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Nanocrystalline antiperovskite GaNxMn3 powders were prepared by mechanically milling. The micrograin GaNxMn3 exhibits an abrupt volume contraction at the antiferromagnetic (AFM) to paramagnetic (PM) (AFM-PM) transition. The temperature window of volume contraction (ΔT) is broadened to 50 K as the average grain size (〈D〉) is reduced to ~30 nm. The corresponding coefficient of linear thermal expansion (α) reaches ~ -70 ppm/K, which are comparable to those of giant NTE materials. Further reducing 〈D〉 to ~10 nm, ΔT exceeds 100 K and α remains as large as -30 ppm/K (-21 ppm/K) for x = 1.0 (x = 0.9). Excess atomic displacements together with the reduced structural coherence, revealed by high-energy X-ray pair distribution functions, are suggested to delay the AFM-PM transition. By controlling 〈D〉, giant NTE may also be achievable in other materials with large lattice contraction due to electronic or magnetic phase transitions. [ABSTRACT FROM AUTHOR]

We report on Bi2Sr2CaCu2O8 (BSCCO) intrinsic Josephson junction stacks with improved cooling, allowing for a remarkable increase in emission frequency compared to the previous designs. We started with a BSCCO stack embedded between two gold layers. When mounted in the standard way to a single substrate, the stack emits in the range of 0.43-0.82 THz. We then glued a second, thermally anchored substrate onto the sample surface. The maximum voltage of this better cooled and dimension-unchanged sample was increased and, accordingly, both the emission frequencies and the tunable frequency range were significantly increased up to 1.05 THz and to 0.71 THz, respectively. This double sided cooling may also be useful for other "hot" devices, e.g., quantum cascade lasers. [ABSTRACT FROM AUTHOR]

We propose that a defect complex comprising a suboxide Hf–Si bond and an interfacial dangling bond is responsible for the stress-induced buildup of interface traps in Si/SiO2/HfO2 capacitors. With the aid of first-principles calculations, we show that these defects possess a symmetric double-well energy minimum with a moderate intervening barrier. The calculated activation energies suggest a relatively easy hopping of H atoms between the two energy minima (a field-aided shuttling mechanism). This mechanism can explain the experimentally measured oscillations of interface-trap densities during switched-bias conditions following x-ray irradiation or constant-voltage stress. [ABSTRACT FROM AUTHOR]

The effects of the surface treatments on the performance of Ti/Al/Ti/Au Ohmic contacts to undoped AlGaN/GaN heterostructure are investigated. Contact resistance and specific contact resistivity as low as 0.25 Ω mm and 5.85×10-7 Ω cm2, respectively, have been achieved through pretreatment in CCl2F2 plasma followed by buffered oxide etch solution, with rapid thermal annealing at 900 °C for 30 s in a N2 ambient. The electrical quality and annealing temperature dependence of the metallization scheme are illustrated. Furthermore, excellent edge acuity is also demonstrated for this annealed Ti/Al/Ti/Au Ohmic contact. [ABSTRACT FROM AUTHOR]

Fluorine is known to have both a beneficial and adverse role on the characteristics of Si–SiO2-based devices. Here we report the results of first-principles calculations in terms of which we elucidate this dual behavior. On one hand, we find that Si–F interfacial bonds are resistant to depassivation by hydrogen species, with the process being shut down in the presence of holes. However, we also show that any excess of fluorine has a negative effect since it either creates stretched bonds, which can act as carrier traps, or disrupts an abrupt interface by cleavage of Si–Si bonds. [ABSTRACT FROM AUTHOR]

Negative bias-temperature instability (NBTI) in metal–oxide–semiconductor capacitors with SiOxNy/HfO2 gate dielectrics is compared to those with thermal SiO2 oxides. Activation energies for interface and oxide-trap charge densities for each device type, estimated from capacitance–voltage measurements versus temperature and electric field, lie in the range 0.2–0.4 eV. This suggests that the release of hydrogen from, e.g., oxide protrusions in Si, followed by the lateral motion of protons along the interface (activation energy ∼0.3 eV), may play a key role in NBTI. Passivation reactions between protons and Si–H can create interface traps, and proton capture by sub-oxide bonds (O vacancies) can lead to positive trapped-oxide charge. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Nanocrystalline antiperovskite GaNxMn3 powders were prepared by mechanically milling. The micrograin GaNxMn3 exhibits an abrupt volume contraction at the antiferromagnetic (AFM) to paramagnetic (PM) (AFM-PM) transition. The temperature window of volume contraction (ΔT) is broadened to 50 K as the average grain size (〈D〉) is reduced to ~30 nm. The corresponding coefficient of linear thermal expansion (α) reaches ~ -70 ppm/K, which are comparable to those of giant NTE materials. Further reducing 〈D〉 to ~10 nm, ΔT exceeds 100 K and α remains as large as -30 ppm/K (-21 ppm/K) for x = 1.0 (x = 0.9). Excess atomic displacements together with the reduced structural coherence, revealed by high-energy X-ray pair distribution functions, are suggested to delay the AFM-PM transition. By controlling 〈D〉, giant NTE may also be achievable in other materials with large lattice contraction due to electronic or magnetic phase transitions. [ABSTRACT FROM AUTHOR]