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At least 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Effects of zinc salts on the structural and optical properties of acidic chemical bath deposited ZnS thin films

Graphical abstract: XRD patterns of annealed ZnS films from different zinc salts. Curves a, b, c, d correspond to the annealed ZnS–C1, ZnS–S{sub 3}, ZnS–Cl{sub 2}, ZnS–N{sub 2} thin films. Display Omitted Highlights: ► ZnS thin films were deposited using different zinc salts. ► The grain sizes of deposited ZnS thin films are about 12.5 15.5 nm. ► The band gaps of deposited ZnS thin films were in the range of 3.66–3.83 eV. -- Abstract: ZnS thin films were deposited from different zinc salts by chemical bath deposition (CBD). Structural, morphological and optical characterizations were performed using different methods such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectra. The particle sizes of as-deposited ZnS thin films were calculated to be about 12.5–15.5 nm and the crystal qualities were improved after annealed at 500 °C in Ar/H{sub 2}S (5%) atmosphere. Optical absorption measurements indicated that the band gaps of ZnS thin films were in the range of 3.66–3.83 eV and they decreased with the increasing of particle sizes. ZnCl{sub 2} was found to the best precursor due to the higher crystal quality and compact surface of deposited ZnS thin films.

36 MATERIALS SCIENCE↗
DOE OSTI2013

AgSb(S{sub x}Se{sub 1−x}){sub 2} thin films for solar cell applications

Highlights: ► AgSb(S{sub x}Se{sub 1−x}){sub 2} thin films were formed by heating Na{sub 2}SeSO{sub 3} dipped Sb{sub 2}S{sub 3}/Ag layers. ► S/Se ratio was varied by changing the dipping time in Na{sub 2}SeSO{sub 3} solution. ► Characterized the films using XRD, XPS, SEM, Optical and electrical measurements. ► Band gap engineering of 1−1.1 eV for x = 0.51 and 0.52 respectively. ► PV Glass/FTO/CdS/AgSb(S{sub x}Se{sub 1−x}){sub 2}/C were prepared showing V{sub oc} = 410 mV, J{sub sc} = 5.7 mA/cm{sup 2}. - Abstract: Silver antimony sulfoselenide (AgSb(S{sub x}Se{sub 1−x}){sub 2}) thin films were prepared by heating glass/Sb{sub 2}S{sub 3}/Ag layers after selenization using sodium selenosulphate solution. First, Sb{sub 2}S{sub 3} thin films were deposited on glass substrates from a chemical bath containing SbCl{sub 3} and Na{sub 2}S{sub 2}O{sub 3}. Then Ag thin films were thermally evaporated onto glass/Sb{sub 2}S{sub 3}, followed by selenization by dipping in an acidic solution of Na{sub 2}SeSO{sub 3}. The duration of selenium dipping was varied as 30 min and 2 h. The heating condition was at 350 °C for 1 h in vacuum. Analysis of X-ray diffraction pattern of the thin films formed after heating showed the formation of AgSb(S{sub x}Se{sub 1−x}){sub 2}. Morphology and elemental analysis were done by scanning electron microscopy and energy dispersive X-ray detection. Depth profile of composition of the thin films was performed by X-ray Photoelectron Spectroscopy. The spectral study showed the presence of Ag, Sb, S, and Se, and the corresponding binding energy analysis confirmed the formation of AgSb(S{sub x}Se{sub 1−x}){sub 2}. Photovoltaic structures (PV) were prepared using AgSb(S{sub x}Se{sub 1−x}){sub 2} thin films as absorber and CdS thin films as window layers on FTO coated glass substrates. The PV structures were heated at 60–80 °C in air for 1 h to improve ohmic contact. Analysis of J–V characteristics of the PV structures showed V{sub oc} from 230 to 490 mV and J{sub sc} 0.28 to 5.70 mA/cm{sup 2}, under illumination of AM1.5 radiation using a solar simulator.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Structure and dielectric properties of La{sub x}Hf{sub (1−x)}O{sub y} thin films: The dependence of components

Graphical abstract: - Highlights: • La{sub x}Hf{sub (1−x)}O{sub y} thin films were grown by pulse laser deposition method. • The thin film with 10% La/(La + Hf) atom ratio forms a cubic HfO{sub 2} phase. • The amorphous thin films due to more La introduced have almost same local structure. • The main infrared phonon modes move to lower frequency for the amorphous thin films. • The static dielectric constants of the amorphous thin films increase with La content. - Abstract: La{sub x}Hf{sub (1−x)}O{sub y} (x = 0, 0.1, 0.3, 0.5, 0.7, y=2−(1/2)x) thin films were grown by pulsed laser deposition (PLD) method. The component dependence of the structure and vibration properties of these thin films is studied by combining X-ray diffraction, X-ray absorption fine structure (XAFS) and infrared spectroscopy. The thin film with 10% La/(La + Hf) atom ratio forms a cubic HfO{sub 2} phase and it has the largest static dielectric constant. More La atoms introduced cause amorphous phase formed and the static dielectric constants increase with the La content. Although XAFS indicates that these amorphous thin films have almost same local structures, the infrared phonon modes with most contribution to the static dielectric constant move to lower frequency, which results in the component dependence of the dielectric constant.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Fabrication and characterization of a nanoporous NiO film with high specific energy and power via an electrochemical dealloying approach

Graphical abstract: The maximum values were 170 Wh kg{sup −1} and 27.5 kW kg{sup −1} for specific energy and power at the potential window of 1.1 V, respectively. As so far as we know, the values of specific energy and power were both the highest than that reported in literatures. - Highlights: • We developed a convenient approach to fabricate the three-dimensional nanoporous NiO film. • The nanoporous films contain irregular 3D interconnected nanosheets structure with open channels. • The film as supercapacitor electrode showed excellent specific capacitance values. • It is noticed that the nanoporous film exhibited high specific energy and high specific power. • The electrochemical electrode presented excellent cycling performance and low retention. - Abstract: A three-dimensional (3D) nanoporous NiO film was fabricated via a two-step process using an electrochemical route. This process included electrodeposition of the Ni/Zn alloy film and electrochemical dealloying using a direct-current power source. The scanning electron microscopy images suggest that the film has an irregular 3D interconnected nanosheet structure with open channels. The adsorption–desorption isotherms indicate that the as-prepared NiO film had a high specific surface area of 198 m g{sup −1} and a narrow pore size distribution, with two peaks at 2.7 and 5.1 nm. The specific capacitance of the sample reached 1670 F g{sup −1} at a discharge current density of 1 A g{sup −1}. In addition, the as-prepared nanoporous film exhibited high performance during a long-term cycling test. The maximum values for the specific energy and specific power at the 1.1 V potential window were 170 and 27.5 kW kg{sup −1}, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Magnetic properties of high Li doped ZnO sol–gel thin films

Highlights: • Ferromagnetism in high Li doped ZnO films. • Magnetic properties observed by Guoy's and VSM method. • The rod and wrinkle like structures are observed from the surface of the films. • Band gap of ZnO does not get altered by high Li doping. - Abstract: Undoped and Li doped ZnO thin films were deposited on a glass substrate using the sol–gel dip coating method. The films were prepared at 5 mol.% and 10 mol.% of Li doped ZnO at 550 °C annealing temperature and the deposited films were characterized by X-ray diffraction (XRD), microscopic studies, Gouy's method, vibrating sample magnetometer (VSM) and UV–visible spectroscopy. All the deposited thin films had a hexagonal wurtzite structure with polycrystalline grains at random. Primarily magnetic properties of pure and Li doped ZnO films were observed by Guoy's method which depicted Dia and Para magnetic behavior at room temperature. VSM measurement reveals a coercivity of 97.7 Oe in the films. An inverse relative ferromagnetism was perceived in Li doped ZnO films which had an average transmission of <90%.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Effects of diethanolamine on sol–gel–processed Cu{sub 2}ZnSnS{sub 4} photovoltaic absorber thin films

Highlights: • DEA content significantly affected the crystal structure and the phase purity. • The films’ crystallite sizes increased with increasing DEA content. • Two different impurity levels were found for each film via R-T characteristics. • Under different illuminations, the n-Si/CZTS exhibited good photo-response. • The light on/off current ratios confirmed the photo-sensitivity of the junction. - Abstract: As a promising solar absorber, the Cu{sub 2}ZnSnS{sub 4} compound has been popular recently for the production of green and economical thin-film solar cells owing to the abundancy and non-toxicity of all the constituents. In this study, we have produced Cu{sub 2}ZnSnS{sub 4} films via the sol–gel technique. As a stabilizer, the effects of the diethanolamine on the properties of the films were investigated. The amount of diethanolamine significantly affected the crystal structure, crystallite sizes and phase purity of the films. X-ray diffraction and Raman spectroscopy analyses confirmed the formation of phase-pure CZTS films. It was found that the film produced by using 2 ml of diethanolamine in sol exhibited pure CZTS phase, compact and dense morphology and enhanced photo-sensitivity. Light on/off current ratio of the n-Si/Cu{sub 2}ZnSnS{sub 4} junction was found to be 47 under 100 mW/cm{sup 2} of illumination. Electrical activation energies of the films were investigated and the variations were attributed to delocalized phonon states generating from the presence of other phases and lattice defects.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Ta{sub 2}O{sub 5}-based high-K dielectric thin films from solution processed at low temperatures

Highlights: • Ta{sub 2}O{sub 5}–Al{sub 2}O{sub 3}–SiO{sub 2} (Ta:Al:Si = 8:1:1 atomic ratio) and Ta{sub 2}O{sub 5} films were processed from solutions. • The XRD-amorphous films, heated at or below 400 °C, are smooth (RMS < 0.5 nm). • The dielectric permittivity of the single- and mixed-oxide films heated at 400 °C is 27 and 22, respectively. • The current–voltage characteristics of the mixed-oxide films reveal the Poole–Frenkel behaviour. - Abstract: Ta{sub 2}O{sub 5}-based thin films were prepared by chemical solution deposition at temperatures not exceeding 400 °C. The aim of the work was to investigate the properties of high-K dielectric films of the ternary composition Ta{sub 2}O{sub 5}–Al{sub 2}O{sub 3}–SiO{sub 2} with the Ta:Al:Si = 8:1:1 atomic ratio. Pure Ta{sub 2}O{sub 5} samples were also prepared. All thin films were amorphous, and had smooth and flat surfaces with the average roughness of below 0.5 nm. The mixed oxide samples heated between 300 °C and 400 °C showed little difference in the dielectric permittivity with the values ranging from about 19 to 22. The Ta{sub 2}O{sub 5} film heated at 400 °C exhibited the highest permittivity of about 27. The current–voltage measurements revealed considerably improved characteristics of the Ta{sub 2}O{sub 5}–Al{sub 2}O{sub 3}–SiO{sub 2} samples within the investigated heating temperature range, with a significant overall decrease of the leakage currents in contrast to that of the pure Ta{sub 2}O{sub 5} thin films.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Morphology and magneto-transport properties of electron doped La{sub 0.85}Te{sub 0.15}MnO{sub 3} thin film deposited on LaAlO{sub 3} substrate

Graphical abstract: Resistivity versus temperature plots of La{sub 0.85}Te{sub 0.15}MnO{sub 3} thin film under the applied magnetic field of 0 T, 5 T and 8 T. - Highlights: • La{sub 0.85}Te{sub 0.15}MnO{sub 3} manganite thin film is deposited on LaAlO{sub 3} using PLD technique. • Film is deposited at 750 °C, and is highly crystalline, single phase and c-axis oriented. • The film consists of grains with an average diameter of 60 nm. • Resistivity plots display double insulator-metal transitions. • XPS results confirm the electron doped (n-type) nature of the film. - Abstract: We report the structural, electronic transport and X-ray photoemission spectroscopic study of 100 nm thin film of La{sub 0.85}Te{sub 0.15}MnO{sub 3} grown on (0 0 1) LaAlO{sub 3} single crystal substrate by pulsed laser deposition. XRD results confirm that the film has good crystalline quality, single phase, and has a c-axis orientation. The atomic force microscopic (AFM) results showed that the film consists of grains with an average diameter of 60 nm. The resistivity measurement showed double insulator-metal transitions in absence and as well as in presence of the magnetic field. The resistivity peaks are ascribed to the intrinsic contribution of LTMO film and the tunnelling of spin-polarized electrons at grain boundaries. X-ray photoemission spectroscopy measurements suggest that Te ions are in the Te{sup 4+} state, while the Mn ions are forced to stay in the Mn{sup 2+} and Mn{sup 3+} valence state.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Double-layer composite film based on hollow TiO{sub 2} boxes and P25 as photoanode for enhanced efficiency in dye-sensitized solar cells

Highlights: • A novel TiO{sub 2} double-layer composite film is successfully fabricated. • The TiO{sub 2}-HB overlayer exhibited intense scattering ability. • The P25 particles underlayer can enlarge the contact area and increase the contact points between TiO{sub 2}-HB and FTO glass. • TiO{sub 2}-DLL film cells have the maximum conversion efficiency. - Abstract: A TiO{sub 2} double-layer composite film consisting of hollow TiO{sub 2} boxes (HB-TiO{sub 2}) as overlayer and commercial-grade TiO{sub 2} nanoparticles (P25) as underlayer is designed as the photoelectrode of dye-sensitized solar cells (DSSCs). The hollow TiO{sub 2} box has been employed as light-scattering part to increase the optical length in the film and enhance light-harvesting. It was found that the double-layer film cell with lower absorbed dye achieved the highest conversion efficiency and reach up to a maximum value of 6.4%, which is 226% higher than that of pure HB-TiO{sub 2} film cell (η = 1.96%) and 57.2% higher than that of pure P25 particles film cell under identical film thickness at a constant irradiation of 100 mW cm{sup −2}. The enhanced efficiency of double-layer film can be attributed to its light-scattering capability.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Processing and structural properties of random oriented lead lanthanum zirconate titanate thin films

Highlights: • Pyrochlore phase crystallizes near the bottom film-electrode interface. • PLZT films show a non-uniform microstrain and crystallite size in depth profile. • Complex grainy structure leads to different elastic modulus at the nanoscale. - Abstract: Polycrystalline lead lanthanum zirconate titanate (PLZT) thin films have been prepared by a polymeric chemical route to understand the mechanisms of phase transformations and map the microstructure and elastic properties at the nanoscale in these films. X-ray diffraction, atomic force microscopy (AFM) and ultrasonic force microscopy (UFM) have been used as investigative tools. On one side, PLZT films with mixed-phase show that the pyrochlore phase crystallizes predominantly in the bottom film-electrode interface while a pure perovskite phase crystallizes in top film surface. On the contrary, pyrochlore-free PLZT films show a non-uniform microstrain and crystallite size along the film thickness with a heterogeneous complex grainy structure leading to different elastic properties at nanoscale.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Silver film on nanocrystalline TiO{sub 2} support: Photocatalytic and antimicrobial ability

Highlights: • Simple photocatalytic rout for deposition of Ag on nanocrystalline TiO{sub 2} films. • High antibactericidal efficiency of deposited Ag on TiO{sub 2} support. • Improved photocatalytic performance of TiO{sub 2} films in the presence of deposited Ag. - Abstract: Nanocrystalline TiO{sub 2} films were prepared on glass slides by the dip coating technique using colloidal solutions consisting of 4.5 nm particles as a precursor. Photoirradiation of nanocrystalline TiO{sub 2} film modified with alanine that covalently binds to the surface of TiO{sub 2} and at the same time chelate silver ions induced formation of metallic silver film. Optical and morphological properties of thin silver films on nanocrystalline TiO{sub 2} support were studied by absorption spectroscopy and atomic force microscopy. Improvement of photocatalytic performance of nanocrystalline TiO{sub 2} films after deposition of silver was observed in degradation reaction of crystal violet. Antimicrobial ability of deposited silver films on nanocrystalline TiO{sub 2} support was tested in dark as a function of time against Escherichia coli, Staphylococcus aureus, and Candida albicans. The silver films ensured maximum cells reduction of both bacteria, while the fungi reduction reached satisfactory 98.45% after 24 h of contact.

36 MATERIALS SCIENCE↗
DOE OSTI2015

High energy-storage performance of 0.9Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}-0.1PbTiO{sub 3} relaxor ferroelectric thin films prepared by RF magnetron sputtering

Highlights: • High-quality PMN-PT 90/10 RFE thin films were prepared by RF magnetron sputtering. • The maximum discharged density of 31.3 J/cm{sup 3} was obtained in the 750-nm-thick film. • PMN-PT RFE films might be a promising material for energy-storage application. - Abstract: 0.9Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}-0.1PbTiO{sub 3} (PMN-PT 90/10) relaxor ferroelectric thin films with different thicknesses were deposited on the LaNiO{sub 3}/Si (100) by the radio-frequency (RF) magnetron sputtering technique. The effects of thickness and deposition temperature on the microstructure, dielectric properties and the energy-storage performance of the thin films were investigated in detail. X-ray diffraction spectra indicated that the thin films had crystallized into a pure perovskite phase with a (100)-preferred orientation after annealed at 700 °C. Moreover, all the PMN-PT 90/10 thin films showed the uniform and crack-free surface microstructure. As a result, a larger recoverable energy density of 31.3 J/cm{sup 3} was achieved in the 750-nm-thick film under 2640 kV/cm at room temperature. Thus, PMN-PT 90/10 relaxor thin films are the promising candidate for energy-storage capacitor application.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Influence of activation parameters on the thickness of MgO thin film on Ag-3Mg alloy and its secondary electron emission property

Highlights: • MgO films with controlled thicknesses on Ag-3Mg alloys were prepared by activation in low vacuum with oxygen. • Superior secondary electron yield was obtained for the Ag-3Mg alloy with proper thickness of MgO film. • Oxygen pressure during the activation process is crucial for obtaining good secondary electron yield for Ag-3Mg alloys. • The mechanism of secondary electron emission in MgO films is discussed. - Abstract: MgO thin films of different thicknesses were prepared on polished Ag-3wt%Mg alloy by an activation process at 500–650 °C under oxygen pressures of 0.5–10.0 Pa. The influence of the thickness of MgO film on the secondary electron yield of the Ag-3wt%Mg alloy is investigated. The alloy with an MgO film of moderate thickness of 65 ± 1 nm shows the highest secondary electron yield of 10. Oxygen pressure below 10.0 Pa is crucial for the formation of intact MgO film on the top surface. Computational simulation analysis reveals that the maximum yield occurs when the penetration depth of primary electrons is 13–18 nm less than the thickness of MgO film. Electron supply of this extra MgO film is allowed by an electron tunneling mechanism under certain bias voltage. The replenishment of new electrons to the electron deficient surface is crucial for obtaining optimized secondary electron yields for Ag-Mg alloy cathodes.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Influence of Fluorine incorporation on the photocatalytic activity of Tin Oxide thin films

Highlights: • Fluorine doped SnO{sub 2} thin films prepared by a facile homemade jet nebulizer spray pyrolysis technique. • XRD, XPS, PL, FESEM, AFM studies support the discussions. • The photocatalytic activities of the prepared tin oxide (TO) and FTO thin films for the degradation of MB aqueous solution were tested. . - Abstract: This work reports the photocatalytic activity of undoped tin oxide (TO) and F doped tin oxide (FTO) thin films for MB dye degradation under visible light irradiation. A facile homemade jet nebulizer spray pyrolysis technique was employed to prepare these samples. The results indicate that FTO film exhibits superior photocatalytic activity compared to TO film. Dye degradation of nearly 95% is achieved using FTO film at 90 min whereas TO film degrades only 78% of dye molecules in the same time interval. This enhancement for FTO films might be due to the generation of large number of free electrons caused by the fluorine incorporation. The mechanism behind the enhancement of photocatalytic activity of FTO films is discussed elaborately with the aid of optical and PL studies. The structure, composition and morphology of the samples were analyzed using XRD, XPS, FTIR, FESEM and AFM. The incorporation of F into SnO{sub 2} lattice is confirmed through FTIR analysis.

36 MATERIALS SCIENCE↗
DOE OSTI2017

A rapid and convenient method for the preparation of thermochromic VO{sub 2} thin films

Highlights: • A simple and efficient route has been developed for the preparation of VO{sub 2} thin films. • VO{sub 2} films annealed at high enough crystallization temperature were obtained and analyzed. • Excellent optical modulation both in the visible and near-infrared region has been achieved in the prepared VO{sub 2} film. - Abstract: The annealing temperature for the preparation of VO{sub 2} films with sputtering method have always been applied in the range of 300–500 °C. Herein, a simple and efficient route has been developed for the preparation of VO{sub 2} thin films through the thermal oxidation of sputtered vanadium film at 585 °C. Structural, morphological, elemental analysis and thermochromic properties of synthesized VO{sub 2} films are reported. Different from the traditional sputtered VO{sub 2} films, large change of transmittance has been found in the visible region during phase transition. The present work shows the feasibility to fabricate reliably reproduced high quality VO{sub 2} films with reversible phase transition and excellent optical modulation both in the visible and near-infrared region.

36 MATERIALS SCIENCE↗
DOE OSTI2017

One-pot electrochemical preparation of BiOCl/BiPO{sub 4} double-layer heterojunction film with efficient photocatalytic performance

Highlights: • A novel BiOCl/BiPO{sub 4} heterojunction film has been synthesized by one-pot electrochemical method. • The as-prepared BiOCl/BiPO{sub 4} heterojunction film exhibited high photocatalytic activity and stability. • The plausible formation process of BiOCl/BiPO{sub 4} heterojunction film has been proposed and demonstrated. • The photocatalytic mechanism of phenol degradation presented by BiOCl/BiPO{sub 4} heterojunction film was investigated and analyzed. - Abstract: A BiOCl/BiPO{sub 4} double-layer heterojunction film on metal Bi plate with reduced recombination of photo-induced carriers has been successfully prepared by one-step electrochemical anodization process. The morphology characterizations displayed that the double-layer film consisted of BiPO{sub 4} rods array at the bottom and BiOCl nanosheets on the top. Meanwhile, the control experiments indicated that the BiPO{sub 4} rods array was transformed by BiOCl rather than Bi{sup 3+} reacting with PO{sub 4}{sup 3−} directly. In addition, the resulting BiOCl/BiPO{sub 4} heterojunction film exhibited excellent photocatalytic activity and stability on the degradation of phenol comparing with pure BiOCl film. Transient photocurrent measurements and PL spectra proved that the enhanced photocatalytic performance of BiOCl/BiPO{sub 4} heterojunction film was attributed to the effective separation of photo-generated electron-hole pairs excited on BiOCl. Moreover, ·O{sub 2}{sup −} and ·OH played a crucial role in the photodegradation process of phenol. Based on these analytical results, a plausible photocatalytic mechanism has been proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Wafer-scale two-dimensional Au-TiO{sub 2} bilayer films for photocatalytic degradation of Palmitic acid under UV and visible light illumination

Highlights: • Successful wafer-scale atomic layer deposition of 2D Au-TiO{sub 2} bilayer photocatalyst films. • The efficient degradation of fatty acid by tailoring 2D TiO{sub 2} films under UV and visible light illumination. • Improved visible light photocatalytic activity and photocurrent density of 2D Au-TiO{sub 2} bilayer films. • Comparable photocatalytic performance of ultra-thin 2D TiO{sub 2} and thick TiO{sub 2} films under UV light illumination. - Abstract: Bilayer Au-TiO{sub 2} configuration with two-dimensional (2D) TiO{sub 2} films enabled sensible improvement in photocatalytic degradation of Palmitic Acid (PA) and also the enhancement of current density under visible light illumination. The improved visible light photocatalytic and photocurrent properties were attained when 35 nm thick 2D TiO{sub 2} film was developed by atomic layer deposition (ALD) on Si/SiO{sub 2}-Au substrate. The Au-TiO{sub 2} bilayer demonstrated the improved photocatalytic and photovoltaic performances compared with those TiO{sub 2} films developed on Si/SiO{sub 2} bare substrate. These improvements can be attributed to the plasmonic effects of Au film acting as antenna for visible light and also serving as hole acceptor during photocatalysis process. The proposed mechanisms for enhanced visible light performance of bilayer films are hot electron injection and the formation of hot spots at Au-TiO{sub 2} interface which contributed to the electron injection to conduction band of TiO{sub 2} or facilitated the separation of generated electron-hole pairs at Au-TiO{sub 2} Schottky junction.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Anomalous Raman and photoluminescence blue shift in mono- and a few layered pulsed laser deposited MoS2 thin films

Highlights: • Mono- and a few layered MoS{sub 2} films deposited using pulsed laser deposition technique by varying the deposition time. • The films experienced an epitaxial compression due to its adhesion with the substrate. • Lattice strain of the films led to a significant Raman frequency shift. • An anomalous PL peak was observed which is attributed to quantum confinement. - Abstract: We report on the Raman blue shift of layered MoS{sub 2} films as well as an anomalous blue shift of the photoluminescence spectra of nanocrystallite MoS{sub 2} films grown by pulsed laser deposition. Monolayer, bilayer and trilayer MoS{sub 2} films were fabricated by ablating MoS{sub 2} target for a deposition time of around 14, 24 and 30 s at a laser fluence of 2.2 Jcm{sup −2}. The two Raman active modes showed lattice strain-induced blue shift of 1–3 cm{sup −1}. The layered films showed an out-of-plane compressive strain as well as an in-plane tensile strain confirmed by Riet-Veld refinement of the X-ray diffraction pattern. TEM image of the MoS{sub 2} film for 14 s demonstrated the presence of nanocrystallites of an average size of 13 nm along with the layered film of MoS{sub 2}. An anomalous photoluminescence peak was observed corresponding to the MoS{sub 2} nanocrystallites at 2.18 eV, attributed to quantum confinement effect.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗