Dopant Chemistry Research Articles

Tuning Dopant Chemistry in the Na3PS4 Glass-Ceramic Electrolyte

Cubic Na3PS4 (c-Na3PS4) [1] is one of the most promising sodium superionic conductor solid electrolytes that may enable safer and more energy dense rechargeable batteries based on sodium-ion chemistry. Experimentally, Na+ conductivities as high as 0.74 mS cm-1 have been achieved via improvements in synthesis and doping.[2] In this talk, we will present an integrated first principles and experimental study of the effect of dopant chemistry on Na+ conductivity in Na3PS4. Using ab initio molecular dynamics (AIMD) simulations,[3] we show that pristine c-Na3PS4 is in fact an extremely poor Na ionic conductor, and it is only with the introduction of Na+ excess via M4+ for P5+ doping that reasonable conductivities close to the experimentally observed values are achieved. A systematic evaluation of different M4+ dopants find that 6.25% Sn4+ doping may yield an even higher Na+ conductivity, albeit with a slight increase in doping energy. We will also present recent results on alternative doping strategies that yield similarly high conductivities in the tetragonal polymorph (t-Na3PS4), with the potential advantages of a simpler synthesis path and improved SEI composition at the electrode-t-Na3PS4 interface.

Computational study of metallic dopant segregation and embrittlement at molybdenum grain boundaries

Mo and its alloys have been widely used as refractory materials owing to their excellent high temperature properties, but a critical limitation is their low ductility. Doping the grain boundaries (GBs) of Mo with metals such as Zr or Al have previously been demonstrated as a promising approach to address this shortcoming, whereas other alloy elements are known to embrittle the GBs. In this work, we investigated the segregation and strengthening/embrittling effects of 29 metallic dopants at the Σ5(310) tilt and Σ5(100) twist Mo GBs using density functional theory (DFT) calculations and empirical continuum models. In agreement with previous works for other metals, we find that the strain, as measured by the relative metallic radius versus Mo, is a good predictor of the segregation tendency, while the difference in cohesive energies between the dopant and Mo is a good predictor of the strengthening/embrittling effect. However, we find that dopant chemistry also plays a significant role in affecting segregation behavior at GBs, particularly in driving the formation of intermetallic precipitates or 2-D interfacial phases (complexions). We also show that the site preference of a dopant in the GB can lead to strengthening effects that deviate from those predicted using simple bond-breaking arguments. Assuming a fast cleavage model of fracture, Ta, Re, Os and W are predicted to have a weak strengthening effect on Mo for the Σ5(310) tilt GB, and Mn, Fe, Co and Nb are predicted to have reasonable strengthening effects for the Σ5(100) twist GB.

Effect of intrachain sulfonic acid dopants on the solid-state charge mobility of a model radical polymer

Radical polymers are an emerging class of non-conjugated, charge-conducting macromolecules that are capable of transporting charge through localized oxidation–reduction (redox) reactions that occur at the stable radical groups present as the pendant groups of the macromolecular chains. The chemical nature and oxidation state of these pendant radical groups are critical to the charge transporting abilities of radical polymers in the solid state. To date, however, the control of this chemistry has been limited to external oxidizing agents, and the concept of intramolecular dopants has not been explored fully. To this end, we have synthesized poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate)-co-poly(vinylsulfonic acid sodium salt) (PTMA-co-PVS). Then, electron paramagnetic resonance spectroscopy and attenuated total reflectance-Fourier transform infrared spectroscopy are implemented to evaluate the exact chemical nature of the pendant groups as a function of the PVS intramolecular dopants and exposure of the materials to external oxidation reactions. We correlate these changes in pendant group chemistry to charge transport ability, and we establish that the inclusion of a moderate amount of PVS dopants can improve the solid-state hole mobility of the material. Conversely, a large amount of sulfonic acidic dopants can be detrimental to the transport of the polymer relative to the homopolymer PTMA. Therefore, refinement of pendant group chemistry and careful addition of intramolecular dopants can enhance the solid-state transport ability of a radical polymer system. These fundamental principles, in turn, provide a vital foothold by which to optimize the solid-state charge transporting ability of current and next-generation radical polymer designs.

Mechanical and Bioactivity Properties of Nano Ceramic Composite-Based Oxyapatite Materials

The aim of the present work was the preparation of nano ceramics made of hydroxyapatite composites. The influence of doping on the physical, mechanical and bioactivity properties of the hydroxyapatite (HA) was evaluated. The nanoparticle sizes of the prepared powders were confirmed by transmission electron microscopy (TEM). In-vitro bioactivity assays of the composites were evaluated in simulated body fluids (SBF). The results proved that the mechanical strength of the composites increased with an increment of MgO compared to other composites and even to pure HA. It was noticed that with increasing MgO concentration, the HA degradation gradually decreased and the formation of apatite was delayed. The addition of a small quantity of nano-SiO2 significantly improved the morphology and bioactivity of the materials. The stability and bioactivity of the HA composite was influenced by both dopant chemistry and is amount. Finally, was concluded that HA composites with low contents of nano-MgO are promising as biomaterials in medical applications, especially for load bearing sites.

Invited Presentation: Elastic Anomalies and Electromechanical Effects in Gd-Doped Ceria

We have recently reported that at room temperature thin films of Gd-doped ceria exhibits a very large electrostriction effect. Our measurements with glass(150 µm)\\Cr(100 nm)\\Ce1-xGdxO2-x/2(500 nm)\\Cr(100 nm) cantilevers demonstrate that the magnitude of the electromechanical effect strongly depends on the value of the in-plane compressive strain. Under a 60 kV/cm field at room temperature, strain-free films may generate stress in the range of 30-150 MPa, whereas the films with compressive strain of a few tenth of a % can generate stress in excess of 500 MPa. The electromechanical response persists till the frequency of at least 6 kHz, which excludes a possibility of macroscopic material transfer. Modulated in-situ EXAFS and XANES measurements indicate that the microscopic origin of the electromechanical response is related to rearrangement of the local environment of cerium rather than gadolinium ions. Electric field affects the equilibrium between locally distorted and undistorted CeCe-VO complexes, which is similar to the mechanism responsible for a number of previously described inelastic anomalies. The magnitude of the electrostriction effect exhibits a complicated dependence on the Gd-content and suggests that cerium-vacancy interaction facilitate the mechanical response whereas vacancy-vacancy interactions weaken it. Our findings confirm that the presence of CeCe-VO complexes is essential for electromechanical activity and elastic anomalies. Tailoring the electrostriction effect in doped or oxygen-deficient ceria may therefore be possible by a proper choice of dopant chemistry and concentration.

Eutectoid decomposition of aluminum titanate (Al2TiO5) ceramics under Spark Plasma (SPS) and Conventional (CRH) thermal treatments

Eutectoid decomposition of Al2TiO5, is a strong function of heating rate, exposure temperature and dopant chemistry. Al2TiO5 specimens formed from the mixture of precursor oxides were subjected to Spark Plasma (SPS) and Conventional Ramp and Hold (CRH) heating to evaluate the extent of decomposition. SPS with heating rates of 200 °C/min and 50 °C/min under 50 MPa have shown phase decomposition of 95% and 74%, respectively. CRH conditions have resulted only in low phase decomposition of 11% however, substantial decomposition of 54% is observed on thermal cycling. A major slope change in dilatometric curve along with appearance of a new XRD peak at 40° in similar temperature regimes close to 1000 °C complements initiation of decomposition. A significant retardation in eutectoid decomposition of Al2TiO5 phase could be achieved by doping with 5 wt% of magnesium silicate as revealed by studies under identical conditions including SPS. Thermo-mechanical properties also correlated well with the observed decomposition profiles.

Thermodynamic modeling of native defects in ZnO

ZnO is an important optical material and is an ideal candidate for light emitting diode applications. The optical property of ZnO is determined by its native defects. In this study, the concentrations of native defects and carriers in ZnO are investigated by a four sublattice point defect thermodynamic model. The intrinsic carrier concentration calculated by this model showed a good consistency with the estimation from Maxwell–Boltzmann function. This demonstrates the feasibility of this model. The concentrations of native defects, zinc vacancy, oxygen vacancy and zinc interstitial, are calculated as a function of temperature under different growth conditions such as zinc-rich and oxygen-rich. The calculation results show that ZnO is an intrinsic n-type material and has a slight zinc excess at the congruent melting point due to oxygen vacancies. This model provides a methodology to obtain the information of defect and dopant chemistry in ZnO from a quantitative thermodynamic analysis.

Comparison of the performance of three ion mobility spectrometers for measurement of biogenic amines

The performance of three different types of ion mobility spectrometer (IMS) devices: GDA2 with a radioactive ion source (Airsense, Germany), UV-IMS with a photo-ionization source (G.A.S. Germany) and VG-Test with a corona discharge source (3QBD, Israel) was studied. The gas-phase ion chemistry in the IMS devices affected the species formed and their measured reduced mobility values. The sensitivity and limit of detection for trimethylamine (TMA), putrescine and cadaverine were compared by continuous monitoring of a stream of air with a given concentration of the analyte and by measurement of headspace vapors of TMA in a sealed vial. Preprocessing of the mobility spectra and the effectiveness of multivariate curve resolution techniques (MCR-LASSO) improved the accuracy of the measurements by correcting baseline effects and adjusting for variations in drift time as well as enhancing the signal to noise ratio and deconvolution of the complex data matrix to their pure components. The limit of detection for measurement of the biogenic amines by the three IMS devices was between 0.1 and 1.2ppm (for TMA with the VG-Test and GDA, respectively) and between 0.2 and 0.7ppm for putrescine and cadaverine with all three devices. Considering the uncertainty in the LOD determination there is almost no statistically significant difference between the three devices although they differ in their operating temperature, ionization method, drift tube design and dopant chemistry. This finding may have general implications on the achievable performance of classic IMS devices.

ZnO, SiO2, and SrO doping in resorbable tricalcium phosphates: Influence on strength degradation, mechanical properties, and in vitro bone–cell material interactions

To understand the combined effects of ZnO, SiO(2), and SrO doping on mechanical and biological properties of tricalcium phosphate (TCP) ceramics, dense β-TCP compacts of different compositions (pure β-TCP; 1.0 wt % SrO; 0.25 wt % ZnO; 1.0 wt % SrO + 0.5 wt % SiO(2); and 1.0 wt % SrO + 0.25 wt % ZnO) were prepared via dry pressing followed by sintering at 1250°C. X-ray diffraction of sintered compacts revealed that dopants retarded β- to α-TCP phase transformation during sintering. Doping with SrO, SrO/SiO(2), and SrO/ZnO reduced compressive strength of the samples to 56% (173 ± 25 MPa), 57% (170 ± 15 MPa), and 47% (208 ± 72 MPa) of pure β-TCP (396 ± 58 MPa), respectively. However, addition of ZnO resulted in only 7% (365 ± 69 MPa) strength degradation. The impact of dopants on long-term in vitro strength degradation was evaluated by soaking in simulated body fluid (SBF) for a period of 8 weeks. In all cases, excellent apatite growth was observed on doped β-TCP samples. However, strength degradation rates were different depending on dopant chemistry and composition. Maximum degradation was observed in undoped and ZnO-doped β-TCP samples, which degraded to 41% and 68% of the original strength before soaking in SBF. Finally, in vitro cell-materials interaction study using human fetal osteoblast cells demonstrated that addition of dopants improved cell attachment and proliferation. These results indicate that tailorable strength and strength degradation behavior can be achieved in β-TCP via compositional modifications using small amount of dopants.

Optoelectronic surface-related properties in boron-doped and irradiated diamond thin films

Elucidation of microscopic properties of synthetic diamond films, such as formation and evolution of bulk and surface defects, chemistry of dopants, is necessary for a reliable quality control and reproducibility in applications. Surface photovoltage (SPV) spectroscopy and photoluminescence (PL) spectroscopy were employed to study diamond thin films grown on silicon by microwave plasma-assisted chemical vapor deposition and hot-filament chemical vapor deposition with different levels of boron doping in conjunction with gamma irradiation. SPV experiments showed that while the increase of boron concentration leads to a semiconductor-metal transition, subsequent gamma irradiation reverts quasi-metallic samples back to a semiconducting state by compensating electrical activity of boron possibly via hydrogen. One of the most pronounced common transitions observed at ∼3.1–3.2 eV in the SPV spectra was also present in all of the PL spectra. It is likely that this is a signature of the sp2-hybridized carbon clusters in or in the vicinity of grain boundaries.

Application of principal component analysis to a full profile correlative analysis of FTIR spectra

We have demonstrated an informatics methodology for finding correlations between the full profile Fourier transform infrared spectra of polycrystalline 3C‐silicon carbide (poly‐SiC) films and their growth conditions, thereby developing high‐throughput structure‐process relationships. Because SiC films are a structural element in photonic sensors, this paper focuses on the interpretation of their optical response, the multivariate tracking of critical processing pathways, and the identification of controlling processing mechanisms. Using principal component analysis, we have developed a data analysis tool to aid in the assessment of the relative contributions of experimental parameters in low‐pressure chemical vapor deposition processes to optical responses on the basis of the size of eigenvalues of the spectral data set. The applied methodology for identifying spectral relationships of stoichiometry, dopant chemistry, and microstructure of poly‐SiC provides more effective guidelines to manipulate optical responses by controlling multiple experimental parameters. Copyright © 2011 John Wiley & Sons, Ltd.

Understanding in vivo response and mechanical property variation in MgO, SrO and SiO2 doped β-TCP

The aim of this work is to evaluate the influence of MgO, SrO and SiO₂ doping on mechanical and biological properties of β-tricalcium phosphate (β-TCP) to achieve controlled resorption kinetics of β-TCP system for maxillofacial and spinal fusion application. We prepared dense TCP compacts of four different compositions, i) pure β-TCP, ii) β-TCP with 1.0wt.% MgO+1.0wt.% SrO, iii) β-TCP with 1.0wt.% SrO+0.5wt.% SiO₂, and iv) β-TCP with 1.0wt.% MgO+1.0wt.% SrO+0.5wt.% SiO₂, by uniaxial pressing and sintering at 1250°C. β phase stability is observed at 1250°C sintering temperature due to MgO doping in β-TCP. In vitro mineralization in simulated body fluid (SBF) for 16 weeks shows excellent apatite growth on undoped and doped samples. Strength degradation of TCP samples in SBF is significantly influenced by both dopant chemistry and amount of dopant. Compressive strengths for all samples show degradation in SBF over the 16 week time period with varying degradation kinetics. MgO/SrO/SiO₂ doped sample shows no strength loss, while undoped TCP shows the maximum strength loss from 419 ± 28 MPa to 158 ± 28 MPa over the 16 week study. In case of MgO/SrO doped TCP, strength loss is slow and gradual. TCP doped with 1.0wt.% MgO and 1.0wt.% SrO shows excellent in vivo biocompatibility when tested in male Sprague-Dawley rats for 16 weeks. Histomorphology analysis reveals that MgO/SrO doped TCP promoted osteogenesis by excellent early stage bone remodeling as compared to undoped TCP.

Structure, Stability and Magnetism of Cobalt Doped (ZnO)<SUB><I>n</I></SUB> Clusters

Clusters of magnetic impurities are believed to play an important role in retaining ferromagnetism in diluted magnetic semiconductors (DMS), the origin of which has been a long debated issue. Controlling the dopant homogeneity in magnetic semiconductors is therefore a critical issue for the fabrication of high performance DMS. The current paper presents a first principle study on the stability and magnetic properties of Co doped (ZnO)n (n = 12 and 15) clusters using density functional theory. The results show that cobalt ions in these clusters tend to increase their stabilities by maximizing their co-ordination numbers to oxygen. This will likely to be the case for (ZnO)n clusters with n other than 12 and 15 in order for Co to reside in a stable local crystal field. Expansive (shrinkage) stress is introduced when cobalt resides in exohedral substitutional (endohedral interstitial) sites; such strain can be offset by the cluster deformation. Bidoped cluster is found to be unstable due to the increase of system strain energy. All the doped clusters were found to preserve 3 microg of magnetic moments from Co in the overall clusters, but with part of the local moments on cobalt re-distributed onto neighboring oxygen atoms. Current findings may provide a better understanding on the structural chemistry of magnetic dopants in nanocrystallined DMS materials.

Bone cell–material interactions on metal-ion doped polarized hydroxyapatite

The objective of this work is to study the influence of Mg 2+ and Sr 2+ dopants on in vitro bone cell–material interactions of electrically polarized hydroxyapatite [HAp, Ca 10(PO 4) 6(OH) 2] ceramics with an aim to achieve additional advantage of matching bone chemistry along with the original benefits of electrical polarization treatment relevant to biomedical applications. To achieve our research objective, commercial phase pure HAp has been doped with MgO, and SrO in single, and binary compositions. All samples have been sintered at 1200 °C for 2 h and subsequently polarized using an external d.c. field (2.0 kV/cm) at 400 °C for 1 h. Combined addition of 1 wt.% MgO/1 wt.% SrO in HAp has been most beneficial in enhancing the polarizability in which stored charge was 4.19 μC/cm 2 compared to pure HAp of 2.23 μC/cm 2. Bone cell–material interaction has been studied by culturing with human fetal osteoblast cells (hFOB) for a maximum of 7 days. Scanning electron microscope (SEM) images of cell morphology reveal that favorable surface properties and dopant chemistry lead to good cellular adherence and spreading on negatively charged surfaces of both Sr 2+ and Mg 2+ doped HAp samples over undoped HAp. MTT assay results at 7 days show the highest viable cell densities on the negatively charged surfaces of binary doped HAp samples, while positive charged doped HAp surfaces exhibit limited cellular growth in comparison to neutral surfaces.

Inter-granular glassy phases in the low-CaO-doped HIPed Si3N4ceramics: a review

AbstractThis review outlines the essence of a progressive study on the glassy inter-granular film (IGF) in a model ceramic system, the low-CaO-doped HIPed high-purity Si3N4. This was initiated from the finding of a systematic variation of equilibrium IGF thickness following the dopant chemistry, manifesting its fundamental important to ceramic processing. By employing analytical transmission electron microscopy to measure the local chemistry in IGF, however, significant discrepancy was found between trends of local IGF chemistry and thickness. A stable IGF composition was revealed in this system, while a bi-level distribution of Ca segregation establishes a correspondence between the IGF structure and the surface crystallography. The detection of similar levels of nitrogen in IGF through the whole series further supports the presence of a rather stable IGF chemistry. After the saturation of dopants in the stable IGF, extra CaO was found to re-distribute in pockets by enrichment at tips, leading to a liquid phase separation with the Ca-rich phase wetting the entrance zone contacting IGF. The perspective for establishing a comprehensive correlation between the inter-granular phases and the bi-modal microstructure induced by faster growth of basal facets is briefly discussed to pave the way for future work.

Calcium Phosphate‐Based Resorbable Ceramics: Influence of MgO, ZnO, and SiO2 Dopants

Resorbable calcium phosphate (CaP)‐based biomaterials are important because they can significantly improve health care by shortening the time necessary for restoration of functional loading of grafted bones. Although synthetic CaPs show exceptional similarities to natural bone, however, they are deficient in one major area, in that they do not have the same mineral content of bone. The focus of our work is to understand the influence of dopants on the physical, mechanical, and biological properties of tricalcium phosphate (TCP) resorbable ceramics with special emphasis toward in vitro strength degradation and cell–materials interactions as a function of time. For this purpose, β‐TCP was doped with magnesia (MgO), zinc oxide (ZnO), and silica (SiO2). Those dopants were added as individual dopants, and their binary and ternary compositions. It was found that these dopants significantly influenced densification behavior and as sintered microstructures of TCP. In vitro mineralization studies in simulated body fluids (SBF) for 12 weeks showed apatite growth on the highly porous compositions either on the surface or inside. From scanning electron microscopic analysis it was evident that surface degradation occurred on all compositions in SBF. Compression strengths for samples up to 12 weeks in SBF showed that it is possible to tailor strength loss behavior through compositional modifications. The highest compression strength was found for binary MgO–ZnO doped TCP. Overall, samples showed either a similar strength level during the 12 weeks test period, or a continuous decrease or a continuous increase in strength depending on dopant chemistry or amount. In vitro human osteoblast cell culture was used to determine influence of dopants on cell‐materials interactions. All samples were non‐toxic and biocompatible. Dopant chemistry also influenced adhesion, proliferation, and differentiation of osteoblastic precursor cell line 1 (OPC1) cells on these matrices.

Interactions Between Chemical Functionality and Nanoscale Surface Topography Impact Fibronectin Conformation and Neuronal Differentiation on Model Sol-gel Silica Substrates

ABSTRACTFunctional relationships between the biomaterial interface and extracellular matrix (ECM) proteins are intimately involved in cellular adhesion and function. Structural changes of ECM proteins upon adsorption to a surface alter the protein's biological activity by varying the availability of molecular binding sites. Recent work using native and organically modified sol-gel silica as a neuronal biointerface revealed that changes in surface nanotopography of bulk versus thin film materials result in dramatic differences in fibronectin structure, cell survival, and neuronal differentiation. In order to further investigate interactions between chemical functionality and surface topography, we evaluated the global conformation of human fibronectin adsorbed to seven different organically modified silica gels and thin films. Chemical functional groups were introduced into the materials either by altering the starting precursor or by doping with poly-l-lysine or polyethylenimine. Surface topography measurements by atomic force microscopy show that films have surface features less than 25 nm while bulk materials of the same precursor chemistry have features ranging from 50 – 100 nm in size. Fluorescence resonance energy transfer spectroscopy (FRET) revealed a strong interaction between surface topography and chemical functionality. Fibronectin remain globular on all bulk materials regardless of chemical modification. The same changes in precursors or dopant chemistry, however, induced changes in the conformation of fibronectin on the thin films. The differentiation of PC12 cells on the surface indicated a strong impact of the surface features and suggest a possible optimal fibronectin folding state.

SIMS depth profiling and direct ion imaging of a 16-megabit DRAM

The use of secondary ion mass spectrometry (SIMS) has long been established as a powerful tool forthe analysis of microelectronic devices. However, as newer fabrication technologies emerge, and device dimensions shrink, increasing demands are placed upon the SIMS analyst.The present work illustrates how the depth profiling and direct ion imaging capabilities of a Cameca ims 4f SIMS can be exploited to determine the structure and dopant chemistry of a state-of-the-art16 megabit DRAM (dynamic random access memory) device. The optical micrograph shown in Fig. 1 is an overview of a portion of the sense amplifiers located between two array blocks. In the centre of this area, p-type devices sitting in an n-well, surrounded on either side by n-type devices, all in a p-type substrate can be observed. The object of the study was to determine if a low concentration p-type implant is present below the n-type devices.

Characterization of the lightguiding structure of optical fibers by atomic force microscopy

For the first time, atomic force microscopy (AFM) is applied to study the lightguiding structure of optical fibers: the local surface topography of an etched fiber endface is profiled with AFM. The etching rate has been studied as a fingerprint to determine the effect of dopant chemistry and preform fabrication conditions on the fiber structure. Structural and geometrical distortions of the lightguiding structure can be directly measured with high spatial resolution. Furthermore, by quantifying the etched depth in relation to the refractive-index change, a spatial mapping of the refractive-index change can be inferred from the AFM profile. These examples demonstrate the effective use of AFM to elucidate, on a nanometric scale, features of the lightguiding structure that contribute to the performance of light transmission. >

New materials synthesis: Characterization of some metal-doped antimony oxides

In order to understand the chemistry of altermetal dopants in antimony oxide, the detailed structural characterization of two β-Sb 2O 4 compounds is reported, Mo-doped β-Sb 2O 4 (1.5 metal%) and V-doped β-Sb 2O 4 (5 metal%). The methods used to characterize these materials are X-ray and neutron diffraction, scanning electron microscopy, Mo K-edge extended X-ray absorption fine structure spectroscopy, and elemental analysis. The atomic position of each of these dopants in Sb 2O 4 is radically different as is the overall effect on the host structure. Molybdenum does not substitute for Sb atoms, rather the Mo atoms are found in channels of electron density formed by Sb 3+ lone pairs. The two nearest Sb 3+ are absent and the oxygen stoichiometry is preserved. The formula is Sb 1.97Mo 0.015O 4. Vanadium incorporates substitutionally for the Sb 3+ atoms and there are random oxygen vacancies in the resultant structure. The formula is Sb 1.9V 0.1O 3.67. In each case the atomic positions of the host structure (Sb and O) are remarkably unaltered. The β-Sb 2O 4 structure can accommodate Mo and V simultaneously, presumably both means of metal incorporation are employed in this ternary oxide.