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23 May 2011

Volume 98, Issue 21, Articles (21xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 212504 (2011); http://dx.doi.org/10.1063/1.3593371 (3 pages)

K. Okumura, T. Ishikura, M. Soda, T. Asaka, H. Nakamura, Y. Wakabayashi, and T. Kimura
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X-ray reflectance studies of interface in ion beam sputtered CoFeB/MgO bilayers

M. Raju, Sujeet Chaudhary, and D. K. Pandya

Appl. Phys. Lett. 98, 212506 (2011); http://dx.doi.org/10.1063/1.3595417 (3 pages) | Cited 4 times

Online Publication Date: 25 May 2011

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This letter reports specular and diffuse x-ray reflectance studies of the interface in the ion beam sputtered CoFeB( ∼ 5–8 nm)/MgO( ∼ 2–5 nm) bilayers. The study reveals the specific roles of oxygen ion energy, substrate temperature, and reactive gas ambient on controlling the interface width in the bilayers. Depending on oxidation-method employed for MgO growth the interface width varies between 0.51 and 0.20 nm. Energy of assist ions ( ≤ 50 eV) plays a key role compared to the growth temperature in determining the sharpness of the interface. The bottom grown CoFeB exhibited significant increase in coercivity (HC), which also depends on MgO-growth process.
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81.15.Cd Deposition by sputtering
81.15.Jj Ion and electron beam-assisted deposition; ion plating
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Direct measurement of the spin diffusion length by Andreev spectroscopy

A. Geresdi, A. Halbritter, F. Tanczikó, and G. Mihály

Appl. Phys. Lett. 98, 212507 (2011); http://dx.doi.org/10.1063/1.3593959 (3 pages) | Cited 1 time

Online Publication Date: 25 May 2011

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The application of point contact Andreev spectroscopy for the measurement of the spin diffusion length is demonstrated by studying the spin relaxation in platinum thin films grown on the top of a ferromagnetic cobalt layer. Using this local probe technique, the temperature dependence of the spin diffusion length was determined, and various sources of the spin relaxation in platinum were identified. At low temperatures the spin lifetime is found to be three orders of magnitude larger than the momentum lifetime. The applied method is selectively sensitive to spin-flip processes even in the presence of a huge background of momentum scattering.
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72.25.Mk Spin transport through interfaces
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Ds Spin waves
68.55.aj Insulators

Element-specific study of epitaxial NiO/Ag/CoO/Fe films grown on vicinal Ag(001) using photoemission electron microscopy

Y. Meng, J. Li, A. Tan, E. Jin, J. Son, J. S. Park, A. Doran, A. T. Young, A. Scholl, E. Arenholz, J. Wu, C. Hwang, H. W. Zhao, and Z. Q. Qiu

Appl. Phys. Lett. 98, 212508 (2011); http://dx.doi.org/10.1063/1.3595274 (3 pages)

Online Publication Date: 26 May 2011

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NiO/Ag/CoO/Fe single crystalline films are grown epitaxially on a vicinal Ag(001) substrate using molecular beam epitaxy and investigated by photoemission electron microscopy. We find that after zero-field cooling, the in-plane Fe magnetization switches from parallel to perpendicular direction of the atomic steps of the vicinal surface at thinner CoO thickness but remains in its original direction parallel to the steps at thicker CoO thickness. CoO and NiO domain imaging result shows that both CoO/Fe and NiO/CoO spins are perpendicularly coupled, suggesting that the Fe magnetization switching may be associated with the rotatable-frozen spin transition of the CoO film.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
79.60.Jv Interfaces; heterostructures; nanostructures
68.55.-a Thin film structure and morphology
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Enhanced ferromagnetism in grain boundary of Co-doped ZnO films: A magnetic force microscopy study

M. N. Lin, H. S. Hsu, J. Y. Lai, M. C. Guo, C. Y. Lin, G. Y. Li, F. Y. Chen, J. J. Huang, S. F. Chen, C. P. Liu, and J. C. A. Huang

Appl. Phys. Lett. 98, 212509 (2011); http://dx.doi.org/10.1063/1.3593384 (3 pages) | Cited 6 times

Online Publication Date: 26 May 2011

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Microscopic grain structures and magnetic properties of Co-doped ZnO-patterned films were studied by combinatorial atomic force microscopy and magnetic force microscopy (MFM) imaging. Whereas Co-doped ZnO was not uniformly magnetized, Co ions were homogeneously doped in the films and substitute from the Zn sites. Most Co:ZnO grains were weakly ferromagnetic (FM) and surrounded by strong FM foamlike grain boundaries networks. No MFM contrast was observed in pure ZnO films grown under similar conditions. The findings clearly demonstrate that defective grain boundaries and magnetic doping have key roles FM properties of diluted magnetic oxides.
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61.72.uj III-V and II-VI semiconductors
68.55.ag Semiconductors
61.72.Mm Grain and twin boundaries
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films

Disentangling the Mn moments on different sublattices in the half-metallic ferrimagnet Mn3−xCoxGa

P. Klaer, C. A. Jenkins, V. Alijani, J. Winterlik, B. Balke, C. Felser, and H. J. Elmers

Appl. Phys. Lett. 98, 212510 (2011); http://dx.doi.org/10.1063/1.3592802 (3 pages) | Cited 7 times

Online Publication Date: 27 May 2011

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Ferrimagnetic Mn3−xCoxGa compounds have been investigated by magnetic circular dichroism in x-ray absorption (XMCD). Compounds with x>0.5 crystallize in the CuHg2Ti structure. A tetragonal distortion of the cubic structure occurs for x ≤ 0.5. For the cubic phase, magnetometry reveals a linearly increasing magnetization of 2x Bohr magnetons per formula unit obeying the generalized Slater–Pauling rule. XMCD confirms the ferrimagnetic character with Mn atoms occupying two different sublattices with antiparallel spin orientation and different degrees of spin localization and identifies the region 0.6<x ≤ 0.8 as most promising for a high spin polarization at the Fermi level. Individual Mn moments on inequivalent sites are compared to theoretical predictions.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
75.50.Gg Ferrimagnetics
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
78.70.Dm X-ray absorption spectra
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Mapping piezoelectric nonlinearity in the Rayleigh regime using band excitation piezoresponse force microscopy

F. Griggio, S. Jesse, A. Kumar, D. M. Marincel, D. S. Tinberg, S. V. Kalinin, and S. Trolier-McKinstry

Appl. Phys. Lett. 98, 212901 (2011); http://dx.doi.org/10.1063/1.3593138 (3 pages) | Cited 5 times

Online Publication Date: 23 May 2011

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Band excitation piezoresponse force microscopy enables local investigation of the nonlinear piezoelectric behavior of ferroelectric thin films. However, the presence of additional nonlinearity associated with the dynamic resonant response of the tip-surface junction can complicate the study of a material’s nonlinearity. Here, the relative importance of the two nonlinearity sources was examined as a function of the excitation function. It was found that in order to minimize the effects of nonlinear tip-surface interactions but achieve good signal to noise level, an optimal excitation function must be used.
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77.80.Dj Domain structure; hysteresis
77.55.hn Other piezoelectric or electrostrictive films
77.84.Cg PZT ceramics and other titanates
77.84.Ek Niobates and tantalates
77.55.hj PZT
77.65.Fs Electromechanical resonance; quartz resonators

Nonvolatile low-voltage memory transistor based on SiO2 tunneling and HfO2 blocking layers with charge storage in Au nanocrystals

V. Mikhelashvili, B. Meyler, S. Yofis, Y. Shneider, A. Zeidler, M. Garbrecht, T. Cohen-Hyams, W. D. Kaplan, M. Lisiansky, Y. Roizin, J. Salzman, and G. Eisenstein

Appl. Phys. Lett. 98, 212902 (2011); http://dx.doi.org/10.1063/1.3595484 (3 pages) | Cited 8 times

Online Publication Date: 26 May 2011

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We demonstrate a low voltage nonvolatile memory field effect transistor comprising thermal SiO2 tunneling and HfO2 blocking layers as the gate dielectric stack and Au nanocrystals as charge storage nodes. The structure exhibits a memory window of ∼ 2 V at an applied sweeping voltage of ±3 V which increases to 12.6 at ±12 V. Retention tests show an extrapolated loss of 16% after ten years in the hysteresis width of the threshold voltage. Dynamic program/erase operation reveal an approximately pulse width independent memory for pulse durations of 1 μs to 10 ms; longer pulses increase the memory window while for pulses shorter than 1 μs, the memory windows vanishes. The effective oxide thickness is below 10 nm with very low gate and drain leakage currents.
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85.30.Tv Field effect devices
84.30.Sk Pulse and digital circuits

Submonolayer barium passivation study for germanium(100)/molecular beam epitaxial Al2O3

X. Sun, C. Merckling, M. Heyns, J. Dekoster, and M. Caymax

Appl. Phys. Lett. 98, 212903 (2011); http://dx.doi.org/10.1063/1.3595685 (3 pages) | Cited 4 times

Online Publication Date: 26 May 2011

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The passivation effect of a Ba submonolayer with (2×1) and (4×1) surface reconstructions are investigated for Ge(001)/Al2O3 interfaces. The interface characteristics are evaluated by capacitance-voltage and ac conductance techniques at various temperatures. It is found that the Ba passivating effect on Ge is dose dependent below one monolayer. At the same time, Ge oxides are suppressed by the presence of a Ba submonolayer. The interface is thermally stable, even at a temperature higher than the desorption temperature of Ge oxides. Forming gas annealing at this temperature yields a relatively symmetric distribution of interface traps in the Ge band gap.
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81.65.Rv Passivation
68.35.bd Metals and alloys
68.43.Nr Desorption kinetics
61.72.Cc Kinetics of defect formation and annealing
73.20.At Surface states, band structure, electron density of states
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
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Large spectral tunability of narrow geometric resonances of periodic arrays of metallic nanoparticles in a nematic liquid crystal

Jia Li, Yi Ma, Ying Gu, Iam-Choon Khoo, and Qihuang Gong

Appl. Phys. Lett. 98, 213101 (2011); http://dx.doi.org/10.1063/1.3592756 (3 pages) | Cited 9 times

Online Publication Date: 23 May 2011

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We investigated the geometric resonances of periodic arrays of gold nanoparticles embedded in a nematic liquid crystal using a semi-analytical method. By changing the liquid crystal’s refractive index seen by the scattered light propagating along the array axis, the geometric resonance can be modulated according to an analytical law. The spectral tunability is proportional to the index difference (ne−no) of the liquid crystal and the interparticle distance i.e., Δλ = (ne−no)d, which is as large as 100 nm. The large and easily controlled tunability of this compound structure makes it desirable for design of plasmon-based sensors and switches.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.15.+e Optical properties of fluid materials, supercritical fluids and liquid crystals
78.68.+m Optical properties of surfaces

Visible electroluminescence from hybrid colloidal silicon quantum dot-organic light-emitting diodes

Chang-Ching Tu, Liang Tang, Jiangdong Huang, Apostolos Voutsas, and Lih Y. Lin

Appl. Phys. Lett. 98, 213102 (2011); http://dx.doi.org/10.1063/1.3593382 (3 pages) | Cited 3 times

Online Publication Date: 23 May 2011

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We demonstrate hybrid colloidal silicon quantum dot (SiQD)-organic light-emitting diodes with electroluminescence (EL) in the visible wavelengths. The device using blue photoluminescence (PL) SiQDs as emitters shows multiple EL peaks which are attributed to carrier recombination in the core quantum confinement states, the hole-transport-layer and the surface trap states, respectively. However, the red PL SiQD device shows a single EL peak consistent with the PL peak. These findings are in agreement with the previous report that large Stokes shift were observed for oxidized blue emission SiQDs due to oxide states while red emission SiQDs show negligible PL shift after oxidation.
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85.60.Jb Light-emitting devices
78.55.-m Photoluminescence, properties and materials
73.21.La Quantum dots
81.07.Ta Quantum dots
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.60.Fi Electroluminescence

Single-molecule refrigerators: Substitution and gate effects

Yu-Shen Liu and Yu-Chang Chen

Appl. Phys. Lett. 98, 213103 (2011); http://dx.doi.org/10.1063/1.3593379 (3 pages) | Cited 3 times

Online Publication Date: 24 May 2011

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Using a first-principles approach, we investigate the quantum cooling effects in single-molecule junctions. In comparison with the unsubstituted butanethiol single-molecule junction as a refrigerator, the amino-substituted butanethiol single-molecule junction shows significant enhancement in the coefficient of performance (COP). The enhancement is attributed to the appearance of new states in the neighborhood of chemical potentials due to amino substitution. The COP of butanethiol refrigerator can be improved further by the gate voltages.
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85.65.+h Molecular electronic devices

Ultralow-voltage design of graphene PN junction quantum reflective switch transistor

Thibault Sohier and Bin Yu

Appl. Phys. Lett. 98, 213104 (2011); http://dx.doi.org/10.1063/1.3593956 (3 pages)

Online Publication Date: 24 May 2011

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We propose the concept of a graphene-based quantum reflective switch (QRS) for low-power logic application. With the unique electronic properties of graphene, a tilted PN junction is used to implement logic switch function with 103 ON/OFF ratio. Carriers are reflected on an electrostatically induced potential step with strong incidence-angle-dependency due to the widening of classically forbidden energies. Optimized design of the device for ultralow-voltage operating has been conducted. The device is constantly ON with a turning-off gate voltage around 180 mV using thin HfO2 as the gate dielectric. The results suggest a class of logic switch devices operating with micropower dissipation.
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84.32.Dd Connectors, relays, and switches
84.30.Sk Pulse and digital circuits

In(Ga)As/GaAs(001) quantum dot molecules probed by nanofocus high resolution x-ray diffraction with 100 nm resolution

M. Dubslaff, M. Hanke, M. Burghammer, S. Schöder, R. Hoppe, C. G. Schroer, Yu. I. Mazur, Zh. M. Wang, J. H. Lee, and G. J. Salamo

Appl. Phys. Lett. 98, 213105 (2011); http://dx.doi.org/10.1063/1.3593960 (3 pages) | Cited 3 times

Online Publication Date: 24 May 2011

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In(Ga)As quantum dots, which laterally self-assemble into quantum dot molecules, have been studied by scanning x-ray nanodiffraction, finite element calculations and subsequent kinematical diffraction simulations. X-ray beam sizes of 100 nm enable small scattering volumes comparable to the object size at extremely high local flux densities ( ≈ 104 photons nm−2 s−1). By that bulk contributions to the scattering are effectively reduced. Area maps of various individual quantum dot molecules have been measured, whereas the diffraction patterns therein reveal spatially resolved information about the inter quantum dot position correlation function.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
02.70.Dh Finite-element and Galerkin methods
81.16.Dn Self-assembly
78.70.Ck X-ray scattering

A simple in situ method to detect graphene formation at SiC surfaces

S. Oida, J. B. Hannon, R. M. Tromp, F. R. McFeely, and J. Yurkas

Appl. Phys. Lett. 98, 213106 (2011); http://dx.doi.org/10.1063/1.3593483 (3 pages)

Online Publication Date: 25 May 2011

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We describe a simple method to detect the formation of graphene during Si sublimation from SiC surfaces at elevated temperature. The method exploits differences in the thermionic emission current density between graphene and SiC. When graphene forms, the thermionic current from the sample increases by a factor of about 20. The increase in thermionic emission can be detected in situ using a biased plate located near the sample. The ability to detect when graphene forms during processing is useful in optimizing graphene synthesis processes.
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81.05.ue Graphene
79.40.+z Thermionic emission

Hydrogenated grain boundaries in graphene

W. H. Brito, R. Kagimura, and R. H. Miwa

Appl. Phys. Lett. 98, 213107 (2011); http://dx.doi.org/10.1063/1.3592578 (3 pages) | Cited 1 time

Online Publication Date: 26 May 2011

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We have investigated by means of ab initio calculations the structural and electronic properties of hydrogenated graphene structures with distinct grain boundary defects. Our total energy results reveal that the adsorption of a single H is more stable at defect. Further total energy calculations indicate that the adsorption of two H on two neighbor carbons, forming a basic unit of graphane, is more stable at the defect region. Therefore, we expect that these extended defects would work as a nucleation region for the formation of a narrow graphane strip embedded in graphene region.
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61.72.Mm Grain and twin boundaries
61.48.Gh Structure of graphene
73.22.Pr Electronic structure of graphene
71.15.Nc Total energy and cohesive energy calculations
68.43.Mn Adsorption kinetics
61.72.Nn Stacking faults and other planar or extended defects
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Pt(II) complex based phosphorescent organic light emitting diodes with external quantum efficiencies above 20%

Z. B. Wang, M. G. Helander, Z. M. Hudson, J. Qiu, S. Wang, and Z. H. Lu

Appl. Phys. Lett. 98, 213301 (2011); http://dx.doi.org/10.1063/1.3593495 (3 pages) | Cited 8 times

Online Publication Date: 24 May 2011

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Phosphorescent organic light emitting diodes with >20% external quantum efficiency have been demonstrated for the first time using a cyclometalated Pt(II) complex with a triarylboron group, i.e., acetylacetonato(5-dimesitylboryl-2-(phenyl)pyridyl)platinum(II), or Pt-BppyA. This unprecedented device performance is mainly attributed to the high quantum yield of the Pt(II) complex that is achieved by using a triarylboron moiety as well as to the highly optimized double emission zone device architecture.
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85.60.Jb Light-emitting devices
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Coupled interfaces for misreading avoidance and write current reduction in passive crossbar memory

M. Yang, P. Hu, J. Q. Lu, Q. B. Lv, and S. W. Li

Appl. Phys. Lett. 98, 213501 (2011); http://dx.doi.org/10.1063/1.3591975 (3 pages) | Cited 1 time

Online Publication Date: 24 May 2011

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Passive crossbar arrays of oxide-based memory elements hold the promise of high density and speed nonvolatile memory. However, realization of the expected paradigm has been hindered by a so-called misreading problem resulting from sneak paths in passive crossbar arrays. We introduce a resistive memory element consisting of two coupled interfaces in a metal/doped oxide/metal structure. The element avoids the misreading problem by the nonlinearity in current-voltage loops and significantly reduces the write current. The distinct device characteristics may also be applicable in programmable analog circuits and neuromorphic circuits.
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84.30.Sk Pulse and digital circuits

Energy gap tuning in uniaxial strained zigzag graphene nanoribbons

Fei Liu, Xiaoyan Liu, and Jinfeng Kang

Appl. Phys. Lett. 98, 213502 (2011); http://dx.doi.org/10.1063/1.3593490 (3 pages) | Cited 1 time

Online Publication Date: 24 May 2011

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The band structures of zigzag graphene nanoribbons under uniaxial strain are investigated within the mean-field Hubbard model. In addition to the intrinsic gap modification, the strain can induce two additional gaps in the conduction and valence bands when the compressive strain along the armchair direction or the tensile strain along the zigzag direction is greater than 13%. These band gap variations can be attributed to uniaxial strain which causes the breaking of the lattice symmetry and two different hopping energies. The ratio of the two different hopping energies impacts on the intrinsic and the strain induced gaps.
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73.22.Pr Electronic structure of graphene
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.63.Bd Nanocrystalline materials
73.20.At Surface states, band structure, electron density of states
72.20.Ee Mobility edges; hopping transport
71.10.Fd Lattice fermion models (Hubbard model, etc.)

Paramagnetic Pb-type interface defects in thermal (110)Si/SiO2

K. Keunen, A. Stesmans, and V. V. Afanas’ev

Appl. Phys. Lett. 98, 213503 (2011); http://dx.doi.org/10.1063/1.3590271 (3 pages)

Online Publication Date: 25 May 2011

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A multifrequency electron spin resonance (ESR) study on thermal (110)Si/SiO2 as a function of oxidation temperature Tox (200–1125 °C) reveals an unexpectedly high density of Pb-type interface centers, which variant, based on pertinent ESR properties, is typified as Pb0(110). In terms of Pb(0) center density, the (110) face is found to be the worst of all three low index Si interfaces, i.e., [Pb0(100)]<[Pb(111)]<[Pb0(110)], over the range Tox< ∼ 900 °C. Unlike previous belief, the density of prevailing Pb(0) centers over the low index Si/SiO2 interfaces is not found to scale with Si surface areal atom density nor available Si bond density; an alternative criterion is suggested.
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68.35.Ct Interface structure and roughness
76.30.-v Electron paramagnetic resonance and relaxation
81.65.Mq Oxidation

Hybrid organic/inorganic ambipolar thin film transistor chemical sensor

Soumya Dutta, Shannon D. Lewis, and Ananth Dodabalapur

Appl. Phys. Lett. 98, 213504 (2011); http://dx.doi.org/10.1063/1.3583594 (3 pages) | Cited 1 time

Online Publication Date: 25 May 2011

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An ambipolar hybrid organic-inorganic thin film transistor, consisting of pentacene and zinc oxide as semiconductors, is reported. The current-voltage characteristics in different operational modes are studied. The transistor is employed as a chemical vapor sensor, operating at room temperature. In p-channel accumulation mode, which is dominated by hole transport, a decrease of current with the introduction of analyte is observed, while in the n-channel triode mode, in which the current is predominantly contributed by electron transport, an increase in current with analyte delivery is observed. A qualitative model based on dipole interaction is proposed to explain the sensing activity.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.30.Tv Field effect devices
82.80.-d Chemical analysis and related physical methods of analysis

Role of stable and metastable Mg–H complexes in p-type GaN for cw blue laser diodes

A. Castiglia, J.-F. Carlin, and N. Grandjean

Appl. Phys. Lett. 98, 213505 (2011); http://dx.doi.org/10.1063/1.3593964 (3 pages) | Cited 2 times

Online Publication Date: 26 May 2011

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Secondary ion mass spectroscopy (SIMS) and capacitance-voltage measurements were combined to thoroughly study Mg doping in GaN layers grown by metal organic vapor phase epitaxy. First we found that the Mg steady-state incorporation regime occurs for a surface coverage of 0.3 monolayer. Additionally SIMS indicates that H incorporates proportionally with Mg until a certain [Mg] where [H] saturates. After thermal activation, [H] while being much lower still scales with [Mg]. These results suggest that H combines with Mg to form two different types of Mg–H complexes: a metastable one leading to the Mg acceptor after annealing, the other one (dominating at high [Mg]) being stable and electrically inactive. The obtained results allowed us optimizing doping conditions for blue laser diodes.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
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A carbon nanotube field emission multipixel x-ray array source for microradiotherapy application

Sigen Wang, Xiomara Calderon, Rui Peng, Eric C. Schreiber, Otto Zhou, and Sha Chang

Appl. Phys. Lett. 98, 213701 (2011); http://dx.doi.org/10.1063/1.3595268 (3 pages) | Cited 4 times

Online Publication Date: 25 May 2011

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The authors report a carbon nanotube (CNT) field emission multipixel x-ray array source for microradiotherapy for cancer research. The developed multipixel x-ray array source has 50 individually controllable pixels and it has several distinct advantages over other irradiation source including high-temporal resolution (millisecond level), the ability to electronically shape the form, and intensity distribution of the radiation fields. The x-ray array was generated by a CNT cathode array (5×10) chip with electron field emission. A dose rate on the order of >1.2 Gy/min per x-ray pixel beam is achieved at the center of the irradiated volume. The measured dose rate is in good agreement with the Monte Carlo simulation result.
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87.85.Rs Nanotechnologies-applications
07.85.-m X- and γ-ray instruments
87.55.dk Dose-volume analysis
87.85.J- Biomaterials

Real-time measurement of Brownian relaxation of magnetic nanoparticles by a mixing-frequency method

Liang Tu, Ying Jing, Yuanpeng Li, and Jian-Ping Wang

Appl. Phys. Lett. 98, 213702 (2011); http://dx.doi.org/10.1063/1.3595273 (3 pages)

Online Publication Date: 26 May 2011

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A detection scheme for real-time Brownian relaxation of magnetic nanoparticles (MNPs) is demonstrated by a mixing-frequency method in this paper. MNPs are driven into the saturation region by a low frequency sinusoidal magnetic field. A high frequency sinusoidal magnetic field is then applied to generate mixing-frequency signals that are highly specific to the magnetization of MNPs. These highly sensitive mixing-frequency signals from MNPs are picked up by a pair of balanced built-in detection coils. The phase delays of the mixing-frequency signals behind the applied field are derived, and are experimentally verified. Commercial iron oxide MNPs with the core diameter of 35 nm are used for the measurement of Brownian relaxation. The results are fitted well with Debye model. Then a real-time measurement of the binding process between protein G and its antibody is demonstrated using MNPs as labels. This study provides a volume-based magnetic sensing scheme for the detection of binding kinetics and interaction affinities between biomolecules in real time.
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87.64.-t Spectroscopic and microscopic techniques in biophysics and medical physics
87.14.E- Proteins
75.75.-c Magnetic properties of nanostructures
75.78.-n Magnetization dynamics
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Rapid confocal Raman imaging using a synchro multifoci-scan scheme for dynamic monitoring of single living cells

Lingbo Kong, Pengfei Zhang, Jing Yu, Peter Setlow, and Yong-qing Li

Appl. Phys. Lett. 98, 213703 (2011); http://dx.doi.org/10.1063/1.3595482 (3 pages) | Cited 4 times

Online Publication Date: 26 May 2011

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We developed a rapid multifoci-scan confocal Raman microscopy system for label-free molecular imaging of single living cells. A pair of galvo-mirrors were used to raster scan a single laser to generate multifoci excitations and another galvo-mirror synchronously projected Raman scattering from each foci onto a multichannel spectrograph such that multiple spectra were collected simultaneously. The image acquisition time is ∼ 40 times faster than in conventional point-scan Raman microscopy with diffraction-limited resolution retained. We demonstrated that this system can be used to monitor the germination dynamics of single bacterial spores with about 1.0 min resolution and 2.5 mW power at each focal point.
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87.64.M- Optical microscopy
87.17.-d Cell processes
87.80.-y Biophysical techniques (research methods)
87.15.M- Spectra of biomolecules

Au nanorods can be used for long-term cell imaging?

Xi Wu, Fei Yang, Tian Ming, Rongling Xiong, Peinan Wang, and Jiyao Chen

Appl. Phys. Lett. 98, 213704 (2011); http://dx.doi.org/10.1063/1.3593961 (3 pages) | Cited 2 times

Online Publication Date: 27 May 2011

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The photostability of Au nanorods in human hepatocellular carcinoma cells under two-photon excitation was investigated to evaluate their potential in cell imaging. The photoluminescence images of the intracellular Au nanorods under the two-photon excitation of an 800 nm femtosecond laser were photobleached rapidly, which is due to the melting of Au nanorods. The images lost their brightness for more than 50% after 15 micrograph scans for the nanorod incubation concentrations of 10, 20, and 40 pM. The confocal reflectance image can prevent the image photobleaching and thus is suitable for long-term cell imaging with Au nanorods.
Show PACS
87.63.L- Visual imaging
87.85.Rs Nanotechnologies-applications
78.67.Qa Nanorods
87.19.xj Cancer
87.16.-b Subcellular structure and processes
87.17.-d Cell processes
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