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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 OSTI2011

EVALUATION OF THE IMPACT OF THE DEFENSE WASTE PROCESSING FACILITY (DWPF) LABORATORY GERMANIUM OXIDE USE ON RECYCLE TRANSFERS TO THE H-TANK FARM

When processing High Level Waste (HLW) glass, the Defense Waste Processing Facility (DWPF) cannot wait until the melt or waste glass has been made to assess its acceptability, since by then no further changes to the glass composition and acceptability are possible. Therefore, the acceptability decision is made on the upstream feed stream, rather than on the downstream melt or glass product. This strategy is known as 'feed forward statistical process control.' The DWPF depends on chemical analysis of the feed streams from the Sludge Receipt and Adjustment Tank (SRAT) and the Slurry Mix Evaporator (SME) where the frit plus adjusted sludge from the SRAT are mixed. The SME is the last vessel in which any chemical adjustments or frit additions can be made. Once the analyses of the SME product are deemed acceptable, the SME product is transferred to the Melter Feed Tank (MFT) and onto the melter. The SRAT and SME analyses have been analyzed by the DWPF laboratory using a 'Cold Chemical' method but this dissolution did not adequately dissolve all the elemental components. A new dissolution method which fuses the SRAT or SME product with cesium nitrate (CsNO{sub 3}), germanium (IV) oxide (GeO{sub 2}) and cesium carbonate (Cs{sub 2}CO{sub 3}) into a cesium germanate glass at 1050 C in platinum crucibles has been developed. Once the germanium glass is formed in that fusion, it is readily dissolved by concentrated nitric acid (about 1M) to solubilize all the elements in the SRAT and/or SME product for elemental analysis. When the chemical analyses are completed the acidic cesium-germanate solution is transferred from the DWPF analytic laboratory to the Recycle Collection Tank (RCT) where the pH is increased to {approx}12 M to be released back to the tank farm and the 2H evaporator. Therefore, about 2.5 kg/yr of GeO{sub 2}/year will be diluted into 1.4 million gallons of recycle. This 2.5 kg/yr of GeO{sub 2} may increase to 4 kg/yr when improvements are implemented to attain an annual canister production goal of 400 canisters. Since no Waste Acceptance Criteria (WAC) exists for germanium in the Tank Farm, the Effluent Treatment Project, or the Saltstone Production Facility, DWPF has requested an evaluation of the fate of the germanium in the caustic environment of the RCT, the 2H evaporator, and the tank farm. This report evaluates the effect of the addition of germanium to the tank farm based on: (1) the large dilution of Ge in the RCT and tank farm; (2) the solubility of germanium in caustic solutions (pH 12-13); (3) the potential of germanium to precipitate as germanium sodalites in the 2H Evaporator; and (4) the potential of germanium compounds to precipitate in the evaporator feed tank. This study concludes that the impacts of transferring up to 4 kg/yr germanium to the RCT (and subsequently the 2H evaporator feed tank and the 2H evaporator) results in <2 ppm per year (1.834 mg/L) which is the maximum instantaneous concentration expected from DWPF. This concentration is insignificant as most sodium germanates are soluble at the high pH of the feed tank and evaporator solutions. Even if sodium aluminosilicates form in the 2H evaporator, the Ge will likely substitute for some small amount of the Si in these structures and will be insignificant. It is recommended that the DWPF continue with their strategy to add germanium as a laboratory chemical to Attachment 8.2 of the DWPF Waste Compliance Plan (WCP).

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2013

Oligogermanes as molecular precursors for germanium(0) nanoparticles: Size control and size-dependent fluorescence

Graphical abstract: Catenated germanium compounds are employed as molecular precursors for germanium(0) nanoparticles. The size of the nanoparticles, and their fluorescence spectra, depend on the number of catenated germanium atoms present in the precursor. - Highlights: • We have used oligogermanes for the size-specific synthesis of germanium(0) nanoparticles. • The size of the nanomaterials obtained depends directly on the degree of catenation present in the oligogermane precursor. • The nanoparticles are shown to exhibit size-dependent fluorescence. • Oligogermanes will function as useful precursors for the synthesis of a variety of nanomaterials. - Abstract: Germanium nanoparticles were synthesized in solution from novel oligogermane molecular precursors. The size of the nanoparticles obtained is directly related to the number of catenated germanium atoms present in the oligogermane precursor and the nanoparticles exhibit size-dependent fluorescence. The germanium nanoparticles were also characterized by TEM, powder XRD, FTIR, EDS and XPS methods. This method appears to be a promising new route for the synthesis of germanium nanoparticles since the size of the materials obtained can be controlled by the choice of the oligogermane used as the precursor.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Capacitance scaling law for diatomic molecules and prediction of their electron detachment energies

The variation or 'scaling' of the quantum capacitances is explored for 45 diatomic molecules as a function of their dimensions. Scaling trends in the capacitances of these diatomic molecules dictate an 'atoms-in-molecules' view of their valence energetics. That is, experimentally derived quantum capacitances for both homonuclear and heteronuclear diatomic molecules scale linearly with the average of the mean radii for the outermost orbitals of their component atoms. This is in accord with Maxwell's law for classical capacitors formed from two conducting atom-sized spheres in tangential contact. However, the scaling behavior for the molecules has some nonclassical features. Notably, the quantum capacitances extrapolate to nonzero values at zero dimensions. Radius-capacitance points of the homonuclear diatomics lie primarily along five scaling lines, with each determined by points for molecules composed of atoms with the same atomic symmetry (i.e., atoms from the same column in the periodic table). Five scaling lines for heteronuclear diatomics each are determined by points for molecules of the same or similar molecular symmetries. The molecules' quantum capacitances are calculated from their ionization potentials (IPs) and electron affinities (EAs). Thus, equations or laws for the scaling lines impose mutual consistency conditions among these electron detachment energies for different diatomics of similar symmetries. By taking advantage of this, the linear quantum capacitance scaling laws and ab initio atomic mean radii are used to predict IPs for two diatomics with known EAs (Ga{sub 2} and SeO), but for which there is no standard value of the IP. Similarly, the laws are used to predict EAs that were unknown or uncertain for several diatomics (Li{sub 2}, LiF, CSe, PN, BF, BCl, SiO, GeO, NCl, CaO, SrO, and BaO) with known IPs.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Mechanisms of edge-dislocation formation in strained films of zinc blende and diamond cubic semiconductors epitaxially grown on (001)-oriented substrates

Ninety degree edge misfit dislocations (MDs) are 'sessile' dislocations; such dislocations, however, were found in large amounts in relaxed films. The commonly accepted formation mechanism of such dislocations is an interaction of two complementary 60 deg. dislocations with appropriate Burger's vectors, for example: a/2[101] + a/2 [011] = a/2 [110]. In the present study, four possible types of interaction were analyzed: (i) random meeting of two complementary MDs; (ii) crossing of two complementary 60 deg. MDs in the vicinity of film-substrate interface in systems grown on substrates misoriented from exact (001) orientation; (iii) formation of edge MDs during cross-slipping of a secondary MD; and (iv) induced nucleation of a secondary complementary 60 deg. MD. Examples of discussed interactions are given. Contrary to the widespread opinion that edge MDs in GeSi and InGaAs films grown by MBE on Si and GaAs substrates predominantly form under elastic strains greater than 2% and at the final stage of plastic relaxation, in the present study, we show that such dislocations may also form at an early stage of plastic relaxation in films with less-than-1% lattice misfit with substrate. A necessary condition for that is a sufficient amount of 60 deg. dislocations available in the system by the moment the strained film starts growing. Dislocations (60 deg. ) can be introduced into the system using a preliminarily grown, partially or fully relaxed buffer layer. This layer serves as a source of threading dislocations for the next growing layer that favor the formation of paired complementary MDs and their 'reagents', edge MDs, at the interface with growing film.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Strain characterization of fin-shaped field effect transistors with SiGe stressors using nanobeam electron diffraction

This study undertook strain analysis on fin-shaped field effect transistor structures with epitaxial Si{sub 1−x}Ge{sub x} stressors, using nano-beam electron diffraction and finite elements method. Combining the two methods disclosed dynamic strain distribution in the source/drain and channel region of the fin structure, and the effects of dimensional factors such as the stressor thickness and fin width, offering valuable information for device design.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Intermixing between HfO{sub 2} and GeO{sub 2} films deposited on Ge(001) and Si(001): Role of the substrate

Thermally driven atomic transport in HfO{sub 2}/GeO{sub 2}/substrate structures on Ge(001) and Si(001) was investigated in N{sub 2} ambient as function of annealing temperature and time. As-deposited stacks showed no detectable intermixing and no instabilities were observed on Si. On Ge, loss of O and Ge was detected in all annealed samples, presumably due to evolution of GeO from the GeO{sub 2}/Ge interface. In addition, hafnium germanate is formed at 600 deg. C. Our data indicate that at 500 deg. C and above HfO{sub 2}/GeO{sub 2} stacks are stable only if isolated from the Ge substrate.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Enhanced Ge/Si(001) island areal density and self-organization due to P predeposition

The predeposition of P, with coverages {theta}{sub P} ranging from 0 to 1 ML, on Si(001) significantly increases both the areal density and spatial self-organization of Ge islands grown by gas-source molecular beam epitaxy from hydride precursors. The Ge island density {rho}{sub Ge} initially increases with {theta}{sub P}, reaching a maximum of 1.4 x 10{sup 10} cm{sup -2} at {theta}{sub P} = 0.7 ML, a factor of four times higher than on bare Si(001) under the same deposition conditions, before decreasing at higher P coverages. The increase in {rho}{sub Ge}({theta}{sub P}) is due to a corresponding decrease in Ge adatom mean free paths resulting from passivation of surface dangling bonds by adsorbed pentavalent P atoms which, in addition, leads to surface roughening and, therefore, higher Ge coverages at constant Ge{sub 2}H{sub 6} dose. As {theta}{sub P} (and hence, {rho}{sub Ge}) increases, so does the degree of Ge island ordering along <100> directions due to the anisotropic strain field surrounding individual islands. Similar results are obtained for Ge island growth on P-doped Si(001) layers where strong P surface segregation provides partial monolayer coverage prior to Ge deposition.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Confocal Raman microscopy of self-assembled GeSi/Si(001) Islands

The method of confocal Raman microscopy is used for the first time to study the spatial distribution of elemental composition and elastic strains in self-assembled GexSi{sub 1-x}/Si(001) islands grown by the method of sublimation molecular-beam epitaxy in the GeH{sub 4} ambient. The lines related to vibrational modes Si-Si, Ge-Ge, and Si-Ge are identified in the Raman spectra measured in the regions with dimensions <100 nm on the surface of the samples. The spatial distribution of the Ge atomic fraction x in the Ge{sub x}Si{sub 1-x} alloy and of the elastic strain {epsilon} (averaged in depth over the island layer) have been calculated from the maps of the Raman shifts of the corresponding lines over the sample surface. The dependences of x and {epsilon} on the islands' growth temperature and on the nominal thickness of the deposited Ge layer have been studied.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Energy upconversion in holmium doped lead-germano-tellurite glass

Holmium doped lead-germano-tellurite glass was prepared by the melt quenching technique. The Judd-Ofelt intensity parameters were estimated as {Omega}{sub 2}=7.6x10{sup -20}, {Omega}{sub 4}=12.9x10{sup -20}, and {Omega}{sub 6}=2.5x10{sup -20} cm{sup 2}. Radiative transition probabilities and lifetimes were also determined for some of the levels. Room temperature upconversion emissions have been observed from Ho{sup 3+} at 497 nm under 532 nm laser excitation, and at 557 and 668 nm under 762 nm laser excitation. The upconversion emission mechanisms were found to be due to a step wise excitation process. Upconversion emission intensity enhanced in a heat treated glass.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Blue Emission Peak of GeO{sub 2} Particles Grown Using Thermal Evaporation

In this paper we report a simple thermal evaporation technique (horizontal tube furnace) to grow large quantities of GeO{sub 2} particles with diameters ranging from tens of nanometer to 500 nm on n-type (100) Si substrate free of catalyst. The particles were grown at temperature about 1000 degree sign C for 2 hrs and characterized by scanning electron microscopy (SEM), X-Ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and photoluminescence (PL) spectroscopy. The photoluminescence spectrum reveals several emission peaks around 400 nm at room temperature. Raman measurement also measured at room temperature for this GeO{sub 2} particles.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2010

Effect of different chemical treatments of surface on the height of Al-p-SiGe and Au-n-SiGe barriers

The effect of different chemical treatments on the properties of Au-n-SiGe and Al-p-SiGe Schottky barriers has been investigated. Etching under different conditions was used to prepare surfaces with different densities of surface states (D{sub ss}). It is shown that the barrier height in the structures under study correlates with the D{sub ss} value and germanium content in the Si{sub 1-x}Ge{sub x} alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Ge/SiGe quantum wells on Si(111): Growth, structural, and optical properties

The epitaxial growth of Ge/Si{sub 0.15}Ge{sub 0.85} multiple quantum wells (MQWs) on Si(111) substrates is demonstrated. A 3 μm thick reverse, double-step virtual substrate with a final composition of Si{sub 0.10}Ge{sub 0.90} has been employed. High resolution XRD, TEM, AFM and defect etching analysis has been used for the study of the structural properties of the buffer and of the QWs. The QW stack is characterized by a threading dislocation density of about 3 × 10{sup 7 }cm{sup −2} and an interdiffusion layer at the well/barrier interface of 2.1 nm. The quantum confined energy levels of this system have been calculated using the k·p and effective mass approximation methods. The Ge/Si{sub 0.15}Ge{sub 0.85} MQWs have been characterized through absorption and photoluminescence measurements. The optical spectra have been compared with those of Ge/Si{sub 0.15}Ge{sub 0.85} QWs grown on Si(001) through a thick graded virtual substrate.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

On the Calculation of the Debye Temperature and Crystal–Liquid Phase Transition Temperature of a Binary Substitution Alloy

A method of estimating the interatomic pair interaction potential parameters for a binary substitution alloy with consideration for the deviation of its lattice parameter from the Vegard law is proposed. This method is used as a basis to calculate the Debye temperature and Grüneisen parameters of a SiGe alloy. It is shown that all these function nonlinearly variate with a change in the germanium concentration. Based on this technique and Lindemann's melting criterion, a method for calculating the liquidus and solidus temperatures of a disordered substitution alloy is proposed. The method is tested on the SiGe alloy and demonstrates good agreement with experimental data. It is shown that when the size of a nanocrystal of a solid substitution solution decreases, the difference between the liquidus and solidus temperatures decreases the more, the more noticeably the nanocrystal shape is deflected from the most energetically optimal shape.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2010

Differential method of analysis of luminescence spectra of semiconductors

A method for analyzing the luminescence spectra of semiconductors is suggested. The method is based on differentiation of the spectra. The potentialities of the method are demonstrated for luminescence in the region of the fundamental absorption edge of Si and SiGe alloy single crystals. The method is superior in accuracy to previously known luminescence methods of determining the band gap of indirect-gap semiconductors and practically insensitive to different conditions of outputting radiation from the sample.

36 MATERIALS SCIENCE↗
DOE OSTI2010

1D X-ray Beam Compressing Monochromators

A total beam compression of 5 and 10 corresponding to the asymmetry angles of 9 deg. and 12 deg. is achieved with V-5 and V-10 monochromators, respectively, in standard single crystal pure germanium (220) X-ray beam compressing (V-shaped) monochromators for CuKalpha{sub 1} radiation. A higher 1D compression of X-ray beam is possible using larger angles of asymmetry, however it is achieved at the expense of the total intensity, which is decreased due to the refraction effect. To increase the monochromator intensity, several ways are considered both theoretically and experimentally. Linearly graded germanium rich Ge{sub x}Si{sub (1-x)} single crystal was used to prepare a V-21 single crystal monochromator with 15 deg. asymmetry angles (compression factor of 21). Its temperature gradient version is discussed for CuKalpha{sub 1} radiation. X-ray diffraction measurements on the graded GeSi monochromator showed more than 3-times higher intensity at the output compared with that of a pure Ge monochromator.

36 MATERIALS SCIENCE↗
DOE OSTI2010

High-Angular-Resolution Microbeam X-Ray Diffraction with CCD Detector

We have introduced a CCD-type two-dimensional X-ray detector for a microbeam X-ray diffraction system using synchrotron radiation, so that we can measure local reciprocal space maps (RSM) of samples rapidly. A local RSM of a strain-relaxed SiGe 004 grown on a Si (001) substrate was measured in higher-angular-resolution and faster than a conventional way. The measurement was achieved in 1 h 40 min. with the 2theta resolution of 80 murad and the spatial resolution of 1.4(h)x0.5(v) {mu}m{sup 2}. The introduction of the CCD enabled us to measure RSMs at many points in a sample, that is, the distribution of strain fields and lattice tilts can be revealed in high-angular- and high-spatial-resolution.

36 MATERIALS SCIENCE↗
DOE OSTI2011

One-Step Growth of Ge doped ZnO Tubes by Thermal Evaporation

In this paper we report a simple thermal evaporation technique (horizontal tube furnace) to grow the bulk-quantity of germanium (Ge) doped zinc oxide (ZnO) tubes on the Si substrate by using one-step thermal evaporation of a mixed powder of Ge and ZnO. The microstructure and optical properties of the Ge doped ZnO tubes have been investigated by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction, photoluminescence (PL) spectrometer and Raman spectrometer. The investigation of structural properties indicated that the structures consist of bulk quantities of cylindrical rod and tube with diameter around 1micron. EDX reveals that the tube structures have Ge, Zn and O{sub 2} compositions and XRD analysis indicated the product is mainly composed of Ge, zinc germanium oxide (Zn{sub 2}GeO{sub 4}) and small proportion of ZnO. Room temperature photoluminescence (PL) spectrum shows broad emission peaks around 400 nm, opening up a route to potential applications in future optoelectronic devices. Raman measurement also measured at room temperature for these tubes.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Controlled drive-in and precipitation of hydrogen during plasma hydrogenation of silicon using a thin compressively strained SiGe layer

We have quantitatively studied by transmission electron microscopy the growth kinetics of platelets formed during the continuous hydrogenation of a Si substrate/SiGe/Si heterostructure. We have evidenced and explained the massive transfer of hydrogen from a population of platelets initially generated in the upper Si layer by plasma hydrogenation towards a population of larger platelets located in the SiGe layer. We demonstrate that this type of process can be used not only to precisely localize the micro-cracks, then the fracture line at a given depth but also to 'clean' the top layer from pre-existing defects.

36 MATERIALS SCIENCE↗