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7 Jul 2008

Volume 93, Issue 1, Articles (01xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 011108 (2008); http://dx.doi.org/10.1063/1.2958910 (3 pages)

E. Mujagić, S. Schartner, L. K. Hoffmann, W. Schrenk, M. P. Semtsiv, M. Wienold, W. T. Masselink, and G. Strasser
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Twenty times lower ignition threshold for laser driven fusion using collective effects and the inhibition factor

H. Hora, B. Malekynia, M. Ghoranneviss, G. H. Miley, and X. He

Appl. Phys. Lett. 93, 011101 (2008); http://dx.doi.org/10.1063/1.2955839 (3 pages) | Cited 23 times

Online Publication Date: 7 July 2008

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Hydrodynamic analysis for ignition of inertial fusion by Chu [Phys. Fluids 15, 413 (1972)] arrived at extremely high thresholds of a minimum energy flux density E* at 4×108 J/cm2 which could be provided, e.g., by spark ignition. In view of alternative schemes of fast ignition, a re-evaluation of the early analysis including later discovered collective stopping power and the inhibition factor results in a 20 times lowering of the threshold for E*.
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28.52.Cx Fueling, heating and ignition
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.57.-z Laser inertial confinement
28.52.Av Theory, design, and computerized simulation

The underlying terahertz vibrational spectrum of explosives solids

Joseph S. Melinger, N. Laman, and D. Grischkowsky

Appl. Phys. Lett. 93, 011102 (2008); http://dx.doi.org/10.1063/1.2949068 (3 pages) | Cited 21 times

Online Publication Date: 8 July 2008

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Using waveguide terahertz time-domain spectroscopy, we demonstrate the measurement of the underlying terahertz vibrational spectrum of the explosive solids hexahydro-1,3,5-trinitro-1,3,5-triazine, and 2,4,6-trinitrotoluene. Each explosive is cast as a polycrystalline thin film with planar ordering on the inner surface of metal parallel plate waveguide. For measurements near 10 K, each explosive reveals a complex spectrum of approximately 20 vibrational modes between 0.5 and 3.5 THz. The explosive films are of sufficient quality to produce vibrational linewidths as much as an order of magnitude sharper compared to conventional terahertz measurements of corresponding pellet samples of explosives.
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82.33.Vx Reactions in flames, combustion, and explosions
78.70.Gq Microwave and radio-frequency interactions
78.66.Qn Polymers; organic compounds

Continuous wave operation of diode lasers at 3.36 μm at 12 °C

L. Shterengas, G. Belenky, T. Hosoda, G. Kipshidze, and S. Suchalkin

Appl. Phys. Lett. 93, 011103 (2008); http://dx.doi.org/10.1063/1.2953210 (3 pages) | Cited 35 times

Online Publication Date: 8 July 2008

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GaSb-based type-I quantum-well diode lasers emitting at 3.36 μm at 12 °C with 15 mW of continuous wave output power are reported. Devices with two or four InGaAsSb compressively strained quantum wells and AlInGaAsSb quinternary barriers were fabricated and characterized. It was shown that increase in the quantum-well number led to improved laser differential gain and reduced threshold current.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Ultrasmall square-lattice zero-cell photonic crystal laser

Ho-Seok Ee, Kwang-Yong Jeong, Min-Kyo Seo, Yong-Hee Lee, and Hong-Gyu Park

Appl. Phys. Lett. 93, 011104 (2008); http://dx.doi.org/10.1063/1.2956670 (3 pages) | Cited 10 times

Online Publication Date: 8 July 2008

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We report optically pumped room-temperature lasing in a square-lattice photonic crystal cavity consisting of two shifted lattice points and heterogeneous lattices with different air hole sizes. Three-dimensional finite-difference time-domain simulation shows that this cavity has an ultrasmall mode volume of 0.017 μm3 ∼ 1.7 (λ/2nslab)3. Photoluminescence spectroscopy exhibits pulsed lasing action at 1511 nm with a low lasing threshold of ∼ 130 μW. The measured Q factor is ∼ 2400 that is well agreed with the theoretical Q of 4200. In addition, the computational analysis based on the actual fabricated structural parameters unambiguously presents the successful demonstration of this ultrasmall lasing mode.
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42.55.Tv Photonic crystal lasers and coherent effects
42.60.Fc Modulation, tuning, and mode locking

Determination of internal parameters in blue InGaN laser diodes by the measurement of cavity-length dependent characteristics

H. Y. Ryu, K. H. Ha, J. K. Son, S. N. Lee, H. S. Paek, T. Jang, Y. J. Sung, K. S. Kim, H. K. Kim, Y. Park, and O. H. Nam

Appl. Phys. Lett. 93, 011105 (2008); http://dx.doi.org/10.1063/1.2956413 (3 pages) | Cited 14 times

Online Publication Date: 9 July 2008

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The characteristics of blue InGaN single-quantum-well laser diodes (LDs) emitting at 445 nm are investigated with varying cavity length of the LDs from 650 to 1450 μm. From the measurement of cavity-length dependent slope efficiency, internal efficiency and internal loss of LD structures have been determined to be 0.89 and 10.5 cm−1, respectively, indicating good quality of the LD structure. In addition, gain parameters have been extracted from the relation of threshold current density and cavity length. It is found that the internal parameters of blue LDs are comparable to those of violet LDs emitting at 405 nm.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.By Design of specific laser systems

Integrated optofluidic Mach–Zehnder interferometer based on liquid core waveguides

Romeo Bernini, Genni Testa, Luigi Zeni, and Pasqualina M. Sarro

Appl. Phys. Lett. 93, 011106 (2008); http://dx.doi.org/10.1063/1.2957031 (3 pages) | Cited 12 times

Online Publication Date: 9 July 2008

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We report the fabrication and the characterization of an integrated optofluidic Mach–Zehnder interferometer based on liquid core waveguides. The light is confined inside a low refractive index liquid core by antiresonant reflecting optical waveguide. Several asymmetric Mach–Zehnder interferometers have been realized with standard silicon technology. An optical characterization of the devices has been carried out by measuring the spectrum of optical transmitted intensity from two different Mach–Zehnder configurations. The results show that interferometers with a good visibility can be achieved in good agreement with the theoretical results.
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07.60.Ly Interferometers
42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.79.Wc Optical coatings
42.82.Cr Fabrication techniques; lithography, pattern transfer
47.85.Np Fluidics

Optical study of lateral carrier transfer in (In,Ga)As/GaAs quantum-dot chains

B. R. Wang, B. Q. Sun, Y. Ji, X. M. Dou, Z. Y. Xu, Zh. M. Wang, and G. J. Salamo

Appl. Phys. Lett. 93, 011107 (2008); http://dx.doi.org/10.1063/1.2957466 (3 pages) | Cited 7 times

Online Publication Date: 9 July 2008

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We have studied the lateral carrier transfer in a specially designed quantum dot chain structure by means of time-resolved photoluminescence (PL) and polarization PL. The PL decay time increases with temperature, following the T1/2 law for the typical one-dimensional quantum system. The decay time depends strongly on the emission energy: it decreases as the photon energy increases. Moreover, a strong polarization anisotropy is observed. These results are attributed to the efficient lateral transfer of carriers along the chain direction.
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78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
78.47.jd Time resolved luminescence
78.55.Cr III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Grating-coupled surface emitting quantum cascade ring lasers

E. Mujagić, S. Schartner, L. K. Hoffmann, W. Schrenk, M. P. Semtsiv, M. Wienold, W. T. Masselink, and G. Strasser

Appl. Phys. Lett. 93, 011108 (2008); http://dx.doi.org/10.1063/1.2958910 (3 pages) | Cited 7 times

Online Publication Date: 10 July 2008

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We report on the fabrication and operation of quantum cascade ring lasers providing grating-coupled surface emission. The devices exhibit tunable far fields, ranging from spot- to ring-shaped symmetric beam cross sections, depending on the grating period. This—along with threshold current densities as low as for comparable Fabry–Pérot lasers—demonstrates the compatibility of reduced beam divergence and two-dimensional integrability, resulting in an attractive light source for applications in midinfrared spectroscopy and imaging.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.86.+b Optical workshop techniques
42.79.Dj Gratings
42.72.-g Optical sources and standards

Top grating index-coupled distributed feedback quantum cascade lasers

M. Carras, M. Garcia, X. Marcadet, O. Parillaud, A. De Rossi, and S. Bansropun

Appl. Phys. Lett. 93, 011109 (2008); http://dx.doi.org/10.1063/1.2950086 (3 pages) | Cited 17 times

Online Publication Date: 10 July 2008

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We report on the modeling and design of top grating distributed feedback (DFB) quantum cascade lasers (QCLs). A low loss, index-coupled, DFB design that is very robust against technological spreads is proposed. Strong DFB coupling conditions are obtained while maintaining a high laser output power. Following this design, DFB QCL lasers with InP cladding layers and InGaAs/AlInAs active regions have been fabricated. Room temperature monomode QCLs with 30 dB side mode suppression ratios are demonstrated over a 4–8 μm wavelength range.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Intense upconversion and infrared emissions in Er3+–Yb3+ codoped Lu2SiO5 and (Lu0.5Gd0.5)2SiO5 crystals

Lin Han, Feng Song, Shu-Qi Chen, Chang-Guang Zou, Xiao-Chen Yu, Jian-Guo Tian, Jun Xu, Xiao-dong Xu, and Guang-jun Zhao

Appl. Phys. Lett. 93, 011110 (2008); http://dx.doi.org/10.1063/1.2954010 (3 pages) | Cited 15 times

Online Publication Date: 10 July 2008

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High optical quality Lu2SiO5 (LSO) and (Lu0.5Gd0.5)2SiO5 (LGSO) laser crystals codoped with Er3+ and Yb3+ have been fabricated by the Czochralski method. Intense upconversion (UC) and infrared emission (1543 nm) are observed under excitation of 975 nm. The luminescence processes are explained and the emission efficiencies are quantitatively obtained by measuring the UC efficiency and calculating the emission cross section. The temperature-dependent optical properties of the crystals are also investigated. Our study indicates that Er3+–Yb3+:LSO and Er3+–Yb3+:LGSO crystals are promising gain media for developing the solid-state 1.5 μm optical amplifiers and tunable UC lasers.
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78.55.Hx Other solid inorganic materials
42.70.Hj Laser materials
81.10.Fq Growth from melts; zone melting and refining

Pulsed ultrasound-modulated optical tomography using spectral-hole burning as a narrowband spectral filter

Youzhi Li, Huiliang Zhang, Chulhong Kim, Kelvin H. Wagner, Philip Hemmer, and Lihong V. Wang

Appl. Phys. Lett. 93, 011111 (2008); http://dx.doi.org/10.1063/1.2952489 (3 pages) | Cited 25 times

Online Publication Date: 11 July 2008

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We applied a submegahertz nonlinear optical filter afforded by a cryogenically cooled spectral-hole burning crystal to ultrasound-modulated optical tomography. Our experimental results show that this technique, having the largest etendue among all available ultrasound-modulated optical tomography techniques and being immune to speckle decorrelation, offers potential for imaging in vivo and forming high resolution optical tomograms in real time. It opens an opportunity for the development of a clinically applicable high resolution optical imaging modality.
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42.30.Wb Image reconstruction; tomography
42.79.Ci Filters, zone plates, and polarizers
07.60.Ly Interferometers
42.30.Ms Speckle and moiré patterns
87.64.-t Spectroscopic and microscopic techniques in biophysics and medical physics

Morphologies and nonlinear scaling of laser damage on glass surfaces by tightly focused femtosecond pulses

Jeffrey F. Herbstman, Alan J. Hunt, and Steven M. Yalisove

Appl. Phys. Lett. 93, 011112 (2008); http://dx.doi.org/10.1063/1.2952832 (3 pages) | Cited 2 times

Online Publication Date: 11 July 2008

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We examine the relationship between pulse energy and the morphology of damage by a femtosecond pulsed laser, tightly focused onto the back surface of glass. For fluences up to three times that of threshold, an unexpected discontinuity in the scaling of damage size is caused by ejection of rings of material surrounding central damage that appear above a sharp threshold fluence. A mechanism for the production of these structures via thermal expansion and shockwave generation is proposed.
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61.43.Fs Glasses
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
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Ultrasmall radio frequency driven microhollow cathode discharge

C. M. O. Mahony, T. Gans, W. G. Graham, P. D. Maguire, and Z. Lj. Petrović

Appl. Phys. Lett. 93, 011501 (2008); http://dx.doi.org/10.1063/1.2956412 (3 pages) | Cited 13 times

Online Publication Date: 8 July 2008

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We have operated 25-100 μm diameter radio frequency microhollow cathode discharges stably, for many hours, in neon and in argon. Electrical and spectroscopic measurements were used to explore three possible electron heating modes and obtain detail regarding the electron energy distribution. Analysis points to the possibility of pendular electron heating at low voltages.
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52.80.Hc Glow; corona
82.45.Fk Electrodes
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

O2(a1Δg) production at atmospheric pressure by microdischarge

J. Santos Sousa, G. Bauville, B. Lacour, V. Puech, M. Touzeau, and L. C. Pitchford

Appl. Phys. Lett. 93, 011502 (2008); http://dx.doi.org/10.1063/1.2957032 (3 pages) | Cited 14 times

Online Publication Date: 8 July 2008

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We report experimental results showing that singlet oxygen O2(a1Δg) can be efficiently produced at atmospheric pressure in a three-electrode microcathode sustained discharge (MCSD) configuration. This configuration consists of a microhollow cathode discharge (MHCD) acting as a plasma cathode to sustain a stable glow discharge between the MHCD and a third planar electrode placed at a distance of 8 mm. Experiments were performed in He/O2/NO mixtures. O2(a1Δg) number densities higher than 1016 cm−3 were measured in the MCSD afterglow at total flow rates up to 30 ln/mn, resulting in O2(a1Δg) fluxes above 10 millimole per hour (mmol/h).
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52.80.Hc Glow; corona
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

A simple cold Ar plasma jet generated with a floating electrode at atmospheric pressure

Qiu-Yue Nie, Chun-Sheng Ren, De-Zhen Wang, and Jia-Liang Zhang

Appl. Phys. Lett. 93, 011503 (2008); http://dx.doi.org/10.1063/1.2956411 (3 pages) | Cited 28 times

Online Publication Date: 9 July 2008

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An experimental study is presented of a cold atmospheric Ar plasma jet with distinct advantages of low-working voltage and high plasma stability. To effectively improve the performance of the jet, a pair of pin electrodes with one floating in the air is applied. Variation in the applied voltage and/or the Ar gas flow causes the transition of the jet plasma from ignition, through stable plume to an unstable stage. The characteristics of the jet discharge are also studied by means of the electrical and spectroscopic diagnosis.
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52.75.-d Plasma devices
52.50.-b Plasma production and heating
52.70.Ds Electric and magnetic measurements
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.80.-s Electric discharges
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Role of the buffer layer thickness on the formation of basal plane stacking faults in a-plane GaN epitaxy on r-sapphire

Z. H. Wu, A. M. Fischer, F. A. Ponce, T. Yokogawa, S. Yoshida, and R. Kato

Appl. Phys. Lett. 93, 011901 (2008); http://dx.doi.org/10.1063/1.2953082 (3 pages) | Cited 9 times

Online Publication Date: 7 July 2008

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The thickness of low temperature AlGaN buffer layers grown on r-sapphire substrates has been found to directly affect the crystalline structure of the buffer layer as well as the structural and optical properties of subsequently grown a-plane GaN films. A buffer layer with a thickness of 30 nm results in randomly distributed fine domains without extended defects. Increasing the thickness to 90 nm leads to a uniform and largely coalesced crystalline structure, with well-defined stacking faults. GaN films grown on the thinner buffer layer contain a lower density of larger stacking faults, and exhibit brighter stacking-fault luminescence as compared to films grown on thicker buffer layers. Our studies indicate that the optimum buffer layer thickness for growth of a-plane GaN is about 30 nm.
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68.55.-a Thin film structure and morphology
61.66.Fn Inorganic compounds
61.72.Nn Stacking faults and other planar or extended defects
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Asymmetric reflectivity from surfaces with distributed dipoles and IR experiments on poled polyvinylidene difluoride films

Jun-Lang Chen, Min-Yen Shieh, Hsin Her Yu, Chungpin Liao, Hsien-Ming Chang, Bin-Huang Yang, and Zi-Peng Zhao

Appl. Phys. Lett. 93, 011902 (2008); http://dx.doi.org/10.1063/1.2955525 (3 pages) | Cited 1 time

Online Publication Date: 7 July 2008

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It is widely accepted that as a monochromatic unpolarized light beam impinges on a flat surface at an angle, the reflection occurs symmetrically with a calculable amount of power in accordance with the Fresnel equations. Furthermore, reversing the light path offers no difference owing to the inherent symmetry. However, this picture changes when the interface is a distributed double layer responsive to the incident light. Theoretical elaboration and then IR experiments on poled polyvinylidene difluoride films were conducted to verify the emergence of asymmetric reflections at varying incident angles, as well as the inverse dependence of reflectivity on the impinging light intensity.
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78.66.Qn Polymers; organic compounds
78.30.Jw Organic compounds, polymers

Compressive film stress in a thin, tensile heteroepitaxial film

Chun-Wei Pao and David J. Srolovitz

Appl. Phys. Lett. 93, 011903 (2008); http://dx.doi.org/10.1063/1.2955833 (3 pages) | Cited 1 time

Online Publication Date: 7 July 2008

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We performed atomistic scale simulations to simulate the heteroepitaxial growth of a film with a 0.62% tensile misfit strain and monitored the stress evolution. The calculated σftf is initially compressive but increases after the first monolayer is completed. We provide theoretical and simulation evidence that this effect is associated with surface stresses. These results demonstrate that wafer curvature measurements lead to unreliable predictions of film stresses when the film is very thin.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology

Conducting transition metal nitride thin films with tailored cell sizes: The case of δ-TixTa1−xN

L. E. Koutsokeras, G. Abadias, Ch. E. Lekka, G. M. Matenoglou, D. F. Anagnostopoulos, G. A. Evangelakis, and P. Patsalas

Appl. Phys. Lett. 93, 011904 (2008); http://dx.doi.org/10.1063/1.2955838 (3 pages) | Cited 19 times

Online Publication Date: 7 July 2008

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We present results on the stability and tailoring of the cell size of conducting δ-TixTa1−xN obtained by film growth and ab initio calculations. Despite the limited solubility of Ta in Ti, we show that TiN and TaN are soluble due to the hybrization of the d and sp electrons of the metal and N, respectively, that stabilizes the ternary system to the rocksalt structure. The stress-free cell sizes follow the Vegard’s rule; nevertheless, process-dependent stresses expand the cell size of the as-grown films. The electronic properties of δ-TixTa1−xN films (ρ = 180 Ω cm) are similar to those of TiN and TaN.
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81.15.Cd Deposition by sputtering
81.15.Fg Pulsed laser ablation deposition
68.55.at Other materials
71.20.Ps Other inorganic compounds
71.15.-m Methods of electronic structure calculations
64.75.Bc Solubility

Oxygen defect induced photoluminescence of HfO2 thin films

Jie Ni, Qin Zhou, Zhengcao Li, and Zhengjun Zhang

Appl. Phys. Lett. 93, 011905 (2008); http://dx.doi.org/10.1063/1.2952288 (3 pages) | Cited 8 times

Online Publication Date: 9 July 2008

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Amorphous HfO2 films prepared by e-beam deposition exhibited room-temperature photoluminescence (PL) in the visible range, i.e., at ∼ 620  and 700 nm, due to oxygen vacancies involved during deposition. This PL can be enhanced by two orders in intensity by crystallizing the amorphous films in flowing argon, where a large amount of oxygen vacancies were introduced, and can be diminished by removal of the oxygen vacancies by annealing HfO2 films in oxygen. This study could help understand the defect-property relationship and provides ways to tune the PL property of HfO2 films.
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78.55.Hx Other solid inorganic materials
78.55.Qr Amorphous materials; glasses and other disordered solids
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.72.jd Vacancies
68.55.aj Insulators

Driving force for Sn whisker growth in the system Cu–Sn

M. Sobiech, U. Welzel, E. J. Mittemeijer, W. Hügel, and A. Seekamp

Appl. Phys. Lett. 93, 011906 (2008); http://dx.doi.org/10.1063/1.2953973 (3 pages) | Cited 20 times

Online Publication Date: 9 July 2008

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The evolution of residual stress gradients in Sn thin films on Cu substrates upon aging at ambient temperature has been investigated, for specimens which do exhibit and which do not exhibit Sn whisker growth, by performing x-ray diffraction stress measurements at constant penetration depths. Comparison of the measured near-surface stress-depth profiles for both types of specimens, as function of aging time at ambient temperature, showed that a significant negative stress gradient from the surface toward the Sn/Cu interface is decisive for Sn whisker growth in the system Cu–Sn.
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68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
68.60.Bs Mechanical and acoustical properties
68.35.Gy Mechanical properties; surface strains

Influence of the hole filling fraction on the ultrasonic transmission through plates with subwavelength aperture arrays

Héctor Estrada, Pilar Candelas, Antonio Uris, Francisco Belmar, Francisco Meseguer, and Francisco J. García de Abajo

Appl. Phys. Lett. 93, 011907 (2008); http://dx.doi.org/10.1063/1.2955825 (3 pages) | Cited 9 times

Online Publication Date: 9 July 2008

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We report on the large impact of the hole filling fraction on the ultrasonic transmission spectra of periodic subwavelength hole arrays. We demonstrate both theoretically and experimentally that transmission peaks become narrower as the filling fraction decreases. Our results are consistent in plates with different thickness values and provide a route map for the design of plates with tailored acoustic transmission profiles.
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43.35.-c Ultrasonics, quantum acoustics, and physical effects of sound
43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves

Multimode quantized thermal conductance tuned by external field in a quantum wire

L. S. Cao, R. W. Peng, and Mu Wang

Appl. Phys. Lett. 93, 011908 (2008); http://dx.doi.org/10.1063/1.2956673 (3 pages) | Cited 1 time

Online Publication Date: 9 July 2008

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In this work, we propose an approach to realize field-dependent multimode quantized thermal conductance by introducing both harmonic and anharmonic couplings to a quantum wire. It is demonstrated theoretically that by stretching (or compressing) the wire, phononic band structures are tuned and multiple phononic channels are opened one by one. In this way, multiple-step quantized thermal conductance is realized. The research opens a way to manipulate heat transfer in mesoscopic phonon systems.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
63.20.Ry Anharmonic lattice modes

Artifact-free dynamic atomic force microscopy reveals monotonic dissipation for a simple confined liquid

G. B. Kaggwa, J. I. Kilpatrick, J. E. Sader, and S. P. Jarvis

Appl. Phys. Lett. 93, 011909 (2008); http://dx.doi.org/10.1063/1.2950324 (3 pages) | Cited 13 times

Online Publication Date: 10 July 2008

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We present definitive interaction measurements of a simple confined liquid (octamethylcyclotetrasiloxane) using artifact-free frequency modulation atomic force microscopy. We use existing theory to decouple the conservative and dissipative components of the interaction, for a known phase offset from resonance (90° phase shift), that has been deliberately introduced into the experiment. Further we show the qualitative influence on the conservative and dissipative components of the interaction of a phase error deliberately introduced into the measurement, highlighting that artifacts, such as oscillatory dissipation, can be readily observed when the phase error is not compensated for in the force analysis.
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68.08.-p Liquid-solid interfaces
61.25.Em Molecular liquids

Composition-dependent damping and relaxation dynamics in miscible polymer blends above glass transition temperature by anelastic spectroscopy

Xuebang Wu, Shuying Shang, Qiaoling Xu, Changsong Liu, Zhengang Zhu, and Guangzhao Zhang

Appl. Phys. Lett. 93, 011910 (2008); http://dx.doi.org/10.1063/1.2945889 (3 pages) | Cited 3 times

Online Publication Date: 11 July 2008

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Anelastic spectroscopy is used to study the composition dependence of the damping and molecular relaxation dynamics in miscible poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) blends above the glass transition temperature. The ultrahigh damping peak of the relaxation type is shown to be associated with the liquid-liquid transition of PMMA. A higher PEO concentration leads to a higher damping performance and a lower transition temperature. The decreasing activation energy with increasing PEO concentration indicates a drastic increase in molecular mobility. Moreover, the relaxation time reveals a transition from the Vogel–Fulcher–Tamman behavior to the Arrhenius behavior due to the intermolecular guest-host interactions.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
64.70.pj Polymers
64.70.Ja Liquid-liquid transitions
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