256 research outputs found
Possible atomic structures for the sub-bandgap absorption of chalcogen hyperdoped silicon
Single-crystal silicon wafers were hyperdoped respectively by sulfur,
selenium, and tellurium element using ion implantation and nanosecond laser
melting. The hyperdoping of such chalcogen elements endowed the treated silicon
with a strong and wide sub-bandgap light absorptance. When these hyperdoped
silicons were thermally annealed even at low temperatures (such as 200~400 oC),
however, this extra sub-bandgap absorptance began to attenuate. In order to
explain this attenuation of absorptance, alternatively, we consider it
corresponding to a chemical decomposition reaction from optically absorbing
structure to non-absorbing structure, and obtain a very good fitting to the
attenuated absorptances by using Arrhenius equation. Further, we extract the
reaction activation energies from the fittings and they are 0.343(+/- 0.031) eV
for S-, 0.426(+/-0.042) eV for Se-, and 0.317(+/-0.033) eV for Te-hyperdoped
silicon, respectively. We discuss these activation energies in term of the bond
energies of chalcogen-Si metastable bonds, and finally suggest that several
high-energy interstitial sites instead of the substitutional site, are very
possibly the atomic structures that are responsible for the sub-bandgap
absorptance of chalcogen hyperdoped silicon.Comment: 18 pages, 3 figures, 1 tabl
Efficiency and Ecological Risks of Reducing Soil pH during Thlaspi caerulescens Phytoextraction of Cadmium and Zinc
The major aims of this research were to determine whether reducing soil pH can enhance phytoextraction and to examine the ecological risks of reducing pH. Two soils differing in Cd and Zn concentrations were used and adjusted to 5 or 6 different pH levels ranging from 7.27 to 4.74 and seeded with a hyperaccumulator of Cd and Zn, Thlaspi caerulescens. Plants were harvested after six months, the pH were restored to above 6.5, incubated for 6 months. Soils were analyzed for biological activities and microbial population changes after both pH adjustments.
Reducing pH significantly (p=0.05) enhanced plant metal uptake. For the high metal soil, plant grew best at the lowest pH treatment (4.74) and the highest metal concentration was at the second lowest pH treatment (5.27). For the low metal soil, due to low pH induced Al and Mn toxicity, plant growth and metal uptake were highest at the intermediate pH level (6.07). Metal sequential extraction results further verified that reducing pH redistributed Cd and Zn among five fractions. The most soluble metal form (F1) was greatly increased. In addition, T. caerulescens was able to differentially utilize Cd in all 5 fractions while it could only access Zn from the F1 and F2 pools.
Reducing soil pH significantly reduced a number of soil biological activities and shifted the community structure at different levels. Generally, soil biological activities were more sensitive than soil microbial populations to pH change. Good indicators of soil pH status were acid phosphatase activity, alkaline phosphatase activity, acid to alkaline phosphatase activity ratio, arylsulphatase, nitrification potential, soil microbial biomass C and N, and population of rhizobium. After raising pH to > 6.5, negatively impacted soil parameters were partially restored to original levels. Soil biological activities showed lower recovery than soil microbial populations. The threshold pHs were 6.1 and 5.3 for low and high metal soils, respectively. Above this value, most soil biological activities and all microbial populations returned to background levels within a short period
Electric-field Control of Magnetism with Emergent Topological Hall Effect in SrRuO3 through Proton Evolution
Ionic substitution forms an essential pathway to manipulate the carrier
density and crystalline symmetry of materials via ion-lattice-electron
coupling, leading to a rich spectrum of electronic states in strongly
correlated systems. Using the ferromagnetic metal SrRuO3 as a model system, we
demonstrate an efficient and reversible control of both carrier density and
crystalline symmetry through the ionic liquid gating induced protonation. The
insertion of protons electron-dopes SrRuO3, leading to an exotic ferromagnetic
to paramagnetic phase transition along with the increase of proton
concentration. Intriguingly, we observe an emergent topological Hall effect at
the boundary of the phase transition as the consequence of the
newly-established Dzyaloshinskii-Moriya interaction owing to the breaking of
inversion symmetry in protonated SrRuO3 with the proton compositional
film-depth gradient. We envision that electric-field controlled protonation
opens a novel strategy to design material functionalities
Preparation of SnS2 colloidal quantum dots and their application in organic/inorganic hybrid solar cells
Dispersive SnS2 colloidal quantum dots have been synthesized via hot-injection method. Hybrid photovoltaic devices based on blends of a conjugated polymer poly[2-methoxy-5-(3",7"dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) as electron donor and crystalline SnS2 quantum dots as electron acceptor have been studied. Photoluminescence measurement has been performed to study the surfactant effect on the excitons splitting process. The photocurrent of solar cells with the hybrid depends greatly on the ligands exchange as well as the device heat treatment. AFM characterization has demonstrated morphology changes happening upon surfactant replacement and annealing, which can explain the performance variation of hybrid solar cells
Plasmonic Nanoparticles with Quantitatively Controlled Bioconjugation for Photoacoustic Imaging of Live Cancer Cells
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135410/1/advs216_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135410/2/advs216-sup-0001-S1.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135410/3/advs216.pd
Observation of Quantum Griffiths Singularity and Ferromagnetism at Superconducting LaAlO3/SrTiO3(110) Interface
Diverse phenomena emerge at the interface between band insulators LaAlO3 and
SrTiO3, such as superconductivity and ferromagnetism, showing an opportunity
for potential applications as well as bringing fundamental research interests.
Particularly, the two-dimensional electron gas formed at LaAlO3/SrTiO3
interface offers an appealing platform for quantum phase transition from a
superconductor to a weakly localized metal. Here we report the
superconductor-metal transition in superconducting two-dimensional electron gas
formed at LaAlO3/SrTiO3(110) interface driven by a perpendicular magnetic
field. Interestingly, when approaching the quantum critical point, the dynamic
critical exponent is not a constant but a diverging value, which is a direct
evidence of quantum Griffiths singularity raised from quenched disorder at
ultralow temperatures. Furthermore, the hysteretic property of
magnetoresistance was firstly observed at LaAlO3/SrTiO3(110) interfaces, which
suggests potential coexistence of superconductivity and ferromagnetism
Efficient organic solar cells enabled by simple non-fused electron donors with low synthetic complexity
Abstract Fusedâring electron donors boost the efficiency of organic solar cells (OSCs), but they suffer from high cost and low yield for their large synthetic complexity (SC > 30%). Herein, the authors develop a series of simple nonâfusedâring electron donors, PF1 and PF2, which alternately consist of furanâ3âcarboxylate and 2,2â˛âbithiophene. Note that PF1 and PF2 present very small SC of 9.7% for their inexpensive raw materials, facile synthesis, and high synthetic yield. Compared to their allâthiopheneâbackbone counterpart PTâE, two new polymers feature larger conjugated plane, resulting in higher hole mobility for them, especially a value up to â10 â4 cm 2 V â1 ¡s for PF2 with longer alkyl side chain. Meanwhile, PF1 and PF2 exhibit larger dielectric constant and deeper electronic energy level versus PTâE. Benefiting from the better physicochemical properties, the efficiencies of PF1â and PF2âbased devices are improved by â16.7% and â71.3% relative to that PTâEâbased devices, respectively. Furthermore, the optimized PF2âbased devices with introducing PC 71 BM as the third component deliver a higher efficiency of 12.40%. The work not only indicates that furanâ3âcarboxylate is a simple yet efficient building block for constructing nonâfusedâring polymers but also provides a promising electron donor PF2 for the lowâcost production of OSCs.A simple structure nonâfusedâring electron donor PF2 alternately consisting of furanâ3âcarboxylate and 2,2â˛âbithiophene presents very small synthetic complexity of 9.7% as well as low material cost of â19.0 $ g â1 . More importantly, PF2 delivers a high efficiency of 12.4% coupled with strong operational stability. imag
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