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Results for “interfaces and thin films”

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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Role of HfO 2 /SiO 2 thin-film interfaces in near-ultraviolet absorption and pulsed laser damage

Here, the role of thin-film interfaces in the near-ultraviolet (near-UV) absorption and pulsed laser-induced damage was studied for ion-beam-sputtered and electron-beam-evaporated coatings comprised from HfO 2 and SiO 2 thin-film pairs. To separate contributions from the bulk of the film and from interfacial areas, absorption and damage threshold measurements were performed for a one-wave (355-nm wavelength) thick, HfO 2 single-layer film and for a film containing seven narrow HfO 2 layers separated by SiO 2 layers. The seven-layer film was designed to have a total optical thickness of HfO 2 layers, equal to one wave at 355 nm and an E-field peak and average intensity similar to a single-layer HfO 2 film. Absorption in both types of films was measured using laser calorimetry and photothermal heterodyne imaging. The results showed a small contribution to total absorption from thin-film interfaces as compared to HfO 2 film material. The relevance of obtained absorption data to coating near-UV, nanosecond-pulse laser damage was verified by measuring the damage threshold and characterizing damage morphology. The results of this study revealed a higher damage resistance in the seven-layer coating as compared to the single-layer HfO 2 film in both sputtered and evaporated coatings. The results are explained through the similarity of interfacial film structure with structure formed during the codeposition of HfO 2 and SiO 2 materials.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Misfit strain driven cation inter-diffusion across an epitaxial multiferroic thin film interface

Cation intermixing at functional oxide interfaces remains a highly controversial area directly relevant to interface-driven nanoelectronic device properties. Here, we systematically explore the cation intermixing in epitaxial (001) oriented multiferroic bismuth ferrite (BFO) grown on a (001) lanthanum aluminate (LAO) substrate. Aberration corrected dedicated scanning transmission electron microscopy and electron energy loss spectroscopy reveal that the interface is not chemically sharp, but with an intermixing of ∼2 nm. The driving force for this process is identified as misfit-driven elastic strain. Landau-Ginzburg-Devonshire-based phenomenological theory was combined with the Sheldon and Shenoy formula in order to understand the influence of boundary conditions and depolarizing fields arising from misfit strain between the LAO substrate and BFO film. The theory predicts the presence of a strong potential gradient at the interface, which decays on moving into the bulk of the film. This potential gradient is significant enough to drive the cation migration across the interface, thereby mitigating the misfit strain. Our results offer new insights on how chemical roughening at oxide interfaces can be effective in stabilizing the structural integrity of the interface without the need for misfit dislocations. These findings offer a general formalism for understanding cation intermixing at highly strained oxide interfaces that are used in nanoelectronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Method for characterizing the contact resistance of metal-vanadium dioxide thin film interfaces

The standard method for determining the contact resistance of planar metal-semiconductor interfaces can underestimate the true contact resistance under normal operating conditions, as it relies on the resistivity of the semiconductor material remaining constant during measurement. However, the strong temperature dependence of the resistivity of VO{sub 2} requires a modified approach that maintains a constant power density dissipated within the film to account for Joule heating. We develop a method for measuring contact resistance in semiconductors with a high thermal coefficient of resistivity, demonstrate this method with an example, and compare the results with the standard technique.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Effect of interfacial coupling on photocatalytic performance of large scale MoS{sub 2}/TiO{sub 2} hetero-thin films

Interface electronic behavior of two-dimensional large scale MoS{sub 2}/TiO{sub 2} hetero-thin films has been studied using photoemission spectroscopy. We show a clear experimental evidence for type II band alignment and upward band bending (∼0.55 eV) at the interface of this system. The valence band offset at monolayer MoS{sub 2}/TiO{sub 2} interface was measured to be 2.15 eV, while the conduction band offset was 1.00 eV. The unique interface band positions introduce a strong build-in electric field for efficient electron-hole separation. In addition, thermal treatment results in better interfacial coupling and charge separation efficiency thus enhanced visible light photoactivity. Our results explicate the mechanism and emphasize its huge potential in visible light photocatalysis.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effect of substrate temperature deposition on the thermal and optical performance of ZnO thin films as thermal interface material

ZnO thin films were deposited onto aluminium substrates at different substrate temperatures from 300 to 450 °C by chemical vapour deposition method using zinc acetate dihydrate as precursor. The effects of substrate temperatures on the thermal and optical performances of a light emitting diode package were investigated. The thermal transients show that thin film deposited at 400 °C has the lowest thermal resistance and junction temperature with a different difference of 1.3421 K/W and 2.7 °C respectively. The correlated colour temperature of the LED interfaced with ZnO prepared at 400 °C showed a good agreement with the thermal performance and exhibited the lowest correlated colour temperature as the driving current increases. The luminance shows that bare Al demonstrate the lowest luminosity compare to the coated thin film as TIM. The excess heat that trapped within the air gaps affects the heat flow. This eventually affects the luminosity of the LED. Furthermore, the AFM measurements of CVD 3 (400 °C) samples show low roughness values which contribute to good thermal resistance and junction temperature values. Overall, the present study shows that the performance of the LED has been enhanced with ZnO thin film used as TIM.

36 MATERIALS SCIENCE↗
NASA NTRS1989

Toughness distribution considerations in a thin film system

The spontaneous mechanical failure of thin films and occasionally substrates, due to the thin film deposition, are relatively common occurrences. Large internal stresses (e.g. 10 MPa to 100 MPa) are an inherent part of the thin film deposition process. In most cases where fracture mechanics has been applied to thin film systems, the failure path is confined a priori to the substrate-thin film interface or in the thin film perpendicular to that interface. This paper considers the contributions which determine the failure path and presents a qualitative model for identifying the failure path in a thin film system taking into account the presence of residual stresses. The most important aspect of this model is that it offers an explanation of the variation in the locus of failure that does not strictly depend on the weakest point of the material (i.e. the least work of fracture) being the first to fail. It does not, inherent to its construction, restrict failure to the interface a priori. The fracture mechanics criterion of the strain energy release rate equaling the material's resistance to crack growth leads to crack propagation at a specific location and defines the selection of the fracture path.

Brown, L. D.↗
DOE OSTI2015

Unidirectional oxide hetero-interface thin-film diode

The unidirectional thin-film diode based on oxide hetero-interface, which is well compatible with conventional thin-film fabrication process, is presented. With the metal anode/electron-transporting oxide (ETO)/electron-injecting oxide (EIO)/metal cathode structure, it exhibits that electrical currents ohmically flow at the ETO/EIO hetero-interfaces for only positive voltages showing current density (J)-rectifying ratio of ∼10{sup 5} at 5 V. The electrical properties (ex, current levels, and working device yields) of the thin-film diode (TFD) are systematically controlled by changing oxide layer thickness. Moreover, we show that the oxide hetero-interface TFD clearly rectifies an AC input within frequency (f) range of 10{sup 2} Hz < f < 10{sup 6} Hz, providing a high feasibility for practical applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Order-disorder behavior at thin film oxide interfaces

Order-disorder processes fundamentally determine the structure and properties of many important oxide systems for energy and computing applications. While these processes have been intensively studied in bulk materials, they are less investigated and understood for nanostructured oxides in highly non-equilibrium conditions. These systems can now be realized through a range of deposition techniques and probed at exceptional spatial and chemical resolution, leading to a greater focus on interface dynamics. In this work, we survey a selection of recent studies of order-disorder behavior at thin film oxide interfaces, with a particular emphasis on the emergence of order during synthesis and disorder in extreme irradiation environments. We summarize key trends and identify directions for future study in this growing research area.

36 MATERIALS SCIENCE↗
DOE OSTI2015

The role of film interfaces in near-ultraviolet absorption and pulsed-laser damage in ion-beam-sputtered coatings based on HfO 2 /SiO 2 thin-film pairs

The role of thin-film interfaces in the near-ultraviolet absorption and pulsed-laser–induced damage was studied for ion-beam–sputtered and electron-beam–evaporated coatings comprised from HfO 2 and SiO 2 thin-film pairs. To separate contributions from the bulk of the film and from interfacial areas, absorption and damage-threshold measurements were performed for a one-wave (355-nm wavelength) thick, HfO 2 single-layer film and for a film containing seven narrow HfO 2 layers separated by SiO 2 layers. The seven-layer film was designed to have a total optical thickness of HfO 2 layers, equal to one wave at 355 nm and an E-field peak and average intensity similar to a single-layer HfO 2 film. Absorption in both types of films was measured using laser calorimetry and photothermal heterodyne imaging. The results showed a small contribution to total absorption from thin-film interfaces, as compared to HfO 2 film material. The relevance of obtained absorption data to coating near-ultraviolet, nanosecond-pulse laser damage was verified by measuring the damage threshold and characterizing damage morphology. The results of this study revealed a higher damage resistance in the seven-layer coating as compared to the single-layer HfO 2 film in both sputtered and evaporated coatings. Here, the results are explained through the similarity of interfacial film structure with structure formed during the co-deposition of HfO 2 and SiO 2 materials.

36 MATERIALS SCIENCE↗
DOE OSTI2012

The limits of ultrahigh-resolution x-ray mapping: estimating uncertainties in thin-film and interface structures determined by phase retrieval methods

Capturing subtle details at the sub-Angstrom level is key to understanding the structural basis of many intriguing interfacial phenomena in epitaxial thin films and nanostructures. X-ray phase retrieval methods are ideally suited to this task but the usual approaches for determination of uncertainties, based on refining a parametrized model, are not applicable in this case. Here we describe a method to estimate the uncertainties of the system electron density, obtained by phase retrieval, and of parameters of interest obtained from it. The method is based on the bootstrap approach and it can be generally applied to surface x-ray scattering data. Several examples are given which illustrate the method's utility in determining uncertainties arising from random and systematic errors. The approach also provides a quantitative measure of the validity of structural solutions obtained by phase retrieval methods.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Record surface state mobility and quantum Hall effect in topological insulator thin films via interface engineering

Material defects remain as the main bottleneck to the progress of topological insulators (TIs). In particular, efforts to achieve thin TI samples with dominant surface transport have always led to increased defects and degraded mobilities, thus making it difficult to probe the quantum regime of the topological surface states. Here, by utilizing a novel buffer layer scheme composed of an In 2 Se 3 /(Bi 0.5 In 0.5 ) 2 Se 3 heterostructure, we introduce a quantum generation of Bi 2 Se 3 films with an order of magnitude enhanced mobilities than before. Furthermore, this scheme has led to the first observation of the quantum Hall effect in Bi 2 Se 3 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Defect Interactions at Metal/Ceramic Interfaces in Thin Film Multilayers

Summary of metal-ceramic multilayer deformation: (1) In nanolayered Al/TiN, Al layers grow in a twin orientation with the underlying TiN/Al layers favored by N-terminated TiN layers; (2) The shear strength of Al/TiN interface varies significantly depending on whether the interface is Ti or N terminated; (3) 2 nm Al - 2 TiN multilayers exhibit unusual mechanical properties as revealed by compression testing - (a) High maximum flow strength of 4.5 GPa, which is significantly higher than hardness (6 GPa) divided by a factor of 3, (b) Extraordinarily high strain hardening rates in Al nanolayers (16-35 GPa, {approx} E/2 to E/4), (c) Co-deformability of the TiN nanolayers with Al (confirmed by TEM on nanoindents) to plastic strains in excess of 5%.

COMPRESSION↗
DOE OSTI2014

Impact of annealing on the chemical structure and morphology of the thin-film CdTe/ZnO interface

To enable an understanding and optimization of the optoelectronic behavior of CdTe-ZnO nanocomposites, the morphological and chemical properties of annealed CdTe/ZnO interface structures were studied. For that purpose, CdTe layers of varying thickness (4–24 nm) were sputter-deposited on 100 nm-thick ZnO films on surface-oxidized Si(100) substrates. The morphological and chemical effects of annealing at 525 °C were investigated using X-ray Photoelectron Spectroscopy (XPS), X-ray-excited Auger electron spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy, and atomic force microscopy. We find a decrease of the Cd and Te surface concentration after annealing, parallel to an increase in Zn and O signals. While the as-deposited film surfaces show small grains (100 nm diameter) of CdTe on the ZnO surface, annealing induces a significant growth of these grains and separation into islands (with diameters as large as 1 μm). The compositional change at the surface is more pronounced for Cd than for Te, as evidenced using component peak fitting of the Cd and Te 3d XPS peaks. The modified Auger parameters of Cd and Te are also calculated to further elucidate the local chemical environment before and after annealing. Together, these results suggest the formation of tellurium and cadmium oxide species at the CdTe/ZnO interface upon annealing, which can create a barrier for charge carrier transport, and might allow for a deliberate modification of interface properties with suitably chosen thermal treatment parameters.

77 NANOSCIENCE AND NANOTECHNOLOGY↗