Dewetting process of Au films on SiO2 nanowires: Activation energy evaluation

SiO₂ nanowires gain scientific and technological interest in application fields ranging from nano-electronics, optics and photonics to bio-sensing. Furthermore, the SiO₂ nanowires chemical and physical properties, and so their performances in devices, can be enhanced if decorated by metal nanoparticles (such Au) due to local plasmonic effects.In the present paper, we propose a simple, low-cost and high-throughput three-steps methodology for the mass-production of Au nanoparticles coated SiO₂ nanowires. It is based on (1) production of the SiO₂ nanowires on Si surface by solid state reaction of an Au film with the Si substrate at high temperature; (2) sputtering deposition of Au on the SiO₂ nanowires to obtain the nanowires coated by an Au film; and (3) furnace annealing processes to induce the Au film dewetting on the SiO₂ nanowires surface. Using scanning electron microscopy analyses, we followed the change of the Au nanoparticles mean versus the annealing time extracting values for the characteristic activation energy of the dewetting process of the Au film on the SiO₂ nanowires surface. Such a study can allow the tuning of the nanowires/nanoparticles sizes for desired technological applications.     

Optical characteristics of thin rutile films on fused quartz substrates

Polycrystalline rutile films are synthesized on fused quartz substrates by the method of thermal oxidation of a titanium metal layer in air at 800°C. The optical parameters of the TiO ₂ films are determined for a wavelength of λ = 0.6328 μm by the method of laser zero ellipsometry. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 15–20, May, 2006.     

Defect formation of Au thin films on SiO2/Si upon annealing

We have studied structural changes of Au film surfaces grown on Si with native oxide layers. Using X-ray photoelectron spectroscopy (XPS), we found that annealing above 200°C can cause formation of defects (or cracks), which is most likely driven by interdiffusion of Au and Si accompanying strong Au–Si interactions at the interface regime. Scanning tunneling microscopy (STM) study is also in line with defect formation upon annealing. Interaction of O₂ with rough Au surfaces is discussed in connection with catalytic activities of Au surfaces.     

SiO2／Si衬底上聚苯乙稀薄膜的退湿润过程观测

采用光学显微镜和原子力显微镜观测了光滑SiO2衬底上聚苯乙稀薄膜的退湿润过程. 观测到成核退湿润过程为:初态时,在聚苯乙稀薄膜中出现随机分布的小孔,并且小孔随着时间的增加而逐渐变大,孔的尺寸的变化与时间成正比;终态时观测到聚苯乙稀小球在SiO2衬底上的蜂窝状分布,聚苯乙稀小球的分布与薄膜表面的缺陷密切相关.     

Thin SiO2 films on GaAs substrates

The formation of thin dielectric SiO₂ films on n-type GaAs substrates and obtained results on the investigation of their physical and chemical parameters are described. The SiO₂ films are produced by low-temperature deposition of tetraethoxisilane in the continuous flow system with argon as a carrier gas. Some of the technological aspects of this preparation (as the growth conditions and proper apparatus) are discussed in great detail. For improvement of some typical parameters (infrared spectra, etch rate and permitivity) a suitable thermal treatment is recommended. From the results we have achieved, the potential possibilities for construction of various types of electronic devices are also proposed.The authors wish to thank Ing. I.Srb for infrared spectra measurements. The technical assistance of Mrs. O.Janouková is also greatly appreciated.     

Crystallization of thin polycrystalline PZT films on Si/SiO2/Pt substrates

This paper reports on a study of crystallization of thin lead zirconate-titanate films deposited on Si/SiO₂/Pt substrates by RF magnetron sputtering at a low temperature and annealed at 540–580°C. In this temperature interval, one observes successively two first-order phase transitions: the low-temperature pyrochlore phase—perovskite-I phase and perovskite-I phase-perovskite-II phase transitions, which are accompanied by film volume shrinkage. The phase transformations have been studied by atomic force microscopy, scanning electron microscopy, X-ray diffraction and visual (optical) observation of the growth of islands of a new phase. It has been found that the dielectric parameters undergo substantial changes upon the transition from phase I to phase II. The origin of the observed effects has been discussed.     

Photoacoustic spectroscopy of thin SiO2 films grown on (100) crystalline Si substrates

Photoacoustic Spectroscopy (PAS) has been used to measure the thickness of thin SiO₂ films grown on (100) Si wafers. The data are in reasonable agreement with a simple theoretical model. It suggests that photoacoustic Spectroscopy is complementary to optical interferometry, in that it is capable of giving quantitative estimates of thin transparent films on opaque substrates of low reflectivity via the transmitted fraction of the optical energy incident on the sample. Both theoretical and experimental results indicate that PAS can be very useful in the measurement of thin films on substrates of low reflectivity.     

Growth of Nb thin films on SiO2

Nb thin films have been prepared by electron beam evaporation under ultrahigh vacuum conditions on fused silica substrates at various temperatures, and their structural and morphological evolutions have been investigated using X-ray diffraction and atomic force microscopy. The crystallographic texture of the Nb films is found to depend on the growth temperature. At room temperature, the [1 1 0] texture is dominant. However, at 200°C, the [3 1 0] oriented growth is favored, co-existing with [1 1 0] and [2 0 0] oriented grains. At 400–600°C, a completely [1 1 0] textured film is formed. At even higher temperature (800°C), a complex texture of [1 1 0] (dominant), [2 0 0] and [3 1 0] is observed again. It is also found that the single [1 1 0] textured Nb films have smooth surfaces, and the complex textured Nb films have rough surfaces.     

Optical properties of ZnO thin films on SiO2 substrates deposited by radio frequency magnetron sputtering

The optical properties of both the annealed and as-deposited ZnO thin films by radio frequency (RF)magnetron sputtering on SiO2 substrates were studied. In the annealed films, two pronounced well defined exciton absorption peaks for the A and B excitons were obtained in the absorption spectra, a strong free exciton emission without deep-level emissions was observed in the photoluminescence (PL) spectra at room temperature. It was found that annealing the films in oxygen dramatically improved the optical properties and the quality of the films.     

Third-order nonlinear optical response of Au:SiO 2 thin films: Influence of gold nanoparticle concentration and morphologic parameters

We report a study on the third-order nonlinear optical properties of nanocomposite thin films composed of gold particles embedded in a silica host matrix. Samples of various metal volume fractions, ranging from 8 to 35%, are synthesized by the sputtering technique. Some of them are annealed. Nonlinear optical measurements, which are performed by using the z-scan technique, reveal both a very large nonlinear absorption and a weak nonlinear refraction close to the surface plasmon resonance frequency of the particles. We especially study the effect of the metal concentration and the influence of thermal treatment on the real and imaginary components of the third-order nonlinear susceptibility. Our results reveal that, as the metal concentration reaches a few percent, the mutual electromagnetic interactions between particles greatly enlarge the nonlinear optical response of the material and can not be neglected in the theoretical analysis. Moreover, the thermal treatment leads, for a given concentration, to a significant increase of the nonlinear response, which is ascribed to a modification of the material morphology. We finally point out that the material nonlinear properties are very sensitive to the incident wavelength through the local field enhancement phenomenon. Received 12 December 2001     

Enhanced hardness in B-doped ZnO thin films on fused quartz substrates by pulsed-laser deposition

B-doped ZnO thin films have been fabricated on fused quartz substrates using boron-ZnO mosaic target by pulsed-laser deposition technique, and the mechanical properties have been studied by nanoindentation continuous stiffness measurement technique and transmission electron microscope (TEM). Nanoindentation measurement revealed that the hardness of B-doped ZnO films, 9.32 ± 0.90 to 12.10 ± 1.00 GPa, is much greater than that of undoped ZnO films and very close to that of traditional semiconductor Si. The mean transmittance (%) is larger than 81% in the visible range (380-780 nm) for all the films, and the Hall effect measurement showed that the carrier density is around 2 × 10²⁰ cm⁻³ and the resistivity lower than 3 × 10⁻³ Ω cm. TEM characteristics show undoped thin films have more amorphous area between grains while the B-doped ZnO films have thin grain boundaries. We suggest that the grain boundaries act as the strain compensation sites and the decrease in thickness of grain boundaries enhances the hardness of the B-doped ZnO films.     

Au/SiO2纳米复合薄膜的微结构及光吸收特性研究

用多靶磁控溅射技术制备了Au/SiO2纳米多层薄膜.利用透射电子显微镜以及吸收光谱对Au/SiO2复合薄膜的微观结构、表面形貌及光学性能进行了表征和测试.研究结果表明:单层Au/SiO2薄膜中Au沉积时间小于10s时,分散在SiO2中的Au颗粒随Au的沉积时间的延长而增大;当沉积时间超过10s后,Au颗粒的尺寸几乎不随沉积时间变化,但Au颗粒的形状由网络状结构变为薄膜状结构.[Au(t1)SiO2(600)]×5多层薄膜在540-560nm波长附近有明显的表面等离子共振吸收峰,且吸收峰的强度随Au的沉积时间增加而增强.基于修正后的Maxwell-Garnett (M-G)有效媒质理论,讨论了金属颗粒的形状对等离子共振吸收峰的峰位和强度的影响.模拟的吸收光谱与实验吸收光谱形状、趋势及吸收峰位相符合.     

(Au,Si)/SiO2复合纳米颗粒薄膜的光谱特性

采用复合靶共溅射法制备了(Au，Si)／SiO2复合纳米颗粒薄膜样品，并对其荧光谱作了测量．在理论上分别计算了在强限域效应下和弱限域效应下Si纳晶吸收光谱的峰值位置与晶粒尺寸之间的关系，并采用Drude理论计算了Au／SiO2复合体系的吸收峰的峰值位置与微粒尺寸的关系．给出了(Au，Si)／SiO2体系复合薄膜共振吸收峰的位置随Au和Si的掺杂浓度比和微粒尺寸的相关特征．     

Structural influence on the 2D-conductivity of thin Au films

Thin gold films (60Å–500Å) are prepared simultaneously onto carbon coated quartz- and NaCl-crystals at different substrate temperatures (5 KT300 K) in uhv. For the Au-films condensed onto the quartz substrates the temperature dependence of the electrical resistivity is measured between 1.7 K and 300 K in situ. The corresponding Au-films condensed onto NaCl are removed and investigated in an EM. The observed hole and channel structures are related to the 2D-conductivity behavior.Dedicated to B. Mühlschlegel on the occasion of his 60th birthday     

Characterization of ZnO thin films grown on various substrates by RF magnetron sputtering

In this study we investigated properties of ZnO thin films deposited on both oxygen-containing substrates and a substrate without oxygen content at various O₂/Ar reactant gas ratios. Deposition of ZnO on indium-tin oxide (ITO) resulted in the best crystallinity, whereas the least degree of crystallization was observed from ZnO deposited on glass. All the films were found to have compressive stress, which was relieved by annealing in O₂ environment. ZnO films deposited on glass revealed p-type conductivity when prepared at O₂/Ar ratio of 0.25 whereas those on SiN_x yielded p-type conductivity when prepared at O₂/Ar ratio of 4. In addition, shallower oxygen interstitial seemed to be found from films with better crystallinity. The largest shift in binding energy of Zn_2p3/2 was observed from ZnO prepared on glass at O₂/Ar ratio of 0.25, whereas that of O_1s was obtained from ZnO deposited on SiN_x at O₂/Ar ratio of 4. A model was proposed in terms of O₂ diffusion and hydrogen desorption in order to account for the observed property variations depending on substrates and O₂/Ar ratios.     

Au/SiO2纳米多层薄膜的制备及其性质表征

利用多靶磁控溅射技术制备了Au/SiO2纳米颗粒分散氧化物多层复合薄膜.研究了在保持Au单层颗粒膜沉积时间一定时薄膜厚度一定、变化SiO2的沉积时间及SiO2的沉积时间一定而改变薄膜厚度时,多层薄膜在薄膜厚度方向的微观结构对吸收光谱的影响.研究结果表明:具有纳米层状结构的Au/SiO2多层薄膜在560nm波长附近有明显的表面等离子共振吸收峰,吸收峰的强度随Au颗粒的浓度增加而增强,在Au颗粒浓度相同的情况下,复合薄膜光学吸收强度随薄膜厚度的增加而增强.但当金属颗粒的浓度增加到一定程度时,金属颗粒相互接触,没有观察到纳米层状结构,薄膜不显示共振吸收峰特征.用修正后的M-G(Maxwell-Garnett)理论对吸收光谱进行了模拟,得到了与实验一致的结果.     

Ferroelectric SrxBa1-xNb2O6 optical waveguiding thin films on SiO2-coated Si(100) substrates

x Ba_1-xNb₂O₆ (x=0.5) films (abbreviated as SBN:0.5) on SiO₂-coated Si substrates are potential components for the application of integrated electro-optics devices. SBN:0.5 optical waveguiding thin films on SiO₂-coated Si substrates with a very thin MgO diffusion buffer have been successfully prepared by pulsed laser deposition. The as-grown films have a refractive index of 2.28, which is close to that of bulk SBN. X-ray analysis showed that the as-grown films have a single-phase tetragonal tungsten bronze structure. The SBN:0.5 thin films prepared by PLD exhibit favorable ferroelectric and optical waveguiding properties. The composition and the morphology of the films were also examined by XPS and by SEM, respectively. Ferroelectric SBN:0.5 optical waveguiding thin films on SiO₂-coated Si substrates are expected to be used in integrated electro-optic devices. Received: 27 February 1997/Accepted: 17 October 1997     

Magnetron sputtering of thin Cu(200) films on Ni(200)/SiO2/Si substrates

The possibility of oriented growth of thin copper films with a (200) texture on a SiO₂/Si substrate by magnetron sputtering in medium vacuum is demonstrated for the case when a predeposited nickel layer with a (200) texture serves as an orienting sublayer.