A highly textured silicon 111 crystalline continuous thin-film film has been deposited on an MgO buffered soda lime glass substrate from an aluminum-silicon (Al-Si) eutectic melt using the ...conventional e-beam deposition. The silicon film growth was accomplished heteroepitaxially on the MgO buffered soda lime glass substrate. The resulting highly oriented crystalline film was then characterized by X-ray diffraction (XRD) and Raman spectroscopy for the detection of Si crystallization, as well as scanning electron microscopy (SEM). The low temperature Si crystallization method presented here requires no secondary annealing step and has the capability for high rate depositions without breaking vacuum. Furthermore, this method has the theoretical feasibility to induce single crystalline growth on the glass substrate, subsequently translating to a highly cost effective process with the potential to play a major role in the adoption of thin film silicon solar technology.
•Highly textured silicon 111 thin-film on ordinary soda-lime glass.•Highly textured MgO 111 buffer layer on soda-lime glass.•No secondary annealing step.•Capability for high rate depositions without breaking vacuum.•Highly cost effective process for solar cell manufacturing.
Sb-doped magnesium silicide compounds have been prepared through ball milling and solid-state reaction. Materials produced were near-stoichiometric. The structural modifications have been studied ...with powder x-ray diffraction. Highly dense pellets of Mg
2
Si
1−
x
Sb
x
(0 ≤
x
≤ 0.04) were fabricated via hot pressing and studied in terms of Seebeck coefficient, electrical and thermal conductivity, and free carrier concentration as a function of Sb concentration. Their thermoelectric performance in the high temperature range is presented, and the maximum value of the dimensionless figure of merit was found to be 0.46 at 810 K, for the Mg
2
Si
0.915
Sb
0.015
member.
Terahertz (THz) radiation is a powerful tool with widespread applications ranging from imaging, sensing, and broadband communications to spectroscopy and nonlinear control of materials. Future ...progress in THz technology depends on the development of efficient, structurally simple THz emitters that can be implemented in advanced miniaturized devices. Here, it is shown how the natural electronic anisotropy of layered conducting transition metal oxides enables the generation of intense terahertz radiation via the transverse thermoelectric effect. In thin films grown on off‐cut substrates, femtosecond laser pulses generate ultrafast out‐of‐plane temperature gradients, which in turn launch in‐plane thermoelectric currents, thus allowing efficient emission of the resulting THz field out of the film structure. This scheme is demonstrated in experiments on thin films of the layered metals PdCoO2 and La1.84Sr0.16CuO4, and model calculations that elucidate the influence of the material parameters on the intensity and spectral characteristics of the emitted THz field are presented. Due to its simplicity, the method opens up a promising avenue for the development of highly versatile THz sources and integrable emitter elements.
Intense terahertz radiation generation via the transverse thermoelectric effect in layered conducting transition metal oxides is demonstrated . Ultrafast out‐of‐plane temperature gradients, induced by femtosecond laser pulses on thin films grown on off‐cut substrates, launch in‐plane thermoelectric currents leading to efficient THz emission. This approach offers a simple and promising avenue for versatile THz sources and integrable emitter elements.
In contrast to the disordered body-centered cubic (bcc) A2 phase, the ordered face-centered cubic (fcc) L12 phase exhibits negative magnetostriction (λ) and has a high elastic modulus (E). Therefore, ...an in-depth understanding of the microstructural evolution of Fe–Ga thin films from bcc A2 phase to fcc L12 phase is essential to obtain Fe–Ga thin films with desirable properties. The transformation of the phase structure, magnetic domain structure, and magnetic properties of Fe72Ga28 thin films is analyzed in this study. The phase transformation of the Fe72Ga28 thin film from A2 to A2 L12 occurred after heat treatment, as determined by high-resolution transmission electron microscopy (HRTEM) and glancing-incidence X-ray diffraction (GI-XRD). Non-continuous lattice distortion at the phase boundaries of A2 and L12 was also observed, as shown by geometric phase analysis (GPA) and electron backscattered scattering detection (EBSD). Numerous edge dislocations at the phase boundaries were revealed by HRTEM. A shift in the magnetic domain structure from the maze-like domain to maze-like domain and honeycomb-like domain was detected by magnetic force microscopy (MFM). The variation in magnetic properties was determined to be related to the structural transformation and ununiform lattice distortion between the phase boundaries of the A2 and L12.
•The A2 to A2+L12 transition in annealed Fe72Ga28 thin films is proved.•The largest lattice distortion is discontinuous along the phase boundaries of the A2 and L12 phases.•The lattice distortion of the L12 phase is not uniform, unlike that of the A2 phase.•Magnetic domain of annealed Fe72Ga28 thin films changed from maze-like domain to maze-like domain and honeycomb-like domain.•The effects of structural transformation and lattice distortion on the magnetic properties of the films are evaluated.
With about two-thirds of all used energy being lost as waste heat, there is a compelling need for high-performance thermoelectric materials that can directly and reversibly convert heat to electrical ...energy. However, the practical realization of thermoelectric materials is limited by their hitherto low figure of merit, ZT, which governs the Carnot efficiency according to the second law of thermodynamics. The recent successful strategy of nanostructuring to reduce thermal conductivity has achieved record-high ZT values in the range 1.5-1.8 at 750-900 kelvin, but still falls short of the generally desired threshold value of 2. Nanostructures in bulk thermoelectrics allow effective phonon scattering of a significant portion of the phonon spectrum, but phonons with long mean free paths remain largely unaffected. Here we show that heat-carrying phonons with long mean free paths can be scattered by controlling and fine-tuning the mesoscale architecture of nanostructured thermoelectric materials. Thus, by considering sources of scattering on all relevant length scales in a hierarchical fashion--from atomic-scale lattice disorder and nanoscale endotaxial precipitates to mesoscale grain boundaries--we achieve the maximum reduction in lattice thermal conductivity and a large enhancement in the thermoelectric performance of PbTe. By taking such a panoscopic approach to the scattering of heat-carrying phonons across integrated length scales, we go beyond nanostructuring and demonstrate a ZT value of ∼2.2 at 915 kelvin in p-type PbTe endotaxially nanostructured with SrTe at a concentration of 4 mole per cent and mesostructured with powder processing and spark plasma sintering. This increase in ZT beyond the threshold of 2 highlights the role of, and need for, multiscale hierarchical architecture in controlling phonon scattering in bulk thermoelectrics, and offers a realistic prospect of the recovery of a significant portion of waste heat.
A major hindrance in developing ferroelectric (FE) devices based on non-centrosymmetric and eco-friendly wurtzite ZnO is its non-switchable polarization. Doping with smaller ionic radii cations ...induces switchable polarization in ZnO; however, the remnant polarization achieved through doping is very low (2Pr < 2 μC/cm2), limiting its functionalities. Here we report V-doped ZnO thin films exhibiting 2Pr value as high as 12 μC/cm2 via a simple solution process. We achieved such a high polarization by controlling the crystallite size, morphology, and valence state of vanadium– which were optimized through variation of V-doping concentration and post-deposition annealing temperature. We found that the FE and dielectric properties of the V–ZnO films were directly linked to the crystalline size, morphology, and valence state of V. We also tested the applicability of V–ZnO as a coating layer on mesh type air filters and achieved a particulate matter filtering efficiency of up to 8%. Our study opens up the possibility of utilizing ferroelectric V–ZnO in particulate matter filtering devices.
•Vanadium doping induces ferroelectricity in sol-gel processed ZnO thin films.•Crystallinity, V-valence state, and the microstructure plays a critical role in inducing FE.•The remnant polarization (2Pr) as high as12 μC/cm2 at 600 °C post-annealed 5% V-doped ZnO film.•The ferroelectricity of V-doped ZnO film coating enhances the dust filtration efficiency of a mesh-type air filter.
In recent years, antimony selenide (Sb2Se3) has shown great potential as a photoactive material for thin film solar cells. To understand the growth mechanism and carrier transport behavior of Sb2Se3 ...thin films with the 1D crystal structure, the structure, properties, and photovoltaic performance of Sb2Se3 thin films with different preferred orientations were systematically characterized. The results show that Sb2Se3 thin films’ microstructure is mainly determined by the competing lateral and vertical growth of (Sb4Se6)n ribbons. As the (Sb4Se6)n ribbons’ lateral growth proportion becomes more significant, the thin film gets a flatter surface and denser microstructure, but the vertical carrier transport capability is correspondingly weaker. In contrast, when (Sb4Se6)n ribbons are dominated by the vertical growth mode, Sb2Se3 thin films tend to form an arranged nanorods structure. This structure has excellent vertical carrier transport capability; however, it also inevitably leads to increased carrier recombination due to the abundant grain boundary. As the deposition of the Sb2Se3 thin film gradually changes from the lateral growth to the vertical growth, the solar cell performance could be improved due to the enhancement of carrier transport. However, when the vertical growth ratio is too high, the fill factor of the device will reduce due to the increase of the leakage current. We demonstrate that the regulation of lateral and vertical growth proportion in Sb2Se3 photoactive layers is essential to yielding an efficient solar cell.
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•Regulation of (Sb4Se6)n ribbons growth simultaneously changes the structure and the conductivity of Sb2Se3 thin films.•The carrier transport of the Sb2Se3 thin films can be enhanced by increasing the vertical growth proportion.•The lateral growth in the Sb2Se3 thin films could fill the voids between grains to reduce leakage current.•A proper ratio of lateral and vertical growth in Sb2Se3 photoactive layers essential to yielding an efficient solar cell.
Nanocrystalline diamond Williams, O.A.
Diamond and related materials,
2011, Letnik:
20, Številka:
5
Journal Article
Recenzirano
Diamond properties are significantly affected by crystallite size. High surface to volume fractions result in enhanced disorder, sp
2 bonding, hydrogen content and scattering of electrons and ...phonons. Most of these properties are common to all low dimensional materials, but the addition of carbon allotropes introduces sp
2 bonding, a significant disadvantage over systems such as amorphous silicon. Increased sp
2 bonding results in enhanced disorder, a significantly more complex density of states within the bandgap, reduction of Young's modulus, increased optical absorption etc. At sizes below 10
nm, many diamond particle and film properties deviate substantially from that of bulk diamond, mostly due not only to the contribution of sp
2 bonding, but also at the extreme low dimensions due to size effects. Despite these drawbacks, nano-diamond films and particles are powerful systems for a variety of applications and the study of fundamental science. Knowledge of the fundamental properties of these materials allows a far greater exploitation of their attributes for specific applications. This review attempts to guide the reader between the various nanocrystalline diamond forms and applications, with a particular focus on thin films grown by chemical vapour deposition.
The fabricated Eu:CdS photodetector shows a significant enhancement in photo detectivity and photocurrent by Eu doping content.
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•A high performance visible light photodetector based ...on Eu:CdS has been fabricated.•The photo-responsitivity was enhanced by several times in 5 wt.% Eu:CdS compared to pure.•EQE was noticed to be many times higher for 5 % Eu:CdS compare to pure.•The photo-detectivity was remarkably enriched from 5 × 1011 to 1.38 × 1012 Jones.•The photo-switching property was remarkably enhanced by Eu doping.
This work deals with the preparation of undoped and rare earth europium-doped cadmium sulfide (Eu:CdS) films by spray pyrolysis procedure. X-ray diffraction (XRD), field emission-scanning electron microscopy, energy dispersive X-ray spectroscopy, ultraviolet-visible spectroscopy and photo-electrical studies were used to analyze the properties of the films. XRD analysis of CdS films showed polycrystalline nature with most preferred orientation along (002) and (101) for Eu:CdS. Eu doping improved the optical properties, the optical band gap of Eu:CdS films is noted to be larger compare to pure CdS thin films. Optical studies reveal the direct band gap variation from 2.43 eV to 2.48 eV with rising Eu doping from 1 wt.% to 5 wt.%. The increase in the nonlinear optical parameter was observed on Eu doping in CdS. The photo-electrical studies done for Eu:CdS films indicates that Eu doping has noticeable influence on electrical properties. The responsitivity for pure was ∼0.0629 AW−1 which increased to 0.614 AW−1, when 5 wt.% Eu was doped. The external quantum efficiency was enriched ∼ 8 times for 5 wt.% Eu:CdS compared to pure. The rise and decay time of Eu:CdS photodetector and its ON/OFF ratio was studied which is noticed ∼10 times larger compared to pure CdS. The observed enhancement in photodetector properties, morphology, crystalline quality and optical properties are caused by Eu doping concentration and hence will be more applicable in optoelectronics.
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