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Results for “doping effect”

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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Doping effects of Li-Sb content on the structure and electrical properties of [(Na{sub 0.5}K{sub 0.5}){sub 1-x}(Li){sub x}(Sb){sub x}(Nb){sub 1} {sub -x}O{sub 3}] lead-free piezoelectric ceramics

Highlights: Black-Right-Pointing-Pointer [Na{sub 0.5}K{sub 0.5}]{sub 1-x}(Li){sub x}(Sb){sub x}(Nb){sub 1-x}O{sub 3} were prepared by solid-state reaction method. Black-Right-Pointing-Pointer XRD analysis of the powder suggests the formation of a single-phase material. Black-Right-Pointing-Pointer The crystal structure changes from orthorhombic to tetragonal with increase in x. Black-Right-Pointing-Pointer Dielectric studies show a diffuse phase transition at 100 Degree-Sign C and 330 Degree-Sign C. Black-Right-Pointing-Pointer The composition x = 0.050 shows maximum remanent polarization (Pr {approx} 0.66 C m{sup -2}). -- Abstract: Ceramic samples of [Na{sub 0.5}K{sub 0.5}]{sub 1-x}(Li){sub x}(Sb){sub x}(Nb){sub 1-x}O{sub 3} (NKNLS) (x = 0.04-0.06) were prepared by high temperature solid-state reaction method. X-ray diffraction analysis of the powder samples suggests the formation of a single-phase material with transformation from orthorhombic to tetragonal crystal structure with increase in Sb content. Dielectric studies show a diffuse phase transition about 100 Degree-Sign C and another phase ferroelectric-paraelectric transition at 330 Degree-Sign C. Polarization vs. electric field (P-E) hysteresis studies show maximum remanent polarization (Pr {approx} 0.66 C m{sup -2}) for composition x = 0.05. AC conductivity in the compound increases with increase in temperature which may be attributed due to oxygen vacancies and show negative temperature coefficient of resistance (NTCR) effect.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Effective doping of low energy ions into superfluid helium droplets

We report a facile method of doping cations from an electrospray ionization (ESI) source into superfluid helium droplets. By decelerating and stopping the ion pulse of reserpine and substance P from an ESI source in the path of the droplet beam, about 10{sup 4} ion-doped droplets (one ion per droplet) can be recorded, corresponding to a pickup efficiency of nearly 1 out of 1000 ions. We attribute the success of this simple approach to the long residence time of the cations in the droplet beam. The resulting size of the doped droplets, on the order of 10{sup 5}/droplet, is measured using deflection and retardation methods. Our method does not require an ion trap in the doping region, which significantly simplifies the experimental setup and procedure for future spectroscopic and diffraction studies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Threshold switching behavior of Ag-Si based selector device and hydrogen doping effect on its characteristics

The effect of hydrogen treatment on the threshold switching property in a Ag/amorphous Si based programmable metallization cells was investigated for selector device applications. Using the Ag filament formed during motion of Ag ions, a steep-slope (5 mV/dec.) for threshold switching with higher selectivity (∼10{sup 5}) could be achieved. Because of the faster diffusivity of Ag atoms, which are inside solid-electrolytes, the resulting Ag filament could easily be dissolved under low current regime, where the Ag filament possesses weak stability. We found that the dissolution process could be further enhanced by hydrogen treatment that facilitated the movement of the Ag atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Atomic-resolution visualization and doping effects of complex structures in intercalated bilayer graphene

Molecules intercalating two-dimensional materials form complex structures that have been characterized primarily by spatially averaged techniques. In this work, we use aberration-corrected scanning transmission electron microscopy and density-functional-theory (DFT) calculations to study the atomic structure of bilayer graphene (BLG) and few-layer graphene (FLG) intercalated with FeC l 3 . In BLG, we discover two distinct intercalated structures that we identify as monolayer FeC l 3 and monolayer FeC l 2 . The two structures are separated by atomically sharp boundaries and induce large free-carrier densities on the order of 10 13 c m - 2 in the graphene layers. In FLG, we observe multiple FeC l 3 layers stacked in a variety of possible configurations with respect to one another. Lastly, we find that the microscope's electron beam can convert the FeC l 3 monolayer into FeOCl monolayers in a rectangular lattice. These results reveal the need for a combination of atomically resolved microscopy, spectroscopy, and DFT calculations to identify intercalated structures and study their properties.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Studies on the Fe3+ Doping Effect on Structural, Optical and Catalytic Properties of Hydrothermally Synthesized TiO2 Photocatalyst

Pure TiO2 and Fe3+-TiO2 nanoparticles have been prepared by simple hydrothermal method with different Fe3+ concentrations. The synthesized nanoparticles are analysed to determine its structural, optical, morphological and compositional properties using X-ray diffraction, Raman, UV-DRS, photoluminescence, Mossbauer, XPS, TEM and SEM/EDS. The EDS micrograph confirms the existence of Fe3+ atoms in the TiO2 matrix with 0.85, 1.52 and 1.87 weight percent. The crystallite size and band gap decrease with increase in Fe3+concentration. The average particle size obtained from TEM is 7-11 nm which is in good agreement with XRD results. Raman bands at 640 cm-1, 517 cm-1 and 398 cm-1 further confirm pure phase anatase in all samples. XPS shows the proper substitutions of few sites of Ti4+ ions by Fe3+ ions in the TiO2 host lattice. The intensity of PL spectra for Fe3+-TiO2 shows a gradual decrease in the peak intensity with increasing Fe3+ concentration in TiO2, and it indicates lower recombination rate as Fe3+ ions increases. These nanoparticles are further studied for its photocatalytic activities using malachite green dye under UV light, visible light and sunlight.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Effect of impurity doping in gapped bilayer graphene

Impurity doping plays a pivotal role in semiconductor electronics. We study the doping effect in a two-dimensional semiconductor, gapped bilayer graphene. By employing in situ deposition of calcium on the bilayer graphene, dopants are controllably introduced. Low temperature transport results show a variable range hopping conduction near the charge neutrality point persisting up to 50 K, providing evidence for the impurity levels inside the gap. Our experiment confirms a predicted peculiar effect in the gapped bilayer graphene, i.e., formation of in-gap states even if the bare impurity level lies in the conduction band. The result provides perspective on the effect of doping and impurity levels in semiconducting bilayer graphene.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Y 1-x La x VO 3 : Effects of doping on orbital ordering

For this research, the effects of isovalent doping on orbital ordering in the perovskite Y 1-x La x VO 3 were investigated using neutron diffraction and the pair distribution function analysis. YVO 3 is a prototype for orbital ordering, exhibiting two consecutive transitions to G-type and C-type ordering with decreasing temperature. Evidence for local orbital ordering above the transition temperature of T OO ~200 K is presented, obtained from the temperature dependence of the oxygen-oxygen octahedral correlations. This suggests that locally, G-type orbital ordering is present above the T OO temperature but it is short range. With doping, it is expected that orbital ordering disappears altogether. In conclusion, by 30% of doping, as in Y 0.7 La 0.3 VO 3 , even though no orbital ordering is expected, we find that locally, C-type orbital correlations are most likely present below the magnetic transition temperature T N , allowing for a direct paramagnetic to orbitally ordered/antiferromagnetic transition in this composition.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of the doping of PC61BM electron transport layer with carbon nanodots on the performance of inverted planar MAPbI3 perovskite solar cells

The doping effect of carbon nanodots (CNDs) in the PC61BM electron-transport layer on the performance of inverted planar MAPbI3 perovskite solar cells (PSCs) having two different kinds of the hole-transport layer, namely organic PEDOT:PSS and inorganic NiOx, was investigated. The CH3NH3PbI3 perovskite layer was deposited in air at 35% humidity. An average 11% and 12% enhancement of the power conversion efficiency (PCE) was achieved for 1 wt% CNDs doping in the PSCs with PEDOT:PSS and NiOx, respectively. This improvement is attributed to high electron density of CNDs resulting in a triple increase of the electrical conductivity of the PC61BM layer and passivation of the perovskite/PC61BM interface that is reflected by an increase of the open-circuit voltage. In line with this, parallel resistance and fill factor of the PSCs are also improved. Moreover, the energy-resolved electrochemical impedance spectroscopy revealed additional free-charge carriers in the PC61BM layer generated under illumination that were detected via the polaron states formation in the band gap with positive effect on the short-circuit current. All these factors contribute to the PCE improvement. Stability tests of the PSC with PEDOT:PSS under a continuous 24 hour 1.5 AM illumination showed a five times smaller final PCE decrease for the 1 wt% CNDs doping of the PC61BM layer comparing to the undoped counterpart. The passivation effect of CNDs, namely electron filling the traps formed by the photo-dimerization and photo-oxidation of PC61BM molecules, is responsible for this remarkable improvement of the short-term stability. © 2019 International Solar Energy Society.

60 APPLIED LIFE SCIENCES↗