Extended scaling and Paschen law for micro-sized radiofrequency plasma breakdown

Lee, Min Uk,Lee, Jimo,Lee, Jae Koo,Yun, Gunsu S IOP PUBLISHING 2017 PLASMA SOURCES SCIENCE AND TECHNOLOGY Vol.26 No.3

<P>The single particle motion analysis and particle-in-cell merged with Monte Carlo collision (PIC/MCC) simulations are compared to explain substantial breakdown voltage reduction for helium microwave discharge above a critical frequency corresponding to the transition from the drift-dominant to the diffusion-dominant electron loss regime. The single particle analysis suggests that the transition frequency is proportional to the product of <img ALIGN='MIDDLE' ALT='${p}^{-{m}}$' SRC='http://ej.iop.org/images/0963-0252/26/3/034003/psstaa52a8ieqn1.gif'/> and <img ALIGN='MIDDLE' ALT='${d}^{-({m}+1)}$' SRC='http://ej.iop.org/images/0963-0252/26/3/034003/psstaa52a8ieqn2.gif'/> where <img ALIGN='MIDDLE' ALT='$p$' SRC='http://ej.iop.org/images/0963-0252/26/3/034003/psstaa52a8ieqn3.gif'/> is the neutral gas pressure, <img ALIGN='MIDDLE' ALT='$d$' SRC='http://ej.iop.org/images/0963-0252/26/3/034003/psstaa52a8ieqn4.gif'/> is the gap distance, and <I>m</I> is a numerical parameter, which is confirmed by the PIC simulation. In the low-frequency or drift-dominant regime, i.e., <img ALIGN='MIDDLE' ALT='$\gamma \mbox{-} {\rm{r}}{\rm{e}}{\rm{g}}{\rm{i}}{\rm{m}}{\rm{e}},$' SRC='http://ej.iop.org/images/0963-0252/26/3/034003/psstaa52a8ieqn5.gif'/> the secondary electron emission induced by ion drift motion is the key parameter for determining the breakdown voltage. The fluid analysis including the secondary emission coefficient, <img ALIGN='MIDDLE' ALT='$\gamma ,$' SRC='http://ej.iop.org/images/0963-0252/26/3/034003/psstaa52a8ieqn6.gif'/> induces the extended Paschen law that implies the breakdown voltage is determined by <img ALIGN='MIDDLE' ALT='$pd,$' SRC='http://ej.iop.org/images/0963-0252/26/3/034003/psstaa52a8ieqn7.gif'/> <img ALIGN='MIDDLE' ALT='$\,f/p,$' SRC='http://ej.iop.org/images/0963-0252/26/3/034003/psstaa52a8ieqn8.gif'/> <img ALIGN='MIDDLE' ALT='$\gamma ,$' SRC='http://ej.iop.org/images/0963-0252/26/3/034003/psstaa52a8ieqn9.gif'/> and<img ALIGN='MIDDLE' ALT='$\,d/R$' SRC='http://ej.iop.org/images/0963-0252/26/3/034003/psstaa52a8ieqn10.gif'/> where <I>f</I> is the frequency of the radio or microwave frequency source, and <I>R</I> is the diameter of electrode. The extended Paschen law reproduces the same scaling law for the transition frequency and is confirmed by the independent PIC and fluid simulations.</P>

Residual zonal flows in tokamaks in the presence of energetic ions

Cho, Y.W.,Hahm, T.S. IOP 2019 Nuclear fusion. Fusion nucléaire. &n.Illiga Vol.59 No.6

<P>We investigate the residual zonal flow (Rosenbluth and Hinton 1998 <I>Phys. Rev. Lett</I>. <B>80</B> 724) in the presence of fusion product <img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/0029-5515/59/6/066026/nfab0ed6ieqn001.gif'/>-particles in tokamak plasmas using the modern gyrokinetic approach in the electrostatic limit. The residual zonal flow is predicted to be enhanced considerably for ITER plasmas in the radial wave-number regime of <img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/0029-5515/59/6/066026/nfab0ed6ieqn002.gif'/>, where <img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/0029-5515/59/6/066026/nfab0ed6ieqn003.gif'/> is the Larmor radius of a thermal ion of background plasma consisting of Deuterium and Tritium. This is a consequence of the fact that larger Larmor radius (banana orbit width, <img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/0029-5515/59/6/066026/nfab0ed6ieqn004.gif'/>) of an energetic <img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/0029-5515/59/6/066026/nfab0ed6ieqn005.gif'/>-particle leads to an enhancement (a reduction) of the classical (neoclassical) polarizability at that wave-number regime compared to the case without <img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/0029-5515/59/6/066026/nfab0ed6ieqn006.gif'/>-particles. This enhancement is slightly more pronounced for the slowing-down distribution compared to the Maxwellian if <img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/0029-5515/59/6/066026/nfab0ed6ieqn007.gif'/> keV for <img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/0029-5515/59/6/066026/nfab0ed6ieqn008.gif'/> MeV. In addition, we find that the Rosenbluth–Hinton formula for the residual zonal flow level that has been derived for the Maxwellian equilibrium ion distribution remains valid in the long wavelength (<img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/0029-5515/59/6/066026/nfab0ed6ieqn009.gif'/>) and high aspect ratio limit for any well-behaved ion distribution function which is isotropic in velocity space.</P>

Yang–Baxter solution of dimers as a free-fermion six-vertex model

Pearce, Paul A,Vittorini-Orgeas, Alessandra IOP 2017 JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL Vol.50 No.43

<P>It is shown that Dimers is Yang–Baxter integrable as a six-vertex model at the free-fermion point with crossing parameter <img ALIGN='MIDDLE' ALT='$ \newcommand{\la}{\lambda} \lambda=\frac{\pi}{2}$ ' SRC='http://ej.iop.org/images/1751-8121/50/43/434001/aaa86bcieqn001.gif'/>. A one-to-many mapping of vertices onto dimer configurations allows the free-fermion solutions to be applied to the anisotropic dimer model on a square lattice where the dimers are rotated by <img ALIGN='MIDDLE' ALT='$45^{\circ}$ ' SRC='http://ej.iop.org/images/1751-8121/50/43/434001/aaa86bcieqn002.gif'/> compared to their usual orientation. This dimer model is exactly solvable in geometries of arbitrary finite size. In this paper, we establish and solve inversion identities for Dimers with periodic boundary conditions on the cylinder. In the particle representation, the local face tile operators give a representation of the fermion algebra, and the fermion particle trajectories play the role of nonlocal (logarithmic) degrees of freedom. In a suitable gauge, the dimer model is described by the Temperley–Lieb algebra with loop fugacity <img ALIGN='MIDDLE' ALT='$ \newcommand{\la}{\lambda} \beta=2\cos\lambda=0$ ' SRC='http://ej.iop.org/images/1751-8121/50/43/434001/aaa86bcieqn003.gif'/>. At the isotropic point, the exact solution allows for the explicit counting of <img ALIGN='MIDDLE' ALT='$45^{\circ}$ ' SRC='http://ej.iop.org/images/1751-8121/50/43/434001/aaa86bcieqn004.gif'/> rotated dimer configurations on a periodic <img ALIGN='MIDDLE' ALT='$M\times N$ ' SRC='http://ej.iop.org/images/1751-8121/50/43/434001/aaa86bcieqn005.gif'/> rectangular lattice. We show that the modular invariant partition function on the torus is the same as that of symplectic fermions and critical dense polymers. We also show that nontrivial Jordan cells appear for the dimer Hamiltonian on the strip with vacuum boundary conditions. We therefore argue that, in the continuum scaling limit, the dimer model gives rise to a <I>logarithmic</I> conformal field theory with central charge <img ALIGN='MIDDLE' ALT='$c=-2$ ' SRC='http://ej.iop.org/images/1751-8121/50/43/434001/aaa86bcieqn006.gif'/>, minimal conformal weight <img ALIGN='MIDDLE' ALT='$ \newcommand{\D}{\Delta} \Delta_{{\rm min}}=-1/8$ ' SRC='http://ej.iop.org/images/1751-8121/50/43/434001/aaa86bcieqn007.gif'/> and effective central charge <img ALIGN='MIDDLE' ALT='$c_{{\rm eff}}=1$ ' SRC='http://ej.iop.org/images/1751-8121/50/43/434001/aaa86bcieqn008.gif'/>.</P>

<i>δ</i>-exceedance records and random adaptive walks

Park, Su-Chan,Krug, Joachim IOP 2016 JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL Vol.49 No.31

<P>We study a modified record process where the <I>k</I>th record in a series of independent and identically distributed random variables is defined recursively through the condition <img ALIGN='MIDDLE' ALT='${Y}_{k}\gt {Y}_{k-1}-{\delta }_{k-1}$' SRC='http://ej.iop.org/images/1751-8121/49/31/315601/jpaaa2634ieqn1.gif'/> with a deterministic sequence <img ALIGN='MIDDLE' ALT='${\delta }_{k}\gt 0$' SRC='http://ej.iop.org/images/1751-8121/49/31/315601/jpaaa2634ieqn2.gif'/> called the handicap. For constant <img ALIGN='MIDDLE' ALT='${\delta }_{k}\equiv \delta $' SRC='http://ej.iop.org/images/1751-8121/49/31/315601/jpaaa2634ieqn3.gif'/> and exponentially distributed random variables it has been shown in previous work that the process displays a phase transition as a function of <I>δ</I> between a normal phase where the mean record value increases indefinitely and a stationary phase where the mean record value remains bounded and a finite fraction of all entries are records (Park <I>et al</I> 2015 <I>Phys. Rev.</I> E <A HREF='http://dx.doi.org/10.1103/PhysRevE.91.042707'> <B>91</B> 042707</A>). Here we explore the behavior for general probability distributions and decreasing and increasing sequences <img ALIGN='MIDDLE' ALT='${\delta }_{k}$' SRC='http://ej.iop.org/images/1751-8121/49/31/315601/jpaaa2634ieqn4.gif'/>, focusing in particular on the case when <img ALIGN='MIDDLE' ALT='${\delta }_{k}$' SRC='http://ej.iop.org/images/1751-8121/49/31/315601/jpaaa2634ieqn5.gif'/> matches the typical spacing between subsequent records in the underlying simple record process without handicap. We find that a continuous phase transition occurs only in the exponential case, but a novel kind of first order transition emerges when <img ALIGN='MIDDLE' ALT='${\delta }_{k}$' SRC='http://ej.iop.org/images/1751-8121/49/31/315601/jpaaa2634ieqn6.gif'/> is increasing. The problem is partly motivated by the dynamics of evolutionary adaptation in biological fitness landscapes, where <img ALIGN='MIDDLE' ALT='${\delta }_{k}$' SRC='http://ej.iop.org/images/1751-8121/49/31/315601/jpaaa2634ieqn7.gif'/> corresponds to the change of the deterministic fitness component after <I>k</I> mutational steps. The results for the record process are used to compute the mean number of steps that a population performs in such a landscape before being trapped at a local fitness maximum.</P>

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>

Extended supersymmetry in Dirac action with extra dimensions

Fujimoto, Yukihiro,Hasegawa, Kouhei,Nishiwaki, Kenji,Sakamoto, Makoto,Tatsumi, Kentaro,Ueba, Inori IOP 2018 JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL Vol.51 No.43

<P>We investigate a new realization of extended quantum-mechanical supersymmetry. We first show that an <img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/1751-8121/51/43/435201/aaadea2ieqn001.gif'/> quantum-mechanical supersymmetry is hidden in the four-dimensional (4D) spectrum of the Kaluza–Klein decomposition for the higher dimensional Dirac field, that is, Kaluza–Klein mode functions of 4D right-handed spinors and 4D left-handed ones form <img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/1751-8121/51/43/435201/aaadea2ieqn002.gif'/> supermultiplets. In addition to <img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/1751-8121/51/43/435201/aaadea2ieqn003.gif'/> supersymmetry, we discover that an <img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/1751-8121/51/43/435201/aaadea2ieqn004.gif'/>-extended supersymmetry (<img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/1751-8121/51/43/435201/aaadea2ieqn005.gif'/> for <I>d</I>  =  even (odd) extra dimensions) is further hidden in the 4D spectrum. The extended symmetry can explain additional degeneracy of the spectrum. Furthermore, we show that a superpotential can be introduced into the <img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/1751-8121/51/43/435201/aaadea2ieqn006.gif'/>-extended supercharges and clarify the condition to preserve the supersymmetry. The partial breaking of the supersymmetry is also demonstrated.</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>

Spin diffusion and non-local spin-valve effect in an exfoliated multilayer graphene with a Co electrode

Li, Lijun,Lee, Inyeal,Lim, Dongsuk,Rathi, Servin,Kang, Moonshik,Uemura, Tetsuya,Kim, Gil-Ho IOP 2016 Nanotechnology Vol.27 No.33

<P>We fabricated a non-local spin valve with a thin layer of graphite with Co transparent electrodes. The spin-valve effect and spin precession were observed at room temperature. The magnitude of the mangetoresistance increases when temperature decreases. The spin-relaxation time, <img ALIGN='MIDDLE' ALT='${\tau }_{s}$' SRC='http://ej.iop.org/images/0957-4484/27/33/335201/nanoaa2bccieqn1.gif'/>, obtained from the fitting of the Hanle curves increases with decreasing temperature with a weak dependence <img ALIGN='MIDDLE' ALT='$\sim {T}^{-0.065}$' SRC='http://ej.iop.org/images/0957-4484/27/33/335201/nanoaa2bccieqn2.gif'/> while the spin-diffusion constant <I>D</I> decreases. At room temperature, <img ALIGN='MIDDLE' ALT='${\tau }_{s}$' SRC='http://ej.iop.org/images/0957-4484/27/33/335201/nanoaa2bccieqn3.gif'/> exceeds 100 ps and the spin-diffusion length, <img ALIGN='MIDDLE' ALT='${\lambda }_{s}$' SRC='http://ej.iop.org/images/0957-4484/27/33/335201/nanoaa2bccieqn4.gif'/>, is ∼2 <I>μ</I>m. The temperature dependence of <img ALIGN='MIDDLE' ALT='${\lambda }_{s}$' SRC='http://ej.iop.org/images/0957-4484/27/33/335201/nanoaa2bccieqn5.gif'/> is not monotonic, and it has the largest value at room temperature. Our results show that multilayer graphene is a suitable material for spintronic devices.</P>

Electrohydrodynamic printing for scalable MoS₂ flake coating: application to gas sensing device

Lim, Sooman,Cho, Byungjin,Bae, Jaehyun,Kim, Ah Ra,Lee, Kyu Hwan,Kim, Se Hyun,Hahm, Myung Gwan,Nam, Jaewook IOP 2016 Nanotechnology Vol.27 No.43

<P>Scalable sub-micrometer molybdenum disulfide (<img ALIGN='MIDDLE' ALT='${\mathrm{MoS}}_{2}$' SRC='http://ej.iop.org/images/0957-4484/27/43/435501/nanoaa3ca9ieqn1.gif'/>) flake films with highly uniform coverage were created using a systematic approach. An electrohydrodynamic (EHD) printing process realized a remarkably uniform distribution of exfoliated <img ALIGN='MIDDLE' ALT='${\mathrm{MoS}}_{2}$' SRC='http://ej.iop.org/images/0957-4484/27/43/435501/nanoaa3ca9ieqn2.gif'/> flakes on desired substrates. In combination with a fast evaporating dispersion medium and an optimal choice of operating parameters, the EHD printing can produce a film rapidly on a substrate without excessive agglomeration or cluster formation, which can be problems in previously reported liquid-based continuous film methods. The printing of exfoliated <img ALIGN='MIDDLE' ALT='${\mathrm{MoS}}_{2}$' SRC='http://ej.iop.org/images/0957-4484/27/43/435501/nanoaa3ca9ieqn3.gif'/> flakes enabled the fabrication of a gas sensor with high performance and reproducibility for <img ALIGN='MIDDLE' ALT='${\mathrm{NO}}_{2}$' SRC='http://ej.iop.org/images/0957-4484/27/43/435501/nanoaa3ca9ieqn4.gif'/> and <img ALIGN='MIDDLE' ALT='${\mathrm{NH}}_{3}$' SRC='http://ej.iop.org/images/0957-4484/27/43/435501/nanoaa3ca9ieqn5.gif'/>.</P>