Shift Of Diffraction Peak Research Articles

Synthesis of La-doped ceria nanoparticles: impact of lanthanum depletion

The present work explores the possible issues involving the synthesis of La-doped ceria-based nanoparticles by co-precipitation; moreover demonstrates the consequence of such issues in the final system. The stoichiometric anomaly as revealed by the X-ray diffraction (XRD) peak shift studies confirmed a massive departure from the final target composition; indicating lanthanum depletion (~30 %) from the resultant oxide. This also revealed that a fraction of this unreacted lanthanum precursor stayed in the system alone. Transmission electron microscopy results revealed the presence of nanocrystalline La-oxycarbonate phase as a fine dispersion co-existing with the lanthanum cerate nanocrystals; XRD could not detect the presence of such a phase at 550 °C. Through Raman and Fourier transform infrared spectroscopy analyses, a possible pathway of this complex thermal transition for the free La-precursor was outlined (100–1200 °C). The Raman data unambiguously pointed out the transition zone for the decomposition sequence for its conversion from La-nitrate to oxycarbonate in the temperature range 400–550 °C. The overall study emphasises the need of special attention for synthesising La-based solid solution systems via colloidal routes; especially considering the solubility and mixing issues for the lanthanum precursor.

Room temperature gas sensing property and sensing mechanism of Sn-doped ZnO thin film

Sn-doped ZnO and pure ZnO thin films are deposited on glass substrates with prepared electrode by the chemical vapor deposition method. The gas sensing performances of Sn-doped ZnO and pure ZnO thin films are investigated by our home-made system at room temperature, and the gas sensing test results reveal that Sn-doped ZnO thin film exhibits high gas response to ethanol and acetone, while no response is detected for pure ZnO to ethanol or acetone at room temperature. Sn-doped ZnO thin film also has high selectivity that the response to ethanol is higher than that to acetone in the same measurement conditions, and the response of Sn-doped ZnO thin film sample to ethanol is almost the third largest when the concentration is 320 ppm. The typical scanning electron microscopy images reveal that these two samples are tetrapod-shaped ZnO whiskers with diameters in a range of about 150-400 nm. X-ray diffraction results indicate that all the samples are of wurtzite structure. Neither trace of Sn, nor that of Sn alloy nor that of Sn oxide is detected in the Sn-doped ZnO film, while its diffraction peak shifts towards the left compared with that of pure ZnO sample, which suggests that Sn atoms exist in the form of interstitial atoms in the ZnO crystal. The energy dispersive spectrum shows that the Sn-doped ZnO thin film is composed of Zn and O elements, and no Sn signal is defected. Photoluminescence spectra reveal that both Sn-doped ZnO and pure ZnO films have ultraviolet light emission peaks and green emission peaks, while the intensities of the defect emissions are significantly enhanced by doping of Sn. In addition, no gas response to ethanol is detected after Sn-doped ZnO thin film has been annealed in the air, which indicates that the room temperature gas sensitivity of the Sn-doped ZnO thin film may be related to its high defect concentration. The working mechanism of Sn-doped ZnO thin film is explained by a free electron random scattering model. As is well known, ZnO semiconductor gas-sensor is of surface-controlled type. In this work, upon exposure to ethanol vapor, the physical absorbed ethanol molecules acting as scattering centers can reduce the mean free path of the electrons in the surface of the film, changing the mean free time n, which would increase the resistance of Sn-doped ZnO thin film at room temperature. This work provides a simple method of fabricating the highly sensitive ethanol gas sensor operating at room temperature, which has great potential applications in gas sensor field.

Synchrotron analysis of toughness anomalies in nanostructured bainite

High-resolution synchrotron X-ray diffraction has been used to characterise the notch root regions of Charpy impact test specimens of a superbainitic steel, both before and after loading. The changes in the volume fraction of austenite induced by the application of a three-point-bending load were quantified. Analysis of diffraction peak shifts revealed the extent of residual tensile and compressive strains present due to both machining and an applied load. The results lend support to the hypothesis that the comparatively low energies absorbed during Charpy impact testing of superbainitic steels, <7 J, are due to the formation of stress-induced martensite at the notch root, prior to crack initiation.

Characterization of high energy Xe ion irradiation effects in single crystal molybdenum with depth-resolved synchrotron microbeam diffraction

Microbeam X-ray diffraction experiments were conducted at beam line 34-ID of the Advanced Photon Source (APS) on fission fragment energy Xe heavy ion irradiated single crystal Molybdenum (Mo). Lattice strain measurements were obtained with a depth resolution of 0.7 μm, which is critical in resolving the peculiar heterogeneity of irradiation damage associated with heavy ion irradiation. Q-space diffraction peak shift measurements were correlated with lattice strain induced by the ion irradiations. Transmission electron microscopy (TEM) characterizations were performed on the as-irradiated materials as well. Nanometer sized Xe bubble microstructures were observed via TEM. Molecular Dynamics (MD) simulations were performed to help interpret the lattice strain measurement results from the experiment. This study showed that the irradiation effects by fission fragment energy Xe ion irradiations can be collaboratively understood with the depth resolved X-ray diffraction and TEM measurements under the assistance of MD simulations.

Effect of doping concentration on the structural, morphological, optical and electrical properties of Mn-doped CdO thin films

AbstractThin films of manganese-doped cadmium oxide (CdO:Mn) with different Mn-doping levels (0, 1, 2, 3 and 4 at.%) were deposited on glass substrates by employing an inexpensive, simplified spray technique using a perfume atomizer at 375 °C. The influence of Mn incorporation on the structural, morphological, optical and electrical properties of CdO films has been studied. All the films exhibit cubic crystal structure with a (1 1 1) preferential orientation. Mn-doping causes a slight shift of the (1 1 1) diffraction peak towards higher angle. The crystallite size of the films is found to decrease from 34.63 nm to 17.68 nm with an increase in Mn doping concentration. The CdO:Mn film coated with 1 at.% Mn exhibit a high transparency of nearly 90 % which decreases for higher doping concentration. The optical band gap decreases with an increase in Mn doping concentration. All the films have electrical resistivity of the order of 10−4 Ω·cm.

Strain induced room temperature ferromagnetism in epitaxial magnesium oxide thin films

We report on the epitaxial growth and room-temperature ferromagnetic properties of MgO thin films deposited on hexagonal c-sapphire substrates by pulsed laser deposition. The epitaxial nature of the films has been confirmed by both θ-2θ and φ-scans of X-ray diffraction pattern. Even though bulk MgO is a nonmagnetic insulator, we have found that the MgO films exhibit ferromagnetism and hysteresis loops yielding a maximum saturation magnetization up to 17 emu/cc and large coercivity, Hc = 1200 Oe. We have also found that the saturation magnetization gets enhanced and that the crystallization degraded with decreased growth temperature, suggesting that the origin of our magnetic coupling could be point defects manifested by the strain in the films. X-ray (θ-2θ) diffraction peak shift and strain analysis clearly support the presence of strain in films resulting from the presence of point defects. Based on careful investigations using secondary ion mass spectrometer and X-ray photoelectron spectroscopy studies, we have ruled out the possibility of the presence of any external magnetic impurities. We discuss the critical role of microstructural characteristics and associated strain on the physical properties of the MgO films and establish a correlation between defects and magnetic properties.

Lattice doped Zn–SnO2 nanospheres: A systematic exploration of dopant ion effects on structural, optical, and enhanced gas sensing properties

A surfactant-free one step hydrothermal method is reported to synthesize zinc (Zn2+) doped SnO2 nanospheres. The structural analysis of X-ray diffraction confirms the tetragonal crystal system of the material with superior crystalline nature. The shift in diffraction peak, variation in lattice constant and disparity in particle size confirm the incorporation of Zn2+ ions to the Sn host lattices. The lattice doped structure, the disparity in morphology, size and shape by the addition of Zn2+ ions are evident from X-ray photoelectron spectroscopic and electron microscopic analysis. Significant changes in the absorption edge and the band gap with increased doping concentration were observed in UV–vis absorption spectral analysis. The formation of acceptor energy levels with the incorporation of Zn2+ ions has a significant effect on the electrical conductivity of SnO2 nanospheres. Comparative tests for gas sensors based on Zn doped SnO2 nanospheres and SnO2 nanospheres clearly show that the former exhibited excellent NO2 sensing performance. The responses of Zn2+ ions incorporated SnO2 nanospheres sensor were increased 3 fold at trace level NO2 gas concentrations ranging from 1 to 5ppm. The excellent sensitivity, selectivity and fast response make the Zn2+ doped SnO2 nanospheres ideal for NO2 sensing.

Fabrication and Characterization of (Mo1‐xNix) (Si1‐xAlx)2 (x = 0.025, 0.05, and 0.1) Alloys

(Mo1‐xNix) (Si1‐xAlx)2 (x = 0.025, 0.05, and 0.1) alloys were prepared using self‐propagating combustion synthesis from Mo, Si, Al, and Ni powders and subsequently hot‐pressed to achieve a high density of above 96.2%. The combustion products were composed of C11b MoSi2 and C40 Mo(Si,Al)2. A systematic shift of diffraction peaks of C11b MoSi2 toward low angles was observed, and C40 Mo(Si,Al)2 diffraction peaks became stronger with increase of alloying elements. The solid‐solution softening and toughening phenomena were observed in (Mo1‐xNix) (Si1‐xAlx)2 alloys. On increasing x from 0.025 to 0.1, the hardness of the alloys decreased from 9.87 to 8.31 GPa, and the fracture toughness increased from 3.79 to 6.48 MPa m1/2.

Probing diffusion of In and Ga in CuInSe2/CuGaSe2 bilayer thin films by x-ray diffraction

The bilayer thin films of CuInSe2 (CIS) and CuGaSe2 (CGS) are fabricated by a molecular beam deposition (MBD) technique by sequential depositions of CGS followed by CIS and vise versa on Mo-coated soda-lime glass (SLG) and Mo/Al2O3-coated (Na blocking) SLG substrates. The thicknesses of CIS/CGS layers are adjusted to have the overall x=[Ga]/([In]+[Ga]) at approximately 0.4 similar to what is generally used in CIGS thin film solar cells. The growth temperature and the Cu-ratio y=[Cu]/([In]+[Ga]) of the CIS and CGS layers are systematically varied for Cu-rich (y>1) and Cu-poor (y<1) conditions. X-ray diffraction (XRD) technique is used to analyze the shift of diffraction peaks of the preferred orientations of the bilayers compared to those of the single-layer CIS, CGS and CIGS thin films. The XRD results show that higher Ga diffusion is observed in the Cu-rich CIS/CGS bilayer rather than others. The results suggest that the diffusion of Ga is enhanced by the excess Cu–Se phase that is dependent upon the substrate temperature. The Na from the SLG substrate is one of the important factors affecting Ga diffusion. The results show alloying CIGS patterns rather than separated CIS and CGS patterns as observed in the bilayers with Na.

Residual stress within nanoscale metallic multilayer systems during thermal cycling

Projected applications for nanoscale metallic multilayers will include wide temperature ranges. Since film residual stress has been known to alter system reliability, stress development within new film structures with high interfacial densities should be characterized to identify potential long-term performance barriers. To understand factors contributing to thermal stress evolution within nanoscale metallic multilayers, stress in Cu/Nb systems adhered to Si substrates was calculated from curvature measurements collected during cycling between 25°C and 400°C. Additionally, stress within each type of component layers was calculated from shifts in the primary peak position from in-situ heated X-ray diffraction. The effects of both film architecture (layer thickness) and layer order in metallic multilayers were tracked and compared with monolithic Cu and Nb films (1µm total thickness). Analysis indicated that the thermoelastic slope of nanoscale metallic multilayer films (with 20nm and 100nm individual layer thicknesses) depends on thermal expansion mismatch, elastic modulus of the components, and also interfacial density. The layer thickness (i.e. interfacial density) affected thermoelastic slope magnitude (−1.23±0.09MPa/°C for 20nmCu/Nb vs. −0.89±0.03MPa/°C for 100nmCu/Nb) while layer order had minimal impact on stress responses after the initial thermal cycle (−0.82±0.07MPa/°C for 100nm Cu/Nb). When comparing stress responses of monolithic Cu and Nb films to those of the Cu/Nb systems, the nanoscale metallic multilayers show a similar increase in stress above 200°C to the Nb monolithic films, indicating that Nb components play a larger role in stress development than Cu. Phase specific stress calculations (Cu vs. Nb) from X-ray diffraction peak shifts in 20nm Cu/Nb collected during heating reveal that the component layers within a multilayer film respond similarly to their monolithic counterparts.

Growth of residual stress-free ZnO films on SiO2/Si substrate at room temperature for MEMS devices

ZnO thick Stress relaxed films were deposited by reactive magnetron sputtering on 2”-wafer of SiO2/Si at room temperature. The residual stress of ZnO films was measured by measuring the curvature of wafer using laser scanning method and found in the range of 0.18 x 109 to 11.28 x 109 dyne/cm2 with compressive in nature. Sputter pressure changes the deposition rates, which strongly affects the residual stress and surface morphologies of ZnO films. The crystalline wurtzite structure of ZnO films were confirmed by X-ray diffraction and a shift in (0002) diffraction peak of ZnO towards lower 2θ angle was observed with increasing the compressive stress in the films. The band gap of ZnO films shows a red shift from ∼3.275 eV to ∼3.23 eV as compressive stress is increased, unlike the stress for III-nitride materials. A relationship between stress and band gap of ZnO was derived and proposed. The stress-free growth of piezoelectric films is very important for functional devices applications.

Structural, electrical and magnetic behavior in high-temperature sintered Zn1–x Mn x O

Nanocrystalline Mn-doped ZnO of compositions Zn1–x Mn x O (0 ≤ x ≤ 0.08) has been synthesised by chemical route for uniform substitution of Mn in Zn site and then sintered at 1300 °C. Systematic investigations show the effect of Mn doping level and the sintering temperature on the structural, electrical and magnetic properties of ZnO. The average size of the nanocrystalline particles is in the order of 30–50 nm, whereas the grain sizes of the sintered specimen are of the order of few microns. Substitution of Mn in ZnO has been confirmed from the X-ray diffraction peak shift. A few peaks related to secondary phases of MnO have been observed in the X-ray diffraction patterns of the doped samples. ZnO and Mn-doped ZnO show Ohmic behavior and increased resistivity value with the increasing concentration of Mn. Effect of Mn concentration in ZnO has also been reflected in the dielectric constant and dielectric loss values. All the sintered samples show paramagnetic behavior even though the presence of MnO with oxygen vacancies is evident in X-ray photoelectron spectroscopic study.

Combinatorial synthesis and high-throughput characterization of the thin film materials system Co-Mn-Ge: Composition, structure, and magnetic properties

Co–Mn–Ge is a system of interest for magnetocaloric applications as a solid state magnetic refrigerant. A thin film materials library covering a large fraction of the Co–Mn–Ge ternary composition space was fabricated by sputter deposition. After deposition, it was annealed at 600 °C for 3 h and quenched subsequently. An energy-dispersive X-ray spectroscopy and X-ray diffraction-based cluster analysis revealed the regions of existence for the CoMnGe and the Co2MnGe single phase areas. Furthermore, high intensity diffraction peaks revealed the presence of the hexagonal (Co, Mn)7Ge6 phase in a region that also featured the CoMnGe phase. In this region, a non-linear, symmetric, and hysteretic shift of the (200) diffraction peak of the (Co, Mn)7Ge6 phase was observed by temperature-dependent X-ray diffraction for Co23Mn33Ge44, indicating a structural phase transition taking place between 350 and 375 K upon heating and 325 and 300 K upon cooling. This coincides with a magnetic transition near 325 K from the ferromagnetic to the paramagnetic state. However, no magnetostructural coupling was identified in the temperature range from 330 to 300 K upon cooling. Magnetostriction and an undetected structural transition of the CoMnGe phase were ruled out as probable causes for the non-linear shifts.

Towards the growth of Cu2ZnSn1−xGexS4 thin films by a single-stage process: Effect of substrate temperature and composition

Cu2ZnSn1−xGexS4 (CZTGS) thin films prepared by flash evaporation of a Zn-rich Cu2ZnSn0.5Ge0.5S4 bulk compound in powder form, and a subsequent thermal annealing in S containing Ar atmosphere are studied. The effect of the substrate temperature during evaporation and the initial composition of the precursor powder on the growth mechanism and properties of the final CZTGS thin film is investigated. The microstructure of the films and elemental depth profiles depend strongly on the growth conditions used. Incorporation of Ge into the Cu2ZnSnS4 lattice is demonstrated by the shift of the relevant X-ray diffraction peaks and Raman vibrational modes towards higher diffraction angles and frequencies respectively. A Raman mode at around 348–351cm−1 is identified as characteristic of CZTGS alloys for x=[Ge]/([Sn]+[Ge])=0.14−0.30. The supply of Ge enables the reduction of the Sn loss via a sacrificial Ge loss. This fact allows increasing the substrate temperature up to 350°C during the evaporation, forming a high quality kesterite material and, therefore, reducing the deposition process to one single stage.

Enhanced Fluorescence, Raman Scattering, and Higher Order Raman Modes in ZnO:Ag Nanorods

We report exciton and phonon properties of pure and Ag-modified ZnO nanostructures are prepared using solution-based refluxing route. X-ray diffraction studies show lower angle shift in the characteristic diffraction peaks of ZnO. Additional diffraction peaks related to nano-sized Ag were observed from XRD. Broad absorption band (which covers the 400–1000 nm range) results from surface plasmon resonance (SPR) absorption of metallic silver is observed from optical absorption studies. Enhancement in luminescence and Raman scattering is observed in Ag-modified sample when compared with pure ZnO sample. This is attributed to the presence of metallic Ag in the samples, and we attempted to understand the observed enhancement from the perspective of the local field associated with the metal nanoparticles.

Spectroscopic and structural characterization of transparent fluorogermanate glass ceramics with LaF3:Tm3+ nanocrystals for optical amplifications

Transparent Tm3+-activated glass ceramics (GC) with ∼26% LaF3 nanocrystallites were developed from the 50GeO2–22Al2O3201313LaF3–15LiF (mol%) glass system. Upon excitation at 468 and 688nm, GC with 0.3mol% Tm3+-doping (GC0.3Tm) reveals remarkably enhanced luminescence within 600–850nm range. This could be ascribed to the change in ligand environment around Tm3+ as evidenced by the decrease of Ω2 from 4.32 (PG0.3Tm) to 3.79 (GC0.3Tm) after ceramming. The concurrent intense infrared emission at ∼1.2 and 1.46μm exhibits a respective full width at half maximum of 76 and 106nm, mean decay time of 229 and 467μs. The stimulated emission cross sections and gain parameters were evaluated using radiative parameters derived from Judd–Ofelt (J–O) analysis. Further discussions on the local structure around rare earth ions are based on Eu3+ as a probe. For GC with 0.05mol% Eu3+-doping (GC0.05Eu), the obvious stark splitting and significantly (6-fold) enhanced emission originating from the excited Eu3+:5D3→1 states is consistent with the red shift of diffraction peaks, revealing the partition of Eu3+ into LaF3 nanocrystals.

NixCd1−xO: Semiconducting alloys with extreme type III band offsets

We have synthesized alloys of NiO and CdO that exhibit an extreme type III band offset and have studied the structural, electrical, and optical properties of NixCd1−xO over the entire composition range. The alloys are rocksalt structured and exhibit a monotonic shift of the (220) diffraction peak to higher 2θ angles with increasing Ni concentration. The electron mobility and electron concentration decrease with increasing x, and samples become insulating for Ni content x &amp;gt; 0.44. This decrease in n-type conductivity is consistent with the movement of the conduction band minimum from below to above the Fermi stabilization energy with increasing Ni content. The optical absorption edge of the alloys can be tuned continuously from CdO to NiO. The intrinsic gap of the alloys was calculated with the electrical and optical measurements and accounting for Burstein-Moss carrier filling and carrier-induced bandgap renormalization effects. We observe an uncommon composition dependence of the intrinsic bandgap on the alloy composition. The effect is tentatively attributed to an interaction between extended states of the conduction band and localized d-states of Ni.

Investigations on the structural, morphological, optical and electrical properties of undoped and nanosized Zn-doped CdS thin films prepared by a simplified spray technique

Abstract CdS and Zn-doped CdS (CdS:Zn) thin films have been deposited on glass substrates by spray pyrolysis technique using a perfume atomizer. The influence of Zn incorporation on the structural, morphological, optical and electrical properties of the films has been studied. All the films exhibit hexagonal phase with (0 0 2) as preferential orientation. A shift of the (0 0 2) diffraction peak towards higher diffraction angle is observed with increased Zn doping. The optical studies confirmed that the transparency increases as Zn doping level increases and the film coated with 2 at.% Zn doping has the maximum transmittance of about 90 %. The sheet resistance (Rsh) decreases as the Zn-doping level increases and a minimum value of 1.113 × 103 Ω/sq is obtained for the film coated with 8 at.% Zn dopant. The CdS film coated with 8 at.% Zn dopant has the best structural, morphological and electrical properties.

Powder diffraction in studies of nanocrystal surfaces: chemisorption on Pt

Atoms at the surface of nanocrystals contribute appreciably to the X-ray diffraction pattern. Phenomena like chemisorption, affecting the displacement of surface atoms with respect to their positions in the perfect crystallographic structure, cause diffraction peak shifts and intensity changes. These effects are easily measurable for small nanocrystals up to 10 nm size. This article reports diffraction effects of chemisorption of adsorbing gases H2, O2, CO and NO for a series ofin situpowder diffraction experiments on nanocrystalline Pt supported on silica. On the basis of previous diffraction observation of Pt surface reconstruction during hydrogen desorption, it was possible to quantify this effectversuscrystallite size and rationalize the observed diffraction peak shift for the other adsorbing species. This enabled the surface reconstruction to be distinguished from the surface relaxation effect, the latter depending monotonically on the adsorption energy. Even if no phase transition occurs, monitoring of a peak's position, intensity, width and gas composition (viamass spectrometry) during a carefully designed physicochemical process (including surface chemical reaction) enables insight into and understanding of the surface structure evolution (e.g.amorphization, relaxation, reconstruction or changes in the overall morphology). The proposed technique can be used as a surface science tool, allowing studies of nanocrystals under high pressure.

Structural, Optical, and Electrical Properties of Zn-Doped CdO Thin Films Fabricated by a Simplified Spray Pyrolysis Technique

Thin films of zinc-doped cadmium oxide with different Zn-doping levels (0, 2, 4, 6, and 8 at%) were deposited on glass substrates by employing an inexpensive, simplified spray technique using perfume atomizer at relatively low substrate temperature (375 °C) compared with the conventional spray method. The effect of Zn doping on the structural, morphological, optical, and electrical properties of the films was investigated. XRD patterns revealed that all the films are polycrystalline in nature having cubic crystal structure with a preferential orientation along the (1 1 1) plane irrespective of Zn-doping level. Zn-doping level causes a slight shift in the (1 1 1) diffraction peak toward higher angle. The crystallite size of the films was found to be in the range of 28–37 nm. The band gap value increases with Zn doping and reaches a maximum of 2.65 eV for the film coated with 6 at% Zn doping and for further higher doping concentration it decreases. Electrical studies indicate that Zn doping causes a reduction in the resistivity of the films and a minimum resistivity of 15.69 Ω cm is observed for the film coated with 6 at% Zn.