Hydrogen/nitrogen/oxygen defect complexes in silicon from computational searches

Point defect complexes in crystalline silicon composed of hydrogen, nitrogen, and oxygen atoms are studied within density-functional theory (DFT). Ab initio Random Structure Searching (AIRSS) is used to find low-energy defect structures. We find new lowest-energy structures for several defects: the triple-oxygen defect, {3O}, triple oxygen with a nitrogen atom, {N, 3O}, triple nitrogen with an oxygen atom, {3N,O}, double hydrogen and an oxygen atom, {2H,O}, double hydrogen and oxygen atoms, {2H,2O} and four hydrogen/nitrogen/oxygen complexes, {H,N,O}, {2H,N,O}, {H,2N,O} and {H,N,2O}. We find that some defects form analogous structures when an oxygen atom is replaced by a NH group, for example, {H,N,2O} and {3O}, and {H,N} and {O}. We compare defect formation energies obtained using different oxygen chemical potentials and investigate the relative abundances of the defects.Comment: 9 pages, 13 figure

Dynamic programming for graphs on surfaces

We provide a framework for the design and analysis of dynamic programming algorithms for surface-embedded graphs on n vertices and branchwidth at most k. Our technique applies to general families of problems where standard dynamic programming runs in 2O(k·log k). Our approach combines tools from topological graph theory and analytic combinatorics.Postprint (updated version

AC hot-carrier-induced degradation in NMOSFET's with N 2O-based gate dielectrics

Frequency-dependent ac-stress-induced degradation in NMOSFET's with N 2O-grown and N 2O-nitrided gate oxides was investigated. Suppressed device degradation is observed in both N 2O-based devices as compared to SiO 2 device for frequency up to 100 kHz, which is attributed to nitrogen incorporation in the gate oxides. Moreover, when comparing the two N 2O-based oxides, N 2O-grown oxide device exhibits enhanced degradation than N 2O-nitrided oxide device. Charge pumping measurements reveal that N 2O-nitrided oxide has better immunity to interface-state and neutral-electron-trap generation under dynamic stress.published_or_final_versio

A comparison of MISiC Schottky-diode hydrogen sensors made by NO, N 2O, or NH 3 nitridations

MISiC Schottky-diode hydrogen sensors with gate insulator grown in three different nitridation gases (nitric oxide (NO), N 2O, and NH 3) are fabricated. Steady-state and transien-t-response measurements are carried out at different temperatures and hydrogen concentrations using a computer-controlled measurement system. Experimental results show that these nitrided sensors have high sensitivity and can give a rapid and stable response over a wide range of temperature. This paper also finds that N 2O provides the fastest insulator growth with good insulator quality and hence the highest sensitivity among the three nitrided samples. The N 2O- nitrided sensor can give a significant response even at a low H 2 concentration of 48-ppm H 2 in N 2, indicating a potential application for detecting hydrogen leakage at high temperature. Moreover, the three nitrided samples respond faster than the control sample. At 300°C, the response times of the N 2O, NO, and NH 3-nitrided sample to the 48-ppm H 2 in N 2 are 11, 11, and 37 s, respectively, as compared to 65 s for the control sample without the gate insulator. © 2006 IEEE.published_or_final_versio

Arbuscular mycorrhizal fungi reduce nitrous oxide emissions from N2O hotspots.

Nitrous oxide (N 2O) is a potent, globally important, greenhouse gas, predominantly released from agricultural soils during nitrogen (N) cycling. Arbuscular mycorrhizal fungi (AMF) form a mutualistic symbiosis with two-thirds of land plants, providing phosphorus and/or N in exchange for carbon. As AMF acquire N, it was hypothesized that AMF hyphae may reduce N 2O production. AMF hyphae were either allowed (AMF) or prevented (nonAMF) access to a compartment containing an organic matter and soil patch in two independent microcosm experiments. Compartment and patch N 2O production was measured both before and after addition of ammonium and nitrate. In both experiments, N 2O production decreased when AMF hyphae were present before inorganic N addition. In the presence of AMF hyphae, N 2O production remained low following ammonium application, but increased in the nonAMF controls. By contrast, negligible N 2O was produced following nitrate application to either AMF treatment. Thus, the main N 2O source in this system appeared to be via nitrification, and the production of N 2O was reduced in the presence of AMF hyphae. It is hypothesized that AMF hyphae may be outcompeting slow-growing nitrifiers for ammonium. This has significant global implications for our understanding of soil N cycling pathways and N 2O production

Algorithms and almost tight results for 3-colorability of small diameter graphs.

The 3-coloring problem is well known to be NP-complete. It is also well known that it remains NP-complete when the input is restricted to graphs with diameter 4. Moreover, assuming the Exponential Time Hypothesis (ETH), 3-coloring cannot be solved in time 2o(n) on graphs with n vertices and diameter at most 4. In spite of extensive studies of the 3-coloring problem with respect to several basic parameters, the complexity status of this problem on graphs with small diameter, i.e. with diameter at most 2, or at most 3, has been an open problem. In this paper we investigate graphs with small diameter. For graphs with diameter at most 2, we provide the first subexponential algorithm for 3-coloring, with complexity 2O(nlogn√). Furthermore we extend the notion of an articulation vertex to that of an articulation neighborhood, and we provide a polynomial algorithm for 3-coloring on graphs with diameter 2 that have at least one articulation neighborhood. For graphs with diameter at most 3, we establish the complexity of 3-coloring by proving for every ε∈[0,1) that 3-coloring is NP-complete on triangle-free graphs of diameter 3 and radius 2 with n vertices and minimum degree δ=Θ(nε). Moreover, assuming ETH, we use three different amplification techniques of our hardness results, in order to obtain for every ε∈[0,1) subexponential asymptotic lower bounds for the complexity of 3-coloring on triangle-free graphs with diameter 3 and minimum degree δ=Θ(nε). Finally, we provide a 3-coloring algorithm with running time 2O(min{δΔ, nδlogδ}) for arbitrary graphs with diameter 3, where n is the number of vertices and δ (resp. Δ) is the minimum (resp. maximum) degree of the input graph. To the best of our knowledge, this is the first subexponential algorithm for graphs with δ=ω(1) and for graphs with δ=O(1) and Δ=o(n). Due to the above lower bounds of the complexity of 3-coloring, the running time of this algorithm is asymptotically almost tight when the minimum degree of the input graph is δ=Θ(nε), where ε∈[12,1), as its time complexity is 2O(nδlogδ)=2O(n1−εlogn) and the corresponding lower bound states that there is no 2o(n1−ε)-time algorithm

Effects of wet N 2O oxidation on interface properties of 6H-SiC MOS capacitors

Oxynitrides were grown on n- and p-type 6H-SiC by wet N 2O oxidation (bubbling N 2O gas through deionized water at 95°C) or dry N 2O oxidation followed by wet N 2O oxidation. Their oxide/SiC interfaces were investigated for fresh and stressed devices. It was found that both processes improve p-SiC/oxide but deteriorate n-SiC/oxide interface properties when compared to dry N 2O oxidation alone. The involved mechanism could be enhanced removal of unwanted carbon compounds near the interface due to the wet ambient, and hence a reduction of donor-like interface states for the p-type devices. As for the n-type devices, incorporation of hydrogen-related species near the interface under the wet ambient increase acceptor-like interface states. In summary, the wet N 2O oxidation can be used for providing comparable reliability for n- and p-SiC MOS devices, and especially obtaining high-quality oxide-SiC interface in p-type MOS devices.published_or_final_versio

Improved performance for OTFT with HfTiO2 as gate dielectric by N2O annealing

OTFTs with HfTiO 2 as gate dielectric have been successfully fabricated. The devices show small threshold voltage and subthreshold slope, and thus are suitable for low-voltage and low-power applications. This work also finds that OTFT with gate dielectric annealed in N 2O has larger dielectric constant, smaller threshold voltage, smaller subthreshold slope and larger on/off ratio than the N 2-annealed sample. This demonstrates that the N 2O annealing is an important surface treatment for preparing a high-quality insulator/organic interface. © 2007 IEEE.published_or_final_versio

Six-coordinate organotin(IV) complexes formed using the Kläui ligands; [CpCo{P(OR′)2O}3]SnR3 − nCln

The complexes [CpCo{P(OR′)2O}3]SnR3 − nCln [R′ = Me, Et; R = Ph, Me] are readily prepared from the corresponding organotin chloride and the sodium salt of the Kläui ligands. The X-ray crystal structures of the full series are reported for R = Ph, n = 0-3, and these show that they are all six-coordinate, including the Ph3Sn derivative which is the first example of a SnC3O3 coordination sphere. 1H, 13C, 31P and 119Sn NMR spectra are reported, and interpreted in terms of significant second-order effects and fluxional processes

Prohibited Floor Trading Activities Under the Commodity Exchange Act

In algorithmic graph theory, a classic open question is to determine the complexity of the Maximum Independent Set problem on Pt -free graphs, that is, on graphs not containing any induced path on t vertices. So far, polynomial-time algorithms are known only for t≤5 (Lokshtanov et al., in: Proceedings of the twenty-fifth annual ACM-SIAM symposium on discrete algorithms, SODA 2014, Portland, OR, USA, January 5–7, 2014, pp 570–581, 2014), and an algorithm for t=6 announced recently (Grzesik et al. in Polynomial-time algorithm for maximum weight independent set on P6 -free graphs. CoRR, arXiv:1707.05491, 2017). Here we study the existence of subexponential-time algorithms for the problem: we show that for any t≥1 , there is an algorithm for Maximum Independent Set on Pt -free graphs whose running time is subexponential in the number of vertices. Even for the weighted version MWIS, the problem is solvable in 2O(tnlogn√) time on Pt -free graphs. For approximation of MIS in broom-free graphs, a similar time bound is proved. Scattered Set is the generalization of Maximum Independent Set where the vertices of the solution are required to be at distance at least d from each other. We give a complete characterization of those graphs H for which d-Scattered Set on H-free graphs can be solved in time subexponential in the size of the input (that is, in the number of vertices plus the number of edges): If every component of H is a path, then d-Scattered Set on H-free graphs with n vertices and m edges can be solved in time 2O(|V(H)|n+m√log(n+m)) , even if d is part of the input. Otherwise, assuming the Exponential-Time Hypothesis (ETH), there is no 2o(n+m) -time algorithm for d-Scattered Set for any fixed d≥3 on H-free graphs with n-vertices and m-edges