Total Dopant Concentration Research Articles

Accurate measurement of dopant concentration in organic light-emitting diodes by combining high-performance liquid chromatography and TOF-SIMS

The authors report the use of high-performance liquid chromatography (HPLC) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) utilizing a gas cluster ion beam to accurately measure the dopant concentration and its depth profile in organic thin films used for organic light-emitting diodes. The total dopant concentrations estimated by HPLC for films of 4,4'-bis(carbazol-9-yl)biphenyl (CBP) doped with tris(2-phenylpyridinato)iridium(III) (Ir(ppy)3) are consistent with those measured by quartz crystal microbalances (QCMs) during the deposition. Concentrations measured for Ir(ppy)3:CBP films by HPLC and TOF-SIMS show a nearly linear relationship in the range of 1–8 wt. %. At concentrations higher than 8 wt. %, TOF-SIMS values significantly deviate because of the matrix effect. The depth profile of the dopant concentration measured by TOF-SIMS was in good agreement with that measured by QCMs during film deposition for concentrations below 8 wt. %. These methods are especially useful for comparing the dopant concentration of films deposited in different batches and equipment.

Microstructure and thermal properties of inflight rare-earth doped thermal barriers prepared by suspension plasma spray

Rare-earth doped yttria-stabilized zirconia (YSZ) coatings with lower thermal conductivity have been fabricated via suspension plasma spray by dissolving rare-earth nitrates into YSZ powder-ethanol suspensions prior to plasma spraying. The effect of dopant concentration and dopant type on properties of the coatings was determined by comparing two coatings containing different concentrations of the same dopant pair (Nd 2 O 3 /Yb 2 O 3 ), and three coatings having similar concentrations of different dopant pairs (Nd 2 O 3 /Yb 2 O 3 , Nd 2 O 3 /Gd 2 O 3 , and Gd 2 O 3 /Yb 2 O 3 ). The porosity content of the coating was found to increase with increased total rare-earth dopant concentration but did not significantly change with dopant pairs. The cross-sectional morphology of every coating displayed a cauliflower-like structure. However, the most heavily doped coating exhibited a larger surface roughness and feathery features in the columnar structures. The thermal conductivity measurement showed that the thermal conductivity decreased with increased Nd 2 O 3 /Yb 2 O 3 concentration. Among coatings containing different dopant pairs, the Gd 2 O 3 /Yb 2 O 3 doped coating exhibited lowest conductivity.

Characterisation, phase stability and surface chemical properties of photocatalytic active Zr and Y co-doped anatase TiO2 nanoparticles

We report on the characterization, phase stability, surface chemical and photocatalytic properties of Zr and Y co-doped anatase TiO2 nanoparticles prepared by homogenous hydrolysis methods using urea as precipitating agent. The materials were analyzed by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, BET isotherm and BJH pore size distribution measurements. It is shown that Y and Zr ions replace Ti ions in the anatase TiO2 structures up to a critical total dopant concentration of approximately 13wt%. The co-doped particles show increased phase stability compared to pure anatase TiO2 nanoparticles. The anatase to rutile phase transformation is shown to be preceded by cation segregation and dissolution with concomitant precipitation of Y2Ti2−xZrxO7 and ZrTiO4. Co-doping modifies the optical absorption edge with a resulting attenuation of the Urbach tail. The band gap is slightly blue-shifted at high doping concentrations, and red shifted at lower doping concentrations. Formic acid adsorption was used as a probe molecule to investigate surface chemical properties and adsorbate structures. It was found that the relative abundance of monodentate formate compared to bidentate coordinated formate decreases with increasing doping concentration. This is attributed to an increased surface acidity with increasing dopant concentration. Photodegradation of formic acid occurred on all samples. With mode-resolved in situ FTIR spectroscopy it is shown that the rate of photodegradation of monodentate formate species are higher than for bidentate formate species. Thus our results show that the trend of decreasing photo-degradation rate with increasing dopant concentration can be explained by the adsorbate structure, which is controlled by the acidity of the surface.

Electrochemical synthesis of nanostructured polyaniline: Heat treatment and synergistic effect of simultaneous dual doping

AbstractDifferent nanostructured polyaniline (PAni) has been synthesized via facile template‐free electrochemical synthesis approach in aqueous medium. Instead of conventionally used aniline, aniline sulphate was used in electrochemical polymerization. The synthesis process involves simultaneous doping with combination of inorganic and organic acid, i.e., sulfuric acid (H2SO4) and p‐toluenesulfonic acid (PTSA) at different ratios keeping total dopant concentration constant. Synergistic increase in conductivity is observed and the best conductivity is achieved at 3:1 ratio of [H2SO4]:[PTSA]. Different nanostructures of PAni are revealed through morphological analysis consisting of nanosphere, nanorod, and clustered particles among which finer nanorods show the best electrical conductivity. Upon controlled heat treatment followed by further cooling, resistivity increases, but after one day it decreases again and in the optimized dual doped PAni, it approaches approximately the same value of initial resistance. Lattice strain and benzenoid to quinonoid ratio increases with heat treatment. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

The phase stability and electrical conductivity of Bi2O3 ceramics stabilized by Co-dopants

In this study, Gd2O3, Nb2O5, Sc2O3, ZrO2, and BaO are chosen as co-dopants with Y2O3 to stabilize δ phase Bi2O3 ceramics. Under a fixed dopant concentration, the effects of the co-dopants on the phase stability and electrical properties of Bi0.76Y0.24−xMxO1.5+δ (M=Gd, Nb, Sc, Zr, and Ba) are investigated. Based on the study results, all co-doped specimens exhibit a sintering temperature lower than that of the Bi0.76Y0.24O1.5 ceramic. The Bi0.76Y0.24−xGdxO1.5, Bi0.76Y0.24−xNbxO1.5+δ, and Bi0.76Y0.24−xScxO1.5 ceramics retain a cubic fluorite structure of δ-Bi2O3 phase while Bi0.76Y0.24−xBaxO1.5−δ displays a mixture of cubic and rhombohedral phases. Despite the fact that the ionic radius of Sc3+ and Zr4+ ions are smaller than that of Y3+ ion, the lattice constant of the Bi0.76Y0.24O1.5 ceramic rises with the Gd2O3, Sc2O3, or ZrO2 replacement but drops with the Nb2O5 substitution. Of the compositions studied, the Bi0.76Y0.20Zr0.04O1.5+δ ceramic emerges with the best electrical conductivities of 0.27 and 0.55Scm−1 at 600 and 700 °C, much higher than those of the Y2O3-doped and ZrO2-doped Bi2O3 ceramics. It is observed that, with the same total dopant concentration, the co-dopant stabilized Bi2O3 ceramics outperforms their single-dopant stabilized counterparts in terms of conductivity, probably due to the larger lattice constants.

Enhancing the magnetic characteristics of BiFeO3 nanoparticles by Ca, Ba co-doping

Multiferroic nanoparticles (NPs) of pristine and Ca, Ba co-doped BiFeO3 were synthesized by a facile sol–gel route. Co-doping was done by fixing the total dopant concentration at 5 mol% and then the relative concentrations of Ca and Ba was varied. Structural, optical and magnetic properties of the NPs were investigated using different techniques. UV–Vis absorption spectra of BiFeO3 NPs showed a substantial blue shift of ∼100 nm (530 nm → 430 nm) on Ca, Ba co-doping which corresponds to increase in band gap by 0.5 eV. 57Fe Mössbauer spectroscopy confirmed that iron is present only in 3+ valence state in all co-doped samples. The coercive field increased by 18 times for Bi0.95Ca0.01Ba0.04FeO3 samples, which is the maximum enhancement, observed amongst all the 5 mol% doped samples. At the equimolar (2.5 mol% each) concentration of co-dopants, the coercive field shows a significant enhancement of about 9 times (220 Oe → 2014 Oe) with concomitant increase in saturation magnetization by 7 times. Thus, equimolar co-doping causes simultaneous enhancement of the twin aspects of magnetic properties thereby making them better suited for device applications.

Effect of Annealing Temperature and Dopant Concentration on the Conductivity Behavior in (DyO1.5)x–(WO3)y–(BiO1.5)1−x−y

Cubic‐stabilized ((DyO1.5)x–(WO3)y–(BiO1.5)1−x−y) electrolytes (DWSB) having higher conductivity than (ErO1.5)0.2 (BiO1.5)0.8 (20ESB) were developed. However, this DWSB composition also experienced a conductivity degradation like other cubic stabilized bismuth oxides in intermediate temperature (IT) ranges, i.e. 500°–700°C. Several DWSB compositions with the same 2:1 dopant content ratio (Dy:W) were annealed to determine the conductivity behavior in the IT range with time. All DWSB compositions maintained their initial conductivity at 700°C, but underwent conductivity degradation at ≤600°C. The effect of total dopant concentration on the conductivity degradation behavior was investigated at 600° and 500°C. It was also found that 8D4WSB, which is the highest conductivity composition, has promise as an electrolyte for an isothermal operation above 650°C or below 400°C.

Enhanced long-term stability of bismuth oxide-based electrolytes for operation at 500 °C

Cubic-stabilized ((DyO1.5) x –(WO3) y –(BiO1.5)1 − x − y ) electrolytes (DWSB) with much higher conductivity than (ErO1.5)0.2(BiO1.5)0.8, 20ESB, were developed through a double-doping strategy. (DyO1.5)0.08–(WO3)0.04–(BiO1.5)0.88, 8D4WSB, is the highest conductivity composition but underwent the greatest conductivity degradation at 500 °C due to its low total dopant concentration. The effect of dopant composition on conductivity behavior with time at 500 °C demonstrates that there is a trade-off between initial conductivity and long-term stability at this temperature. Therefore, it is necessary to find an optimal total and relative concentration of dopants to provide the enhanced long-term stability needed to make this DWSB electrolyte system feasible for 500 °C operation. To this end, it was found that (DyO1.5)0.25–(WO3)0.05–(BiO1.5)0.70, 25D5WSB, maintained a conductivity of 0.0068 S/cm without appreciable degradation after annealing at 500 °C for 500 h. Moreover, since bismuth oxide-based electrolytes do not exhibit any grain boundary impedance, the total conductivity of 25D5WSB is significantly higher than that of alternate electrolytes (e.g., GDC: Gd0.1Ce0.9O1.95) at this temperature.

Enhancement of the critical current density and upper critical field in Zr and Mo co-dopedNb3Sn

We prepared a series of Nb3−2xZrxMoxSn (0≤x≤0.2) samples which have the same number of electrons per cell asNb3Sn in order tostudy the doping effect. The formation of the single phase samples was confirmed by x-ray diffraction whenx≤0.1. It was found that thelattice parameters a decrease slightly with the increasing dopant concentration. The grain morphologiesof the sample are irregular. As the dopant content increases, the size ofthe coarse grain decreases and the content of the fine grain increases. TheTc value of theNb3−2xZrxMoxSn samples drops slowlywhen x<0.1, whereas asharp decline of Tc occurs when x>0.1. The Tc drop in the co-doped samples is slower than that in the single-dopedones with the same total dopant concentrations, indicating that theN(EF) plays an importantrole in the change of Tc. At 4 T and 10 K, the Jc value of Nb2.8Zr0.1Mo0.1Sn sample reached 3.4 × 106 A cm−2, which is significantly enhanced by more than 400 and 23 times that of the pureNb3Sn and single-dopedNb2.8Mo0.2Sn samples,respectively. The Hc2(0) values of the co-doped sample are higher than the pure and single-doped sample. TheHc2(0) valueof the Nb2.8Zr0.1Mo0.1Sn sample reached 30 T.

Effect of total dopant concentration and dopant ratio on conductivity of (DyO 1.5) x–(WO 3) y–(BiO 1.5) 1−x−y

Dysprosium- and tungsten-stabilized bismuth oxide (DWSB) electrolytes were developed to achieve higher conductivity. With double doping, stabilization of the cubic phase was achieved with as little as 12 mol.% total dopant concentration, resulting in higher conductivity. The conductivity of DWSB electrolytes increased linearly as the total dopant concentrations decreased with fixed dopant ratio. Overall, DWSB has a closer inherent structure to pure δ-Bi 2O 3 than any singly doped compositions. Both lattice parameter and conductivity linearly extrapolate with total dopant concentration to that of pure δ-Bi 2O 3, resulting in the ability to stabilize δ-phase at lower dopant concentration, and thus achieving higher conductivity.

Effectiveness of Ga Additive to Sinterability and Electrical Properties on Y-Doped BaZrO3 Proton Conductors Sintered at 1600{degree sign}C

Gallium and yttrium co-doped BaZrO3 based proton conductors sintered at 1600oC, in which total dopant concentration is fixed at 15mol%, are fabricated using the conventional solid state reaction method. Ga concentration dependence on sinterability and electrical properties is evaluated. Lattice parameter a, relative density and grain size show local maximum at 1mol% Ga concentration, i.e. BaZr0.85Y0.14Ga0.01O2.925 (BZY14Ga1). Relative density of it is over 95%. Also, it is found that grain boundary conductivity of BZY15 is drastically improved by 1mol% Ga additives, although bulk conductivity is slightly lower than that of 15mol% Y-doped BaZrO3. As a result, total conductivity of BZY14Ga1 is highest in the specimens and the value is over 2 x 10-3 Scm-1. On the other hand, 3 and 5mol% Ga-doped specimens show significantly low bulk and grain boundary conductivity. So, the results suggest that the Ga additive is effective for sintering at 1600oC, but the range of concentration is very limited.

The effects of Ti and Cr co-doping on the structure and superconductivity ofV3Si

V3Si is a well known A15 superconductor with a superconducting transition temperature(Tc) value of 17 K. Weprepared a series of V3−2xTixCrxSi (0≤x≤0.2) samples which have the same number of electrons per cell asV3Si in orderto study the doping effect. The formation of the single-phase samples was confirmed by x-ray diffraction whenx≤0.1. It was found thatthe lattice parameter a decreases slightly with increasing dopant concentration. TheTc value of theV3−2xTixCrxSi samples drops slowlywhen x<0.1 whereas asharp decline of Tc occurs when x>0.1. TheTc drop in the Tiand Cr co-doped V3Si is slower than that in the single-element Ti or Cr dopedV3Si with the same total dopant concentrations, indicating that the density of states at the Fermi level,N(EF), plays an important role in the change ofTc. The criticalcurrent density of V2.8Ti0.1Cr0.1Si is significantly enhanced to more than six times that of pureV3Si at 10 K in magnetic fields up to 4 T.

Reduction of magnetization in Zn0.9Fe0.1O diluted magnetic semiconducting nanoparticles by doping of Co or Mn ions

We have investigated structural, magnetic, optical, and electrical transport properties of Zn0.9−xFe0.1(Co∕Mn)xO (x=0.05,0.1 for Co and x=0.1 for Mn) diluted magnetic semiconducting nanoparticles synthesized through low temperature chemical “pyrophoric reaction process.” From transmission electron micrograph, particle sizes are found to be in the nanometric regime (∼7nm) and single crystalline in nature. The magnetization measurements reveal that doping of Co or Mn ions in ZnFeO nanometric matrix decreases the values of coercive field and average magnetization, not due to just increasing the total dopant concentration. It has been attributed to the formation of antiferromagnetic or paramagnetic states in ferromagnetic infinite cluster (spanning of magnetic polarons) by doping of Co or Mn ions. The strong irreversibility has been observed to persist at and above room temperature in magnetization versus temperature curve. The semiconducting band gap of those nanoparticles has been estimated using recorded absorbance spectra. The electrical behaviors of those samples have been investigated over the wide temperature and frequency range using ac complex impedance spectroscopy.

Structural studies of Sr- and Mg-doped LaGaO 3

A series of La 1− x Sr x Ga 1− y Mg y O 3− δ (LSGM) solid solution were prepared by solid state synthesis and characterized by X-ray phase analysis at room temperature. A systematic change of crystal structure with the increase in A- and B-site dopant contents was observed. At a total dopant concentration of 25 at%, the crystal structure was found to be orthorhombic whereas at a total dopant concentration of 35 at% keeping at least one component at 20 at%, the structure was observed to be cubic. Mixed structures of orthorhombic and rhombohedral were also found at intermediate dopant concentrations. A structural phase diagram is proposed based on the findings and co-related with the oxygen ionic conductivity.

Doubly Doped Bi2O3 Electrolytes with Higher Conductivity

Bi2O3 electrolytes doubly doped with Dy2O3 and WO3 (DyWSB) were developed to obtain high ionic conductivity. Various compositions having 2:1 mol dopant ratio between Dy and W were tested to obtain a pure single phase, and the trend in conductivity according to total dopant concentration determined. The dopants were selected based on their radii and polarizability. The conductivity of DyWSB electrolytes increases linearly as the total dopant concentration decreases with fixed dopant ratio. The conductivity of 8Dy4WSB is 0.098 S/cm (4 times higher than that of 20ErSB) at 500oC, and the conductivity is 0.569 S/cm at 700oC.

Development of Higher Ionic Conductivity Ceria Electrolyte

A co-dopant strategy was used to further investigate the doping effects on the ionic conductivity of ceria based electrolyte. Experiments were conducted using Lu3+ and Nd3+ as co-dopants, added in a proportion such that the effective dopant ionic radius matches critical dopant ionic radius for ceria electrolyte. Ionic conductivity measurements were performed on LuxNdyCe1-x-yO2-d (where x/y = 1.16) electrolytes with different total dopant concentration (x+ y) using two-point probes electrochemical impedance spectroscopy technique from 150oC to 700oC in air. In addition, to understand the effect of polarizibility alone, Lu3+ doped CeO2 was also investigated as the ionic radius of Lu3+ is approximately the same as Ce4+. LuxNdyCe1-x-yO2-d electrolytes exhibit higher ionic conductivity than LuxCe1-xO2-d, which indicates that co-doping strategy works. Around 700oC, its grain ionic conductivity surpasses that of the GdxCe1-xO2-d, which is the highest ionic conductive ceria based electrolyte.

EFFECT OF Co–Ga PAIRED SUBSTITUTION ON SUPERCONDUCTIVITY IN YBa2Cu3O7-δ

The effect of Co–Ga paired substitution on the superconducting properties of YBa 2 Cu 3 O 7-δ (Y-123) has been investigated by X-ray diffraction, ac susceptibility, dc resistivity and oxygen content measurements. We report in this paper the results of our studies on the paired substitution of a magnetic and non-magnetic ion at Cu site in Y-123, while keeping the total dopant concentration fixed. The simultaneous substitution of Co and Ga at Cu site shows variation in the transition temperature (T c ), oxygen content and hole concentration as a function of change in the balance of magnetic (Co) and non-magnetic (Ga) concentration. Orthorhombicity (D), given as (b-a)/a, also varies as a function of increasing dopant concentration. The variation in T c due to Co–Ga substitution is discussed in the light of dopant valency and hole filling mechanism.

Lanthanide co-doping of solid electrolytes: AC conductivity behaviour

Solid electrolytes of cubic structure employed in Solid Oxide Fuel Cells (SOFC) like ceria (CeO 2) and zirconia (ZrO 2) are typically doped with a single selected element from the (Y, lanthanide)-series. Co-doping of ceria with several elements is investigated here in terms of its influence on ionic conductivity. It is found that, for a same total dopant concentration, mixtures of dopants give a higher total ionic conductivity (by 10–30%) than the best singly doped material.

Characterization of Chemical Dopants in ICF Targets

Capsules that contain doped GDP layers must be characterized for dopant concentration level and uniformity. X–ray µ-fluorescence (XRF), with its unique capability to quantitatively determine concentrations of most elements simultaneously and non-destructively, and in an efficient manner, is generally the method of choice for total dopant (Z>11) concentration within ICF capsules. Dopant homogeneity (as well as concentration) within the target has been determined using Rutherford Backscatter Spectroscopy (RBS). Other methods which have provided information are SEM/EDXS; combustion analyses; mass spectroscopy and thermogravimetric analysis (TGA)

Positron-annihilation study of vacancy defects in InAs

Positron lifetime measurements on InAs wafers have shown that the positron bulk lifetime in InAs is 246\ifmmode\pm\else\textpm\fi{}2 ps. Most samples exhibit a defect lifetime of 287\ifmmode\pm\else\textpm\fi{}6 ps, which is attributable to monovacancy-impurity complexes with a concentration of 7\ifmmode\pm\else\textpm\fi{}2\ifmmode\times\else\texttimes\fi{}${10}^{16}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ . Very heavily doped n-type samples exhibit a defect lifetime of 332--340 ps. The defects in these samples have divacancy character, but change their configuration at low temperatures to a monovacancy-type defect. The concentration of these defects is also close to ${10}^{17}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ . Both types of defects are stable for rapid thermal annealing up to 850 \ifmmode^\circ\else\textdegree\fi{}C, and both defects are neutral. It is proposed that the formation of the divacancy-type defects may be correlated with a discrepancy between the carrier concentration and the total dopant concentration.