Cross-sectional Field-emission Scanning Electron Microscopy Research Articles

Sophisticated strategies for designing fast-charging lithium-ion batteries without sacrificing the energy density

The use of electric vehicles (EVs) is a green approach to mitigating climate change and pollution associated with the emissions of internal combustion engines. Therefore, research on lithium-ion batteries (LIBs), which are major EV components, has become vital. LIBs in EVs should be characterised by high energy and power densities for long-term use. In this study, the electrochemical performance during fast charging was examined with the active material (AM) content kept constant at 94 wt% so as not to sacrifice energy density, and the ratio of conducting agent (CA) to binder altered to account for the remaining 6 wt% of the composition. We evaluated the charging properties of Ni-rich cathodes and carried out cyclic voltammetry, electrochemical impedance spectroscopy, cross-sectional field-emission scanning electron microscopy and pore size distribution analyses. Evidence reveals that when the CA:binder ratio is 4:6, AM is hampered by the binder, which inhibits electronic conduction and hence increases its resistance to electrochemical reactions. On the other hand, at 7:3 CA:binder ratio, the void spaces in the cathode are filled by CA, decreasing porosity and hindering Li+ transfer through the electrolyte. As a result, a 6:4 CA:binder ratio is optimal for fast-charging in terms of electronic and ionic conduction. The results of this study indicate that electrochemical performance can be controlled by the inactive components' ratio, and our research proposes the best electrode composition with respect to the CA:binder ratio for fast-charging.

Evaluation of structural and mechanical properties of CrAlN single layer coating deposited by reactive magnetron sputtering

The objective of this study is to evaluate the structural and mechanical properties of CrAlN coating obtained by reactive RF magnetron sputtering with (Cr0.5Al0.5) alloy targets in a mixed atmosphere of Argon–Nitrogen (Ar:N2). During deposition, the RF power and substrate temperature were fixed at 120 W and 300 °C, respectively. The Ar: N2 contents were varied at different ratios like 20:2, 20:4, 20:6, 20:8 and 20:10. Grazing Incidence X-ray Diffraction (GIXRD) study was performed to identify the phases present in the coating. The surface morphology and mechanical properties were studied using Field Emission Scanning Electron Microscopy (FESEM) and Nanoindentation, respectively. GIXRD shows the presence of a dominant Face Centered Cubic (FCC) CrN phase. Plane view and cross-sectional FESEM micrographs presented the different Ar:N2 ratios-dependent changes in the microstructures. The CrAlN coating deposited at Ar:N2 contents of 20:6 shows maximum elastic modulus and hardness value compared to other coatings. In our studies, the maximum hardness (H), elastic modulus (Er), elastic recovery (We), and resistance to plastic deformation (H3/E2) were obtained to be 22.96 GPa, 225.79 GPa, 74.81%, and 273 MPa respectively for 20:6 CrAlN deposited coating. This study also shows that different Ar:N2 ratio strongly affects the crystalline microstructure and mechanical properties of the deposited coatings.

Design of Non-Ammoniacal Solution for Electrodeposition of CuO on Cu2o Substrate

Semiconductor materials are attracting increasing attention as photoelectrodes and photovoltaic devices. Cuprous oxide (Cu2O), which has been intensively studied due to its high absorption coefficient, low cost, and low toxicity, is a p-type semiconductor with a bandgap energy of approximately 2.1 eV. However, Cu2O has a narrow solar absorption region due to its high bandgap energy. CuO (bandgap energy of 1.4 eV) has been combined with Cu2O to increase the absorption wavelength range [1]. Thermal oxidation of Cu2O surfaces for forming CuO/Cu2O bi-layer films has been reported [2]. However, this thermal oxidation creates nanopores and voids in the films and degrades the film performance. In this study, an electrochemical formation of CuO on a Cu2O surface is investigated. Previously reported methods of electrochemical CuO formation include an anodic electrodeposition using an ammoniacal aqueous solution [3]. In ammoniacal solutions, however, the Cu2O surface is unstable and can be dissolved as Cu(I)-ammine complexes. In this study, suitable non-ammoniacal ligands, which can be used to stabilize Cu2O during CuO electrodeposition, are examined through thermodynamic calculations, and the electrodeposition behavior of CuO films on Cu2O is experimentally investigated.An appropriate ligand, 2-aminoethanol, i.e., mono-ethanolamine (MEA), was obtained by drawing the pH speciation diagram using thermodynamic data [4, 5]. It is difficult to use MEAs to form complexes with Cu(I) and easy to form with Cu(II), and MEAs are relatively inexpensive and versatile. Figure 1 shows that CuO is stable at a pH region lower than the region where the Cu(II)-MEA complex is dominant, suggesting that it is feasible to achieve CuO electrodeposition using a local pH drop, through, for example, anodic oxygen evolution reaction.In a 0.05 M Cu(II) + 0.125 M MEA aqueous solution without NaOH addition (pH = 8.5), precipitates − probably hydroxide − were formed (Figure 2(b)). In contrast, when the pH was increased to 12.5, a deep blue aqueous solution was obtained without any precipitates (Figure 2(c)). While a set of existing stability constants [5] indicated the presence of CuO or Cu(OH)2 precipitates in the 0.05 M Cu(II) + 0.125 M MEA aqueous solution at a pH value of 12.5, a clear solution was obtained at [Cu(II)] = 0.05 M, [MEA] = 0.125 M, and pH = 12.5. A Cu2O substrate was immersed in this solution for 5 h to confirm the stability of Cu2O in the solution. From the results, almost no weight change was observed, unlike the case of ammoniacal solutions, when nitrogen degassing was carried out for 30 min before performing the immersion test to prevent the oxidation of Cu2O by dissolved oxygen. Potentiostatic electrodeposition of CuO was conducted on +0.45 V vs. Ag/AgCl reference electrode at 313 K. Cu2O/FTO —Cu2O was electrodeposited on fluorine-doped tin oxide (FTO) in advance [2]— and Pt plates were used as both the working electrode (WE) and the counter electrode. Figure 3 shows the X-ray diffraction (XRD) profiles of the Cu2O/FTO WE before and after the electrodeposition. Along with cubic Cu2O, monoclinic CuO was detected. Additionally, the cross-sectional field-emission scanning electron microscopy (FE-SEM) images depicted in Fig. 4 indicate a bi-layer structure. Therefore, we conclude that CuO was stacked, keeping the Cu2O layer intact. Figure 5 shows the visible spectroscopy near-infrared region (vis-NIR) absorbance spectra of the Cu2O and CuO/Cu2O films. The absorption edge of the Cu2O films was 630 nm, while that of the CuO/Cu2O films shifted to 900 nm, demonstrating that the CuO/Cu2O films had a broader absorption wavelength range than pure Cu2O or pure CuO films. In summary, a non-ammoniacal bath is surveyed from the thermodynamics database, and CuO/Cu2O bi-layer films are electrochemically fabricated.

Characterization of nanoporous Al2O3 films at terahertz frequencies.

Terahertz birefringence in nanoporous Al2O3 films grown on Al substrates is characterized nondestructively by polarization-resolved terahertz spectroscopy. Sparse deconvolution is used to find the film thicknesses from the data, showing good agreement with the values measured directly by destructive cross-sectional field-emission scanning electron microscopy.

Vanadium oxide thin films on quartz and Al6061 with reduced phase transition temperature and low solar absorptance for advanced thermal control application in space

Doped and co-doped vanadium oxide (VO) thin films were deposited on quartz substrates with varying concentrations of doping elements by sol-gel spin coating technique. The VO thin films were characterized by the X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), cross-sectional FESEM and X-ray photoelectron spectroscopy (XPS) techniques. The optical properties, e.g., the average solar absorptance (αs), the average solar reflectance (ρs) and the average solar transmittance (τs) of the films deposited on quartz were evaluated by using a solar spectrum reflectometer. Based on the optical characterizations, an optimized doping concentration was identified. Further, a process optimized condition was utilized to grow both doped and co-doped vanadium oxide films on metallic Al6061 substrates; which are generally used in spacecraft. The phase transitions of all as grown vanadium oxide films on Al6061 were characterized by the differential scanning calorimetry (DSC) technique. The thin films showed reversible and repeatable phase transitions at sub-zero level of temperatures e.g., ∼ ( ̶ 23.3 °C). Thus, the VO thin films developed in the present work emerge out to be of paramount importance for the smart radiative device applications in spacecraft.

Formation of titanium carbide on the titanium surface using laser ablation in n-heptane and investigating its corrosion resistance

Laser ablation of titanium in liquid (LAL) using a fiber laser was studied. Firstly, LAL was carried out in toluene, n-hexane, n-heptane, and acetone as liquid media at the same irradiation conditions. Samples were characterized by different diagnostic techniques X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDS). It was found that titanium carbide (TiC) structure has been generated on the surface of laser ablated samples in toluene, n-hexane, and n-heptane. Also, titanium dioxide was formed on the surface of laser ablated sample in acetone along with TiC. After that, n-heptane was chosen as the adequate liquid medium. LAL process was repeated in n-heptane for different ablation process times at the same irradiation conditions. Samples were investigated by XRD, Raman spectroscopy, EDS, nuclear reaction analysis (NRA), and cross sectional FESEM. It was concluded that the ablation process time of about 30 s is threshold time to form detectable TiC structure by XRD. Additionally, it was deduced that the amount of the carbon (in two forms of amorphous and carbidic) on the surface of the irradiated titanium for about 2 min (S8 sample) is more than the other samples. The corrosion behavior of samples was studied by electrochemical impedance spectrometry (EIS) tests. The EIS plots obtained after 24, 48, 72, and 96 h immersion time showed the corrosion resistance of S8 sample enhancement in Ringer's solution compared with the other samples, and the corrosion resistance of this sample increased by rising the immersion time up to 96 h.

Implementation and characterization of coating pure titanium dental implant with sintered β-TCP by using Nd:YAG laser

ObjectivesThis work presents laser coating of grade 1 pure titanium (Ti) dental implant surface with sintered biological apatite beta-tricalcium phosphate (β-TCP), which has a chemical composition close to bone. Materials and methodsPulsed Nd:YAG laser of single pulse capability up to 70 J/10 ms and pulse peak power of 8 kW was used to implement the task. Laser pulse peak power, pulse duration, repetition rate and scanning speed were modulated to achieve the most homogenous, cohesive and highly adherent coat layer. Scanning electron microscopy (SEM), energy dispersive X-ray microscopy (EDX), optical microscopy and nanoindentation analyses were conducted to characterise and evaluate the microstructure, phases, modulus of elasticity of the coating layer and calcium-to-phosphate ratio and composition.Results showed that the laser power and scanning speed influenced coating adherence. The cross-sectional field-emission scanning electron microscopy images at low power and high speed showed poor adherence and improved as the laser power increased to 2 kW. Decreasing the scanning speed to 0.2 mm/s at the same power of 2 kW increased adherence. EDX results of the substrate demonstrated that the chemical composition of the coat layer did not change after processing. Moreover, the maps revealed proper distribution of Ca and P with some agglomeration on the surface. The sharp peaks on the X-ray diffraction patterns indicated that β-TCPs in the coat layer were mostly crystalline. The elastic modulus was low at the surface and increased gradually with depth to reach 19 GPa at 200 nm; this value was close to that of bone. The microhardness of the coated substrate increased by about 88%. The laser pulse energy of 8.3 J, pulse peak power of 2 kW, pulse duration of 4.3 min, repetition rate of 10 Hz and scanning speed of 0.2 ms−1 yielded the best results. ConclusionBoth processing and coating have potential use for dental implant applications.

Influence of Mg ion concentration in ZrO2 gate dielectric layered silicon based MOS capacitors for memory applications: Thorough understanding of conduction processes

Various high-κ metal-oxide-semiconductor (MOS) capacitors with different concentrations of Mg doped ZrO2 (Mg:ZrO2) gate dielectric on p-type silicon (100) substrates were fabricated by using electron beam evaporation. A uniform and crack free dielectric layers of Mg:ZrO2 having RMS surface roughness in the range from 0.25 to 0.83 nm were achieved. The dielectric layers were structurally and electrically studied. Structural analysis from GIXRD and Williamson-Hall plots revealed that Mg incorporation into ZrO2 lattice has stabilized the tetragonal phase and the residual strain in the tetragonal stabilized Mg:ZrO2 layers had increased with increasing Mg concentration. Elemental composition studies of different layers in the MOS capacitors using Rutherford backscattering spectrometry (RBS) revealed the presence of very thin, unintentional and non-stoichiometric SiOx interfacial layer between dielectric and semiconductor interfaces. Thickness of the Mg:ZrO2 dielectric layers in the MOS capacitors measured by using RBS and cross-sectional field-emission scanning electron microscopy was in the range from 44.7 to 96.6 nm. A high dielectric constant of 29.8 with the equivalent oxide thickness of 6.5 nm was achieved in the 5 mol% Mg:ZrO2 dielectric layer. The hysteresis in the C-V characteristics of the MOS capacitors has been explained in detail based on the interactions of Mg ions with oxygen vacancies in the dielectric layer. Various conduction mechanisms have been elucidated to explain the leakage currents in the MOS capacitors. The decrease in Schottky and Poole-Frenkel barrier heights at the lower voltages (0 to − 3V) was found responsible for the increase in the leakage current as the Mg ion concentration was increased. Space charge limited conduction mechanism has been found to be dominant in larger applied voltage region (− 3V to − 10V). The Fowler-Nordheim tunneling and trap-assisted tunneling were dominant at the higher negative voltage regions greater than − 10V.

Differently-charged graphene-based multilayer films by a layer-by-layer approach for oxygen gas barrier application

Polyelectrolyte-decorated graphene with positive and negative charges was prepared using graphene oxide as a precursor along with polyallylamine hydrochloride and poly (styrenesulfonate sodium) as surface modifiers, respectively. Driven by an electrostatic interaction, the as-obtained polyelectrolyte-decorated graphene sheets were self-assembled via a layer-by-layer method, producing graphene based composite multilayers. Field emission scanning electron microscopy (FE-SEM) images showed that the surface of composite film exhibited a mass of characteristic wrinkles of graphene. Interestingly, the cross-sectional FE-SEM of the film exhibited an unstratified structure, indicating a good dispersion of graphene sheets in the composite film. The results of oxygen gas permeability testing demonstrated that the resulting composite films exhibited excellent oxygen gas barrier properties. The oxygen gas transmission rate (OTR) of the composite film with 24 bilayers was as low as 1.2 cm3 m-2 d-1∙atm−1, exhibiting potential for use in packaging applications.

Nanomechanical Properties of ALD Hafnium Oxide (HfO2) on Silicon-on-Insulator (SOI) and Strained Silicon-on-Insulator (sSOI) Films

Hafnium oxide is used as replacement for silicon oxide as a gate insulator in field-effect transistors [1]. HfO2 is used as a high-κ dielectric in DRAM capacitors and in advanced metal-oxide-semiconductor FET devices and in optical coatings [2]. Thin films of hafnium oxide (HfO2) were deposited by atomic layer deposition (ALD) on silicon-on-insulator (SOI) and benchmarked against strained-silicon-on-insulator (sSOI). Both types of films have been tested for surface morphology, crystal structure and nanomechanical properties. The nanomechanical properties have been tested using a nanoindenter from Keysight equipped with a three sided Berkovich diamond tip. The crystalline structure has been verified using X-ray diffraction. The surface morphology has been examined using atomic force microscopy (AFM) and the film thickness was verified using field emission scanning electron microscopy (FE-SEM) as indicated by the cross-sectional FE-SEM image as shown in Figure 1. We will discuss the structural and mechanical properties of the films citing the superiority of the ALD technique that is particularly used in the fabrication of the films that are presented in this study. References Intel (11 November 2007). "Intel's Fundamental Advance in Transistor Design Extends Moore's Law, Computing Performance".Zhu, C. Tang, L. R. C. Fonseca, and R. Ramprasad 47, 7399 (2012). Figure 1

Investigation of the Nanomechanical Properties of Titanium Oxide Films Synthesized Using Atomic Layer Deposition

Titanium oxides thin films are used in artificial heart valves due to their superb biocompatibility. They are used as photocatalysts in solar cells for the production of hydrogen and electric energy due to their stability, nontoxicity, and excellent photocatalytic properties [1]. TiO2 films are also used in heterogeneous catalysis, as a corrosion protective coating [2] and as electrode material in lithium rechargeable batteries. Above all TiO2 is utilized in massive amounts as white pigments in paints and toothpaste and cosmetic products. It is reported that TiO2 exists in three different crystalline structures: rutile, anatase (both tetragonal) and brookite (rhombohedral). Many of the properties in these applications are strongly dependent on titanium oxide’s crystal morphology, surface area, and mechanical properties. TiO2 films of 500 nm thickness were synthesized using atomic layer deposition (ALD) on p-type Si (100). The films are tested for surface morphology, crystal structure and nanomechanical properties. The nanomechanical properties are tested using a nanoindenter from Keysight equipped with a three sided Berkovich diamond tip. The crystalline structure is verified using X-ray diffraction. The surface morphology is examined using atomic force microscopy (AFM) and the film thickness was verified using field emission scanning electron microscopy (FE-SEM) as indicated by the cross sectional FE-SEM image, shown in Figure 1. We will discuss the structural and mechanical properties of the films citing the superiority of the ALD technique that is particularly used in the fabrication of the films that are presented in this study. References -Q. Hou, D.-M. Zhuang, G. Zhang, M. Zhao, and M.-S. Wu, Applied Surface Science, 218, 97 (2003).Diebold, Surface Science reports, 48, 53 (2003).X. Feng,G. Q.Xu, J. Lv,Q. M. Huang, Z. X. Zheng, andY. C.Wu, J. Electrochem. Soc, 160, H727 (2013). Figure 1

Preparation of rare earth CeO2 thin films using metal organic decomposition method for metal-oxide–semiconductor capacitors

Investigation of metal organic decomposed rare earth cerium oxide thin films deposited on Si substrate by sol–gel spin coating technique was carried out. The structural properties have been examined by using XRD, Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The XRD confirms the cubic phase of CeO2 thin films with (111) plane observed at 28.54°. The FTIR and EDAX spectra confirm the formation of CeO2 films with atomic percentage of 19.39 and 54.82% of Ce and O2, respectively. Thickness of 60.11 nm of CeO2 film measured by cross sectional FESEM image, the average roughness of ~0.6 nm of 400 °C annealed CeO2 films were observed from AFM micrograph. The MOS capacitors were fabricated by using Ti/Au bilayer metal contact depositing by E-beam evaporator on CeO2/Si thin film for electrical measurements. Capacitance and conductance voltage measurement was carried out to determine the effective oxide charges (Qeff), interface trap density (Dit) and dielectric constant (k) and are 2.48 × 1012 cm−2, 1.26 × 1012 eV−1cm−2 and ~39, respectively. The effective metal work function of 5.68 for Ti/Au bilayer is observed to be higher than the work function of Ti or Au metals in vacuum.

Preparation and Characterization of Antibacterial Cellulose/Chitosan Nanofiltration Membranes.

Presently, most nanofiltration membranes are prepared with non-biodegradable petrochemical materials. This process is harmful to the ecosystem and consumes a large amount of non-renewable energy. In this study, biodegradable and biocompatible antibacterial cellulose/chitosan nanofiltration membranes (BC/CS-NFMs) were fabricated and characterized for their mechanical strength, antimicrobial activity, salt and dye filtration performance, and polyethylene glycol (PEG) retention using Thermal gravimetric analysis (TGA), Field emission scanning electron microscopy(FE-SEM), Fourier transform infrared spectroscopy(FT-IR), and X-ray diffraction (XRD). The BC/CS-NFMs were obtained by the hydrolysis and carboxymethylation of dense cellulose/chitosan membranes (BC/CSMs). The tensile strength of the BC/CS-NFMs decreased as the chitosan content increased. In addition, the thermal stability and antibacterial ability of the BC/CS-NFMs improved. The pore size is less than 1 nm, and a spongy, layered structure is observed in the cross-sectional FE-SEM images. FT-IR analysis shows that a part of the hydroxyl in cellulose transforms to carboxymethyl during the hydrolysis and carboxymethylation of the BC/CSMs. No obvious changes can be observed in the cellulose and chitosan after the blend membrane formation from the XRD measurements. Based on the experimental results on the permeation and rejection of BC/CS-NFMs, different proportions of cellulose and chitosan nanofiltration membranes almost did not affect the water flux and rejection rate. The BC/CS-NFMs showed better water flux and a higher rejection rate in aqueous dye-salt solutions.

Effects of post-annealing treatment on the structure and photoluminescence properties of CdS/PS nanocomposites prepared by sol-gel method

CdS nanocrystals have been successfully grown on porous silicon (PS) by sol-gel method. The plan-view field emission scanning electron microscopy (FESEM) shows that the pore size of PS is smaller than 5 μm in diameter and the agglomerates of CdS are broadly distributed on the surface of PS substrate. With the increase of annealing time, the CdS nanoparticles grow in both length and diameter along the preferred orientation. The cross-sectional FESEM images of ZnO/PS show that CdS nanocrystals are uniformly penetrated into all PS layers and adhere to them very well. photoluminescence (PL) spectra demonstrate that the intensity of PL peak located at about 425 nm has almost no change after the annealing time increases. The range of emission wavelength of CdS/PS is from 425 nm to 455 nm and the PL intensity is decreasing with the annealing temperature increasing from 100 °C to 200 °C.

The influence of current density on the morphology and corrosion properties of MAO coatings on AZ31B magnesium alloy

Micro-arc oxidation (MAO) coatings were prepared on AZ31B magnesium alloy using alkaline silicate electrolyte at different current densities (0.026, 0.046 and 0.067 A/cm2). Field Emission Scanning Electron Microscopy (FESEM) analysis of the coating revealed an irregular porous structure with cracked morphology. Compositional analysis carried out for MAO coating showed the presence of almost an equal amount of Mg and O (34 wt.%) apart from other elements such as F, Si and Al. The cross-sectional FESEM images clearly portrayed that the MAO coating was dense along with the presence of very few fine pores. The surface roughness (Ra) of the coatings increased with an increase in the current density. Potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) studies were carried out for both the bare and MAO coated AZ31B Mg alloy in 3.5% NaCl solution. The corrosion potential (Ecorr) and corrosion current density (icorr) values obtained for the bare substrate were − 1.49 V and 46 μA/cm2, respectively. The coating prepared at 0.046 A/cm2 exhibited the lowest icorr value of 7.79 × 10− 10 A/cm2 and highest polarization resistance (41.6 MΩ cm2) attesting to the better corrosion resistance of the coating compared to other samples. EIS results also indicated almost similar corrosion behavior for the MAO coatings. Mott–Schottky analysis showed n-type and p-type semiconductor behavior for the oxide layer present on the bare magnesium alloy and MAO coatings respectively.

Flux-boosted coating of idiomorphic CuInS2crystal layers on Mo-coated glass substrate

Cu–In–Ga–S–Se (CIGSSe) is a promising light-absorber in thin-film photovoltaic cells, as well as a photocathode for solar H2 production, but the fabrication of layers of CIGSSe crystals on substrates is both time- and cost-intensive. Here, we report the fabrication of CuInS2 crystal layers on various precursor-loaded Mo/soda-lime glass (SLG) substrates using a flux coating method. X-ray diffraction analysis indicated that the main phase was CuInS2, while MoS2 which formed through the sulfurization of the Mo substrate was present as a minor phase. Top-surface field-emission scanning electron microscopy (FE-SEM) images indicated that the CuInS2 crystals were sparsely formed on the bare Mo/SLG, In/Mo/SLG, and Cu/Mo/SLG substrates. In contrast, closely packed CuInS2 crystals were formed on Cu2S/Mo/SLG. Smaller CuInS2 crystals 0.5–1 μm in size were grown on Cu2S/Mo/SLG compared to those on other substrates. This sharp difference in crystal population and size could be attributed to the pre-loading effect of the precursors. Cross-sectional FE-SEM analysis with energy-dispersive X-ray spectroscopy mapping revealed the homogenous fabrication of idiomorphic CuInS2 crystals on the partially sulfurized Mo substrate, yielding a CuInS2/MoS2/Mo heterostructure amenable to photovoltaic applications. The formation mechanism of this unique heterostructure was discussed based on the experimental results.

The properties of PMMA/DCJTB thin-film luminescent solar concentrator with various thicknesses

The PMMA/DCJTB thin-film luminescent solar concentrators (LCSs) with various thicknesses have been successfully prepared with the spin coating process. The properties of PMMA/DCJTB thin-film LSCs with various thicknesses have been studied. The cross-sectional field-emission scanning electron microscopy (FESEM) micrographs show that the thin-films on the glass substrate are very smooth. The thicknesses are 1.36±0.03, 1.93±0.07, 2.80±0.05 and 4.00±0.06μm. The value of the absolute fluorescence quantum yield (Φf) of the as-prepared LSCs decreases from 59.09% to 51.91% when the PMMA/DCJTB thin-film thickness increases from 1.36 to 4.00μm. The values of open-circuit voltage (Voc), short-circuit current density (Jsc), fill factor (FF), and overall power conversion efficiency (η) are 0.51V, 29.47mA/cm2, 65.54%, and 9.85%, respectively, for the PMMA/DCJTB thin-film LSCs with a thickness of 4.00μm.

Design and fabrication of spectrally selective TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber for high-temperature solar thermal power applications

A new nanostructured TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber has been designed for high-temperature solar thermal power applications. The first three layers in this tandem act as an absorbing layer, whereas, TiAlSiCO and TiAlSiO act as semi-transparent and anti-reflecting layers. The tandem absorber was deposited on stainless steel substrates using a four-cathode reactive direct current unbalanced magnetron sputtering system. The composition and thicknesses of the individual component layers have been optimized by adjusting the reactive flow rate of C2H2, N2, O2, and also Al, Ti and Si target power densities to achieve high absorptance (0.961) and low emittance (0.07 at 82°C). The reflectance data showed that the absorptance increases gradually with shift of reflectance minimum to higher wavelengths from first layer to last layer (i.e., TiAlC to TiAlSiO). The thickness of optimized tandem absorber was calculated from the cross-sectional field-emission scanning electron microscopy images and confirmed using transmission electron microscopy. The performance evaluation of the tandem absorber has been evaluated by heating it in air and vacuum under cycling conditions at different temperatures. These results showed that the tandem absorber was stable up to 325°C in air for 400h and up to 650°C in vacuum for 100h, thus demonstrating its suitability for high-temperature solar thermal power generation applications.

Plasma-assisted hot filament chemical vapor deposition of AlN thin films on ZnO buffer layer: toward highly c-axis-oriented, uniform, insulative films

c-Axis-oriented aluminum nitride (AlN) thin film with improved quality was deposited on Si(111) substrate using ZnO buffer layer by plasma-assisted hot filament chemical vapor deposition. The optical and electrical properties and surface morphology as well as elemental composition of the AlN films deposited with and without ZnO buffer layer were investigated using a host of measurement techniques: X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, field emission scanning electron microscopy (FESEM), and current–voltage (I–V) characteristic measurement. The XRD and XPS results reveal that the AlN/ZnO/Si films are free of metallic Al particles. Also, cross-sectional FESEM observations suggest formation of a well-aligned, uniform, continuous, and highly (002) oriented structure for a bi-layered AlN film when Si(111) is covered with ZnO buffer. Moreover, a decrease in full width at half maximum of the E2 (high)-mode peak in Raman spectrum indicates a better crystallinity for the AlN films formed on ZnO/Si substrate. Finally, I–V curves obtained indicate that the electrical behavior of the AlN thin films switches from conductive to insulative when film is grown on a ZnO-buffered Si substrate.

Microstructure Control of Absorber Sb2S3 and p-Type Semiconductor CuSCN for Semiconductor-Sensitized Solar Cells (TiO2/Sb2S3/CuSCN)

INTRODUCTION Semiconductor-sensitized solar cells (SSSCs) have greater stability of the semiconductor compared to organic dyes. Antimony sulfide (Sb2S3) is considered as a remarkable absorber for SSSCs due to its high absorption coefficient[1], low toxicity, abundance of its elements, and direct band gap with absorption in the visible range (approximately 1.8eV[2]). Sb2S3-based extremely thin absorber (ETA) solar cells reportedly have a 3.7% efficiency when the structure is porous TiO2 as n-type semiconductor and CuSCN as p-type semiconductor[3]. Photo-generated carriers are produced in Sb2S3 films, and a fast charge separation occurs due to the “thinness” of the absorber. However, the relation between the microstructure of absorber Sb2S3and the power generation characteristics of this type of ETA solar cells remains unclear.In this study, two deposition methods were introduced, namely, sputtering, which allows easy control of Sb2S3 deposition on thin TiO2 films by adjusting the deposition time, and inkjet-printing, which promises no physical contact with Sb2S3 when depositing CuSCN. Compared with Sb2S3 and CuSCN’s previous deposition methods, chemical bath deposition (CBD) and wiping, new deposition methods have their advantages. Improved cell efficiency is expected by controlling the microstructure of absorber Sb2S3and p-type semiconductor CuSCN with these two deposition methods. EXPERIMENTAL A thin TiO2 film was deposited on transparent conductive oxide (TCO) glass by spray pyrolysis. Sb2S3 was then deposited on this film by CBD from a solution of SbCl3 and Na2S2O3 (Aldrich). Alternatively, Sb2S3 film was deposited by sputtering using a Sb2S3 target of 99.9% purity (Kojundo Chemical) in an argon atmosphere with a base pressure of 5×10−4 Pa and with a launch power of 50 W. Both of these amorphous Sb2S3 films deposited by CBD and sputtering were then annealed in nitrogen at 320°C for 20 min to yield dark-brown crystalline stibnite. CuSCN was deposited by wiping or by inkjet-printing in an ambient atmosphere using a slightly under-saturated solution of CuSCN in dipropyl sulfide heated to 80°C. ETA solar cells were completed by depositing a gold film as the electrode by vacuum evaporation. I-V curves were measured using a solar simulator (CEP-25MLH) under simulated AM1.5, 100mW/cm2 sunlight and in the dark. Photovoltaic parameters, i.e. short circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF) and cell efficiency (η) were determined from the I-V curves. For the field emission scanning electron microscopy (FE-SEM) images, samples were prepared with a cross-section polisher (CP) and by deposition of a platinum coating. RESULTS AND DISCUSSION Figure 1 shows the dependence of Jsc of ETA solar cells upon absorbance of sputter-deposited Sb2S3 at 500 nm. Absorbance depends on the thickness of Sb2S3. By controlling the deposition time of Sb2S3, the film thickness can easily be controlled by sputtering. Sb2S3 absorbance around 0.6 yielded the highest Jsc. With thinner films, the number of absorbed photons is not sufficient to yield a high amount of photo-generated carriers, whereas thicker films increase the amount of recombination of photo-generated carriers. Cell efficiency of ETA solar cells with sputter-deposited Sb2S3 is clearly improved compared with CBD-deposited Sb2S3(Table 1).Figure 2 compares cross-sectional FE-SEM images of typical cells with wiping-deposited and inkjet-printed CuSCN films. The inkjet-printed CuSCN film exhibited large holes and was approximately two times thicker than the wiping-deposited CuSCN film. Table 2 shows the photovoltaic parameters of ETA solar cells with wiping-deposited and inkjet-printed CuSCN films. In this study, ETA solar cells with wiping-deposited CuSCN films exhibited better power generation characteristic compared with inkjet-printed CuSCN films. However, the deposition conditions for inkjet-printing still need optimization, and cell efficiency is expected to improve for this method. CONCLUSION In summary, with the new deposition methods introduced in this study, namely sputtering and inkjet-printing, absorber Sb2S3 and p-type semiconductor CuSCN were deposited successfully. By controlling the microstructure of Sb2S3, ETA solar cell efficiency was improved. The inkjet-printing conditions still need optimization to yield a higher cell efficiency. REFERENCE [1] Versavel et al. ,Thin Solid Films, 515,7171-7176(2007)[2]Mane et al.,Master.Chem.Phys,141,2871-2877(1994)[3]S.Nezu et al., J.Phys.Chem.C, 114, 6854-6859(2010)