Increasing Doping Level Research Articles

Raman study on structure of U1−yGdyO2−x (y=0.005, 0.01, 0.03, 0.05 and 0.1) solid solutions

The U1−yGdyO2−x solid solutions with y = 0.005, 0.01, 0.03, 0.05 and 0.1 were characterized by Raman spectroscopy to investigate the defect structure induced by oxygen vacancies. The oxygen deficiencies of solid solutions were estimated by the relation between the doping level and a lattice parameter calculated from X-ray diffraction patterns. Raman mode shifts to higher wavenumber with increasing doping level showed that crystal lattice disorder due to oxygen vacancies. The frequency shifts and relative ratio of Raman modes were enabled to be the indicator for composition, defect and oxygen vacancy of U1−yGdyO2−x solid solutions.

Synthesis of polymers containing polyaniline fragments linked by 1,4-benzoquinone groups

Michael reaction of 1,4-benzoquinone and N-acetyl-4,4'-diaminodiphenylamine has afforded a new polymer; hydrolysis of the latter has yielded a product containing polyaniline fragments connected by 1,4- benzoquinone units in the backbone. The interaction of 1,4-benzoquinone and 1,4-phenylenediamine has afforded an earlier described polymer that has been characterized by IR and UV spectroscopy. 2,5-Bis[(4-aminophenyl)amino]-1,4-benzoquinone prepared from the mentioned compounds at a 3: 2 molar ratio under the same reaction conditions, can exist in three tautomeric forms. Electroconductivity of the prepared polymers increases from <10–10 to 10–6 S/cm with the doping level increase.

Novel Nanocomposites of Polypyrrole Doped with Fullerene C60

ABSTRACTThis paper reports on the structural, thermal, and dielectric properties of polypyrrole/fullerene C60 nanocomposites synthesized by a interfacial polymerization method. Fourier transform infrared (FT-IR) and ultraviolet-visible (UV-vis) analyses clearly indicated the existence of interactions between polypyrrole (PPy) and the fullerene C60 nanoparticles. Thermal analyses indicated that the extrapolated onset degradation temperature (Tdeg) of PPy increased with increasing doping level. Scanning electron microscopy (SEM) images showed that the fullerene C60 changed the morphology of PPy. Dielectric analyses showed a temperature dependent dielectric relaxation behavior. The relaxation time of the nanocomposites with high doping levels tended to increase with increasing temperature. This behavior of the polypyrrole/fullerene C60 nanocomposites indicated that they could be used as a high temperature ultrasonic transducer.

Comprehensive understanding of dark count mechanisms of single-photon avalanche diodes fabricated in deep sub-micron CMOS technologies

The dark count noise mechanisms of single-photon avalanche diodes (SPADs) fabricated in deep sub-micron (DSM) CMOS technologies are investigated in depth. An electric field dependence of tunneling model combined with carrier thermal generation is established for dark count rate (DCR) prediction. Applying the crucial parameters provided by Geiger mode TCAD simulation such as avalanche triggering probability and electric field distribution in the SPAD avalanche region, the individual contribution of each noise source to DCR is calculated for several SPADs in DSM CMOS technologies. The model calculation results reveal that the trap-assisted tunneling is the main DCR generation source for these DSM CMOS SPADs. With the increase of doping levels in the device avalanche region, the band-to-band tunneling will be the dominant factor that could lead to the higher DCR in scaled DSM CMOS technologies.

Electrical conduction in Ga3+-doped SnP2O7/polytetrafluoroethylene inorganic–organic composite electrolytes

In this study, dense polytetrafluoroethylene (PTFE)/Sn1−xGaxP2O7 (x = 0.05, 0.10, 0.15, 0.20) inorganic–organic composite electrolytes were prepared. The result of SEM images indicates that all the composite electrolytes are sufficiently uniform and dense. The conductivities which is given consideration to the influence of Ga3+ doping level increase in the order: σ (x = 0.20) < σ (x = 0.15) < σ (x = 0.10) < σ (x = 0.05). The highest conductivity 1.9 × 10−2 S cm−1 is observed for PTFE/Sn1−xGaxP2O7 (x = 0.05) in wet O2 at 225 °C. The H2/O2 fuel cells using PTFE/Sn1−xGaxP2O7 (x = 0.05, 0.10) as electrolytes generate the maximum power densities of 63 mW cm−2 for x = 0.05 and 36.3 mW cm−2 for x = 0.10 at 150 °C, respectively.

Transport properties and modification of potassium dihydrogen orthophosphate

We have studied the thermal behavior, proton conductivity, and structural properties of composite proton electrolytes based on KH2PO4, the mixed salt K0.97Cs0.03(H2PO4)0.97(HSO4)0.03, and silicon dioxide with a pore size of 70 A in a wide composition range. The results demonstrate that the proton conductivity of the (1–x)KH2PO4–xSiO2 (x = 0.1–0.5) composite systems increases by more than two orders of magnitude, reaching 3 × 10–3 S/cm at a temperature of 225°C. The increase in conductivity is due to the formation of a disordered amorphous state of the salts as a result of partial KH2PO4 dehydration and the formation of K4H6(PO4)2P2O7 as an intermediate product. In the composites based on the highly conductive, disordered K0.97Cs0.03(H2PO4)0.97(HSO4)0.03 mixed salt, close in composition to KH2PO4, heterogeneous doping causes no increase in conductivity, and the conductivity decreases with increasing doping level, which is caused by dispersion of the salt and the dehydration process, leading to the formation of K4H6(PO4)2P2O7 and KPO3.

Electrospinning of poly(vinylpyrrodine) template for formation of ZrO2 nanoclusters for enhancing properties of composite proton conducting membranes

ABSTRACTNanosized ZrO2 clusters were prepared by electrospinning a poly(vinylpyrrodine) (PVP)/ZrO2 mixture for calcination to remove PVP template and sizing. The morphological, chemical, structural, and thermal resistance changes during preparation stages were investigated using scanning electron microscope, energy-dispersive X-ray spectroscopy, transmission electron microscope, X-ray diffraction, and thermogravimetric analysis. The obtained ZrO2 clusters were used for preparation of nanocomposite membranes by dispersion in 2,6-pyridine polybenzimidazole (2,6-Py-PBI) matrix at 5 wt% content followed by phosphoric acid (PA) doping. The ZrO2 nanoclusters were found to be uniformly distributed in 2,6-Py-PBI/PA matrix leading to a remarkable increase in the PA doping level and proton conductivity of the obtained composite membrane.

Evaluation of optoelectronic response and Raman active modes in Tb3+ and Eu3+-doped gadolinium oxide (Gd2O3) nanoparticle systems

Rare earth oxide (Tb3+ :Gd2O3 and Eu3+ :Gd2O3) nanophosphors are exploited through spectroscopic and microscopic tools with special emphasis on D–F mediated radiative emission and Raman active vibrational modes. Powder X-ray diffraction measurements have revealed cubic crystal structure of the nanosystems and with an average crystallite size varying between ~3.2 and 4.8 nm. Photoluminescence (PL) spectra of Tb3+ doped systems signify intense blue-green (~490 nm) and green (~544 nm) emissions mediated by 5 D 4 → 7 F 6 and 5 D 4 → 7 F 5 transitional events; respectively. In the PL responses of Eu3+ doped nanoparticle systems, we also identify magnetically-driven 5 D 0 → 7 F 1 (~591 nm) and electrically driven 5 D 0 → 7 F 2 (~619 nm) radiative features which seem to improve with increasing doping level. However, the magnitude of Judd–Ofelt (J–O) intensity parameters (Ω 2, 4), is significantly lowered for the high doping cases. Raman spectra of the undoped and RE doped systems exhibited several Ag and Fg modes in the range of Raman shift ~100–600 cm−1. In the Raman spectra, the peaks located at ~355 cm−1 are assigned to the mixed mode of F g + A g, the line width of which was found to increase with RE doping. Moreover, owing to the enhanced defect concentration in the doped systems than its undoped counterpart, we anticipate a faster phonon relaxation and consequently, a suppression of phonon lifetime in the former case.

Magnetic recoverable Fe3O4-TiO2:Eu composite nanoparticles with enhanced photocatalytic activity

This work refers to the influence of Eu doping on the morphologic, structural and compositional properties of magnetic separable Fe3O4-TiO2 composite nanoparticles with photocatalytic activity. In this respect, Fe3O4-TiO2:Eu nanocomposites were prepared by seed mediated growth of TiO2:Eu through a sol-gel method onto preformed magnetite resulted from co-precipitation method. Different Eu concentration precursors were used for doping. The thermal behavior and the conversion of precursors into corresponding Fe3O4-TiO2:Eu composite nanoparticles were evidenced by FT-IR spectra and thermal analysis. The XRD, XPS and HRTEM investigations results indicate that nanocomposites contain besides Fe3O4-TiO2:Eu some amounts of iron titanate. Formation of FeTiO3 is suppressed by the increase of Eu doping level. Magnetic studies also indicated that nanocomposite exhibit superparamagnetic behavior at room temperature. The large surface area and mesoporous structure of magnetic nanocomposite were confirmed by the surface area (BET) and porosity measurements. It was demonstrated that the composite nanoparticles exhibit good photocatalytic activity toward the degradation of RhB solution and they can be used as efficient and conveniently recoverable photocatalyst.

Strain-controlled boron and nitrogen doping of amorphous carbon layers for hard mask applications

Nitrogen- and boron-doped amorphous carbon layers (ACLs) were grown by plasma- enhanced chemical vapor deposition (PECVD) on a Si substrate and characterized by Raman and X-ray photoelectron spectroscopy (XPS) techniques. Increasing doping levels resulted in a shift in the Raman G-peak of the doped ALCs, indicating a change in bond lengths upon doping. The XPS N1s and B1s spectra revealed the presence of different types of N-related (involving pyridinic, pyrrolinic, and graphitic N) and B-related (corresponding to BC2O and BC species) bonds in the N- and B-doped ACLs, with N and B doping levels ranging from 2.03 to 3.94at.% and from 1.44 to 10.4at.%, respectively. These results suggest that the dry etch resistance of the present ACLs was enhanced by B doping and negatively affected by N doping. Density functional theory calculations highlighted the strengthening of CC bonds induced by B doping and their corresponding weakening caused by N doping as possible explanations for the effects of doping on the dry etching characteristics of the ACLs.

Effects of Zn-Cr-substitution on the structural and magnetic properties of Ni1−xZnxFe2−xCrxO4 ferrites

Cr and Zn-substituted nickel ferrites, general formula Ni1−xZnxFe2−xCrxO4 (x=0, 0.1, 0.3, 0.5, 0.7), were prepared using the sol-gel auto-combustion method. For precise analysis, the Ni1−xZnxFe2O4and NiFe2−xCrxO4 (x=0, 0.1, 0.3, 0.5, 0.7) samples were also checked individually. The effects of Cr and Zn doping on the structural, morphological, and magnetic properties of the samples were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). The full pattern fitting of Rietveld method using MAUD program was also applied to determine the exact coordinates of the atoms, unit cell dimensions, and ion occupancy. XRD measurement by Rietveld refinement confirmed the crystalline structure and phase purity of all the ferrites. SEM images showed that the particles were in the nanosize range. VSM results revealed that the values of MS in the NiFe2−xCrxO4 samples decreased and that HC had no regular behavior with increasing Cr content. The maximum value of HC=16Oe was obtained for a Cr content of x=0.7. On the other hand, saturation magnetization values initially increased in both the Ni1−xZnxFe2−xCrxO4 and Ni1−xZnxFe2O4 samples, with changing the doping level up to x=0.3, while for further content, MS decreased. In addition, coercivity decreased with increasing doping level.

Effect of tungsten-doping on the properties and photocatalytic performance of titania thin films on glass substrates

Highly-transparent TiO2 thin films with varying W-dopant levels (0.010–0.100mol%) were deposited on soda-lime-silica glass substrates by spin coating, followed by annealing in air at 450°C for 2h. Characterization was by GAXRD, AFM, SIMS, XPS, UV–vis, and MB degradation. The films were comprised of single-crystal anatase grains. Increasing doping levels increased the crystallite sizes, grain sizes, and film thicknesses; they also changed the grain morphology from anhedral to euhedral. W6+ ions formed a substitutional solid solution in anatase and probably exhibited charge compensation by Ti vacancy formation, which led to lattice contraction. Contamination from the glass substrates was homogeneously distributed on the grain boundaries. Doping decreased the optical indirect band gap. However, at the highest doping level, it is not certain if this was an artificial effect of precipitation from overdoping or a true effect of lattice stress. The 0.010mol% W sample showed the best performance probably owing to its formation of a homogeneous solid solution within the range of semiconducting properties, which could have narrowed the band gap or introduced mid-gap states. The 0.100mol% W sample may have been overdoped and caused WO3 precipitation. If so, the presence of the TiO2–WO3 couple may have enhanced charge separation and hence photocatalytic performance.

Solvothermal synthesized boron doped TiO2 catalysts: Photocatalytic degradation of endocrine disrupting compounds and pharmaceuticals under visible light irradiation

Boron doped TiO2 (B-TiO2) photocatalysts with visible light activity were successfully synthesized by solvothermal method. The characterizations of the synthesized products were carried out by XRD, SEM-EDAX, BET, XPS, TGA-DTG and UV–vis spectroscopy. The band gap values of TiO2 were decreased with the increase of the boron doping level. XPS analysis revealed that the interstitial TiO2 structure was modified via formation of TiOB bonds. Photocatalytic degradations of endocrine disrupting compounds (2,4-dichlorophenol (DCP), bisphenol-A (BPA)) and non-steroidal anti-inflammatory drugs (ibuprofen (IBU), flurbiprofen (FLU)) were examined by using raw and boron doped TiO2 catalysts under UV-A and visible irradiation. Boron doping can remarkably enhance light utilization and improve the photocatalytic activity of TiO2 toward the selected organics. The effects of boron content, initial solution pH and H2O2 on the photocatalytic performance were studied. The BPA, DCP, IBU and FLU reaction rate constants of B-TiO2 (8wt.% B) were found as kBPA=5.989×10−2, kDCP=2.087×10−2, kIBU=1.818×10−2, and kFLU=1.319×10−2min−1. B-doped TiO2 catalysts were found to be effective for the consecutive degradation tests referring their potentiality in extended applications.

Eu^3+-activated CdY_4Mo_3O_16 nanoparticles with narrow red-emission and broad excitation in near-UV wavelength region

Eu3+-activated CdY4MoO16 nanoparticles were synthesized via the sol-gel method. The phase formations were confirmed by the structural refinements. The photoluminescence properties such as the excitation and emission spectra, optimal doping level, internal absolute quantum efficiency (QE), decay lifetimes and the thermal stability, were measured. The charge transfer band (CTB) has a dependence on the Eu3+-content, showing an obvious red-shift with the increase of doping levels. Especially, CTB could reach a longer wavelength than the reported Eu3+-doped molydates. Moreover, the phosphor has some priorities such as high quantum efficiency, high doping levels and good thermal stability, etc. The excellent luminescence of Eu3+-activated CdY4MoO16 was discussed on its structural characteristics such as the cubic fluorite-like crystalline phase, framework constructed by Mo-O polyhedral groups, and the positive charge deficiency in the Eu3+-occupied cation sites of (Cd0.5, Y0.5)2.5 in the lattices.

Rectification of sulphur deficiency defect in CdS based films by introducing a novel modification in the SILAR cyclic process

In the present study, a novel modification is introduced in the dipping process of the SILAR (successive ionic layer adsorption and reaction) technique which is one of the important chemical solution techniques, generally used for the deposition of cadmium sulphide films. This study clearly establishes that this improved SILAR (ISILAR) technique enables one to rectify the sulphur deficiency, generally present in CdS films and there by obtain a near stoichiometric undoped and doped CdS thin films. In the present work, Fe doped CdS thin films are also deposited on glass substrates using this ISILAR technique. In this ISILAR technique, during the automated dipping process, a fresh anionic solution bath replaces the used one when the supply of S2− ions from this anionic solution declines to an optimized threshold value. As a result of this modification, the stoichiometric deviation drastically reduces from 12.9% to 3.3% for CdS films and from 20.2% to 0.6% for CdS:Fe films. The underlying mechanism for this observed improvement in the stoichiometry is elaborated in this article. The CdS films deposited using this ISILAR technique exhibit better transmittance values compared to several reported values. The XRD studies reveal that the deposited films have good crystalline quality. The magnetic studies show that at higher Fe doping (15 at.%) level, a ferromagnetic nature is observed in the lower applied magnetic field region. The optical band gap decreases gradually with the increase in the Fe doping level and this result is found to be supported by photoluminescence results.

Deep ultraviolet photoconductive and near-infrared luminescence properties of Er3+-doped β-Ga2O3 thin films

Highly oriented (2¯01) Er3+-doped β-Ga2O3 (Er:Ga2O3) thin films with different doping concentrations were grown on (0001) sapphire substrates using radio frequency magnetron sputtering. The crystal structure, optical absorption, near-infrared luminescence, and ultraviolet photoresponse properties of Er:Ga2O3 films were systematically studied. The evolution of lattice and energy band gap with increasing doping level confirms the chemical substitution of Er3+ ions into the Ga2O3 crystal lattice. The down-shifting near-infrared luminescence (∼1538 nm: ascribed to Er3+: 4I13/2−4I15/2) was observed under ultraviolet excitation. Moreover, an obvious deep ultraviolet photoresponse was also obtained in the formed thin films.

Preparation and Characterization of Fe-Doped TiO2 Films Covered on Silicagel

This study describes sol–gel preparation of (TiO2:Fex)/SiO2 (x = 0–0.8%) on silicagel grains using titanium tetraisopropoxide and iron (III) chloride as titanium precursor and doping agent, respectively. The structural properties, morphology, and chemical composition of the samples were thoroughly studied using x-ray diffraction, field emission scanning electron microscopy, and energy-dispersive x-ray spectroscopy, respectively. The results demonstrated the formation of highly pure anatase TiO2:Fex crystals with diameters of several tens of nanometers. With increasing doping level, no significant change in porosity of TiO2 material was observed, whereas the decrease in crystalline size was easily recorded. In addition, the bandgap (observed by UV–Vis) was dramatically shifted from 2.9 eV to 1.7 eV as doping with TiO2 with Fe at doping content as low as 0.8%. The use of silicagel as a solid support to carry photocatalytic crystals enables recycling of the material. These findings represent a simple pathway to design reusable catalyst for highly effective water detoxification under visible illumination.

The Influence of Cu2+ and Mn2+ Ions on the Structure and Crystallization of Diopside–Calcium Pyrophosphate Bioglasses

The influence of two divalent cations, Cu2+ and Mn2+, on the structure, sintering, and crystallization of glasses and glass‐ceramics in the diopside–calcium pyrophosphate system (90 wt.% diopside (CaMgSi2O6), 10 wt.% calcium pyrophosphate (Ca2P2O7)) was investigated. Glasses with 1, 3, and 5 wt% MnO or CuO additives were prepared by melt‐quenching and characterized by XRD, 29Si and 31P NMR, DTA, and FTIR This revealed that the silicate network is predominantly coordinated in Q2 (Si) units for all glasses, while phosphorus tends to inhabit an orthophosphate (Q0) environment. All glasses had a high rate of bioactivity after immersion in simulated body fluid. A slight depolymerization was observed in the doped glasses leading to lower Tg values in comparison with the parent glass. All glass‐ceramics exhibited the formation of diopside as the primary crystalline phase after sintering at 850°C/1 h. In comparison with the parent glass, the doped glasses featured significantly larger processing windows (∆T = Tc–Tg), ensuring good sinterability. Further, with increasing doping levels, the glasses exhibited a gradual decrease in Tp and ∆T, suggesting an increased tendency toward devitrification. All Cu‐ and Mn‐containing glasses exhibited the formation of hydroxyapatite, making them good candidates for biomedical applications and tissue engineering.

Effect of Fe substitution on charge order state and magnetocaloric effect in Pr0.5Sr0.5Mn1−xFexO3 (0.00 ≤ x ≤ 0.08) manganites

The charge order state and magnetocaloric effect have been studied in Pr0.5Sr0.5Mn1−xFexO3 (0.00 ≤ x ≤ 0.08) prepared by conventional solid-state reaction. Charge order state is weak in parent Pr0.5Sr0.5MnO3 and absent with increasing doping level. The long range charge order antiferromagnetic state (CO/AFM) reemerges for x = 0.06 and subsequently weak accompanied with rapid collapse in double exchange ferromagnetic order for x = 0.08. Magnetic measurements indicate that Fe does not participate in the double exchange interaction, the Curie temperature (TC) is systematically depressed with increasing Fe content from 265 K (x = 0.00) down to 185 K (x = 0.06). Negative magnetic entropy change (ΔSMmax) of −0.96 J/kg K and large positive value of 2.57 J/kg K in Pr0.5Sr0.5Mn0.94Fe0.06O3 are achieved when it undergoes paramagnetic to ferromagnetic (PM-FM) and ferromagnetic to antiferromagnetic (FM-AFM) magnetic phase transition in a magnetic change of 15.0 kOe. Though the materials with considerable magnetic hysteresis in FM-CO/AFM because of first order magnetic phase transition, it gives a strategy to obtain change order state in manganites.

Effect of nitrogen doping on structural, morphological, optical and electrical properties of radio frequency magnetron sputtered zinc oxide thin films

Zinc oxide receives remarkable attention due to its several attractive physical properties. Zinc oxide thin films doped with nitrogen were grown by employing RF magnetron sputtering method at room temperature. Doping was accomplished in gaseous medium by mixing high purity nitrogen gas along with argon sputtering gas. Structural studies confirmed the high crystalline nature with c-axis oriented growth of the nitrogen doped zinc oxide thin films. The tensile strain was developed due to the incorporation of the nitrogen into the ZnO crystal lattice. Surface roughness of the grown films was found to be decreased with increasing doping level was identified through atomic force microscope analysis. The presenting phonon modes of each film were confirmed through FTIR spectral analysis. The increasing doping level leads towards red-shifting of the cut-off wavelength due to decrement of the band gap was identified through UV–vis spectroscopy. All the doped films exhibited p-type conductivity was ascertained using Hall measurements and the obtained results were presented.