Influence of the addition of silsesquioxane on the dewetting behavior of polystyrene thin film

A strategy to suppress the dewetting of polystyrene (PS) thin films by the addition of octacyclopentylsilsesquioxane (cPOSS) as a nanofiller was proposed. PS thin films with cPOSS were prepared by spin-coating. The bulk glass transition temperature of PS was not changed with an addition of the nanofiller up to 10 wt%. On the other hand, the addition of cPOSS to the PS thin films led to a great inhibition of dewetting. After annealing for 3 h at 373 K, no appreciable dewetting was observed by optical microscopy in the PS film with 15 wt% cPOSS, in contrast, the PS film without cPOSS was completely dewetted. Holes formed on the PS films with 10 wt% cPOSS. However, in that case, the growth of the holes stopped before reaching the final stage of the dewetting. This suggests that the increase of the cPOSS concentration per unit area at the rim of the holes prevents further growth of the holes, and this inhibition effect can be attributed to the interaction between cPOSS and the substrate accompanying modification of the PS-substrate interface.     

Effect of substrate temperature on the surface and interface oxidation of NiTi thin films

NiTi shape memory alloy thin films are deposited on pure Cu substrate at substrate ambient temperatures of 300 °C and 450 °C. The surface and interface oxidation of NiTi thin films are characterized by X-ray photoelectron spectroscopy (XPS). After a subsequent annealing treatment the crystallization behavior of the films deposited on substrate at different temperatures is studied by X-ray diffraction (XRD). The effects of substrate temperature on the surface and interface oxidation of NiTi thin films are investigated. In the film surface this is an oxide layer composed of TiO₂. The Ni atom has not been detected on surface. In the film/substrate interface there is an oxide layer with a mixture Ti₂O₃ and NiO in the films deposited at substrate temperatures 300 °C and 450 °C. In the films deposited at ambient temperature, the interface layer contains Ti suboxides (TiO) and metallic Ni.     

The effect of ion energy on the formation of the silicon carbide interface of hydrogenated amorphous carbon films grown on silicon by plasma assisted chemical vapor deposition

The interface of hydrogenated amorphous carbon films grown on single crystal silicon by plasma assisted chemical vapor deposition from methane was studied by angle-resolved X-ray photoelectron spectroscopy. The effect of varying RF power for films grown on a RF-powered electrode was investigated, as well as the effect of varying pulse height for films grown under high voltage pulsed biasing on a non-RF-powered electrode. The spectra of the films deposited at the powered electrode revealed the presence of an approximately stoichiometric silicon carbide layer at the interface. In contrast, the interfacial carbide for films formed at the pulsed biased electrode was found to be nonstoichiometric and silicon rich, which could be ascribed to the relatively much smaller high-energy ion flux to the substrate. The effective thickness of the interfacial layer, as determined from the angle-resolved spectra, however, correlated well with the kinetic energy of plasma ions impinging on the silicon substrate, regardless of the average stoichiometry. The thickness varied from ˜ 4 to 12 Å for kinetic energies ranging from ˜ 150 to 1100 eV. The results indicate that the thickness of the interfacial carbide is determined by the average penetration depth of plasma ions into the silicon substrate, as controlled by their kinetic energy.     

Structure and photoluminescence properties of ZnS films grown on porous Si substrates

ZnS films were deposited on porous silicon (PS) substrates with different porosities. With the increase of PS substrate porosity, the XRD diffraction peak intensity decreases and the surface morphology of the ZnS films becomes rougher. Voids appear in the films, due to the increased roughness of PS structure. The photoluminescence (PL) spectra of the samples before and after deposition of ZnS were measured to study the effect of substrate porosity on the luminescence properties of ZnS/PS composites. As-prepared PS substrates emit strong red light. The red PL peak of PS after deposition of ZnS shows an obvious blueshift. As PS substrate porosity increases, the trend of blueshift increases. A green emission at about 550 nm was also observed when the porosity of PS increased, which is ascribed to the defect-center luminescence of ZnS. The effect of annealing time on the structural and luminescence properties of ZnS/PS composites were also studied. With the increase of annealing time, the XRD diffraction peak intensity and the self-activated luminescence intensity of ZnS increase, and, the surface morphology of the ZnS films becomes smooth and compact. However, the red emission intensity of PS decreases, which was associated with a redshift. White light emission was obtained by combining the luminescence of ZnS with the luminescence of PS.     

Annealing effects on the surface morphologies of thin PS/PMMA blend films with different film thickness

The surface morphology evolution of three thin polystyrene (PS)/polymethyl methacrylate (PMMA) blend films (<70 nm) on SiO_x substrates upon annealing were investigated by atomic force microscopy (AFM) and some interesting phenomena were observed. All the spin-coated PS/PMMA blend films were not in thermodynamic equilibrium. For the 67.1 and the 27.2 nm PS/PMMA blend films, owing to the low mobility of the PMMA-rich phase layer at substrate surfaces and interfacial stabilization caused by long-range van der Waals forces of the substrates, the long-lived metastable surface morphologies (the foam-like and the bicontinuous morphologies) were first observed. For the two-dimensional ultrathin PS/PMMA blend film (16.3 nm), the discrete domains of the PS-rich phases upon the PMMA-rich phase layer formed and the secondary phase separation occurred after a longer annealing time.     

溶液法制备PVP为界面修饰层的红荧烯结晶性薄膜

为了获得低成本、高结晶度的红荧烯薄膜,采用溶液加工的方法和聚合物界面修饰层研究了红荧烯薄膜的性质。首先,通过旋涂方法在Si/SiO₂衬底上先沉积一层聚乙烯吡咯烷酮（PVP）作为界面修饰层,利用偏光显微镜（POM）、原子力显微镜（AFM）研究了PVP层表面形貌及粗糙度。接着在PVP上滴涂红荧烯溶液后固化烘干,制备红荧烯晶体薄膜,研究了不同PVP浓度和不同成膜温度下界面修饰层对红荧烯表面形貌的影响。然后,利用X射线衍射（XRD）表征对比研究了薄膜的微观结构。最后,分析了红荧烯晶体薄膜的生长机制。实验结果表明：80~140℃及低浓度的PVP条件下能得到结晶度高、连续的红荧烯球晶,并且温度升高时,球晶尺寸变大。PVP作为界面修饰层有利于改善红荧烯的成膜性,制备高结晶度的晶体薄膜。     

Photon irradiation-induced structural and interfacial phenomena in pure and alio-valently doped zirconia thin films

We report on the effect of ultra-violet (UV) irradiation on structural and interfacial phenomena in pure and doped zirconia thin film grown by physical vapour deposition. Interfacial layer formation by substrate oxidation and resultant densification of zirconia layer was found in yttria-doped zirconia (YDZ) films grown on Si, while no change was observed in identical films grown on Ge. A comparison of un-doped zirconia and YDZ films indicates yttria-doping significantly assists structural changes during UV irradiation. Interestingly, the effect of UV photons becomes minimal at ～300°C in films grown on Si, while the effect of UV becomes more pronounced in YDZ films grown on Ge. An interfacial layer was formed between the YDZ and Ge substrate at 300°C in the presence of UV irradiation, in contrast to the sharp interface maintained, even after annealing at 300°C, without UV. The results suggest that photon irradiation may be an elegant approach to tailor structural and interfacial properties at near-atomic length scales.     

Substrate effect on mechanical relaxation of polystyrene in ultrathin films

Mechanical relaxation behavior in ultrathin polystyrene (PS) films supported on silicon oxide (SiO_x) and gold (Au) substrates has been studied by dynamic viscoelastic measurement. Based on the method, effects of free surface and substrate interface on the segmental dynamics were discussed. In the case of thin PS films with a thickness of approximately 200 nm, α_a-relaxation process corresponding to the segmental motion did not show any deviation from the bulk behavior. In contrast, for the films thinner than about 50 nm, the relaxation time distribution for the α_a-process became broader, probably due to a mobility gradient in the surface and interfacial regions. When we sandwiched an ultrathin PS film between SiO_x layers, another relaxation process, in addition to the original α_a-process, appeared at a higher temperature side that we assigned to the interfacial α_a-relaxation process. However, this was never seen for an ultrathin PS film between Au layers, implying that restriction from the substrate interface might be weak in this case.     

The timescale of spinodal dewetting at a polymer/polymer interface

We investigate the dynamics of spinodal dewetting in liquid-liquid polymer systems. Dewetting of poly(methyl-methacrylate) (PMMA) thin films on polystyrene (PS) “substrates” is followed in situ using neutron reflectivity. By following the development of roughness at the PS/PMMA interface and the PMMA surface we extract characteristic growth times for the dewetting process. These characteristic growth times are measured as a function of the molecular weight of the two polymers. By also carrying out experiments in the regime where the dynamics are independent of the PS molecular weight, we are able to use dewetting to probe the scaling of the PMMA thin film viscosity with temperature and molecular weight. We find that this scaling reflects bulk behaviour. However, absolute values are low compared to bulk viscosities, which we suggest may be due in part to slippage at the polymer/polymer interface. Received 25 June 2001 and Received in final form 5 December 2001     

Glass transition temperature of freely-standing films of atactic poly(methyl methacrylate)

We have used ellipsometry to measure the glass transition temperature T(g) of high molecular weight (M(w)=790 x 10(3)), freely-standing films of atactic poly(methyl methacrylate) (a-PMMA), as well as films of the same polymer supported on two different substrates: the native oxide layer of silicon (Si) and gold-covered Si. We observe linear reductions in T(g) with decreasing film thickness h for the freely-standing PMMA films with 30 nm < h<100 nm, which is qualitatively similar to previous results obtained for freely-standing polystyrene (PS) films. However the magnitude of the T(g) reductions for PMMA is much less than for freely-standing films of PS of comparable molecular weight and thickness. We also find that for films supported on either substrate, with thicknesses as small as 30 nm, the T(g) values do not deviate substantially from the value measured for thick films.     

矫顽力可调的多孔硅基Fe膜

采用电化学腐蚀法制备了不同多孔度的多孔硅(PS),再通过磁控溅射法在该PS衬底上沉积了一定厚度的Fe膜;并对样品进行了X射线衍射的结构分析、扫描隧道显微技术的表面形貌观察和磁光克尔效应的测量.发现在同一Fe膜厚度下，相对于参考样品硅上的Fe膜，多孔硅上Fe膜的矫顽力更大;同时观察到多孔硅基Fe膜随着PS多孔度的增加，矫顽力相应变大;而对于多孔度相同的多孔硅基样品,随着Fe膜厚度的增加矫顽力却逐步减小.得出了多孔硅特有的海绵状疏松结构能有效调节Fe膜矫顽力大小的结论. 关键词： 多孔硅 海绵状结构 Fe薄膜 矫顽力     

Vertical phase separation in spin-coated films of a low bandgap polyfluorene/PCBM blend—Effects of specific substrate interaction

We report on the effect of the substrate on the vertical phase separation in spin-coated thin films of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-5,5-4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole] (APFO-3) blended with [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM). Compositional depth profiles of the films are measured by dynamic secondary ion mass spectrometry (SIMS). We found that changing the substrate from silicon to gold affects the composition profile near the substrate interface. This is caused by a specific interaction between the polymer (APFO-3) and the gold surface, as confirmed by X-ray photoelectron spectroscopy (XPS). The composition profile in the area away from the substrate interface, as well as the enrichment of the free surface with APFO-3, remain however unaffected by the choice of substrate. The vertical composition was also analysed for APFO-3:PCBM films spin-coated on indium tin oxide (ITO) coated with a thin layer of (3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS).     

The properties of free polymer surfaces and their influence on the glass transition temperature of thin polystyrene films

We present a detailed study of free polymer surfaces and their effects on the measured glass transition temperature (T_g) of thin polystyrene (PS) films. Direct measurements of the near-surface properties of PS films are made by monitoring the embedding of 10 and 20 nm diameter gold spheres into the surface of spin-cast PS films. At a temperature T = 378K( > T_g), the embedding of the spheres is driven by geometrical considerations arising from the wetting of the gold spheres by the PS. At temperatures below T_g ( 363K < T < 370K), both sets of spheres embed 3-4 nm into the PS films and stop. These studies suggest that a liquid-like surface layer exists in glassy PS films and also provide an estimate for the lower bound of the thickness of this layer of 3-4 nm. This qualitative idea is supported by a series of calculations based upon a previously developed theoretical model for the indentation of nanoscale spheres into linear viscoelastic materials. Comparing data with simulations shows that this surface layer has properties similar to those of a bulk sample of PS having a temperature of 374 K. Ellipsometric measurements of the T_g are also performed on thin spin-cast PS films with thicknesses in the range 8nm < h < 290nm. Measurements are performed on thin PS films that have been capped by thermally evaporating 5 nm thick metal (Au and Al) capping layers on top of the polymer. The measured T_g values (as well as polymer metal interface structure) in such samples depend on the metal used as the capping layer, and cast doubt on the general validity of using evaporative deposition to cover the free surface. We also prepared films that were capped by a new non-evaporative procedure. These films were shown to have a T_g that is the same as that of bulk PS (370±1 K) for all film thicknesses measured (> 7 nm). The subsequent removal of the metal layer from these films was shown to restore a thickness-dependent T_g in these samples that was essentially the same as that observed for uncapped PS films. An estimate of the thickness of the liquid-like surface layer was also extracted from the ellipsometry measurements and was found to be 5±1 nm. The combined ellipsometry and embedding studies provide strong evidence for the existence of a liquid-like surface layer in thin glassy PS films. They show that the presence of the free surface is an important parameter in determining the existence of T_g reductions in thin PS films.     

金刚石薄膜红外椭圆偏振参量的计算与拟合

用红外椭圆偏振仪对热丝化学气相沉积法制备的金刚石薄膜的光学参量进行了测量。由于表面状态和界面特性的差异，分别对镜面抛光硅片和粗糙氧化铝基片上的金刚石薄膜建立了不同的模型，并在此基础上进行了测试结果的计算拟合。为了综合反应诸如表面粗糙度等表面界面因素对测试结果的影响，根据衬底特性将表面层和界面层分离出来，并采用Bruggeman有效介质方法对它们的影响进行了近似处理。结果表明，硅衬底上金刚石薄膜的椭偏数据在模型引入了厚度为879nm的表面粗糙层之后能得到很好的拟合。而对于氧化铝衬底上的金刚石薄膜而言，除了在薄膜表面引入了粗糙层之外，还必须在衬底和金刚石界面处加入一层由体积分数为0．641的氧化铝、体积分数为0．2334的金刚石和体积分数为0．1253的空隙组成的复合过渡层(厚度995nm)，才能使计算值与实验参量很好地吻合。     

退火对ZnS/PS复合体系光致发光特性的影响

用脉冲激光沉积(PLD)技术以多孔硅(PS)为衬底生长了ZnS薄膜,分别测量了ZnS、PS以及ZnS/PS复合体系在室温下的光致发光(PL)光谱。结果发现,ZnS/PS复合体系的PL光谱中PS的发光峰位相对于新制备的PS有所蓝移。把该ZnS/PS样品分成三块,在真空400℃分别退火10,20,30 min,研究不同退火时间对ZnS/PS复合体系光致发光特性的影响。发现退火后样品的PL光谱中都出现了一个新的绿色发光带,归结为ZnS的缺陷中心发光。随着退火时间的延长,PS的发光强度逐渐降低且峰位红移。把ZnS的蓝、绿光与PS的红光相叠加,整个ZnS/PS复合体系在可见光区450~700 nm形成一个较宽的光致发光谱带,呈现较强的白光发射。     

Thickness dependence of the work function in double-layer metallic films

The work function of metallic thin films limited by symmetric surfaces is expected to be thickness dependent at a level of 0.1 eV and a thickness range of about 5 nm. Recent experiments, however, demonstrated that Cu films on glass or Ni substrates show a long ranging (10–20 nm) increase of the work function with increasing film thickness [1]. This effect was attributed to a violation of local charge neutrality in films with unlike surfaces. In this paper we show that the barrier height of thin film diodes like metal-insulator-metal (MIM)-, metal-semiconductor (Schottky contacts)-and metal-vacuum-metal (Kelvin capacitors) structures decreases with increasing thickness of one metal electrode. This metal electrode consists of a double layer whose single layer thicknesses are of the order of few tens of nm. The observed effect can be attributed to a decrease of the work function at the counter limiting interface not exposed to the evaporation beam. A possible explanation can be found again in the violation of the local charge neutrality in films with unlike surfaces.     

表面增强拉曼光谱研究高分子共混物薄膜相结构

采用拉曼光谱法研究了由聚苯乙烯(PS)/聚甲基丙烯酸甲酯(PMMA)的四氢呋喃(THF)溶液在玻璃基板上旋转涂膜得到的共混物薄膜。应用显微共焦拉曼光谱,根据PS在1604,1585cm-1处苯环的伸缩振动峰和PMMA在1728cm-1处羰基的伸缩振动峰,可以确定薄膜(厚度约为800nm)表面海岛状相结构的组分分布信息。另外,还对210℃下PS/PMMA(30/70)共混物薄膜退火过程中表面的变化进行了分析。采用表面增强拉曼散射效应对高聚物的增强作用得到了薄膜(厚度约为400nm)的Raman光谱,并且成功地对其组成进行了分析。     

Surface dynamics of polymer films

The dynamics of supported polymer films were studied by probing the surface height fluctuations as a function of lateral length scale using x-ray photon correlation spectroscopy. Measurements were performed on polystyrene (PS) films of thicknesses varying from 84 to 333 nm at temperatures above the PS glass transition temperature. Within a range of wave vectors spanning 10(-3) to 10(-2) nm(-1), good agreement is found between the measured surface dynamics and the theory of overdamped thermal capillary waves on thin films. Quantitatively, the data can be accounted for using the viscosity of bulk PS.     

Titanium carbonitride films on cemented carbide cutting tool prepared by pulsed high energy density plasma

Hard films prepared by pulsed high energy density plasma (PHEDP) are characterized by high film/substrate adhesive strength, and high wear resistance. Titanium carbonitride (TiCN) films were deposited onto YG11C (ISO G20) cemented carbide cutting tool substrates by PHEDP at room temperature. XRD, XPS, SEM, AES, etc. were adopted to analyze the phases (elements) composition, microstructure and the interface of the films, respectively. The results show that, the uniform dense films are composed of grains ranging from 70 to 90 nm. According to the AES result, there is a broad transition layer between the film and the substrate, due to the ion implantation effect of the PHEDP. The transition layer is favorable for the film/substrate adhesion.     

A comparative microstructural study of compositionally up- and down-graded (Ba,Sr)TiO3 thin films epitaxially grown on (La,Sr)CoO3-covered MgO(100) substrates by pulsed laser deposition

We report a comparative study of the microstructure of compositionally graded (Ba_1-xSr_x)TiO₃ (BST) films with two compositionally graded directions, up and down, with respect to the substrate, which were deposited epitaxially on (La,Sr)CoO₃ (LSCO)-covered MgO(100) single-crystal substrates by pulsed laser deposition. Cross-sectional transmission electron microscopy (TEM) images and electron diffraction show that the graded films grow epitaxially with their (100) plane parallel to the (100) surface of the MgO single-crystal substrate, and with an in-plane orientation relationship of 〈001〉_BST//〈001〉_LSCO//〈001〉_MgO. The crystalline quality and surface morphology of the graded films are closely related to the direction of the compositional gradient built into the graded films. Down-graded films (starting with a BaTiO₃ layer at the film/substrate interface) have a much better crystalline quality and a smoother surface than the up-graded films (starting with a (Ba_0.75Sr_0.25)TiO₃ layer at the film/substrate interface). Obviously, the BaTiO₃ bottom layer in the down-graded film acts not only as a part of the graded film but also as an excellent seeding layer to enhance the crystallization of the subsequent film layers, resulting in a high crystalline quality of the down-graded film and an enhanced dielectric behavior. Planar (high-resolution) TEM images also demonstrate that down-graded films have a larger, and more uniform, grain size than up-graded films, and that the latter contain voids. PACS 81.15.-z; 77.55.+f; 68.37.Lp; 61.14.-x