Synthesis and characterization of low particle size nanocrystalline SnSe thin films

Tin selenide (SnSe) nanocrystalline thin films of different thickness from 15 to 70 nm were prepared by inert gas condensation technique. Argon gas flow and substrate temperature were kept constant during deposition process at 2 × 10^?3 Torr and 27 °C respectively. Polycrystalline orthorhombic phase structured was deduced for the prepared SnSe ingot powder by X-ray diffraction pattern. The grazing incident in-plane X-ray diffraction (GIIXD) pattern showed nanocrystalline orthorhombic structure for deposited SnSe thin film. The TEM micrographs showed that thin films were nanocrystalline with particle size in the range from 2 to 5.7 nm. The optical band gap E_g of the thin films due to direct allowed transition have values ranging from 2.5 to 2.13 eV as the particle size increases from 2 to 5.7 nm. The photoconductivity spectra of the nanostructured SnSe thin films of different particle size showed transitions at 2.45, 2.34 and 2.21 eV for films of different particle size.     

Nanostructured leaf like hydroxyapatite/TiO2 composite coatings by simple sol-gel method

We demonstrate an approach for the coating of nanostructured leaf like hydroxyapatite (HAp)/TiO₂ composite on glass substrate by sol-gel dip coating process. HAp/TiO₂ nanocomposite thin film was obtained by controlling the dipping rate and the dipping cycle. It was observed from Scanning Electron Microscope that leaf like nanostructured film was deposited on the glass substrate. However, the structure of the film was changed with the dipping cycle and dipping rate. Transmission Electron Microscopic analysis further confirms the morphology of the nanostructured coatings. The presence of Ti, O, Ca and P was detected by Energy Dispersive X-ray Analysis. We further confirmed the composite by X-ray diffraction analysis. Atomic Force Microscope analysis indicates that the films are composed of nanoparticles ranging from 100 to 200 nm and the films were observed to present well-defined grain boundaries. It has been shown that nanocomposite coatings are dependent on the sol concentration, dipping parameters, and the composition of HAp and TiO₂.     

Thin Film Tin Selenide (SnSe) Thermoelectric Generators Exhibiting Ultralow Thermal Conductivity

Tin selenide (SnSe) has attracted much attention in the field of thermoelectrics since the discovery of the record figure of merit (ZT) of 2.6 ± 0.3 along the b‐axis of the material. The record ZT is attributed to an ultralow thermal conductivity that arises from anharmonicity in bonding. While it is known that nanostructuring offers the prospect of enhanced thermoelectric performance, there have been minimal studies in the literature to date of the thermoelectric performance of thin films of SnSe. In this work, preferentially orientated porous networks of thin film SnSe nanosheets are fabricated using a simple thermal evaporation method, which exhibits an unprecedentedly low thermal conductivity of 0.08 W m^?1 K^?1 between 375 and 450 K. In addition, the first known example of a working SnSe thermoelectric generator is presented and characterized.     

Application of the gas phase condensation to the preparation of nanoparticles

The evaporation of materials in ultra-high vacuum leads to the growth of thin films on appropriated substrates. In the presence of an inert gas (pressure above 10⁻¹ Torr), the evaporated materials lose kinetic energy by collisions with the inert gas molecules in the gas phase and condense in the form of nanometric size crystallites that can be collected on the substrate as an ultrafine powder. In the present communication, we discuss how thin film deposition methods can be modified to collect ultrafine powders instead of continuous films. We describe, with some examples, the use of the gas phase condensation in the preparation of two different types of materials as nanometric powders. On one hand, CdS nanoparticles have been obtained in the form of homogeneous spheres with a mean particle size of 16 nm in diameter. This material, with applications in catalysis and optical devices, has been characterised by UV–VIS Absorption Spectroscopy, Transmission Electron Microscopy and X-ray Diffraction. On the other hand, magnetic nanoparticles of Co have also been prepared as nanostructured materials with an average particle size of 10 nm. Transmission Electron Microscopy, X-Ray Photoelectron Spectroscopy and X-ray Diffraction have been used to characterise this sample. The formation of an interesting material, consisting of Co cores covered by an oxide passivation layer, has been demonstrated.     

Effect of annealing on conversion efficiency of nanostructured CdS/CuInSe2 heterojunction thin film solar cell prepared by chemical ion exchange route at room temperature

We report, the effect of air annealing on solar conversion efficiency of chemically grown nanostructured heterojunction thin films of CdS/CuInSe₂, such 100, 200 and 300 °C air annealed thin films characterized for physicochemical and optoelectronic properties. XRD pattern obtained from annealed thin films confirms tetragonal crystal geometry of CuInSe₂ and an increase in average crystallite size from 16 to 32 nm. An EDAX spectrum confirms expected and observed elemental composition in thin films. AFM represents high energy induced grain growth and agglomeration due to polygonization process. Increase in optical absorbance strength and decrease in energy band gap from 1.36 to 1.25 eV is observed. Increase in charge carrier concentration from 2 × 10¹⁶ to 8 × 10¹⁷ cm^?3 is observed as calculated from Hall effect measurements and an enhancement in solar conversion efficiency from 0.26 to 0.47% is observed upon annealing.     

Chemical synthesis, structural and optical properties of quantum sized semiconducting tin(II) selenide in thin film form

A chemical route to nanocrystalline photoconducting tin(II) selenide quantum dots in thin film form was developed and the structural and optical properties of the synthesized materials were studied. The synthesized SnSe nanocrystals deposited as thin films belong to the orthorhombic crystalline system. Unit cell parameters of the as-deposited and thermally treated semiconducting quantum dots in thin film form were determined from experimental X-ray diffraction data employing multiple regression analysis technique. An average crystal size of 14.8 nm was estimated for as-deposited SnSe quantum dots using the Debye-Scherrer approach which increases to 23.3 nm upon annealing. Average crystal size increase upon thermal treatment is accompanied by slight enlargement of the unit cell parameters. On the basis of optical absorption studies of the SnSe films, conclusions regarding the band structure of this material in reciprocal space were derived. The as-deposited films are characterized by indirect band gap energy of 1.20 eV which exhibits a slight red shift to 1.10 eV upon annealing. Additional electronic transition of a direct type was found to occur at 1.74 eV in the case of as-deposited films, shifting to 1.65 eV in the course of annealing. All these values are blue-shifted with respect to the macrocrystalline material ones, which along with the red shift detected upon annealing, is a strong indication of the three-dimensional confinement effects in the studied nanocrystals.     

Preparation, Growth, and Magnetic Properties of Co-doped Yb2O3 Nanoparticles and Thin Films by the Sol–Gel Process

In this study, the preparation, growth, structure and magnetic properties of Co-doped Yb₂O₃ (with the Co concentration of x=0.2) nanoparticles and thin films are studied. Precursor solutions were prepared by using the sol?Cgel synthesis process to produce nanoparticles and thin films. Co-doped Yb₂O₃ thin films with different thickness were produced on Si(100) substrate using the sol?Cgel dip coating procedure. The particle size and the crystal structure of nanoparticles were ascertained by X-ray diffraction and Scanning Electron Microscope. The surface morphologies and the microstructure of all samples were investigated by means of the Scanning Electron Microscope and the X-ray diffraction. A Quantum Design PPMS was used for magnetic measurements. Surface morphologies of Co-doped Yb₂O₃ thin films were found to be dense, without porosity, uniform, and devoid of cracks and pinholes. The grain size and thin-film thickness of Co-doped Yb₂O₃ were determined to be approximately 50?nm and 84?nm, respectively.     

Analysis of different vacuum annealing levels for ZnSe thin films as potential buffer layer for solar cells

In order to seek potential buffer layer, the influence of different vacuum annealing levels on physical properties to e-beam evaporated Zinc Selenide (ZnSe) thin films are meticulously investigated herein. The X-ray diffraction patterns of vacuum-annealed ZnSe films confirmed the prominent (111) reflection of the cubic phase where the crystallite size is found maximum (29 nm). The wavy optical transmittance spectra are observed for these ZnSe films, where higher transparency is observed in the visible region. A blue shift in the optical band gap (2.56–2.81 eV) and shrink in refractive index from 2.49 to 2.40 is observed with increasing vacuum levels. The HRTEM images demonstrated (111), (220), and (311) orientations of the lattice planes, and EDS patterns confirmed deposition of ZnSe films. The ohmic nature of the analyzed ZnSe thin films is validated by the I–V characteristics where the resistivity is found in the order of 10² Ω-cm for vacuum-annealed and 10⁴ Ω-cm for the pristine films. The AFM images indicated hill-like structures where the roughness is found to vary with vacuum level. The physical properties of ZnSe films are conspicuously tailored by vacuum annealing levels, and the findings recommend the use of?~?5?×?10^?3 mbar vacuum-annealed ZnSe thin films as potential buffer layer to the solar cells.

     

Microanalysis of Pd and V-doped TiO2 thin films prepared by sputtering

Thin films of TiO₂ doped with vanadium and palladium, prepared by the magnetron sputtering method, were studied by means of X-ray diffraction (XRD), Scanning Electron Microscopy with Energy Disperse Spectrometer (SEM-EDS) and Atomic Force Microscopy (AFM). Investigations have brought important information about microstructure due to dopant incorporation in the TiO₂ host lattice. Directly after deposition thin films were XRD-amorphous and SEM investigations did not reveal details on the microstructure. Analysis of the topography of prepared thin films required application of Atomic Force Microscope. The AFM images show that as-deposited sample was dense with grain sizes varied in the range of 5.5 nm-10 nm, that indicated high quality nanocrystalline behavior. Additional annealing results in the formation of three phases in the thin film, e.g. (Ti,V)O₂ — solid solution, PdO and metallic inclusions of Pd. SEM-EDS system allowed analysis of the elemental composition, especially the V one, which lines have not been evidenced in the XRD diffraction pattern. EDS maps show homogenous distribution of elements Ti, O, V, Pd in prepared thin films.     

The effect of growth conditions and N<Subscript>2</Subscript>/O<Subscript>2</Subscript> ambient on LO-phonon replicas during epitaxial growth of ZnO on c-sapphire

High quality heteroepitaxial thin films of ZnO:N were grown by pulsed laser deposition using a two-step growth method and annealed in situ at different temperatures and ambient conditions. Films were analyzed by X-ray diffraction (XRD), electrical measurements, and photoluminescence experiments at low temperatures to investigate the effect of nitrogen doping. The XRD results demonstrate epitaxial growth on the c-sapphire substrates, with average grain size of 57 nm. Photoluminescence spectra reveals a peak at 3.061 eV (405.1 nm) which is part of the longitudinal-optical-phonon replicas of excitons bound to neutral acceptors \textA₁⁰  \textX_\textA {\text{A}}_{1}^{0} \,{\text{X}}_{\text{A}} at 3.348 eV (370.4 nm), attributed in recent investigations to a newly reported donor–acceptor pair. Electrical resistivity and Hall effect measurements were performed using standard four point van der Pauw geometry at room temperature. Fresh films exhibited a resistivity of 3.1 × 10⁻³ Ω cm, a carrier density of 1.3 × 10¹⁹ cm⁻³, and a mobility of 53 cm²/V s. During approximately 2 weeks the as-deposited films presented a p-type behavior, as shown by the positive sign of the Hall constant measured. Thereafter, films reverted to n-type. From electrical measurements and photoluminescence spectra, the acceptor energy was determined to be 150 meV, in close agreement with reported values. These results are consistent with those presented in the literature for high purity crystals or homoepitaxial thin films, even though samples for the present study were processed at lower annealing temperature.     

Influence of annealing on humidity response of RF sputtered nanocrystalline MgFe2O4 thin films

Humidity response of Radio Frequency sputtered MgFe₂O₄ thin films onto alumina substrate, annealed at 400 °C, 600 °C and 800 °C has been investigated. Crystalline phase formation of thin films annealed at different temperature was analyzed by X-ray Diffraction. A particle/grain like microstructure in the grown thin films was observed by Scanning Electron Microscope and Atomic Force Microscope images. Film thickness for different samples was measured in the range 820-830 nm by stylus profiler. Log R (Ω) response measurement was taken for all thin films for 10-90% relative humidity (% RH) change at 25 °C. Resistance of the film increased from 5.9 × 10¹⁰ to 3 × 10¹² at 10% RH with increase in annealing temperature from 400 °C to 800 °C. A three-order magnitude, 10¹² Ω to 10⁹ Ω drop in resistance was observed for the change of 10 to 90% RH for 800 °C annealed thin film. A good linear humidity response, negligible humidity hysteresis and minimum response/recovery time of 4 s/6 s have been measured for 800 °C annealed thin film.     

The effect of LaNiO3 buffer layer thickness on the electric properties of Pb(Zr0.53Ti0.47)O3 thin films deposited on titanium foils

Sol-gel derived Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films were prepared on LaNiO₃ (LNO) buffered titanium foils. The effect of LNO buffer layer thickness on the electric properties of PZT thin films was investigated. The room temperature dielectric constant of PZT thin films increased with increasing LNO thickness. The remnant polarization of PZT thin films on 150 and 250 nm LNO was about 20 uC/cm². Curie temperatures of PZT thin films were 310, 330 and 340 °C for LNO of 250, 150 and 50 nm respectively. The current-voltage characteristics of PZT thin films were examined for different LNO buffer layer thicknesses, and the space charge limited conduction model was followed in PZT thin films on 50 nm LNO.     

Improvement of multiferroic properties of the Bi5Ti3FeO15 thin films by Ni doping

Pentabismuth trititanium iron pentadecaoxide (Bi₅Ti₃FeO₁₅, BTFO), which is a multiferroic four-layer Aurivillius phase compound, has received much attention in recent years. In this work, the BTFO and Bi₅Ti₃Fe_0.5Ni_0.5O₁₅ (BTFNO) films grown on Pt (200 nm)/TiO₂ (50 nm)/SiO₂ (500 nm)/Si substrates by pulsed laser deposition. The microstructure, morphology, ferroelectricity, and ferromagnetism of the films were studied at room temperature. It can be seen from the X-ray diffraction diagrams that BTFO and BTFNO films match well with the perovskite structure without other oxide phases. Scanning electron microscope (SEM) images show that BTFNO films exhibit uniform fine grains and higher density, which is instrumental for the development of ferroelectric properties. Therefore, under the electric field strength of 1116 kV/cm, the remnant polarization of BTFNO films (2P_r?=?23.32 μC/cm²) is larger than that of BTFO thin films at room temperature. Furthermore, compared with BTFO films, the saturation magnetization (2M_s) of BTFNO films is significantly enhanced. It demonstrated that BTFNO films show not only excellent ferroelectricity but also good ferromagnetism, which provides potential applications in information storage.

     

Properties of pulse plated SnSe films

In this work, the pulse electrodeposition technique has been employed for the first time to deposit SnSe films from a bath containing Analar grade 50?mM tin chloride (SnCl₄) and 5?mM SeO₂. The XRD profile of SnSe thin films deposited at different duty cycles indicate the peaks corresponding to SnSe. Atomic force microscopy studies indicated that the surface roughness increased from 0.5 to 1.5?nm with duty cycle. The transmission spectra exhibited interference fringes. The value of refractive index at 780?nm was 2.1, this value decreased to 1.95 with decrease of duty cycle. The room temperature resistivity increased from 0.1 to 10?Ωcm with decrease of duty cycle. Photo electrochemical cell studies were made using the films deposited at different duty cycles. For duty cycles greater than 15% photo output was observed. For a film deposited at 50% duty cycle, an open circuit voltage of 0.55?V and a short circuit current density of 5.0?mA?cm^?2 at 60 mW?cm^?2 illumination. Capacitance voltage measurements indicated V_fb?=?0.67?V (SCE) and p type, carrier density?=?6.98?×?10¹⁶?cm^?3.     

Hydrothermal synthesis of β-nickel hydroxide nanocrystalline thin film and growth of oriented carbon nanofibers

Novel well-crystallized β-nickel hydroxide nanocrystalline thin films were successfully synthesized at low temperature on the quartz substrates by hydrothermal method, and the oriented carbon nanofibers (CNFs) were prepared by acetylene cracking at 750 °C on thin film as the catalyst precursor. High resolution transmission electron microscopy (HR-TEM) measurement shows that thin films were constructed mainly with hexagonal β-nickel hydroxide nanosheets. The average diameter of the nanosheets was about 80 nm and thickness about 15 nm. Hydrothermal temperature played an important role in the film growth process, influencing the morphologies and catalytic activity of the Ni catalysts. Ni thin films with high catalytic activity were obtained by reduction of these Ni(OH)₂ nanocrystalline thin films synthesized at 170 °C for 2 h in hydrothermal condition. The highest carbon yield was 1182%, and was significantly higher than the value of the catalyst precursor which was previously reported as the carbon yield (398%) for Ni catalysts. The morphology and growth mechanism of oriented CNFs were also studied finally.     

Ultrahigh Power Factor and Ultralow Thermal Conductivity at Room Temperature in PbSe/SnSe Superlattice: Role of Quantum-Well Effect

Reduced dimension is one of the effective strategies to modulate thermoelectric properties. In this work, n-type PbSe/SnSe superlattices with quantum-well (QW) structure are fabricated by pulsed laser deposition. Here, it is demonstrated that the PbSe/SnSe multiple QW (MQW) shows a high power factor of ≈25.7 µW cm^?1 K^?2 at 300 K, four times larger than that of PbSe single layers. In addition, thermal conductivity falls below 0.32 ± 0.06 W m^?1 K^?1 due to the phonon scattering at interface when the PbSe well thickness is confined within the scale of phonon mean free path (1.8 nm). Featured with ultrahigh power factor and ultralow thermal conductivity, ZT at room temperature is significantly increased from 0.14 for PbSe single layer to 1.6 for PbSe/SnSe MQW.     

Photo-sensing properties of Cd-doped In2S3 thin films fabricated via low-cost nebulizer spray pyrolysis technique

In this study, we report the fabrication of cadmium-doped indium sulfide thin films (In₂S₃:Cd) using a low-cost nebulizer-aided spray pyrolysis process at 350 °C on glass substrates for photo-sensing applications. The impact of 0, 2, 4, and 8 wt% cadmium concentrations on the structure, morphology, optical properties, and photo-sensing capabilities of In₂S₃ thin films were examined systematically. From X-ray diffraction (XRD) analysis, the major peak is located in the (103) plane for all Cd-doped In₂S₃ thin film samples, and the maximum crystallite size for the 4 wt% sample is 59 nm. The field emission scanning electron microscope (FESEM) image revealed a homogenous large-grained surface of Cd-doped In₂S₃ film that completely covered the substrate. UV–Vis absorption analysis demonstrated good absorption for all thin film samples in the visible and ultraviolet regions of the electromagnetic spectrum, particularly, the 4% Cd-doped concentration showed excellent absorption as is observed from Tauc relation. The highest PL intensity at 680 nm was observed for the sample coated with 4 wt% of Cd. Under UV light, the I–V behavior depicts a light current of 1.06?×?10^–6 A for a 5 V bias voltage. The In₂S₃: Cd (4%) sample had the highest responsivity of 2.12?×?10^?1A/W and a detectivity of 1.84?×?10¹¹ Jones, with a high EQE of 50%. The study manifests that the developed Cd (4%)-doped In₂S₃ thin film sample might be better suited for the application of photodetectors.

     

Controllable Colloidal Synthesis of Tin(II) Chalcogenide Nanocrystals and Their Solution‐Processed Flexible Thermoelectric Thin Films

A systematic colloidal synthesis approach to prepare tin(II, IV) chalcogenide nanocrystals with controllable valence and morphology is reported, and the preparation of solution‐processed nanostructured thermoelectric thin films from them is then demonstrated. Triangular SnS nanoplates with a recently‐reported π‐cubic structure, SnSe with various shapes (nanostars and both rectangular and hexagonal nanoplates), SnTe nanorods, and previously reported Sn(IV) chalcogenides, are obtained using different combinations of solvents and ligands with an Sn⁴⁺ precursor. These unique nanostructures and the lattice defects associated with their Sn‐rich composition allow the production of flexible thin films with competitive thermoelectric performance, exhibiting room temperature Seebeck coefficients of 115, 81, and 153 μV K^?1 for SnS, SnSe, and SnTe films, respectively. Interestingly, a p‐type to n‐type transition is observed in SnS and SnSe due to partial anion loss during post‐synthesis annealing at 500 °C. A maximum figure of merit (ZT) value of 0.183 is achieved for an SnTe thin film at 500 K, exceeding ZT values from previous reports on SnTe at this temperature. Thus, a general strategy to prepare tin(II) chalcogenide nanocrystals is provided, and their potential for use in high‐performance flexible thin film thermoelectric generators is demonstrated.     

Effect of film thickness on ferroelectric domain structure and properties of Pb(Zr0.35Ti0.65)O3/SrRuO3/SrTiO3 heterostructures

Epitaxial Pb(Zr_0.35Ti_0.65)O₃ (PZT) thin films with tetragonal symmetry and thicknesses ranging from 45 to 230 nm were grown at 540 °C on SrRuO₃-coated (001)SrTiO₃ substrates by pulse-injected metalorganic chemical vapor deposition. The effect of the film thickness on the ferroelectric domain structure and the dielectric and ferroelectric properties were systematically investigated. Domain structure analysis of epitaxial PZT films was accomplished with high-resolution X-ray diffraction reciprocal space mapping and high-resolution transmission electron microscopy. Fully polar-axis (c-axis)-oriented epitaxial PZT thin films with high ferroelectric polarization values [e.g., remanent polarization (P _r) ~ 90 μC/cm²] were observed for film thicknesses below 70 nm. Films thicker than 70 nm had a c/a/c/a polydomain structure and the relative volume fraction of c-domains monotonously decreased to about 72% on increasing the film thickness up to 230 nm , and finally P _r diminished to about 64 μC/cm² for the 230-nm-thick epitaxial film. These polarization values were in good agreement with the estimated values taking into account the volume fraction of the c-axis-oriented domains while assuming a negligible contribution of 90° domain reorientation caused by an externally applied electric field.     

The fabrication of SnSe/Ag nanoparticles on TiO2 nanotubes

SnSe and silver (Ag) nanoparticles were sequentially deposited on TiO₂ nanotube (NT) by pulsed electrochemical deposition and polyol chemistry process, respectively. The morphological observation under scanning electron microscope (SEM) showed that the average size of SnSe was about 30 nm and the Ag was about 5 nm. Transmission electron microscopy (TEM) combined with selected area electron diffraction (SAED) examination indicated that Ag nanoparticles exhibited a well-defined crystallinity. However, SnSe nanoparticles were amorphous and they turned to crystalline after being annealed at 300 °C in the atmosphere. The photocatalytic behavior of SnSe/Ag-TiO₂ NT was evaluated by UV–vis diffuse reflectance spectra (DRS). The results showed that the deposition of SnSe and Ag nanoparticles increased light absorption intensity in the wavelength range of visible light, which implied that the SnSe/Ag-TiO₂ NT is a promising ternary hybrid material in photocatalysis.