Effects of zinc concentration on output of zinc doped germanium detectors
Effects of zinc concentration on output of zinc doped germanium infrared detectors
Hesketh, W. D.↗
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Coexistence of positive and negative exchange bias effect in Pr-doped NdCrO 3 samples
Positive and negative exchange bias effects are observed in Nd 1-x Pr x CrO 3 (0.00 ≤ x ≤ 1.00) polycrystalline samples. The shift of hysteresis loops, either opposing or following the direction of the field cooling, depends on the concentration of praseodymium. The temperature dependence of magnetization reveals a magnetic transition at T ≈ 220 K likely ascribed to the N é el temperature of Cr 3+ magnetic moments. The non-Kramer Pr 3+ ion seems to play an important role in the magnetic properties of this compound. In the range 0.00 ≤ x ≤ 0.60, all samples presented a decrease in the magnetization below TN and a clear compensation point. Pr-rich samples (x ≥ 0.70) show a paramagnetic-like behavior down to low temperatures. We report the most impressive result is the relation between reversal magnetization and the signal of exchange bias effect which seems be tuned by the Pr-doping.
36 MATERIALS SCIENCE↗
Local structure effects of carbon-doping on the phase change material Ge 2 Sb 2 Te 5
Ge 2 Sb 2 Te 5 is used in phase change memory, a nonvolatile memory technology, due to its phase change properties. The primary advantage of phase change memory over the state-of-the-art (flash memory) is its simple and small device geometry, which allows for denser nodes and lower power consumption. In phase change memory, resistive heating induces fast switching between the high resistance amorphous and low resistance crystalline phases, corresponding to storage of low and high digital states, respectively. However, the instability of the amorphous phase of Ge 2 Sb 2 Te 5 presents issues with processing and long-term data storage; such issues can be resolved by C doping, which stabilizes the amorphous phase and raises the crystallization temperature. To better understand the local structural effects of C doping on Ge 2 Sb 2 Te 5 , in situ Ge K-edge X-ray absorption spectroscopy measurements were taken during heating of films with various C doping concentrations. Here, the range of structural transformation temperatures derived from X-ray absorption near-edge structure analysis across the C doping series proved narrower than crystallization temperatures reported in similar in situ X-ray diffraction experiments, which may reflect changes in local structure that precede long-range ordering during crystallization. In addition, rigorous extended X-ray absorption fine structure fitting across and between temperature series revealed effects of C doping on the rigidity of Ge–Te bonds at low (2 at% and 4 at%) C concentrations.
Langhout, John D.↗
Heavily neodymium doped ceria as an effective barrier layer in solid oxide electrochemical cells
10 mol% gadolinium doped ceria (GDC10) is widely used as a barrier layer between oxygen electrode and electrolyte to prevent interfacial reactions. A 50 mol% neodymium doped ceria (NDC50) barrier layer has been proposed and studied in this paper. Symmetrical cells with NDC50 and GDC10 barrier layers, Nd 2 NiO 4+δ (NNO)–Ce 0.5 Nd 0.5 O 2-δ (NDC50) electrode, and YSZ electrolyte have been systematically studied using impedance spectroscopy (EIS) at various temperatures and oxygen partial pressure (pO 2 ). The NDC50 barrier layer has significantly decreased polarization resistance across a wide temperature and pO 2 range compared to the GDC10 barrier layer. The rare earth C-type structure of the NDC50 barrier layer causes barrier free migration of oxygen ions resulting in improved ionic conductivity compared to GDC10. Finally, distribution of relaxation time (DRT) modeling has been used to obtain insights into the electrode processes.
08 HYDROGEN↗
Enhancement of Critical Current Density of MgB{sub 2} by Glutaric Acid Doping: a Simultaneous Improvement on the Intrinsic and Extrinsic Properties
In this study, we report an enhancement of critical current density of bulk MgB{sub 2} superconductors by glutaric acid (C{sub 5}H{sub 8}O{sub 4}) doping. The effects of glutaric acid doping on MgB{sub 2} lattice resulted in a record self-field J{sub c} of the order of 10{sup 6} A/cm{sup 2}. A simultaneous improvement in the connectivity, pinning force, and H{sub c2} is the major factor that determined excellent J{sub c} performance. X-ray diffraction analysis showed that samples were single-phase MgB{sub 2} with a minor trace of impurities. A dramatic change in grain morphology and homogeneity in grain distribution was found in the SEM images of doped samples. We observed that homogeneity in grain distribution played a crucial role in the connectivity and the upper critical field (H{sub c2}) of the doped samples. We were able to introduce a new dopant through a two-step mixing approach which is suitable to overcome the degradation of low field and self-field J{sub c} reported for carbon-doped MgB{sub 2} superconductor samples.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Study of radiation effects in lithium-doped Si using infrared spectroscopy /1 to 50 microns/ and photoconductivity /1 to 10 microns/
Infrared spectroscopic and photoconductivity determinations of electron irradiation effects in Li-doped floating zone and crucible grown silicon
Corelli, J. C.↗
Experimental and Computational Investigation of Lanthanide Ion Doping on BiVO 4 Photoanodes for Solar Water Splitting
N-type bismuth vanadate (BiVO4) has emerged as one of the most promising photoanodes for use in water-splitting photoelectrochemical cells in recent years. However, its photoelectrochemical properties may be further enhanced by optimizing its band gap and its charge-transport properties. Doping at the V5+ and O2- sites of BiVO4 has proven to be an effective strategy to alter the oxide electronic band structure and/or charge-transport properties, but the effect of doping at the Bi3+ site is not nearly as well understood. In this study, we performed a combined experimental and theoretical study of BiVO4 doped with lanthanide (Ln) elements (La, Ce, Sm, and Yb) at the Bi3+ site, and we elucidated the effect of doping on the electronic band structure and charge-transport properties of BiVO4. Furthermore, we performed density functional theory calculations to investigate the combined effect of the Ln doping and oxygen vacancies, which are intrinsic defects in BiVO4. Our results showed that for some cases, the simultaneous consideration of Ln doping and O vacancy leads to changes that cannot be obtained by the sum of the changes caused by Ln doping alone and O vacancy alone, which was critical for understanding the experimental results. The various ways that the Ln dopants modified the electronic band structure and charge-transport properties of BiVO4 demonstrated in this study can provide useful guidelines for the tuning of the composition of oxide-based photoelectrodes.
Govindaraju, Gokul V.↗
Effects of Nd, Al Doping on the Structure and Properties of BiFeO{sub 3}
The BiFeO{sub 3}(BFO) and Bi{sub 0.95}Nd{sub 0.05}Fe{sub 1-x}Al{sub x}O{sub 3} (x = 0, 0.03, 0.05, 0.075, 0.1) powders were prepared at 200 °C for 24 h by hydrothermal method. The effects of Al doping content on the structure, morphology, magnetic, and photocatalytic properties were studied. X-ray diffraction (XRD) and Fourier transform infrared spectrometer (FTIR) demonstrated the compounds are distorted rhombohedral perovskite structure without any other heterogeneity and structural transition. Field emission scanning electron microscope (FESEM) reflected surface of compounds is a dense, agglomerated sphere. As the concentration of Al{sup 3+} increases, a small part of the spherical crystallites eventually becomes cauliflower shape. Energy-dispersive X-ray (EDS) showed the Bi{sub 0.95}Nd{sub 0.05}Fe{sub 0.95}Al{sub 0.05}O{sub 3} sample mainly consists of five elements (Bi, Fe, O, Nd, Al) and atom radio matched well with the formula. Vibrating sample magnetometer (VSM) integrated in a physical property measurement system (PPMS-9) illustrated introducing Nd{sup 3+} ions into BFO will enhance its magnetism at room temperature. However, with the increase of non-magnetic ion Al{sup 3+} concentration in Bi{sub 0.95}Nd{sub 0.05}Fe{sub 1-x}Al{sub x}O{sub 3} (x = 0, 0.03, 0.05, 0.075, 0.1), the network structure of Fe-O-Fe was destroyed, which led to the decrease of its net magnetization, so that the hysteresis loop shows paramagnetism. The photocatalytic performance of BFO increased initially and decreased afterwards as Al{sup 3+} concentration increased, and the best catalytic performance was achieved at x = 0.05.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
First-Principles Investigation of Magnetic Properties and Faraday Rotation of Co Doping CdTe
In this paper, we aimed to study the effect of doping of the compound CdTe with the cobalt impurity (Co), as well as the vacancy defects in Cd sites. On one hand, this leads to the investigation of the magnetic properties and the Faraday rotation effect for the studied alloy, doped with different concentrations of cobalt (0.01, 0.05, 0.1, 0.15, 0.2, 0.25). On the other hand, we have created 0.01 of vacancy defects in Cd sites. Then, we raised the vacancy defect concentration to 0.05, keeping the same concentrations of cobalt. As a result, we have investigated that there is a magnetism appearing with the cobalt doping, while the vacancy defects in Cd sites affect the stability of the magnetic states. In general, it improves the ferromagnetic state that will be well explained in the discussion. Our calculations were performed using the KKR-CPA method within the spin-polarized density functional theory (DFT) with the local density approximation (LDA). The curves of the density of states (DOS) illustrate the results of this study which has been discussed, analyzed, and explained below. In addition, the energy of each case was calculated and given in the tables below for both the DLM (half of the cobalt spins are up while the other half are down) and the ferromagnetic state in order to confirm which one of them is stable.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Effects of N-Doping on Silicon Carbide
Silicon carbide (SiC) is a widely preferred material within many industries due to its favorable properties, most notably its low electrical resistivity at high temperatures, excellent thermal conductivity, and sturdy mechanical properties. Doping, particularly n-type doping, is shown to extremely reduce electrical resistivity, but due to structural changes within the lattice caused by interaction with thermal neutrons, it is possible that other attributes of SiC may also be affected. In addition to review of past literature and data, four-point probe testing, scanning electron microscopy, nanoindentation, strength tests, differential scanning calorimetry and laser flash analysis were used to investigate the effects of n-doping 3C ß-phase SiC. According to temperature dependent measurements, electric resistivity and thermal conductivity both declined as dopant levels increases. Dopant levels are shown to have a significant effect on the mechanical performance of SiC, with the highest dopant levels (4 x 1018 cm-3) providing a 40% decrease in elastic modulus from 420 GPa to 258 GPa and a 30% decrease in hardness from 40 GPa to 27.7 GPa. These values are still above average and doped SiC may prove valuable for nuclear applications.
36 MATERIALS SCIENCE↗
Precursor of pair-density wave in doping Kitaev spin liquid on the honeycomb lattice
Abstract We study the effects of doping the Kitaev model on the honeycomb lattice where the spins interact via the bond-directional interaction J K , which is known to have a quantum spin liquid as its exact ground state. The effect of hole doping is studied within the t - J K model on a three-leg cylinder using density-matrix renormalization group. Upon light doping, we find that the ground state of the system has a dominant quasi-long-range charge-density-wave correlations but short-range single-particle correlations. In the pairing channel, the even-parity superconducting correlation is dominant with d -wave-like symmetry, which oscillates in sign as a function of separation with a period equal to that of the spin-density wave and two times the charge-density wave. Although these correlations fall rapidly (possibly exponentially) at long distances, this is never-the-less the example where a pair-density wave is the leading instability in the pairing channel on the honeycomb lattice.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Effects of interaction strength, doping, and frustration on the antiferromagnetic phase of the two-dimensional Hubbard model
Recent quantum-gas microscopy of ultracold atoms and scanning tunneling microscopy of the cuprates reveal new detailed information about doped Mott antiferromagnets, which can be compared with calculations. Using cellular dynamical mean-field theory, we map out the antiferromagnetic (AF) phase of the two-dimensional Hubbard model as a function of interaction strength U, hole doping δ, and temperature T . The Néel phase boundary is nonmonotonic as a function of U and δ. Frustration induced by second-neighbor hopping reduces Néel order more effectively at small U. The doped AF is stabilized at large U by kinetic energy and at small U by potential energy. The transition between the AF insulator and the doped metallic AF is continuous. At large U, we find in-gap states similar to those observed in scanning tunneling microscopy. Finally, we predict that, contrary to the Hubbard bands, these states are only slightly spin polarized.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Construction of N-doped TiO2/MoS2 heterojunction with synergistic effect for enhanced visible photodegradation activity
Highlights: • An N-doped TiO{sub 2}/MoS{sub 2} heterojunction is successfully synthesized by a hydrothermal method. • N-doped TiO{sub 2}/MoS{sub 2} heterojunction photocatalyst exhibits enhanced visible photodegradation activity. • The synergistic effect is between N-doping and coupling with MoS{sub 2}. • Superoxide radicals (O{sub 2}{sup −}) and photogenerated holes (h{sup +}) are chiefly responsible for the degradation process. - Abstract: An N-doped TiO{sub 2}/MoS{sub 2} heterojunction photocatalyst constructed by two-dimension MoS{sub 2} nanosheets and N-doped TiO{sub 2} nanoparticles was successfully synthesized by a hydrothermal method. The synthesized N-TiO{sub 2}/MoS{sub 2} composites were characterized by XRD, XPS, TEM, UV–vis DRS and PL, and its visible photocatalytic activity was evaluated by degradation of methylene blue. The results showed that N-doped TiO{sub 2}/MoS{sub 2} heterojunction photocatalyst achieved more enhanced photocatalytic activity compared with pure TiO{sub 2}, MoS{sub 2} and N-doped TiO{sub 2} for degradation of MB. Trapping tests with different scavengers indicated that not hydroxyl radicals (OH) but superoxide radicals (O{sub 2}{sup −}) and photogenerated holes (h{sup +}) were highly responsible for the degradation process. The reusable experiments showed that the prepared N-doped TiO{sub 2}/MoS{sub 2} heterojunction photocatalyst was stable during the photodegradation of MB and will have practical applications for environmental remediation.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Synergistic effects in Fe nanoparticles doped with ppm levels of (Pd + Ni). A new catalyst for sustainable nitro group reductions
A remarkable synergistic effect has been uncovered between ppm levels of Pd and Ni embedded within iron nanoparticles that leads to mild and selective catalytic reductions of nitro-containing aromatics and heteroaromatics in water at room temperature. NaBH4 serves as the source of inexpensive hydride. Broad substrate scope is documented, along with several other features including: low catalyst loading, low residual metal in the products, and recycling of the catalyst and reaction medium, highlight the green nature of this new technology.
Pang, Haobo↗
Potential Resolution to the Doping Puzzle in Iron Pyrite: Carrier Type Determination by Hall Effect and Thermopower.
Pyrite FeS2 has outstanding potential as an earth-abundant, low-cost, nontoxic photovoltaic, but underperforms dramatically in solar cells. While the full reasons for this are not clear, one certain factor is the inability to understand and control doping in FeS2. This is exemplified by the widely accepted but unexplained observation that unintentionally doped FeS2 single crystals are predominantly n type, whereas thin films are p type. Here we provide a potential resolution to this "doping puzzle," arrived at via Hall effect, thermopower, and resistivity measurements on a large set of FeS2 single crystals and films that span five orders of magnitude in mobility. The results reveal three main findings. First, in addition to crystals, the highest mobility thin films in this study are shown to be definitively n type, from both Hall effect and thermopower. Second, as mobility decreases an apparent crossover to p type occurs, first in thermopower, then in Hall measurements. This can be understood, however, in terms of the crossover from diffusive to hopping transport that is clearly reflected in resistivity. Third, universal behavior is found for both crystals and films, suggesting a common n dopant, possibly sulfur vacancies. We thus argue that n-type doping is facile in FeS2 films, that apparent p-type behavior in low mobility samples can be an artifact of hopping, and that the prevailing notion of predominantly p-type films must be revised. These conclusions have deep implications, both for interpretation of prior work on FeS2 solar cells and for the design of future studies.
Zhang, Xin↗