Exclusive rare <i>B_s</i> → (<i>K</i>, η, η′)ℓ⁺ℓ⁻ decays in the light-front quark model

IOP Pub 2010 Journal of Physics. G, Nuclear and Particle Physic Vol.37 No.8

<P>Using the light-front quark model, we calculate the transition form factors, decay rates and longitudinal lepton polarization asymmetries for the exclusive rare <img SRC='http://ej.iop.org/images/0954-3899/37/8/085005/jpg346669ieqn1.gif' ALIGN='MIDDLE' ALT='B_s\rightarrow (K,\eta ^{(\prime )})(\ell ^+\ell ^-,\nu _{\ell }\bar{\nu _{\ell }}'/>) (ℓ = <I>e</I>, μ, τ) decays within the standard model, taking into account the η − η′ mixing angle. For the mixing angle &thetas; = −20° (−10°) in the octet-singlet basis, we obtain <img SRC='http://ej.iop.org/images/0954-3899/37/8/085005/jpg346669ieqn2.gif' ALIGN='MIDDLE' ALT='{\rm BR}\big(B_s\rightarrow \eta \sum \nu _{\ell }\bar{\nu }_{\ell }\big)=1.1(1.7)\times 10^{-6}'/>, BR(<I>B<SUB>s</SUB></I> → ημ<SUP>+</SUP>μ<SUP>−</SUP>) = 1.5(2.4) × 10<SUP>−7</SUP>, BR(<I>B<SUB>s</SUB></I> → ητ<SUP>+</SUP>τ<SUP>−</SUP>) = 3.8(5.8) × 10<SUP>−8</SUP>, <img SRC='http://ej.iop.org/images/0954-3899/37/8/085005/jpg346669ieqn3.gif' ALIGN='MIDDLE' ALT='{\rm BR}(B_s\rightarrow \eta ^{\prime }\sum \nu _{\ell }\bar{\nu }_{\ell })=1.8(1.3)\times 10^{-6}'/>, BR(<I>B<SUB>s</SUB></I> → η′μ<SUP>+</SUP>μ<SUP>−</SUP>) = 2.4(1.8) × 10<SUP>−7</SUP> and BR(<I>B<SUB>s</SUB></I> → η′τ<SUP>+</SUP>τ<SUP>−</SUP>) = 3.4(2.6) × 10<SUP>−8</SUP>, respectively. The branching ratios for the <img SRC='http://ej.iop.org/images/0954-3899/37/8/085005/jpg346669ieqn4.gif' ALIGN='MIDDLE' ALT='B_s\rightarrow K(\nu _{\ell }\bar{\nu _{\ell }},\ell ^+\ell ^-)'/> decays are at least an order of magnitude smaller than those for the <img SRC='http://ej.iop.org/images/0954-3899/37/8/085005/jpg346669ieqn5.gif' ALIGN='MIDDLE' ALT='B_s\rightarrow \eta ^{(\prime )}(\nu _{\ell }\bar{\nu _{\ell }},\ell ^+\ell ^-)'/> decays. The averaged values of the lepton polarization asymmetries for <I>B<SUB>s</SUB></I> → (<I>K</I>, η<SUP>(′)</SUP>)ℓ<SUP>+</SUP>ℓ<SUP>−</SUP> are obtained as <img SRC='http://ej.iop.org/images/0954-3899/37/8/085005/jpg346669ieqn6.gif' ALIGN='MIDDLE' ALT='\big\langle P^K_L\big\rangle _\mu =\big\langle P^\eta _L\big\rangle _\mu =\big\langle P^{\eta ^{\prime }}_L\big\rangle _\mu =-0.98'/>, ⟨<I>P<SUP>K</SUP><SUB>L</SUB></I>⟩<SUB>τ</SUB> = −0.24, ⟨<I>P</I><SUP>η</SUP><SUB><I>L</I></SUB>⟩<SUB>τ</SUB> = −0.20 and <img SRC='http://ej.iop.org/images/0954-3899/37/8/085005/jpg346669ieqn7.gif' ALIGN='MIDDLE' ALT='\big\langle P^{\eta ^{\prime }}_L\big\rangle _\tau =-0.14'/>, respectively.</P>

Emission properties of hydrothermal Yb^{3 +}, Er^{3 +} and Yb^{3 +}, Tm^{3 +}-codoped Lu₂O₃ nanorods: upconversion, cathodoluminescence and assessment of waveguide behavior

Barrera, Elixir William,Pujol, Marí,a Cinta,Dí,az, Francesc,Choi, Soo Bong,Rotermund, Fabian,Park, Kyung Ho,Jeong, Mun Seok,Cascales, Concepció,n IOP Pub 2011 Nanotechnology Vol.22 No.7

<P>Yb<SUP>3 + </SUP> and Ln<SUP>3 + </SUP> (Ln<SUP>3 + </SUP> = Er<SUP>3 + </SUP> or Tm<SUP>3 + </SUP>) codoped Lu<SUB>2</SUB>O<SUB>3</SUB> nanorods with cubic <img SRC='http://ej.iop.org/images/0957-4484/22/7/075205/nano368878ieqn1.gif' ALIGN='MIDDLE' ALT='Ia\bar 3 '/> symmetry have been prepared by low temperature hydrothermal procedures, and their luminescence properties and waveguide behavior analyzed by means of scanning near-field optical microscopy (SNOM). Room temperature upconversion (UC) under excitation at 980 nm and cathodoluminescence (CL) spectra were studied as a function of the Yb<SUP> + </SUP> concentration in the prepared nanorods. UC spectra revealed the strong development of <img SRC='http://ej.iop.org/images/0957-4484/22/7/075205/nano368878ieqn2.gif' ALIGN='MIDDLE' ALT='\mathrm {Er}^{3+}\,^{4}\mathrm {F}_{9/2}\to {}^4\mathrm {I}_{15/2} '/> (red) and <img SRC='http://ej.iop.org/images/0957-4484/22/7/075205/nano368878ieqn3.gif' ALIGN='MIDDLE' ALT='\mathrm {Tm}^{3+}\,{}^{1}\mathrm {G}_{4} \to {}^{3}\mathrm {H}_{6} '/> (blue) bands, which became the pre-eminent and even unique emissions for corresponding nanorods with the higher Yb<SUP>3 + </SUP> concentration. Favored by the presence of large phonons in current nanorods, UC mechanisms that privilege the population of <SUP>4</SUP>F<SUB>9/2</SUB> and <SUP>1</SUP>G<SUB>4</SUB> emitting levels through phonon-assisted energy transfer and non-radiative relaxations account for these observed UC luminescence features. CL spectra show much more moderate development of the intensity ratio between the <img SRC='http://ej.iop.org/images/0957-4484/22/7/075205/nano368878ieqn2.gif' ALIGN='MIDDLE' ALT='\mathrm {Er}^{3+}\, {}^{4}\mathrm {F}_{9/2} \to {}^4\mathrm {I}_{15/2} '/> (red) and <SUP>2</SUP>H<SUB>11/2</SUB>, <img SRC='http://ej.iop.org/images/0957-4484/22/7/075205/nano368878ieqn4.gif' ALIGN='MIDDLE' ALT='^{4}\mathrm {S}_{3/2}\to {}^{4}\mathrm {I}_{15/2} '/> (green) emissions with the increase in the Yb<SUP>3 + </SUP> content, while for Yb<SUP>3 + </SUP>, Tm<SUP>3 + </SUP>-codoped Lu<SUB>2</SUB>O<SUB>3</SUB> nanorods the dominant CL emission is <img SRC='http://ej.iop.org/images/0957-4484/22/7/075205/nano368878ieqn5.gif' ALIGN='MIDDLE' ALT='\mathrm {Tm}^{3+}\,{}^{1}\mathrm {D}_{2}\to {}^{3}\mathrm {F}_{4} '/> (deep-blue). Uniform light emission along Yb<SUP>3 + </SUP>, Er<SUP>3 + </SUP>-codoped Lu<SUB>2</SUB>O<SUB>3</SUB> rods has been observed by using SNOM photoluminescence images; however, the rods seem to be too thin for propagation of light. </P>

Photoemission, soft x-ray absorption, and magnetic circular dichroism spectroscopy study of Fe_1−<i>x</i>Cu_<i>x</i>Cr₂S₄ (0.1≤<i>x</i>≤0.5) spinel sulfides

Han, S W,Kang, J-S,Lee, S S,Kim, G,Kim, S J,Kim, C S,Kim, J-Y,Shin, H J,Kim, K H,Jeong, J I,Park, B-G,Park, J-H,Min, B I IOP Pub 2006 Journal of Physics, Condensed Matter Vol.18 No.31

<P>The electronic and magnetic structures of Fe<SUB>1−<I>x</I></SUB>Cu<SUB><I>x</I></SUB>Cr<SUB>2</SUB>S<SUB>4</SUB> (0.1≤<I>x</I>≤0.5) spinel sulfides have been investigated systematically by performing photoemission spectroscopy (PES), soft x-ray absorption spectroscopy (XAS), and soft x-ray magnetic circular dichroism (XMCD) measurements using synchrotron radiation. Cr and Cu ions are found to be nearly trivalent (Cr<SUP>3+</SUP>) and monovalent (Cu<SUP>+</SUP>), respectively, and their valence states do not change with <I>x</I>. The Fe 2p XAS spectra of Fe<SUB>1−<I>x</I></SUB>Cu<SUB><I>x</I></SUB>Cr<SUB>2</SUB>S<SUB>4</SUB> are very similar to that of Fe metal, indicating that the Fe 3d electrons are strongly hybridized to other valence electrons. The Fe and Cr 2p XMCD spectra show that the magnetic moments of Cr ions and Fe ions are aligned antiparallel to each other and that both the Cr and Fe magnetic moments increase with increasing <I>x</I>. The valence-band PES study reveals that the Cr<SUP>3+</SUP> (<img SRC='http://ej.iop.org/images/0953-8984/18/31/033/cm224080ieqn1.gif' ALIGN='MIDDLE' ALT='\mathrm {t_{2g}^3} \downarrow '/>) 3d states are located at ∼1.5?eV below <I>E</I><SUB>F</SUB>. The occupied Fe 3d states consist of the broad <img SRC='http://ej.iop.org/images/0953-8984/18/31/033/cm224080ieqn2.gif' ALIGN='MIDDLE' ALT='\mathrm {t_{2g}^3} \uparrow '/> states, the <img SRC='http://ej.iop.org/images/0953-8984/18/31/033/cm224080ieqn3.gif' ALIGN='MIDDLE' ALT='\mathrm {e_g^2} \uparrow '/> states at ∼4?eV below <I>E</I><SUB>F</SUB>, and the <img SRC='http://ej.iop.org/images/0953-8984/18/31/033/cm224080ieqn4.gif' ALIGN='MIDDLE' ALT='\mathrm {e_g} \downarrow '/> states very close to <I>E</I><SUB>F</SUB>. The filled Cu 3d<SUP>10</SUP> states lie at ∼2.5?eV below <I>E</I><SUB>F</SUB>. This study suggests that the hybridized Fe <img SRC='http://ej.iop.org/images/0953-8984/18/31/033/cm224080ieqn4.gif' ALIGN='MIDDLE' ALT='\mathrm {e_g}\downarrow '/> and S 3p states near <I>E</I><SUB>F</SUB> play an important role in determining the transport properties of Fe<SUB>1−<I>x</I></SUB>Cu<SUB><I>x</I></SUB>Cr<SUB>2</SUB>S<SUB>4</SUB> for <I>x</I>≤0.5. </P>

Synergistic effects of SPR and FRET on the photoluminescence of ZnO nanorod heterostructures

Chang, Jee-Young,Kim, Tae Geun,Sung, Yun-Mo IOP Pub 2011 Nanotechnology Vol.22 No.42

<P>Solution-grown ZnO nanorods (NRs) were successfully conjugated with CdSe/ZnS quantum dots (QDs) and Ag nanoparticles (NPs) to suppress intrinsic defect emission and to enhance band-edge emission at the same time. First, high-density and high-crystallinity ZnO NRs of diameter 80–90 nm and length 1.2–1.5 µm were grown on glass substrates using a low-temperature seed-assisted solution method. The as-synthesized ZnO NRs showed sharp photoluminescence (PL) band-edge emission centered at ∼ 377 nm together with broad defect emission in the range of ∼ 450–800 nm. The ZnO NRs were decorated with CdSe/ZnS QDs and Ag NPs, respectively, by sequential drop-coating. The PL of CdSe/ZnS <img SRC='http://ej.iop.org/images/0957-4484/22/42/425708/nano398556ieqn1.gif' ALIGN='MIDDLE' ALT='\mathrm {QD{\parallel } ZnO} '/> NR conjugates showed that ZnO band-edge emission decreased by 73.8% due to fluorescence resonance energy transfer (FRET) and charge separation between ZnO and CdSe/ZnS by type II energy band structure formation. On the other hand, Ag <img SRC='http://ej.iop.org/images/0957-4484/22/42/425708/nano398556ieqn2.gif' ALIGN='MIDDLE' ALT='\mathrm {NP{\parallel } CdSe\mbox {/}ZnS}~\mathrm {QD{\parallel } ZnO} '/> NR conjugates showed increased band-edge emission (by 25.8%) and suppressed defect emission compared to bare ZnO NRs. A possible energy transfer mechanism to explain the improved PL properties of ZnO NRs was proposed based upon the combined effects of FRET and surface plasmon resonance (SPR). </P>

Patterned carbon nanotube field emitter using the regular array of an anodic aluminium oxide template

Yu, Wan Jun,Cho, You Suk,Choi, Gyu Seok,Kim, Dojin IOP Pub 2005 Nanotechnology Vol.16 No.5

<P>The carbon nanotube (CNT) is a promising nanomaterial in emitter device applications. However, the self-assembling nature of CNT growth causes fluctuations in length and weak adhesion to substrates even in the morphology of aligned CNTs, whereas CNTs synthesized on an anodic aluminium oxide (AAO) template show uniformity in diameter, length and spatial distribution due to the inherent regularity of the fabricated nanotemplate. These features are essential in developing emitter devices that are improved in emission uniformity and current density. Here we report a new field emitter structure made with CNTs deposited on AAO. The fabrication of the structure and its preliminary emission performance of the patterned emitters were investigated. A high current density of <img SRC='http://ej.iop.org/images/0957-4484/16/5/029/nano186645ieqn1.gif' ALIGN='MIDDLE' ALT='{\sim }4~\mathrm {mA~cm^{-2}} '/> was measured from the relatively poor quality of the CNTs due to the high density of the edges for emission in the patterned structure. Comparison with the performance from plain geometry was made. A very high field enhancement factor of <img SRC='http://ej.iop.org/images/0957-4484/16/5/029/nano186645ieqn2.gif' ALIGN='MIDDLE' ALT='{\sim }2500 '/> was also obtained.</P>

Thermal properties of various Kondo ground states in the heavy-fermion system CeNi_1−<i>x</i>Co_<i>x</i>Ge₂

Hong, J B,Park, Tuson,Kwon, Y S IOP Pub 2005 Journal of Physics, Condensed Matter Vol.17 No.15

<P>We report results of the specific heat of the heavy-fermion compounds of the alloying series CeNi<SUB>1−<I>x</I></SUB>Co<SUB><I>x</I></SUB>Ge<SUB>2</SUB>. With increasing <I>x</I>, hybridization between the localized 4f and conduction band electrons is enhanced. The magnetic order observed for the <I>x</I> = 0 composition is completely suppressed at a critical concentration of <I>x</I><SUB>c</SUB> = 0.3, yielding Fermi-liquid behaviour for <I>x</I>>0.3. We observe significant deviations from the Fermi-liquid behaviour at <I>x</I><SUB>c</SUB> = 0.3. Anomalies found in the specific heat are well explained by the Kondo model for a degenerate impurity spin <I>J</I> = 1/2,3/2, and 5/2 in the Coqblin–Schrieffer limit for the Co concentration ranges of <img SRC='http://ej.iop.org/images/0953-8984/17/15/019/cm192839ieqn1.gif' ALIGN='MIDDLE' ALT='x\leq 0.6 '/>, <img SRC='http://ej.iop.org/images/0953-8984/17/15/019/cm192839ieqn2.gif' ALIGN='MIDDLE' ALT='0.7\leq x\leq 0.8 '/>, and <img SRC='http://ej.iop.org/images/0953-8984/17/15/019/cm192839ieqn3.gif' ALIGN='MIDDLE' ALT='x\geq 0.9 '/>, respectively.</P>

The luminescence characterization and structure of Eu^{2 +} doped LiMgPO₄

Zhang, Suyin,Huang, Yanlin,Shi, Liang,Seo, Hyo Jin IOP Pub 2010 Journal of Physics, Condensed Matter Vol.22 No.23

<P>An Eu<SUP>2 + </SUP>-doped LiMgPO<SUB>4</SUB> phosphor was prepared by a high temperature solid-state reaction. The formation was confirmed by x-ray powder diffraction measurements to be a single LiMgPO<SUB>4</SUB> phase. The photoluminescence excitation and emission spectra were investigated. The luminescence shows a broad emission from the <img SRC='http://ej.iop.org/images/0953-8984/22/23/235402/cm344840ieqn1.gif' ALIGN='MIDDLE' ALT='\mathrm {4f^{6}5d} \to \mathrm {4f^{7}(^{8}S_{7/2})} '/> transition at room temperature. At low temperature the zero-phonon line for transitions to the 4f<SUP>7</SUP> (<SUP>8</SUP>S<SUB>7/2</SUB>) level of the 4f<SUP>6</SUP>(<SUP>7</SUP>F<SUB><I>j</I></SUB>)5d<SUP>1</SUP> excited state is observed at 360 nm and it is found that the emission line of the <img SRC='http://ej.iop.org/images/0953-8984/22/23/235402/cm344840ieqn2.gif' ALIGN='MIDDLE' ALT='\mathrm {4f^{7}(^{6}P_{7/2})} \to \mathrm {4f^{7}(^{8}S_{7/2})} '/> transition overlaps the zero-phonon line at nearly the same position of 360 nm. The influences of temperature on the luminescence spectra and decay times were investigated. The doping mechanism of Eu<SUP>2 + </SUP> ions in LiMgPO<SUB>4</SUB> was discussed. The Eu<SUP>2 + </SUP> ions were suggested to occupy the Li<SUP> + </SUP> sites in LiMgPO<SUB>4</SUB> to induce the small crystal field splitting and weak nephelauxetic effect. </P>

TiO₂ nanotubes with a ZnO thin energy barrier for improved current efficiency of CdSe quantum-dot-sensitized solar cells

Lee, Wonjoo,Kang, Soon Hyung,Kim, Jae-Yup,Kolekar, Govind B,Sung, Yung-Eun,Han, Sung-Hwan IOP Pub 2009 Nanotechnology Vol.20 No.33

<P>This paper reports the formation of a thin ZnO energy barrier between a CdSe quantum dot (Q dots) sensitizer and TiO<SUB>2</SUB> nanotubes (TONTs) for improved current efficiency of Q dot-sensitized solar cells. The formation of a ZnO barrier between TONTs and the Q dot sensitizer increased the short-circuit current under illumination and also reduced the dark current in a dark environment. The power conversion efficiency of Q dot-sensitized TONT solar cells increased by 25.9% in the presence of the ZnO thin layer due to improved charge-collecting efficiency and reduced recombination. </P>

Nanogap biosensors for electrical and label-free detection of biomolecular interactions

Kyu Kim, Sang,Cho, Hyunmin,Park, Hye-Jung,Kwon, Dohyoung,Min Lee, Jeong,Hyun Chung, Bong IOP Pub 2009 Nanotechnology Vol.20 No.45

<P>We demonstrate nanogap biosensors for electrical and label-free detection of biomolecular interactions. Parallel fabrication of nanometer distance gaps has been achieved using a silicon anisotropic wet etching technique on a silicon-on-insulator (SOI) wafer with a finely controllable silicon device layer. Since silicon anisotropic wet etching resulted in a trapezoid-shaped structure whose end became narrower during the etching, the nanogap structure was simply fabricated on the device layer of a SOI wafer. The nanogap devices were individually addressable and a gap size of less than 60 nm was obtained. We demonstrate that the nanogap biosensors can electrically detect biomolecular interactions such as biotin/streptavidin and antigen/antibody pairs. The nanogap devices show a current increase when the proteins are bound to the surface. The current increases proportionally depending upon the concentrations of the molecules in the range of 100  fg ml<SUP>−1</SUP>–100  ng ml<SUP>−1</SUP> at 1 V bias. It is expected that the nanogap developed here could be a highly sensitive biosensor platform for label-free detection of biomolecular interactions.</P>

The influence of surface chemical dynamics on electrical and optical properties of ZnO nanowire field effect transistors

Sohn, Jung Inn,Hong, Woong-Ki,Lee, Mi Jung,Lee, Takhee,Sirringhaus, Henning,Kang, Dae Joon,Welland, Mark E IOP Pub 2009 Nanotechnology Vol.20 No.50

<P>We demonstrate the effect of surface chemical dynamics on carrier transport and recombination processes of electron–hole pairs in ZnO nanowire field effect transistors. We have found that the electrical conductance decreases and the threshold voltages shift in a positive gate voltage direction, as electrical characteristics are measured repeatedly. We associate this with the enhancement of oxygen adsorption by capturing electrons from the induced current during the probing. This results in an overall depletion of electrons and thus causes the positive shift in threshold voltages associated with the origin and width of characteristic hysteresis loops. In addition, the surface environment dependence of the photo-response related to a recombination process in ZnO nanowires is discussed in terms of the surface chemical reaction and band bending. </P>