Metal-insulator Interface Research Articles

Spectra of Plasmon Polaritons at Metal―Insulator Interfaces of a Nanosized Gold Film: Expansion into Components and Their Systematization

The spectral characteristics of surface plasmon resonance (SPR) in nanosized gold films were studied with method of internal reflection in the Kretschmann geometry. (For more information,please refer to the PDF.)

Mapping electronic reconstruction at the metal-insulator interface in LaVO3/SrVO3heterostructures

A \ce{(LaVO_3)_6/(SrVO_3)_3} superlattice is studied with a combination of sub-{\AA} resolved scanning transmission electron microscopy and monochromated electron energy-loss spectroscopy. The V oxidation state is mapped with atomic spatial resolution enabling to investigate electronic reconstruction at the \ce{LaVO_3}/\ce{SrVO_3} interfaces. Surprisingly, asymmetric charge distribution is found at adjacent chemically symmetric interfaces. The local structure is proposed and simulated with double channeling calculation which agrees qualitatively with our experiment. We demonstrate that local strain asymmetry is the likely cause of the electronic asymmetry of the interfaces. The electronic reconstruction at the interfaces extends much further than the chemical composition, varying from 0.5 to 1.2 nm. This distance corresponds to the length of charge transfer previously found in the \ce{(LaVO_3)_m}/\ce{(SrVO_3)_n} metal/insulating and the \ce{(LaAlO_3)_m}/\ce{(SrTiO_3)_n} insulating/insulating interfaces.

Thermal transport across metal–insulator interface via electron–phonon interaction

The thermal transport across a metal–insulator interface can be characterized by electron–phonon interaction through which an electron lead is coupled to a phonon lead if phonon–phonon coupling at the interface is very weak. We investigate the thermal conductance and rectification between the electron part and the phonon part using the nonequilibrium Green’s function method. It is found that the thermal conductance has a nonmonotonic behavior as a function of average temperature or the coupling strength between the phonon leads in the metal part and the insulator part. The metal–insulator interface shows a clear thermal rectification effect, which can be reversed by a change in average temperature or the electron–phonon coupling.

Improved retention of nonvolatile bipolar BiFeO3 resistive memories validated by memristance measurements

AbstractThe transport properties of metal‐insulator‐metal (MIM) capacitor‐like structures have been demonstrated to be sensitive to the metal‐insulator interface. BiFeO3 thin films have been grown on Pt/Ti/SiO2/Si substrates with pulsed laser deposition and RF sputtered Au has been used for the top electrode. As quantified by validated memristance measurements, Ar+ irradiation before deposition of the Au top electrode improved the retention of the BiFeO3 –based MIM structures. In principle it is possible to realize multilevel resistive switching with a very large number of intermediate low resistance states in BiFeO3‐based MIM structures which is mainly limited by the writing bias. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

New model of heat transport across the metal-insulator interface by the example of boundaries in a diamond-copper composite

A model of heat transport from an insulator (diamond) to a metal (copper) has been proposed taking into account energy transport to the oscillations inherent in the insulator but having frequencies much higher than the frequencies inherent in the fundamental oscillations of the metal. This problem is solved exactly in the one-dimensional case and in the one-constant approximation of bonding at the interface. It has been established that energy transport occurs in a thin layer near the metal boundary.

Imaging the Electron-Phonon Interaction at the Atomic Scale

Thin Pb films epitaxially grown on 7×7 reconstructed Si(111) represent an ideal model system for studying the electron-phonon interaction at the metal-insulator interface. For this system, using a combination of scanning tunneling microscopy and inelastic electron tunneling spectroscopy, we performed direct real-space imaging of the electron-phonon coupling parameter. We found that λ increases when the electron scattering at the Pb/Si(111) interface is diffuse and decreases when the electron scattering is specular. We show that the effect is driven by transverse redistribution of the electron density inside a quantum well.

Improved Sensing Characteristics of a Novel $\hbox{Pt} \hbox{/HfTiO}_{2}\hbox{/SiC}$ Schottky-Diode Hydrogen Sensor

A novel metal-insulator-silicon carbide Schottky-diode hydrogen sensor with HfTiO2 gate insulator annealed in three different gases (N2, O2, or NO) is fabricated. Measurements are carried out at various hydrogen concentrations at high temperature using a computer-controlled measurement system. The hydrogen-sensing characteristics of the devices are studied with the help of ellipsometry, transmission electron microscopy, scanning electron microscope, energy-dispersive spectroscopy, and atomic force microscopy. Experimental results show that these sensors have high sensor output and can give significant response even at low hydrogen concentration. This work also finds that the NO-annealed sensor has the highest sensor output. When 800-ppm H2 in N2 gas is introduced, the NO-annealed sensor exhibits a high sensor output of 782% at 450°C, which is about three and six times higher than those of the O2- and N2-annealed sensors, respectively. As compared to another sensor with HfO2 gate insulator annealed in NO, the proposed NO-annealed sensor shows higher sensor output, which should be mainly attributed to the larger barrier height at the metal-insulator interface. The excellent hydrogen-sensing characteristics of this novel sensor make it very suitable for detecting hydrogen leakage, particularly in high-temperature environments.

Theoretical analysis of the characteristic impedance in metal–insulator–metal plasmonic transmission lines

We propose a closed form formulation for the impedance of the metal-insulator-metal (MIM) plasmonic transmission lines by solving the Maxwell's equations. We provide approximations for thin and thick insulator layers sandwiched between metallic layers. In the case of very thin dielectric layer, the surface waves on both interfaces are strongly coupled resulting in an almost linear dependence of the impedance of the plasmonic transmission line on the thickness of the insulator layer. On the other hand, for very thick insulator layer, the impedance does not vary with the insulator layer thickness due to the weak-coupling/decoupling of the surface waves on each metal-insulator interface. We demonstrate the effectiveness of our proposed formulation using two test scenarios, namely, almost zero reflection in T-junction and reflection from line discontinuity in the design of Bragg reflectors, where we compare our formulation against previously published results.

Spontaneous Magnetization of a Metal–Insulator Interface

Spontaneous magnetization of an eutectic In0.15Ga0.85-sapphire interface is discovered. Magnetic moment is directed from an insulator to a metal, its density corresponds to 1.8×1018 m−2 localized spin-1/2 states.

Electron-phonon interaction in a local region

The paper reports on a study of electron-phonon interaction within a limited nanosized region. We invoked the modified Fr\"{o}hlich's Hamiltonian to calculate the electron self-energy, as well as the elastic and inelastic scattering cross sections. New effects have been revealed, more specifically: a bound state forms within the limited nanosized region, electrons undergo resonant elastic scattering, with strong inelastic scattering being possible from this state even at low electron energies. The effect of scattering on the magnetic-field-independent dephasing time, in particular, in a diamond-decorated carbon nanotube, has been determined. The effect of strong inelastic electron scattering on thermal resistance at the metal-insulator interface is discussed.

Electric Field-Induced Modification of Magnetocrystalline Anisotropy in Transition-metal Films and at Metal-Insulator Interfaces

We report results of first principles calculations for effects of an external electric field (E-field) on the magnetocrystalline anisotropy (MCA) in transition-metal (Fe, Co, and Ni) monolayers and at metal-insulator (Fe/MgO) interfaces by means of full-potential linearized augmented plane wave method. For the monolayers, the MCA in the Fe monolayer (but not in the Co and Ni) is modified by the E-field, and a giant modification is achieved in the Fe0.75Co0.25. For the Fe/MgO interfaces, the ideal Fe/MgO interface gives rise to a large out-ofplane MCA, and a MCA modification is induced when an E-field is introduced. However, the existence of an interfacial FeO layer between the Fe layer and the MgO substrate may play a key role in demonstrating an Efield-driven MCA switching, i.e., from out-of-plane MCA to in-plane MCA.

Metal-induced gap states modeling of metal-Ge contacts with and without a silicon nitride ultrathin interfacial layer

Metal-induced gap states (MIGS) modeling is used to elucidate the lack of Fermi level pinning at metal-insulator−Ge interfaces. Energy band diagram assessment reveals the existence of two dipoles at the metal-insulator and the insulator−semiconductor interface. The metal−insulator dipole modulates the metal-insulator interface electron barrier and the voltage drop across the insulator but does not affect the barrier to electron transport across the metal-insulator−Ge interface. Rather, this electron transport barrier is established by the metal-semiconductor work function difference and the insulator−semiconductor dipole. Thus, the lack of Fermi level pinning at a metal-insulator−Ge interface is attributed to the fact that the electron transport barrier does not depend upon MIGS screening. A quantitative formulation of this metal-insulator−semiconductor interface MIGS-based model confirms the lack of Fermi level pinning. Furthermore, it indicates that care must be taken when assessing experimental barrier height- work function data since the slope parameter should only be evaluated for the range of metal work function in which the semiconductor is in depletion. This range of work function for which the semiconductor is in depletion is quite limited for the case of a narrow bandgap semiconductor, such as Ge.

Localization of Metal-Induced Gap States at the Metal-Insulator Interface: Origin of Flux Noise in SQUIDs and Superconducting Qubits

The origin of magnetic flux noise in superconducting quantum interference devices with a power spectrum scaling as 1/f (f is frequency) has been a puzzle for over 20 years. This noise limits the decoherence time of superconducting qubits. A consensus has emerged that the noise arises from fluctuating spins of localized electrons with an areal density of 5x10(17) m(-2). We show that, in the presence of potential disorder at the metal-insulator interface, some of the metal-induced gap states become localized and produce local moments. A modest level of disorder yields the observed areal density.

Kondo Proximity Effect: How Does a Metal Penetrate into a Mott Insulator?

We consider a heterostructure of a metal and a paramagnetic Mott insulator using an adaptation of dynamical mean-field theory to describe inhomogeneous systems. The metal can penetrate into the insulator via the Kondo effect. We investigate the scaling properties of the metal-insulator interface close to the critical point of the Mott insulator. At criticality, the quasiparticle weight decays as 1/x;{2} with distance x from the metal within our mean-field theory. Our numerical results (using the numerical renormalization group as an impurity solver) show that the prefactor of this power law is extremely small.

Profiling of hydrogen in metal-insulator-semiconductor sensors using neutron reflectivity

Although interfacial hydrogen has long been accepted as the species responsible for H2 detection in metal-insulator-semiconductor (MIS) sensors, direct observation of this species has been elusive. In this work, the use of neutron reflectivity (NR) to quantify the hydrogen concentration in regions of an MIS device is reported. The presence of multiple states at both the metal-insulator interface and within the insulator that may contribute to the hydrogen response is suggested by the scattering length density profiles obtained from NR. This technique provides a great promise for direct study of the detection mechanisms for MIS sensors.

A mechanism for unipolar resistance switching in oxide nonvolatile memory devices

We propose a mechanism for unipolar resistance switching in metal-insulator-metal sandwich structures. The commutation from the high to low resistance state and back can be achieved with successive voltage sweeps of the same polarity. Electronic correlation effects at the metal-insulator interface are found to play a key role to produce a resistive commutation effect in qualitative agreement with recent experimental reports on binary transition metal oxide based sandwich structures.

Photoemission study of SrTiO3 surface layers instability upon metal deposition

In this work we study the Pt/SrTiO3 (STO) interface system using X-ray photoelectron spectroscopy (XPS). The polycrystalline Pt layers with a thickness of about 2–3 nm are deposited by sputtering and thermal evaporation methods on STO(100) single crystals with two different type of terminations. We propose and show local conductivity (LC) measurements as a good method to check whether such very thin metal layers are continuous. The XPS data show that both methods of Pt deposition lead to changes of the chemical composition of the crystal surface layers, and such chemical instability should be taken into consideration when studying the physical properties of a metal–insulator interface.

Giant Metal Compression at Liquid-Solid (Pb-Si, In-Si) Schottky Junctions

Using a high-energy x-ray transmission-reflection scheme we have studied the density profile of solid-liquid Schottky contacts close to the interface. We found a massive disturbance of the electronic system on the liquid metal side at different interfaces with pronounced density anomalies on a new length scale. The liquid metal at the interface forms a strongly compressed layer followed by a density depleted layer. The experimental evidence points to a charge transfer phenomenon in the metallic system. Control experiments performed at a metal-insulator interface confirm this picture.

Integration of a high density Ta 2O 5 MIM capacitor following 3D damascene architecture compatible with copper interconnects

To face with the continuous integrated circuit densification, passive components size has to be reduced, particularly for RF and analog applications where lots of them are needed. A Metal–Insulator–Metal (MIM) capacitor is integrated with a high developed area architecture to increase the capacitance density and limit encumbrance. The combination of this architecture with Ta 2O 5 dielectric with a permittivity of 25 allows capacitance densities of more than 15 fF/μm 2. As metal insulator interface is critical, two stacks TiN/Ta 2O 5/TiN and TiN/Ta 2O 5/Cu are integrated among copper interconnects, evaluated and compared.

Formation of Ohmic contacts: A breakdown mechanism in metal-insulator-metal structures

The occurrence of low currents in metal-insulator-metal (MIM) structures when high fields are present depends on the presence of a large energy barrier to charge injection at both metal-insulator interfaces. Formation of an Ohmic contact at either metal-insulator interface results in the easy injection of charge carriers into the insulator. The temperature dependence of current-voltage (I-V) characteristics of an Al–Al2O3–Au diode with 23nm of anodically formed Al2O3, after nondestructive dielectric breakdown, is reported. An Ohmic contact forms after initial breakdown as shown by the occurrence of space-charge limited currents, I∝V2, with an effective barrier height of 0.01–0.02eV that is independent of bias. Further breakdown of the MIM sample results in the forming of voltage-controlled negative resistance (VCNR) in the I-V characteristic and the observation of electroluminescence. Elimination of the VCNR conduction regime results in I-V characteristics of a form I∝Vn, where n is temperature dependent and varies between 3.2 and 2.25 as the diode temperature increases from 100to300K. The effective barrier height decreases with bias. All three conduction regimes depend on the presence of an Ohmic contact at both metal-insulator interfaces. The Ohmic contact results from the interaction of the metal electrodes with an impurity band in the insulator.