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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Superconducting Phases of Phosphorus Hydride Under Pressure: Stabilization by Mobile Molecular Hydrogen

At 80 GPa, phases with the PH 2 stoichiometry, which are composed of simple cubic like phosphorus layers capped with hydrogen atoms and layers of H 2 molecules, are predicted to be important species contributing to the recently observed superconductivity in compressed phosphine. In this work, the electron–phonon coupling in these phases results from the motions of the phosphorus atoms and the hydrogen atoms bound to them. The role of the mobile H 2 layers is to decrease the Coulomb repulsion between the negatively charged hydrogen atoms capping the phosphorus layers. An insulating PH 5 phase, the structure and bonding of which is reminiscent of diborane, is also predicted to be metastable at this pressure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Quasi-two-dimensional metallic hydrogen in diphosphide at a high pressure

The structural, electronic, phonon, and other characteristics of the normal phases of phosphorus hydrides with stoichiometry PH{sub k} are analyzed. The properties of the initial substance, namely, diphosphine are calculated. In contrast to phosphorus hydrides with stoichiometry PH{sub 3}, a quasi-two-dimensional phosphorus-stabilized lattice of metallic hydrogen can be formed in this substance during hydrostatic compression at a high pressure. The formed structure with H–P–H elements is shown to be locally stable in phonon spectrum, i.e., to be metastable. The properties of diphosphine are compared with the properties of similar structures of sulfur hydrides.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Diselenophosphate-Induced Conversion of an Achiral [Cu 20 H 11 {S 2 P(O i Pr) 2 } 9 ] into a Chiral [Cu 20 H 11 {Se 2 P(O i Pr) 2 } 9 ] Polyhydrido Nanocluster

A polyhydrido copper nanocluster, [Cu 20 H 11 {Se 2 P(OiPr) 2 } 9 ] (2 H ), which exhibits an intrinsically chiral inorganic core of C-3 symmetry, was synthesized from achiral [Cu 20 H 11 {S 2 P(OiPr) 2 } 9 ] (1(H)) of C-3h symmetry by a ligand-exchange method. Likewise, the structure has a distorted cuboctahedral Cu-13 core, two triangular faces of which are capped along the C-3 axis, one by a Cu-6 cupola and the other by a single Cu atom. The Cu-20 framework is further stabilized by 9 diselenophosphate and 11 hydride ligands. The number of hydride, phosphorus, and selenium resonances and their splitting patterns in multinuclear NMR spectra of 2(H) indicate that the chiral Cu20H11 core retains its C-3 symmetry in solution. Moreover, the 11 hydride ligands were located by neutron diffraction experiments and shown to be capping (3)-H and interstitial (5)-H ligands (in square-pyramidal and trigonal-bipyramidal cavities), as supported by DFT calculations on [Cu 20 H 11 (Se 2 PH 2 ) 9 ] (2 H ') as a simplified model.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Development of a microwave ion source for ion implantations

A microwave ion source is expected to have a long lifetime, as it has fewer consumables. Thus, we are in the process of developing a microwave ion source for ion implantation applications. In this paper, we report on a newly developed plasma chamber and the extracted P{sup +} beam currents. The volume of the plasma chamber is optimized by varying the length of a boron nitride block installed within the chamber. The extracted P{sup +} beam current is more than 30 mA, at a 25 kV acceleration voltage, using PH{sub 3} gas.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Plasma chemistry study of PLAD processes

Plasma doping (PLAD) shows very different impurity profiles compared to the conventional beam-line-based ion implantations due to its non-mass separation property and plasma environment. There is no simulation for PLAD process so far due to a lack of a dopant profile model. Several factors determine impurity profiles of PLAD process. The most significant factors are: plasma chemistry and deposition/etching characteristics of multi-ion species plasmas. In this paper, we present plasma chemistry and deposition/etching characteristics of PLAD processes versus co-gas dilutions. Four dopant plasmas including B{sub 2}H{sub 6}, BF{sub 3}, AsH{sub 3}, and PH{sub 3}, and two non-dopant plasmas including CH{sub 4} and GeH{sub 4} are studied and demonstrated.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Growth strategies to control tapering in Ge nanowires

We report the effect of PH{sub 3} on the morphology of Au catalyzed Ge nanowires (NWs). Ge NWs were grown on Si (111) substrate at 400 °C in the presence of PH{sub 3}, using vapor-liquid-solid method by chemical vapor deposition. We show that high PH{sub 3}/GeH{sub 4} ratio causes passivation at NW surface. At high PH{sub 3} concentration phosphorous atoms attach itself on NW surface and form a self-protection coating that prevents conformal growth and leads to taper free nanostructures. However, in case of low PH{sub 3} flux the combination of axial and radial growth mechanism occurs resulting in conical structure. We have also investigated axial PH{sub 3}-intrinsic junctions in Ge NWs. The unusual NW shape is attributed to a combination of catalyzed, uncatalyzed and diffusion induced growth.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Plasma process optimization for N-type doping applications

Plasma doping (PLAD) has been adopted across the implant technology space and into high volume production for both conventional DRAM and NAND doping applications. PLAD has established itself as an alternative to traditional ion implantation by beamline implantation. The push for high doping concentration, shallow doping depth, and conformal doping capability expand the need for a PLAD solution to meet such requirements. The unique doping profile and doping characteristics at high dose rates allow for PLAD to deliver a high throughput, differentiated solution to meet the demand of evolving transistor technology. In the PLAD process, ions are accelerated to the wafer as with a negative wafer bias applied to the wafer. Competing mechanisms, such as deposition, sputtering, and etching inherent in plasma doping require unique control and process optimization. In this work, we look at the distinctive process tool control and characterization features which enable an optimized doping process using n-type (PH{sub 3} or AsH{sub 3}) chemistries. The data in this paper will draw the relationship between process optimization through plasma chemistry study to the wafer level result.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Multi-cusp ion source for doping process of flat panel display manufacturing

We developed a multi-cusp ion source for Nissin ion doping system iG5 which is used in low temperature poly-crystalline silicon processes for flat panel display (FPD) manufacturing. In this ion source, BF{sub 3} or PH{sub 3} diluted H{sub 2} plasmas are produced and large area ribbon ion beams are extracted. In general, ion ratio of B{sup +} in BF{sub 3} plasma is much smaller than BF{sub 2}{sup +} in multi-cusp ion sources. We developed a new method to increase B{sup +} ratio and obtained mass analyzed B{sup +} target current of 130 mA. We employed newly improved multi-slot type electrodes for the beam extraction system and obtained stable beams with the uniformity of below 3%. In BF{sub 3} plasmas, several undesirable metal fluorides are produced in the plasma chamber and deposited on the electrode system, which cause glitches and poor beam uniformity. We introduce several cleaning methods.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Drastic reduction in the surface recombination velocity of crystalline silicon passivated with catalytic chemical vapor deposited SiN{sub x} films by introducing phosphorous catalytic-doped layer

We improve the passivation property of n-type crystalline silicon (c-Si) surface passivated with a catalytic chemical vapor deposited (Cat-CVD) Si nitride (SiN{sub x}) film by inserting a phosphorous (P)-doped layer formed by exposing c-Si surface to P radicals generated by the catalytic cracking of PH{sub 3} molecules (Cat-doping). An extremely low surface recombination velocity (SRV) of 2 cm/s can be achieved for 2.5 Ω cm n-type (100) floating-zone Si wafers passivated with SiN{sub x}/P Cat-doped layers, both prepared in Cat-CVD systems. Compared with the case of only SiN{sub x} passivated layers, SRV decreases from 5 cm/s to 2 cm/s. The decrease in SRV is the result of field effect created by activated P atoms (donors) in a shallow P Cat-doped layer. Annealing process plays an important role in improving the passivation quality of SiN{sub x} films. The outstanding results obtained imply that SiN{sub x}/P Cat-doped layers can be used as promising passivation layers in high-efficiency n-type c-Si solar cells.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Intermolecular interactions of trifluorohalomethanes with Lewis bases in the gas phase: An ab initio study

We perform an ab initio computational study of molecular complexes with the general formula CF{sub 3}X—B that involve one trifluorohalomethane CF{sub 3}X (X = Cl or Br) and one of a series of Lewis bases B in the gas phase. The Lewis bases are so chosen that they provide a range of electron-donating abilities for comparison. Based on the characteristics of their electron pairs, we consider the Lewis bases with a single n-pair (NH{sub 3} and PH{sub 3}), two n-pairs (H{sub 2}O and H{sub 2}S), two n-pairs with an unsaturated bond (H{sub 2}CO and H{sub 2}CS), and a single π-pair (C{sub 2}H{sub 4}) and two π-pairs (C{sub 2}H{sub 2}). The aim is to systematically investigate the influence of the electron pair characteristics and the central atom substitution effects on the geometries and energetics of the formed complexes. The counterpoise-corrected supermolecule MP2 and coupled-cluster single double with perturbative triple [CCSD(T)] levels of theory have been employed, together with a series of basis sets up to aug-cc-pVTZ. The angular and radial configurations, the binding energies, and the electrostatic potentials of the stable complexes have been compared and discussed as the Lewis base varies. For those complexes where halogen bonding plays a significant role, the calculated geometries and energetics are consistent with the σ-hole model. Upon formation of stable complexes, the C–X bond lengths shorten, while the C–X vibrational frequencies increase, thus rendering blueshifting halogen bonds. The central atom substitution usually enlarges the intermolecular bond distances while it reduces the net charge transfers, thus weakening the bond strengths. The analysis based on the σ-hole model is grossly reliable but requires suitable modifications incorporating the central atom substitution effects, in particular, when interaction components other than electrostatic contributions are involved.

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

Quantum dynamics on a three-sheeted six-dimensional ab initio potential-energy surface of the phosphine cation: Simulation of the photoelectron spectrum and the ultrafast radiationless decay dynamics

A diabatic three-sheeted six-dimensional potential-energy surface has been constructed for the ground state and the lowest excited state of the PH{sub 3}{sup +} cation. Coupling terms of Jahn-Teller and pseudo-Jahn-Teller origin up to eighth order had to be included to describe the pronounced anharmonicity of the surface due to multiple conical intersections. The parameters of the diabatic Hamiltonian have been optimized by fitting the eigenvalues of the potential-energy matrix to ab initio data calculated at the CASSCF/MRCI level employing the correlation-consistent triple-ζ basis. The theoretical photoelectron spectrum of phosphine and the non-adiabatic nuclear dynamics of the phosphine cation have been computed by propagating nuclear wave packets with the multiconfiguration time-dependent Hartree method. The theoretical photoelectron bands obtained by Fourier transformation of the autocorrelation function agree well with the experimental results. It is shown that the ultrafast non-radiative decay dynamics of the first excited state of PH{sub 3}{sup +} is dominated by the exceptionally strong Jahn-Teller coupling of the asymmetric bending vibrational mode together with a hyperline of conical intersections with the electronic ground state induced by the umbrella mode. Time-dependent population probabilities have been computed for the three adiabatic electronic states. The non-adiabatic Jahn-Teller dynamics within the excited state takes place within ≈5 fs. Almost 80% of the excited-state population decay to the ground state within about 10 fs. The wave packets become highly complex and delocalized after 20 fs and no further significant transfer of electronic population seems to occur up to 100 fs propagation time.

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

On the truncation of the number of excited states in density functional theory sum-over-states calculations of indirect spin spin coupling constants

It is investigated, whether the number of excited (pseudo)states can be truncated in the sum-over-states expression for indirect spin-spin coupling constants (SSCCs), which is used in the Contributions from Localized Orbitals within the Polarization Propagator Approach and Inner Projections of the Polarization Propagator (IPPP-CLOPPA) approach to analyzing SSCCs in terms of localized orbitals. As a test set we have studied the nine simple compounds, CH{sub 4}, NH{sub 3}, H{sub 2}O, SiH{sub 4}, PH{sub 3}, SH{sub 2}, C{sub 2}H{sub 2}, C{sub 2}H{sub 4}, and C{sub 2}H{sub 6}. The excited (pseudo)states were obtained from time-dependent density functional theory (TD-DFT) calculations with the B3LYP exchange-correlation functional and the specialized core-property basis set, aug-cc-pVTZ-J. We investigated both how the calculated coupling constants depend on the number of (pseudo)states included in the summation and whether the summation can be truncated in a systematic way at a smaller number of states and extrapolated to the total number of (pseudo)states for the given one-electron basis set. We find that this is possible and that for some of the couplings it is sufficient to include only about 30% of the excited (pseudo)states.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Reaction paths of phosphine dissociation on silicon (001)

Using density functional theory and guided by extensive scanning tunneling microscopy (STM) image data, we formulate a detailed mechanism for the dissociation of phosphine (PH{sub 3}) molecules on the Si(001) surface at room temperature. We distinguish between a main sequence of dissociation that involves PH{sub 2}+H, PH+2H, and P+3H as observable intermediates, and a secondary sequence that gives rise to PH+H, P+2H, and isolated phosphorus adatoms. The latter sequence arises because PH{sub 2} fragments are surprisingly mobile on Si(001) and can diffuse away from the third hydrogen atom that makes up the PH{sub 3} stoichiometry. Our calculated activation energies describe the competition between diffusion and dissociation pathways and hence provide a comprehensive model for the numerous adsorbate species observed in STM experiments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Water clouds in Y dwarfs and exoplanets

The formation of clouds affects brown dwarf and planetary atmospheres of nearly all effective temperatures. Iron and silicate condense in L dwarf atmospheres and dissipate at the L/T transition. Minor species such as sulfides and salts condense in mid- to late T dwarfs. For brown dwarfs below T {sub eff} ∼ 450 K, water condenses in the upper atmosphere to form ice clouds. Currently, over a dozen objects in this temperature range have been discovered, and few previous theoretical studies have addressed the effect of water clouds on brown dwarf or exoplanetary spectra. Here we present a new grid of models that include the effect of water cloud opacity. We find that they become optically thick in objects below T {sub eff} ∼ 350-375 K. Unlike refractory cloud materials, water-ice particles are significantly nongray absorbers; they predominantly scatter at optical wavelengths through the J band and absorb in the infrared with prominent features, the strongest of which is at 2.8 μm. H{sub 2}O, NH{sub 3}, CH{sub 4}, and H{sub 2} CIA are dominant opacity sources; less abundant species may also be detectable, including the alkalis, H{sub 2}S, and PH{sub 3}. PH{sub 3}, which has been detected in Jupiter, is expected to have a strong signature in the mid-infrared at 4.3 μm in Y dwarfs around T {sub eff} = 450 K; if disequilibrium chemistry increases the abundance of PH{sub 3}, it may be detectable over a wider effective temperature range than models predict. We show results incorporating disequilibrium nitrogen and carbon chemistry and predict signatures of low gravity in planetary mass objects. Finally, we make predictions for the observability of Y dwarfs and planets with existing and future instruments, including the James Webb Space Telescope and Gemini Planet Imager.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Optimization of a plasma immersion ion implantation process for shallow junctions in silicon

A plasma immersion ion implantation (PIII) process has been developed for realizing shallow doping profiles of phosphorus and boron in silicon using an in-house built dual chamber cluster tool. High Si etch rates observed in a 5% PH{sub 3} in H{sub 2} plasma have been ascribed to high concentration of H(α) radicals. Therefore, subsequent work was carried out with 5% PH{sub 3} in He, leading to much smaller etch rates. By optical emission spectroscopy, the radical species H(α), PH*{sub 2}, and PH* have been identified. The concentration of all three species increased with pressure. Also, ion concentrations increased with pressure as evidenced by Langmuir data, with a maximum occurring at 0.12 mbar. The duty cycle of pulsed DC bias has a significant bearing on both the implantation and the etching process as it controls the leakage of positive charge collected at the surface of the silicon wafer during pulse on-time generated primarily due to secondary electron emission. The P implant process was optimized for a duty cycle of 10% or less at a pressure of 0.12 mbar with implant times as low as 30 s. Secondary ion mass spectroscopy showed a P dopant depth of 145 nm after rapid thermal annealing (RTA) at 950 °C for 5 s, resulting in a sheet resistance of 77 Ω/◻. Si n{sup +}/p diodes fabricated with phosphorus implantation using optimized PIII and RTA conditions exhibit J{sub on}/J{sub off} > 10{sup 6} with an ideality factor of nearly 1.2. Using similar conditions, shallow doping profiles of B in silicon have also been realized.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Synthesis and characterization of large-grain solid-phase crystallized polycrystalline silicon thin films

n-type polycrystalline silicon (poly-Si) films with very large grains, exceeding 30 μm in width, and with high Hall mobility of about 71.5 cm{sup 2}/V s are successfully prepared by the solid-phase crystallization technique on glass through the control of the PH{sub 3} (2% in H{sub 2})/SiH{sub 4} gas flow ratio. The effect of this gas flow ratio on the electronic and structural quality of the n-type poly-Si thin film is systematically investigated using Hall effect measurements, Raman microscopy, and electron backscatter diffraction (EBSD), respectively. The poly-Si grains are found to be randomly oriented, whereby the average area weighted grain size is found to increase from 4.3 to 18 μm with increase of the PH{sub 3} (2% in H{sub 2})/SiH{sub 4} gas flow ratio. The stress in the poly-Si thin films is found to increase above 900 MPa when the PH{sub 3} (2% in H{sub 2})/SiH{sub 4} gas flow ratio is increased from 0.025 to 0.45. Finally, high-resolution transmission electron microscopy, high angle annular dark field-scanning tunneling microscopy, and EBSD are used to identify the defects and dislocations caused by the stress in the fabricated poly-Si films.

36 MATERIALS SCIENCE↗