Effects of dopants with various valences on densification behavior and phase composition of a ZrO2–SiO2 nanocrystalline glass-ceramic

Effects of dopants with different valences on the densification behavior and phase composition of a ZrO₂–SiO₂ nanocrystalline glass-ceramic (NCGC) during pressureless sintering were investigated in this study. The raw powder of Ca²⁺, La³⁺, Ce⁴⁺ and Ta⁵⁺ ions doped ZrO₂–SiO₂ (referred to as Ca-ZS, La-ZS, Ce-ZS, Ta-ZS, respectively) and pure ZrO₂–SiO₂ (PZS) sample were synthesized by sol-gel method, followed by pressureless sintering. Compared with the PZS sample, doping of Ca²⁺ and La³⁺ ions significantly promoted the densification of the NCGCs. The “densification promotion” effect was attributed to the formation of oxygen vacancies and the decrease of SiO₂ viscosity due to doping of aliovalent cations. The dopants with various valences showed significant effects on the phase compositions of the NCGCs during sintering. Doping of Ca²⁺ ion accelerated the reaction kinetics between ZrO₂ nanocrystallites and amorphous SiO₂ to yield ZrSiO₄. The La³⁺ ion acted as destabilizer of t-ZrO₂, which resulted in a rapid tetragonal (t) to monoclinic (m) ZrO₂ phase transformation during sintering, while in the Ta⁵⁺ and Ce⁴⁺ ions doped sample, the phase transformation occurred gradually. All the doping ions increased the lattice parameters and the volume of t-ZrO₂ unit cell, while the effects of the doping ions on the lattice parameters of m-ZrO₂ unit cell were more complex.     

Grain boundary segregation and its influences on ionic conduction properties of scandia doped zirconia electrolytes

Solid oxide fuel cell is a promising energy conversion system which converts chemical energy into electrical energy directly. Electrolyte is the key component and determines the working temperature. In this paper,ceria and scandia co-doped zirconia electrolytes sintered from 1300 to 1550 ℃ were chosen as research objects. Scanning electron microscopy, X-ray diffraction and transmission electron microscopy were performed to characterize the ceramic samples. The effects of grain size and grain boundary element segregation on the electrical conductivity were focused. Electrochemical impedance spectroscopy was used to calculate the bulk, grain boundary and specific grain boundary conductivity. Results show that the bulk and grain boundary ionic conductivity increases with the increasing grain size.However, the specific grain boundary conductivity decreases with the increasing grain size. This is explained by the fact that Sc~(3+) is segregated at the grain boundary, which leads to higher oxygen vacancy concentration when sintered at lower temperature.     

Optimization of Gallium concentration to improve the performance of ZnO nanopowders for nanophotonic applications

This study reports the effects of gallium concentration on the properties of doped zinc oxide nanopowders. Both pure and gallium doped zinc oxide (GZO) nanoparticles were prepared via a simple and effective sol-gel method. The structural, morphological and optical properties of synthesized GZO nanopowders were investigated using different characterization methods such as X-ray diffraction, Raman, X-ray photoelectron spectroscopy, Fourier transform infrared spectrometer, UV–Vis diffuse reflectance spectroscopy, Transmission electron microscopy, Photoluminescence spectroscopy, X-ray and ion-beam-induced luminescence (IBIL) measurements. Firstly, in the presence of Ga ions in the host the purity of synthesized sample was evaluated by X-ray diffraction analysis. X-ray photoelectron spectroscopy confirmed the presence of bonding states of Zn, O, and Ga on the surface of powders. Raman spectroscopy analysis showed that the increase of Ga content upper than 1 at.% leads to an increase in the number of defects in the ZnO lattice. Field emission scanning electron microscopy (FESEM) confirmed that the uniform integration of spherical and hexagonal rod shape particles can be found in the doped samples. According to FESEM images, the particle size of prepared nanopowders increased from 101 to 200 nm by increasing in the Ga doping concentration. The photoluminescence, X-ray and ion beam induced luminescence results of the pure and doped ZnO powders revealed novel blue-green emission band from 400 up to 550 nm at room temperature. Optical and structural studies confirmed the optimized Ga concentration is 1 at.%.     

Impact of grain size,Pr~(3+) concentration and host composition on non-contact temperature sensing abilities of polyphosphate nano- and microcrystals

In this article,varied praseodymium polyphosphate hosts:M~I(Li,Na K)Pr(PO_3)_4 microcrystals and LiLa_(1-x)Pr_x(PO_3)_4(x = 0.01-1)nanocrystals were successfully synthesized by the flux method and the coprecipitation technique,respectively.The size of stoichiometric nanocrystals of LiPr(PO_3)_4 was tuned by the te mpe rature of thermal treatment in range of 35-145 nm.In order to dete rmine the most suitable material for the non-contact optical thermometric applications,the temperature sensing measurements were carried out by using luminescence intensity ratio(LIR)of emission bands corresponding to the ~3 P_1→~3H_5 and ~3P_0→~3 H_5 electronic transitions of Pr~(3+) ions into the 123-423 K temperature range.The influence of the host material composition of M~Ⅰ(Li,Na,K)Pr(PO_3)_4 microcrystals on the sensitivity of luminescent thermometers was studied.It is found that the sensitivity of lithium praseodymium polyphosphate is the highest of all micropowders under investigation.Moreover,it is found that the nanocrystals reveal much higher relative sensitivity in respect to the microcrystalline counterparts.The highest sensitivity of LIR temperature sensing is found for LiPr(PO_3)_4 nanocrystals(35 nm grain size)in the whole temperature range,reaching 0.283%/K at 164 K.The impact of the average grain size on the sensitivity of LIR based thermometers of LiPr(PO_3)_4 nanocrystals was investigated.It is found that the reduction of the grain size from 145 to 35 nm results in the enhancement of the relative sensitivity from0.156 to 0.240%/K at 223 K.Additionally it is found that the high dopant concentration possesses favorable influence on the relative sensitivity of LiLa_(1-x)Pr_x(PO_3)_4 nanocrystalline luminescent thermometers.     

Theoretical and experimental investigations of the thermoelectric properties of Al-, Bi- and Sn-doped ZnO

In this paper, the thermoelectric properties of ZnO doped with Al, Bi and Sn were investigated by combining experimental and theoretical methods. The average Seebeck coefficient of Bi doped ZnO over the measured temperature range is improved from −90 to −497 μV/K. However, segregation of Bi₂O₃ in ZnO:Bi sample, confirmed by FESEM, lead to enormous grain growth and low electrical conductivity, which makes Bi is not a good dopant to improve ZT value of ZnO. As a 4+ valence cation, Sn doping actually show an increase in carrier concentration to 10²⁰ cm⁻³, further enhancing the electrical conductivity. Unfortunately, the Seebeck coefficient of ZnO:Sn samples is even lower than pure ZnO sample, which lead to a low ZT value. As for ZnO:Al sample, with nearly no change in lattice thermal conductivity, electrical conductivity and Seebeck coefficient were both enhanced. Threefold enhancement in ZT value has been achieved in ZnO:Al sample at 760 °C compared with pure ZnO.     

Scanning spreading resistance microscopy for failure analysis of nLDMOS devices with decreased breakdown voltage

Scanning Spreading Resistance Microscopy (SSRM) is successfully applied to investigate failing nLDMOS test devices that exhibit a lowered break down voltage (BVDSS) in electrical test. Cross-sectional, two-dimensional maps of the local sample resistivity from fail and reference (pass) devices reveal significant differences of the dopant concentration in individual, specific regions. This important information enables unambiguous identification of the root cause of the device failure to be dopant related. Furthermore, from a set of hypothesis, which explains the failed electrical test, SSRM results confirm exactly one and rule out the other. These are two important steps towards root cause identification. Since a relative comparison of fail and pass SSRM scans is sufficient for this failure analysis, an extensive data calibration for the absolute dopant concentration by means of additional SSRM measurements on test samples with known dopant concentration is not required. The ability of SSRM to prove or disprove miscellaneous fail hypothesis even without data calibration makes this method a very powerful tool for analysis of dopant related failure types.     

Hydrogen evolution reaction: The role of arsenene nanosheet and dopant

The state-of-the-art density functional theory (DFT) is employed to study the catalytic activity of arsenene for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). We have included dispersion correction to get accurate adsorption energy on the individual catalytic surface (top site). Using binding energy calculation, arsenene is shown to be a potential candidate for HER. Here we investigate the stability and electronic properties of the honeycomb structure of the arsenene system using first-principles calculation to find the effect of different dopants on the fundamental band gap, which is one of the primary parameters in the photocatalytic water splitting. Further, we sieved the dopant for better HER catalytic activity by substituting one of the arsenene (As) atoms by B, N, O, Ge, Ga and Se atoms to make arsenene a better candidate for HER. Our studies depict that HER activity is increased by 82% for O-doped arsenene and OER activity by 87% for B-doped arsenene as compared to pristine arsenene.     

Diffusion and doping issues in germanium

This paper gives a review on self- and dopant diffusion in germanium (Ge) under thermal equilibrium and irradiation conditions and specifies the underlying mechanisms of diffusion and the point defects involved. Diffusion in Ge under thermal equilibrium conditions is mainly controlled by vacancies. However, Ge interstitials mediate the diffusion under concurrent annealing and irradiation. This is verified by the diffusion behavior of self-atoms, boron, phosphorus and arsenic under proton irradiation. The diffusion under irradiation is explained with the property of the Ge surface that is proposed to be an insufficient sink for Ge interstitials. As a consequence, a supersaturation of self-interstitials is established during irradiation, whereas the vacancy concentration is kept at thermal equilibrium. This explains that under irradiation the diffusion of self- and dopant atoms via self-interstitials becomes visible that is otherwise negligible under conventional annealing conditions. Our findings demonstrate ways to switch between vacancy and self-interstitial mediated diffusion and shows new strategies in the diffusion doping of Ge for technological applications.     

Atomistic modeling of dopant segregation in α-alumina ceramics: Coverage dependent energy of segregation and nominal dopant solubility

Microstructural control is a key aspect in producing ceramics with tailored properties and is often achieved by using dopants in a rather empirical fashion. Atomic scale simulations could provide much needed insight but the long-standing challenge of linking simulation results on isolated grain boundaries to those measured in real ceramics needs to be resolved. Here a novel Monte-Carlo simulation method based on a microstructural model in combination with energies obtained from atomic scale energy minimization is presented. This approach allows, for the first time, the prediction of the nominal solubility of dopants (Y, La and Mg) in a ceramic purely from theory.Results compare well with segregation/precipitation data as a function of grain size, found in the literature. The method can therefore be used in developing experimental guidelines for the effective use of dopants in ceramic production, thus accelerating the development of novel materials required for innovative applications.     

Study on silicon surface oxidation of post-implant resist cleaning

Minimum substrate loss is required for resist strip of high dose, ultra shallow junction implant for source/drain extensions. Silicon surface oxidation of downstream plasma resist strip results in silicon recess of the source/drain extension regions. This paper reports the study of silicon surface oxidation for different resist strip plasma chemistries and the effect of plasma strip process parameters such as power, pressure and temperature on silicon surface oxidation. A good agreement was found between optical ellipsometry, XPS (X-ray photoelectron spectroscopy) and TEM (transmission electron spectroscopy) for thickness measurement of very thin (<20 Å) oxide grown on silicon surface due to plasma exposure. Selectivity of crust breakthrough and resist removal over silicon oxidation was also discussed in this paper along with dopant loss.