193-nm Radiation Research Articles

Solvothermal synthesis, crystal structure, and second-order nonlinear optical properties of a new noncentrosymmetric gallium-organic framework material, [N(C3H7)4]3Ga3[C6H3(CO2)3

A novel noncentrosymmetric (NCS) gallium-organic framework material, [N(C3H7)4]3Ga3[C6H3(CO2)3]4 (CAUMOF-11) has been synthesized by a solvothermal reaction using Ga(NO3)3·xH2O, 1,3,5-C6H3(CO2H)3, N(C3H7)4Cl, HNO3, and HCON(CH3)2 at 180°C. The structure of the reported material has been determined by single-crystal X-ray diffraction. CAUMOF-11 has an anionic three-dimensional framework with aligned four-coordinate GaO4 tetrahedra and 1,3,5-benzenetricarboxylate groups. Tetrapropylammonim cations reside within the channel and maintain the charge balance. Detailed structural analyses with full characterization including infrared spectroscopy, thermogravimetric analysis, elemental analysis, ion-exchange reactions, topotactic decomposition, and gas adsorption experiments are reported. Powder second-harmonic generating (SHG) measurements on CAUMOF-11, using 1064nm radiation, exhibit SHG efficiency of 15 times that of α-SiO2 and the material is phase-matchable (type-1).

Observation of a Curve Crossing Mechanism in the Field Ionization of Inner-Shell Excited Single <formula formulatype="inline"><tex Notation="TeX">${\rm Xe}^{33+}{(2\bar{\rm p})}$</tex></formula> and Double <formula formulatype="inline"><tex Notation="TeX">${\rm Xe}^{34+}{(2\bar{\rm s}2\bar{\rm p})}$</tex></formula> Vacancy States

Anomalous intensity dependent quenching of the Xe(L) hollow atom emission from the single Xe33+(2p) and double Xe34+(2s2p) vacancy 3d→2p transition arrays indicates the presence of a state-selective curve crossing mechanism for the field ionization of the excited 3d4 configuration by intense (2-3 × 1020 × W/cm2) 248-nm radiation.

Long-distance directed transfer of microwaves in tubular sliding-mode plasma waveguides produced by KrF laser in atmospheric air

A new regime of the sliding-mode propagation of microwave radiation in plasma waveguides in atmospheric air is studied both experimentally and theoretically. The mechanisms of air photoionization and relaxation under propagation of 25-ns pulses of KrF laser are investigated. It is shown that a tubular plasma waveguide of large radius (much larger than wavelength of the microwave signal) can be produced in the photoionization of air molecules by 248-nm radiation of KrF-laser. We experimentally demonstrate the laser-enhanced transfer of 38-GHz microwave signal to a distance of at least 60 m. The mechanism of the transfer is determined by total internal reflection of the signal on the optically less dense wall of the plasma waveguide. Analytical and numerical simulations performed for various waveguide radii and microwave radiation wavelengths show that the propagation length increases with decrease in the wavelength reaching a few kilometers for submillimeter waves. Medium-size KrF laser facility with about 400-J energy in a train of picosecond pulses is suggested for the directed transfer of microwave radiation to 1-km distance.

FEM numerical analysis of excimer laser induced modification in alternating multi-layers of amorphous and nano-crystalline silicon films

UV excimer laser annealing (UV-ELA) is an alternative annealing process that, during the last few years, has gained enormous importance for the CMOS nano-electronic technologies, with the ability to provide films and alloys with electrical and optical properties to fit the desired device performance. The UV-ELA of amorphous (a-) and/or doped nano-crystalline (nc-) silicon films is based on the rapid (nanoseconds) formation of temperature profiles caused by laser radiation that is absorbed in the material and lead to crystallisation, diffusion in solid or even in liquid phase.To achieve the desired temperature profiles and to optimize the parameters involved in the processing of hydrogenated nanocrystalline silicon (nc-Si:H) films with the UV-ELA, a numerical analysis by finite element method (FEM) of a multilayer structure has been performed. The multilayer structures, consisting of thin alternating a-Si:H(10nm) and n-doped nc-Si:H(60nm) layers, deposited on a glass substrate, has also been experimentally analyzed.Temperature profiles caused by 193nm radiation with 25ns pulse length and energy densities ranging from 50mJ/cm2 to 400mJ/cm2 have been calculated. Numerical results allowed us to estimate the dehydrogenation process of the different layers and the diffusion of phosphorous (P) in Si layers as well as their structural modifications as a function of the applied laser energy density. Numerical results are compared with exhaustive characterization of the experimental results.

Laser induced simultaneous etching of silicon and deposition of carbon materials

Silicon (100) substrates have been irradiated in a gaseous atmosphere of diiodo-methane (CH2I2) by employing two different types of laser sources. Either focused 248nm excimer laser pulses or 532nm cw laser radiation have been used. Below the melting temperature of Si, complex etching of Si and deposition of carbon appear simultaneously only for irradiation with 248nm. Above the Si-melting point, the precursor allows efficient etching of Si with a simultaneous deposition of carbon materials for both wavelengths. In particular with focused 532nm radiation high processing rates and aspect ratios of the structures can be achieved.

Recording volume holograms on color centers in a CaF2 crystal

The conditions for preparing photochromic CaF2 crystals, recording holograms with 532-nm radiation in them, and postexposure photothermal treatment of samples with holograms that provide the formation of holographic elements of significant thickness (about 1 cm) are considered. It is shown that the diffraction efficiency of volume holograms in such crystals in the case of reading out by radiation with wave-lengths of 532 and 632.8 nm can be as high as 10–15%. The role of the recording mechanism and the Borrmann effect in the fabrication of these holograms is demonstrated.

Centrosymmetric [N(CH3)4]2TiF6 vs. noncentrosymmetric polar [C(NH2)3]2TiF6: A hydrogen-bonding effect on the out-of-center distortion of TiF6 octahedra

The syntheses, structures, and characterization of organically templated zero-dimensional titanium fluoride materials, A2TiF6 (A[N(CH3)4] or [C(NH2)3]), are reported. Phase pure samples of A2TiF6 were synthesized by either solvothermal reaction method or a simple mixing method. While [N(CH3)4]2TiF6 crystallizes in a centrosymmetric space group, R-3, [C(NH2)3]2TiF6 crystallizes in a noncentrosymmetric polar space group, Cm. The asymmetric out-of-center distortion of TiF6 octahedra in polar [C(NH2)3]2TiF6 are attributable to the hydrogen-bonding interactions between the fluorine atoms in TiF6 octahedra and the nitrogen atoms in the [C(NH2)3]+ cation. Powder second-harmonic generation (SHG) measurements on the [C(NH2)3]2TiF6, using 1064nm radiation, indicate the material has SHG efficiency of 25× that of α-SiO2, which indicates an average nonlinear optical susceptibility, 〈deff〉exp of 2.8pm/V. Additional SHG measurements reveal that the material is not phase-matchable (Type 1). The magnitudes of out-of-center distortions and dipole moment calculations for TiF6 octahedra will be also reported.

New Quaternary Tellurite and Selenite: Synthesis, Structure, and Characterization of Centrosymmetric InVTe2O8 and Noncentrosymmetric InVSe2O8

Two new quaternary mixed metal oxide materials--InVTe(2)O(8) and InVSe(2)O(8)--have been synthesized, as crystals and pure bulk powders by standard solid-state reactions using In(2)O(3), V(2)O(5), and TeO(2) (or SeO(2)) as reagents. The crystal structures of the reported materials were determined using single-crystal X-ray diffraction. InVTe(2)O(8) crystallizes in the monoclinic centrosymmetric space group P2(1)/n (No. 14), with unit-cell parameters of a = 7.8967(16) Å, b = 5.1388(10) Å, c = 16.711(3) Å, β = 94.22(3)°, and Z = 4, and InVSe(2)O(8) crystallizes in the noncentrosymmetric space group Pm (No. 6) with unit-cell parameters of a = 4.6348(9) Å, b = 6.9111(14) Å, c = 10.507(2) Å, β = 97.77(3)°, and Z = 2. While the centrosymmetric InVTe(2)O(8) shows a two-dimensional (2D) layered structure composed of InO(6) octahedra, VO(4) tetrahedra, and TeO(4) polyhedra, the noncentrosymmetric InVSe(2)O(8) exhibits a three-dimensional (3D) framework structure with distorted InO(6) octahedra, VO(5) square pyramids, and SeO(3) polyhedra. Powder second-harmonic generation (SHG) measurements on InVSe(2)O(8), using 1064-nm radiation, indicate that the material has a SHG efficiency ~30 times that of α-SiO(2). Additional SHG measurements reveal that the material is not phase-matchable (Type 1). Infrared, ultraviolet-visible light (UV-vis) diffuse reflectance, and thermogravimetric analyses for the two compounds are also presented, as are dipole moment calculations.

Picosecond Laser Patterning of ITO Thin Films

We present a comparative study of picosecond laser patterning of ITO thin films for OLED applications using 355nm, 532nm and 1064nm radiation. Front side and rear side patterning was investigated and single pulse ablation thresholds were determined for all three wavelengths and both irradiation sides. Good ablation quality was achieved by using 1064nm front side irradiation resulting in a smooth groove bottom, almost vanishing ridges at the groove rims and a neglectable heat affected zone.

Effect of laser shock processing on fatigue crack growth of duplex stainless steel

Duplex stainless steels have wide application in different fields like the ship, petrochemical and chemical industries that is due to their high strength and excellent toughness properties as well as their high corrosion resistance. In this work an investigation is performed to evaluate the effect of laser shock processing on some mechanical properties of 2205 duplex stainless steel. Laser shock processing (LSP) or laser shock peening is a new technique for strengthening metals. This process induces a compressive residual stress field which increases fatigue crack initiation life and reduces fatigue crack growth rate. A convergent lens is used to deliver 2.5J, 8ns laser pulses by a Q-switched Nd:YAG laser, operating at 10Hz with infrared (1064nm) radiation. The pulses are focused to a diameter of 1.5mm. Effect of pulse density in the residual stress field is evaluated. Residual stress distribution as a function of depth is determined by the contour method. It is observed that the higher the pulse density the greater the compressive residual stress. Pulse densities of 900, 1600 and 2500pul/cm2 are used. Pre-cracked compact tension specimens were subjected to LSP process and then tested under cyclic loading with R=0.1. Fatigue crack growth rate is determined and the effect of LSP process parameters is evaluated. In addition fracture toughness is determined in specimens with and without LSP treatment. It is observed that LSP reduces fatigue crack growth and increases fracture toughness if this steel.

Polar Hexagonal Tungsten Oxide (HTO) Materials: (1) Synthesis, Characterization, Functional Properties, and Structure−Property Relationships in A2(MoO3)3(SeO3) (A = Rb+ and Tl+) and (2) Classification, Structural Distortions, and Second-Harmonic Generating Properties of Known Polar HTOs

Two new polar noncentrosymmetric (NCS) oxides, Rb2(MoO3)3(SeO3) and Tl2(MoO3)3(SeO3), have been synthesized and characterized. The materials exhibit the layered hexagonal tungsten oxide (HTO) structural topology—Class 2, i.e., the MoO6 layers are “capped” on one side by the SeO3 polyhedra. The Rb+ and Tl+ cations are found between the layers. The Mo6+ and Se4+ cations are present in asymmetric coordination environments that are attributable to second-order Jahn−Teller (SOJT) effects. In addition to structural characterization, the materials were characterized by second-harmonic generation (SHG), piezoelectric, and polarization measurements. SHG measurements using 1064-nm radiation revealed doubling efficiencies of 300 and 400 × α-SiO2 for the Rb- and Tl-phases, respectively. Piezoelectric experiments revealed d33 values of ∼9−13 pm/V. Polarization measurements indicate that the materials are not ferroelectric, i.e., the polarization is not “switchable”. The materials are pyroelectric, with total pyroelect...

Shapes of laser radiation pulses modified by nonlinear scattering in aqueous suspension of carbon nanotubes

An improved scheme of z-scanning was used to study the parameters of nanosecond 1064-nm laser radiation pulses scattered at right angle under the conditions of optical limiting in an aqueous suspension of purified carbon nanotubes (CNTs). CNTs were synthesized by the electric-arc evaporation of graphite. It is established that the amplitude, shape, duration, and temporal position of the peak of scattered light pulses significantly depend on the laser radiation power density. The results agree with the mechanism of thermoinduced nonlinear scattering that is operative during the optical limiting of laser pulses in CNT suspensions.

Chemically amplified photoresists for 193‐nm photolithography: Effect of molecular structure and photonic parameters on photopatterning

AbstractNext generations of microelectronic devices request further miniaturized systems. In this context, photolithography is a key step and many efforts have been paid to develop new irradiation setup and materials compatible with sub‐100 nm resolution. Among other resist platforms, chemically amplified photoresists (CAR) are widely used because of their excellent properties in terms of resolution, sensitivity, and etching resistance. However, low information on the impact of the polymer structure on the lithography performance is available. CAR with well‐controlled polymer structures were thus prepared and investigated. In particular, the impact of the polymer structure on the lithographic performance was evaluated. Linear and branched polymers with various molecular weights and polydispersities were compared. We focused on the dependency of the photosensitivity of the resist with the structural parameters. These results allow further understanding the fundamental phenomena involved by 193‐nm irradiation. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1271–1277, 2010

Interaction of vacuum ultraviolet excimer laser radiation with fused silica: II. Neutral atom and molecule emission

We report mass-resolved time-of-flight measurements of neutral Si, O, and SiO from ultraviolet-grade fused silica during pulsed 157-nm irradiation at fluences well below the threshold for optical breakdown. Although the emission intensities are strongly affected by thermal treatments that affect the density of strained bonds in the lattice, they are not consistently affected by mechanical treatments that alter the density of point defects, such as polishing and abrasion. We propose that the absorption of single 157 nm photons cleave strained bonds to produce defects that subsequently diffuse to the surface. There they react with dangling bonds to release neutral atoms and molecules. Hartree–Fock calculations on clusters containing these defects support the contention that defect interactions can yield emission. More direct emission by the photoelectronic excitation of antibonding chemical states is also supported.

Investigating the action of the 193-nm and 223-nm radiation of excimer lasers on the cornea of the human eye in refractive surgery

This paper presents a study of the optical properties of the components of the stroma of the human cornea in the wavelength range 190–250nm. It is shown that absorption of 223‐nm radiation by the corneal fluid is a factor of 20 less than of 193‐nm radiation. Because of this effect, the rate and efficiency of ablation of the cornea is about a factor 2 greater for laser radiation with a wavelength of 223nm than for 193‐nm radiation. The temperature on the surface of the cornea has been measured when radiation with wavelengths 193 and 223nm is acting on it. It was found that the relative temperature increase on the surface of the cornea during ablation by wavelength 193nm was 11°C, and during ablation at 223nm only 5°C for identical parameters of operation and laser radiation. It is shown that 223‐nm radiation is preferable for performing refractive operations, as having a number of advantages over the traditionally used 193‐nm radiation.

Ablation of Intraocular Tissue with Fiber-optic Probe–Delivered 266-nm and 213-nm Laser Energy

To explore the tissue ablation properties of pulsed 266-nm and 213-nm laser radiation in porcine retina and the potential for 213-nm laser radiation to cut through human trabecular meshwork. Segments of porcine retinas were used, and localized areas of tissue were exposed to 266-nm or 213-nm laser. Human trabecular meshwork from donor eyes was also ablated using pulsed 213-nm laser. Ocular tissue was bathed in fluid to mimic the intraocular environment. Single or multiple pulses at various fluence levels were delivered with a tapered fiber-optic probe. The tissue was then fixed for histologic examination. Ablation depth and extent of damage were measured and related to fluence level and number of pulses applied. Ablation of the inner retina was achieved by single pulses at fluence levels of 0.6 J/cm(2) and higher with 266-nm laser radiation and 0.2 J/cm(2) and higher with 213-nm laser radiation. At the same fluence, ablation depth was greater (P < 0.001) with 213-nm than 266-nm laser, with less collateral damage. Ablation of human trabecular meshwork using 213-nm laser was highly dependent on fluence after exposure to single and multiple pulses, allowing good control of ablation depth. Laser radiation at 213 nm has greater ablation efficiency, less collateral damage, and a more linear dose-response than ablation at 266 nm. Precise removal of human trabecular meshwork was demonstrated using pulsed 213-nm laser radiation.

Type IIA Grating Inscription in a Highly Nonlinear Microstructured Optical Fiber

The fabrication of Type IIA Bragg reflectors in a highly Ge-doped microstructured optical fiber using 193-nm 10-ns laser radiation is reported. Refractive index evolution curves for both average and modulated index changes are presented, for all the guided modes. Average refractive index changes of the order of 10-3 were obtained, under exposures of 215 mJ/cm2 energy density per pulse. The refractive index evolution curves denote that the two guiding modes do not exhibit the same index engineering behavior due to different overlap with the induced perturbations. The above finding was also confirmed during the thermal annealing performed, where the spectral notches corresponding to these two modes, exhibit a substantially different erasing trend.

Rearrangement of a phosphosilicate glass network induced by the 193-nm radiation

The IR absorption and Raman spectra of phosphosilicate glass (PSG) are measured during its exposure to radiation at a wavelength of 193 nm. The obtained data demonstrate the complicated rearrangement dynamics of the glass network around phosphor atoms and of the glass network as a whole. The experimental dependences are explained by the model of the PSG network based on the concepts of the theory of rigidity percolation.

Experimental Investigation of 193-nm Laser Breakdown in Air

We present the measurements and analysis of laser-induced breakdown processes in dry air at a wavelength of 193 nm by focusing 180-mJ 10-MW high-power 193-nm UV ArF laser radiation onto a 30-mum-radius spot size. We examine pressures ranging from 40 torr to 5 atm, for laser power densities of 1 TW/cm2, well above the threshold power flux for air ionization. The breakdown threshold electric field is measured and compared with classical and quantum theoretical ionization models at this short wavelength. A universal scaling analysis of these results allows one to predict aspects of high-power microwave breakdown based on measured laser breakdown observations. Comparison of 193-nm laser-induced effective field intensities for air breakdown data calculated based on the collisional cascade and multiphoton breakdown theories is used successfully to determine the collisional microwave scaled portion with good agreement regarding both pressure dependence and breakdown threshold electric fields. Using a laser shadowgraphy diagnostic technique, the plasma and shock-wave dynamics are analyzed. Blast shock-wave expansion of the plasma and laser-heated neutral gas is observed with average velocities of 47 km/s, and the temporal shock-wave velocity variation is used to determine electron temperature evolution just behind the shock wave.

Observation of negative alkali ions from alkali halides during 248-nm laser irradiation

Below laser fluences where a plasma is formed (the so-called plasma or plume formation threshold) a number of fundamental phenomena can occur where particles such as atomic and molecular ions, atoms and molecular neutrals, and electrons can be emitted. An understanding of such processes is necessary to develop predictive models for material removal from laser irradiated surfaces—at the foundation of laser etching, machining, and pulsed laser deposition. We have reported on a number of the mechanisms for such emission processes. Here, due to space limitations, we present a summary of our studies on the formation of negative alkali ions from single crystal KCl during exposure to pulsed 248-nm radiation at fluences well below the threshold for plasma formation. Despite the high electron affinities of the corresponding halogen atoms, negative halogen ions were not detected. Significantly, the positive and negative alkali ion distributions overlap strongly in time and space, consistent with K formation by the sequential attachment of two electrons to K+. Negative alkali ions are also observed under comparable conditions from LiF, NaCl, and KBr. In each material, the strong overlap between the positive and negative alkali ion distributions, and the lack of detected negative halogen ions, suggest that negative ion formation involves a similar mechanism.