Mass spectroscopy and ablation characteristics of nylon 6.6 in the ultraviolet

We report on the mass spectroscopic and the laser ablative characteristics of nylon 6.6 [-NH-(CH₂)₆-NH-CO-(-CH₂)₄-CO-] at 193 and 248 nm, using the ArF and KrF excimer lasers. The characteristic parameters of the laser ablative process, such as etch rate at different fluences, the threshold fluence, and the absorption coefficient for both wavelengths were determined. Even at low laser energy, there was a complete breaking of the polymeric chain bonds. The following photofragments were observed at 248 nm: H, H₂, C, CH, CH₂, N, NH, O, OH, H₂O, C₂H, C₂H₂, CN, C₂H₃, HCN, N₂, CO, C₂H₄, COH, C₂H₅, N₂H, NO, C₂H₆, H₂CO, N₂H₂, C₂, CH₂NH, O₂, C₃H₃, C₃H₄, C₃H₅, C₃H₆, CNO, HCNO, and H₂CNO. At 193 nm no photofragments were observed for m/e larger than 30 amu. The photofragments with two carbon atoms have a relatively higher probability to be dissociated from the parent monomer, than heavier photofragments with four carbon atoms. The mass spectroscopic studies and the absorption spectrum of nylon 6.6 in the ultraviolet, suggest photochemical bond-breaking at 248 and 193 nm. The monomer dissociates into fragments with the predominant mass at 28 amu for both laser wavelengths. Therefore the amide group is mainly involved in the photodissociation process of nylon 6.6 in the ultraviolet. The experimental results suggest that the photochemical dissociation of the polymeric chain is the dominant mechanism of the laser ablation of nylon 6.6 at 193 and 248 nm.     

Growth dynamics of carbon-metal particles and nanotubes synthesized by CO2 laser vaporization

To study the growth of carbon-Co/Ni particles and single-wall carbon nanotubes (SWNTs) by 20 ms CO₂ laser-pulse irradiation of a graphite-Co/Ni (1.2 at. %) target in an Ar gas atmosphere (600 Torr), we used emission imaging spectroscopy and shadowgraphy with a temporal resolution of 1.67 ms. Wavelength-selected emission images showed that C₂ emission was strong in the region close to the target (within 2 cm), while for the same region the blackbody radiation from the large clusters or particles increased with increasing distance from the target. Shadowgraph images showed that the viscous flow of carbon and metal species formed a mushroom or a turbulent cloud spreading slowly into the Ar atmosphere, indicating that particles and SWNTs continued to grow as the ejected material cooled. In addition, emission imaging spectroscopy at 1200 °C showed that C₂ and hot clusters and particles with higher emission intensities were distributed over much wider areas. We discuss the growth dynamics of the particles and SWNTs through the interaction of the ambient Ar with the carbon and metal species released from the target by the laser pulse.     

Pulsed laser deposition of tantalum pentoxide film

We report thin tantalum pentoxide (Ta₂O₅) films grown on quartz and silicon substrates by the pulsed laser deposition (PLD) technique employing a Nd:YAG laser (wavelength 5=532 nm) in various O₂ gas environments. The effect of oxygen pressure, substrate temperature, and annealing under UV irradiation using a 172-nm excimer lamp on the properties of the grown films has been studied. The optical properties determined by UV spectrophotometry were also found to be a sensitive function of oxygen pressure in the chamber. At an O₂ pressure of 0.2 mbar and deposition temperatures between 400 and 500 °C, the refractive index of the films was around 2.18 which is very close to the bulk Ta₂O₅ value of 2.2, and an optical transmittance around 90% in the visible region of the spectrum was obtained. X-ray diffraction measurements showed that the as-deposited films were amorphous at temperatures below 500 °C and possessed an orthorhombic (#-Ta₂O₅) crystal structure at temperatures above 600 °C. The most significant result of the present study was that oxygen pressure could be used to control the composition and modulate optical band gap of the films. It was also found that UV annealing can significantly improve the optical and electrical properties of the films deposited at low oxygen pressures (<0.1 mbar).     

Size distributions and synthesis of nanoparticles by photolytic dissociation of ferrocene

Iron-containing nanoparticles were made by laser-assisted (ArF excimer laser, λ=193 nm) photolytic dissociation of ferrocene (Fe(C₅H₅)₂ or FeCp₂) in argon and an oxygen/argon gas mixture. The particle-size distributions were obtained on-line by using differential mobility analysers (DMAs) and were found to be log-normal with a geometric standard deviation of 1.85. In argon, particle sizes between 3 and 100 nm were generated. The volumes of these particles were found to increase linearly with the increased repetition rate, fluence and beam size of the laser. These observations are explained on the basis of the residence-time approach model. Received: 23 November 1999 / Accepted: 19 September 2000 / Published online: 22 November 2000     

Mass spectroscopic and degassing characteristics of polymeric materials for 157 nm photolithography

We report on the mass spectroscopic and the degassing characteristics of an epoxy novolac-based chemically amplified photoresist, with triphenylsulfonium hexafluoroantimonate as photoacid generator, using an F₂ pulsed discharge molecular laser at 157 nm. This photoresist has been used previously for optical (248 nm), e-beam, and X-ray microlithography both in wet and dry development processes. For laser energy of 1 mJ per pulse focused on the sample and 5 MW/cm² intensity, photofragments with m/e less than 40 amu have a higher probability of formation. These fragments are mainly attributed to the breaking of the substituents of the aromatic rings. The specific fragments observed are: H, H₂, C, CH, CH₂, CH₃, O, OH, H₂O, HF, C₂, C₂H, C₂H₂, C₂H₃, CO, C₂H₄, C₂H₅, C₂H₆, H₂CO, OCH₃, O₂, C₃H₃, C₃H₄, C₃H₅, C₃H₆, C₃H₇, C₂H₃O, C₃H₈, C₂H₅O, C₃O, C₃HO, C₃H₂O, C₃H₃O, C₃H₄O, C₃H₅O, C₂HO₂, C₂H₂O₂, C₂H₃O₂, C₂H₄O₂, C₂H₅O₂ and C₂H₆O₂. Comparison of these results with the ones obtained from samples with pure epoxy novolac polymer show that the direct fragmentation of the side polymer bonds is predominant over bond breaking arising from the presence of the triphenylsulfonium salt sensitizer.     

静高压熔态淬火Al70Co15Ni10Tb5合金中十次准晶的相关晶体相C4和C5

 使用静高压熔态淬火方法，在Al₇₀Co₁₅Ni₁₀Tb₅合金中截获到两个新的十次准晶相关相C₄和C₅。其晶胞参数分别为：底心正交晶体（C₄），α=1.38 nm，b=1.60 nm，c=2.0 nm；简单正交晶体（C₅），α=1.20 nm，b=1.60 nm，c=2.30 mn。对二者的高分辨象进行了分析和研究，发现他们有着密切的关系，且可以认为是Penros拼图有序化的结果。     

Gd2O2S:Eu荧光谱及能级的高压研究

 在21 500~11 500 cm^-1光谱区间内测量了Gd₂O₂S:Eu的荧光光谱，测量是在室温和液氮条件下进行的，对122条低温谱线和96条常温谱线进行了指认。识别了Eu³⁺离子⁵D_0~2及⁷F_0~6的39个斯塔克能级中的35个能级。在0~15 GPa压力范围内，研究了Gd₂O₂S:Eu高压下的发射光谱。在压力作用下，发现所有观测到的谱线都红移，强度降低。6个⁵D_0~2能级下降速度大于⁷F_J，⁵D₂、⁷F_2~5多重态的斯塔克劈裂变大，而⁵D₁和⁷F₁的劈裂变小。     

Thermodynamics of Phase Transitions of a Kerr Nonlinear Blackbody

We study the thermodynamics of phase transitions of a blackbody whose interior is filled by a Kerr nonlinear crystal. There is a transition temperature To, above which the Kerr nonlinear blackbody is in the normal thermal radiation state, and below which it is in the squeezed thermal radiation state. At To, the Gibbs free energy of the two phases is continuous but the entropy density of the two phases is discontinuous. Hence, there is a jump in the entropy density and this leads to a latent heat density. The photon system undergoes a first-order phase transition from the normal to the squeezed thermal radiation state.     

Nanocrystalline growth and diagnostics of TiC and TiB2 hard coatings by pulsed laser deposition

Nanocrystalline coatings of TiC and TiB₂ were grown by pulsed laser deposition on Si(100) and on X155 steel at low substrate temperatures ranging from 40 °C to 650 °C. A pulsed KrF excimer laser was used with the deposition chamber at a base pressure of 10^-6 mbar. The morphology and structure of the films, studied with SEM, XRD, and TEM, showed that nanocrystalline films with a fine morphology of TiC and TiB₂ were deposited with a grain size of 10 nm-70 nm at all substrate temperatures. The growth of the polycrystalline coatings possessed a columnar morphology with a 𘜄¢ preferred orientation. The hardness of the coatings was determined to be 40 GPa and the elastic modulus, 240 GPa. The composition and the kinetics of the plume produced during the pulsed laser deposition of TiC and TiB₂ was studied under film growth conditions. The mass analysis of ions of the ejected material was performed by time-of-flight mass spectroscopy (TOF-MS) and showed the presence of Ti⁺ and C⁺ during TiC ablation and B⁺, B₂⁺, and Ti⁺ during TiB₂ ablation. The kinetic energies (KE) of the ions depended on the laser fluence which was between 0.5 eV and 340 eV. The kinetic energy and the evolution of the plasma was studied with a streak camera. The velocity of the plasma was of the order of 10⁶ cm/sec and was linearly dependent on the energy fluence of the laser. The emission spectroscopy of the plasma plume confirmed the atomic neutral and single excited species of Ti. These results show that coating growth basically occurs by the recombination of the ionic species at the surface of the substrate.     

Shadowgraphic and emission imaging spectroscopic studies of the laser ablation of graphite in an Ar gas atmosphere

Laser ablation of graphite in an Ar atmosphere at 560 Torr was done using a nanosecond-pulse Nd:YAG laser (1064 nm) at a fluence of 12 J/cm². Dynamics in the ejection of carbon species and in their confinement near the graphite surface (<1 mm) due to their numerous collisions with Ar atoms were investigated by shadowgraphy, emission imaging, and emission spectroscopy at delay times of 0.01-100 7s following the laser irradiation. A shock wave was generated, and temporally and spatially dependent emissions from Ar⁺ and Ar were observed in addition to those from carbon species (C, C⁺, and C₂) and the Bremsstrahlung radiation from a hot plasma. We suggest that the dissipation of the kinetic and thermal energies of the carbon species, their backward motion, and their collisions with each other lead to the formation of clusters and particles through the interaction with Ar atoms.     

UV Radiation of Low Pressure XeCl* and KrCl* Glow Discharges

The positive column of low pressure DC glow discharges in Xe/Cl₂ and Kr/Cl₂ gas mixtures has been investigated with respect to its UV radiation power and radiative efficiency for a wide range of parameters (total gas pressure: 1–30 mbar, current 10–30 mA, partial pressure of Cl₂: 1–33%). Also the radial distribution of the particle number densities of XeCl* (B) and KrCl* (B) has been determined by absolutely calibrated emission spectroscopy. Optimum UV (190–350 nm) output and efficiency has been found in gas mixtures with a relative Cl₂ partial pressure of 2–3% and total gas pressure of 12–18 mbar. At these parameters, the UV radiation power per column length is greater than 40 Watt/m with a radiative efficiency of 15–18%. These discharges could be used for UV induced photochemical processes.     

Structural and electrical properties of La0.5Sr0.5CoO3 films on SrTiO3 and porous a-Al2O3 substrates

Films of La_0.5Sr_0.5CoO₃ (LSCO) have been deposited on specially treated TiO₂-terminated (001) SrTiO₃ substrate surfaces and on macroporous polycrystalline !-Al₂O₃ substrates, having a mean pore diameter of 80 nm, by pulsed laser deposition. The films deposited on SrTiO₃ are good conducting, (001) textured, and exceptionally smooth (1-2 Å for 100 nm thick films). LSCO films deposited on porous !-Al₂O₃ are polycrystalline and exhibit good crystallographic and electrical properties despite the large substrate roughness and the differences in lattice parameters and crystal structure between the film and the substrate. Different growth modes have been observed on the porous !-Al₂O₃ substrates depending on the oxygen pressure during film deposition. Films grown at an oxygen pressure of 10^-1 mbar are macroporous, whereas films grown at 10^-2 mbar completely cover the substrate pores. In the latter case, strain effects lead to film cracking.     

Analysis of thermal radiation from laser-heated nanoparticles formed by laser-induced decomposition of ferrocene

Thermal radiation, originating from laser-heated gas-phase nanoparticles, was detected in the 400–700 nm wavelength range by means of optical emission spectroscopy. The particles were formed upon laser-induced photolytic decomposition of ferrocene (Fe(C₅H₅)₂) and consisted of an iron core surrounded by a carbon shell. The laser-induced excitation was performed as the particles were still within the reactor zone, and the temperature of the particles could be determined from thermal emission. Both the temperature of the nanoparticles and the relative intensity changes of the emission were monitored as a function of time (with respect to the laser pulse), laser fluence and Ar ambient pressure. At high laser fluences, the particles reached high temperatures, and evidence was found for boiling of iron. Modeling of possible energy-releasing mechanisms such as black-body radiation, thermionic electron emission, evaporation and heat transfer by the ambient gas was also performed. The dominant cooling mechanisms at different ranges of temperature were clarified, together with a determination of the accommodation factor for the Ar–nanoparticle collisions. The strong evaporation at elevated temperatures also led to significant iron loss from the produced particles. PACS 61.46.+w; 81.16.Mk; 65.80.+n     

Optimization of a Dielectric Barrier Discharge for Pulsed UV Emission of XeCl at 308 nm

A pulsed dielectric barrier discharge (DBD) has been investigated in a wide range of experimental conditions with the purpose of optimization for XeCl excimer radiation. For that the following operation parameters had been considered: four different lamps of coaxial geometry with gas gaps in the range of 1.3 ‐ 6.5 mm; gas mixtures of xenon and chlorine containing admixtures of 1%, 2% and 4% Cl₂ at total filling pressures between 5 mbar and 600 mbar; voltage rise times of 20 ‐ 50 ns and voltage amplitudes of up to 12 kV. A maximum radiation pulse energy of 1.8 µ J has been detected at 310 ± 10 nm with an estimated radiation decay by three orders of magnitude within about 5 µ s. It was shown that the minimization of the voltage rise time is essential for enhancing the radiation pulse energy. Furthermore a correlation between the discharge geometry and the optimum pressure for maximum radiation output was observed. The decay characteristics of the excimer emission provides evidence of the harpoon reaction being the main channel of XeCl formation under our operation conditions (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

压力对六角密堆结构金属锂弹性的影响

 采用密度泛涵理论第一原理赝势方法,利用应力和应变的关系计算了压力下六角密堆结构金属锂的弹性常数。计算结果显示,C₁₂、C₁₃随着压力的增加而线性增加,而压力对C₄₄和C₆₆的影响并不大。在各个压力点C₃₃值都要比C₁₁的值大,表明金属锂在z方向的硬度要比x、y方向的硬度大。还发现在理论预测的结构相变区域,C₁₁和C₃₃有一个跳跃。通过对压缩波各向异性参数Δp和剪切波各向异性参数Δs₁、Δs₂的计算发现,零压下Δp＝1,并且高压下Δp值也接近1,表明压缩时金属锂表现出各向同性。Δs₁、Δs₂值远离1,并且随着压力的增加这种远离趋势不断增强,表现很强的剪切弹性各向异性。还讨论了压力对Cauchy关系和相对弹性常数的影响。     

Energy and pressure dependence of the CO2 laser induced dissociation of sulfur hexafluoride

Low pressure SF₆ with its isotopes in natural abundance was irradiated by a pulsed CO₂ laser operated on theP20 line (10.6 μm band). Dissociation yields of³²SF₆ and³⁴SF₆ were measured separately. If the radiation is focussed into the cell, the dissociation yield is proportional to the 3/2 power of the laser energy, as was derived under general conditions and confirmed experimentally. The reaction probabilityP(Φ), the fraction of molecules dissociated by an energy flux Φ, was measured using parallel light. For both isotopes,P(Φ) saturates at high energy flux close toP=1. At a lower flux (2 J cm⁻²), the dissociation probability of³²SF₆ displays a threshold, whereas the dissociation probability of³⁴SF₆ is a very steep function of Φ over the whole range of fluxes.P(Φ) at the higher energy flux was measured in a cavity absorption cell, in which up to 80% of the molecules were dissociated by a single pulse. Below 0.2 mbar SF₆ the dissociation yields for both isotopes are pressure independent. Above 2 mbar the isotopic selectivity is completely lost. Addition of hydrogen always decreases the dissociation yields.     

冲击波作用下碳水混合物发射光谱研究

 利用二级轻气炮和OMA-Ⅲ光多通道系统,分别研究金刚石与水、石墨与水两种碳水混合物在冲击波作用下的发射光谱。冲击压力高于16.41 GPa时,观测到350～750 nm波段内叠加在连续辐射背景上的发射谱;当冲击压力高于33.95 GPa时,C₂、CO、CO₂的谱线辐射明显,表明碳和水发生了化学反应。     

Effect of ambient nitrogen pressure on the formation and spatio-temporal behaviour of C<Subscript>2</Subscript> and CN

We report the effect of ambient gas on the formation as well as propagation behaviour of ablated species C₂ and CN within the carbon plasma created by focussing a high-power Nd:YAG (λ = 1064 nm) laser onto the rotating graphite target in the nitrogen ambient. The formation of C₂ takes place earlier as well as nearer the target compared to that of CN which forms later and far from the target, in 1.2 mbar pressure of N₂ gas. Peak arrival time vs. nitrogen gas pressure plot shows a shock wave-like dependence t ∝ p ⁿ in the pressure range 1.2–120 mbar (collisional regime) which indicates plume confinement with increases in ambient pressure. At higher pressure, thermalization takes place.     

高温高压下SrB4O7：Eu2+玻璃的晶化

 利用X射线衍射和Eu²⁺发射光谱方法研究了非晶玻璃SrB₄O₇在高温高压下的晶化。结果表明：在5.0 GPa压力下，200 ℃仍为玻璃态，只有几个强度极低的小峰，表明有晶化的迹象；600 ℃时已基本晶化，但为SrB₄O₇正交相与SrB₄O₇高压立方相二相共存；当温度提高到1 000 ℃时，晶化成了近单相的与常压SrB₄O₇粉末晶体相同的正交结构。伴随晶化度的加强，Eu²⁺发射强度增强，与Ｘ射线衍射结果相一致。     

Magnetic Behaviour of Sm2Co7/Fe/Sm2 Co7, Nanocomposite Trilayers with Cr and Ti Additions

Trilayered Sm2Co7/Fe/Sm2Co7 spring exchange magnets are fabricated by dc magnetron sputtering on MgO substrates. Very thin layers （0.3-0.7 nm） of Cr and Ti are added at the interfaces of the two magnetic phases. The thickness of StucCo7 is kept at 20nm and Fe at 6nm while the thickness of Cr and Ti are varied as 0.3, 0.5, and 0.7nm. The base pressure of sputtering chamber is kept below 10^-7 Torr and Ar pressure at 3-8m Torr. The samples are characterized by x-ray diffraction （XRD） and SQUID magnetometer. We report improvement in exchange coupling of nonacomposite magnets by addition of thin layers of Cr at interfaces.