Search NASA⌕ Search

SEARCH · Search NASA

Results for “NANOELECTRONICS”

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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Semiconductor to metal transition by tuning the location of N{sub 2}{sup AA} in armchair graphene nanoribbons

The electronic band structures and transport properties of N{sub 2}{sup AA}-doped armchair graphene nanoribbons (aGNRs) with two quasi-adjacent substitutional nitrogen atoms incorporated in pairs of neighboring carbon atoms in the same sublattice A are investigated by using non-equilibrium Green function formalism in combination with density functional theory. The results show that the coupling effect between the Pz orbitals of carbon and nitrogen atoms plays an important role in the transition between semiconductor and metal by different locations of N{sub 2}{sup AA}-doped aGNRs. And the striking negative differential resistance behaviors can be found in such devices. These tremendous properties suggest potential application of N{sub 2}{sup AA}-doped aGNRs in graphene-based nanoelectronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Interface and nanostructure evolution of cobalt germanides on Ge(001)

Cobalt germanide (Co{sub x}Ge{sub y}) is a candidate system for low resistance contact modules in future Ge devices in Si-based micro and nanoelectronics. In this paper, we present a detailed structural, morphological, and compositional study on Co{sub x}Ge{sub y} formation on Ge(001) at room temperature metal deposition and subsequent annealing. Scanning tunneling microscopy and low energy electron diffraction clearly demonstrate that room temperature deposition of approximately four monolayers of Co on Ge(001) results in the Volmer Weber growth mode, while subsequent thermal annealing leads to the formation of a Co-germanide continuous wetting layer which evolves gradually towards the growth of elongated Co{sub x}Ge{sub y} nanostructures. Two types of Co{sub x}Ge{sub y} nanostructures, namely, flattop- and ridge-type, were observed and a systematic study on their evolution as a function of temperature is presented. Additional transmission electron microscopy and x-ray photoemission spectroscopy measurements allowed us to monitor the reaction between Co and Ge in the formation process of the Co{sub x}Ge{sub y} continuous wetting layer as well as the Co{sub x}Ge{sub y} nanostructures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Realistic-contact-induced enhancement of rectifying in carbon-nanotube/graphene-nanoribbon junctions

Carbon-nanotube/graphene-nanoribbon junctions were recently fabricated by the controllable etching of single-walled carbon-nanotubes [Wei et al., Nat. Commun. 4, 1374 (2013)] and their electronic transport properties were studied here. First principles results reveal that the transmission function of the junctions show a heavy dependence on the shape of contacts, but rectifying is an inherent property which is insensitive to the details of contacts. Interestingly, the rectifying ratio is largely enhanced in the junction with a realistic contact and the enhancement is insensitive to the details of contact structures. The stability of rectifying suggests a significant feasibility to manufacture realistic all-carbon rectifiers in nanoelectronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Photon assisted current in molecular nanojunctions with novel types of contacts

We propose new approaches to coherent control of transport via molecular junctions, which bypasses several of the hurdles to experimental realization of optically manipulated nanoelectronics noted in the previous literature. The first method is based on the application of intrinsic semiconductor contacts and optical frequencies below the semiconductor bandgap. Our analytical theory predicts a new phenomenon, referred to as coherent destruction of induced tunnelling, which extends the phenomenon of coherent destruction of tunnelling frequently discussed in the previous literature. We also propose to use graphene electrodes as a platform for effective photon assisted tunneling through molecular conduction nanojunctions. We predict dramatic increasing currents evaluated at side-band energies ∼nħω (n is a whole number) related to the modification of graphene gapless spectrum under the action of external electromagnetic field of frequency ω. Our results illustrate the potential of semiconductor and graphene contacts in coherent control of photocurrent.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Stacking-dependent electronic structure of bilayer silicene

Bilayer silicene (BLS) is a class of material that possibly holds both topological and superconducting properties; however, its structure is not fully understood. By scanning stacking modes and lattice constants using first principles calculations, several meta-stable configurations are identified, including a slightly faulted-AA packing structure, named slide-2AA. Different from the metallic properties of conventional AA and AB stacking forms, band structure of slide-2AA bilayer presents a sizeable indirect energy gap of ∼1.16 eV. A metal-semiconductor phase transition along the sliding pathway with a small energy barrier is also observed, indicating its electronic properties can be easily tuned by applying small shear force along the BLS surface plane. Such unique quantitative relationship of structure and electronic properties has profound implications in nanoelectronics and electromechanical devices.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Effect of gamma irradiation on electrical properties of Cu nanowires

Metallic nanowires are of great interest due to their unique electrical, optical, chemical and magnetic properties. Characterization and explanations of electronic properties of nanowires are extremely important due to their potential applications in the field of nanoelectronics and optoelectronics. In the present study, we synthesized the copper nanowires of different diameters (80nm, 100nm and 200nm) and exposed them with gamma rays of 100 KGy and 150 KGy doses. The I-V characteristics of different diameter of Cu nanowires before and after the irradiation were recorded.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Effect of top metal contact on the electrical properties of suspended spiral multiwalled carbon nanotube

The electrical transport behavior of individual spiral multiwalled carbon nanotube (MWCNT), functionalized via chemical route, has been investigated. The electrical current and conductance of such dangling bond attached tube, has been increased, after deposition of platinum (Pt) metal contacts at the two ends using electron beam induced deposition technique (EBID). The increment in the conductance is explained in terms of the change in the density of the states (DOS) near the Fermi level by dangling bonds and Pt atoms presence on the tube. Scanning electron microscope (SEM) image confirms its spiral nature after functionalization. Current –voltage measurements reveal a significant enhancement in the electrical transport of the same tube after the deposition of side metal contact. These results can be useful for the fabrication of nanoelectronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Graphene-assisted near-field radiative heat transfer between corrugated polar materials

Graphene has attracted great attention in nanoelectronics, optics, and energy harvesting. Here, the near-field radiative heat transfer between graphene-covered corrugated silica is investigated based on the exact scattering theory. It is found that graphene can improve the radiative heat flux between silica gratings by more than one order of magnitude and alleviate the performance sensitivity to lateral shift. The underlying mechanism is mainly attributed to the improved photon tunneling of modes away from phonon resonances. Besides, coating with graphene leads to nonlocal radiative transfer that breaks Derjaguin's proximity approximation and enables corrugated silica to outperform bulk silica in near-field radiation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Carbon nanotube quantum dots on hexagonal boron nitride

We report the fabrication details and low-temperature characteristics of carbon nanotube (CNT) quantum dots on flakes of hexagonal boron nitride (hBN) as substrate. We demonstrate that CNTs can be grown on hBN by standard chemical vapor deposition and that standard scanning electron microscopy imaging and lithography can be employed to fabricate nanoelectronic structures when using optimized parameters. This proof of concept paves the way to more complex devices on hBN, with more predictable and reproducible characteristics and electronic stability.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Energy band modulation of graphane by hydrogen-vacancy chains: A first-principles study

We investigated a variety of configurations of hydrogen-vacancy chains in graphane by first-principles density functional calculation. We found that graphane with two zigzag H-vacancy chains segregated by one or more H chain is generally a nonmagnetic conductor or has a negligible band gap. However, the same structure is turned into a semiconductor and generates a magnetic moment if either one or both of the vacancy chains are blocked by isolated H atoms. If H-vacancy chains are continuously distributed, the structure is similar to a zigzag graphene nanoribbon embedded in graphane. It was also found that the embedded zigzag graphene nanoribbon is antiferromagnetic, and isolated H atoms left in the 2-chain nanoribbon can tune the band gap and generate net magnetic moments. Similar effects are also obtained if bare carbon atoms are present outside the nanoribbon. These results are useful for designing graphene-based nanoelectronic circuits.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Compact chromium oxide thin film resistors for use in nanoscale quantum circuits

We report on the electrical characterisation of a series of thin amorphous chromium oxide (CrO{sub x}) films, grown by dc sputtering, to evaluate their suitability for use as on-chip resistors in nanoelectronics. By increasing the level of oxygen doping, the room-temperature sheet resistance of the CrO{sub x} films was varied from 28 Ω/◻ to 32.6 kΩ/◻. The variation in resistance with cooling to 4.2 K in liquid helium was investigated; the sheet resistance at 4.2 K varied with composition from 65 Ω/◻ to above 20 GΩ/◻. All of the films measured displayed linear current–voltage characteristics at all measured temperatures. For on-chip devices for quantum phase-slip measurements using niobium–silicon nanowires, interfaces between niobium–silicon and chromium oxide are required. We also characterised the contact resistance for one CrO{sub x} composition at an interface with niobium–silicon. We found that a gold intermediate layer is favourable: the specific contact resistivity of chromium-oxide-to-gold interfaces was 0.14 mΩcm{sup 2}, much lower than the value for direct CrO{sub x} to niobium–silicon contact. We conclude that these chromium oxide films are suitable for use in nanoscale circuits as high-value resistors, with resistivity tunable by oxygen content.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Fabrication and optical properties of multishell InAs quantum dots on GaAs nanowires

Hybrid nanostructures combining nanowires with quantum dots promote the development of nanoelectronic and nanophotonic devices with integrated functionalities. In this work, we present a complex nanostructure with multishell quantum dots grown on nanowires. 1–4 shells of Stranski-Krastanov InAs quantum dots are grown on the sidewalls of GaAs nanowires by metal organic chemical vapor deposition. Different dot shells are separated by 8 nm GaAs spacer shells. With increasing the number of shells, the quantum dots become sparser and tend to align in one array, which is caused by the shrinkage of facets on which dots prefer to grow as well as the strain fields produced by the lower set of dots which influences the migration of In adatoms. The size of quantum dots increases with the increase of shell number due to enhanced strain fields coupling. The spectra of multishell dots exhibit multiwavelength emission, and each peak corresponds to a dot shell. This hybrid structure may serve as a promising element in nanowire intermediate band solar cells, infrared nanolasers, and photodetectors.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Structural and electrical characterization of CoTiN metal gates

As the gate size continues to decrease in nanoscale transistors, having metal gates with amorphous or near amorphous structures can potentially reduce grain-induced work function variation. Furthermore, amorphous materials are known to have superior diffusion barrier properties, which can help prevent work function change due to the diffusion of metals in contact with the gate. In this work we show that with the addition of cobalt, thin films of polycrystalline TiN become more amorphous with a smaller grain size. Co{sub x}(TiN){sub 1-x} films, where x = 60–80%, appear to consist of nanocrystals embedded in an amorphous matrix, and are thermally stable with no significant crystallization up to an annealing temperature of at least 600 °C. Reducing the nitrogen gas flow ratio during sputter deposition from 9% to 2.5% further decreases the films' crystallinity, which is apparent by more sparse and even smaller nanocrystals. In addition to being partially amorphous, these CoTiN films also exhibit good thermal stability, low resistivity, low roughness, and have the potential for atomic layer deposition compatibility. Even though these materials are not completely amorphous, their small crystal size and amorphous matrix can potentially reduce work function variation and improve their diffusion barrier property. These properties make CoTiN a good candidate as a gate material for future nanoelectronic devices and technology.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Spin-orbit torque induced spike-timing dependent plasticity

Nanoelectronic devices that mimic the functionality of synapses are a crucial requirement for performing cortical simulations of the brain. In this work, we propose a ferromagnet-heavy metal heterostructure that employs spin-orbit torque to implement spike-timing dependent plasticity. The proposed device offers the advantage of decoupled spike transmission and programming current paths, thereby leading to reliable operation during online learning. Possible arrangement of such devices in a crosspoint architecture can pave the way for ultra-dense neural networks. Simulation studies indicate that the device has the potential of achieving pico-Joule level energy consumption (maximum 2 pJ per synaptic event) which is comparable to the energy consumption for synaptic events in biological synapses.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Probing the nature of electron transfer in metalloproteins on graphene-family materials as nanobiocatalytic scaffold using electrochemistry

Graphene-based nanomaterials have shown great promise not only in nanoelectronics due to ultrahigh electron mobility but also as biocatalytic scaffolds owing to irreversible protein surface adsorption and facilitating direct electron transfer. In this work, we synthesized stable dispersions of graphene using liquid-phase exfoliation approach based on non-covalent interactions between graphene and 1-pyrenesulfonic acid sodium salt (Py–1SO{sub 3}), 1-pyrenemethylamine salt (Py − Me-NH{sub 2}) and Pluronic{sup ®} P-123 surfactant using only water as solvent compatible with biomolecules. The resulting graphene nanoplatelets (Gr-LPE) are characterized by a combination of analytical (microscopy and spectroscopy) techniques revealing mono- to few-layer graphene displaying that the exfoliation efficiency strongly depends upon the type of pyrene-based salts and organic surfactants. Moreover being completely water-based approach, we build robust nanoscaffolds of graphene-family nanomaterials (GFNs) namely, monolayer graphene, Gr-LPE (the one prepared with Pluronic{sup ®} P-123), graphene oxide (GO) and its reduced form (rGO) on glassy carbon electrode surface with three important metalloproteins include cytochrome c (Cyt c) [for electron transfer], myoglobin (Mb) [for oxygen storage] and horseradish peroxidase (HRP) [for catalyzing the biochemical reaction]. In order to demonstrate the nanobiocatalytical activity of these proteins, we used electrochemical interfacial direct electron transfer (DET) kinetics and attempt to determine the rate constant (k{sub ET}) using two different analytical approaches namely, linear sweep voltammetry and Laviron’s theory. We elucidated that all of the metalloproteins retain their structural integrity (secondary structure) upon forming mixtures with GFNs confirmed through optical and vibrational spectroscopy and biological activity using electrochemistry. Among the GFNs studied, Gr-LPE, GO and rGO support the efficient electrical wiring of the redox centers (with an increase in catalytic efficiency of Cyt c and Mb in the presence of GFNs attributed partially to the surface functional (carboxyl, epoxide and hydroxyl) groups on GO and rGO facilitating rapid charge transfer.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Electrochemical synthesis of highly crystalline copper nanowires

Copper nanowires were fabricated within the pores of anodic alumina template (AAT) by template synthesis method at pH = 2.9. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to investigate the structure, morphology and composition of fabricated nanowires. These characterizations revealed that the deposited copper nanowires were highly crystalline in nature, dense and uniform. The crystalline copper nanowires are promising in application of future nanoelectronic devices and circuits.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Direct synthesis of Cu{sub 2}O-RGO nanocomposite on Cu foil by thermal evaporation method and its field emission study

In this work, a facile one step thermal evaporation method for deposition of Cu{sub 2}O nanoparticles on RGO sheets to form Cu{sub 2}O-RGO nanocomposite is discussed. To the best of our knowledge, this is the first report on Cu{sub 2}O-RGO nanocomposite, directly grown on Cu foil by a simple thermal evaporation route. The as –prepared nanocomposite exhibits well dispersed Cu{sub 2}O nanoparticles distributed all over the graphene sheet. Field emission properties of the nanocomposite were investigated at a base pressure of 1*10{sup −8} torr. The turn on field, required to draw emission current density of 0.1µA/cm2, was found to be 3.8V/µm with a maximum emission current density of 80 µA/cm2 at an applied field of 6.8 V/µm. Moreover, the nanocomposite shows fairly good emission stability without significant degradation of emission current. The FE results seem to be encouraging, indicative of potential candidature of the Cu{sub 2}O-RGO nanocomposite emitter as an electron source for practical applications in vacuum nanoelectronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

MoS{sub 2} on an amorphous HfO{sub 2} surface: An ab initio investigation

The energetic stability, electronic and structural properties of MoS{sub 2} adsorbed on an amorphous a-HfO{sub 2} surface (MoS{sub 2}/HfO{sub 2}) are examined through ab initio theoretical investigations. Our total energy results indicate that the formation of MoS{sub 2}/HfO{sub 2} is an exothermic process with an adsorption energy of 34 meV/Å{sup 2}, which means that it is more stable than similar systems like graphene/HfO{sub 2} and MoS{sub 2}/SiO{sub 2}. There are no chemical bonds at the MoS{sub 2}-HfO{sub 2} interface. Upon formation of MoS{sub 2}/HfO{sub 2}, the electronic charge distribution is mostly localized at the interface region with no net charge transfer between the adsorbed MoS{sub 2} sheet and –HfO{sub 2} surface. However, the MoS{sub 2} sheet becomes n-type doped when there are oxygen vacancies in the HfO{sub 2} surface. Further investigation of the electronic distribution reveals that there are no electron- and hole-rich regions (electron-hole puddles) on the MoS{sub 2} sheet, which makes this system promising for use in high-speed nanoelectronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗