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The layered solid electrolyte Li2ZrCl6 and Li metal electrodes have a very good contact stability, but the thermal transport properties of Li2ZrCl6 are still unclear. Here, we systematically study the intrinsic lattice thermal conductivity ( κp) of Li2ZrCl6 using the machine-learning potential approach based on first-principles calculations combined with the Boltzmann transport theory. The results show that the κp of Li2ZrCl6 at room temperature is 3.94 W/mK along the in-plane (IP) direction and 1.05 W/mK along the out-plane (OP) direction, which means that the κp is significantly anisotropic. In addition, under the compressive stress in the OP direction, the κp evolution along the IP and OP directions exhibits completely different trends, because the stress has a significant regulatory effect on the contribution of optical phonons to κp. With the increase in stress, the κp in the IP direction monotonically decreases, while the κp in the OP direction increases by a factor of 2.2 under a compressive strain of 13%. This is because the contribution of low-frequency optical phonons to κp in the IP direction is as high as 58% when no stress is applied, and this contribution is significantly suppressed with increasing compressive strain. However, the contribution of optical phonons in the OP direction to the κp increases with the increase in stress. Our results reveal the thermal transport properties of Li2ZrCl6 and the effect of the compressive strain on the κp of Li2ZrCl6, thereby providing a reference for the use of Li2ZrCl6 in Li-metal batteries.

Two-dimensional (2D) Bi2O2Se has attracted much attention as a promising candidate for electronic and optoelectronic applications. However, the transport and optical properties in Bi2O2Se nanoribbons (NRs) are not yet fully understood. In this work, by using first-principles calculations, the intrinsic carrier mobility (μ) and the optical absorption properties of Bi2O2Se NRs are investigated. In contrast to the dramatic deterioration of μ in graphene upon the formation of NRs, the magnitude of μ in Bi2O2Se NRs can reach up to 3600 cm2 V−1 s−1 at a width ranging from 3.3 to 4.5 nm, which is about ten times higher than its sheet counterpart. Such a high intrinsic electron mobility of Bi2O2Se NRs can be attributed to the weaker edge state perturbations due to external strain inherent in Bi2O2Se NRs. Moreover, in Bi2O2Se NRs, the optical absorption at the visible (2.4–3.1 eV) and ultraviolet (4.3 eV) region reaches 5%–10% and 19.2%, respectively. Furthermore, the optical absorption properties can be well tuned by the width of NRs. In addition, the relatively small stretching modulus ranging from 0.40 to 2.24 × 10−7 J/m and the moderate critical strain ranging from 0.04 to 0.14 guarantee its moderate flexibility and ductility. Our results indicate that width modulation provides a potential approach for improving the transport and optical properties of Bi2O2Se nanostructures.

Two dimensional (2D) auxetic materials with large negative Poisson's ratio (NPR) are highly desirable for applications in medicine, tougher composites, defense, and so on. In this paper, by using first-principles calculations, we identify that the CaAs3 monolayer is an excellent auxetic material with large NPR value up to −0.36 along the hinges direction. The relatively small Young's modulus ranging from 23.61 to 40.50 N/m and the moderate critical strain ranging from 0.06 to 0.16 guarantee its extraordinary flexibility and moderate ductility. Owing to its unique crystal structure, the anisotropy of basic mechanical parameters, electrical conductance, and optical absorption are concentrated on the CaAs3 monolayer. Moreover, the electric field-induced tunability of optical absorption also emerged in the CaAs3 monolayer. All of these extraordinary properties allow 2D CaAs3 to have great potential applications in designing electromechanical devices and photoelectric devices as well.

Usually, open-circuit voltage ( V oc ) of thin film solar cells significantly depends on the band bending at the front interface of an absorber/buffer. The failed band bending at a Cu2ZnSnS4/CdS (CZTS/CdS) interface severely hinders the increase in V oc due to the excessively high concentration of holes at the CZTS side. Alleviating the strong p-type or converting it to weak n-type at the CZTS surface is a credible idea to overcome the V oc − deficit. First-principles calculations show that the Li-based selenized CZTS surface presents the desired property with excellent advantages: (i) The greatly improved defects and band offset suppress carrier nonradiative recombination and facilitate electrons transmission, respectively. (ii) Its intrinsic weak n-type characteristic effectively promotes the large band bending at the interface.

Twisted bilayer and multilayer two-dimensional materials linked by van der Waals interactions exhibit various unique physical properties. The phonon properties of such systems are of great importance, but have not been explored in detail. In this work, we use a hybrid neural-network potential to systematically investigate the evolution of the phonon structure of twisted multilayer graphene under out-of-plane strain. With increasing out-of-plane strain, the evolution of the phonon structure of the moire superlattice exhibits different behavior from that of AA and AB stacked multilayer graphene. Meanwhile, with twisting of the interlayer, a higher Gruneisen parameter and a lower phonon group velocity can be obtained. A possible method is revealed by which phonon anharmonic scattering in stacked multilayer graphene could be enhanced by varying the twist angle in combination with out-of-plane strain. Our work shows that the application of out-of-plane strain can serve as an effective way to amplify the effect of twist angle on phonon structures of twisted multilayer two-dimensional systems, with potential application to thermoelectric and thermal logical devices.

Based on first-principles density-functional theory calculations, we have systematically investigated the electronic and magnetic properties of zigzag IVA-VA nanoribbons (ZIV-VNRs). We find that the ZIV-VNRs can exhibit ferromagnetic semiconducting ground states for CP and CAs while simultaneously exhibiting antiferromagnetic states for SiP and SiAs in their edges. What is more, their spin-polarized energy and magnetic moment are quite large in such special systems. Further, we find that a Peierls-like distortion semiconducting state could also take place when the bonding of the edge state is weaker enough as the atom number increases. The physical origin is the competition between charge, spin, and lattice degrees of freedom in different localization characteristics of ZIV-VNR edge states' p orbitals. Our work provides a route for potential functionalities of spintronics devices at the nanoscale.

Tellurene is an elementary two-dimensional (2D) semiconductor material that has attracted intensive attention. Here, first-principles methods are used to explore the effects of excitons on the optical properties of few-layer α-tellurene by considering the thickness and strain effects. Compared to other 2D materials, an α-tellurene monolayer possesses the characteristics of bound exciton states with a binding energy of 0.18 eV and a high optical absorption and oscillator strength in the infrared region. In addition, increasing the thickness and biaxial strain can cause a red-shift of the absorption spectra. The obtained results enrich the current understanding of the underlying physical mechanisms of α-tellurene, which are useful when designing related optoelectronic nanodevices.

Parametric resonance in mechanical oscillators can onset from the periodic modulation of at least one of the system parameters, and the behaviour of the principal (1st order) parametric resonance has long been well established. However, the theoretically predicted higher orders of parametric resonance, in excess of the first few orders, have mostly been experimentally elusive due to the fast diminishing instability intervals. A recent paper experimentally reported up to 28 orders in a micromachined membrane oscillator. This paper reports the design and characterisation of a micromachined membrane oscillator with a segmented proof mass topology, in an attempt to amplify the inherent nonlinearities within the membrane layer. The resultant oscillator device exhibited up to over a hundred orders of parametric resonance, thus experimentally validating these ultra-high orders as well as overlapping instability transitions between these higher orders. This research introduces design possibilities for the transducer and dynamic communities, by exploiting the behaviour of these previously elusive higher order resonant regimes.

In this letter, the effects of hot carriers on amorphous In-Ga-Zn-O thin film transistors (TFTs) of different geometric structures were investigated. Three types of via-contact structure TFTs are used in this experiment, defined as source-drain large (SD large), source-drain normal (SD normal), and fork-shaped. After hot-carrier stress, the I-V curves of both SD normal and fork-shaped TFTs with U-shaped drains show a threshold voltage shift along with the parasitic transistor characteristic in the reverse-operation mode. Asymmetrical degradation is exhibited in an ISE-TCAD simulation of the electric field, which shows the distribution of hot electrons injected into the etch-stop layer below the redundant drain electrode.

This paper investigates the degradation behavior of InGaZnO thin film transistors (TFTs) under negative bias illumination stress (NBIS). TFT devices with two different source and drain layouts were exanimated: one having a parallel format electrode and the other with UI format electrode. UI means that source/drain electrodes shapes is defined as a forked-shaped structure. The I-V curve of the parallel electrode exhibited a symmetric degradation under forward and reverse sweeping in the saturation region after 1000 s NBIS. In contrast, the I-V curve of the UI electrode structure under similar conditions was asymmetric. The UI electrode structure also shows a stretch-out phenomenon in its C-V measurement. Finally, this work utilizes the ISE-Technology Computer Aided Design (ISE-TCAD) system simulations, which simulate the electron field and IV curves, to analyze the mechanisms dominating the parallel and UI device degradation behaviors.

Superlattice-like GaSb/Sb4Te phase change film was proposed for multilevel phase change memory with the feature of three stable resistance states. Two distinct transition temperatures of around 170 and 230 °C were observed in the superlattice-like GaSb/Sb4Te thin film. Under elevated temperature, the precipitated rhombohedral Sb phase was found in the Sb4Te layer, which was followed by the crystallization of rhombohedral Sb2Te3, whereas the GaSb layer remained almost in the amorphous state except the impinged Sb grains. The formation of percolation path for crystallization in the GaSb layer can account for the multilevel resistance states. For the GaSb/Sb4Te-based device, the reversibly electrical switching was realized under the electrical pulse as short as 10 ns, and the endurance was achieved at least 105 cycles among different resistance states.

Electroreflectance of surface-intrinsic-n+ type doped GaAs has been measured over a various biased voltage. The spectra have exhibited many Franz–Keldysh oscillations (FKOs) above band gap energy Eg. The electric field F and critical point energy Ec can be determined from the slope and intercept of FKOs fitting. Hence, we can obtain Ec as a function of F. In most of previous works, Ec is taken as Eg. However, it was found that Ec increases with F in this work. In order to explain this, the gain of energy of electron and hole in F was discussed.

Tunable superstructures were generated by hydrothermally etching silicon wafers in the solution of HF containing ferric nitrate. The structural units of these superstructures arrayed perpendicular to the surface and their shapes could be formed as cone-like, pillar-like, or crater-pit-like through changing the solution concentration of Fe3+ in the etching process. The photoluminescence (PL) in as-prepared porous silicon was found to be independent of the microlocations chosen to carry out the PL measurements.

We have investigated, by means of ab initio calculations, the electronic and magnetic structures of zigzag edge phosphorene nanoribbons (ZPNRs) with various widths. The stable magnetic state was found in pristine ZPNRs by allowing the systems to be spin-polarized. The ground state of pristine ZPNRs prefers ferromagnetic order in the same edge but antiferromagnetic order between two opposite edges. The magnetism arises from the dangling bond states as well as edge localized π-orbital states. The presence of a dangling bond is crucial to the formation of the magnetism of ZPNRs. The hydrogenated ZPNRs get nonmagnetic semiconductors with a direct band gap. While, the O-saturated ZPNRs show magnetic ground states due to the weak P-O bond in the ribbon plane between the pz-orbitals of the edge O and P atoms.

Using first-principles calculations, we have investigated the electronic and magnetic properties of zigzag graphene-like carbon-nitride nanoribbons (Zg-CNNRs) with mono- and dihydrogen-terminated edges asymmetrically. The results demonstrate that spin-down channel completely dominates the states adjacent Fermi level, which is an intrinsic feature and can be accounted for the valence band maximum derived from the nonbonding N-(px,py) orbitals, instead of the bonding C/N-pz π state. Importantly, ferromagnetic ordering is found to be preferred and the magnetism is entirely localized on the N sites of saturated edge due to its stronger electronegativity. Additionally, various edge saturations are further proposed to try to enhance the ferromagnetic ordering and to manipulate the magnetism distributions of Zg-CNNRs.

p-type ZnO thin films have been realized by the N–Al co-doping method. Secondary ion mass spectroscopy demonstrated that the N incorporation was enhanced evidently by the presence of Al in ZnO. The lowest room-temperature resistivity was found to be 57.3Ωcm with a Hall mobility of 0.43cm2∕Vs and carrier concentration of 2.25×1017cm−3 for the N–Al co-doped p-type ZnO film deposited on glass substrate. The results were much better than those for the N-doped p-type ZnO. Moreover, the co-doped film possesses a good crystallinity with c-axis orientation and a high transmittance (90%) in the visible region.

Quasialigned, single-crystal Zn1−xMgxO (x=0–0.32) nanorods were synthesized on Si substrates by thermal evaporation. Zn1−xMgxO nanorods grew along the [0001] crystal direction and had uniform hexagonal planes with diameters of 420–120nm. The predominant ultraviolet luminescence could be tuned from 379 (x=0) to 305nm (x=0.32) at room temperature. This blueshift indicated the band gap engineering in Zn1−xMgxO nanorods. Temperature-dependent photoluminescence was used to illustrate the free-exciton emission from Zn1−xMgxO nanorods. The exciton binding energy decreased from 59 (x=0) to 49meV (x=0.18) and then increased to 54meV (x=0.32).

ZnO homojunction light-emitting diodes (LEDs), comprised of N–Al codoped p-type ZnO and Al-doped n-type ZnO layers, were fabricated on Si substrates with homobuffer layers. The current-voltage measurements showed typical diode characteristic with a threshold voltage of about 3.3V. The electroluminescence (EL) bands at 110K consisted of a near-band-edge emission at 3.18eV and a deep level emission at 2.58eV. The EL emissions were assigned as radiative recombinations, presumably of donor-acceptor pairs, in the p-type layer of the LED. The quenching of EL with temperature was attributed to the degradation of p-type conducting of the ZnO:(N,Al) layer.

A set of ten-period ZnO∕Zn0.85Mg0.15O multiple quantum wells with well thickness varying from 2.5to5nm has been grown on Si(111) substrates by pulsed laser deposition. A periodic structure with sharp interfaces was observed by cross-sectional transmission electron microscopy. The room-temperature photoluminescence resulting from the well regions exhibits a significant blueshift with respect to the ZnO single layer. The well layer thickness dependence of the emission energy from the well regions was investigated and compared with a simple theoretical model. The results suggest that the quantum confinement effects in the quantum wells can be observed up to room temperature.

ZnMgO pleated nanosheets and quasinanotubes were synthesized in the same region on Si substrate using [Mg(H2O)6](NO3)2 and zinc diethyl as the reactant source. The nanosheets are periodically pleated with the angles of 120° and 60° between two adjacent pleats. Some of the nanosheets fold into quasinanotubes. Homoepitaxial interconnections are observed at the boundaries of the pleats, and the whole pleated nanosheet is a single wurtzite crystal. The growth mechanism is discussed, which is proposed to be a combination of vapor-solid process of two-dimensional growth of the (1¯21¯0) planes and their random along the ⟨101¯0⟩ directions.

The authors report on reproducible growth of ZnMgO quantum dots (QDs) by a metal organic chemical vapor deposition method. Mg is introduced into ZnO QDs, as confirmed by x-ray photoelectron spectroscopy and photoluminescence measurements. The size, density, and optical band gap of ZnMgO QDs can be well controlled by simply modulating the growth parameters. ispartof: Applied Physics Letters vol:90 issue:1 pages:1-3 status: published