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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Zero-dimensional to three-dimensional nanojoining: current status and potential applications

We report that the continuing miniaturization of microelectronics is pushing advanced manufacturing into nanomanufacturing. Nanojoining is a bottom-up assembly technique that enables functional nanodevice fabrication with dissimilar nanoscopic building blocks and/or molecular components. Various conventional joining techniques have been modified and re-invented for joining nanomaterials. Our review surveys recent progress in nanojoining methods, as compared to conventional joining processes. Examples of nanojoining are given and classified by the dimensionality of the joining materials. At each classification, nanojoining is reviewed and discussed according to materials specialties, low dimensional processing features, energy input mechanisms and potential applications. The preparation of new intermetallic materials by reactive nanoscale multilayer foils based on self-propagating high-temperature synthesis is highlighted. This review will provide insight into nanojoining fundamentals and innovative applications in power electronics packaging, plasmonic devices, nanosoldering for printable electronics, 3D printing and space manufacturing.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Silicon compatible Sn-based resistive switching memory

Large banks of cheap, fast, non-volatile, energy efficient, scalable solid-state memories are an increasingly essential component for today's data intensive computing. Conductive-bridge random access memory (CBRAM) – which involves voltage driven formation and dissolution of Cu or Ag filaments in a Cu (or Ag) anode/dielectric (HfO 2 or Al 2 O 3 )/inert cathode device – possesses the necessary attributes to fit the requirements. Cu and Ag are, however, fast diffusers and known contaminants in silicon microelectronics. In this paper, employing a criterion for electrode metal selection applicable to cationic filamentary devices and using first principles calculations for estimating diffusion barriers in HfO 2 , we identify tin (Sn) as a rational, silicon CMOS compatible replacement for Cu and Ag anodes in CBRAM devices. We then experimentally fabricate Sn based CBRAM devices and demonstrate very fast, steep-slope memory switching as well as threshold switching, comparable to Cu or Ag based devices. Furthermore, time evolution of the cationic filament formation along with the switching mechanism is discussed based on time domain measurements (I vs. t) carried out under constant voltage stress. Finally, the time to threshold is shown to be a function of both the voltage stress (V stress ) as well as the initial leakage current (I 0 ) through the device.

42 ENGINEERING↗
DOE OSTI2021

Epitaxial nanotwinned metals and alloys: synthesis-twin structure–property relations

Extensive studies have been performed to understand the structure–property relationship in nanotwinned (NT) metals, where the average twin thickness or twin spacing is less than 100 nm. NT metals may have high strength, ductility, good electrical conductivity and corrosion resistance and have promising applications in microelectronics, structural materials and coatings for gas and oil industry. Most prior studies focus on the computational and experimental investigations of NT metals with low stacking fault energy (SFE) and often in polycrystalline forms. In this highlight, we review recent findings on epitaxial growth of NT metals and alloys with low and high SFEs deposited on single crystal substrates, and focus primarily on advancing our comprehension towards tailoring the microstructures and properties of NT metals via extrinsic factors, including the synthesis technique, parametric control and growth template, and intrinsic factors, such as SFE and thermodynamic, kinetic alloying effects. The review intends to illuminate how to synthesize and design epitaxial NT structures to achieve desirable properties.

36 MATERIALS SCIENCE↗
DOE OSTI2023

High- χ diblock copolymers containing poly(vinylpyridine- N -oxide) segments

Block copolymers exhibiting an enhanced segregation strength due to an underlying high Flory–Huggins interaction parameter (high χ) have attracted considerable attention because of their potential of forming microphase-separated domains with very small feature sizes (<10 nm) useful for next-generation lithography. Here, we report the synthesis, characterization, and self-assembly of poly(styrene)- block -poly(2-vinylpyridine N -oxide) (PS- b -P2VPNO) and poly(styrene)- block -poly(4-vinylpyridine N -oxide) (PS- b -P4VPNO) block copolymers. These PS- b -PVPNOs were obtained from the oxidation of their precursors, poly(styrene)- block -poly(2-vinylpyridine) (PS- b -P2VP) and poly(styrene)- block -poly(4-vinylpyridine) (PS- b -P4VP), respectively. The PS- b -PVPNOs exhibit an enhanced segregation as revealed by ordered cylindrical and lamellar structures in the sub-10 nm scale from copolymers with relatively low molecular weight. The morphologies and periodicities of the ordered structures were determined by small-angle X-ray scattering, while atomic-force microscopy was used to image the self-assembly in thin films. Estimates of the changes in disorder–order transition temperature and domain spacing are derived from a theory based on the effects of dipolar interactions. All the experimentally observed morphological changes resulting from the oxidation of P2VP and P4VP precursors can be qualitatively explained in terms of an increased dipole moment of vinylpyridine N -oxide segments. Therefore, our results demonstrate that PVPNO based block copolymers are versatile candidates toward nanopatterned structures with small feature sizes critical for the future microelectronics industry and beyond.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Assessment of wafer scale MoS 2 atomic layers grown by metal–organic chemical vapor deposition using organo-metal, organo-sulfide, and H 2 S precursors

Transition Metal Dichalcogenides (TMDs) are a unique class of materials that exhibit attractive electrical and optical properties which have generated significant interest for applications in microelectronics, optoelectronics, energy storage, and sensing. Considering the potential of these materials to impact such applications, it is crucial to develop a reliable and scalable synthesis process that is compatible with modern industrial manufacturing methods. Metal–organic chemical vapor deposition (MOCVD) offers an ideal solution to produce TMDs, due to its compatibility with large-scale production, precise layer control, and high material purity. Optimization of MOCVD protocols is necessary for effective TMD synthesis and integration into mainstream technologies. Additionally, improvements in metrology are necessary to measure the quality of the fabricated samples more accurately. In this work, we study MOCVD of wafer-scale molybdenum disulfide (MoS 2 ) utilizing two common chalcogen precursors, H 2 S and DTBS. We then develop a metrology platform for wafer scale samples quality assessment. For this, the coalesced films were characterized using Raman spectroscopy, atomic force microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Kelvin probe force microscopy. We then correlate the structural analysis of these grown films with electrical performance by using aerosol jet printing to fabricate van der Pauw test structures and assess sheet resistance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Importance of cross reaction covariance data for user applications

The characterization of the uncertainty in radiation damage metrics presents many challenges. This paper examines the current approaches to characterizing radiation damage metrics such as hydrogen and helium gas production, material heating, trapped charge in microelectronics, and lattice displacement damage. Critical uncertainty aspects go beyond just the material cross sections and involve the consideration of energy-dependent cross reaction correlations, the recoil ion energy spectrum, and models used for the partitioning of the recoil ion energy into various forms of energy deposition. This paper starts with a review of terminology and then examines the current approaches in the characterization of uncertainty in radiation damage metrics for several applications. The major deficiencies in the uncertainty of the damage metric characterization are also identified.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Confined phase separation in SiO{sub X} nanometric thin layers

Phase separation in silicon-rich silica/silica multilayers was investigated using Atom Probe Tomography and Atomistic Kinetic Monte Carlo simulation. It is shown that the thickness of silicon-rich silicon oxide sublayers plays an important role during phase transformation. It determines the morphology of Si-rich phase formed after subsequent annealing, which is of prime interest for microelectronic and optoelectronic applications. Monte Carlo simulation reveals that the formation of isolated Si clusters can be achieved even in the case of spinodal decomposition and is directly related to the ratio between the spinodal wavelength and the sublayer thickness.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Controlled deposition of sulphur-containing semiconductor and dielectric nano-structured films on metals in SF{sub 6} ion-ion plasma

In the present paper, the deposition processes and formation of films in SF{sub 6} ion-ion plasma, with positive and negative ion flows accelerated to the surface, are investigated. The PEGASES (acronym for Plasma Propulsion with Electronegative GASES) source is used as an ion-ion plasma source capable of generating almost ideal ion-ion plasma with negative ion to electron density ratio more than 2500. It is shown that film deposition in SF{sub 6} ion-ion plasma is very sensitive to the polarity of the incoming ions. The effect is observed for Cu, W, and Pt materials. The films formed on Cu electrodes during negative and positive ion assisted deposition were analyzed. Scanning electron microscope analysis has shown that both positive and negative ion fluxes influence the copper surface and leads to film formation, but with different structures of the surface: the low-energy positive ion bombardment causes the formation of a nano-pored film transparent for ions, while the negative ion bombardment leads to a continuous smooth insulating film. The transversal size of the pores in the porous film varies in the range 50–500 nm, and further analysis of the film has shown that the film forms a diode together with the substrate preventing positive charge drain, and positive ions are neutralized by passing through the nano-pores. The film obtained with the negative ion bombardment has an insulating surface, but probably with a multi-layer structure: destroying the top surface layer allows to measure similar “diode” IV-characteristics as for the nano-pored film case. Basing on results, practical conclusions for the probes and electrodes cleaning in ion-ion SF{sub 6} plasmas have been made. Different applications are proposed for the discovered features of the controlled deposition from ion-ion plasmas, from Li-sulphur rechargeable batteries manufacturing and nanofluidics issues to the applications for microelectronics, including low-k materials formation.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Low-noise low-jitter 32-pixels CMOS single-photon avalanche diodes array for single-photon counting from 300 nm to 900 nm

We developed a single-photon counting multichannel detection system, based on a monolithic linear array of 32 CMOS SPADs (Complementary Metal-Oxide-Semiconductor Single-Photon Avalanche Diodes). All channels achieve a timing resolution of 100 ps (full-width at half maximum) and a photon detection efficiency of 50% at 400 nm. Dark count rate is very low even at room temperature, being about 125 counts/s for 50 μm active area diameter SPADs. Detection performance and microelectronic compactness of this CMOS SPAD array make it the best candidate for ultra-compact time-resolved spectrometers with single-photon sensitivity from 300 nm to 900 nm.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Direct current-self-sustained non-ambipolar plasma at low pressure

For decades, non-ambipolar diffusion has been observed and studied in laboratory plasmas that contain a double layer. However, self-sustained non-ambipolar plasma has yet to be demonstrated. This article reports the method and results for achieving such a condition at low pressure, with a wide power range (as low as 6 W). The findings reveal that to achieve self-sustained non-ambipolar plasma, both the balance between electron and ion heating and the space-potential gradient are critical. The plasma reactor developed in this work has potential applications that include microelectronic surface processing and space propulsion, via space-charge-neutral plasma-beam thruster, when operated in the high power regime.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Strain controlled metal-insulator transition in epitaxial NdNiO{sub 3} thin films

We have fabricated epitaxial thin films of NdNiO{sub 3} (NNO) on various single crystal substrates. The transport properties of NNO films are very sensitive to substrate-controlled epitaxial strain. As the strain varies from tensile to compressive, the Mott metal-insulator transition of NNO films shifts to low temperatures. Under a larger compressive strain, the film on LaSrAlO{sub 4} substrate exhibits a practically metallic transport characteristic. We have found that the conductivities of NNO films at low temperatures follow Mott's variable range hopping mechanism rather than thermal activation model and the epitaxial strain has a strong effect on Mott's parameters of NNO films. These findings demonstrate that the electronic transport of NNO thin films can be tuned by the epitaxial strain for next-generation perovskite-based microelectronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Compositional characterization of atomic layer deposited alumina

As the microelectronic industry demands feature size in the order of few and sub nanometer regime, the film composition and other film properties become critical issues and ALD has emerged as the choice of industry. Aluminum oxide is a material with wide applications in electronic and optoelectronic devices and protective and ion barrier layers. Al{sub 2}O{sub 3} is an excellent dielectric because of its large band gap (8.7eV), large band offsets with silicon. We have deposited thin layers of alumina on silicon wafer (p-type) for gate dielectric applications by ALD technique and compositional characterizations of the deposited thin films were done using EDS, XPS and FTIR spectra.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Effect of band alignment on photoluminescence and carrier escape from InP surface quantum dots grown by metalorganic chemical vapor deposition on Si

A detailed analysis of photoluminescence (PL) from InP quantum dots (QDs) grown on Si has been carried out to understand the effect of substrate/host material in the luminescence and carrier escape process from the surface quantum dots. Such studies are required for the development of monolithically integrated next generation III-V QD based optoelectronics with fully developed Si microelectronics. The samples were grown by atmospheric pressure metalorganic chemical vapor deposition technique, and the PL measurements were made in the temperature range 10–80 K. The distribution of the dot diameter as well as the dot height has been investigated from atomic force microscopy. The origin of the photoluminescence has been explained theoretically. The band alignment of InP/Si heterostructure has been determined, and it is found be type II in nature. The positions of the conduction band minimum of Si and the 1st excited state in the conduction band of InP QDs have been estimated to understand the carrier escape phenomenon. A blue shift with a temperature co-efficient of 0.19 meV/K of the PL emission peak has been found as a result of competitive effect of different physical processes like quantum confinement, strain, and surface states. The corresponding effect of blue shift by quantum confinement and strain as well as the red shift by the surface states in the PL peaks has been studied. The origin of the luminescence in this heterojunction is found to be due to the recombination of free excitons, bound excitons, and a transition from the 1st electron excited state in the conduction band (e{sub 1}) to the heavy hole band (hh{sub 1}). Monotonic decrease in the PL intensity due to increase of thermally escaped carriers with temperature has been observed. The change in barrier height by the photogenerated electric-field enhanced the capture of the carriers by the surface states rather than their accumulation in the QD excited state. From an analysis of the dependence of the PL intensity, peak position, and line width with temperature and excitation source, the existence of free and bound excitonic recombination together with e{sub 1} → hh{sub 1} transitions in the QDs is established.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Simultaneous determination of the elastic modulus and density/thickness of ultrathin films utilizing micro-/nanoresonators under applied axial force

Thin films are widely used in microelectronics, optics, filters, and various sensing devices. We propose a method to simultaneously determine the elastic modulus and density or thickness of ultrathin films deposited on various substrate materials. This methodology utilizes measurement of the resonant frequencies of the micro-/nanoresonator under intentionally applied axial tension and, consequently, the beam to string transition. Elastic modulus and density/thickness of thin film are obtained from the ratio between the resonant frequencies of the nanoresonator with and without applied axial force.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

A hybrid magnetic/complementary metal oxide semiconductor three-context memory bit cell for non-volatile circuit design

After decades of continued scaling to the beat of Moore's law, it now appears that conventional silicon based devices are approaching their physical limits. In today's deep-submicron nodes, a number of short-channel and quantum effects are emerging that affect the manufacturing process, as well as, the functionality of the microelectronic systems-on-chip. Spintronics devices that exploit both the intrinsic spin of the electron and its associated magnetic moment, in addition to its fundamental electronic charge, are promising solutions to circumvent these scaling threats. Being compatible with the CMOS technology, such devices offer a promising synergy of radiation immunity, infinite endurance, non-volatility, increased density, etc. In this paper, we present a hybrid (magnetic/CMOS) cell that is able to store and process data both electrically and magnetically. The cell is based on perpendicular spin-transfer torque magnetic tunnel junctions (STT-MTJs) and is suitable for use in magnetic random access memories and reprogrammable computing (non-volatile registers, processor cache memories, magnetic field-programmable gate arrays, etc). To demonstrate the potential our hybrid cell, we physically implemented a small hybrid memory block using 45 nm × 45 nm round MTJs for the magnetic part and 28 nm fully depleted silicon on insulator (FD-SOI) technology for the CMOS part. We also report the cells measured performances in terms of area, robustness, read/write speed and energy consumption.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Carbon nanotube forests growth using catalysts from atomic layer deposition

We have grown carbon nanotubes using Fe and Ni catalyst films deposited by atomic layer deposition. Both metals lead to catalytically active nanoparticles for growing vertically aligned nanotube forests or carbon fibres, depending on the growth conditions and whether the substrate is alumina or silica. The resulting nanotubes have narrow diameter and wall number distributions that are as narrow as those grown from sputtered catalysts. The state of the catalyst is studied by in-situ and ex-situ X-ray photoemission spectroscopy. We demonstrate multi-directional nanotube growth on a porous alumina foam coated with Fe prepared by atomic layer deposition. This deposition technique can be useful for nanotube applications in microelectronics, filter technology, and energy storage.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Corrosion in low dielectric constant Si-O based thin films: Buffer concentration effects

Organosilicate glass (OSG) is often used as an interlayer dielectric (ILD) in high performance integrated circuits. OSG is a brittle material and prone to stress-corrosion cracking reminiscent of that observed in bulk glasses. Of particular concern are chemical-mechanical planarization techniques and wet cleans involving solvents commonly encountered in microelectronics fabrication where the organosilicate film is exposed to aqueous environments. Previous work has focused on the effect of pH, surfactant, and peroxide concentration on the subcritical crack growth of these films. However, little or no attention has focused on the effect of the conjugate acid/base concentration in a buffer. Accordingly, this work examines the “strength” of the buffer solution in both acidic and basic environments. The concentration of the buffer components is varied keeping the ratio of acid/base and therefore pH constant. In addition, the pH was varied by altering the acid/base ratio to ascertain any additional effect of pH. Corrosion tests were conducted with double-cantilever beam fracture mechanics specimens and fracture paths were verified with ATR-FTIR. Shifts in the threshold fracture energy, the lowest energy required for bond rupture in the given environment, G{sub TH}, were found to shift to lower values as the concentration of the base in the buffer increased. This effect was found to be much larger than the effect of the hydroxide ion concentration in unbuffered solutions. The results are rationalized in terms of the salient chemical bond breaking process occurring at the crack tip and modeled in terms of the chemical potential of the reactive species.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Thermomechanical characterization and modeling for TSV structures

Continual scaling of devices and on-chip wiring has brought significant challenges for materials and processes beyond the 32-nm technology node in microelectronics. Recently, three-dimensional (3-D) integration with through-silicon vias (TSVs) has emerged as an effective solution to meet the future technology requirements. Among others, thermo-mechanical reliability is a key concern for the development of TSV structures used in die stacking as 3-D interconnects. This paper presents experimental measurements of the thermal stresses in TSV structures and analyses of interfacial reliability. The micro-Raman measurements were made to characterize the local distribution of the near-surface stresses in Si around TSVs. On the other hand, the precision wafer curvature technique was employed to measure the average stress and deformation in the TSV structures subject to thermal cycling. To understand the elastic and plastic behavior of TSVs, the microstructural evolution of the Cu vias was analyzed using focused ion beam (FIB) and electron backscattering diffraction (EBSD) techniques. Furthermore, the impact of thermal stresses on interfacial reliability of TSV structures was investigated by a shear-lag cohesive zone model that predicts the critical temperatures and critical via diameters.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗