Block Copolymer Packing Limits and Interfacial Reconfigurability in the Assembly of Periodic Mesoporous Organosilicas

Here poly(N,N‐dimethylacrylamide)‐block‐poly(styrene) block copolymer micelles (BCPs) are advanced and applied to assemble periodic mesoporous organosilicas (PMOs) with noncylindrical pores. Using these BCP micelles, it is found that pore dimensions (11–23 nm), wall thicknesses (5–9 nm), and overall porosities (26%–78%) are independently programable, depending only on relative inputs for BCP and matrix former. Notably, the degree of order in all films improves as BCP loading approaches a packing limit of 63 vol%. Beyond this limit and regardless of pore dimensions, both porogen packing in the film and pore structure after thermal processing show significant deviations away from spherical close‐packed lattices. The surprising absence of film collapse in this regime allows here to quantify the evolution of pore structure through the thermally driven interfacial reconfigurability of BCP micelles in the hybrid films when porogen loading exceeds the packing limit by using both scattering techniques and scanning transmission electron microscopy tomography. Finally, the PMOs here give dielectric constants of 1.2 and 1.5 above and below the BCP packing limit, respectively—the lowest ever reported for this matrix material.     

Silica Films with Bimodal Pore Structure Prepared by Using Membranes as Templates and Amphiphiles as Porogens

Extended porous silica films with thicknesses in the range of 60 to 130 μm and pores on both the meso‐ and macroscale have been prepared by simultaneously using porous membrane templates and amphiphilic supramolecular aggregates as porogens. The macropore size is determined by the cellulose acetate or polyamide membrane structure and the mesopores by the chosen ethylene‐oxide‐based molecular self‐assembly (block copolymer or non‐ionic surfactants). Both the template and the porogen are removed during an annealing step leaving the amorphous silica material with a porous structure that results from sol–gel chemistry occurring in the aqueous domains of the amphiphilic liquid‐crystalline phases and casting of the initial template membrane. The surface area and total pore volume of the inorganic films vary from 473 to 856 m² g^–1, and 0.50 to 0.73 cm³ g^–1, respectively, depending on the choice of template and porogen. The combined benefits of both macro‐ and mesopores can potentially be obtained in one film. Such materials are envisaged to have applications in areas of large molecule (biomolecule) separation and catalysis. Enhanced gas and liquid flow rates through such membranes, due to the presence of the larger pores, also makes them attractive as supports for other catalytic materials.     

Preparation of porous ultra low k films using different sacrificial porogen precursors for 28 nM technological node

In order to reduce resistance capacitance (RC) delay and crosstalk between adjacent interconnect lines, the porous ultra low k (PULK) film with dielectric constant value ranging from 2.4 to 2.6 was introduced to be used as an insulator of the Cu integration in back end of the line (BEOL) for 28 nm technological node. In this paper, the PULK films were deposited by plasma enhanced chemical vapor deposition (PECVD) using two different sacrificial organic porogen precursors of bicycloheptadiene (BCHD) and alpha-terpinene (ATRP), and then the above co-deposited films were expose to UV radialization for removing sacrificial organic porogens to create pores. The effects of the different sacrificial organic porogen on the PULK film properties such as the dielectric constant, pore and porosity, k shift, mechanic strength, and RC were studied in detail. Results indicated that the hardness and modulus of the PULK film for the BCHD and ATRP precursors were 0.7 and 5.1 GPa and 1.0 and 7.1 Gpa, and their pore radiuses and porosities were 1.18 nm and 25% and 0.95 nm and 23%. The dielectric constant value of the PULK film for the BCHD and ATRP precursors were measured as 2.48 and 2.59 with Hg probe. The adhesion test indicated that the interfacial strength of the PULK film for the ATRP precursor was higher than that of the PULK film for the BCHD precursor. By the RC examination, it was seen that RC curve of the PULK film for the ATRP precursor was located below the curve of the PULK film for the BCHD precursor.     

The Preparation and Characterization of Small Mesopores in Siloxane‐Based Materials That Use Cyclodextrins as Templates

Porous thin films containing very small closed pores (～ 20 Å) with a low dielectric constant (～ 2.0) and excellent mechanical properties have been prepared using the mixture of cyclic silsesquioxane (CSSQ) and a new porogen, heptakis(2,3,6‐tri‐O‐methyl)‐β‐cyclodextrin (tCD). The pore sizes vary from 16.3 Å to 22.2 Å when the content of tCD in the coating mixture increases to 45 wt.‐% according to positronium annihilation lifetime spectroscopy (PALS) analysis. It has also been found that the pore percolation threshold (the onset of pore interconnectivity) occurs as the ～ 50 % tCD porogen load. The dielectric constants (k = 2.4 ～ 1.9) and refractive indices of these porous thin films decreased systematically as the amount of porogen loading increased in the coating mixture. The electrical properties and mechanical properties of such porous thin films were fairly good as interlayer dielectrics.     

Morphological Control of Nanoporous Films by the Use of Functionalized Cyclodextrins as Porogens

Porous cyclic silsesquioxane (CSSQ) thin films containing nanopores (～ 2 nm) with low dielectric constant (k < 2.2), have been prepared by using various kinds of cyclodextrin (CD) derivatives as porogenic materials. The pore structure, including average pore size and interconnectivity, can be controlled by changing the functional groups of the cyclodextrin derivatives. The pore structure is found to be strongly related to the affinity of the functional groups between CD molecules. The electrical and mechanical properties of the porous thin films were monitored in order to determine the relationship between the pore structure and film properties. The mechanical properties of porous low‐k thin films (total porosity ～ 30 %) prepared with CD derivatives are found to be correlated with the pore interconnection length. The longer the deduced interconnection length in the thin film, the worse the mechanical properties (such as hardness and modulus) of the thin film, even though the porogen‐induced pore diameters are very small (～ 2 nm).     

Mesoporous Separation Membranes of Polymer‐Coated Copper Hydroxide Nanostrands

Extremely long and thin nanocomposite fibers are prepared by oxidative polymerization of pyrrole (or aniline) around the surfaces of copper hydroxide nanostrands. The individual nanostrands of 2.5 nm are uniformly coated with a polypyrrole layer of 3 to 4 nm, resulting in hybrid core/shell fibers of about 10 nm in diameter and a few micrometers in length, as confirmed by high‐resolution electron microscopy. The as‐prepared nanocomposite fibers are dispersive in water and can be converted into thin free‐standing films by simply filtering a small volume of the aqueous solution using a polycarbonate membrane filter. The films covering the submicrometer pores of the membrane filter have a thickness of a few tens of nanometers, and provide a mechanically stable nanofiber network with abundant pores of a few nanometers. The network is stable in acidic and basic media, and can be used for protein separation under pressures of at least 90 kPa. The permeation rates of cytochrome c, myoglobin, and ferritin were examined by changing the pH around their isoelectric points. It is seen that the nanofibrous free‐standing films on the polycarbonate membrane filter show clear size selectivity for the proteins, retaining extremely high filtration rates for water. We demonstrate herein durable mesoporous separation membranes made of organic–inorganic nanocomposite fibers and their outstanding performance.     

铜薄膜内微孔对其力学性能影响及开裂行为研究

研究了铜薄膜内微孔对其力学性能影响及开裂行为,采用磁控溅射工艺制备聚酰亚胺柔性基板上铜薄膜,通过扫描电镜(SEM)对铜薄膜表面形貌表征、EDS能谱分析及SEM原位拉伸观察实验,得出磁控溅射工艺制备出超薄铜薄膜多为柱状晶结构,且带有微米级孔洞.并测得不同孔隙率铜薄膜载荷与位移增量的变化,由相关公式求出应力-应变关系;分析了不同孔径微孔的上下边缘沿晶开裂,微裂纹萌生、扩展的行为.结果表明:磁控溅射工艺在聚酰亚胺柔性基板上制备的微米级铜薄膜受拉伸时微孔沿晶开裂形成初始微裂纹,孔径≤4μm微孔处局部应力偏低,未能使微裂纹沿晶界改变方向继续扩展,微裂纹受到抑制;在较高的局部应力下,孔径>10μm微孔裂纹继续沿新的晶界方向扩展,与其他微孔裂纹连通;孔隙率越高,多孔微裂纹连通几率越高,薄膜力学性能就越差,且铜薄膜开裂可能性也越高.     

Periodically Ordered Meso‐ and Macroporous SiO2 Thin Films and Their Induced Electrochemical Activity as a Function of Pore Hierarchy

Silica thin films with variable pore hierarchy (different combinations of small meso‐, large meso‐, and macropores) were produced via evaporation induced self‐assembly in a one‐pot synthesis. A suitable block copolymer and an ionic liquid served as porogens for the generation of different types of mesopores whereas polymethylmethacrylate particles were used as macrotemplate. The silica architectures were characterized by various state‐of‐the‐art techniques, such as 2D‐SAXS, TEM, SEM, AFM, krypton and nitrogen sorption. Moreover, electrochemical functionalization was utilized as a tool to study the hierarchy‐property relationship. Thus, hierarchically porous films prepared on FTO‐coated glass were post‐synthetically silylated and electrochemically active ferrocene groups subsequently grafted onto the pore walls. Cyclic voltammetry was used to monitor the induced electrochemical activity as a function of variations in the pore hierarchy. It turned out that multimodal pore systems possess a relatively higher electrochemical response due to better connection between the pores and higher surface area.     

Sol–gel synthesized Titania nanoparticles deposited on porous polycrystalline silicon: Improved carbon dioxide sensor properties

Titania nanoparticles (TNPs) were synthesized by a sol–gel method in our laboratory using titanium tetrachloride as the precursor and isopropanol as the solvent. The particles׳ size distribution histogram was determined using ImageJ software and the size of TNPs was obtained in the range of 7.5–10.5 nm. The nanoparticle with the average size of 8.5 nm was calculated using Scherrer׳s formula. Homogeneous and spherical nanoparticles were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM) and UV–visible spectroscopy (UV–vis). The X-ray powder diffraction analysis showed that the prepared sample (TNPs) has pure anatase phase. TNPs were deposited on porous polycrystalline silicon (PPS) substrate by electron beam evaporation. The TNPs thickness was 23±2 nm at 10⁻⁵ mbar pressure at room temperature. Porosity was performed by an anodization method. Since polycrystalline silicon wafers consist of different grains with different orientations, the pore size distribution in porous layer is non-uniform [1]. Therefore, the average diameter of pores can be reported in PPS layer analysis. Average diameter of pores was estimated in the range of 5 μm which was characterized by FESEM. The nanostructured thin films devices (Al/Si/PPS/TNPs/Al and Al/Si/PPS/Al) were fabricated in the sandwich form by aluminum (Al) electrodes which were also deposited by electron beam evaporation. Electrical measurements (I–V curves) demonstrated the semiconducting behavior of thin film devices. The gas sensitivity was studied on exposure to 10% CO₂ gas. As a result, conductivity of devices increased on exposure to CO₂ gas. The device with TNPs thin film (Al/Si/PPS/TNPs/Al) was more sensitive and, had better response and reversibility in comparison with the device without TNPs thin film (Al/Si/PPS/Al).     

红外宽频吸收硅基复合气凝胶的制备及表征

以正硅酸乙酯为硅源,采用酸碱两步催化法经过溶胶-凝胶和冷冻干燥制备出SiO2气凝胶基材,并在凝胶老化过程中添加三乙胺盐酸盐得到兼具中远红外吸收特性的硅基复合气凝胶。利用X射线衍射、扫描电子显微镜、氮吸附-脱附和傅里叶红外吸收光谱对气凝胶的结构和性能进行了表征。结果表明:胺盐在硅气凝胶网络结构中穿插结晶;基材的比表面积、最大孔容和平均孔径分别为524.5 m2/g、1.2 cm3/g和9.2 nm,复合材料的比表面积、最大孔容和平均孔径分别为37.93~138.7 m2/g、0.08~0.28 cm3/g和7.1~8.8 nm;基材和复合气凝胶的表观密度分别为0.25 g/cm3和0.35~0.51 g/cm3;复合气凝胶在中远红外窗口具有宽频吸收的特性,且三乙胺盐酸盐含量的增加,中红外相对吸收强度成比例增强。     

Nanoporous Low‐κ Polyimide Films via Poly(amic acid)s with Grafted Poly(ethylene glycol) Side Chains from a Reversible Addition–Fragmentation Chain‐Transfer‐Mediated Process

Thermally‐initiated living radical graft polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA) with ozone‐pretreated poly[N,N′‐(1,4‐phenylene)‐3,3′,4,4′‐benzophenonetetra‐carboxylic amic acid] (PAmA) via a reversible addition–fragmentation chain‐transfer (RAFT)‐mediated process was carried out. The chemical compositions and structures of the copolymers were characterized by nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), X‐ray photoelectron spectroscopy (XPS), and molecular weight measurements. The “living” character of the grafted PEGMA side chains was ascertained in the subsequent extension of the PEGMA side chains. Nanoporous low‐dielectric‐constant (low‐κ) polyimide (PI) films were prepared by thermal imidization of the PAmA graft copolymers under reduced argon pressure, followed by thermal decomposition of the side chains in air. The nanoporous PI films obtained from the RAFT‐mediated graft copolymers had well‐preserved PI backbones, porosity in the range of 5–17 %, and pore size in the range of 30–50 nm. The pores were smaller and the pore‐size distribution more uniform than those of the corresponding nanoporous PI films obtained via graft copolymers from conventional free‐radical processes. Dielectric constants approaching 2 were obtained for the nanoporous PI films prepared from the RAFT‐mediated graft copolymers.     

The influence of porous silicon on axonal outgrowth in vitro.

xonal outgrowth on smooth and porous silicon surfaces was studied in organ culture. The pore size of the silicon substrata varied between 100 and 1500 nm. We found that axons preferred to grow and elongate on porous silicon surfaces only when pores of (150-500 nm) are available.     

The Influence of Porous Silicon on Axonal Outgrowth in Vitro

Axonal outgrowth on smooth and porous silicon surfaces was studied in organ culture. The pore size of the silicon substrata varied between 100 and 1500 nm. We found that axons preferred to grow and elongate on porous silicon surfaces only when pores of (150-500 nm) are available.     

Two‐Dimensionally Ordered Copper Grid Patterns Prepared via Electroless Deposition Using a Colloidal‐Crystal Film as the Template

Two‐dimensionally ordered copper grid patterns with different pore sizes and thickness have been fabricated via electroless copper deposition using a colloidal‐crystal film as the template. The pore size of the grid can be adjusted by altering the deposition time. The copper films, with thicknesses of ≈ 100–130 nm and pore sizes of ≈ 100 nm, are flexible and can be peeled off a silicon wafer and rolled up into a reel. Three‐dimensionally ordered porous copper materials have also been prepared using a similar method.     

Single Step Preparation of Novel Hydrophobic Composite Films for Low‐k Applications

Composite films with low dielectric constants (k) containing micro‐ and mesopores are synthesized from precursor solutions for the preparation of mesoporous silica and ethanolic suspensions of silicalite‐1 nanoparticles. The material contains silicalite‐1 nanoparticles (include nanocrystals and nanoslabs/intermediates) embedded in a randomly oriented matrix of highly porous mesoporous silica. Micropores result from the incorporated silicalite‐1 nanoparticles, while decomposition of the porogen F127 leads to additional mesopores. The porosity of the composite films increases from 9 to 60% with the increase in porogen loading, while in parallel the elastic modulus and hardness decrease. The elastic moduli of the films are in the range of 13–20 GPa. Hydrophobic surfaces of the composite films are obtained by introducing methyl triethoxysilane during the preparation of both precursor solutions, leading to the incorporation of ? CH₃ groups in the final composite films. These methyl groups are stable up to at least 500 °C. A low k value of approximately 2 is observed for films cured at 400 °C in N₂ flow, which is ideal for removing templates without decomposing methyl groups. Due to the intrinsic hydrophobicity of the material, post‐silylation is not required rendering the composite films attractive candidates for future low k materials.     

阳极氧化铝(AAO)模板法制作的直径和长度一致的碳纳米管

我们在铝衬底上制作了不同参数条件下的阳极氧化铝(AAO)模板.通过改变初次阳极化时间来得到不同尺寸的纳米孔.改变初次阳极化时间可容易地调节,而使用刻蚀技术又可以控制氧化铝孔的长度.在该研究中,控制阳极极化和刻蚀参量成功地制备了不同直径和不同长度的AAO纳米孔.在AAO模板的竖直沟道中生长了方向性强的碳纳米管,而AAO纳米孔的直径和长度可以控制这一过程.通过二次阳极极化法制备了有着六边形孔洞排列方式的纳米AAO模板.由于AAO纳米孔的直径和长度依赖于阳极化参量,故通过控制阳极化参量就可控制AAO纳米孔的直径和长度.     

Self‐Organized Nanoporous Anodic Titania Films and Ordered Titania Nanodots/Nanorods on Glass

We report a new method to fabricate self‐organized nanoporous titania films (pore diameter ≈ 30 nm; ≈ 1100 nm thick) and ordered titania nanorod arrays (rod diameter ≈ 30–60 nm; 70–260 nm high) by combined anodizing of superimposed Al/Ti layers sputter‐deposited on glass substrates. The titania nanostructures mimic the ordered nanoporous anodic alumina films via a through‐mask anodization. We propose a new anodizing electrolyte, i.e., a diluted nitric acid solution, for fabricating uniform, self‐organized, ordered nanoporous titania films with parallel cylindrical pores and without any thickness limit. More significantly, the nanoporous titania films contain a small amount of titanium nitride and dissociated nitrogen, and exhibit a moderate transparency and an enhanced absorption throughout the UV and visible light regions of the electromagnetic spectrum. After heating at 600 °C for 2 h, the nanoporous titania films develop a small absorption red‐shift and exhibit high photocatalytic activity under UV illumination.     

磁控溅射制作金红石——TiO_2

用磁控溅射方法制备了粒径大小为20nm的金红石———TiO2,用X射线(XRD)和扫描电镜(SEM)观察表面形貌,局部表观致密,颗粒大小均匀。     

Surface Wettability of Nanostructured Zinc Oxide Films

Zinc oxide (ZnO) nanograin and nanorod films were prepared by magnetron sputter deposition and an aqueous solution growth method. Their surface wettability was studied in relation to their surface morphologies. While the surfaces of both films were hydrophobic, the nanorod films exhibited higher surface hydrophobicity. A superhydrophobic surface was obtained on a ZnO nanorod film with a water contact angle of 151 deg. Results have shown that their surface wettability was influenced by the morphology of ZnO nanostructures, including the grain size, the length, and density of nanorods. Both types of ZnO films showed switchable wettability under ultraviolet irradiation and dark storage.     

红外宽频吸收硅基复合气凝胶的制备及表征

以正硅酸乙酯为硅源,采用酸碱两步催化法经过溶胶-凝胶和冷冻干燥制备出SiO2气凝胶基材,并在凝胶老化过程中添加三乙胺盐酸盐得到兼具中远红外吸收特性的硅基复合气凝胶。利用X射线衍射、扫描电子显微镜、氮吸附-脱附和傅里叶红外吸收光谱对气凝胶的结构和性能进行了表征。结果表明:胺盐在硅气凝胶网络结构中穿插结晶;基材的比表面积、最大孔容和平均孔径分别为524.5 m2/g、1.2 cm3/g和9.2 nm,复合材料的比表面积、最大孔容和平均孔径分别为37.93~138.7 m2/g、0.08~0.28 cm3/g和7.1~8.8 nm;基材和复合气凝胶的表观密度分别为0.25 g/cm3和0.35~0.51 g/cm3;复合气凝胶在中远红外窗口具有宽频吸收的特性,且随着三乙胺盐酸盐含量的增加,中红外相对吸收强度成比例增强。