Condensed Matter Physics Commons^™

Heterostructure Of 2d Materials: Hfs2/Hfo2/Si, Christopher J. Robledo

MSU Graduate Theses

Heterostructures have been utilized in electronic devices for over 50 years with the proposal for the first heterostructure transistor in 1957. With the scaling of devices, it is necessary to create new heterostructures that will comply with Moore’s Law, as well as make devices faster and consume less power. Novel 2D materials, such as hafnium disulfide, have shown promise as an active channel layer, while hafnium dioxide is already proven to be a replacement of silicon dioxide for the gate insulating layer. However, fabrication techniques for wide-scale integration of these heterostructures have not yet been achieved. Also, the dielectric properties …

Fabrication Of Magnetocaloric La(Fe,Si)13 Thick Films, N H. Dung, N B. Doan, P De Rango, L Ranno, Karl G. Sandeman, N M. Dempsey

Publications and Research

La(Fe,Si)₁₃–based compounds are considered to be very promising magnetocaloric materials for magnetic refrigeration applications. Many studies have focused on this material family but only in bulk form. In this paper we report on the fabrication of thick films of La(Fe,Si)₁₃, both with and without post-hydriding. These films exhibit magnetic and structural properties comparable to bulk materials. We also observe that the ferromagnetic phase transition has a negative thermal hysteresis, a phenomenon not previously found in this material but which may have its origins in the availability of a strain energy reservoir, as in the cases of …

Investigation Of Mnxni1-Xo Thin Films Using Pulsed Laser Deposition, Md Ashif Anwar

MSU Graduate Theses

The exchange bias (EB) effect, especially in nanomaterials, is highly promising for use in antiferromagnet-based spintronics applications. NiO is a well known antiferromagnetic material with a high Néel temperature (525K) and can exhibit ferromagnetism/ ferrimagnetism by adding other magnetic transition elements. Our previous work has shown that the antiferromagnetic characteristics of conventional NiO insulating nanostructured material can be altered to have substantial ferrimagnetic characteristics by doping NiO with Mn or Co. Pulsed laser deposition (PLD) was used to grow heterostructures comprised of a nanostructured thin NiO film deposited on the surface of a MgO (100) and Al₂O_{3 …}

Voltage Controlled Magnetism In Cr2o3 Based All-Thin-Film Systems, Junlei Wang, Will Echtenkamp, Ather Mahmood, Christian Binek

Christian Binek Publications

Voltage-control of exchange biases through active selection of distinct domain states of the magnetoelectric and antiferromagnetic pinning layer is demonstrated for Cr2O3/CoPd heterostructures. Progress and obstacles towards an isothermal switching of exchange bias are discussed. An alternative approach avoiding exchange bias for voltage-controlled memory exploits boundary magnetization at the surface of Cr2O3 as voltage-controlled state variable. We demonstrate readout and switching of boundary magnetization in ultra-thin Cr2O3/Pt Hall bar devices where reversal of boundary magnetization is achieved via magnetoelectric annealing with simultaneously applied ±0.5 V and 400 mT electric and magnetic fields.

Space-Charge Limited Conduction In Epitaxial Chromia Films Grown On Elemental And Oxide-Based Metallic Substrates, C.-P. Kwan, Mike Street, Ather Mahmood, Will Echtenkamp, M. Randle, K. He, J. Nathawat, N. Arabchigavkani, B. Barut, S. Yin, R. Dixit, Uttam Singisetti, Christian Binek, J. P. Bird

Christian Binek Publications

We study temperature dependent (200 – 400 K) dielectric current leakage in high-quality, epitaxial chromia films, synthesized on various conductive substrates (Pd, Pt and V2O3). We find that trap-assisted space-charge limited conduction is the dominant source of electrical leakage in the films, and that the density and distribution of charge traps within them is strongly dependent upon the choice of the underlying substrate. Pd-based chromia is found to exhibit leakage consistent with the presence of deep, discrete traps, a characteristic that is related to the known properties of twinning defects in the material. The Pt- and V2O3-based films, in contrast, …

Dielectric Properties Of Thin Cr2o3 Films Grown On Elemental And Oxide Metallic Substrates, Ather Mahmood, Mike Street, Will Echtenkamp, Chun Pui Kwan, Jonathan P. Bird, Christian Binek

Christian Binek Publications

In an attempt to optimize leakage characteristics of α-Cr₂O₃ thin films, its dielectric properties were investigated at local and macroscopic scale. The films were grown on Pd(111), Pt(111), and V₂O₃ (0001), supported on Al₂O₃ substrate. The local conductivity was measured by conductive atomic force microscopy mapping of Cr₂O₃ surfaces, which revealed the nature of defects that formed conducting paths with the bottom Pd or Pt layer. A strong correlation was found between these electrical defects and the grain boundaries revealed in the corresponding topographic scans. In comparison, …

Electronic And Optical Properties Of La-Doped Sr3Ir2O7 Epitaxial Thin Films, Maryam Souri, Jsaminka Terzic, J. M. Johnson, John G. Connell, John H. Gruenewald, J. Thompson, Joseph W. Brill, J. Hwang, Gang Cao, Sung S. Ambrose Seo

Physics and Astronomy Faculty Publications

We have investigated structural, transport, and optical properties of tensile strained (Sr_1−xLa_x)₃Ir₂O₇ (x = 0, 0.025, 0.05) epitaxial thin films. While high-T_c superconductivity is predicted theoretically in the system, we have observed that all of the samples remain insulating with finite optical gap energies and Mott variable-range hopping characteristics in transport. Cross-sectional scanning transmission electron microscopy indicates that structural defects such as stacking faults appear in this system. The insulating behavior of the La-doped Sr₃Ir₂O₇ thin films is presumably due to disorder-induced …

Optical Signatures Of Spin-Orbit Exciton In Bandwidth-Controlled Sr2Iro4 Epitaxial Films Via High-Concentration Ca And Ba Doping, Maryam Souri, B. H. Kim, John H. Gruenewald, John G. Connell, J. Thompson, J. Nichols, Jsaminka Terzic, B. I. Min, Gang Cao, Joseph W. Brill, Sung S. Ambrose Seo

Physics and Astronomy Faculty Publications

We have investigated the electronic and optical properties of (Sr_1−xCa_x)₂IrO₄ (x = 0–0.375) and (Sr_1−yBa_y)₂IrO₄ (y = 0–0.375) epitaxial thin films, in which the bandwidth is systematically tuned via chemical substitutions of Sr ions by Ca and Ba. Transport measurements indicate that the thin-film series exhibits insulating behavior, similar to the J_eff = 1/2 spin-orbit Mott insulator Sr₂IrO₄. As the average A-site ionic radius increases from (Sr_1−xCa_x)₂IrO₄ to (Sr …

Direct Imaging Of Coexisting Ordered And Frustrated Sublattices In Artificial Ferromagnetic Quasicrystals, Barry Farmer, Vinayak Shantaram Bhat, Eric Teipel, J. Unguris, D. J. Keavney, Jeffrey Todd Hastings, Lance E. De Long

Physics and Astronomy Faculty Publications

We have used scanning electron microscopy with polarization analysis and photoemission electron microscopy to image the two-dimensional magnetization of permalloy films patterned into Penrose P2 tilings (P2T). The interplay of exchange interactions in asymmetrically coordinated vertices and short-range dipole interactions among connected film segments stabilize magnetically ordered, spatially distinct sublattices that coexist with frustrated sublattices at room temperature. Numerical simulations that include long-range dipole interactions between sublattices agree with images of as-grown P2T samples and predict a magnetically ordered ground state for a two-dimensional quasicrystal lattice of classical Ising spins.

Engineering The Ground State Of Complex Oxides, Derek Joseph Meyers

Graduate Theses and Dissertations

Transition metal oxides featuring strong electron-electron interactions have been at the forefront of condensed matter physics research in the past few decades due to the myriad of novel and exciting phases derived from their competing interactions. Beyond their numerous intriguing properties displayed in the bulk they have also shown to be quite susceptible to externally applied perturbation in various forms. The dominant theme of this work is the exploration of three emerging methods for engineering the ground states of these materials to access both their applicability and their deficiencies.

The first of the three methods involves a relatively new set …

Nanoscale Thermoelectrics: A Study Of The Absolute Seebeck Coefficient Of Thin Films, Sarah J. Mason

Electronic Theses and Dissertations

The worlds demand for energy is ever increasing. Likewise, the environmental impact of climate change due generating that energy through combustion of fossil fuels is increasingly alarming. Due to these factors new sources of renewable energies are constantly being sought out. Thermoelectric devices have the ability to generate clean, renewable, energy out of waste heat. However promising that is, their inefficiency severely inhibits applicability and practical use. The usefulness of a thermoelectric material increases with the dimensionless quantity, ZT, where, Z = S²σ/κ, and S, σ, and κ are the Seebeck coefficient and electrical and thermal …

Origin Of The Low Frequency Radiation Emitted By Radiative Polaritons Excited By Infrared Radiation In Planar La2o3 Films, Anita J. Vincent-Johnson, Yosep Schwab, Harkirat S. Mann, Mathieu Francoeur, James S. Hammonds Jr., Giovanna Scarel

Department of Physics and Astronomy - Faculty Scholarship

Upon excitation in thin oxide films by infrared radiation, radiative polaritons are formed with complex angular frequency ω, according to the theory of Kliewer and Fuchs (1966 Phys. Rev. 150 573). We show that radiative polaritons leak radiation with frequency ωi to the space surrounding the oxide film. The frequency ωi is the imaginary part of ω. The effects of the presence of the radiation leaked out at frequency ωi are observed experimentally and numerically in the infrared spectra of La2O3 films on silicon upon excitation by infrared radiation of the 0TH type radiative polariton. The frequency ωi is found …

Investigation Of Nbnx Thin Films And Nanoparticles Grown By Pulsed Laser Deposition And Thermal Diffusion, Ashraf Hassan Farha

Electrical & Computer Engineering Theses & Dissertations

Niobium nitride films (NbNx) were grown on Nb and Si (100) substrates using pulsed laser deposition (PLD), laser heating, and thermal diffusion methods. Niobium nitride films were deposited on Nb substrates using PLD with a Q-switched Nd: YAG laser (λ = 1064 nm, 40 ns pulse width, and 10 Hz repetition rate) at different laser fluences, different nitrogen background pressures and deposition temperatures. The effect of changing PLD parameters for films done by PLD was studied. The seen observations establish guidelines for adjusting the laser parameters to achieve the desired morphology and phase of the grown NbNx films.

When the …

Pulse Sharpening Effects Of Thin Film Ferroelectric Transmission Lines, Robert J. Sleezer

Graduate Theses and Dissertations

Advances in material science have resulted in the development of electrically nonlinear high dielectric thin film ferroelectrics, which have led to new opportunities for the creation of novel devices. This dissertation investigated one such device: a low voltage nonlinear transmission line (NLTL). A finite element simulation of ferroelectric transmission lines showed that NLTLs are capable of creating shockwaves. Additionally, if the losses are kept sufficiently low, it was shown that voltage gain should be possible. Furthermore, a method of accounting for material dispersion was developed. Results from simulations including material dispersion showed that temporal solitons might be possible from a …

Wrinkling Of Floating Thin Polymer Films, Jiangshui Huang

Doctoral Dissertations 1896 - February 2014

This thesis presents an extensive study of wrinkling of thin polystyrene films, tens of nanometers in thickness, floating on the surface of water or water modified with surfactant.

First, we study the wrinkling of floating thin polystyrene films under a capillary force exerted by a drop of water placed on its surface. The wrinkling pattern is characterized by the number and length of wrinkles. A metrology for measuring the elasticity and thickness of ultrathin films is constructed by combining the scaling relations that are developed for the length of the wrinkles with those for the number of wrinkles. This metrology …

A Solution-Based Approach To The Fabrication Of Novel Chalcogenide Glass Materials And Structures, Nathan Carlie

All Dissertations

Chalcogenide glasses (ChGs) are well known for their large optical nonlinearities and high infrared transparency, and are candidate materials for next-generation thin film-based planar infrared (IR) optical applications. They are also known, however, to possess low thermal and mechanical stability as compared to oxide glasses. Traditional physical vapor deposition (PVD) methods used for the deposition of these materials as thin films often suffer from low deposition rates, deviation from stoichiometry, and cannot coat over complex surfaces. In order to retain the attractive optical properties of ChGs while enabling new fabrication routes and hybrid and composite material systems, we have developed …

Spectroscopic Analysis Of Tungsten Oxide Thin Films For Sensor Applications, Jose Luis Enriquez Carrejo

Open Access Theses & Dissertations

The objective of this study is targeted toward improving the quality of pure tungsten oxide (WO3) for application to the detection of poisoning gases, especially of H2S. While pure WO3 is a recognized candidate for gas sensing, its characteristics are strongly dependent on the conditions and methods used in its deposition.

Samples of WO3 thin films analyzed in this work were grown on silicon and sapphire substrates using RF magnetron sputtering at a number of different substrate temperatures and Ar:O2 pressure ratios. The properties of the samples were investigated spectroscopically with the goal of determining how variations in the above …

A Finite Difference Method For Studying Thermal Deformation In Three-Dimensional Thin Films Exposed To Ultrashort Pulsed Lasers, Suyang Zhang

Doctoral Dissertations

Thermal analysis related to ultrashort-pulsed lasers has been intensely studied in science and engineering communities in recent years, because the pulse duration of ultrashort-pulsed lasers is only the order of sub-picoseconds to femtoseconds, and the lasers have exclusive capabilities in limiting the undesirable spread of the thermal process zone in the heated sample. Studying the thermal deformation induced by ultrashort-pulsed lasers is essential for preventing thermal damage. For the ultrashort-pulsed laser, the thermal damage is different from that caused by the long pulsed lasers and cracks occur after heating.

This dissertation presents a new finite difference method for studying thermal …

Femtosecond Spectrotemporal Magneto-Optics, J.-Y. Bigot, L. Guidoni, E. Beaurepaire, Peter N. Saeta

All HMC Faculty Publications and Research

A new method to measure and analyze the time and spectrally resolved polarimetric response of magnetic materials is presented. It allows us to study the ultrafast magnetization dynamics of a CoPt₃ ferromagnetic film. The analysis of the pump-induced rotation and ellipticity detected by a broad spectrum probe beam shows that magneto-optical signals predominantly reflect the spin dynamics in ferromagnets.

Photoluminescence Properties Of Silicon Quantum-Well Layers, Peter N. Saeta, A. C. Gallagher

All HMC Faculty Publications and Research

Nanometer-scale crystal silicon films surrounded by SiO₂ were prepared by oxidizing silicon-on-insulator substrates prepared from SIMOX (separation by implantation of oxygen) and crystallized hydrogenated amorphous silicon films. Average silicon layer thickness was determined from reflection spectra. When sufficiently thin (<2 >nm), all layers emitted red photoluminescence under blue and UV cw excitation, with a spectrum that did not depend on the mean layer thickness. The spectrum was roughly Gaussian with a peak energy of 1.65 eV, which is lower than for most porous silicon spectra. The time scale for the luminescence decay was ~35 μs at room temperature and …

Reflection High-Energy Electron-Diffraction Study Of Melting And Solidification Of Pb On Graphite, Z. H. Zhang, P. Kulatunga, H. E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

The melting and solidification of Pb thin films on pyrolytic graphite are investigated in situ by reflection high-energy electron diffraction. Thin films with thicknesses of 4-150 monolayers are investigated. The surface morphology of the thin films were studied by scanning electron microscopy. Superheating of the Pb thin films by 4±2 to 12±2 K is observed from diffraction intensity measurements. Upon cooling the substrate, the Pb on graphite is seen to supercool by ∼69±4 K.

Optical Rectification At Semiconductor Surfaces, Shun Lien Chuang, Stefan Schmitt-Rink, Benjamin I. Greene, Peter N. Saeta, Anthony F. J. Levi

All HMC Faculty Publications and Research

We show that far-infrared radiation can be generated in the depletion field near semiconductor surfaces via the inverse Franz-Keldysh effect or electric-field-induced optical rectification. This mechanism is conceptually different from those previously proposed and accounts for many recent experimental observations.

Ultrafast Electronic Disordering During Femtosecond Laser Melting Of Gaas, Peter N. Saeta, J.-K. Wang, Y. Siegal, N. Bloembergen, E. Mazur

All HMC Faculty Publications and Research

We have observed an ultrarapid electronic phase transformation to a centrosymmetric electronic state during laser excitation of GaAs with intense femtosecond pulses. Reflection second-harmonic intensity from the upper 90 atomic layers vanishes within 100 fs; reflectivity rises within 0.5 ps to a steady value characteristic of a metallic molten phase, long before phonon emission can heat the lattice to the melting temperature.