727 km/mol, as a consequence of the reduced polarity of the Si-O bond. Also the hyperfine constants differ by large percentages along the series. Although limited to a single defect, the present study shows that both the IR and EPR techniques are able to discriminate the charge state of the defect, also in the cases in which more than one charge state is present in the same sample.

The relative stability ΔEof the cubicPm3¯m(C), of the two tetragonalP4mbm(T1) andI4mcm(T2), and of the orthorhombicPbnm(O) phases of KVF3has been computed both for the ferromagnetic (FM) and antiferromagnetic (AFM) solutions, by using the B3LYP full range hybrid functional and the Hartree-Fock (HF) Hamiltonian, an all-electron Gaussian type basis set and the CRYSTAL code. The stabilization of the T2 phase with respect to the C one (152μHa for B3LYP, 180μHa for HF, per 2 formula units) is due to the rotation of the VF6octahedra with respect to thecaxis, by 4.1-4.6 degrees. The O phase is slightly less stable than the T2 phase (by 6 and 20μHa for B3LYP and HF); it is, however, a stable structure as the dynamical analysis confirms. The mechanism of the stabilization of the AFM solution with respect to the FM one is discussed through the spin density maps, and is related to the key role of the exact exchange term (20% in B3LYP, 100% in HF). The G-AFM phase (the first six neighbors of the reference V ion with spin reversed) is more stable than the FM one by about 500 (HF) and 1800 (B3LYP)μHa per two formula units. A volume reduction is observed in the C to T passage, and in the FM to AFM one, both being of the order of 0.3-0.5A˚3at the B3LYP level. Atomic charges, magnetic moments and bond populations, evaluated according to a Mulliken partition of the charge a spin density functions, complete the analysis. The IR and Raman spectra of the FM and AFM C, T2 and O cells are discussed; the only noticeable difference between the various space groups appears in the modes with wavenumbers lower than 100 cm-1.

The spin density function and hyperfine coupling constants of the NV- defect (a vacancy with one nitrogen atom as a first neighbor) in its triplet ground state, are computed by using hybrid functionals, a Gaussian type all electron basis set, the supercell scheme (216 atoms before the defect formation), and the CRYSTAL code. The charged defect has been simulated by using the charge compensated (CC) scheme, in which a background of positive charge is added to restore the neutrality of the unit cell. The local geometry, charge and spin distribution are also reported and discussed. The EPR constants (Fermi contact, the hyperfine coupling and electric field gradient tensors) of the N (both 14N and 15N) and of two C (for the 13C isotope) atoms around the vacancy are in excellent agreement with the recent experimental results by Felton et al. (Phys. Rev. B, 79,075 203, 2009). The comparison is extended to the many other experimental data collected in the last 30 years, to simpler functionals (LDA and PBE), larger supercells (512 atoms), and to recent simulations. It is shown that the present results are much closer to experiment than previous theoretical studies, with a quantitative, rather than qualitative, agreement.

Chlorine oxyanions namely: hypochlorite ClO-, chlorite ClO2-, chlorate ClO3-, and perchlorate ClO4-, are considered to be harmful for public health since they are disinfectant by-products and are usually found in the disinfection process of drinking water treatment plants (DWTPs). The removal of these oxyanions is, therefore, an important demand. In the current work, the adsorption of chlorine oxyanions on some graphene flakes (Gr) such as coronene (C24H12), circumcoronene (C54H18), and circumcircumcoronene (C96H24), has been theoretically investigated. Favorable adequate (anion-π) interaction between the chlorine oxyanions and the electron-rich graphene flakes have been elucidated, where the stabilization largely originates from attractive electrostatic and dispersion effects. The exponential increase in the attractive electrostatic and dispersion components of the adsorption energies is found to be, in part, a consequence of a charge transfer contribution from the oxygen lone pairs of electrons of oxyanions (donors) to the low-lying π*-orbitals of graphene flakes (acceptors). This finding means that the favorable anion−π interaction between a chlorine oxyanion and a graphene surface is not purely non-covalent.

The NV0 defect in diamond has been investigated quantum-mechanically, by analyzing its structural, electronic, vibrational and magnetic properties. The possible spin states for NV0 are a quartet NVq0 ((4)A(2) symmetry) and a doublet (E-2 symmetry). In the latter state a single electron occupies a double degenerate level producing a Jahn Teller distortion that removes the degeneracy and lowers the total energy. The symmetry reduces from C-3v to C-S and two local minima are indeed identified, to be indicated as NVd1 0((2)A' symmetry) and NVd20 ((2)A '' symmetry). NVd10 is the ground state, and is more stable than NVq0 by similar to 0.5 eV, and than NVd20 by similar to 0.2 eV, irrespective of the functional or basis set adopted. The EPR hyperfine coupling tensor has been computed for NVq0, 1 and has been found to be in excellent agreement with available experimental data. The IR spectra of the NV defects (the three neutral cases and also the negatively charged one, for comparison) show specific peaks and shape that characterize each system and differentiate the spectra according to the spin and charge state. The Raman spectra of the NV0 defects shows a single peak, redshifted with respect to the single peak of pristine diamond by 2 cm(-1) only, but in turn well separated from the negatively charged form of the defect.

Novel multifunctional flexible strain sensors with enhanced properties have become an urgent requirement to comprehensively study the challenges of monitoring the full-range of human activities.

The NV-N+ charged pair in diamond has been investigated by using a Gaussian-type basis set, the B3LYP functional, the supercell scheme and the CRYSTAL code. It turns out that: (i) when the distance between the two defects is larger than 6-7 Å, the properties of the double defect are the superposition of the properties of the individual defects. (ii) The energy required for the reaction NV0 + Ns→ NV- + N+ is roughly -1.3 eV at about 12 Å, irrespective of the basis set and functional adopted, and remains negative at any larger distance. (iii) These results support the observation of a charge transfer mechanism through a Ns→ NV0 donation occurring in the ground state, through a tunnelling process, without irradiation. (iv) The IR spectrum of the two subunits is characterized by specific peaks, that might be used as fingerprints. (v) Calculation of electrostatic interaction permitted an estimate of the effective charge of the defects.

Formic acid (HCOOH) is an important intermediate in chemical synthesis, pharmaceuticals, the food industry, and leather tanning and is considered to be an effective hydrogen storage molecule. Direct contact with its vapor and its inhalation lead to burns, nerve injury, and dermatosis. Thus, it is critical to establish efficient sensing materials and devices for the rapid detection of HCOOH. In the present study, we introduce a chemical sensor based on a quartz crystal microbalance (QCM) sensor capable of detecting trace amounts of HCOOH. This sensor is composed of colloidal phenyl-terminated carbon nitride (Ph-g-C3N4) quantum nanoflakes prepared using a facile solid-state method involving the supramolecular preorganization technology. In contrast to other synthetic methods of modified carbon nitride materials, this approach requires no hard templates, hazardous chemicals, or hydrothermal treatments. Comprehensive characterization and density functional theory (DFT) calculations revealed that the QCM sensor designed and prepared here exhibits enhanced detection sensitivity and selectivity for volatile HCOOH, which originates from chemical and hydrogen-bonding interactions between HCOOH and the surface of Ph-g-C3N4. According to DFT results, HCOOH is located close to the cavity of the Ph-g-C3N4 unit, with bonding to graphitic carbon and pyridinic nitrogen atoms of the nanoflake. The sensitivity of the Ph-g-C3N4-nanoflake-based QCM sensor was found to be the highest (128.99 Hz ppm-1) of the substances studied, with a limit of detection (LOD) of HCOOH down to a sub-ppm level of 80 ppb. This sensing technology based on phenyl-terminated attached-g-C3N4 nanoflakes establishes a simple, low-cost solution to improve the performance of QCM sensors for the effective discrimination of HCOOH, HCHO, and CH3COOH vapors using smart electronic noses.