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30 Jun 2003

Volume 82, Issue 26, pp. 4633-4843

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 4797 (2003); http://dx.doi.org/10.1063/1.1587262 (3 pages)

Ongi Englander, Dane Christensen, and Liwei Lin
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Transition between two states of surface coverage and etch rate during Si etching in inductively coupled Cl2–Ar plasmas with changing mixtures

N. C. M. Fuller, Donald A. Telesca, Vincent M. Donnelly, and Irving P. Herman

Appl. Phys. Lett. 82, 4663 (2003); http://dx.doi.org/10.1063/1.1585124 (3 pages) | Cited 2 times

Online Publication Date: 24 June 2003

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The etch rate and surface SiCl and SiCl2 concentrations abruptly increase and the surface Si concentration abruptly decreases as the chlorine fraction is increased above a threshold value during Si etching by an inductively coupled Cl2–Ar mixture plasma. The surface species are detected by laser desorption of the chlorinated adlayer using laser-induced fluorescence and plasma-induced emission of the desorbed species. This threshold chlorine fraction is 75% for 80 eV average ion energy, and increases with the average energy of ions incident on the surface. This unexpected observation is attributed to a phase transition between two states of surface chlorination and morphology. © 2003 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.43.Tj Photon stimulated desorption
81.05.Cy Elemental semiconductors
78.55.Ap Elemental semiconductors

Cubic GaN formation in Mn/GaN multilayer films grown on 6H-SiC(0001)

Y. Cui, V. K. Lazorov, M. M. Goetz, H. Liu, D. P. Robertson, M. Gajdardziska-Josifovska, and L. Li

Appl. Phys. Lett. 82, 4666 (2003); http://dx.doi.org/10.1063/1.1586455 (3 pages) | Cited 13 times

Online Publication Date: 24 June 2003

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Cubic GaN was grown on 6H-SiC(0001) by electron-cyclotron resonance plasma-assisted molecular-beam epitaxy. The growth process consisted of first depositing a 20-nm GaN buffer, followed by ten periods of alternating layers of 1 monolayer (ML) Mn and 10 ML GaN, and finally capped with 30 nm GaN. High-resolution transmission electron micrographs of film cross sections were recorded and digital diffractograms were calculated to determine the lattice structures of the different film layers. It was found that the crystal structure in the GaN buffer and capping layer matches the 2H-wurtzite GaN. However, uniform cubic zinc-blende GaN phase was observed in place of the nominal multilayer Mn/GaN region. The density of defects typically observed in GaN films is drastically reduced within the cubic and capping layer, indicating improved film quality possibly due to the surfactant effect of Mn. Based on the one-dimensional Ising model of polytype formation, a mechanism is proposed to explain the growth of cubic GaN in the Mn/GaN region. © 2003 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.65.Ac Multilayers
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.-y Defects and impurities in crystals; microstructure

Effect of N incorporation on boron penetration from p+ polycrystalline-Si through HfSixOy films

M. A. Quevedo-Lopez, M. El-Bouanani, M. J. Kim, B. E. Gnade, R. M. Wallace, M. R. Visokay, A. LiFatou, J. J. Chambers, and L. Colombo

Appl. Phys. Lett. 82, 4669 (2003); http://dx.doi.org/10.1063/1.1586483 (3 pages) | Cited 40 times

Online Publication Date: 24 June 2003

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We demonstrate that incorporating N in Hf-silicate films reduces B penetration through the dielectric film. By modeling the B depth profiles, we calculated the B diffusivities through Hf-silicate (HfSixOy) to be ∼2× higher than the corresponding diffusivities for Hf-silicon oxynitride (HfSixOyNz). B diffusion through grain boundaries after HfSixOy crystallization is believed to be responsible for the enhanced B diffusivity observed. Suppression of crystallization observed in HfSixOyNz films is attributed to the lower Hf content in the films and the incorporation of N. The decreased B penetration observed in HfSixOyNz is a combination of absence of grain boundaries and the fact that N blocks B diffusion by occluding diffusion pathways. The minimum temperatures for B penetration are estimated to be approximately 950 and 1050 °C for HfSixOy and HfSixOyNz, respectively. © 2003 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
61.72.S- Impurities in crystals
66.30.J- Diffusion of impurities
61.72.Mm Grain and twin boundaries

Field-induced cation migration in Cu oxide films by in situ scanning tunneling microscopy

J. P. Singh, T.-M. Lu, and G.-C. Wang

Appl. Phys. Lett. 82, 4672 (2003); http://dx.doi.org/10.1063/1.1586461 (3 pages) | Cited 3 times

Online Publication Date: 24 June 2003

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We observed the formation of Cu metallic nanoscale structures of ∼20-nm diameter and ∼2-nm height on a Cu2O covered polycrystalline Cu film under an applied field using a scanning tunneling microscope tip in a high vacuum condition. We interpreted the results as the Cu cation transport through the copper oxide film towards the surface when a positive biased voltage (>1.5 V) was applied to the film to lower the activation energy of the cation migration. Scanning tunneling spectroscopy measurements showed that the field-induced nanostructures were pure metallic Cu with a characteristic broad peak near −0.45 eV. No structural change was observed when a negative bias was applied to the film. © 2003 American Institute of Physics.
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66.30.Qa Electromigration
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
85.40.Ls Metallization, contacts, interconnects; device isolation

Isotope and crystal orientation effects in low-energy H/D blistering of Si

O. Moutanabbir, B. Terreault, and G. G. Ross

Appl. Phys. Lett. 82, 4675 (2003); http://dx.doi.org/10.1063/1.1580637 (3 pages) | Cited 3 times

Online Publication Date: 24 June 2003

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In this letter we report a giant isotope effect in silicon blistering induced by low-energy (5 keV) H or D ion implantation and annealing. Atomic force microscopy and thermal desorption spectroscopy revealed abundant blistering and exfoliation with a D fluence of 6×1016 D cm−2, whereas no blistering was observed with a H fluence up to 1×1017 H cm−2. This is accompanied by premature H2 release, and the evidence suggests that inefficient defect trapping is the cause. The blister density and the degree of exfoliation also depend strongly on the crystal orientation. © 2003 American Institute of Physics.
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61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.uf Ge and Si
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Cc Kinetics of defect formation and annealing
68.37.Ps Atomic force microscopy (AFM)
68.43.Vx Thermal desorption

Influence of growth conditions on the lattice constant and composition of (Ga,Mn)As

G. M. Schott, G. Schmidt, G. Karczewski, L. W. Molenkamp, R. Jakiela, A. Barcz, and G. Karczewski

Appl. Phys. Lett. 82, 4678 (2003); http://dx.doi.org/10.1063/1.1586778 (3 pages) | Cited 19 times

Online Publication Date: 24 June 2003

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The lattice constant and the alloy composition of (Ga,Mn)As are investigated by high-resolution x-ray diffraction and secondary ion mass spectroscopy. The (Ga,Mn)As layers are grown by low-temperature molecular-beam epitaxy under various growth conditions. We find that, while the alloy composition is mainly determined by the Mn cell temperature (TMn), the substrate temperature (Tsub) and the arsenic to gallium flux ratio (As/Ga) strongly influence the lattice constant. In particular, layers which have the same composition but different growth parameters have quite different lattice constants, caused by the amount of excess As incorporation in the (Ga,Mn)As crystal. This implies that the lattice parameter of (Ga,Mn)As cannot even serve as a rough measure of the crystal composition. (Ga,Mn)As is therefore an example of a system which does not obey Vegard’s law. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Strain-driven composition gradients in nanocrystalline SiGe

C. Tzoumanekas and P. C. Kelires

Appl. Phys. Lett. 82, 4681 (2003); http://dx.doi.org/10.1063/1.1586780 (3 pages) | Cited 1 time

Online Publication Date: 24 June 2003

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Monte Carlo simulations shed light onto the structure and composition of nanocrystalline SiGe. A strong enhancement of Ge content in nanocrystals is found, driven by the stress gradient between the crystalline and amorphous components of the network. For a stoichiometric amorphous matrix and for small nanocrystals, typically 4 nm in diameter, the Ge content in the nanocrystals reaches ∼80%. The composition gradient declines with increasing size. The nanocrystals consist of a large ordered Ge-rich core and an outer less-ordered region where alloying is enhanced. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
61.66.Bi Elemental solids
61.66.Dk Alloys
61.43.Bn Structural modeling: serial-addition models, computer simulation
61.43.Dq Amorphous semiconductors, metals, and alloys
81.05.Gc Amorphous semiconductors

Real-time in situ x-ray diffraction as a method to control epitaxial growth

A. S. Bader, W. Faschinger, C. Schumacher, J. Geurts, L. W. Molenkamp, R. B. Neder, and G. Karczewski

Appl. Phys. Lett. 82, 4684 (2003); http://dx.doi.org/10.1063/1.1582360 (3 pages) | Cited 3 times

Online Publication Date: 24 June 2003

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We developed a real-time in situ x-ray Bragg diffraction technique for monitoring epitaxial growth. In our setup, the x-ray diffraction requirement of an extremely exact sample adjustment and an angular scan of sample and detector are circumvented by using a slightly divergent x-ray beam and observing an extremely asymmetric Bragg reflection with a multichannel detector. The angular range covered by the stationary multichannel detector corresponds nearly exactly to the qz interval of a conventional ω−2θ scan. The technique is demonstrated by monitoring the molecular-beam epitaxial growth of a ZnSe epilayer on (001)GaAs. The exposure time of each diffraction pattern is only a few seconds, which enables a real-time x-ray diffraction monitoring of the epitaxial growth process. © 2003 American Institute of Physics.
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61.05.cp X-ray diffraction
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Dz II-VI semiconductors
29.40.-n Radiation detectors

Improved field emission at electric-discharge-conditioned sites on diamond surfaces due to the formation of carbon nanotubes

N. Koenigsfeld, R. Kalish, and A. Hoffman

Appl. Phys. Lett. 82, 4687 (2003); http://dx.doi.org/10.1063/1.1581372 (3 pages) | Cited 3 times

Online Publication Date: 24 June 2003

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The role of local materials modification to field emission (FE) from diamond is studied. FE properties of a boron-doped hydrogenated diamond film containing an array of sp2 rich channels that extend from surface to substrate and of diamond films subjected to an electric discharge are reported. Whereas the implantation-graphitized regions do not show any improvement in emission properties, compared to unirradiated or fully irradiated regions of the same sample, much improved emission is found for all regions once conditioned by an electric discharge. We show that carbon nanowhiskers (most likely carbon nanotubes) were formed in the vicinity of all conditioned sites and can account for the improved emission following “conditioning” that have been reported for many carbon-based field emitters. © 2003 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
68.35.Dv Composition, segregation; defects and impurities
68.55.-a Thin film structure and morphology

High-strength Zr-Nb-(Cu,Ni,Al) composites with enhanced plasticity

J. Das, W. Löser, U. Kühn, J. Eckert, S. K. Roy, and L. Schultz

Appl. Phys. Lett. 82, 4690 (2003); http://dx.doi.org/10.1063/1.1587254 (3 pages) | Cited 74 times

Online Publication Date: 24 June 2003

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Zr73.5Nb9Cu7Ni1Al9.5 and Zr66.4Nb6.4Cu10.5Ni8.7Al8.0 composites of bcc β-Zr(Nb) dendrites embedded in a nanocrystalline matrix were prepared by slow cooling from melt. The increase of Nb content from 6.4 to 9 at. % slightly reduces the strength, but considerably improves the plastic elongation under uniaxial compressive loading from ϵp = 0.6% to 14.8%. The interaction of strain with dendrites and the nanocrystalline matrix is suggested as origin of the improvement of the mechanical properties. © 2003 American Institute of Physics.
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81.05.Ni Dispersion-, fiber-, and platelet-reinforced metal-based composites
81.40.Lm Deformation, plasticity, and creep
62.25.-g Mechanical properties of nanoscale systems
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
81.07.Bc Nanocrystalline materials
62.20.F- Deformation and plasticity
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Yx Interaction between different crystal defects; gettering effect

Space-charge-mediated delayed electroluminescence from polyfluorene thin films

S. Sinha, A. P. Monkman, R. Güntner, and U. Scherf

Appl. Phys. Lett. 82, 4693 (2003); http://dx.doi.org/10.1063/1.1587879 (3 pages) | Cited 2 times

Online Publication Date: 24 June 2003

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In polyfluorene thin films, an electrically induced short-lived delayed fluorescence (of the order of μs) is observed, which grows in intensity as the temperature is increased from 30 K to 290 K. From bias-offset-dependent electroluminescence intensity measurements and decay kinetics measurements, we conclude that the delayed recombination of space-charge carriers, along with the long-lasting tail of the prompt electrofluorescence, give rise to the short-lived delayed fluorescence. © 2003 American Institute of Physics.
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78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds
73.61.Ph Polymers; organic compounds
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Acoustic properties of (Pb0.9La0.1)(Zr0.65Ti0.35)O3 relaxor ferroelectric ceramics studied by Brillouin scattering

Ghulam Shabbir, Jae-Hyeon Ko, Seiji Kojima, and Qing-Rui Yin

Appl. Phys. Lett. 82, 4696 (2003); http://dx.doi.org/10.1063/1.1588754 (3 pages) | Cited 15 times

Online Publication Date: 24 June 2003

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Acoustic properties of PLZT 10/65/35 relaxor ferroelectric ceramic samples have been studied by high resolution Brillouin scattering technique in the temperature range from 90 to 800 K. The Brillouin frequency shift and the elastic moduli, related to the LA and TA phonon modes, show a broad softening on cooling towards the dielectric maximum temperature Tm. The hypersonic damping shows broad maxima at 328 K, which we attribute to order parameter fluctuations. The softening in the elastic moduli L, E, and G is maximum in the temperature range from 300 to 340 K. The temperature dependence of maximum relaxation time τmax reveals good correlation between dielectric and Brillouin scattering data. © 2003 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
62.65.+k Acoustical properties of solids
78.35.+c Brillouin and Rayleigh scattering; other light scattering
81.40.Jj Elasticity and anelasticity, stress-strain relations
77.80.-e Ferroelectricity and antiferroelectricity
62.20.D- Elasticity
63.20.-e Phonons in crystal lattices
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions

A highly glass-forming alloy with low glass transition temperature

Z. F. Zhao, Z. Zhang, P. Wen, M. X. Pan, D. Q. Zhao, W. H. Wang, and W. L. Wang

Appl. Phys. Lett. 82, 4699 (2003); http://dx.doi.org/10.1063/1.1588367 (3 pages) | Cited 70 times

Online Publication Date: 24 June 2003

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A rare-earth Pr-based bulk metallic glass (BMG) is obtained in the shape of rod up to 5 mm in diameter by die cast. Unlike other rare-earth-based BMGs, it exhibits a distinct glass transition, the low glass transition temperature (Tg = 409 K), a large and stable supercooled liquid region, and paramagnetic property. The glass transition as well as its kinetic nature and the fragility parameters of the BMG have been studied. The BMG offers an ideal model to investigate the nature of glass transition as well as the relaxation and nucleation with a large experimentally accessible time and temperature window at low temperatures. © 2003 American Institute of Physics.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition

Anomalous compositional pulling effect in InGaN/GaN multiple quantum wells

M. Hao, H. Ishikawa, T. Egawa, C. L. Shao, and T. Jimbo

Appl. Phys. Lett. 82, 4702 (2003); http://dx.doi.org/10.1063/1.1588731 (3 pages) | Cited 17 times

Online Publication Date: 24 June 2003

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A series of InGaN/GaN multiple quantum wells (MQWs) was grown by metalorganic chemical vapor deposition with different well thickness. High-resolution x-ray diffraction studies revealed that the In composition is increasing along the growth direction from the bottom to the top of each well layer in these MQWs. While the In composition at the bottom of each well layer almost keeps constant, the increasing rate of In composition becomes obviously larger when the growth temperature is decreased. The important conclusion of this study is that the InGaN/GaN MQWs is shaped like a triangle due to the increasing of In composition from the bottom to the top of the well layer. The emission mechanism of the InGaN/GaN MQWs has to be discussed based on the triangular band gap structure. © 2003 American Institute of Physics.
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68.65.Fg Quantum wells
68.65.Cd Superlattices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
73.21.Fg Quantum wells
78.67.De Quantum wells
73.21.Cd Superlattices
68.35.Ct Interface structure and roughness

Wetting effect and morphological stability in growth of short-period strained multilayers

Zhi-Feng Huang, Daniel Kandel, and Rashmi C. Desai

Appl. Phys. Lett. 82, 4705 (2003); http://dx.doi.org/10.1063/1.1588739 (3 pages) | Cited 4 times

Online Publication Date: 24 June 2003

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We explore the morphological stability during the growth of strained multilayer structures in a dynamical model which describes the coupling of elastic fields, wetting effect, and deposition process. We quantitatively show the significant influence of the wetting effect on the stability properties, in particular for short-period multilayers. Our results are qualitatively similar to recent experimental observations in AlAs/InAs/InP(001) system. We also give predictions for strain-balanced multilayers. © 2003 American Institute of Physics.
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68.65.Cd Superlattices
68.35.Ct Interface structure and roughness
68.08.Bc Wetting

Structural and electrical characteristics of Ge nanoclusters embedded in Al2O3 gate dielectric

Q. Wan, C. L. Lin, W. L. Liu, and T. H. Wang

Appl. Phys. Lett. 82, 4708 (2003); http://dx.doi.org/10.1063/1.1588373 (3 pages) | Cited 27 times

Online Publication Date: 24 June 2003

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Structural and electrical characteristics of the metal–insulator–semiconductor (MIS) structures of Al/Al2O3/Si containing Ge nanoclusters are experimentally demonstrated. Secondary ion mass spectroscopy results indicate the out-diffusion of Ge after annealing at 800 °C in N2 ambient for 30 min. An increment of leakage current is observed due to the out-diffusion of Ge. Capacitance–voltage studies indicate that annealing can effectively passivate the negatively charged trapping centers. Memory effect of the Ge nanoclusters is verified by the hysteresis in the C–V curves in the annealed sample. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
73.63.Bd Nanocrystalline materials
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
66.30.Pa Diffusion in nanoscale solids
81.40.Gh Other heat and thermomechanical treatments
66.30.Ny Chemical interdiffusion; diffusion barriers
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Bismuth volatility effects on the perfection of SrBi2Nb2O9 and SrBi2Ta2O9 films

M. A. Zurbuchen, J. Lettieri, S. J. Fulk, Y. Jia, A. H. Carim, D. G. Schlom, and S. K. Streiffer

Appl. Phys. Lett. 82, 4711 (2003); http://dx.doi.org/10.1063/1.1574406 (3 pages) | Cited 15 times

Online Publication Date: 24 June 2003

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The volatility of bismuth and bismuth oxide species complicates the growth of phase-pure films of SrBi2Nb2O9 and SrBi2Ta2O9. Films that appear phase-pure by x-ray diffraction can have microstructural defects caused by transient bismuth nonstoichiometry which have a significant impact on properties. Such defects are resolved by transmission electron microscopy. Post-growth loss of bismuth from a slowly cooled SrBi2Ta2O9 film resulted in the generation of a high density of out-of-phase boundaries (OPBs), which are demonstrated to be ferroelectrically inactive. In another film, the difference in the rate of desorption of bismuth oxides from SrTiO3 versus that from SrBi2Nb2O9 led to bismuth enrichment at the film–substrate interface, and the formation of an epitaxial reaction layer in an otherwise stoichiometric SrBi2Nb2O9 film. This different-composition layer would be expected to alter the electrical properties of the film as a whole. These results help explain the scatter in electrical data reported for similarly oriented films. © 2003 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
77.80.Dj Domain structure; hysteresis
68.35.Fx Diffusion; interface formation
68.37.Lp Transmission electron microscopy (TEM)
77.22.Ej Polarization and depolarization

Two-photon absorption and multiphoton-induced photoluminescence of bulk GaN excited below the middle of the band gap

Y. Toda, T. Matsubara, R. Morita, M. Yamashita, K. Hoshino, T. Someya, and Y. Arakawa

Appl. Phys. Lett. 82, 4714 (2003); http://dx.doi.org/10.1063/1.1587260 (3 pages) | Cited 10 times

Online Publication Date: 24 June 2003

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Optical nonlinearity in the yellow luminescence (YL) band of GaN was investigated using thick bulk samples. Transient pump–probe measurements revealed strong transmission changes due to two-photon absorption (TPA) even at the middle of the YL band. The TPA coefficient evaluated reaches ∼ 5 cm/GW at about 1.3 eV, which was as large as the mid-gap resonance. The TPA spectrum clearly showed that the observed large nonlinearity originated from the YL band. On the basis of efficient TPA in the YL band, relaxation processes in the multiphoton-induced photoluminescence excitation spectrum were also investigated. © 2003 American Institute of Physics.
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78.55.Cr III-V semiconductors
42.65.-k Nonlinear optics

Optical power limiting and stabilization using a two-photon absorbing neat liquid crystal in isotropic phase

Guang S. He, Tzu-Chau Lin, Paras N. Prasad, Chih-Chien Cho, and Liang-Jye Yu

Appl. Phys. Lett. 82, 4717 (2003); http://dx.doi.org/10.1063/1.1588364 (3 pages) | Cited 22 times

Online Publication Date: 24 June 2003

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This letter reports on a neat liquid crystal that incorporates a two-photon-absorbing chromophore in its structure. The nonlinear optical properties including two-photon-induced fluorescence spectrum and decay behavior, as well as the effective two-photon absorption coefficient of this liquid crystal in its isotropic phase are presented. Fairly good optical limiting and stabilization performance with this nonlinear material have been achieved by using ∼ 815-nm and ∼ 5-ns laser pulses. © 2003 American Institute of Physics.
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42.70.Df Liquid crystals
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
33.50.Dq Fluorescence and phosphorescence spectra
78.55.Bq Liquids
61.30.-v Liquid crystals
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
33.80.Wz Other multiphoton processes
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