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Nanostructured topological insulators (TIs) have the potential to impact a wide array of condensed matter physics topics, ranging from Majorana physics to spintronics. However, the most common TI materials, the B i 2 S e 3 family, are easily damaged during nanofabrication of devices. In this paper, we show that electron beam lithography performed with a 30 or 50 kV accelerating voltage—common for nanopatterning in academic facilities—damages both nonmagnetic TIs and their magnetically doped counterparts at unacceptable levels. We additionally demonstrate that electron beam lithography with a 10 kV accelerating voltage produces minimal damage detectable through low-temperature electronic transport. Although reduced accelerating voltages present challenges in creating fine features, we show that with careful choice of processing parameters, particularly the resist, 100 nm features are reliably achievable. [ABSTRACT FROM AUTHOR]

Topological valley states, emerging as an exciting field in condensed matter physics, are attracting attention because of their potential as a new type of information carrier with orbital angular momentum. In this paper, we exhibit that the acoustic valley states can achieve trapping of microparticles due to the acoustic radiation force induced by the acoustic vortex. In addition, we can achieve the separation of microparticles based on different acoustic contrast factors. Our study shows a demonstration of acoustic valley states in the field of particle contactless manipulation. Potential applications can be predicted by the exotic interaction of acoustic vortices with microparticles, such as cell separation, drug delivery, and other biomedical applications. [ABSTRACT FROM AUTHOR]

Dynamic effective negative parameters are principal to the representation of the physical properties of metamaterials. In this paper, a bi-layer plate-type unit was proposed with both a negative mass density and a negative bulk modulus; moreover, through analysis of these bi-layer structures, some important problems about acoustic metamaterials were studied. First, dynamic effective mass densities and the bulk modulus of the bi-layer plate-type acoustic structure were clarified through both the direct and the retrieval methods, and, in addition, the intrinsic relationship between the sound transmission (absorption) characteristics and the effective parameters was analyzed. Furthermore, the properties of dynamic effective parameters for an asymmetric bi-layer acoustic structure were further considered through an analysis of experimental data, and the modified effective parameters were then obtained through consideration of the Willis coupling in the asymmetric passive system. In addition, by taking both the clamped and the periodic boundary conditions into consideration in the bi-layer plate-type acoustic system, new perspectives were presented for study on the effective parameters and sound insulation properties in the range below the cut-off frequency. The special acoustic properties established by these effective parameters could enrich our knowledge and provide guidance for the design and installation of acoustic metamaterial structures in future sound engineering practice. [ABSTRACT FROM AUTHOR]

Thermite multilayered films have the potential to be used as local high intensity heat sources for a variety of applications. Improving the ability of researchers to more rapidly develop Micro Electro Mechanical Systems devices based on thermite multilayer films requires predictive modeling in which an understanding of the relationship between the properties (ignition and flame propagation), the multilayer structure and composition (bilayer thicknesses, ratio of reactants, and nature of interfaces), and aspects related to integration (substrate conductivity and ignition apparatus) is achieved. Assembling all these aspects, this work proposes an original 2D diffusion-reaction modeling framework to predict the ignition threshold and reaction dynamics of Al/CuO multilayered thin films. This model takes into consideration that CuO first decomposes into Cu2O, and then, released oxygen diffuses across the Cu2O and Al2 O3 layers before reacting with pure Al to form Al2O3. This model is experimentally validated from ignition and flame velocity data acquired on Al/CuO multilayers deposited on a Kapton layer. This paper discusses, for the first time, the importance of determining the ceiling temperature above which the multilayers disintegrate, possibly before their complete combustion, thus severely impacting the reaction front velocity and energy release. This work provides a set of heating surface areas to obtain the best ignition conditions, i.e., with minimal ignition power, as a function of the substrate type. [ABSTRACT FROM AUTHOR]

Electrical tunable meander line inductor using coplanar waveguide structures with patterned permalloy (Py) thin film has been designed and implemented in this paper. High resistivity Si substrate is used to reduce the dielectric loss from the substrate. Inductor is implemented with a 60 nm thick Py deposited and patterned on top of the gold meander line, and Py film is patterned with dimension of 440 nm×10 μm to create the shape anisotropy field, which in turn increases the FMR frequency. Compared to a regular meanderline inductor without the application of sub-micrometer patterned Py thin film, the inductance density has been increased to 20% for the implemented inductor with patterned Py. Measured FMR frequency of the patterned Py is 4.51GHz without the application of any external magnetic field. This has enabled the inductor application in the practical circuit boards, where the large external magnet is unavailable. Inductance tunability of the implemented inductor is demonstrated by applying a DC current. Applied DC current creates a magnetic field along the hard axis of the patterned Py thin film, which changes the magnetic moment of the thin film and thus, decreases the inductance of the line. Measured results show that the inductance density of the inductor can be varied 5% by applying 300mA DC current, larger inductance tunability is achievable by increasing the thickness of Py film. [ABSTRACT FROM AUTHOR]

Based on Bloch's theorem in condensed matter physics, the band folding effect occurs when using a supercell model and gives rise to complicated band structures.[2] As illustrated in Fig. 1, when the primitive cell extends three times in a specific direction and forms a supercell model, the corresponding reciprocal direction in the Brillouin zone shrinks to 1/3 and the original primitive cell bands in the first Brillouin zone will be folded into the compressed supercell first Brillouin zone. Illustration of band folding in the supercell calculations: (a) a schematic plot of the band structure of a 1 × 1 primitive cell with one artificial band, (b) a plot obtained from a 3 × 1 supercell. [Extracted from the article]

Dynamical bubble-like solitons have been recently investigated in nanocontact-based spin-torque oscillators with a perpendicular free layer. Those magnetic configurations can be excited also in different geometries as long as they consist of perpendicular materials. Thus, in this paper, a systematic study of the influence of both external field and high current on that kind of dynamics is performed for a spin-valve point-contact geometry where both free and fixed layers present strong perpendicular anisotropy. The usage of the topological density tool highlights the excitation of complex bubble/antibubble configurations. In particular, at high currents, a deformation of the soliton and its simultaneous shift from the contact area are observed and can be ascribable to the Oersted field. Results provide further detailed information on the excitation of solitons in perpendicular materials for application in spintronics, magnonics, and domain wall logic. [ABSTRACT FROM AUTHOR]

Topological insulators (TIs) are a new type of quantum state materials. Due to their novel physical properties, such as topological protection defect immunity to edge states, TIs have become the focus of attention in condensed matter and material physics. At present, the research on TIs has been gradually extended to classical wave fields such as electromagnetic waves, acoustic waves, and elastic waves, and has aroused extensive research interest. However, for elastic wave systems, most TIs cannot actively control topological interface states due to the limitation of fixed structure, which hinders their application in practical situations. Here, we propose a kind of tunable three-dimensional (3D) valley Hall insulator composed of magnetoelastic materials. First, the topological phase transition can be induced by the asymmetric geometry. Then, the working frequency of topological interface states can be changed by using static magnetic fields. Second, topological phase transformation can also be induced by independently tuning the distribution of static magnetic fields or pre-stress in each unit. Based on this, reconfigurable propagation routes of interface states with arbitrary shapes can be realized by tuning the distribution of static magnetic fields or pre-stress in each unit. Finally, considering the sandwich structure composed of different magnetic fields or pre-stress distribution modes, the waveguide with tunable width and route is designed by coupling edge and bulk states, which is convenient for application and better energy transfer. This study provides a reference for the design of a tunable intelligent elastic waveguide. [ABSTRACT FROM AUTHOR]

In recent years, magnon and spin texture are attracting great interest in condensed matter physics and magnetism. Magnonics is aiming to use magnon as information carriers to realize functions for storage, transmission, and processing. Magnetic skyrmion is representative spin texture due to its topologically nontrivial properties. Since skyrmions are topologically protected, their transformation to other spin configurations requires overcoming additional topological energy barriers. Therefore, skyrmions are more stable than other trivial spin textures. In addition, the characters of nanoscale size, quasiparticle properties, and various excitation modes make them a potential candidate for spintronic application. Magnon and skyrmion, as two fundamental excitations, can coexist in magnetic systems and interplay with each other through direct exchange interactions. In this review, we provide an overview of recent theoretical and experimental studies on magnon–skyrmion interactions. We mainly focus on three kinds of magnon–skyrmion interactions: (i) magnon scattering by skyrmion, (ii) skyrmion motion driven by magnon, and (iii) coupling between magnon and skyrmion modes. The first two kinds of interactions could be clearly explained by the wave-particle interaction model on the classical level. Alternatively, the last kind of interaction could be understood by the coupled harmonic oscillator model on the quantum level, which indicates fast energy exchange and hybrid magnon states. The exploration focused on quantum phenomena of magnon has led to the emerging field of quantum magnonics and promoted applications of magnon in quantum information storage and processing. In the end, we give a perspective on the exploration of magnon–skyrmion interaction in quantum magnonics. [ABSTRACT FROM AUTHOR]

A dense layer of nitrogen-vacancy (NV) centers near the surface of a diamond can be interrogated in a widefield optical microscope to produce spatially resolved maps of local quantities such as magnetic field, electric field, and lattice strain, providing potentially valuable information about a sample or device placed in proximity. Since the first experimental realization of such a widefield NV microscope in 2010, the technology has seen rapid development and demonstration of applications in various areas across condensed matter physics, geoscience, and biology. This Perspective analyzes the strengths and shortcomings of widefield NV microscopy in order to identify the most promising applications and guide future development. We begin with a brief review of quantum sensing with ensembles of NV centers and the experimental implementation of widefield NV microscopy. We then compare this technology to alternative microscopy techniques commonly employed to probe magnetic materials and charge flow distributions. Current limitations in spatial resolution, measurement accuracy, magnetic sensitivity, operating conditions, and ease of use are discussed. Finally, we identify the technological advances that solve the aforementioned limitations and argue that their implementation would result in a practical, accessible, high-throughput widefield NV microscope. [ABSTRACT FROM AUTHOR]

Phononic crystals (PnCs) control the transport of sound and heat similar to the control of electric currents by semiconductors and metals or light by photonic crystals. Basic and applied research on PnCs spans the entire phononic spectrum, from seismic waves and audible sound to gigahertz phononics for telecommunications and thermal transport in the terahertz range. Here, we review the progress and applications of PnCs across their spectrum, and we offer some perspectives in view of the growing demand for vibrational isolation, fast signal processing, and miniaturization of devices. Current research on macroscopic low-frequency PnCs offers complete solutions from design and optimization to construction and characterization, e.g., sound insulators, seismic shields, and ultrasonic imaging devices. Hypersonic PnCs made of novel low-dimensional nanomaterials can be used to develop smaller microelectromechanical systems and faster wireless networks. The operational frequency, compactness, and efficiency of wireless communications can also increase using principles of optomechanics. In the terahertz range, PnCs can be used for efficient heat removal from electronic devices and for novel thermoelectrics. Finally, the introduction of topology in condensed matter physics has provided revolutionary designs of macroscopic sub-gigahertz PnCs, which can now be transferred to the gigahertz range with advanced nanofabrication techniques and momentum-resolved spectroscopy of acoustic phonons. [ABSTRACT FROM AUTHOR]

Majorana zero mode, the bound state of Majorana fermion in a condensed matter system, plays a critical role in fault-tolerant topological quantum computation. It can be realized in the vortex of a two-dimensional topological superconductor as a zero-energy excitation. A topological superconductor can be constructed by coupling superconductivity to the topological surface states by the proximity effect. In this review article, we discuss the fabrication of such artificially engineered topological superconductors by molecular beam epitaxy. The topological phase and superconductivity are exhibited in Bi2Se3/NbSe2 and Bi2Te3/NbSe2 heterostructures simultaneously. Several characteristic features of Majorana zero mode have been revealed in the vortex by a low-temperature scanning tunneling microscope and corroborated by theoretical results. The discovery of Majorana zero mode may pave the way for further applications in topological quantum computing. [ABSTRACT FROM AUTHOR]

Spin waves, whose quanta are called magnons, are propagating excitations of magnetic materials. Magnonics is an emerging field of modern condensed matter physics that aims to study and utilize the properties and behaviors of magnons. The topological magnon band is an interesting topic of magnonics, and nontrivial topology is usually accompanied with many exotic phenomena such as emergence of robust edge states and the magnon Hall effect. In this Tutorial, using a honeycomb ferromagnet as a prototypical platform, we pedagogically demonstrate how to compute the magnon spectra and the topological invariants characterizing the topology of the magnon bands. We also briefly discuss some numerical techniques. [ABSTRACT FROM AUTHOR]

The study of homonuclear diatomic molecules under high pressure and high temperature is a fundamental problem of condensed matter physics. In this research work, a cryogenic target (CT) was built to liquefy the gas and execute shock compression. The characteristics of the CT and the diagnostic system are explained in detail. We performed a shock compression of liquid nitrogen by using a two-stage light-gas gun at pressures up to 93 GPa (0.93 Mbar). Impactor velocities were measured with the magnetic velocimetry system, with a precision of 0.2%. The optical waveforms were recorded with the Doppler pin system, then further fast Fourier transform obtained velocity profiles in the sample. The measured velocity profiles were used to identify optical reflectance and obtain first-shock velocities, independent of the sample thickness above dissociative pressure (>30 GPa). The measured shock velocities had an uncertainty of less than 1%. First particle velocities were calculated by impedance matching, and the second velocities were directly calculated from the velocity profiles in an LiF anvil. The experimental shock Hugoniot results were observed to be consistent with those of the previous work. However, the principal Hugoniot softened above 27 GPa, and the uncertainties in the first and second-shock volumes were less than 0.7% and 3%, respectively. [ABSTRACT FROM AUTHOR]

We report experimental results which show that the order parameter β, which determines the long-range (spin) ordering in magnetic thin films [Mα(1-T/TC)β], changes abruptly due to a crossover in dimensionality at different thicknesses in Ni(100), Ni(110), and Ni(111) films. We argue that the different critical thicknesses arise from finite-size quantization energies of the (spin) excitations, which are dependent on the magnitudes of associated wave vectors spanning the different crystallographic directions of the fcc Fermi surface. Experimental data on Ni alloys support this view. [ABSTRACT FROM AUTHOR]

Oxygen ion conduction and relaxation mechanisms in bismuth substituted La2Mo2O9 have been reported in this paper. The phase transition observed in La2Mo2O9 is suppressed in bismuth substituted samples, and the cubic β form is stabilized at room temperature. A transition of the dc anionic conductivity from low temperature Arrhenius type to high temperature Arrhenius type has been observed in La2Mo2O9. However, for bismuth doped samples the dc anionic conductivity shows a transition from Arrhenius behavior at low temperatures to Vogel-Tamman-Fulcher in the high temperature regime. The frequency dependence of the ac conductivity shows a power law behavior. The ac conductivity remains constant in low frequency region but shows dispersion at the crossover frequency. The crossover frequency shifted towards higher value with the increase of temperature. The dimensionality of the conduction space does not change with bismuth doping. The scaling behavior of the conductivity spectra for different temperatures and compositions indicates that dynamics of oxygen ions is independent of temperatures and compositions. [ABSTRACT FROM AUTHOR]

Bipolar resistive switching has been reported in ITO/V2O5/ITO structures. Synthesized from the sol-gel process, the nanostructured V2O5·nH2O xerogel thin film endures significant structural transition during the post-annealing step. The impact of the structural transition of the V2O5 film on the resistive switching properties is studied in this work. The switching voltage decreases from 6.5 V to 3.0 V when the annealing temperature increases from 220 °C to 280 °C and then increases up to 5.0 V at 350 °C. Above the annealing temperature of 350 °C, the reversible switching characteristics disappear. The thermogravimetric measurement shows that intercalated H2O molecules fully evaporate above 350 °C. X-ray diffraction shows that the xerogel phase gradually vanishes as the annealing temperature increases, and only α-V2O5 and β-V2O5 exist at high annealing temperatures. Ab initio simulations are performed to evaluate the formation energies of the oxygen vacancy in xerogel, α-V2O5, and β-V2O5 phases. The results are in good agreement with the experiments: the formation energy of the oxygen vacancy is significantly lower in xerogel than in α-V2O5 and β-V2O5, enabling the occurrence of reversible switching when the xerogel phase exists in the sandwich structure. [ABSTRACT FROM AUTHOR]

The effect of the surface roughness on the electrical resistivity of metallic thin films is described by electron reflection at discrete step edges. A Landauer formalism for incoherent scattering leads to a parameter-free expression for the resistivity contribution from surface mound-valley undulations that is additive to the resistivity associated with bulk and surface scattering. In the classical limit where the electron reflection probability matches the ratio of the step height h divided by the film thickness d, the additional resistivity Δρ=√3/2/(g0d) x ϖ/..., where g0 is the specific ballistic conductance and ϖ/... is the ratio of the root-mean-square surface roughness divided by the lateral correlation length of the surface morphology. First-principles non-equilibrium Green's function density functional theory transport simulations on 1-nm-thick Cu(001) layers validate the model, confirming that the electron reflection probability is equal to h/d and that the incoherent formalism matches the coherent scattering simulations for surface step separations ≥2 nm. Experimental confirmation is done using 4.5-52nm thick epitaxial W(001) layers, where ϖ=0.25-1.07nm and ...=10.5-21.9 nm are varied by in situ annealing. Electron transport measurements at 77 and 295K indicate a linear relationship between Δρ and ϖ/(...d), confirming the model predictions. The model suggests a stronger resistivity size effect than predictions of existing models by Fuchs [Math. Proc. Cambridge Philos. Soc. 34, 100 (1938)], Sondheimer [Adv. Phys. 1, 1 (1952)], Rossnagel and Kuan [J. Vac. Sci. Technol., B 22, 240 (2004)], or Namba [Jpn. J. Appl. Phys., Part 1 9, 1326 (1970)]. It provides a quantitative explanation for the empirical parameters in these models and may explain the recently reported deviations of experimental resistivity values from these models. [ABSTRACT FROM AUTHOR]

We review the conventional measuring standard for dc Hall measurements in van der Pauw configuration with particular focus on the challenges arising from a small Hall signal compared to sizable offset voltages, which is a typical scenario for many material systems, particularly low-mobility thin films. We show that the conventional approach of using a simple field-reversal technique is often unsuited to obtain reliable results, and present an improved correction scheme to extend the accessible measurement range to mobility values well below 1 cm2/(V s). We discuss procedures to limit the impact of temperature fluctuations and long stabilization times for highly resistive materials. We further address potential sources of error due to the presence of grain boundaries in polycrystalline specimen and due to multi-carrier conduction, both of which might yield low apparent Hall mobilities significantly underestimating the actual mobility. [ABSTRACT FROM AUTHOR]

We report on the structural, magnetic, optical, and electrical properties of iron titanate thin films prepared using a spin-coating technique having nominal compositions of FeTiO3 and Fe1.4Ti0.6O3. X-ray diffraction measurements show clear evidence for the presence of both ilmenite and pseudobrookite crystal structures, which is confirmed using Raman spectroscopy. X-ray photoemission spectroscopy studies indicate that Fe is present mainly in the 2+ valence state, with some Fe3+ present on the more heavily oxidized surface of the films. The as-prepared samples exhibit weak ferromagnetism at room temperature. While the valence state of Fe is not significantly affected by vacuum annealing, the saturation magnetization is increased dramatically, reaching nearly 220 emu mole−1 for the Fe-rich film. The optical band gap was found to be roughly 2.0 eV for all samples, with negligible changes on vacuum annealing. [ABSTRACT FROM AUTHOR]

The phase transition of iron under shock compression has attracted much attention in recent decades because of its importance in fields such as condensed matter physics, geophysics, and metallurgy. At room temperature, the transition of iron from the α-phase (bcc) to the ε-phase (hpc) occurs at a stress of 13 GPa. At high temperature, a triple point followed by transformation to the γ-phase (fcc) is expected. However, the details of the high-temperature phase transitions of iron are still under debate. Here, we investigate the phase-transition behavior of polycrystalline iron under compression from room temperature to 820 K. The results show that the shock-induced phase transition is determined unequivocally from the measured three-wave-structure profiles, which clearly consist of an elastic wave, a plastic wave, and a phase-transition wave. The phase transition is temperature-dependent, with an average rate Δσtr/ΔT of -6.91 MPa/K below 700 K and -34.7 MPa/K at higher temperatures. The shock α-ε and α-γ phase boundaries intersect at 10.6 ± 0.53 GPa and 763 K, which agrees with the α-ε-γ triple point from early shock wave experiments and recent laser-heated diamond-anvil cell resistivity and in situ X-ray diffraction data but disagrees with the shock pressure-temperature phase diagram reported in 2009 by Zaretsky. [ABSTRACT FROM AUTHOR]

We have investigated the thickness-dependent transport properties of La1/3Sr2/3FeO3 thin films grown on SrTiO3 (001) and (111) substrates. At a thickness of ∼40nm, both films show a clear transition in resistivity associated with the characteristic charge disproportionation at approximately 190 K. The transition temperature of the charge disproportionation is nearly unchanged with decreasing film thickness down to a certain thickness of ∼13 nm for both orientations, while the change in resistivity gradually decreases. Below this thickness, the transition becomes unclear, strongly suggesting the suppression of the charge disproportionation at the critical thickness of ∼13nm. Furthermore, there is no significant difference in the thickness dependence of La1/3Sr2/3FeO3 thin films between the (001) and (111) orientations. The negligible crystallographic-orientation dependence may reflect the isotropic nature for the domain of charge disproportionation states in La1/3Sr2/3FeO3. [ABSTRACT FROM AUTHOR]

We present the modulation of anisotropy field, coercivity, and domain wall (DW) velocity in CoFeB/MgO thin films with perpendicular anisotropy by applying voltages across an ionic liquid gate. Domain wall velocities in the creep regime can be modulated by a factor of 4.2, and the anisotropy field of the device can be modulated by 40 mT when going from +0.8V to -0.8V. The applied E-fields are seen to significantly influence DWs' pinning, depinning, and nucleation processes. In addition, we report on the evolution of the magnetic properties of the liquid/solid device as a function of time going from the pristine CoFeB/MgO film through device fabrication and operation up to one month. These results show that the solid/liquid device structure based on CoFeB/MgO thin films can be an efficient way to control magnetic properties with voltages below 1V. [ABSTRACT FROM AUTHOR]

Accurate optical methods are required to determine the energy bandgap of amorphous semiconductors and elucidate the role of quantum confinement in nanometer-scale, ultra-thin absorbing layers. Here, we provide a critical comparison between well-established methods that are generally employed to determine the optical bandgap of thin-film amorphous semiconductors, starting from normal-incidence reflectance and transmittance measurements. First, we demonstrate that a more accurate estimate of the optical bandgap can be achieved by using a multiple-reflection interference model. We show that this model generates more reliable results compared to the widely accepted single-pass absorption method. Second, we compare two most representative methods (Tauc and Cody plots) that are extensively used to determine the optical bandgap of thin-film amorphous semiconductors starting from the extracted absorption coefficient. Analysis of the experimental absorption data acquired for ultra-thin amorphous germanium (a-Ge) layers demonstrates that the Cody model is able to provide a less ambiguous energy bandgap value. Finally, we apply our proposed method to experimentally determine the optical bandgap of a-Ge/SiO2 superlattices with single and multiple a-Ge layers down to 2nm thickness. [ABSTRACT FROM AUTHOR]

Stress is inevitable during thin film growth. It is demonstrated here that the growth stress has a significant effect on the dielectric constant of high-k thin films. ZrO2 thin films were deposited on Ge by reactive direct current sputtering. Stress in these films was measured using in-situ curvature measurement tool. The growth stress was tuned from -2.8 to 0.1 GPa by controlling deposition rate. Dielectric permittivity of ZrO2 depends on temperature, phase, and stress. The correct combination of parameters—phase, texture, and stress—is shown to yield films with an equivalent oxide thickness of 8 Å. Growth stresses are shown to affect the dielectric constant both directly by affecting lattice parameter and indirectly through the effect on phase stability of ZrO2. [ABSTRACT FROM AUTHOR]

Mg doped (Pb0.35Sr0.65)TiO3 (PST) thin films were fabricated on indium tin oxide /glass substrates by the sol–gel technique. The formation of the PST phase and control of the magnesium doping on the microstructure, defect states, and dielectric properties of the thin film were investigated by means of XRD, SEM, AFM, XPS, and impedance analysis. Results showed that the oxygen vacancies and the associated Ti3+ ions formed as V••o∼Ti′Ti dipole pairs, and the dipole pairs were aligned opposite to the direction of the intrinsic dipole moments in the PST thin film. The amount of dipole pairs was strongly affected by the formed Mg″Ti in the thin film. The minimum amount of the dipole pairs appeared in the PST thin film with Mg doping content of 6% in molar ratio. The thin film with Mg doping content of 6% showed high permittivity due to low offset from V••o∼Ti′Ti dipole pairs and low dielectric loss due to low defect electrons generated in the thin film simultaneously. The formed Mg″Ti in the oxygen octahedral contributed lower response of the dipole moments to external electric field and resulted in lower tunability of the PST thin film with increasing Mg doping content. Controlled by the substitution of Mg2+ ions for Ti4+ ions and the induced V••O∼Ti′Ti dipole pairs, the optimal figure of merit was obtained in the PST thin film with Mg doping content of 6% with which the thin film possessed the smallest dielectric loss and still high tunability simultaneously. [ABSTRACT FROM AUTHOR]

We investigate the structural and electronic properties of VO2 thin films on c-plane sapphire substrates with three different surface morphologies to control the strain at the substrate-film interface. Only non-annealed substrates with no discernible surface features (terraces) provided a suitable template for VO2 film growth with a semiconductor-metal transition (SMT), which was much lower than the bulk transition temperature. In addition to strain, oxygen vacancy concentration also affects the properties of VO2, which can be controlled through deposition conditions. Oxygen plasma-assisted pulsed laser deposition allows favorable conditions for VO2 film growth with SMTs that can be easily tailored for device applications. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) is commonly used for investigations of Cu2ZnSnS(e)4 [CZTS(e)] and Cu(In,Ga)Se2 (CIGS) thin film solar cells. The influence of interference effects on these measurements is, however, largely overlooked in the community. Here, it is demonstrated that PL spectra of typical CZTS absorbers on Mo/glass substrates can be heavily distorted by interference effects. One reason for the pronounced interference in CZTS is the low reabsorption of the PL emission that typically occurs below the band gap. A similar situation occurs in band gap graded CIGS where the PL emission originates predominantly from the band gap minimum located at the notch region. Based on an optical model for interference effects of PL emitted from a thin film, several approaches to reduce the fringing are identified and tested experimentally. These approaches include the use of measured reflectance data, a calculated interference function, use of high angles of incidence during PL measurements as well as the measurement of polarized light near the Brewster angle. [ABSTRACT FROM AUTHOR]

Sub-monolayer iron atoms were deposited at room temperature on Ge (111)-c(2 × 8) substrates with and without Ag buffer layers. The behavior of Fe islands growth was investigated by using scanning tunneling microscope (STM) after different annealing temperatures. STM images show that iron atoms will cause defects and holes on substrates at room temperature. As the annealing temperature rises, iron atoms pull out germanium to form various kinds of alloyed islands. However, the silver layer can protect the Ag/Ge(111)-(√3×√3) reconstruction from forming defects. The phase diagram shows that ring, dot, and triangular defects were only found on Ge (111)-c(2 × 8) substrates. The kinds of islands found in Fe/Ge system are similar to Fe/Ag/Ge system. It indicates that Ge atoms were pulled out to form islands at high annealing temperatures whether there was a Ag layer or not. But a few differences in big pyramidal or strip islands show that the silver layer affects the development of islands by changing the surface symmetry and diffusion coefficient. The structure characters of various islands are also discussed. [ABSTRACT FROM AUTHOR]