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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Silicon/HfO{sub 2} interface: Effects of gamma irradiation

Quality of MOS devices is a strong function of substrate and oxide interface. In this work we have studied how gamma photon irradiation affects the interface of a 13 nm thick, atomic layer deposited hafnium dioxide deposited on silicon wafer. CV and GV measurements have been done for pristine and irradiated samples to quantify the effect of gamma photon irradiation. Gamma photon irradiation not only introduces positive charge in the oxide and at the interface of Si/HfO{sub 2} interface but also induce phase change of oxide layer. Maximum oxide capacitances are affected by gamma photon irradiation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Electron Doping by Charge Transfer at LaFeO 3 /Sm 2 CuO 4 Epitaxial Interfaces

The breakdown of the lattice translational invariance symmetry that occurs at complex oxide interfaces may profoundly modify their electronic structure, leading to interfacial states with properties drastically different from those of the superlattice individual components. The appearance of a conducting two dimensional (2D) electron gas at the interface between two insulating oxides and induced magnetism in a non-magnetic material are just two among many fascinating examples. [ 1 8 ] One of the key factors underlying novel properties is the modifi cation of the doping and orbital occupancy near those interfaces, which may result from charge transfer processes. [ 3 , 9 11 ] If materials used in heterostructures have different work functions, a non-equilibrium situation will be created at the interface and charge will be transferred until the chemical potential levels off. [ 12 ] The use of such phenomena to modify doping in heterostructures has been proposed theoretically as a new route to avoid the quenched disorder that inevitably accompanies the chemical doping. At the interface between a Mott insulating parent compound of the high critical temperature superconductor (HTSC) family and a suitable material that would act as the charge donor, electron doped phases could be stabilized which would eventually turn metallic and perhaps superconducting. [ 12 , 13 ] Such charge transfer processes have been observed at interfaces involving copper oxides such as La 0.7 Ca 0.3 MnO 3 / YBa 2 Cu 3 O 7 , [ 14 ] La 2 x Sr x CuO 4 /La 2 CuO 4 [ 15 ] and SrTi 1 x Nb x O 3 / Sm 2 CuO 4 . [ 16 ] While a novel 2D superconducting state was found at the La 2-x Sr x CuO 4 /La 2 CuO 4 interface, [ 17 ] the effect of doping by charge transfer could not be examined in the other two cases due to the detrimental effect on the YBa 2 Cu 3 O 7 superconductivity of the spin polarized electrons from La 0.7 Ca 0.3 MnO 3 in one case and due to the conducting nature of the SrTi 1 x Nb x O 3 in the other case, which obscures changes in the conducting properties of the interface layer. In this paper, the structural and

Bruno, Flavio Y.↗
DOE OSTI2014

Engineering of silicon/HfO{sub 2} interface by variable energy proton irradiation

Surfaces and interfaces between materials are of paramount importance for various phenomena, such as painting a house, catalyst driven chemical reactions, intricate life processes, corrosion of materials, and fabrication of various semiconductor devices. Interface of silicon or other such substrates with any of the oxides has profound effect on the performance of metal oxide field effect transistors and other similar devices. Since a surface is an abrupt termination of a periodic crystal, surface atoms will have some unsaturated valence electrons and these unsaturated bonds at the semiconductor surface make it chemically highly reactive. Other than annealing, there is not much that can be done to manage these unsaturated bonds. This study was initiated to explore the possibility of repairing these unsaturated dangling bonds that are formed at the silicon and oxide interface during the deposition of oxide layer above silicon, by the use of proton irradiation. In order to improve the interface characteristics, we present a method to modify the interface of silicon and hafnium dioxide after its fabrication, through proton irradiation. Results of the study are promising and probably this method might be used along with other methods such as annealing to modify the interface, after its fabrication.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The behavior of inverse oxide/metal catalysts: CO oxidation and water-gas shift reactions over ZnO/Cu(111) surfaces

There is a general desire to improve the configuration of industrial catalysts by taking advantage of the intrinsic properties of metal oxides. On an inverse oxide/metal catalyst, the reactants can interact with defect sites of the oxide nanoparticles, metal sites, and the metal-oxide interface. We have investigated the oxidation of carbon monoxide (CO + 0.5O 2 → CO 2 ) and the water-gas shift (WGS, CO + H 2 O → H 2 + CO 2 ) reaction on a series of ZnO/Cu(111) surfaces prepared in different ways. Oxidation of a Zn-Cu(111) alloys with O 2 at 460 K produces ZnO/CuO x /Cu(111) systems where the size of the ZnO islands is in the range of 5–20 nm. These systems are highly active for the oxidation of CO at moderate temperatures (400–500 K) but have problems of stability when performing the water-gas shift at temperatures above 550 K. ZnO/CuO x /Cu(111) surfaces prepared by vapor deposition of Zn at 600 K in O 2 exhibit islands of ZnO which are extremely large (400–500 nm) and contain a minimum of 3–4 layers of the oxide. These large islands of ZnO are not as chemically active as the small ZnO clusters yet they have high stability and produce ZnO-Cu interfaces which are efficient as catalysts for the water-gas shift reaction at 550–625 K.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Activation Energies for Oxide- and Interface-Trap Charge Generation Due to Negative-Bias Temperature Stress of Si-Capped SiGe-pMOSFETs

We investigate negative-bias temperature instabilities in SiGe pMOSFETs with SiO 2 /HfO 2 gate dielectrics. The measured activation energies for interface-trap charge buildup during negative-bias temperature stress are lower for SiGe channel pMOSFETs with SiO 2 /HfO 2 gate dielectrics and Si capping layers than for conventional Si channel pMOSFETs with SiO 2 gate dielectrics. Electron energy loss spectroscopy and scanning transmission electron microscopy images demonstrate that Ge atoms can diffuse from the SiGe layer into the Si capping layer, which is adjacent to the SiO 2 /HfO 2 gate dielectric. Density functional calculations show that these Ge atoms reduce the strength of nearby Si-H bonds and that Ge-H bond energies are still lower, thereby reducing the activation energy for interface-trap generation for the SiGe devices. Activation energies for oxide-trap charge buildup during negative-bias temperature stress are similarly small for SiGe pMOSFETs with SiO 2 /HfO 2 gate dielectrics and Si pMOSFETs with SiO 2 gate dielectrics, suggesting that, in both cases, the oxide-trap charge buildup likely is rate-limited by hole tunneling into the near-interfacial SiO 2 .

activation energy↗
DOE OSTI2025

Facet-dependent structure and dissociation of water at pristine IrO 2 /water interfaces

Understanding the microscopic structure of water at metal oxide interfaces is crucial for advancing electrocatalysis. IrO 2 , specifically, has shown exceptional activity for electrochemical water oxidation, but we currently lack a fundamental understanding of how the surface structure of IrO 2 impacts water reactivity. In this work, we developed a machine learning potential trained to first-principles accuracy for modeling IrO 2 /water interfaces across different facets: (110), (100), (101), and (001). Using extensive machine learning molecular dynamics simulations, we investigated the spontaneous dissociation of water molecules at these interfaces. Our results reveal a distinct dissociation probability trend: (110) > (100) ≈ (101) > (001), which we attribute primarily to the reaction thermodynamics of surface water dissociation. A strong correlation is observed between the surface Ir–O bond distances and the dissociation probabilities, highlighting the role of surface geometry in modulating reactivity. As a consequence, the interfacial solvation structures and hydrogen bonding environments are dynamically tuned by the varying water dissociation capabilities across facets. This work elucidates how water dissociation energetics depend on surface orientation and interfacial structure, offering atomistic insights into manipulating reaction chemistry at electrocatalytic interfaces.

organic↗
DOE OSTI2015

Perspective: Emergent magnetic phenomena at interfaces

The discovery of emergent magnetic phenomena is of fundamental and technological interest. This perspective highlights recent promising examples of emergent ferromagnetism at complex oxide interfaces in the context of spin based electronics.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Interfacial Charge Engineering in Ferroelectric-Controlled Mott Transistors

Heteroepitaxial coupling at complex oxide interfaces introduces a powerful tool for engineering the charge degree of freedom in strongly correlated materials, which can be utilized to achieve tailored functionalities that are inaccessible in the bulk form. In this work, the charge-transfer effect between two strongly correlated oxides, Sm 0.5 Nd 0.5 NiO 3 (SNNO) and La 0.67 Sr 0.33 MnO 3 (LSMO), is exploited to realize a giant enhancement of the ferroelectric field effect in a prototype Mott field-effect transistor. By switching the polarization field of a ferroelectric Pb(Zr,Ti)O 3 (PZT) gate, nonvolatile resistance modulation in the Mott transistors with single-layer SNNO and bilayer SNNO/LSMO channels is induced. For the same channel thickness, the bilayer channels exhibit up to two orders of magnitude higher resistance-switching ratio at 300 K, which is attributed to the intricate interplay between the charge screening at the PZT/SNNO interface and the charge transfer at the SNNO/LSMO interface. X-ray absorption spectroscopy and X-ray photoelectron spectroscopy studies of SNNO/LSMO heterostructures reveal about 0.1 electron per 2D unit cell transferred between the interfacial Mn and Ni layers, which is corroborated by first-principles density functional theory calculations. The study points to an effective strategy to design functional complex oxide interfaces for developing high-performance nanoelectronic and spintronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Concomitant appearance of conductivity and superconductivity in (111) LaAlO 3 /SrTiO 3 interface with metal capping

In epitaxial polar-oxide interfaces, conductivity sets in beyond a finite number of monolayers (ML). This threshold for conductivity is explained by accumulating sufficient electric potential to initiate charge transfer to the interface. Here we experimentally and theoretically study the LaAlO 3 /SrTiO 3 (111) interface where a critical thickness $t_c$ of nine epitaxial LaAlO 3 ML is required to turn the interface from insulating to conducting and even superconducting. In this work, we show that $t_c$ decreases to 3 ML when depositing a cobalt overlayer (capping) and 6 ML for platinum capping. The latter result contrasts with the (001) interface, where platinum capping increases $t_c$ beyond the bare interface. Our density functional theory calculations with a Hubbard U term confirm the observed threshold for conductivity for the bare and the metal-capped interfaces. Interestingly, conductivity appears concomitantly with superconductivity for metal/LaAlO 3 /SrTiO 3 (111) interfaces, in contrast with the metal/LaAlO 3 /SrTiO 3 (001) interfaces where conductivity appears without superconductivity. We attribute this dissimilarity to the different orbital polarization of eg for the (111) versus dxy for the (001) interface.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Color Anodizing of Titanium Coated Rolled Carbon Steel Plate

As an important kind of structural materials, the titanium cladded steel plates have the advantages of both metals and have been applied in aviation, spaceflight, chemical and nuclear industries. In this study, the specimens which were prepared under soldering mechanism during rolling were anodized by electrochemical process under a given conditions. The color anodizing takes place by physical phenomenon of color interference. Part of incident light on the titanium oxide is reflected and the other part reflects inside coated titanium layer. Major part of the light which reflects from titanium-oxide interface, reflects again inside of the oxide layer.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Terrace site hydroxylation upon water dimer formation on monolayer NiO/Ag(100)

The interaction of water vapor with monolayer NiO/Ag(100) was examined using both experimental and computational techniques. Initial film growth was characterized by scanning tunneling microscopy and low energy electron diffraction showing the formation of NiO(1×1). X-ray photoelectron spectroscopy (XPS) reveals that the initial film was mainly composed of NiO oxide with a small amount of hydroxyl groups (OH) attributed to the dissociation of background water vapor at highly reactive edge sites. Density functional theory (DFT) reveals that the adsorption of a water monomer on NiO/Ag(100) terrace sites prefers to be in the molecular rather than the dissociate state. XPS results indicate that upon exposing the oxide film to high water vapor pressures (maximum 333.3 Pa), extensive hydroxylation occurs which is attributed to water dissociation at terrace sites. DFT reveals that upon aggregation of water monomers to dimers at the oxide interface the dissociated dimer is energetically stable. The results herein are consistent with previous MgO/Ag(100) studies, further revealing that for certain metal oxides the formation of water dimers at the metal oxide-vapor interface is a key mechanism leading to extensive terrace site hydroxylation.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Tuning band alignment using interface dipoles at the Pt/anatase TiO 2 interface

The Schottky barrier heights at the Pt/TiO 2 (001) junctions are modulated over 0.8 eV by inserting <1 nm of LaAlO 3 . The large electric field in the LaAlO 3 is stabilized by preserving the continuity of in-plane lattice symmetry at the oxide interface. Lastly, these results greatly expand the application of dipole engineering to versatile polycrystalline metal/binary oxide functional interfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Oxide-free InAs(111)A interface in metal-oxide-semiconductor structure with very low density of states prepared by anodic oxidation

In this letter, we present structural, compositional, and electrical characteristics of anodic oxide layer-based metal-oxide-semiconductor (MOS) capacitors on n-type InAs(111)A, along with the effect of a thin fluorinated interfacial passivation layer. Electrochemical oxidation in acid electrolyte with addition of fluorine (NH{sub 4}F) led to the formation of oxygen free well-ordered wide gap fluorinated interfacial layer at InAs(111)A with the fixed charge (Q{sub fix}) and density of interface states (D{sub it}) in the range of (4–6) × 10{sup 10 }cm{sup −2} and (2–12) × 10{sup 10 }eV{sup −1 }cm{sup −2}, respectively. We found that MOS capacitors showed excellent capacitance-voltage characteristics with very small frequency dispersion (<1% and <15 mV). Fluorinated interfacial layer consists of crystalline isostructural compound with the InAs substrate, which remains intact with the atomic smoothness and sharpness that explain unpinned behavior of the Fermi level.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Degradation of the electrical characteristics of MOS structures with erbium, gadolinium, and dysprosium oxides under the effect of an electric field

The degradation of the characteristics of silicon metal-oxide-semiconductor (MOS) structures with oxides of rare-earth elements under the effect of electric fields with intensities of 0.1–4 MV/cm during the course of electroforming is studied. A specific feature of electroforming consists in the possibility of multiple switching of the structures from the insulating state to the low-resistivity one and back. The temporal characteristics of the degradation of MOS structures during the course of electroforming are exponential. The current-voltage characteristics follow the power law in the range of 0.2–3 V; the effect of an electric field brings about a variation in the distribution of the energy density of traps responsible for currents limited by space charge. It is established that multiple cycles of electroforming lead to an increase in the density of surface states at the Si-oxide interface and to a variation in the energy position of the trap levels, which affects the charge state of the traps.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Amorphorized tantalum-nickel binary films for metal gate applications

Amorphous metal gates have the potential to eliminate the work function variation due to grain orientation for poly-crystalline metal gate materials, which is a leading contributor to threshold voltage variation for small transistors. Structural and electrical properties of TaNi alloys using co-sputtering with different compositions and multilayer structures with different thicknesses are investigated in this work. It is found that TaNi films are amorphous for a wide range of compositions as deposited, and the films stay amorphous after annealing at 400 °C in RTA for 1 min and up to at least 700 °C depending on the composition. The amorphous films eventually crystallize into Ni, Ta, and TaNi{sub 3} phases at high enough temperature. For multilayer Ta/Ni structures, samples with individual layer thickness of 0.12 nm and 1.2 nm are amorphous as deposited due to intermixing during deposition, and stay amorphous until annealed at 500 °C. The resistivity of the films as-deposited are around 200 μΩ·cm. The work function of the alloy is fixed at close to the Ta work function of 4.6 eV for a wide range of compositions. This is attributed to the segregation of Ta at the metal-oxide interface, which is confirmed by XPS depth profile. Overall, the excellent thermal stability and low resistivity makes this alloy system a promising candidate for eliminating work function variation for gate last applications, as compared to crystalline Ta or TiN gates.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Reversed Remanent Magnetic Configuration in Epitaxial La 1-xSrxMnO3 Films

The polar discontinuity which can occur at oxide interfaces can modify the properties of oxide thin films. In such a system, an unusual reversed orientation of the remanent magnetic state was observed recently for La{sub 0.7}Sr{sub 0.3}MnO{sub 3} on Nb-doped SrTiO{sub 3}(0 0 1) deposited via pulsed laser deposition (Lee et al 2010 Phys. Rev. Lett. 105 257204). Here, we report on a similar effect for La{sub 0.7}Sr{sub 0.3}MnO{sub 3} grown via molecular beam epitaxy, a deposition method with different growth kinetics, onto both Nb-doped and undoped SrTiO{sub 3} (STO) substrates. The reversed magnetic state occurred in both samples, while enriched Mn{sup 3+} regions (intermediate layer) are slightly different. Intriguingly, the onset of the reversed remanent state occurred at different temperatures: {approx}125 K for the Nb : STO substrate and {approx}240 K for the undoped STO substrate. Our results point to an additional mechanism for controlling the magnetism in mixed-valence oxide films.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Oxidation of 3D-printed SiC in air and steam environments

Here, the high-temperature oxidation of additively manufactured and chemically vapor infiltrated (3D-printed SiC) has been compared to chemical vapor deposited (CVD) SiC. 100-h isothermal exposures were conducted at 1425° and 1300°C at 1 atm under both dry air and steam environments. A SiC reaction tube was utilized to reduce silica volatility. After steam oxidation at 1425° and 1300°C, on the 3D-printed SiC surface, which was intrinsically rougher than the CVD surface, scales were 70%–90% thicker at the convex regions compared to concave/flat regions. In the convex regions, large cracks perpendicular to the oxidizing interface were observed. After dry air oxidation, scale thicknesses were comparable between 3D-printed SiC and CVD SiC, regardless of geometry. Finite element modeling, conducted to elucidate the relationship between SiC geometry and ß- to α-cristobalite transformation stress, determined cristobalite transformation tensile stresses to be on the order of 103 MPa during cool down, assuming a 6 vol% reduction. Compared to flat SiC substrates, tensile transformation stresses were elevated at concave regions and relaxed at convex regions. Combined with specimen mass gain (accounting for the rougher surface) of 3D-printed SiC being 15%–32% higher for 3D-printed SiC after 1300°C and 1425°C steam oxidation, the work presented concludes that the increased oxidation of 3D-printed SiC is primarily caused by tensile hoop stresses driven by oxidation volume expansion. Lastly, the efficacy of the 3D-printing method is demonstrated through the production of tristructural isotropic imbedded 3D-printed SiC fuel forms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗