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Nanoparticles (NPs) with reactive oxygen species (ROS)-regulating ability have recently attracted great attention as promising agents for nanomedicine. In the present study, we have analyzed the effects of TiO2 defect structure related to the presence of stoichiometric (Ti4+) and non-stoichiometric (Ti3+ and Ti2+) titanium ions in the crystal lattice and TiO2 NPs aggregation ability on H2O2- and tert-butyl hydroperoxide (tBOOH)-induced ROS production in L929 cells. Synthesized TiO2-A, TiO2-B, and TiO2-C NPs with varying Ti3+(Ti2+) content were characterized by x-ray powder diffraction, transmission electron microscopy, small-angle x-ray scattering, x-ray photoelectron spectroscopy, and optical spectroscopy methods. Given the role of ROS-mediated toxicity for metal oxide NPs, L929 cell viability and changes in the intracellular ROS levels in H2O2- and tBOOH-treated L929 cells incubated with TiO2 NPs have been evaluated. Our research shows that both the amount of non-stoichiometric Ti3+ and Ti2+ ions in the crystal lattice of TiO2 NPs and NPs aggregative behavior affect their catalytic activity, in particular, H2O2 decomposition and, consequently, the efficiency of aggravating H2O2- and tBOOH-induced oxidative damage to L929 cells. TiO2-A NPs reveal the strongest H2O2 decomposition activity aligning with their less pronounced additional effects on H2O2-treated L929 cells due to the highest amount of Ti3+(Ti2+) ions. TiO2-C NPs with smaller amounts of Ti3+ ions and a tendency to aggregate in water solutions show lower antioxidant activity and, consequently, some elevation of the level of ROS in H2O2/tBOOH-treated L929 cells. Our findings suggest that synthesized TiO2 NPs capable of enhancing ROS generation at concentrations non-toxic for normal cells, which should be further investigated to assess their possible application in nanomedicine as ROS-regulating pharmaceutical agents. [ABSTRACT FROM AUTHOR]

Construction of various nanostructures with nanometre-scale precision through various DNA building blocks depends upon self-assembly, base-pair complementarity and sequence programmability. During annealing, unit tiles are formed by the complementarity of base pairs in each strand. Enhancement of growth of target lattices is expected if seed lattices (i.e. boundaries for growth of target lattices) are initially present in a test tube during annealing. Although most processes for annealing DNA nanostructures adopt a one-step high temperature method, multi-step annealing provides certain advantages such as reusability of unit tiles and tuneability of lattice formation. We can construct target lattices effectively (through multi-step annealing) and efficiently (via boundaries) by multi-step annealing and combining boundaries. Here, we construct efficient boundaries made of single, double, and triple double-crossover DNA tiles for growth of DNA lattices. Two unit double-crossover DNA tile-based lattices and copy-logic implemented algorithmic lattices were introduced to test the growth of target lattices on boundaries. We used multi-step annealing to tune the formation of DNA crystals during fabrication of DNA crystals comprised of boundaries and target lattices. The formation of target DNA lattices was visualized using atomic force microscopy (AFM). The borders between boundaries and lattices in a single crystal were clearly differentiable from AFM images. Our method provides way to construct various types of lattices in a single crystal, which might generate various patterns and enhance the information capacity in a given crystal. [ABSTRACT FROM AUTHOR]

In this work we provide a step by step derivation of an angular-averaged Ewald potential suitable for numerical simulations of disordered Coulomb systems. The potential was first introduced by E Yakub and C Ronchi without a clear derivation. Two methods are used to find the coefficients of the series expansion of the potential: based on the Eulerâ€"Maclaurin and Poisson summation formulas. The expressions for each coefficient is represented as a finite series containing derivatives of Jacobi theta functions. We also demonstrate the formal equivalence of the Poisson and Eulerâ€"Maclaurin summation formulas in the three-dimensional case. The effectiveness of the angular-averaged Ewald potential is shown by the example of calculating the Madelung constant for a number of crystal lattices. [ABSTRACT FROM AUTHOR]

The repetitive unclamped inductive switching (UIS) avalanche stress is conducted to investigate the degradation and breakdown behaviors of conventional shield gate trench MOSFET (C-SGT) and P-ring SGT MOSFETs (P-SGT). It is found that the static and dynamic parameters of both devices show different degrees of degradation. Combining experimental and simulation results, the hot holes trapped into the Si/SiO2 interface and the increase of crystal lattice temperature should be responsible for the degradation and breakdown behaviors. Moreover, under repetitive UIS avalanche stress, the reliability of P-SGT overcomes that of C-SGT, benefitting from the decreasing of the impact ionization rate at bottom of field oxide caused by the existence of P-ring. [ABSTRACT FROM AUTHOR]

Carbon ion irradiation and precise diamond blade dicing are applied to fabricate Nd:GdCOB ridge waveguides. The propagation properties of the fabricated Nd:GdCOB waveguides are investigated through experiments and theoretical analysis. Micro-Raman analysis reveals that the Nd:GdCOB crystal lattice expands during the irradiation process. Micro-second harmonic spectroscopic analysis suggests that the original nonlinear properties of the Nd:GdCOB crystal are greatly enhanced within the waveguide volume. Under pulsed 1064 nm laser pumping, second harmonic generation (SHG) at 532 nm has been achieved in the fabricated waveguides. The maximum SHG conversion efficiencies are determined to be ∼ 8.32 %â‹...Wâˆ'1 and ∼ 22.36 %â‹...Wâˆ'1 for planar and ridge waveguides, respectively. [ABSTRACT FROM AUTHOR]

Non-Hermitian quasicrystals possess P T and metalâ€"insulator transitions induced by gain and loss or nonreciprocal effects. In this work, we uncover the nature of localization transitions in a generalized Aubryâ€"AndrĂ©â€"Harper model with dimerized hopping amplitudes and complex onsite potential. By investigating the spectrum, adjacent gap ratios and inverse participation ratios, we find an extended phase, a localized phase and a mobility edge phase, which are originated from the interplay between hopping dimerizations and non-Hermitian onsite potential. The lower and upper bounds of the mobility edge are further characterized by a pair of topological winding numbers, which undergo quantized jumps at the boundaries between different phases. Our discoveries thus unveil the richness of topological and transport phenomena in dimerized non-Hermitian quasicrystals. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) emission materials can be widely applied in various fields, such as food detection, imaging, treatment, electronic products. With the trend of miniaturization of equipment, smaller materials are needed. In this work, we successfully synthesized a series of M2Ga2GeO7:N3+ (M = Ca, Ba, Sr; N = Cr, Nd, Er) samples and then focused on the study of Nd3+ doped Sr2Ga2GeO7 (SGGO). A series of SGGO:xNd3+ sub-micron phosphors were prepared via a microwave-assisted sol–gel process combined with subsequent calcination at 750 ℃, and the structural information and luminescent properties were systematically studied. SGGO is a representative tetragonal crystal and belonging to the space group of P 21m (113). The Nd3+ ions occupy eight-coordinated Sr2+ sites in the crystal lattice. From SEM analysis, the average particle size distribution is 219.7 ± 41.4 nm. The sub-micron phosphors have rich excitation spectra ranging from 350 nm to 850 nm and can produce multiband NIR emissions of 1331, 1056, and 905 nm when excited by ultraviolet and NIR light. The maximum emission intensity was obtained by optimizing the doping ratio of Nd3+ ions. A commercial chip was then utilized to fabricate light-emitting diodes (LEDs) to verify its application potential in NIR-II mini-LEDs. Compared with blue light LEDs, the as-prepared LEDs had good imaging penetration depth and could be clearly observed under 10 mm of chicken breast coverage. The maximum imaging penetration depth can be 33 mm. [ABSTRACT FROM AUTHOR]

In the present study, pure and zinc (Zn) doped tin oxide (SnO2) thin films were grown by successive ionic layer adsorption and reaction method on the soda lime glass slides at 293 K. The prepared samples were examined to observe the impact of Zn doping on structural, morphological, electrical, and optical properties of SnO2 crystal lattice. The x-ray diffractometer (XRD), ultraviolet–visible spectrometer, energy dispersive x-ray analysis (EDAX), scanning electron microscope (SEM), Raman, x-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectra measurements were conducted. And, two probe detection method was applied to find the shift in resistance values corresponding to varying temperatures. The XRD results depicted that the prepared thin films have the tetragonal rutile structure. The surface morphologies were observed to be affected by the changing concentrations of Zn doping. The EDAX evaluation exposed the existence of Zn ions in the prepared samples in addition to Sn and O. Resistivity vs temperature (r–t) measurements exhibited that all the samples possess the common 'r–t' characteristics of semiconductors. The XPS results uncovered the fact that the binding energy of SnO2 nanostructures was decreased by 0.9 eV due to the existence of Zn ions. It was also found out that the band gaps, calculated by using the absorption measurements, can be tuned from 2.02 eV to 2.50 eV by the different rates of Zn dopants in the SnO2 nanostructures. The Raman spectras of pure SnO2 and Zn doped SnO2 (Zn:SnO2) samples gave three peaks that were in the range of 490 cm−1, 580 cm−1 and 620 cm−1 for each peak separately. The PL spectra displayed that the emission intensity decreased with the introduction of impurities into the SnO2 lattice. [ABSTRACT FROM AUTHOR]

Reactions between dislocations are investigated in two-dimensional colloidal crystals. It is found that, because of the conservation of total Burgers vectors, the kinetics of the reaction is dependent on the the symmetry of the crystal lattice. Merging is possible only when the total Burgers vector of the reacting dislocations is in line with existing crystal lines. In non-merging reactions, the number of dislocations cannot be reduced but the interacting dislocations can exchange their Burgers vectors and migrate to different gliding lines. The changing of gliding lines promises additional annihilation in multi-dislocation reactions. The bonding of non-merging dislocations determines the configuration and the orientation of the grain boundaries. The findings in this study may shed new light on understanding of dislocations and have potential applications in fabrication of crystalline materials. [ABSTRACT FROM AUTHOR]

In this paper, we develop the quantum theory that has discrete Poincaré symmetry on the one-dimensional Bravais lattice. We review the recently discovered discrete Lorentz symmetry which coexists with the discrete space translational symmetry on a Bravais lattice. The discrete Lorentz transformations and spacetime translations form the discrete Poincaré group, which are represented by unitary operators in a quantum theory. We find the conditions for the existence of representation, which are expressed as the congruence relation between quasi-momentum and quasi-energy. We then build the Lorentz-invariant many-body theory of indistinguishable particles by expressing both the unitary operators and Floquet Hamiltonians in terms of the field operators. Some typical Hamiltonians include the long-range hopping which fluctuates as the distance between sites increases. We calculate the Green's function of the theory. The spacetime points where the Green's function is nonzero display a lattice structure. During the propagation, the particle stays localized on a single or a few sites to preserve the Lorentz symmetry. [ABSTRACT FROM AUTHOR]

The doping effects of transition metals (TMs = Mn, Co, Ni, and Cu) on the superconducting critical parameters are investigated in the films of iron selenide (Li,Fe)OHFeSe. The samples are grown via a matrix-assisted hydrothermal epitaxy method. Among the TMs, the elements of Mn and Co adjacent to Fe are observed to be incorporated into the crystal lattice more easily. It is suggested that the doped TMs mainly occupy the iron sites of the intercalated (Li,Fe)OH layers rather than those of the superconducting FeSe layers. We find that the critical current density Jc can be enhanced much more strongly by the Mn dopant than the other TMs, while the critical temperature Tc is weakly affected by the TM doping. [ABSTRACT FROM AUTHOR]

The high-frequency edge of the first-order Raman mode of diamond reflects the stress state at the culet of anvil, and is often used for the pressure calibration in diamond anvil cell (DAC) experiments. Here we point out that the high-frequency edge of the diamond Raman phonon corresponds to the Brillouin zone (BZ) center Γ point as a function of pressure. The diamond Raman pressure gauge relies on the stability of crystal lattice of diamond under high stress. Upon the diamond anvil occurs failure under the uniaxial stress (197 GPa), the loss of intensity of the first-order Raman phonon and a stress-dependent broad Raman band centered at 600 cm−1 are observed, which is associated with a strain-induced local mode corresponding to the BZ edge phonon of the L1 transverse acoustic phonon branch. [ABSTRACT FROM AUTHOR]

Using molecular dynamics simulations, we have revealed a novel wetting phenomenon with a droplet on composite structures formed by embedded water into (111) surface of β-cristobalite hydroxylated silica. This can be attributed to the formation of a composite structure composed of embedded water molecules and the surface hydroxyl (–OH) groups, which reduces the number of hydrogen bonds between the composite structure and the water droplet above the composite structure. Interestingly, a small uniform strain (±3%) applied to the crystal lattice of the hydroxylated silica surface can result in a notable change of the contact angles (>40°) on the surface. The finding provides new insights into the correlation between the molecular-scale interfacial water structures and the macroscopic wettability of the hydroxylated silica surface. [ABSTRACT FROM AUTHOR]

The thermoluminescence (TL) mechanism for un-doped and europium (Eu3+) doped barium aluminate (BaAl2O4) were investigated and the location of energy levels for electrons/holes traps were determined in the aluminate for TL dosimetry applications. The solution combustion technique was used to synthesize the un-doped and Eu3+ doped BaAl2O4 nanopowders. X-ray diffraction showed a hexagonal crystal structure with the space group P63. The average crystallite size were found to be 50 nm and between 41 and 61 nm for un-doped and doped samples. Scanning electron microscopy showed irregular spherical and needle shapes for the un-doped and doped samples. The Kubelka–Munk function was used to calculate the optical bandgap values of 5.47 and 5.26 eV, for the un-doped and doped samples, from the diffuse reflectance spectra. The fitted x-ray photoelectron spectroscopy data demonstrated that Ba occupied two different sites, Ba1 and Ba2. Time-of-flight secondary ion mass spectroscopy in spectral mode showed the formation of the crystal lattice with the presence of the dopant. The photoluminescent and cathodoluminescent spectra were characterized by the 5D0-7FJ transitions (J = 1, 2, 3, 4) of Eu3+ with the dominate emission obtained at J = 2. A strong TL glow curve with peaks at 397 and 453 K were observed for the un-doped and doped nanopowders after irradiation with γ-rays. The doped nanopowders showed the highest TL intensity because doping with Eu3+ lead to the formation of additional trapped electrons and holes. The un-doped sample showed strong green (546 nm) TL emission due to the presence of a Vk3+ center. Whereas the Eu doped nanopowders exhibited strong TL emission at 615 nm. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) quadrupole topological insulators, featured by topologically protected 0D corner modes, have recently attracted tremendous interest in condensed matter and materials physics. Herein, we construct a specific electric circuit made of capacitors and inductors forming a 2D Kekulé hexagonal lattice for quadrupole topological phase and corner modes. Trivial–nontrivial topological phase transition can be controlled by varying capacitance in the circuit, so that distinct topological edge states appear in 1D ribbons and corner states emerge in 0D flakes. We explore the field strength distribution and two-point impedance with respect to excitation frequency, and reveal that the topological corner resonance is robust against size of the LC network and randomness of the capacitors/inductors, a great benefit for experimental detection. Our results enrich the family of designer topoelectrical circuit as a flexible and tunable platform to achieve exotic quantum phases, which may have potential for future telecommunications, signal processing and quantum computing. [ABSTRACT FROM AUTHOR]

Recent advances in rechargeable Zn/MnO2 alkaline batteries have shown promise for scalable energy storage systems which provide a safe, low-cost alternative with a demonstrated lifetime over thousands of cycles. This cathode technology is based on a 2-electron Mn redox process where a layered birnessite-type phase has been shown to form after the first cycle with excellent reversibility between the discharge product, Mn(OH)2. Herein, we investigate the reversible reaction between birnessite and Mn(OH)2 with and without a Bi2O3 additive using multimodal structural characterization techniques during active battery cycling. Diffraction results provide evidence of Bi3+ residing in the interlayer of birnessite which prevents irreversible Mn3O4 formation by limiting Mn3+ diffusion within the crystal lattice. Also, upon charge no MnOOH intermediate phases are observed. Instead, X-ray absorption and Raman spectroscopy indicate a disordered, non-crystalline birnessite-type phase consisting of mostly neutral H2O within the interlayer. Birnessite phases will reform without Bi2O3 present, but Mn3O4 formation severely polarizes the potential they are formed at, leading to capacity fade. Also, we discuss the reversible Bi2O3 conversion to Bi0 and its contribution to the observed capacity. We expect the results will provide crucial insight into the development of aqueous, rechargeable battery systems utilizing MnO2. [ABSTRACT FROM AUTHOR]

In this work, the temperature dependence of the extended x-ray absorption fine structure (EXAFS) amplitude and phase of the first shell of face-centered cubic crystals was studied using the anharmonic correlated Einstein model and quantum statistical theory with first-order perturbation. The thermodynamic parameters of a system are derived from an anharmonic effective potential that has taken into account the influence of all nearest neighbors of absorbing and backscattering atoms in the crystal lattice with thermal vibrations, where the Morse potential is assumed to characterize the interactions between each pair of atoms and the function of anharmonic EXAFS spectra presented in terms of the cumulant expansion up to the fourth-order. The analytical expressions of the temperature dependence of the first four EXAFS cumulants were calculated and evaluated in both low-temperature and high-temperature limits. The numerical results for crystalline copper were in good agreement with those obtained by the other theoretical procedures and experiments at several other temperatures. The analytical results of the contributions of the EXAFS cumulants to the amplitude reduction and phase shift of the EXAFS spectra discovered the role and meaning of high-order cumulants in the analysis of the temperature dependence of the EXAFS spectra. [ABSTRACT FROM AUTHOR]

A new method for accurately characterizing the tip geometry of critical dimension atomic force microscopy (CD-AFM) has been introduced. A sample type IVPS100-PTB whose line features have vertical sidewall, round corner with a radius of approx. 5 ∼ 6 nm and very low surface roughness has been applied as the tip characterizer. The geometry of the line features has been accurately and traceably calibrated to the lattice constant of crystal silicon. In this paper, detailed measurement strategies and data evaluation algorithms have been introduced, particularly concerning several important influence factors such as the line width roughness of the tip characterizer, measurement noise, measurement point density, and the calculation of the averaged tip geometry. Thorough experimental studies have been carried out, indicating high measurement accuracy of the developed method. For instance, tip geometry of a probe type CDR120 with a nominal tip diameter of 120 nm is reconstructed using two different tip characterizers before, during and after it is applied for a calibration of a user sample. The agreement of all 20 obtained tip profiles reaches 0.4 nm, confirming the high measurement stability, low tip wear as well as the high measurement consistency between two tip characterizers. Furthermore, the results of a nanofeature of the user sample after correcting the tip contribution show a repeatability of approximately 0.3 nm when it is repeatedly measured by a same tip, and a reproducibility of 0.9 nm when it is measured using two different tips, confirming the good performance of the tip correction method as well. [ABSTRACT FROM AUTHOR]

Realizing manipulation of the photoelectric properties of wide bandgap semiconductors is a main challenge for successful next-generation functional optoelectronics. As an intriguing wide bandgap semiconductor, β-Ga2O3 (e.g. ∼4.9 eV) is emerging as a promising candidate for photodetectors operating in the solar-blind region. Here, we show that by selecting substrates with different symmetries and lattice parameters (i.e. (100) MgO, (100) MgAl2O4 and (0001) α-Al2O3), epitaxial β-Ga2O3 films with (100)-or -orientation could be fabricated. We found that the photoresponse characteristics are strongly correlated with the lattice mismatch and film orientation. In particular, (100)-oriented β-Ga2O3 film grown on MgO substrate with smaller lattice mismatch exhibited a 254 nm responsivity of 0.1 A · W−1 and detectivity of 4.3 × 1012 Jones, which are approximately an order of magnitude higher than that of the -oriented β-Ga2O3 film. Our work may provide a strategy to develop further high performance solar-blind photodetectors. [ABSTRACT FROM AUTHOR]

We demonstrate that the transport of hot carriers may result in the phenomenon where an oscillated output current appears at the waveforms in a high-power photoconductive semiconductor switch (PCSS) working at long pulse width when the laser disappears or the electric field changes. The variational laser and electric field will affect the scattering rates of hot carriers and crystal lattice in high-power PCSS, and the drift velocity of hot carriers and also the on-state resistance will be changed. The present result is important for reducing the on-state resistance and improving the output characteristics of high-power Si/GaAs PCSS. [ABSTRACT FROM AUTHOR]

Li2ZnTi3O8 (LZTO) and reduced graphite oxide modified Li2ZnTi3O8 which are designated as LZTO@RGO10, LZTO@RGO25 and LZTO@RGO50 anodeswere successfully prepared by a facile and cost effective ball mill assisted solid state method. RGO/LZTO mass ratioswere selected as 0.1: 1, 0.25:1 and 0.5:1, respectively. The effects ofRGOcontent on the crystal lattice, particle morphology and electrochemical properties were investigated. The electrochemical performance of LZTO could be improved by adjusting the content of RGO. Among all the samples, LZTO@RGO25 exhibits excellent electrochemical performance in terms of high capacities (302, 250, 221, 194 and 154 mAh g-1 at current densities of 0.1, 0.5, 1, 2 and 5C, respectively). Cycling performance measurements show that, LZTO@RGO25 has 200 mAh g-1 residual capacity compared with that (66 mAh g-1) of LZTO after 100 cycles at 1C rate. [ABSTRACT FROM AUTHOR]

A mechanical diamond, with the classical mechanics of a spring-mass model arrayed on a diamond lattice, is discussed topologically. Its frequency dispersion possesses an intrinsic nodal structure in the three-dimensional Brillouin zone (BZ) protected by the chiral symmetry. Topological changes of the line nodes are demonstrated, associated with the modification of the tension. The line nodes projected into two-dimensional BZ, form loops, which are characterized by the quantized Berry phases with 0 or p. With boundaries, the edge states are discussed in relation to the Berry phases and winding numbers, and the bulk-edge correspondence of the mechanical diamond is established. [ABSTRACT FROM AUTHOR]

The anti-continuum limit of a monotone variational recurrence relation consists of a lattice of uncoupled particles in a periodic background. This limit supports many trivial equilibrium states that persist as solutions of the model with small coupling. We investigate when a persisting solution generates a so-called lamination and prove that near the anti-continuum limit the collection of laminations of solutions is homeomorphic to the (N�−�1)-dimensional simplex, with N the number of distinct local minima of the background potential. This generalizes a result by Baesens and MacKay on twist maps near an anti-integrable limit. [ABSTRACT FROM AUTHOR]

Here we report a structural and electronic investigation of the recently discovered CaCuO2/SrTiO3 superconducting artificial superlattices based on two insulating oxides. We show that Tc = 50 K is reached in the superlattices grown on NdGaO3 substrate under optimized growth conditions. If the superlattices are grown on LaAlO3 substrate the Tc is drastically reduced due to the much higher lattice mismatch between CaCuO2 and LaAlO3, which has lattice parameters substantially smaller than NdGaO3. The consequent in-plane lattice contraction also makes the incorporation of extra oxygen atoms more difficult, leading to a decrease of hole doping and Tc. Finally, x-ray absorption spectroscopy study as a function of the thickness of the CaCuO2 block in CaCuO2/SrTiO3 superconducting superlattices has revealed the important role played by the interfaces as the location of hole doping and superconductivity in these systems. [ABSTRACT FROM AUTHOR]

In order to study the relation between martensitic transformation temperature range ΔT (where ΔT is the difference between martensitic transformation start and finish temperature) and lattice distortion ratio (c/a) of martensitic transformation, a series of Ni46Mn28−xGa22Co4Cux (x = 2–5) Heusler alloys is prepared by arc melting method. The vibration sample magnetometer (VSM) experiment results show that ΔT increases when x > 4 and decreases when x < 4 with x increasing, and the minimal ΔT (about 1 K) is found at x = 4. Ambient X-ray diffraction (XRD) results show that ΔT is proportional to c/a for non-modulated Ni46Mn28−xGa22Co4Cux (x = 2–5) martensites. The relation between ΔT and c/a is in agreement with the analysis result obtained from crystal lattice mismatch model. About 1000-ppm strain is found for the sample at x = 4 when heating temperature increases from 323 K to 324 K. These properties, which allow a modulation of ΔT and temperature-induced strain during martensitic transformation, suggest Ni46Mn24Ga22Co4Cu4 can be a promising actuator and sensor. [ABSTRACT FROM AUTHOR]

Metal-polar In0.17Al0.83N barriers, lattice-matched to GaN, were grown under N-rich conditions by plasma-assisted molecular beam epitaxy. The compositional homogeneity of these barriers was confirmed by plan-view high-angle annular dark-field scanning transmission electron microscopy and atom probe tomography. Metal-polar In0.17Al0.83N/(GaN)/(AlN)/GaN structures were grown with a range of AlN and GaN interlayer (IL) thicknesses to determine the optimal structure for achieving a low two-dimensional electron gas (2DEG) sheet resistance. It was determined that the presence of a GaN IL was necessary to yield a 2DEG sheet density above 2 × 1013 cm−2. By including AlN and GaN ILs with thicknesses of 3 nm and 2 nm, respectively, a metal-polar In0.17Al0.83N/GaN/AlN/GaN structure regrown on a GaN-on-sapphire template yielded a room temperature (RT) 2DEG sheet resistance of 163 Ω/□. This structure had a threading dislocation density (TDD) of ∼5 × 108 cm−2. Through regrowth on a free-standing GaN template with low TDD (∼5 × 107 cm−2), an optimized metal-polar In0.17Al0.83N/GaN/AlN/GaN structure achieved a RT 2DEG sheet resistance of 145 Ω/□ and mobility of 1822 cm2 V−1 s−1. High-electron-mobility transistors with output current densities above 1 A mm−1 were also demonstrated on the low-TDD structure. [ABSTRACT FROM AUTHOR]

The formation of CuIn(1-x) GaxSe2 (CIGS) by electrochemical atomic layer deposition (E-ALD) is reported. Two different CIGS E-ALD cycle programs were investigated. The first consisted of the sequential deposition of alternating atomic layers (AL) metal and Se. That is, AL of Cu, In and Ga were alternated with AL of Se, in what is referred to as a quaternary CIGS program. The second was a superlattice program, composed of differing numbers of the binary compound cycles repeated in a period. The use of the superlattice program allowed better control of the overall stoichiometry. Electron probe microanalysis was used to characterize deposit compositions. A discussion of how variations in the deposition programs affected the resulting deposit compositions is presented. Deposits were formed with the classic CIGS stoichiometry (CuIn0.7Ga0.3Se2) using the superlattice program. XRD patterns for the E-ALD deposited chalcopyrite CIGS are reported as deposited, no annealing. [ABSTRACT FROM AUTHOR]

Accurate and traceable measurements of critical dimension (CD) and sidewall profile of extreme ultraviolet (EUV) photomask structures using atomic force microscopes (AFMs) are introduced in this paper. An instrument complementarily applied with two kinds of AFM techniques, the CD-AFM and the tilting-AFM, has been developed. High measurement stability of the instrument is demonstrated, for instance, the long-term CD stability is better than 1 nm over 500 successive measurements over 55 h. To traceably calibrate the effective tip geometry, transmission electron microscopes-based method is applied, which uses either the silicon crystal lattice or the structure pitch value calibrated by metrological AFMs as an internal scale. Several grating patterns with different nominal CDs and line/space ratios of an EUV photomask have been measured using the developed methods. A data evaluation method with considered higher order tip effect due to the non-vertical sidewall is introduced. Detailed measurement results of a test EUV photomask, such as middle CD, left and right sidewall angle, feature height, line edge roughness and edge profiles are given. Finally, the AFM results are compared to that of a PTB EUV scatterometer. The comparison of the middle CD yields a linear relation within a spread of only about ±2 nm and an offset of the absolute values below 3 nm. For the sidewall angle, both methods yield consistent results within a range of about 2°. [ABSTRACT FROM AUTHOR]

Understanding the effects of an anisotropic grain boundary energy model is difficult analytically, so simulations provide a valuable insight into the dynamics and characteristics of grain structure evolution. A brute-force analysis of the common Read–Shockley model in two dimensions for grains of the topological class of n-sided grains with 3 ⩽ n ⩽ 8 is performed. In this approach, we rotate all cubic two-dimensional crystal lattices of n-sided grain neighbors stepwise with high resolution in two dimensions, and compute the growth rates of each configuration to obtain detailed growth rate distributions. To perform the computationally intense task of computing the growth rates for billions of configurations, a vertex type model and a supercomputer are utilized. Modern computation facilities deliver the required computation power to carry out such studies in a reasonable amount of time. The vertex model is validated by comparison with 700 phase-field simulations. Our findings support the isotropic behavior of grain structures with randomly oriented lattices and Read–Shockley grain boundary energy, where the average values of the growth rate distributions follow the isotropic Neumann–Mullins relation. Further, all computed growth rate distributions are not symmetric and adapt a normal distribution for n → 8. Abnormal grain growth does not occur for the Read–Shockley model with neighbors in the range 3 ⩽ n ⩽ 8. The brute-force method of scanning the parameter space in high resolution reaches its limit fast, but contributes a new perspective. [ABSTRACT FROM AUTHOR]

We have prepared the Li-rich layered NMC composite cathode material of the composition 0.3Li2MnO30.7LiMn0.33Ni0.33Co0.33O2, (NMC) with 5 wt% Na doping. The latter material with composition of 0.3Li2MnO3.0.7Li0.97Na0.03Mn0.33.33Ni0.33Co0.33O2, synthesized as 200-300 nm size particles, was compared to its counterpart without Na. The discharge rate capability of the Li-rich NMC was greatly improved at both room temperature and 50°C with the Na doping. The Na doped material exhibited significantly higher conductivity than its un-doped analog as evidenced by dc electronic conductivity data and impedance of Li cells. Charge/discharge cycling results of Li cells at 50°C indicated that the voltage decay of Li-rich NMC accompanied by a layer to spinel structural conversion was mitigated with Na doping. XRD analysis revealed that ionic exchange of Na occurs upon contact of the cathode material with the electrolyte and produces a volume expansion of the crystal lattice which triggers a favorable metal (probably Ni) migration to Li depleted regions during oxidation of Li2MnO3 in the first cycle. XANES data showed that Na doped NMC has better Ni reduction efficiency to provide higher rate capability. EXAFS data supported this conclusion by showing that in the case of Na doped NMC, the structure has larger crystal cage allowing for better metal migration into the Li depleted regions located in the layered unit cell of C2/m space group. XANES of Mn K-edge supported by pre-edge analysis also revealed that during charging of the electrode, the Na doped NMC was oxidized to a higher Mn valence state compared to its undoped counterpart. [ABSTRACT FROM AUTHOR]

DNA tile based self-assembly provides a bottom-up approach to construct desired nanostructures. DNA tiles have been directly constructed from ssDNA and readily self-assembled into 2D lattices and 3D superstructures. However, for more complex lattice designs including algorithmic assemblies requiring larger tile sets, a more modular approach could prove useful. This paper reports a new DNA ‘sub-tile’ strategy to easily create whole families of programmable tiles. Here, we demonstrate the stability and flexibility of our sub-tile structures by constructing 3-, 4- and 6-arm DNA tiles that are subsequently assembled into 2D lattices and 3D nanotubes according to a hierarchical design. Assembly of sub-tiles, tiles, and superstructures was analyzed using polyacrylamide gel electrophoresis and atomic force microscopy. DNA tile self-assembly methods provide a bottom-up approach to create desired nanostructures; the sub-tile strategy adds a useful new layer to this technique. Complex units can be made from simple parts. The sub-tile approach enables the rapid redesign and prototyping of complex DNA tile sets and tiles with asymmetric designs. [ABSTRACT FROM AUTHOR]

We study the propagation of non-diffracting images in kagome photonic lattices. In a weak-coupling regime (discrete approach), the linear spectrum is composed by only three bands, including a completely degenerated and flat one. The states forming this special band are well localized in space and constitute building blocks for this lattice. By linearly combining these non-diffractive fundamental modes, different shapes can be composed and, therefore, a given image will propagate without distortion. As an example, we compare the linear propagation of a particular image for kagome and rectangular lattices. At the end, we test our concept by performing numerical simulations in a continuous kagome potential. [ABSTRACT FROM AUTHOR]

Beam splitting upon refraction in a triangular sonic crystal composed of aluminum cylinders in air is experimentally and numerically demonstrated to occur due to finite source size, which facilitates circumvention of a directional band gap. Experiments reveal that two distinct beams emerge at crystal output, in agreement with the numerical results obtained through the finite-element method. Beam splitting occurs at sufficiently-small source sizes comparable to lattice periodicity determined by the spatial gap width in reciprocal space. Split beams propagate in equal amplitude, whereas beam splitting is destructed for oblique incidence above a critical incidence angle. [ABSTRACT FROM AUTHOR]

We propose an experimental scheme to observe prethermalization and a dynamic phase transition in a one-dimensional XY spin chain with long-range interactions and inhomogeneous lattice spacing, which can be readily implemented with a recently developed trapped-ion quantum simulator. Local physical observables are found to relax to prethermal values at an intermediate timescale, followed by complete relaxation to thermal values at much longer time. The physical origin of prethermalization is shown to result from a non-trivial structure in the lower half of the energy spectrum. The dynamic behavior of the system is shown to cross different phases when the interaction range is continuously tuned, indicating the existence of a dynamic phase transition. [ABSTRACT FROM AUTHOR]

Pyramids and nanoholes are integrated together to form a micro–nano-texture on silicon surface in order to suppress reflection for silicon solar cell application. The nanoholes are formed by inductively coupled plasma (ICP) dry etching employing a nanoporous aluminum (Al) mask which is fabricated by caesium chloride (CsCl) nanoislands lift-off technique. Reflection of less than 4% can be reached by pyramid–nanohole texture, which is much lower than that from pure pyramids or nanoholes texture. Higher short circuit current density (Jsc) and photovoltaic conversion efficiency (PCE) are obtained for the solar cell with pyramid–nanohole texture due to its better antireflection. The average diameter and depth of the nanoholes affect the solar cell properties. The smaller and deeper nanoholes can suppress reflection a lot, but meanwhile, the formation of them means more crystal lattice defects generated from ICP etching. An optimized diameter of 800 nm and depth of 1μm for the nanoholes are obtained in our experiments to get the best photovoltaic performance that is a PCE of 14.89% with a Jsc of 38.25mAcm−2 and an open circuit voltage (Voc) of 544.8mV. [ABSTRACT FROM AUTHOR]

Traps, such as dislocation cores, foreign atoms, surfaces of nano-precipitates, etc, can significantly influence the kinetics of diffusion of interstitial atoms in a crystal lattice. Trapping is reflected in the chemical diffusion coefficient, whose value can be up to several orders of magnitude lower than the corresponding diffusion coefficient in a trap-free system. If we consider trapping only at dilute foreign atoms, we may assume only one sort of traps in the system, the depth of which is characterized by ΔE (trapping enthalpy) given by the decrease in energy due to trapping of one mole of interstitials. In this paper, a rigorous thermodynamically based concept is offered to extract the value of trapping enthalpy ΔE from chemical potentials of interstitial atoms which are, for instance, available in the form of CALPHAD-type thermodynamic databases. Exemplarily, the values of ΔE for C-trapping at Cr impurities are evaluated. For comparison, trapping enthalpies of C at various typical alloying elements in steel are also extracted and compared with literature values. The chemical diffusion coefficient of C in an Fe-Cr-C system at 500°C is calculated for different mole fractions of C and Cr atoms. The influence of traps on diffusion becomes evident from this analysis. [ABSTRACT FROM AUTHOR]

Traceable and accurate reference dimensional metrology of nano-structures by scanning transmission electron microscopy (STEM) is introduced in the paper. Two methods, one based on the crystal lattice constant and the other based on the pitch of a feature pair, were applied to calibrate the TEM magnification. The threshold value, which was defined as the half-intensity of boundary materials, is suggested to extract the boundary position of features from the TEM image. Experimental investigations have demonstrated the high potential of the proposed methods. For instance, the standard deviation from ten repeated measurements of a line structure with a nominal 100 nm critical dimension (CD) reaches 1a = 0.023 nm, about 0.02%. By intentionally introduced defocus and larger sample alignment errors, the investigation shows that these influences may reach 0.20 and 1.3 nm, respectively, indicating the importance of high-quality TEM measurements. Finally, a strategy for disseminating the destructive TEM results is introduced. Using this strategy, the CD of a reference material has been accurately determined. Its agreement over five independent TEM measurements is below 1.2 nm. [ABSTRACT FROM AUTHOR]

The spin-1 Blume-Capel model with transverse W and longitudinal external magnetic fields h, in addition to a longitudinal random crystal field D, is studied in the mean-field approximation. It is assumed that the crystal field is either turned on with probability p or turned off with probability 1- p on the sites of a square lattice. Phase diagrams are then calculated on the reduced temperature crystal field planes for given values of γ = Ω/J and p at zero h. Thus, the effect of changing γ and p are illustrated on the phase diagrams in great detail and interesting results are observed. [ABSTRACT FROM AUTHOR]

We investigate the stability properties of optical solitons in a chirped PT-symmetric lattice whose frequency changes in the transverse direction. Linear-stability analysis together with the direct propagation simulations demonstrates that the chirped lattice can improve the stability of optical solitons dramatically. The instability of fundamental solitons can be completely suppressed if the chirp rate exceeds a critical value. A broad stability area of dipole solitons appears if the lattice is appropriately chirped. Thus, we propose an effective way to suppress the instability of solitons in PT-symmetric potentials. [ABSTRACT FROM AUTHOR]

We study the thermal conduction behaviors of one-dimensional lattice models with asymmetric harmonic interparticle interactions. Normal thermal conductivity that is independent of system size is observed when the lattice chains are long enough. Because only the harmonic interactions are involved, the result confirms, without ambiguity, that asymmetry plays a key role in normal thermal conduction in one-dimensional momentum conserving lattices. Both equilibrium and nonequilibrium simulations are performed to support the conclusion. [ABSTRACT FROM AUTHOR]

The article presents a study conducted to visualize a Maze-Like Reconstruction of Graphene on a Copper Surface at the Atomic Scale using a scanning tunneling microscope (STM). It mentions that the reconstruction pattern is a three-for-six triangular lattice and an orthogonal lattice, separately visualized with functionalized STM tips. It suggests a new method to effectively induce partial hybridization in a single-layer graphene.

Using the first principle method, we investigate the influence of Sr/Ti ratio on the atomic structure and dislocation behavior of Srn+1TiO3n+1 (Ruddlesden-Popper phase) and SrnTin+1O3n+2 (Magnéli phase). A linear lattice expansion versus the Sr/Ti ratio exhibits in the Ruddlesden-Popper and Magnéli phases. The Ruddlesden-Popper phase has lower formation energy and superior structural stability than the Magnéli phase. The two phases show different dislocation behaviors and it is found that a possibly preferred slip system (110) {110} emerges in the two phases, and the dislocations are more likely to dissociate into partial dislocations in Magnéli phases. [ABSTRACT FROM AUTHOR]

Theoretical studies of the cubic perovskite CaFeO3 are performed using the full potential linearized augmented plane-wave method with GGA+U. The calculated structural parameters are consistent with the experimental results. The tolerance factor reveals the cubic phase of the compound. The spin polarized electronic band structures and densities of states as well as the integer value of the magnetic moment of the unit cell (4µB) demonstrate that CaFeO3 is half metal. Ferromagnetism in CaFeO3 is due to Fe+4-O²-Fe+4 superexchange interaction. The robust properties of the compound show that with their compression up to a certain critical lattice constant, known as the robust transition lattice constant, an abrupt change in the electronic and magnetic properties occurs; the compounds lose their integer magnetic moment and become metallic. [ABSTRACT FROM AUTHOR]

Using the first principle method, we investigate the influence of Sr/Ti ratio on the atomic structure and dislocation behavior of Srn+1TiO3n+1 (Ruddlesden-Popper phase) and SrnTin+1O3n+2 (Magnéli phase). A linear lattice expansion versus the Sr/Ti ratio exhibits in the Ruddlesden-Popper and Magnéli phases. The Ruddlesden-Popper phase has lower formation energy and superior structural stability than the Magnéli phase. The two phases show different dislocation behaviors and it is found that a possibly preferred slip system (110) {110} emerges in the two phases, and the dislocations are more likely to dissociate into partial dislocations in Magnéli phases. [ABSTRACT FROM AUTHOR]

Theoretical studies of the cubic perovskite CaFeO3 are performed using the full potential linearized augmented plane-wave method with GGA+U. The calculated structural parameters are consistent with the experimental results. The tolerance factor reveals the cubic phase of the compound. The spin polarized electronic band structures and densities of states as well as the integer value of the magnetic moment of the unit cell (4µB) demonstrate that CaFeO3 is half metal. Ferromagnetism in CaFeO3 is due to Fe+4-O²-Fe+4 superexchange interaction. The robust properties of the compound show that with their compression up to a certain critical lattice constant, known as the robust transition lattice constant, an abrupt change in the electronic and magnetic properties occurs; the compounds lose their integer magnetic moment and become metallic. [ABSTRACT FROM AUTHOR]

The role of several sorts of traps for one diffusing interstitial component is investigated. The site fraction of this component in each trap is calculated due to the local thermodynamic equilibrium condition with its site fraction in the lattice. Combining Fick's first law for diffusive fluxes of individual site fractions with the equilibrium condition and the mass balance allows deriving an extended nonlinear diffusion equation. If the molar volumes of the trap positions are constant with respect to time, then a generalized chemical diffusion coefficient can be derived, which allows performing the diffusion study in terms of the total concentration of the interstitial component. As an alternative way, the total diffusion flux can also be treated as the sum of diffusion fluxes of individual fractions combined with local redistribution of individual fractions based on the thermodynamic local equilibrium condition. Both concepts are presented in simulations for the diffusion of hydrogen in the system with traps as immobile dislocations, substitutional impurities and interfaces of incoherent carbide nanoprecipitates. Both concepts provide equivalent results and exhibit an asymmetric behaviour with respect to a charging/discharging process. [ABSTRACT FROM AUTHOR]

(Al100-xCrx)N thin-film materials libraries (x = 31-79 at%) were fabricated on micro-machined cantilever arrays, in order to simultaneously investigate the evolution of stresses during film growth as well as during thermal processing by analysing the changes in cantilever curvature. The issue of the dependence of stress in the growing films on composition, at comparable film thicknesses, was investigated. Among the various experimental parameters studied, it was found that the applied substrate bias has the strongest influence on stress evolution and microstructure formation. The compositions of the films, as well as the applied substrate bias, have a pronounced effect on the lattice parameter and the coherence length. For example, applying a substrate bias in general leads to compressive residual stress, increases the lattice parameter and decreases the coherence length. Moreover, bias can change the film texture from [1 1 1] orientation to [2 0 0]. Further detailed analysis using x-ray diffraction and transmission electron microscopy clearly revealed the presence of a [1 1 1] highly textured face centred cubic (B1 type) Al-Cr-N phase in the as-deposited state as well as the coexistence of the hexagonal [1 1 0] textured Cr2N phase, which forms in the Cr-rich region. These results show that the combinatorial approach provides insight into how stresses and compositions are related to phases and microstructures of different Al-Cr-N compositions fabricated in the form of materials libraries. [ABSTRACT FROM AUTHOR]

The impact of oxygen additions on phase stability and elastic properties of titanium aluminum nitride is studied by ab initio calculations. Fcc-Ti0.5Al0.5N and fcc-Ti0.5Al0.5O show a negative energy of mixing with an interaction parameter ΩTiAlNO of -37.6 kJmol-1. The lattice parameter of Ti0.5Al0.5N1-xOx increases with increasing x while the bulk modulus decreases by 35%. The reason is the metallic bonding character which increases at the expense of the covalent character with increasing oxygen content. It is shown that the incorporation of oxygen in Ti0.5Al0.5N1-xOx on interstitial sites is energetically favourable. This can be understood based on the compensation of metallic bonding as the population of metal-oxygen bonds that are similar to a-Al2O3 and rutile-TiO2 is increased. Based on the oxygen incorporation-induced stability increase of Ti0.5Al0.5N1-xOx+y, a new design concept for transition metal oxynitride based hard coatings is developed. [ABSTRACT FROM AUTHOR]

The processes of hole localization in double-doped PbWO4 : Mo,La and PbWO4 : Mo,Y single crystals are studied by continuous wave and pulse electron spin resonance (ESR) and thermally stimulated luminescence (TSL) methods. We show that the holes created by UV irradiation are preferably trapped at the oxygen lattice ions in the vicinity of perturbing defects such as lead vacancies, impurity ions (La, Y, Mo), and other lattice imperfections forming mainly two types of O- centres. The hyperfine structures of their spectra suggest that in the first centre (OI), a hole is trapped near the YPb-VPb and LaPb-VPb pairs (VPb denotes the lead ion vacancy). In the second centre (OII), a hole is probably localized within a [WO4-MoO4]3- complex defect. The recombination of thermally released holes with the electrons stored at different traps, including the oxygen-vacancy related Pb+-WO3 and (MoO4)3- centres, is systematically studied by TSL. The thermal stability parameters are evaluated by ESR and TSL techniques for different O--type defects. [ABSTRACT FROM AUTHOR]

One-dimensional Mn-ZnSe nanostructures with high crystallite quality were synthesized by the CVD method. Transmission electron microscopy was used to study the defect state, crystal lattice and growth direction of as-prepared nanostructures. Raman spectra under varied excitation wavelengths confirmed the dopant modes of Mn(II) and the inhomogeneity. The micro-photoluminescence (PL) spectra of individual nanostructures under CW laser excitation with different powers showed the dominant trapped state emission with periodic multi-peaks. The selected peak mapping indicated that there were many integrated Fabry-Perot cavities and whispering gallery mode cavities within the nanowires/nanoneedles and nanobelts, respectively, which can be accounted for by inhomogeneous optical phases in the Mn-ZnSe nanostructure. The phase may be introduced by both Mn doping and structural relaxation. The micro-PL spectra under nanosecond pulse laser excitation produce low threshold lasing lines near the band edge of Mn-ZnSe nanostructures. The lasing occurs due to the dominant interaction between bound excitons at high density, evidenced by its appearance close to the LO phonon replica. The belts show much stronger lasing emission due to larger 2D coherent space than the wires due to the inhomogeneity induced by the doping process. The different optical behavior with changing excitation pulses may find applications in future photonic devices of II-VI nanostructures. [ABSTRACT FROM AUTHOR]