Search NASA⌕ Search

SEARCH · Search NASA

Results for “Layers”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

High‐Performance Zinc Tin Oxide TFTs with Active Layers Deposited by Atomic Layer Deposition

Abstract New deposition techniques for amorphous oxide semiconductors compatible with silicon back end of line manufacturing are needed for 3D monolithic integration of thin‐film electronics. Here, three atomic layer deposition (ALD) processes are compared for the fabrication of amorphous zinc tin oxide (ZTO) channels in bottom‐gate, top‐contact n‐channel transistors. As‐deposited ZTO films, made by ALD at 150–200 °C, exhibit semiconducting, enhancement‐mode behavior with electron mobility as high as 13 cm 2 V −1 s −1 , due to a low density of oxygen‐related defects. ZTO deposited at 200 °C using a hybrid thermal‐plasma ALD process with an optimal tin composition of 21%, post‐annealed at 400 °C, shows excellent performance with a record high mobility of 22.1 cm 2 V –1 s –1 and a subthreshold slope of 0.29 V dec –1 . Increasing the deposition temperature and performing post‐deposition anneals at 300–500 °C lead to an increased density of the X‐ray amorphous ZTO film, improving its electrical properties. By optimizing the ZTO active layer thickness and using a high‐ k gate insulator (ALD Al 2 O 3 ), the transistor switching voltage is lowered, enabling electrical compatibility with silicon integrated circuits. This work opens the possibility of monolithic integration of ALD ZTO‐based thin‐film electronics with silicon integrated circuits or onto large‐area flexible substrates.

Allemang, Christopher R.↗
DOE OSTI2018

Obtaining a Low and Wide Atomic Layer Deposition Window (150-275 °C) for In 2 O 3 Films Using an In III Amidinate and H 2 O

Indium oxide is a major component of many technologically important thin films, most notably the transparent conductor indium tin oxide (ITO). Despite being pyrophoric, homoleptic indium(III) alkyls do not allow atomic layer deposition (ALD) of In 2 O 3 using water as a co-precursor at substrate temperatures below 200 °C. Several alternative indium sources have been developed, but none allows ALD at lower temperatures except in the presence of oxidants such as O 2 or O 3 , which are not compatible with some substrates or alloying processes. We have synthesized a new indium precursor, tris( N , N' -diisopropylformamidinato)indium(III), compound 1 , which allows ALD of pure, carbon-free In 2 O 3 films using H 2 O as the only co-reactant, on substrates in the temperature range 150–275 °C. In contrast, replacing just the H of the anionic i PrNC(H)N i Pr ligand with a methyl group (affording the known tris( N , N' -diisopropylacetamidinato)indium(III), compound 2 ) results in a considerably higher and narrower ALD window in the analogous reaction with H 2 O (225–300 °C). Kinetic studies demonstrate that a higher rate of surface reactions in both parts of the ALD cycle gives rise to this difference in the ALD windows.

charge transport↗
DOE OSTI2014

Insulating gallium oxide layer produced by thermal oxidation of gallium-polar GaN: Insulating gallium oxide layer produced by thermal oxidation of gallium-polar GaN

We report the benefits of dry oxidation of n -GaN for the fabrication of metal-oxide-semiconductor structures. GaN thin films grown on sapphire by MOCVD were thermally oxidized for 30, 45 and 60 minutes in a pure oxygen atmosphere at 850 °C to produce thin, smooth GaO x layers. Moreover, the GaN sample oxidized for 30 minutes had the best properties. Its surface roughness (0.595 nm) as measured by atomic force microscopy (AFM) was the lowest. Capacitance-voltage measurements showed it had the best saturation in accumulation region and the sharpest transition from accumulation to depletion regions. Under gate voltage sweep, capacitance-voltage hysteresis was completely absent. The interface trap density was minimum (D it = 2.75×10 10 cm –2 eV –1 ) for sample oxidized for 30 mins. These results demonstrate a high quality GaO x layer is beneficial for GaN MOSFETs.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Vacuum-Free, All-Solution, and All-Air Processed Organic Photovoltaics with over 11% Efficiency and Promoted Stability Using Layer-by-Layer Codoped Polymeric Electrodes

Nonfullerene organic photovoltaics (OPVs) have achieved a breakthrough in pushing the efficiency beyond 15%. Although this sheds light on OPV commercialization, the high cost associated with the scalable device fabrications remains a giant challenge. Herein, a vacuum-free, all-solution and all-air processed OPV is reported that yields 11.12% efficiency with a fill factor of 0.725, due to the usages of high-merit polymeric electrodes and modified active blends. The design principle toward the high-merit electrodes is to induce heavy acid doping into the matrices for a raised carrier concentration and mobility, make a large removal of insulating components in the whole matrices rather than surfaces, and restrain the formation of large-domain aggregates. A unique layer-by-layer doping is developed to enable the polymeric electrodes with record-high trade-offs between optical transmittance and electrical conductivity. Moreover, solvent vapor annealing is proposed to boost device efficiency and it has the advantages of finely adjusting the active blend morphology and raising the electron mobility. The resulting devices are highly efficient and most (≈91%) of the initial efficiency are maintained in 30 day storage. Finally, this work indicates bright future for making cost-effective all-solution processed OPVs in air.

14 SOLAR ENERGY↗
DOE OSTI2018

Layer-by-layer assembled PEI-based vector with the upconversion luminescence marker for gene delivery

The upconversion luminescence (UCL) marker based on upconversion nanoparticles (UCNPs) shows unique advantages over traditional fluorescence markers, such as enhanced tissue penetration, better photostability, and less autofluorescence. Herein, we constructed a new UCL gene-delivery nonviral vector via layer-by-layer self-assembly of poly(ethylene imine) (PEI) with UCNPs. To reduce the cytotoxicity of PEI, citric acid (CA) was introduced for aqueous modification, and PEI assembly was introduced on the UCNP surface. Our data show that the nonviral vector for UCL gene-delivery demonstrates excellent photostability, low toxicity, and good stability under physiological or serum conditions and can strongly bind to DNA. Moreover, this UCL PEI-based vector could serve as a promising fluorescent gene-delivery carrier for theranostic applications.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Few layer graphene synthesis on transition metal ferrite catalysts

Development of cheap, green and up scalable production methods for graphene is one of the most challenging problems in its manufacture on an industrial scale. We report here a large scale substrate-free fluidized bed catalytic chemical vapour deposition (FB-CCVD) process for few layer graphene (FLG) powder production that uses a crystalline oxide catalyst of the general formula A(x)B(3-x)O(4), wherein the FLG layer thickness and domain sizes can be varied. A and B can be chosen from a list of transition elements including Co, Fe, Ni, Mn, Cu and Zn. The best results in terms of activity and selectivity are obtained for the CoxFe3-xO4 system. We also investigated the reaction mechanism using in situ EXAFS and Raman spectroscopy, and electron tomography. Since FB-CCVD processes are already used for industrial scale production of carbon nanotubes, this process should enable the large scale production of free standing FLG in the near future.

Bacsa, Revathi R.↗
DOE OSTI2019

Bio-inspired nanocomposite by layer-by-layer coating of chitosan/hyaluronic acid multilayers on a hard nanocellulose-hydroxyapatite matrix

We report on a layer-by-layer technique on the hard CNCs/hydroxyapatite (HAP) matrix using biodegradable and biocompatible chitosan and hyaluronic acid (HA). Inspired by the mineralized collagen in human bone, the CNCs/HAP matrix was synthesized by a facile in situ HAP coating on the CNCs fibers. The chemical and crystalline structure of the CNCs/HAP matrix was investigated with FTIR, XRD, HRTEM, and SAED. The surface of the CNCs/HAP matrix was analyzed by AFM which showed a flat structure with a roughness of 23.12 nm, however, the surface roughness increased to 56.09 nm with the assembly of chitosan and HA. After the LBL assembly, the surface hydrophilicity of the CNCs/HAP films was improved. Furthermore, the CNCs/HAP matrix showed enhanced mechanical property than pure CNCs matrix. Although there is compromise in the mechanical property after the LBL assembly, it is anticipated its bioaffinity and biocompatibility will increase with the incoporation of chitosan and HA.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Mechanical Characteristics of SiC Coating Layer in TRISO Fuel Particles

Tristructural isotropic (TRISO) particles are considered as advanced fuel forms for a variety of fission platforms. While these fuel structures have been tested and deployed in reactors, the mechanical properties of these structures as a function of production parameters need to be investigated in order to ensure their reliability during service. Nanoindentation techniques, indentation crack testing, and half sphere crush testing were utilized in order to evaluate the integrity of the SiC coating layer that is meant to prevent fission product release in the coated particle fuel form. The results are complimented by scanning electron microscopy (SEM) of the grain structure that is subject to change as a function of processing parameters and can alter the mechanical properties such as hardness, elastic modulus, fracture toughness and fracture strength. Through utilization of these advanced techniques, subtle differences in mechanical properties that can be important for in-pile fuel performance can be distinguished and optimized in iteration with processing science of coated fuel particle production.

99 GENERAL AND MISCELLANEOUS↗