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15 Nov 2010

Volume 108, Issue 10, Articles (10xxxx)

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J. Appl. Phys. 108, 102701 (2010); http://dx.doi.org/10.1063/1.3510244 (1 page)

Jurgen Daniel, Gyoujin Cho, Peter Burke, and Ali Javey
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Preface to Special Topic: Selected Papers from the International Conference on Flexible and Printed Electronics, Jeju Island, Korea, 2009

Jurgen Daniel, Gyoujin Cho, Peter Burke, and Ali Javey

J. Appl. Phys. 108, 102701 (2010); http://dx.doi.org/10.1063/1.3510244 (1 page)

Online Publication Date: 24 November 2010

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Abstract Unavailable
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01.30.Ww Editorials
85.30.Tv Field effect devices
85.40.Ls Metallization, contacts, interconnects; device isolation

Future direction of direct writing

Nam-Soo Kim and Kenneth N. Han

J. Appl. Phys. 108, 102801 (2010); http://dx.doi.org/10.1063/1.3510359 (6 pages) | Cited 1 time

Online Publication Date: 24 November 2010

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Direct write technology using special inks consisting of finely dispersed metal nanoparticles in liquid is receiving an undivided attention in recent years for its wide range of applicability in modern electronic industry. The application of this technology covers radio frequency identification-tag (RFID-tag), flexible-electronics, organic light emitting diodes (OLED) display, e-paper, antenna, bumpers used in flip-chip, underfilling, frit, miniresistance applications and biological uses, artificial dental applications and many more. In this paper, the authors have reviewed various direct write technologies on the market and discussed their advantages and shortfalls. Emphasis has given on microdispensing deposition write (MDDW), maskless mesoscale materials deposition (M3D), and ink-jet technologies. All of these technologies allow printing various patterns without employing a mask or a resist with an enhanced speed with the aid of computer. MDDW and M3D are capable of drawing patterns in three-dimension and MDDW, in particular, is capable of writing nanoinks with high viscosity. However, it is still far away for direct write to be fully implemented in the commercial arena. One of the hurdles to overcome is in manufacturing conductive inks which are chemically and physically stable, capable of drawing patterns with acceptable conductivity, and also capable of drawing patterns with acceptable adhesiveness with the substrates. The authors have briefly discussed problems involved in manufacturing nanometal inks to be used in various writing devices. There are numerous factors to be considered in manufacturing such inks. They are reducing agents, concentrations, oxidation, compact ability allowing good conductivity, and stability in suspension.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography

Reliability of gravure offset printing under various printing conditions

Taik-Min Lee, Jae-Ho Noh, Inyoung Kim, Dong-Soo Kim, and Sangki Chun

J. Appl. Phys. 108, 102802 (2010); http://dx.doi.org/10.1063/1.3510466 (6 pages) | Cited 1 time

Online Publication Date: 24 November 2010

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This paper focuses on the reliability of gravure offset printing and presents a mechanism on how the width of the printed line increases on repeated printings. Of the various printing process parameters, such as the resting times between doctoring, off, and set, printing velocity, printing pressure, and so forth, we investigated the effects of printing velocity, printing pressure, and blanket’s thickness on the reliability of gravure offset printing. As the printing velocity increases, the reliability of gravure offset printing also increases. This is because the actual contact time between ink and blanket decreases, resulting in less solvent absorption into the blanket. Printing pressure does not have much influence on reliability. Even though some change was observed, it was within the range of experimental error. Under sufficient printing pressure, this observation implies that the more important factor as regards the absorption model is time rather than pressure. As the thickness of the blanket increases, the reliability also increases. In the case of a thin blanket, in particular, the reliability of gravure offset printing is sensitive to changes in thickness.
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85.40.Hp Lithography, masks and pattern transfer

Rheological properties of Ag suspended fluid for inkjet printing

B. J. Park, B. O. Park, B. H. Ryu, Y. M. Choi, K. S. Kwon, and H. J. Choi

J. Appl. Phys. 108, 102803 (2010); http://dx.doi.org/10.1063/1.3511682 (5 pages) | Cited 1 time

Online Publication Date: 24 November 2010

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Rheological characterization of inks for the inkjet printing application has been considered to be essential with dissemination of applying the inkjet printing technology into many related industries. In this study, the high concentrated Ag suspension was prepared using poly(acrylic acid) as both a polyelectrolyte and a polymeric dispersant, and rheological properties of the suspension such as shear stress, shear viscosity, and dynamic moduli were examined using a rotational rheometer. The difference of rheological properties was investigated with different concentrations of the polyelectrolyte. The shear thinning effects and yield behavior of suspension were analyzed using rheological constitutive equations of state.
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82.70.Kj Emulsions and suspensions
47.57.Ng Polymers and polymer solutions
83.60.Bc Linear viscoelasticity
47.50.Ef Measurements
47.80.Jk Flow visualization and imaging
47.57.Qk Rheological aspects

Onset condition of pulsating cone-jet mode of electrohydrodynamic jetting for plane, hole, and pin type electrodes

Hyojun Kim, Junyoung Song, Jaewon Chung, and Daehie Hong

J. Appl. Phys. 108, 102804 (2010); http://dx.doi.org/10.1063/1.3511685 (10 pages) | Cited 1 time

Online Publication Date: 24 November 2010

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In this work, electrohydrodynamic (EHD) jetting phenomena were observed for three different types of bottom electrode (plane, hole, pin) at constant back pressure condition of the reservoir. Especially, we have focused on the measurement and numerical prediction of the onset voltage for pulsating Taylor cone jetting, changing glass capillary nozzle diameter (outer diameter: 16–47 μm), hydrostatic back pressure head in the reservoir, and the distance between the nozzle and the bottom electrode to provide design information on the EHD multinozzle head.
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47.65.-d Magnetohydrodynamics and electrohydrodynamics
47.60.Kz Flows and jets through nozzles
47.55.nb Capillary and thermocapillary flows
47.85.-g Applied fluid mechanics

Preparation of aqueous Ag Ink with long-term dispersion stability and its inkjet printing for fabricating conductive tracks on a polyimide film

Sunho Jeong, Hae Chun Song, Won Woo Lee, Youngmin Choi, and Beyong-Hwan Ryu

J. Appl. Phys. 108, 102805 (2010); http://dx.doi.org/10.1063/1.3511686 (5 pages) | Cited 1 time

Online Publication Date: 24 November 2010

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We synthesized silver nanoparticles via chemical reduction method in aqueous medium and poly(acrylic acid) sodium salt (PAA), a kind of anionic polyelectrolyte, was used as a capping agent as well as a dispersant. Owing to the electrosteric repulsion characteristic of PAA, the prepared aqueous Ag ink exhibited a remarkable dispersion stability, which was confirmed by sedimentation test, zeta-potential measurement, and rheological analysis. We fabricated narrow conductive features onto the polyimide substrate using ink-jet printing method and demonstrated the influence of substrate temperature on the morphology of printed patterns. After annealing at 250 °C, the resistivity of the Ag pattern with a linewidth of 60 μm was 4 μΩ cm.
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81.16.-c Methods of micro- and nanofabrication and processing
82.45.-h Electrochemistry and electrophoresis
81.40.Gh Other heat and thermomechanical treatments
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
73.63.Bd Nanocrystalline materials

A simulation and experimental study on packing of nanoinks to attain better conductivity

Anthony K. Amert, Dong-Hoon Oh, and Nam-Soo Kim

J. Appl. Phys. 108, 102806 (2010); http://dx.doi.org/10.1063/1.3511687 (5 pages) | Cited 1 time

Online Publication Date: 24 November 2010

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A simulation and experimental study on the packing of nanoinks has been carried out. Simulation predicted that the packing of two different sized monodispersed colloids would results in a more densely packed structure than a single sized monodispered colloid alone. The simulated results were confirmed by conducting experiments with two different sized-monodispersed silver colloids. A binary sized ink was printed in a rectangular pattern using a direct write method system and then the final pattern was sintered. The pattern was confirmed to be highly conductive and the final conductivity obtained from this pattern gave 47% of the bulk conductivity of silver.
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47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)
47.85.Np Fluidics
82.70.Dd Colloids

The effect of reduction atmospheres on the sintering behaviors of inkjet-printed Cu interconnectors

Inyoung Kim and Jongryoul Kim

J. Appl. Phys. 108, 102807 (2010); http://dx.doi.org/10.1063/1.3511688 (5 pages) | Cited 2 times

Online Publication Date: 24 November 2010

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In order to overcome the serious problems posed by Cu ink, which include the strong tendency to the oxidation of Cu nanopowders, various reduction atmospheres were investigated. As a result, a resistivity of ∼ 4 μΩ cm was achieved in the Cu interconnectors sintered at 200 °C with a gaseous mixture of formic acid (HCOOH) and alcohol. As regards this sample, micrographs show the facet boundaries and an average grain size of ∼ 300 nm. The use of formic acid was an effective way to decrease the sintering temperature to 150 °C, at which temperature the resistivity was ∼ 72 μΩ cm. This low temperature sintering and microstructural densification was due to the decomposition of capping molecules and the reduction in Cu oxide by formic acid.
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81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
82.30.-b Specific chemical reactions; reaction mechanisms
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.07.Wx Nanopowders
61.72.Mm Grain and twin boundaries

Effects of Te nanowire microstructure and Bi3+ reduction rate on Bi2Te3 nanotubes

Sook Hyun Kim and Byung Ki Park

J. Appl. Phys. 108, 102808 (2010); http://dx.doi.org/10.1063/1.3511689 (5 pages) | Cited 1 time

Online Publication Date: 24 November 2010

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To synthesize Bi2Te3 nanotubes with a one-dimensional structure, Te nanowires were prepared as templates via a solvothermal method. Subsequently, on the basis of atomic diffusion, Te was alloyed with Bi obtained by liquid-phase reduction in Bi3+. A hollow structure was formed as a result of a difference in the diffusion rates between the two atoms. Microstructural features of Te nanowires such as a particle morphology, crystal density, and aspect ratio, were determined by the synthetic temperature, and had a great influence on the alloying between Bi and Te into Bi2Te3 nanotubes. In addition, alloying was affected by the diffusion rate of Te atoms and the concentration of the agent for reducing Bi3+ to Bi.
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81.16.-c Methods of micro- and nanofabrication and processing
81.07.Gf Nanowires
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
81.07.De Nanotubes
61.46.Fg Nanotubes
66.30.Pa Diffusion in nanoscale solids

Inkjet-printing of nonsintered alumina-resin hybrid films and their dielectric properties

Myung-sung Hwang, Jihoon Kim, Hyo-tae Kim, Youngjoon Yoon, Sangil Hyun, Jonghee Kim, Sung-nam Lee, and Jooho Moon

J. Appl. Phys. 108, 102809 (2010); http://dx.doi.org/10.1063/1.3511692 (5 pages) | Cited 1 time

Online Publication Date: 24 November 2010

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We used the inkjet printing method to fabricate alumina-resin hybrid films without a high temperature sintering process. The dielectric properties of the alumina-resin hybrid films were studied in order to assess if the alumina-resin hybrid films are applicable to the electronic package substrates. Various numerical models were introduced to understand the relative permittivity of the alumina-resin hybrid films. Q-values of the alumina-resin hybrid films are also measured and compared to the commercially available substrate materials. The impact of microvoids on the Q-value of the inkjet-printed alumina-resin hybrid films was also studied. The microstructures of the inkjet-printed hybrid materials were investigated in order to confirm if the microvoids in the films were filled with the resin.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
77.22.Ch Permittivity (dielectric function)
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Low-voltage-operated top-gate polymer thin-film transistors with high capacitance poly(vinylidene fluoride-trifluoroethylene)/poly(methyl methacrylate) dielectrics

Soon-Won Jung, Kang-Jun Baeg, Sung-Min Yoon, In-Kyu You, Jong-Keun Lee, Young-Soon Kim, and Yong-Young Noh

J. Appl. Phys. 108, 102810 (2010); http://dx.doi.org/10.1063/1.3511697 (5 pages) | Cited 1 time

Online Publication Date: 24 November 2010

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We report on low-voltage-operated polymer transistors with poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)]/poly(methyl methacrylate) (PMMA) blended films as a gate dielectric layer. Top-gate polymer transistors are fabricated by all-solution processes on poly(9,9-dioctylfuorene-co-bithiophene) (F8T2) as an active layer. Both the operating voltage and charge carrier mobility are improved using P(VDF-TrFE)/PMMA blended films as a dielectric layer and by optimization of the ratio of the composite. F8T2 transistors have a high field-effect mobility of 1×10−2 cm2/V s and a low operation gate voltage of less than 10 V. The operation voltage effectively decreases owing to the high permittivity of the P(VDF-TrFE)]/(PMMA) blended film (10.4–8.4). The hysteresis induced by the ferroelectric polymer effectively disappears with the addition of a small amount of amorphous PMMA (5 wt %).
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85.30.Tv Field effect devices

Modeling of printed single walled carbon nanotube thin film transistors for attaining optimized clock signals

Jinsoo Noh, Minhun Jung, Kyunghwan Jung, Soyeon Lim, Gwangyong Lee, Vivek Subramanian, Ashley D. Leonard, James Tour, and Gyoujin Cho

J. Appl. Phys. 108, 102811 (2010); http://dx.doi.org/10.1063/1.3511698 (7 pages) | Cited 2 times

Online Publication Date: 24 November 2010

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As all-printed digital circuits are in high demand to produce all-printed active devices, providing accurate and synchronized clocks to all of the printed circuits is an indispensible step. To supply the clock signal to a printed digital circuit, a printed ring oscillator has been considered as a practical solution. However, it is difficult to fully print the ring oscillators with a consistent and stable clock signal. To resolve this problem, we employed single walled carbon nanotube network (SWNTn) as active layers of printed thin film transistors (TFTs) to completely print the ring oscillator. In addition, using the extracted electronic properties from the printed SWNTn-TFTs, we designed a simulation model based on AIM-Spice Model 15 for the printed ring oscillator and compared the simulated clock signals with the experimentally measured values of the printed ring oscillator.
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85.30.Tv Field effect devices
85.35.Kt Nanotube devices
84.30.Sk Pulse and digital circuits
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Friction effect on the rotation of bichromal ball in a monolayer rotating ball display

Youngwoo Lee, Sangmoon Lee, Jeong-Bok Kwak, Sangjin Kim, Hye-Yeon Cha, Choong Hee Lee, Chong Seo Lee, and Hwan-Soo Lee

J. Appl. Phys. 108, 102812 (2010); http://dx.doi.org/10.1063/1.3511710 (3 pages) | Cited 1 time

Online Publication Date: 24 November 2010

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A rotating ball display was tested with a thin monolayer sheet. An oil cavity was formed in the shape of a spheroid in a thin elastomer sheet. The rotation of a bichromal ball was investigated from the point of rotation time from one color to the other color. Bichromal balls were under friction during rotation. The friction caused an abnormal change in the rotation time. The rotation time of the elastomer sheet was compared with that of a microcup rotating ball display. The friction explained the difference of rotation time variation between the elastomer sheet display and the microcup display.
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42.79.Kr Display devices, liquid-crystal devices

Thermal stability of Si-doped InGaN multiple-quantum wells for high efficiency light emitting diodes

Sung-Nam Lee, Jihoon Kim, Kyoung-Kook Kim, Hyunsoo Kim, and Han-Ki Kim

J. Appl. Phys. 108, 102813 (2010); http://dx.doi.org/10.1063/1.3511712 (4 pages) | Cited 2 times

Online Publication Date: 24 November 2010

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Excitation power dependent photoluminescence (PL) spectroscopy was employed to determine the thermal degradation of InGaN quantum wells (QWs) structure with different Si doping in well region. At a low excitation power density, PL intensity of undoped InGaN well was significantly decreased, while those of interfacial and full Si-doped InGaN well were slightly reduced by rapid thermal annealing (RTA) process. However, PL measurement with high excitation power density showed that PL intensities of InGaN QWs regardless of Si doping were almost similar with/without RTA process. In addition, x-ray diffraction results indicated that Si-doping in well could improve the interfacial quality of InGaN QWs. Therefore, we suggest that Si doping suppress the generation of nonradiative recombination centers by thermal degradation at weaker localization states which could be easily filled by low excitation carriers.
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78.67.De Quantum wells
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
78.55.Cr III-V semiconductors
81.07.St Quantum wells
81.05.Ea III-V semiconductors

Use of laser lift-off for flexible device applications

Choong Hee Lee, Sang Jin Kim, Yongsoo Oh, Mi Yang Kim, Yeo-Joo Yoon, and Hwan-Soo Lee

J. Appl. Phys. 108, 102814 (2010); http://dx.doi.org/10.1063/1.3511716 (5 pages) | Cited 3 times

Online Publication Date: 24 November 2010

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This paper presents an approach of “film separation” and “transfer” to fabricating functional films or devices on polymeric substrates. For either a ferroelectric La-doped Pb(Zr,Ti)O3, PLZT thin film or a ZnO thin film, using laser lift-off (LLO), film separation from the transparent rigid substrate (sapphire or glass) was achieved. The film transfer to a polymeric receptor substrate was obtained by laminating the polymeric substrate on the film stack prior to LLO. The introduction of a sacrificial layer between the film and the substrate mostly resolved concerns to induce damages during LLO. Electrical testing of the films before and after LLO demonstrated the film properties on the original substrate were satisfactorily retained even for the transferred films on the polymeric substrate.
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68.35.bg Semiconductors
77.80.-e Ferroelectricity and antiferroelectricity
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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Photoluminescence spectroscopy of Cr3+ in CaY2Mg2Ge3O12

H. Örücü, J. Collins, and B. Di Bartolo

J. Appl. Phys. 108, 103101 (2010); http://dx.doi.org/10.1063/1.3510508 (6 pages)

Online Publication Date: 17 November 2010

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We have conducted a thorough investigation of the luminescence spectrum of Cr3+ in CaY2Mg2Ge3O12. The spectrum presents a line whose width is 60 cm−1 at 25 K and 82 cm−1 at 200 K, and a number of peaks of vibronic origin superimposed on a large band that extends from 700 to 800 nm. Going up in temperature the superimposed peaks broaden and disappear while the band persists. The response of the system to pulsed excitation presents at low temperature a great variety of patterns at different wavelengths. These patterns tend to collapse into one as the temperature is raised. This investigation confirms that the continuous interest in Cr-doped garnets is rewarding in terms of interesting experimental results.
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78.55.Hx Other solid inorganic materials
75.50.Gg Ferrimagnetics

An atomic-level study of material ablation and spallation in ultrafast laser processing of gold films

Yong Gan and J. K. Chen

J. Appl. Phys. 108, 103102 (2010); http://dx.doi.org/10.1063/1.3504192 (5 pages)

Online Publication Date: 17 November 2010

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Ablation and spallation of gold thin films by an ultrashort laser pulse are simulated by using an integrated two-temperature model and molecular dynamics method with inclusion of the hot electron blast force. The simulation results show that the ultrafast laser-induced nonthermal ablation and spallation both are essentially due to dynamic tensile stress that exceeds the local material strength. It is also demonstrated that a simultaneous use of femtosecond and picosecond laser pulses could induce spallation without causing undesired front-side damage to the film. This may be suited to peel an ultrathin film (1 μm in thickness or less) from its substrate or to improve the material removal rate of precise laser processing.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.62.Cf Industrial applications
42.60.-v Laser optical systems: design and operation
79.20.Eb Laser ablation

Control of the local devitrification on oxyfluoride glass doped with Er3+ ions under diode laser irradiation

S. González-Pérez, I. R. Martín, D. Jaque, P. Haro-González, and N. Capuj

J. Appl. Phys. 108, 103103 (2010); http://dx.doi.org/10.1063/1.3504857 (5 pages)

Online Publication Date: 17 November 2010

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Temperature control of the devitrification process in an erbium doped oxyfluoride glass under laser irradiation is reported. The green upconversion emissions around 525 and 545 nm originated from the thermalized 2H11/2 and 4S3/2 levels were studied when the glass structure changes to glass ceramic during irradiation with a laser beam. Power dependence of the fluorescence intensity ratio was used to determine the temperature of the irradiated zone. The transition from glass to glass ceramic takes place under 2300 mW of laser power with an estimated temperature around 783 K. This result agrees with the one obtained in the samples devitrified under conventional furnace treatment. Therefore, the estimation of the temperature of the irradiated zone through the fluorescence intensity ratio method allows a controlled devitrification. Moreover, an irradiated line has been written in the glass showing an important diffusion of the Pb2+ and F− ions. These results confirm that nanocrystals have been created due to the laser action.
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81.05.Pj Glass-based composites, vitroceramics
61.43.Fs Glasses
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Rx Nanocrystalline materials
81.07.Bc Nanocrystalline materials

Luminescence enhancement of CdTe nanostructures in LaF3:Ce/CdTe nanocomposites

Mingzhen Yao, Xing Zhang, Lun Ma, Wei Chen, Alan G. Joly, Jinsong Huang, and Qingwu Wang

J. Appl. Phys. 108, 103104 (2010); http://dx.doi.org/10.1063/1.3506416 (7 pages) | Cited 1 time

Online Publication Date: 17 November 2010

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Radiation detection demands new scintillators with high quantum efficiency, high energy resolution, and short luminescence lifetimes. Nanocomposites consisting of quantum dots and Ce3+ doped nanophosphors may be able to meet these requirements. Here, we report the luminescence enhancement of LaF3:Ce/CdTe nanocomposites which were synthesized by a wet chemistry method. CdTe quantum dots in LaF3:Ce/CdTe nanocomposites are converted into nanowires, while in LaF3/CdTe nanocomposites no such conversion is observed. As a result, the CdTe luminescence in LaF3:Ce/CdTe nanocomposites is enhanced about five times, while in LaF3/CdTe nanocomposites no enhancement was observed. Energy transfer, light reabsorption, and defect passivation are the likely reasons for the luminescence enhancement.
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78.55.Hx Other solid inorganic materials
78.70.Ps Scintillation
81.16.-c Methods of micro- and nanofabrication and processing

2–3 μm mid infrared light sources using InGaAs/GaAsSb “W” type quantum wells on InP substrates

C. H. Pan, S. D. Lin, and C. P. Lee

J. Appl. Phys. 108, 103105 (2010); http://dx.doi.org/10.1063/1.3506427 (5 pages) | Cited 2 times

Online Publication Date: 18 November 2010

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We have investigated the InGaAs/GaAsSb/InAlGaAs/InAlAs type-II “W” quantum wells (QWs) grown on InP substrates by molecular beam epitaxy. The photoluminescence (PL) emission wavelength longer than 2.56 μm at room temperature (RT) is demonstrated for the first time in this material system. The PL emission peaks of our designed samples can cover a wide range from 2 to 2.5 μm at cryogenic temperature. The samples show good optical quality that the reduction in integrated PL intensity is only around one order of magnitude from 35 K to RT. We found that the integrated PL intensity decreased as the emission wavelength increased, which is due to the reduction in the electron-hole wave function overlap. This is consistent with the calculated result. In the power dependent PL measurements, the emission peak of “W” type QWs show blue shifts with the excitation power (Pex) but does not follow the Pex1/3 rule as predicted by type-II band bending model. The localized states filling effect gives reasonable explanations for the observed phenomena.
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42.72.Ai Infrared sources
81.07.St Quantum wells
81.05.Ea III-V semiconductors
78.67.De Quantum wells
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Pump-probe imaging of nanosecond laser-induced bubbles in distilled water solutions: Observations of laser-produced-plasma

R. Evans and S. Camacho-López

J. Appl. Phys. 108, 103106 (2010); http://dx.doi.org/10.1063/1.3506657 (9 pages)

Online Publication Date: 18 November 2010

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This article presents the analysis of the laser-produced-plasma (LPP) formed by the focusing of a 9 ns laser pulse, λ = 532 nm, with a NA = 0.6 aspherical lens using energies between 100–1500 μJ, into distilled water with varying solutions of table salt. Observations of the filamentation plasma were made, which are explained by self-focusing of the laser pulse by the LPP through ponderomotive cavitation of the electron plasma in the center of the beam. The filamentation of the beam through a low density plasma wave guide explains why the transmission of the pump laser through the interaction region was notably higher on previous experiments that we performed [ R. Evans et al., Opt. Express 16, 7481 (2008) ], than a very similar set of experiments performed by Noack and Vogel [IEEE J. Quantum Electron. 35, 1156 (1999) ].
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.38.Hb Self-focussing, channeling, and filamentation in plasmas
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Biaxial and uniaxial strain effects on the ultraviolet emission efficiencies of AlxGa1−xN films with different Al concentrations

D. Y. Fu, R. Zhang, B. G. Wang, B. Liu, Z. L. Xie, X. Q. Xiu, H. Lu, Y. D. Zheng, and G. Edwards

J. Appl. Phys. 108, 103107 (2010); http://dx.doi.org/10.1063/1.3511339 (5 pages)

Online Publication Date: 18 November 2010

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The influences of biaxial and uniaxial strain on the ultraviolet emission efficiencies of both c- and m-plane AlxGa1−xN films with different Al concentrations are investigated under the framework of k⋅p perturbation theory. The optimal high efficiency windows, for ultraviolet light emissions are quantitatively estimated. c-plane AlxGa1−xN modified by uniaxial strain, shows more advantages over biaxial-strained AlxGa1−xN. This is due to the relatively more flexible tuning range and the advantage of obtaining pure linear polarization, which can be utilized to design polarized emission devices. For m-plane AlxGa1−xN, there are always in-plane polarized emissions under both biaxial and uniaxial strain conditions, thus, it is more likely to obtain high surface emission efficiency.
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68.60.Bs Mechanical and acoustical properties
78.66.Fd III-V semiconductors
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
78.55.Cr III-V semiconductors

Analysis of the slope efficiency for terahertz quantum-cascade lasers

L. Schrottke, M. Wienold, M. Giehler, R. Hey, and H. T. Grahn

J. Appl. Phys. 108, 103108 (2010); http://dx.doi.org/10.1063/1.3511470 (6 pages) | Cited 4 times

Online Publication Date: 18 November 2010

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The slope efficiency is, in addition to the threshold current density and operating voltage, a decisive target value for the operation of quantum-cascade lasers (QCLs) in order to achieve an optimal total efficiency for the conversion of electrical input power into optical output power. We analyze the light-current characteristics for a set of similar, high-power, bound-to-continuum terahertz QCLs. The calculated internal slope efficiency shows a clear dependence on the height and thickness of the barriers. In contrast to the simulations, we found experimentally a significant difference in the threshold current densities and slope efficiencies for QCLs with nominally identical layer structures, which we mainly attribute to different line broadening.
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42.55.Px Semiconductor lasers; laser diodes

Surface plasmon resonator: Design, construction, and observation in the farfield

Ahmet Arca, Matt Clark, and Mike Somekh

J. Appl. Phys. 108, 103109 (2010); http://dx.doi.org/10.1063/1.3487940 (8 pages)

Online Publication Date: 18 November 2010

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We have studied the behavior of surface plasmons (SPs) in valley like structures [ Schroter et al., Ultramicroscopy 68, 223 (1997) ] and found that SPs traveling in both directions in such a cavity yield interference patterns in the farfield, which can be measured as specular and retroreflection. We have studied and designed the structures using finite element method in addition to a heuristic model, fabricated the devices using photolithography and experimentally verified the operation of the resonators, by observing the interference patterns of the specular and retroreflection in the farfield. We have found that the experimental results agree with the simulations, and explained the discrepancies. These structures can be useful in the study of the propagation length of SPs via observation in the farfield of the specular and the retroreflected light in laser industry and could be miniaturized to yield small biosensors.
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42.15.Eq Optical system design
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.87.-d Optical testing techniques
42.86.+b Optical workshop techniques
42.79.-e Optical elements, devices, and systems

Phenomenological quantum description of the ultrafast response of arrayed waveguide gratings

L. Grave de Peralta

J. Appl. Phys. 108, 103110 (2010); http://dx.doi.org/10.1063/1.3512860 (11 pages)

Online Publication Date: 19 November 2010

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This work presents a detailed and quantitative quantum description of the ultrafast response of arrayed waveguide gratings (AWG) illuminated with relatively intense short pulses of light. This is achieved with no more mathematical or conceptual complexities than that required by a classical description. The presented approach is based on the phenomenological interpretation of the photon, that is, a photon is what produces a “click” in a photodetector. This phenomenological approach was combined with the application of Feynman’s rules for describing interference and Bohr’s correspondence principle, i.e., quantum theory should somehow converge in the limit with the classical description of the interference phenomena. This basic approach reveals that, in apparent opposition to wide-held beliefs, especially designed AWGs can be used to produce interference in conditions where the “which-path” information is available.
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42.79.Gn Optical waveguides and couplers
42.79.Dj Gratings
42.82.-m Integrated optics
85.60.Gz Photodetectors (including infrared and CCD detectors)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
03.65.-w Quantum mechanics
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