Interstitial Phosphorus Research Articles

Synergistic effect of interstitial phosphorus doping and MoS2 modification over Zn0.3Cd0.7S for efficient photocatalytic H2 production

ZnxCd1-xS photocatalysts have been widely investigated due to their diverse morphologies, suitable band gaps/band edge positions, and high electronic mobility. However, the sluggish charge separation and severe charge recombination impede the application of ZnxCd1-xS for hydrogen evolution reaction (HER). Herein, doping of phosphorus (P) atoms into Zn0.3Cd0.7S has been implemented to elevate S vacancies concentration as well as tune its Fermi level to be located near the impurity level of S vacancies, prolonging the lifetime of photogenerated electrons. Moreover, P doping induces a hybridized state in the bandgap, leading to an imbalanced charge distribution and a localized built-in electric field for effective separation of photogenerated charge carriers. Further construction of intimate heterojunctions between P-Zn0.3Cd0.7S and MoS2 accelerates surface redox reaction. Benefiting from the above merits, 1 % MoS2/P-Zn0.3Cd0.7S exhibits a high hydrogen production rate of 30.65 mmol·g−1·h−1 with AQE of 22.22 % under monochromatic light at 370 nm, exceeding most ZnxCd1-xS based photocatalysts reported so far. This work opens avenues to fabricate examplary photocatalysts for solar energy conversion and beyond.

Nutrient fluxes from recent deposits of fine-grained, organic-rich sediments in a Florida estuary

Nutrient fluxes from fine-grained, organic-rich sediments in estuaries can hasten the onset and progression of eutrophication and harmful algal blooms. Targeted efforts to manage degraded sediments and improve estuarine water quality require a better understanding of physicochemical controls and the relative importance of benthic fluxes. Toward that end, we determined fluxes from organic-rich, high porosity sediments deposited during the past 5-6 decades along 60 km of the Indian River Lagoon, a barrier island lagoon in Florida, USA. Highly bioavailable ammonium and phosphate were the predominant chemical forms of interstitial nitrogen and phosphorus in these highly-reducing sediments. Median fluxes of ammonium and phosphate were 320 µmol m-2 h-1 and 11 µmol m-2 h-1, respectively. Fluxes were 3-10 times greater when sediment temperatures were >28°C and interstitial sulfide concentrations were >1 mM. Temperature-compensated fluxes of ammonium and phosphate were significantly correlated with sediment organic matter content; total organic carbon averaged 5.3 ± 2.4% and the maximum was 12.4% for the sediments studied. Fine-scale physical probing, plus lidar data, showed that these organic-rich sediments covered <10% of our study area; however, fluxes from these sediments were estimated to supply 20-40% of internal + external annual loads of nitrogen and phosphorus. Furthermore, 60% of nitrogen and phosphorus fluxes from sediments in the northern Indian River Lagoon came from just 22% of the total surface area. Lagoon segments with high benthic fluxes overlapped in part with areas prone to harmful algal blooms. Effective strategies to manage degraded sediments in the Indian River Lagoon depend on knowing the relative magnitude of internal loading of nutrients as well as appropriate techniques to mitigate sediment fluxes.

Stitching electron localized heptazine units with “carbon patches” to regulate exciton dissociation behavior of carbon nitride for photocatalytic elimination of petroleum hydrocarbons

The electron localized heptazine units make it difficult to separate photoinduced electeron-hole pairs for graphitic carbon nitride (g-C3N4), which limits the application prospect of graphitic-like carbon nitride. Changing inherent N-(C)3 bridging mode of in-plane heptazine units and built more electron channel could be a reasonable strategy. Herein, “carbon patches” were introduced to stitch heptazine units, high speed electron transfer path were thus constructed due to delocalized p orbital electron in “carbon patches” as a result. Simultaneously, interlayers’ high speed electron transfer channel was also constructed by distorted molecular layer because of presence of large electronegative interstitial phosphorus atoms. Such photoinduced electron-holes’ spatial separation in-plane and interlayers were built concurrently and confirmed by XANES and DFT calculation for the first time. The resulted PCCNv series photocatalysts exhibited superior photon absorption capability, excellent charge carriers’ separation kinetics, good O2 molecule adsorption as well as activation capability, the resulted abundant reactive radicals contributed to petroleum hydrocarbons photocatalytic degradation significantly. This work shed light on efficient separation of photoinduced excition for carbon nitride in photocatalysis, simultaneously presented a promising candidate non-metal photocatalytic environmental material for marine oil spill remediation.

Prolonged electron lifetime in sulfur vacancy-rich ZnCdS nanocages by interstitial phosphorus doping for photocatalytic water reduction

Sulfur vacancy-rich ZnCdS nanocages with interstitial P dopant atoms were fabricated. The promoted Fermi level caused by interstitial P doping facilitates the S vacancy level to be an effective electron trapping center, thus enhancing the photocatalytic performance.

Atomistic simulation of phosphorus segregation to Σ3 (111) symmetrical tilt grain boundary in α-iron

Irradiation-induced grain boundary (GB) phosphorus segregation is an important factor for estimating the embrittlement of nuclear reactor pressure vessel steels, but the physical process of phosphorus migration to grain boundaries is still unclear. We numerically studied phosphorus migration toward a Σ3(111) symmetrical tilt GB in α-iron using molecular dynamics. We found that, in the vicinity of the GB within ∼1 nm distance, an iron–phosphorus mixed dumbbell and an octahedral interstitial phosphorus atom push a self-interstitial atom into the GB, and the phosphorus atom becomes a substitutional atom. A phosphorus-vacancy complex in the region also becomes dissociated, and the vacancy is absorbed in the GB without dragging phosphorus. The results claim that a novel view of the segregation process is required.

Phosphorus-Doped Graphitic Carbon Nitride Nanotubes with Amino-rich Surface for Efficient CO2 Capture, Enhanced Photocatalytic Activity, and Product Selectivity.

Phosphorus-doped graphitic carbon nitrides (P-g-C3N4) have recently emerged as promising visible-light photocatalysts for both hydrogen generation and clean environment applications because of fast charge carrier transfer and increased light absorption. However, their photocatalytic performances on CO2 reduction have gained little attention. In this work, phosphorus-doped g-C3N4 nanotubes are synthesized through the one-step thermal reaction of melamine and sodium hypophosphite monohydrate (NaH2PO2·H2O). The phosphine gas generated from the thermal decomposition of NaH2PO2·H2O induces the formation of P-g-C3N4 nanotubes from g-C3N4 nanosheets, leads to an enlarged BET surface area and a unique mesoporous structure, and creates an amino-rich surface. The interstitial doping phosphorus also down shifts the conduction and valence band positions and narrows the band gap of g-C3N4. The photocatalytic activities are dramatically enhanced in the reduction both of CO2 to produce CO and CH4 and of water to produce H2 because of the efficient suppression of the recombination of electrons and holes. The CO2 adsorption capacity is improved to 3.14 times, and the production of CO and CH4 from CO2 increases to 3.10 and 13.92 times that on g-C3N4, respectively. The total evolution ratio of CO/CH4 dramatically decreases to 1.30 from 6.02 for g-C3N4, indicating a higher selectivity of CH4 product on P-g-C3N4, which is likely ascribed to the unique nanotubes structure and amino-rich surface.

Growth and characterization of indium-doped Zn3P2 bulk crystals

In this paper, we report the crystal growth of indium-doped zinc phosphide bulk crystals to obtain n-type conduction. The crystal growth experiments were carried out by unidirectional solidification from In–Zn–P ternary solution, and n-type Zn3P2 bulk crystals were successfully obtained. It was also revealed that the electrical properties of indium-doped Zn3P2 crystals could be controlled by heat treatment under controlled partial pressure of phosphorus or zinc. The relationship between the electron concentration and the partial pressure of zinc or phosphorus even in indium-doped Zn3P2 can be understood on the basis of defect equilibria, as in the case of undoped Zn3P2. However, the controllable range of the electron concentration was 1010–1013 cm−3, which was too low in terms of the concentration of doped indium. This is due to the low formation energy of the intrinsic acceptor, interstitial phosphorus, and carrier compensation should be discussed. According to recent reports on ab initio calculation, a weakly n-type Zn3P2 is expected to be formed under extremely Zn-rich growth conditions. The results obtained in this study coincide with the prediction based on calculations, and provide useful knowledge for the formation of the p–n junction of Zn3P2.

Limitation of Industrial Phosphorus-diffused Emitters by SRH Recombination

It is commonly assumed in the PV community that Auger recombination is the dominant loss mechanism in heavily phosphorus-doped emitters of industrial Si solar cells. Contrary to this assumption, we show in this work that most of the losses are caused by Shockley-Read-Hall (SRH) recombination via defect states introduced by inactive phosphorus. Using numerical device simulations, we successfully reproduce all the measured J0e values of a series of profiles (with various concentrations of inactive phosphorus) with an effective SRH capture crosses-section for holes, σp = 7.5×10-18 cm2. The composition of inactive phosphorus (e.g. in form of clusters of interstitial phosphorus, fine and rod-shaped precipitates) may vary under different fabrication conditions, hence we do not claim that this σp value is globally valid. However, because the series of profiles is representative for many emitters in mass production, our result implies generally higher SRH than Auger recombination rates and has decisive implications on the improvement of such industrial emitters: many emitters have not yet reached the Auger-limit and they may still be significantly improved by reducing their density of inactive phosphorus.

Submerged macrophyte biomass distribution in the shallow saline lake Fuente de Piedra (Spain) as function of environmental variables

Aquatic macrophyte biomass, diaspore bank distribution and their relationship to spatial variability of depth, nutrients (nitrite, nitrate, ammonium and soluble reactive phosphorus) as well as sediment granulometry in an athalassohaline lake have been studied during one wet hydrological year. The results indicate that species growing in the lake show different spatial distribution patterns throughout the lake. Indirect gradient analysis (canonical analysis) results showed a first axis defined as a function of Ulva flexuosa Wulfen biomass which is, in turn, positively correlated with interstitial ammonium and Soluble Reactive Phosphorus (SRP). The second axis was mainly established due to Lamprothamnium papulosum (Wallr.) J. Groves biomass which correlated positively to depth and negatively to interstitial ammonium and SRP. These results revealed a NESW eutrophic gradient allowing the U. Flexuosa biomass proliferation. This phenomenon could increase the shadow effect over the rest of the macrophytes inhabiting this shallow lake. Moreover, the eutrophic harmful effect on the macrophyte physiology and over the diaspore bank could have important consequences in the survival of such important populations. The results reported in this study show the need for studies as the base to select sampling points for monitoring this wetland.

PHYSICAL AND PLANT COMMUNITY CONTROLS ON NITROGEN AND PHOSPHORUS LEACHING FROM IMPOUNDED RIVERINE WETLANDS FOLLOWING DAM REMOVAL

ABSTRACTDam removal has emerged as a critical issue in water resources engineering and management. Of particular concern in many regions of the USA is the effect of dam removal on downstream water quality and potential methods of decreasing sediment and nutrient loading to downstream reaches. Rapid revegetation of reservoir sediments has been suggested as a means of reducing the impact of dam removal, although little data exist about the role of vegetation in controlling the downstream release of sediment or nutrients.This study investigated an impounded riverine wetland complex on the Little River, North Carolina, before and after the removal of a low‐head dam. We quantified the leaching of interstitial nitrogen (N) and phosphorus (P) to the adjacent river channel during reservoir dewatering and, through experimental manipulations, isolated the difference between physical (soil) and biological (plant) controls on N and P leaching from dewatering impoundment sediments. We found that the rate and the quantity of N and P leaching from impounded dewatering sediment are predominately controlled by sediment porosity and specific yield. Although vegetation controls on N and P leaching were statistically significant during the first growing season following dam removal, vegetation is likely to be more important as a long‐term control on sediment and nutrient loads. Our results suggest that the initial release of N and P from a dewatered reservoir will be difficult to control but that vegetation may play an important long‐term role. Copyright © 2011 John Wiley & Sons, Ltd.

Decrease in Work Function of Transparent Conducting ZnO Thin Films by Phosphorus Ion Implantation

To confirm the possibility of engineering the work function of ZnO thin films, we have implanted phosphorus ions into ZnO thin films deposited by radio-frequency magnetron sputtering. The fabricated films show n-type characteristics. It is shown that the electrical and optical properties of those thin films vary depending sensitively on the ion dose and rapid thermal annealing time. Compared to as-deposited ZnO films, the work-function of phosphorus ion-implanted ZnO thin films is observed to be lower and decreases with increasing ion doses. It is likely that the zinc or oxygen vacancies are firstly filled with the implanted phosphorus ions. With further increased ions, free electrons are generated as Zn2+ sites are replaced by those ions or interstitial phosphorus ions increase at the lattice sites, the fermi level by which approaches the conduction band and thus the work function decreases. Those films exhibit the optical transmittance higher than 85% within the visible wavelength range (up to 800 nm).

Fracture Toughness Enhanced by Grain Boundary Shielding in Submicron-Grained Low Carbon Steel

The enhancement of toughness at low temperatures in fine grained low carbon steel was studied, basing on a shielding theory due to dislocations and grain boundaries. Fully annealed low carbon steel was subjected to an accumulative roll bonding (ARB) process for grain refining. The grain size perpendicular to the normal direction was found to be approximately 200 nm after the ARB process. The fracture toughness of low carbon steel ARB applied was measured at 77 K by four-point bending, comparing with the fracture toughness of those without the ARB process. It was found that the value of fracture toughness at 77 K was increased by grain refining due to the ARB, indicating that the ARB process enhances toughness at low temperatures as reported in interstitial free steel and phosphorus doped interstitial free steel. It also deduces that the brittle-ductile transition (BDT) temperature shifted to a lower temperature. The enhancement of toughness and the decrease of the BDT temperature due to grain refining cannot be explained completely by the dislocation pile-up model of dislocations at grain boundaries. Quasi-two-dimensional simulations of dislocation dynamics, taking into account of crack tip shielding due to dislocations, were performed to investigate the effect of a dislocation source spacing along a crack front on the BDT. The simulation indicated that the BDT temperature is decreased by decreasing the dislocation source spacing. In addition to the simulation, the authors suggest a new concept of accommodating stress intensity at the crack tip due to grain boundaries to explain the enhancement of toughness and the decrease of the BDT temperature in fine grained materials.

Self- and foreign-atom diffusion in semiconductor isotope heterostructures. II. Experimental results for silicon

We report the diffusion of boron, arsenic, and phosphorus in silicon isotope multilayer structures at temperatures between $850\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ and $1100\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. The diffusion of all dopants and self-atoms at a given temperature is modeled with the same setting of all native-point-defect-related parameters. The evaluation of the relative contributions of charged native-point defects to self-diffusion enables us to determine the defect energy levels introduced by the native-point defects in the Si band gap. Making allowance for the fact that the band gap and the energy levels change with temperature, an energy-level diagram of the native-point defects is obtained that shows a reversed level ordering for the donor levels of the self-interstitials. In accord with the general state of knowledge, the diffusion of boron is mainly mediated by self-interstitials whereas the properties of both vacancies and self-interstitials are important to model arsenic and phosphorus diffusion. The simultaneous diffusion of phosphorus and silicon requires the existence of a singly positively charged interstitial phosphorus. It is the diffusion of this defect that strongly affects the shape of the phosphorus diffusion tail and not entirely the supersaturation of self-interstitials argued so far. Taking into account the mechanisms of dopant diffusion and the properties of native-point defects determined from the simultaneous diffusion experiments, let us describe accurately dopant profiles given in the literature. Altogether, this work provides overall consistent data for modeling dopant and self-diffusion in Si for various experimental conditions. A comparison of experimentally and theoretically determined activation enthalpies of self- and dopant diffusion shows excellent agreement for self-interstitial-mediated diffusion but significant differences for vacancy-mediated diffusion in Si. This disagreement either reflects the deficiency of first-principle calculations to accurately predict the energy band gap of Si or points to a still-remaining lack in our understanding of diffusion in Si.

Observation of substitutional and interstitial phosphorus on cleanSi(100)−(2×1)with scanning tunneling microscopy

We have used scanning tunneling microscopy to identify phosphorus that is present at the clean silicon $(100)\text{\ensuremath{-}}(2\ifmmode\times\else\texttimes\fi{}1)$ surface as a result of the thermal cycling necessary for preparation of samples cut from heavily doped wafers. Substitutional phosphorus is observed in top layer sites as buckled $\mathrm{Si}\text{\ensuremath{-}}\mathrm{P}$ heterodimers. We also observe a second type of feature that appears as a single depressed dimer site. Within this site, the atoms appear as a pair of protrusions in the empty states and a single protrusion in the filled states. These properties are not consistent with known adsorbate signatures or previously reported observations of $\mathrm{P}\text{\ensuremath{-}}\mathrm{P}$ dimers on the $(100)\text{\ensuremath{-}}(2\ifmmode\times\else\texttimes\fi{}1)$ surface. The lack of other impurity sources suggests that they are due to either phosphorus or silicon. The symmetry of the features and their magnitude are consistent with one of those elements residing in an interstitial site just below the top layer of atoms. To identify the type of interstitial, we performed density functional theory calculations for both phosphorus and silicon located below a surface dimer. The resulting charge density plots and simulated STM images are consistent with interstitial phosphorus and not interstitial silicon.

Dimethyl sulfoxide (DMSO) reduction potential in Mediterranean seagrass ( Posidonia oceanica) sediments

Microbial activity was assayed in sediments under five nutrient-limited Posidonia oceanica meadows on the north-east coast of Spain by measuring potential DMSO reduction to dimethylsulfide (DMS) throughout an annual cycle. Nutrient enrichment of the sediments was used to examine the importance of nutrient availability for potential DMSO reduction. DMSO reduction was observed in all the sediments analysed. Values were higher under anaerobic conditions, and low in spring when seagrass uptake removed most of the interstitial sediment phosphorus. DMSO reduction was correlated with α-glucosidase activity suggesting a link with other microbial activities. Nutrient additions significantly increased DMSO reduction in the meadows studied. The extent of the response varied substantially over the year and was highest during November–December. Microbial DMSO reduction was coupled with nutrient cycles like other bacterial activities. This suggests a possibly important role of nutrient additions in bacterial activity in Mediterranean seagrass sediments.

Diffusion of nonstoichiometric defects in n-GaP crystals

Diffusion of nonstoichiometry-related point defects from a LEC-grown GaP substrate to a Te-doped GaP n-type epitaxial layer was investigated by means of photocapacitance. It was revealed that deep donor level at E C−2.1 eV was introduced into GaP substrate with annealing under phosphorus vapor pressure. Thus, the 2.1 eV deep level is thought to be involved with excess P atoms such as interstitial phosphorus atoms. In Te-doped crystal, 2.1 eV level was detected and the density increased as the time of substrate annealing increased. By measuring PHCAP spectra of samples with different thickness of epitaxial layer, diffusion profile of the defects from the substrate interface was obtained. From this, the diffusion coefficient at 850°C is estimated to be ∼8×10 –11 cm 2/s.

Controlled vapor-pressure heat-treatment effect on deep levels in liquid-encapsulated czochralski-grown GaP crystals

Photocapacitance (PHCAP) measurements have been carried out on GaP crystals grown by the liquid-encapsulated Czochralski (LEC) method with heat treatment under various phosphorus-vapor pressures at different temperatures. Electron traps of Ec-1.1 eV, Ec-1.6 eV, Ec-1.9 eV, and a hole trap of Ev+2.26 eV are mainly detected. The phosphorus-vapor pressure dependence of the Ec-1.9 eV trap density and their diffusion behavior indicate that they are interstitial phosphorus atoms. The densities of both Ec-1.1 eV and Ec-1.6 eV traps are strongly dependent on the shallow impurity concentrations. Moreover, the density of Ec-1.1 eV traps increases with increasing phosphorus-vapor pressure. From these results, we suggest that Ec-1.1 eV traps are the complexes of shallow donors and antisite phosphorus atoms. Deep-level densities in GaP crystals after annealing at 860°C or 960°C for 60 min are decreased almost one order of magnitude lower than those in untreated substrate crystals, which should have occurred via out-diffusion of interstitial phosphorus atoms. However, such an effect is not prominent for 800°C treatment for 60 min.

Effects of phosphorus on defects accumulation and annealing in electron-irradiated Fe–Ni austenitic alloys

Pure austenitic alloy Fe–36% Ni and the same alloy doped with phosphorus (0.1% P) were irradiated with 5 MeV electrons at different temperatures (270–573 K). Using the methods of positron annihilation and residual resistivity it was shown that at the irradiation temperature of 270 K vacancies are mobile in both alloys and form vacancy clusters. In Fe–36Ni–0.1P alloy vacancy clusters are decorated with phosphorus atoms. After the irradiation at 423 K the decoration effect is not observed. At the irradiation temperature of 573 K the addition of phosphorus results in the suppression of vacancy supersaturation. A conclusion is made that, at the elevated irradiation temperatures, suppression of vacancy supersaturation occurs due to the interstitial–phosphorus interaction.

One Bond-Type Migration of Phosphorus in Silicon by Interstitialcy Mechanism

It is assumed that an interstitial phosphorus atom and a self-interstitial, Pi and I, are of the interstitialcy type. One bond-type migration is applied to their migration. It is concluded that there is essentially no difference between the migrations of a P-I pair, (PI), and Pi by the interstitialcy mechanism and between the chemical processes for the formation-dissociation of (PI) and the kick-out mechanism of Pi.

Enhanced activation of implanted dopant impurity in hydrogenated crystalline silicon

We propose a physical model for enhanced activation of (implanted) dopant atoms in crystalline Si when the Si vacancy contains atomic hydrogen. Calculations of the potential barriers for inserting the interstitial phosphorus dopant into both hydrogenated and unhydrogenated vacancy sites of the crystalline Si dependent on the charge state of the hydrogenated vacancy, the hydrogen localization, and the transport direction of the interstitial atom to the vacancy are reported using the self-consistent field molecular-orbital linear combination of atomic orbitals technique in the neglect of diatomic differential overlap approach. The results suggest a decrease of the activation temperature for the phosphorus atoms by more than 300 \ifmmode^\circ\else\textdegree\fi{}C.