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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 1,693 records · Page 94
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Atmospheric Pressure Plasma CVD of Amorphous Hydrogenated Silicon Carbonitride (a-SiCN:H) Films Using Triethylsilane and Nitrogen

Amorphous hydrogenated silicon carbonitride (a-SiCN:H) thin films are synthesized by atmospheric pressure plasma enhanced chemical vapor (AP-PECVD) deposition using the Surfx Atomflow{trademark} 250D APPJ source with triethylsilane (HSiEt{sub 3}, TES) and nitrogen as the precursor and the reactive gases, respectively. The effect of the substrate temperature (T{sub s}) on the growth characteristics and the properties of a-SiCN:H films was evaluated. The properties of the films were investigated via scanning electron microscopy (SEM), atomic force microscopy (AFM) for surface morphological analyses, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) for chemical and compositional analyses; spectroscopic ellipsometry for optical properties and thickness determination and nanoindentation to determine the mechanical properties of the a-SiCN:H films. Films deposited at low T{sub s} depict organic like features, while the films deposited at high T{sub s} depict ceramic like features. FTIR and XPS studies reveal that an increases in T{sub s} helps in the elimination of organic moieties and incorporation of nitrogen in the film. Films deposited at T{sub s} of 425 C have an index of refraction (n) of 1.84 and hardness (H) of 14.8 GPa. A decrease in the deposition rate between T{sub s} of 25 and 250 C and increase in deposition rate between T{sub s} of 250 and 425 C indicate that the growth of a-SiCN:H films at lower T{sub s} are surface reaction controlled, while at high temperatures film growth is mass-transport controlled. Based on the experimental results, a potential route for film growth is proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Measurement of Absorption Coefficient of Paraformaldehyde and Metaldehyde with Terahertz Spectroscopy

The characteristic absorption spectra of paraformaldehyde and metaldehyde in the terahertz frequency region are obtained by terahertz time-domain spectroscopy (THz-TDS). In order to reduce the absorption of terahertz (THz) wave by water vapor in the air and the background noise, the measurement system was filled with dry air and the measurements were conducted at the temperature of 24°C. Meanwhile, the humidity was controlled within 10% RH. The THz frequency domain spectra of samples and their references from 0 to 2.5 THz were analyzed via Fourier transform. The refractive index and absorption coefficients of the two aldehydes were calculated by the model formulas. From 0.1 to 2.5 THz, there appear two weak absorption peaks at 1.20 and 1.66 THz in the absorption spectra of paraformaldehyde. Only one distinct absorption peak emerges at 1.83 THz for metaldehyde. There are significant differences between the terahertz absorption coefficients of paraformaldehyde and metaldehyde, which can be used as 'fingerprints' to identify these substances. Furthermore, the relationship between the average absorption coefficients and mass concentrations was investigated and the average absorption coefficient–mass concentration diagrams of paraformaldehyde and metaldehyde were shown. For paraformaldehyde, there is a linear relationship between the average absorption coefficient and the natural logarithm of mass concentration. For metaldehyde, there exists a simpler linear relationship between the average absorption coefficient and the mass concentration. Because of the characteristics of THz absorption of paraformaldehyde and metaldehyde, the THz-TDS can be applied to the qualitative and quantitative detection of the two aldehydes to reduce the unpredictable hazards due to these substances.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Accounting for the Complex Surface Structure in Ellipsometric Studies of the Effects of Magnetron Sputtering Modes on the Growth and Optical Properties of In{sub 2}O{sub 3} Films

The efficiency of invoking additional information on optical transmission in solving the inverse problem of ellipsometry by a minimization method is demonstrated in practice for In{sub 2}O{sub 3} fi doped and nondoped with Sn on Al{sub 2}O{sub 3} (012) substrates. This approach allows the thickness and refractive index of thin films with rough surfaces to be uniquely determined. Solutions of the inverse problem in the framework of one-, two-, and multilayer models are compared. The last provides the best description of the experimental data and the correct parameters of the samples. The dependences of the investigated properties of films produced with different magnetron sputtering modes are found using the above methods and models and do not contradict general concepts about the film formation by this material.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Verification of an Algorithm for Processing Data from Multifrequency Lidar Sensing of Aerosols

We consider an algorithm for processing lidar signals, which for a lidar path with constant qualitative aerosol characteristics (particle size distribution in each aerosol mode, complex refractive index of the particles) lets us obtain a concentration profile for the fine aerosol component without using additional a priori information. The algorithm was verified based on lidar data from the Institute of Physics (National Academy of Sciences of Belarus). The vertical volume concentration profile for fine particles obtained by our algorithm is quite consistent with the results of its independent retrieval, based on integrated processing of lidar and sun photometer data.

42 ENGINEERING↗
DOE OSTI2018

Optical Properties and Electronic Characteristics of Cerium in the Condensed State

The results of investigating optical properties of metallic cerium in the liquid and solid fi lm state are presented. Optical constants were measured by the ellipsometric Beattie method in the range of 0.42–2.6 μm at ambient temperature. Based on the measured refractive indices and the absorption coefficients, spectra of light conductivity σ, reflectivity R, and characteristic loss function Im ε{sup –1} were calculated. Based on experimental measurements in the IR region, electronic characteristics of liquid cerium and its polycrystalline film and their correlation with electrical conductivity have been determined.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Optical Characteristics of Zinc Oxide Films on Glass Substrates

An algorithm is developed for solving the inverse problem of multiangular spectrophotometry of a layer on a planeparallel substrate of fi nite thickness using s- and p-polarized waves. It allows the dispersive properties of the layer and substrate to be studied both far from and in the vicinity of the resonant wavelengths. The dispersive properties of layers of pure and Al-doped ZnO on glass substrates are investigated using it. It is shown that doping shifts the absorption band maximum to shorter wavelength and decreases the refractive index of the material. The applicability limits of known approximate expressions for determining the spectral dependence of the absorption coeffi cient of a layer from spectrophotometric data are estimated.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

A New Candidate Laser Dye Based 1,4-Bis[β-(2-Naphthothiazolyle)Vinyl]Benzene. Spectroscopic Behavior, Laser Parameters and Excitation Energy Transfer

A new candidate laser dye based 1,4-bis[β-(2-naphthothisolyl) vinyl] benzene (BNTVB) were prepared, and characterized in various organic solvents. The center polarity is less sensitive than electronic absorption. A red shift was noticed in the fluorescence spectra (ca. 40 nm) with increment in the solvent’s polarity, this means that BNTVB’s polarity appreciates upon excitation. The dipole moment of ground state (μ{sub g}) and the excited singlet state dipole moment (μ{sub e}) are determined from Kawski – Chamma and Bakshiev–Viallet equations using the disparity of Stokes shift with solvent polarity function of ε (dielectric constant) and n (refractive index) of the solvent. The result was found to be 0.019D and 5.13D for ground and exited state, in succession. DFT/TD-DFT manners were used to understand the electronic structures and geometric of BNTVB in other solvents. The experimental and theoretical results showed a good agreement. The photochemical quantum yield (Ф{sub c}) of BNTVB was calculated in variable organic reagents such as Dioxane, CHCl{sub 3}, EtOH and MeOH at room temperature. The values of φ{sub c} were calculated as 2.3 × 10{sup −4}, 3.3 × 10{sup −3}, 9.7 × 10{sup −5} and 6.2 × 10{sup −5} in Dioxane, CHCl{sub 3}, EtOH and MeOH, respectively. The dye solutions (2 × 10{sup −4} M) in DMF, MeOH and EtOH give laser emission in the blue-green region. The green zone is excited by nitrogen pulse 337.1 nm. The tuning range, gain coefficient (α) and cross – section emission (σ{sub e}) of laser were also estimated. Excitation energy transfer from BNTVB to rhodamine-6G (R6G) and N,N-bis(2,6-dimethyphenyl)-3,4:9,10-perylenebis-(dicarboximide) (BDP) was also studied in EtOH to increase the laser emission output from R6G and BDP when excited by nitrogen laser. The dye-transfer power laser system (ETDL) obeys the Foster Power Transmission (FERT) mechanism with a critical transmission distance, R{sub o} of 40 and 32 A and k{sub ET} equals 2.6 × 10{sup 13} and 1.06 × 10{sup 13} M{sup −1} s{sup −1} for BNTVB / R6G and BNTVB / BDP pair, respectively.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Fluorescence and Nonlinear Optical Properties of Alizarin Red S in Solvents and Droplet

The enhancement of the nonlinear properties of materials is an interesting topic since it has many applications in optical devices and medicines. The Z-scan technique was used to study the values of the two-photon absorption (β), second-order molecular hyperpolarizability (γ{sub R}), third-order susceptibility (χ{sub R}), and nonlinear refractive index (n{sub 2}) of Alizarin Red S in different media using a continuous-wave diode-pump laser radiation at 532 nm. For Alizarin Red S in a droplet, the β, n{sub 2}, χ{sub R,} and γ{sub R} were estimated at the order of 10{sup −7} cm{sup 2}/W and 10{sup −12} cm/W, 10{sup −3} m{sup 3} W{sup −1} s{sup −1} and 10{sup −24} m{sup 6} W{sup −1} s{sup −1}, respectively. The results indicated that the values of β and n{sub 2} reduced, whereas the values of χ{sub R} and γ{sub R} were enhanced when the solvent was changed from droplet to water, DMF, and dimethyl sulfoxide due to the change in the solvent’s dielectric constant (ε). Moreover, the values of β were enhanced by an increase in the concentration of the surfactant in the aqueous solution. The absorption spectra of Alizarin Red S in the aqueous solution was observed at 428 nm, and a few red shifts in the absorption spectra were observed with a reduction in the dielectric constant of the medium. The same effect was observed in the absorption spectra of Alizarin Red S in the droplet when the bulk dielectric constant reduced. The dielectric constant can affect the fluorescence spectra of Alizarin Red S when the solution is changed from water to dimethyl sulfoxide. The dipole moments of Alizarin Red S in the different media were studied using the quantum perturbation theory.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

RF Plasma Polymerization of Orange Oil and Characterization of the Polymer Thin Films

The present study describes an environmentally friendly approach to fabricate hydrocarbon-rich polymer thin films from a bio-renewable precursor, orange oil, cold extracted from orange peels using radio frequency plasma polymerization. The polymer thin films fabricated at different RF power level (10–75 W) were characterized with variable angle spectroscopic ellipsometry, UV–visible spectroscopy, Fourier transform infrared spectroscopy and atomic force microscopy. Optical characterization showed that independent of deposition power films exhibited good transparency (~ 90%) in the visible region and a refractive index of 1.55 at 500 nm. The optical band gap measured around 3.60 eV and falls within the insulating region. The atomic force microscopic images revealed that the surface is pinhole-free in nature and smooth at nanoscale, with average surface roughness dependent on the deposition power. Film hardness increased from 0.50 to 0.78 GPa as applied power increased from 10 to 75 W.

36 MATERIALS SCIENCE↗
DOE OSTI2017

First-Principle Investigation of V and Cr Doping on the Dilute Magnetic Semiconducting Properties of Rutile SnO{sub 2}: a Modified Becke-Johnson (TB-mBJ) Exchange Potential Study

Theoretical investigations on rutile SnO{sub 2} doped with V and Cr were performed by using recently implemented Tran and Blaha’s modified Becke-Johnson exchange potential model (TB-mBJ) based on density functional theory. The electronic, magnetic, dielectric and optical properties of V and Cr-doped tin oxide have been calculated by full-potential linearized augmented plane wave method (FP-LAPW) by WIEN2k code. The present works demonstrate accurate prediction of band structures and properties using the TB-mBJ model. The calculated values of magnetic moment, dielectric constant and refractive index of doped and undoped compounds agree well with the experimental results. The TB-mBJ model is a direct method without using empirical corrections and hence, the furnished data are useful in material modelling for spintronics applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Structural, Electronic, Magnetic, and Optical Properties of Half-Heusler Alloys RuMnZ (Z = P, As): a First-Principle Study

Half-Heusler alloys RuMnZ (Z = P, As ) are studied in the framework of Density Functional Theory (DFT). Structural, electronic, magnetic, and optical properties are calculated and analyzed using the WIEN2k simulation code. All the calculations are done using the full potential linearized augmented plane wave (FP-LAPW) method. Equilibrium lattice parameters are found to be in the range 5.5–5.6 Å. Band gaps of the compounds and density of states (DoS) analysis reveal that the minority spin-down states are semi-conducting while the majority spin-up states are conducting confirming the half-metallic nature of the compounds. Hence, at Fermi level, states are 100 % polarized. The value of the total magnetic moment is found to be 2, i.e., M{sub Tot} = 2μ{sub B}. Several optical properties, including dielectric function, reflectivity, refractive index, conductivity, and absorption coefficient are calculated as well. It is revealed from the imaginary part of the dielectric function that the compounds are optically metallic.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

A First Principle Study of Half-Heusler Compounds CrTiZ (Z = P, As)

Half-Heusler compounds CrTiZ (Z = P, As) are studied in the framework of Density Functional Theory (DFT). Structural, mechanical, elastic, electronic, magnetic, and optical properties are derived using first principles. The full-potential linearized augmented plane wave (FP-LAPW) method is used for these investigations as implemented in the WIEN2k simulation package. We have found that the equilibrium lattice parameters are in the range 5.5–5.9 Å. Small band gaps of 0.5–0.6 eV in the minority spin-down states are observed. On the other hand, in the majority spin-up states, there is no band gap. Hence, the compounds are of half-metallic nature, having 100 % polarization at Fermi level. Comparatively, a higher total magnetic moment of ∼ 3μ{sub B} is found for both the compounds. Furthermore, optical properties are derived using dielectric function. Reflectivity, refractive index, conductivity and absorption coefficient are calculated. It is revealed from the imaginary part of the dielectric function that the compounds are optically metallic.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Structural, Electronic, Magnetic and Optical Investigations of Half-Heusler Compounds YZSb (Z = Cr, Mn): FP-LAPW Method

Half-Heusler compounds YZSb (Z = Cr, Mn) are theoretically explored in the framework of density functional theory (DFT). We have investigated a number of different properties with the help of the WIEN2k simulation package. Equilibrium lattice constants fall in the range 6.0–7.0 Å for both compounds. Elastic properties are also studied and it is found that the compound YCrSb is of brittle and YMnSb is of ductile nature as indicated by a number of parameters including Cauchy pressure, Pugh’s ratio and Poisson’s ratio. Electronically, these compounds are found to be half-metals as their spin-up states are semiconducting and hence 100% spin polarized at the Fermi level while spin-down states are conducting. The total magnetic moments are equal to 4μ{sub B} and 3.15μ{sub B} for YCrSb and YMnSb, respectively. The optical properties including dielectric function, reflectivity, refractive index, conductivity and absorption coefficients are calculated and discussed. Optical characteristics of the compounds hint that they are more active in the infrared region.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

A Density Functional Theory Investigations of Half-Heusler Compounds RhVZ (Z = P, As, Sb)

We have studied the half-Heusler compounds RhVZ (Z = P, As, Sb) using Density Functional Theory (DFT). The method of the Full Potential Linearly Augmented Plane Wave (FP-LAPW) is employed in the Wien2k package for calculation of structural, elastic, mechanical, electronic, magnetic, and optical properties. Lattice constants are found in the range 5.67 − 5.80 Å. Analysis of elastic properties shows that two of the compounds namely RhVP and RhVAs are ductile while RhVSb is brittle in nature. All three compounds are half-metals as revealed from the band structures and Density of States (DoS) calculations. In all of them, spin-down channels have the small band gaps, while spin-up channels are conducting. These compounds follow the Slater-Pauling 18 (M{sub Tot} = Z{sub Tot} − 18) electron rule with the total magnetic moments in the range 1 − 2 μ{sub B}. Optical properties like dielectric function, refractive index, reflectivity, conductivity, and absorption coefficient are calculated and discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

First-Principles Study of Pressure Dependence of Optical Spectra of MnS

MnS is a semiconductor material that can be used in solar cell coatings as window/buffer material and in many other applications. The present contribution deals with the optical properties of MnS in the zinc-blende structure using ab initio calculations within the generalized gradient approximation. Features such as dielectric function, refractive index, reflectivity, optical absorption, conductivity, and electron loss function spectra have been reported and their pressure dependence has been examined and discussed. The information gathered from the present study can be useful for photovoltaic applications.

14 SOLAR ENERGY↗
DOE OSTI2018

Theoretical Investigations of Properties of New Half-Heusler Compounds NiFeZ (Z = Si, Ge)

The half-Heusler alloys NiFeZ (Z = Si, Ge) are investigated theoretically in the general framework of Density Functional Theory (DFT). We have calculated structural, mechanical, elastic, electronic, magnetic, and optical properties using WIEN2k simulation package. To incorporate the electronic exchange-correlation energy we have used the GGA+U approximation. Both the compounds are found structurally stable, however, elastic properties show that NiFeSi is ductile while NiFeGe is brittle. Electronically, the compounds are found to be half-metals with small band gaps in the spin-down channels whereas spin-up channels are conducting. The total magnetic moments for both the compounds are ≈ 2μ{sub B}. Optical properties including dielectric function, refractive index, extinction coefficient, reflectivity, conductivity, and absorption coefficient are also calculated and analyzed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Structural, Magnetic, and Optoelectronic Properties of CuMnSe{sub 2}-Chalcopyrite: DFT + U and Hybrid Functional Investigation

The work presented in this manuscript is a study of structural, magnetic, and optoelectronic properties of CuMnSe{sub 2}-chalcopyrite by FP-(L)APW + lo method using semilocal and hybrid functional. Structural properties such as cell parameters, bulk modulus, and its pressure derivative, as well as the cohesive energy and total energy of the unit cell were determined for the three magnetic phases (AFM, FM, and NM) from which it has been found that CuMnSe{sub 2}-chalcopyrite is ferromagnetic. The studied elastic properties confirm the mechanical stability of CuMnSe{sub 2} in its chalcopyrite structure. Electronic properties, such as the band gap energy, density of states, and charge density, and magnetic properties, such as Hubbard term estimation, magnetic moment, and polarization of the CuMnSe{sub 2}, have been predicted by several methods (GGA-PBEsol + U{sub eff}, GGA-PBEsol-(mBJ) + U{sub eff}, and hybrid functional). Optical properties such as the analysis of the dielectric function and the prediction of the refractive index and birefringence variations were also studied.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Fano Resonance by Means of the One-Dimensional Superconductor Photonic Crystals

In the present work, we introduce a study about the reflectance properties of a one-dimensional superconductor photonic crystal in a different manner. Our structure is designed from alternately layers of high-temperature superconducting material (BSCCO) and a conventional superconducting material (Nb) terminated by the dielectric cap layer. The investigated numerical results are essentially based on the basics of the transfer matrix method and the two-fluid model. The numerical results showed the appearance of two sharp peaks, which are referred to Fano and electromagnetic-induced reflectance resonances. Also, we demonstrate the effects of many parameters on the reflectance properties of Fano resonance and the electromagnetic-induced reflectance. The effects of the constituent layer thicknesses, the number of periods, the operating temperature, the angle of incidence, and the refractive index of the dielectric cap layer are all considered. Finally, the effects of hydrostatic pressure on the Fano and EIR resonances are studied and calculated. This structure can play an important role in optical switching devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗