Dependence Of Structural Properties Research Articles

On-surface Synthesis of a Chiral Graphene Nanoribbon with Mixed Edge Structure.

Chiral graphene nanoribbons represent an important class of graphene nanomaterials with varying combinations of armchair and zigzag edges conferring them unique structure‐dependent electronic properties. Here, we describe the on‐surface synthesis of an unprecedented cove‐edge chiral GNR with a benzo‐fused backbone on a Au(111) surface using 2,6‐dibromo‐1,5‐diphenylnaphthalene as precursor. The initial precursor self‐assembly and the formation of the chiral GNRs upon annealing are revealed, along with a relatively small electronic bandgap of approximately 1.6 eV, by scanning tunnelling microscopy and spectroscopy.

Influence of ZnO nanostructure configuration on tailoring the optical bandgap: Theory and experiment

Exploiting the link between form and function of semiconductor nanostructure provides a new prospect for tailoring the features of nanoscale materials. However, achieving this remains a challenge in the fabrication of optoelectronic devices. Therefore, this research systematically presents theoretical and experimental investigations of shape dependent structural and optical properties of ZnO nanostructures (nanoparticles, vertically oriented nanorods and compact ZnO) synthesized using the electroless deposition technique to understand the principles of bandgap modification. FESEM, XRD, Photoluminescence (PL) and UV–Vis spectroscopic characterizations were employed. The characterizations show increase in lattice parameters, bandgap and density of dislocations from 0.3236 nm to 0.3258 nm, ~3.14 eV to ~3.51 eV and ~17 × 10-4 to ~39 × 10-4, respectively as the ZnO nanostructures are transformed from compact ZnO to ZnO nanoparticles. The expansion in lattice parameter is attributed to lower compressive stress that exists in ZnO nanoparticles compared to compact ZnO. The blue shift (0.06 eV) in bandgap is ascribed to overlapping of the orbitals and energy level in ZnO nanoparticles which causes a substantial increase in energy gap between valence and conduction bands. The small size-induced hardening in ZnO nanoparticles accounts for their comparatively higher dislocation density. Theoretically, conversion from compact ZnO to ZnO nanoparticles extends the bandgap from 3.38 eV to 3.44 eV, which is consistent with the experimental results. This study confirms the shape dependency of the structure and bandgap of ZnO nanostructures, which may provide a new insight into future integrated optoelectronic device applications.

(Invited) Manipulating Carrier Polarization in Semiconductor Nanocrystals

Degenerately-doped semiconductor nanocrystals exhibiting tunable localized surface plasmon resonance (LSPR) have attracted significant attention in recent years due to their unique optoelectronic properties. Unlike noble metal nanoparticles, colloidal plasmonic semiconductor nanocrystals have LSPR frequencies tunable in the infrared region, which makes them appealing for terahertz imaging, heat-responsive devices, and surface-enhanced infrared spectroscopic measurements. Besides expanding the LSPR frequency range, plasmonic semiconductor nanocrystals could potentially bring about numerous other opportunities related to single-phase plasmon-exciton interactions. However, non-resonant nature of the LSPR and exciton in semiconductors has been a major obstacle toward realizing such opportunities. In this talk I will discuss the results of our recent work on the structure and composition dependent plasmonic properties of colloidal semiconductor nanostructures. I will particularly focus on generating robust excitonic splitting in degenerately-doped transparent metal oxide nanocrystals, enabled by non-resonant plasmon-exciton coupling in an external magnetic field. This phenomenon allows for controlling carrier polarization in semiconductor nanocrystals using circularly polarized light. Furthermore, the ability to control carrier localization and nanocrystal morphology allows for further manipulation of the excitonic splitting pattern and quantum states in these non-magnetic semiconductor nanostructures. Possible applications of this emerging class of multifunctional materials for new electronic and quantum information technologies will also be discussed.

Annealing temperature dependent structural and optical properties of nanocrystalline ZnTe thin films developed by electrodeposition technique

ZnTe is a potential material for device fabrication because of the suitable optoelectronic properties. In this work, a nanocrystalline binary semiconductor zinc telluride (ZnTe) was developed in non-aqueous medium through an electrochemical deposition process. We report the structural and optical properties of developed ZnTe films deposited on nickel and glass substrate at various temperatures (350–500 °C). The solid state and optical properties of developed film was characterized by XRD, SEM, EDS, UV Vis spectroscopy and Photoluminescence spectroscopy. XRD analysis indicates the polycrystalline deposits in all the cases. The sharpness of the peak increases due to annealing of the film and average crystalline size increases. SEM photograph indicate that grains are uniform and densely distributed over the surface. The main effect of annealing temperature was helpful to improve crystalline structure, whereas the bandgap of semiconductor was reduced due to large density of dislocations. This study is vital for the optimization of the annealing temperature for growth of good-quality ZnTe films, which are necessary for device fabrication and applications.

Structure-Dependent Thermoelectric Properties of GeSe1-xTex (0 ≤ x ≤ 0.5).

GeSe was theoretically predicted to have thermoelectric (TE) performance as high as SnSe. However, the relatively high TE performance was not achieved experimentally in doped GeSe samples with an original orthorhombic structure but observed in Ag(Sb,Bi)(Se,Te)2 alloyed samples that crystalize in either a rhombohedral or cubic structure. Herein, to clarify the crystal structure-dependent properties, the electrical and thermal transport properties of GeSe1-xTex (0 ≤ x ≤ 0.5), where orthorhombic, hexagonal, and rhombohedral phases are stable at room temperature for different Te content, have been studied, without any intentional manipulation on carrier concentration. It is found that the three phases show intrinsically different hole concentrations: ∼1016 cm-3 for the orthorhombic phase but as high as 1021 cm-3 for the hexagonal and rhombohedral phases. Ge-rich status in the orthorhombic phase and Ge-poor status in hexagonal and rhombohedral phases may be responsible for the huge difference in hole concentrations. The rhombohedral phase shows a much higher Seebeck coefficient than the hexagonal phase with similar hole concentration, indicating that the profile of valance band maximum for the rhombohedral structure is more favorable for high TE performance than the hexagonal phase in GeSe1-xTex. The highest zT of 0.69 has been obtained in GeSe0.55Te0.45 at 778 K, at which temperature the rhombohedral phase has already transformed to a cubic phase; however, a zT value of 1.74 at 628 K is predicted by the quality factor analysis for rhombohedral GeSe0.55Te0.45 if optimum hole concentration can be achieved.

Synthesis of 3D-MoS2 nanoflowers with tunable surface area for the application in photocatalysis and SERS based sensing

Nanostructured two-dimensional transition metal dichalcogenides (2D-TMDCs) have been attracting great attention in the field of environmental remediation and sensing due to their high surface area and layer dependent optical and structural properties. Surface area dependent performance of MoS2 nanostructures is one of the important aspects which need to be explored for various environmental applications. In this work, MoS2 nanoflowers with tunable surface area (5–20 m2/g) were prepared by the facile hydrothermal method and their surface area dependent SERS and photodegradation activity were explored. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) studies assure the growth of MoS2 nanoflowers by the assembly of 2D-MoS2 nanosheets. MoS2 nanoflowers exhibit excellent sunlight-induced photocatalytic activity towards the degradation of methylene blue, methyl orange, rhodamine 6G and oxytetracycline hydrochloride molecules. We report that a very low amount (0.025 mg) of MoS2 nanoflowers (20 m2/g) can tremendously decompose 10 μM of MB, MO and R6G dye molecules in just 12 min, 30 min and 45 min respectively and 0.5 mg/10 mL OTC-HCl molecule in 60 min under sunlight which has not been reported yet. MoS2 nanoflowers based substrates show the remarkable SERS based detection towards the rhodamine B (RhB) molecule. Tunability in the SERS for the account of different surface areas poses by the different MoS2 sample has been well explored. Charge transfer mechanism for ultrafast SERS detection and enhanced photodegradation activity has been proposed and explained precisely.

Particle size dependent structural, magnetic and electrical properties of Cr-doped lead-free multiferroic AlFeO3 prepared by co-precipitation and solid state method

Polycrystalline samples AlFe0.95Cr0.05O3 synthesized by a solid state (s) and a co-precipitation method (cop). Particle size dependent studies on structural, magnetic and dielectric properties of Cr-doped AlFeO3 have been investigated. The magnetic structure was found to be ferromagnetic. The Fe3+ ions distribution among different sites seems to be related to the preparation methods. The, saturation magnetization (Ms), remanent magnetization (Mr), are enhanced as the particle size decrease, however, coercivity (Hc) decreases. Temperature and frequency electrical impedance and modulus analysis reveal that permittivity in Cr-doped AFO is strongly dependent on microstructure and preparation condition of the samples. Two relaxation processes are detected: high-frequency grain conduction and the low-frequency grain boundary conduction. The grain boundary activation energy was estimated to be higher than that of grain, both grain and grain boundary conduction activation energies increase with decreasing particle size making AFCr5-cop samples better insulators.

Multi aspect investigation of crude oil concentration detecting via optical fiber sensor coated with ZnO/Ag nano-heterostructure

Determining the crude oil concentration changes as an essential factor in reservoir engineering, via proposed modified optical fiber sensor, offers a novel approach in oil production optimization. A highly sensitive optical fiber probe is fabricated via partially removing the cladding and coating the sensing part with zinc oxide/silver (ZnO/Ag) heterostructre layer. The ZnO outer layer has three configurations including nanoparticle, horizontally and vertically oriented nanorods. The fabricated optical fiber sensors are subjected to detect the crude oil concentration variations through detection of both wavelengths shift and intensity changes. The effect of ZnO outer layer shape, and the type of light source is used, on sensitivity of the probe is examined. Comprehensive investigation on shape dependent structural and optical properties of ZnO outer layer demonstrates that vertically oriented ZnO has larger surface area, higher average dispersion relation, better crystallinity, larger surface roughness and better adhesion (interaction) with crude oil molecules and these characteristics are responsible for its superior performance compare to other ZnO configurations. For the probe coated with vertically aligned ZnO nanorods when the infrared (IR) light source is used, the intensity and wavelength sensitivity of 0.044 dB/Δ%crude oil and 0.112 nm/Δ %crude oil are obtained respectively.

Thickness dependent structural, morphological and optical properties of molybdenum oxide thin films

Molybdenum oxide ( $${\text {MoO}}_3$$ ) is a chromogenic and a wide band gap n-type semiconductor. Thickness of thin films is usually observed to have significant influence on various properties of chromogenic materials. $${\text {MoO}}_3$$ thin films of different thicknesses (100 nm, 200 nm and 400 nm) were deposited on glass substrates by thermal evaporation technique. The effect of thickness of deposited thin films on the structural, morphological and optical properties was investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM) and UV–visible spectroscopy. XRD analysis revealed the amorphous nature of deposited thin films of different thicknesses. FTIR spectrum showed the characteristic vibrations of intermolecular bonds in molybdenum oxide. The surface morphology of $${\text {MoO}}_3$$ films showed nanoflakes like structures which became densely stacked with increase in film thickness and transformed to large grains with uniform coverage of the substrate surface with randomly oriented morphology. The transmission spectra revealed the slight increase in average transmittance in the visible-NIR region with increase in thickness of thin films. The optical band gap of the deposited thin films of different thicknesses was found to be increasing with increase in thickness of the films which may be attributed to decreased defect centres. The decrease in the values of Urbach energy with increase in thickness may be due to the increased homogeneity and decrease in scattering centres.

Ontological model of multi-agent Smart-system for predicting drug properties based on modified algorithms of artificial immune systems

BackgroundCurrently, due to the huge progress in the field of information technologies and computer equipment, it is important to use modern approaches of artificial intelligence in order to process extensive chemical information at creating new drugs with desired properties.The interdisciplinary of research creates additional difficulties in creating new drugs. Currently, there are no universal algorithms and software for predicting the “structure-property” dependence of drug compounds that can take into account the needs of specialists in this field.In this regard, the development of a modern Smart-system based on the promising bio-inspired approach of artificial immune systems for predicting the structure-property dependence of drug compounds is relevant.The aim of this work is to develop a multi-agent Smart-system for predicting the “structure-property” dependence of drug compounds using the ontological approach and modified algorithms of artificial immune systems using the example of drug compounds of the sulfonamide group. The proposed system makes it possible to increase the accuracy of prediction models of the “structure-property” dependence, to reduce the time and financial costs for obtaining candidate drug compounds.MethodsDuring the creation of a Smart-system, there are used multi-agent and ontological approaches, which allow to structure input and output data, optimally to distribute computing resources and to coordinate the work of the system. As a promising approach for processing a large amount of chemical information, extracting informative descriptors and for the creation of an optimal data set, as well as further predicting the properties of medicinal compounds, there are considered modified algorithms of artificial immune systems and various algorithms of artificial intelligence.ResultsThere was developed an ontological model of a multi-agent Smart-system. There are presented the results of the «structure-property» dependence simulation based on a modified grey wolf optimization algorithm and artificial immune systems. During the simulation, there was used information from the Mol-Instincts sulfonamide descriptor database.ConclusionThe developed multi-agent Smart-system using ontological models allows visually to present the structure and interrelationships of agents functioning, which greatly facilitates the development of software and reduces time and financial costs during the development of new drugs.

Significant effect of film thickness on morphology and third-order optical nonlinearities of Cd1−xZnxO semiconductor nanostructures for optoelectronics

The work presented here reported the thickness dependent structural, linear and nonlinear optical properties of nanostructured Cd1−xZnxO thin films. Thin films were prepared with two different thickness (≈ 0.5 µm and 1 µm) by employing a spray pyrolysis (SP) technique for different Zn-doping levels (Cd1−xZnxO with the x value of 0.00, 0.01, 0.05 and 0.1). X-ray diffraction studies confirm the polycrystalline nature having a cubic crystal structure. In terms of an aspect ratio of the columnar structure and dispersion in hexagonal (1 1 1) basal plane orientation, a thickness dependency of structural evolution was discussed. The Scherrer rule was employed to determine the crystallite size and found to be decreased. FESEM images indicate grains which are uniform and grain size slightly increased with an increase in dopant concentration, annealing and thickness of the films, respectively. The optical energy band gap (Eg) of the prepared films was found to be increased from 2.50 to 2.67 eV. The NLO parameters of the samples were measured from the Z-scan data under DPSS continuous wave laser excitation at 532 nm and the results reveal that reverse saturable absorption (RSA) and self-defocusing natures are the attributed and observed nonlinearity of the nanostructures. The third-order NLO components such as β, $$n_{2}$$ and χ(3) are found to be enhanced with one order of magnitude higher with the influence of thickness from 1.25 × 10–4 to 2.47 × 10–3 (cm W−1), 7.08 × 10–9 to 3.35 × 10–8 (cm2 W−1) and 4.06 × 10–7 to 1.96 × 10–6 (esu) respectively. The inspiring results of NLO parameters are also due to the increasing localized defect states on grain boundaries as the film thickness increases, suggesting the prepared films are a promising material for nonlinear photonic device applications.

Assessing Rietveld refinement results on silicon carbide nanoparticles produced by magnesiothermal treatment

Collection and evaluation of X-ray diffraction (XRD) data are essential not purely for phase and structural investigation, but more importantly for all intends and purposes of comprehensive materials characterizations. Incorrect XRD analysis result will lead to misinterpretation of the phase and structural characteristics. The worst part is that instigates inappropriate interpretation of other phase-dependent or structural-dependent properties, e.g. electric, magnetic, or thermodynamic properties. Consequently, accurate phase identification and crystal structure quantification from XRD data is inevitable prior to further materials characterizations, most significantly for nanomaterials. In this present study, we reported the complete XRD qualitative and quantitative analyses of silicon carbide (SiC) nanoparticles. The phase identification was run using X’Pert High Score Plus (HSP) software. Furthermore, the crystal structure computation was executed by means of different Rietveld-based computer programs, i.e. HSP, MAUD (Material Analysis using Diffraction), GSAS (General Structure Analysis System) and Rietica. Our research revealed that the synthesized silicon carbide preserved a cubic crystal structure. MAUD and GSAS could predict the equivalent particle size which was close to that of captured by transmission electron microscopy (TEM). In addition, MAUD produced the most accurate value of the particle size. In this case, Rietica and MAUD extracted similar lattice parameter of the silicon carbide. At last but not least, the electron density mapping also presented to confirm the cubic crystal structure formation of the silicon carbide nanoparticles.

Epitaxial strain and thickness dependent structural, electrical and magnetic properties of La0.67Sr0.33MnO3 films

The crystal structural quality and the strain induced by the substrate strictly impose the magnetic and transport properties of La0.67Sr0.33MnO3 (LSMO) films. In particular, the magnetic anisotropy (MA) of epitaxial LSMO can be finely tuned by varying its thickness and by choosing single crystal substrates with a suitable lattice mismatch with the film. Here, we have deposited LSMO films with thicknesses in the 12–50 nm range by pulsed laser deposition on different single crystal substrates inducing either compressive or tensile in-plane strain on the manganites. The epitaxial quality of films was quantified by ω-scans around a (002) peak with full-width half-maximum values as low as 0.08° for films on the nearly matched NGO (110) substrate to 1.4° films on the high mismatched MgO (001) substrate. As the epitaxial strain in a thin-film increases, a significant reduction in the metal-insulation transition temperature (Tp) was observed. The magnetic properties of the films probed by Kerr magnetometry show that the symmetry of the room temperature MA varies significantly as a function of both strain and thickness. Specifically, we observed pure uniaxial MA on NGO (110) and pure biaxial MA on STO buffered MgO (001), whereas a spin reorientation from uniaxial in-plane to out-of-plane on LSAT (001) and uniaxial to nearly isotropic in-plane on STO (001) substrate as the film thickness is increased. We provide an efficient tool to tune the MA according to the specific spintronic application targeted.

Structural, optical and temperature dependent photoluminescence properties of Cr3+-activated LaGaO3 persistent phosphor for optical thermometry

Cr3+ doped LaGaO3 phosphor was prepared by hydrothermal reaction method with post-annealing treatment. XRD pattern showed the pure orthorhombic phase of LaGaO3 at an annealing temperature of 1000 °C. TEM image showed the particles in the range 40-120 nm. The bandgap energy and Urbach tail increased in the doped sample as compared to the undoped sample as estimated from UV–visible diffuse reflectance spectra. PL excitation spectra showed peaks in UV, blue and orange regions. The emission spectra showed broadband with peaks in the NIR region due to emission from 4T2 and 2E states. The intermediate strength of the crystal field has been calculated from the estimated spectroscopic parameter. The average lifetime was found to be in the ms range. Afterglow decay was also recorded. From the low-temperature PL, the zero phonon line, stokes shift energy, vibrational energy and Huang-Rhys parameter were calculated. With rising the temperature, PL emission peak intensity and lifetime values decreased and FWHM increased because of increased numbers of electrons in 4T2 state and increasing non-radiative transition. Temperature-dependent peak intensity ratios and lifetime values were utilized for temperature sensing applications in below room temperature and above room temperature. The results indicate the possibility of present phosphor to be used as optical nanothermometer.

Structural, optical and magnetic properties of SnS2 nanoparticles and photo response characteristics of p-Si/n-SnS2 heterojunction diode

As an emanating layered metal dichalcogenides (LMDs), tin disulfide (SnS2) has immense potentials in next generation nanodevices considering their facile synthesis and versatile attributes. Here, we describe the hydrothermal synthesis of SnS2 nanoparticles at different temperatures and growth times and discussed its structural, optical and magnetic characteristics in detail. The SnS2 nanoparticles displayed growth time dependent structural, optical and magnetic properties. The structural analysis displayed hexagonal phase of SnS2 nanoparticles whose thickness increase with duration of growth. The vibrational modes of SnS2 nanoparticles in Raman spectra exhibited an increase in intensity with growth time, indicating an increased layer thickness with growth time. In addition, the optical properties were also affected by the growth time. Moreover, excitation dependent photoluminescence emission from these nanoparticles is observed, which is attributed to the polydispersity of nanoparticles. The realisation of room temperature ferromagnetism makes it a promising material for spintronic applications. Photocurrent properties of the spin coated n-SnS2 on p-silicon were analysed by studying J-V relationships. Tunable optical, electrical and magnetic properties of SnS2 layers could capacitate a great deal of freedom in modelling atomically thin optoelectronic and spintronic devices.

Self-templating assembly of soft microparticles into complex tessellations.

Encoding Archimedean and non-regular tessellations in self-assembled colloidal crystals promises unprecedented structure-dependent properties for applications ranging from low-friction coatings to optoelectronic metamaterials1-7. Yet, despite numerous computational studies predicting exotic structures even from simple interparticle interactions8-12, the realization of complex non-hexagonal crystals remains experimentally challenging13-18. Here we show that two hexagonally packed monolayers of identical spherical soft microparticles adsorbed at a liquid-liquid interface can assemble into a vast array of two-dimensional micropatterns, provided that they are immobilized onto a solid substrate one after the other. The first monolayer retains its lowest-energy hexagonal structure and acts as a template onto which the particles of the second monolayer are forced to rearrange. The frustration between the two lattices elicits symmetries that would not otherwise emerge if all the particles were assembled in a single step. Simply by varying the packing fraction of the two monolayers, we obtain not only low-coordinated structures such as rectangular and honeycomb lattices, but also rhomboidal, hexagonal and herringbone superlattices encoding non-regular tessellations. This is achieved without directional bonding, and the structures formed are equilibrium structures: molecular dynamics simulations show that these structures are thermodynamically stable and develop from short-range repulsive interactions, making them easy to predict, and thus suggesting avenues towards the rational design of complex micropatterns.

Liquid-Phase Synthesis of Iron Oxide Nanostructured Materials and Their Applications.

Owing to their high natural abundance, low cost, easy availability, and excellent magnetic properties, considerable interest has been devoted to the synthesis and applications of iron oxide nanostructured materials. Liquid-phase synthesis methods are economical and environmentally friendly with low energy consumption and volatile emissions, and as such have received much attention for the preparation of iron oxide nanostructured materials. Herein, the liquid-phase synthesis methods of iron oxide nanostructured materials including the co-precipitation method, microemulsion method, conventional hydrothermal and solvothermal methods, microwave-assisted heating method, sonolysis method, and other methods are summarized and reviewed. Many iron oxide nanostructured materials, self-assembled nanostructures, and nanocomposites have been successfully prepared, which are of great significance to enhance their structure-dependent properties and applications. The specific roles of liquid-phase chemical reaction parameters in regulating the chemical composition, structure, crystallinity, morphology, particle size, and dispersive behavior of the as-prepared iron oxide nanostructured materials are emphasized. The biomedical, environmental, and electrochemical energy storage applications of iron oxide nanostructured materials are discussed. Finally, challenges and perspectives are proposed for future investigations on the liquid-phase synthesis and applications of iron oxide nanostructured materials.

Spin-phonon coupling in Mn-Bi co-doped SmFeO3: An experimental study

The intriguing physical properties of SmFeO3 such as spin-phonon coupling and spin reorientation transition (~480 K) make it interesting from fundamental point of view and a suitable candidate for oxide-based spintronic applications. Here, we have studied the temperature dependent structural, vibrational, and magnetic properties of polycrystalline Sm0.9Bi0.1Fe0.9Mn0.1O3 prepared by conventional solid-state reaction method. The compound stabilizes in orthorhombic structure with space group “Pnma” and exhibits no structural phase transitions in the investigated temperature range (300–500 K). Magnetic measurements reveal the weak ferromagnetic–paramagnetic transition at 620 K. Thermal evolution of phonon modes investigated using Raman spectroscopy in the temperature range 300–800 K reveal that Ag(3) phonon mode related to FeO6 vibrations exhibits anomalous behaviour below magnetic transition temperature, which we attribute to spin-phonon coupling. The optical band gap value of ∼ 5.17 eV has been estimated from the analysis of UV–Vis diffuse reflectance spectroscopy using the Tauc relation. The value of ΔEt2u→t2g is estimated to be ~ 2.6 eV for p-d charge transfer transitions in Fe/MnO6 octahedra. The obtained valence states from X-ray photoelectron spectroscopy analysis of all the elements of the sample are in excellent agreement with the expected values.

Solution molarity dependent structural and optical properties of CdO nanostructured thin films

Cadmium oxide (CdO) thin films were prepared on soda lime glasses using sol–gel spin coating method. The optimized annealing temperature of the samples was determined to be 400 °C. The structural and optical properties of the films were examined depending on the solution molarity. X-ray diffraction (XRD) patterns confirming that CdO has a cubic crystal structure reveal that the crystallite size gradually increases with increasing solution molaritiy. It is concluded that the molarity of Cd2+ precursor solution does not affect crystallinity. The surface morphology of the CdO thin films was conducted by the solution molarity. The molarity also has an impact on some optical parameters such as extinction coefficient, volume/surface energy loss and refractive index. The band gap obtained form the photoluminescence (PL) measurements of CdO with 0.5 M is in agreement with that of optical absorption spectra.

Deposition pressure dependent structural and optoelectronic properties of ex-situ boron-doped poly-Si/SiOx passivating contacts based on sputtered silicon

Among common methods to form polycrystalline silicon (poly-Si) films for passivating-contact solar cells, physical vapor deposition, in particular sputtering, is the safest one as it does not require any toxic gaseous precursors. One of the critical parameters to control the properties of sputtered silicon films is their deposition pressure. In this work, structural and optoelectronic characteristics of ex-situ boron-doped poly-Si/SiOx passivating contacts, formed from sputtered intrinsic amorphous silicon (a-Si) deposited at different pressures on top of SiOx/c-Si substrates and subjected to a high-temperature boron diffusion step, are investigated. The deposition rate and density of the as-deposited a-Si films increase with reducing pressure. Low-temperature photoluminescence spectra captured from the as-deposited samples at different pressures do not show typical emissions from hydrogenated a-Si. Meanwhile, their Fourier-transform infrared absorption spectra all show Si–H stretching modes, indicating that hydrogen had been initially incorporated into the chemical SiOx layers and eventually hydrogenated the a-Si/SiOx interfaces during the sputtering process. After the high-temperature boron-diffusion step, all hydrogen-related peaks disappear. Lower pressure films (1.5 and 2.5 mTorr) show more consistent improved performance after hydrogen treatments, compared to higher pressure films (4 and 5 mTorr). The resultant passivating contacts at 2.5 mTorr achieve a low single-side recombination current density Jo of ~9 fA/cm2, whereas their contact resistivity is still low at 15 mΩ cm2.