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15 Oct 2012

Volume 101, Issue 16, Articles (16xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 161105 (2012); http://dx.doi.org/10.1063/1.4744947 (4 pages)

Nan Niu, Tsung-Li Liu, Igor Aharonovich, Kasey J. Russell, Alexander Woolf, Thomas C. Sadler, Haitham A. R. El-Ella, Menno J. Kappers, Rachel A. Oliver, and Evelyn L. Hu
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Dual-band asymmetry chiral metamaterial based on planar spiral structure

Xiaoliang Ma, Cheng Huang, Mingbo Pu, Yanqin Wang, Zeyu Zhao, Changtao Wang, and Xiangang Luo

Appl. Phys. Lett. 101, 161901 (2012); http://dx.doi.org/10.1063/1.4756901 (4 pages) | Cited 1 time

Online Publication Date: 15 October 2012

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A dual-band asymmetric chiral metamaterial is constructed by using two pairs of planar spiral structures with a certain twisted angle. Numerical simulation results show that when a y-polarized wave is incident on the chiral metamaterial the left circularly polarized wave is emitted at 12.25 GHz and 15.57 GHz, while right circularly polarized wave is excited at 13.9 GHz and 16.86 GHz. The measured transmissions are higher than −2.4 dB, and the absolute values of the transmission differences between the right and left circularly polarized waves exceed 15 dB at the four frequencies, which agree well with the simulated results.
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42.70.-a Optical materials

Electronic structure and optical band gap of CoFe2O4 thin films

A. V. Ravindra, P. Padhan, and W. Prellier

Appl. Phys. Lett. 101, 161902 (2012); http://dx.doi.org/10.1063/1.4759001 (4 pages) | Cited 1 time

Online Publication Date: 16 October 2012

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Electronic structure and optical band gap of CoFe2O4 thin films grown on (001) oriented LaAlO3 have been investigated. Surprisingly, these films show additional Raman modes at room temperature as compared to a bulk spinel structure. The splitting of Raman modes is explained by considering the short-range ordering of Co and Fe cations in octahedral site of spinel structure. In addition, an expansion of band-gap is observed with the reduction of film thickness, which is explained by the quantum size effect and misfit dislocation. Such results provide interesting insights for the growth of spinel phases.
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71.20.Ps Other inorganic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators

Influences of lattice vibration and electron transition on thermal emissivity of Nd3+ doped LaMgAl11O19 hexaaluminates for metallic thermal protection system

Hong-Zhi Liu, Zhan-Guo Liu, Jia-Hu Ouyang, and Ya-Ming Wang

Appl. Phys. Lett. 101, 161903 (2012); http://dx.doi.org/10.1063/1.4759006 (4 pages) | Cited 1 time

Online Publication Date: 16 October 2012

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Normal spectral emissivity of La1−xNdxMgAl11O19 (x = 0.05, 0.10, 0.15, 0.25) ceramics has a maximum value at the Nd3+ content of x = 0.10 in the wavelength range of 3–6 μm. The difference in emissivity at short wavelengths of 3–6 μm is tightly linked to the absorption transitions from 4I9/2 to 4F3/2, 4I15/2, and 4I13/2 and the intensities of radiation transitions from 4F3/2 to 4I11/2 and 4I13/2 of Nd3+ in LaMgAl11O19 ceramics. However, in the wavelength range of 6–14 μm, the emissivity is quite similar for all the samples, which can be ascribed to the stretching vibration of Al-O tetrahedron and Al-O octahedron.
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61.72.up Other materials
63.20.-e Phonons in crystal lattices
78.55.Hx Other solid inorganic materials
78.30.Hv Other nonmetallic inorganics

Atomic-scaled investigation of structure-dependent luminescence in Sialon:Ce phosphors

Fangfang Xu (许钫钫), Erwan Sourty, Xionghui Zeng (曾雄辉), Linlin Zhang (张琳琳), Lin Gan (甘霖), Xinliang Mou (牟新亮), Wei Shi (史 为), Yingchun Zhu (祝迎春), Fuqiang Huang (黄富 强), and Jingtai Zhao (赵景泰)

Appl. Phys. Lett. 101, 161904 (2012); http://dx.doi.org/10.1063/1.4759110 (5 pages) | Cited 1 time

Online Publication Date: 17 October 2012

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Here, we present direct correlation of luminescence properties to the atomic structures of Sialon:Ce phosphors. Luminescence of β-Sialon is revealed attributed to the intergrowth of a unit layer of α-Sialon:Ce-type structure on β-grain surfaces. The dense doping at fault sites either on the surface of or inside the α-Sialon crystallites might lead to intensified emission of light depending on the fault morphology. It seems that concentration quenching would not appear for Sialon:Ce phosphors unless high density of dislocations is created upon dense doping. Finally, structural evolution has been discussed aiming to greatly enhance the luminescence of Sialon phosphors.
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78.55.Hx Other solid inorganic materials
61.72.up Other materials
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Improvement of optical performance of ZnO/GaN p-n junctions with an InGaN interlayer

T. Wang, H. Wu, Z. Wang, C. Chen, and C. Liu

Appl. Phys. Lett. 101, 161905 (2012); http://dx.doi.org/10.1063/1.4760271 (4 pages) | Cited 1 time

Online Publication Date: 17 October 2012

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The ZnO films were deposited on GaN and with an interlayer of InGaN by atomic layer deposition. The orientation of the ZnO films was 〈0001〉 on InGaN, whereas it was 〈70math4〉 (perpendicular to (10math0) plane) on GaN. The lattice mismatch between ZnO and InGaN was about 0.3%, which is lower than that between ZnO and GaN (1.6%). With a lower lattice mismatch, the intensity of the near-band-edge emission increased about 120% and the full width at half maximum decreased 7.3 nm. Furthermore, ZnO/InGaN/GaN heterostructured light emitting diodes were fabricated. The electroluminescence spectra under forward bias showed a blue emission accompanied by a broad peak centered at 600 nm.
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85.60.Jb Light-emitting devices
68.55.ag Semiconductors
78.66.-w Optical properties of specific thin films
78.60.Fi Electroluminescence
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Voltage-assisted ion reduction in liquid crystal-silica nanoparticle dispersions

Shu-Wei Liao, Chia-Ting Hsieh, Chih-Chin Kuo, and Chi-Yen Huang

Appl. Phys. Lett. 101, 161906 (2012); http://dx.doi.org/10.1063/1.4760277 (4 pages) | Cited 1 time

Online Publication Date: 18 October 2012

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We demonstrate an effective method of reducing mobile ions in a silica nanoparticle (SN)-doped liquid crystal (LC) cell by alternating-current high-voltage pulse treatment (ACHVPT). In this method, the director distortion in LCs near the substrate creates a lifting force that moves the SNs toward the substrate. The moving SNs trap mobile ions in the cell bulk. After ACHVPT, the SNs and mobile ions are adsorbed onto the substrates, thereby significantly decreasing cell ion density. The ion density of the SN-doped LC cell after ACHVPT treatment is 1.5% of that of a pristine LC cell.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
82.70.-y Disperse systems; complex fluids

Branched carbon nanotube reinforcements for improved strength of polyethylene nanocomposites

Ling Liu, Lin Zhang, and Jim Lua

Appl. Phys. Lett. 101, 161907 (2012); http://dx.doi.org/10.1063/1.4761936 (5 pages) | Cited 1 time

Online Publication Date: 19 October 2012

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A bio-inspired design of polyethylene nanocomposites is presented in this letter using branched carbon nanotubes (BCNTs) as reinforcements. Using coarse-grained molecular dynamics simulations, we demonstrate that the pullout strength of the proposed BCNT nanofibers can be an order of magnitude higher than that of CNT reinforcements. The drastically improved interfacial shearing strength is found to be strongly dependent on the geometry of nanofibers, the molecular weight of matrix polymers, and the pullout velocity. By analyzing the time-evolving molecular configurations of BCNT nanofibers and surrounding polymer chains, the underlying strengthening mechanisms are discussed and strategies for further improvement are suggested.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
FREE

Scalable control of terahertz radiation from ultrashort laser-gas interaction

Min Chen, Xiao-Hui Yuan, and Zheng-Ming Sheng

Appl. Phys. Lett. 101, 161908 (2012); http://dx.doi.org/10.1063/1.4761941 (4 pages) | Cited 1 time

Online Publication Date: 19 October 2012

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Terahertz radiation from ultrashort laser pulse interaction with a neutral gas target via ionization induced transverse currents is studied analytically and by particle-in-cell simulations. It is shown that the radiation amplitude and temporal shape depend not only on the driving laser parameters but also on the target parameters both for the forward and backward emissions. For given laser parameters, simply by tuning the gas length and the concentration of the effective ionized electrons, the terahertz temporal shape can be changed in scale with the gas length while keeping the radiation amplitude unchanged. This provides an easy way for terahertz radiation control for applications.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.-v Laser optical systems: design and operation
78.70.Gq Microwave and radio-frequency interactions
42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems

Internal friction and dynamic modulus in Ru-50Nb ultra-high temperature shape memory alloys

L. Dirand, M. L. Nó, K. Chastaing, A. Denquin, and J. San Juan

Appl. Phys. Lett. 101, 161909 (2012); http://dx.doi.org/10.1063/1.4761475 (4 pages) | Cited 1 time

Online Publication Date: 19 October 2012

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The martensitic transformations in ultra-high temperature Ru-50Nb shape memory alloys have been studied by internal friction and dynamic modulus measurements. Two successive transformations from the high temperature cubic β phase to a tetragonal β′ martensite and then to another monoclinic β″ martensite have been found. Both transformations exhibit a sharp internal friction peak and a clear softening of the dynamic modulus, being a signature of the thermo-elastic martensitic transformations. In addition, a pseudo relaxation peak strongly dependent on time has been found and analyzed, concluding that it is linked to a pinning effect of martensite interfaces by point defects.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity
64.70.kd Metals and alloys
81.30.Kf Martensitic transformations
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