Molecular and lamellar orientation in polyethylene thin films

Summary A combined wide (WA) and small angle X-ray diffraction (SAXS) study of melt compressed low density PE samples into the form of very thin films is reported. The WAXD patterns show an uniaxialb axis orientation normal to the film surface which can be interpreted in terms of a row structure in the plane of the film. The analysis of SAXS data indicates, in addition, a preferential orientation of bundles of stacked lamellae parallel to the film surface separated by longitudinal microvoids.With 3 figures     

In-plane and out-of-plane defectivity in thin films of lamellar block copolymers

We investigate the ordering of poly(styrene-b-methyl methacrylate) (PS-PMMA) lamellar copolymers (periodicity L₀ = 46 nm) confined between a free surface and brushed poly(styrene-r-methyl methacrylate) silicon substrate. The processing temperature was selected to eliminate wetting layers at the top and bottom interfaces, producing approximately neutral boundaries that stabilize perpendicular domain orientations. The PS-PMMA film thickness (t = 0.5L₀ − 2.5L₀) and brush grafting density (Σ = 0.2–0.6 nm⁻²) were systematically varied to examine their impacts on in-plane and out-of-plane ordering. Samples were characterized with a combination of high-resolution microscopy, X-ray reflectivity, and grazing-incidence small-angle X-ray scattering. In-plane order at the top of the film (quantified through calculation of orientational correlation lengths) improved with tⁿ, where the exponent n increased from 0.75 to 1 as Σ decreased from 0.6 to 0.2 nm⁻². Out-of-plane defects such as tilted domains were detected in all films, and the distribution of domain tilt angles was nearly independent of t and Σ. These studies demonstrate that defectivity in perpendicular lamellar phases is three-dimensional, comprised of in-plane topological defects and out-of-plane domain tilt, with little or no correlation between these two types of disorder. Strong interactions between the block copolymer and underlying substrate may trap both kinds of thermally generated defects. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 339–352     

Water sorption and activation energy in polyimide thin films

The water sorption behavior and the activation energy were investigated for various chemical structure polyimide thin films; BPDA‐PDA, BPDA‐ODA, PMDA‐ODA, and 6FDA‐ODA. The activation energy for the water diffusion varied in the range of 5.53 to 9.27kcal/mol, and was in the increasing order: BPDA‐PDA < BPDA‐ODA < PMDA‐ODA < 6FDA‐ODA. BPDA‐PDA and BPDA‐ODA polyimide films showed relatively well‐ordered morphological structure, which results in relatively low diffusion coefficient and high activation energy. It was found that the diffusion coefficient and the activation energy are significantly related to the in‐plane orientation, crystallinity, and packing order in the polyimide thin films. The morphological structure was predominant factors for the water diffusion coefficient and activation energy in the polyimide thin films. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2714–2720, 2000     

Development of a method for direct determination of solids as thin films by energy dispersive X-ray fluorescence analysis

Solid samples can be analysed as without a prior decomposition step, if they are pulverized and then embedded in a thin layer of a cold-setting polymer. This method is very appropriate for materials which are difficult to decompose or which can be easily contaminated. The sample components are evenly distributed in a thin layer, which improves considerably the signal-tonoise-ratio, and this leads to a decrease of the limits of detection. The reproducibility of the method was tested with cobalt oxide and yttrium oxide and also a mixture of these with silver oxide and manganese dioxide. Between 20 and 60 ng of these elements can be determined without difficulty, with a precision of ± 2–4%. The correlation coefficients found for the calibration graphs were between 0.994 and 0.999.     

Sequential deposition of block copolymer thin films and formation of lamellar heterolattices by electrospray deposition

The delivery of sub-micron droplets of dilute polymer solutions to a heated substrate by electrospray atomization enabled precisely controlled and continuous deposition, or growth, of block copolymer thin films. It also provided, in principle, the ability to fabricate heterolattice materials using sequential depositions. This possibility was explored and the morphology of resulting composite films produced by such sequential electrospray deposition (ESD) of lamellar diblock copolymers of poly(styrene-b-4-vinylpyridine) with differing molecular weights was examined. The structure of the heterolattice interface was a strong function of temperature. Sharp interfaces with abrupt changes in the lamellar period were observed at lower deposition temperatures, while higher temperatures produced a smooth variation in the lamellar period from one molecular weight to the next. The ordering kinetics of a secondary high molecular weight layer could be substantially enhanced depending on the molecular weight of the polymer present in the underlying primary layer. These findings were discussed in the context of temperature and molecular weight dependent diffusion dynamics of the polymers in the melt which control the inter-mixing of the layers and therefore the structure of the heterolattice interface. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 247–253     

Three dye energy transfer cascade within DNA thin films

An efficient cascade FRET was realized in solid state DNA-CTMA thin films using a three chromophore system without any covalent attachments. The extent of energy transfer from Cm102 to SRh was studied and found to improve eight-fold using the bridging dye Pm567.     

Photocurrent generation in multilayer organic-inorganic thin films with cascade energy architectures

Zirconium organobisphosphonate multilayer thin films of viologen derivatives were grown on copper dithiolate multilayers of 5,15-di(p-thiolphenyl)-10,20-di(p-tolyl)porphyrin (POR) and 5,15-di(p-thiolphenyl)-10,20-di(p-tolyl)porphyrinzinc (ZOR) on a variety of substrates (e.g. Au, SiO(2)), using solution depositions methods. The multilayer structures were studied by atomic force microscopy, UV-vis spectroscopy, and ellipsometry. In the case of copper dithiolate thin films, layer-by-layer lamellar growth with low surface roughness resulted, while higher surface roughness was observed in the growth of Zr viologen bisphosphonate films. Gold electrodes modified with zirconium bisphosphonate multilayers of viologen on top of copper dithiolate multilayers of porphyrin derivatives (ZOR or POR) were photoelectroactive and produced efficient and stable photocurrents using visible light. By arranging the zinc-porphyrin (ZOR) and the free base porphyrin (POR) donors in an energetically favorable fashion, according to their redox potentials and optical energy gaps, the photoinduced charge separation was improved, and higher photocurrent quantum yields ( approximately 4%) and fill factor ( approximately 50%) of the photoelectrode were achieved.     

Selective control over the lamellar thickness of one domain in thin binary blends of block copolymer films

Thin binary blends of poly(styrene‐b‐methyl methacrylate) (PS‐PMMA) block copolymers in films where the lamellar thickness of one domain is controlled while preserving the thickness of the other domain were demonstrated without microphase separation. One of the block copolymers used here was short and symmetric, and the other was long and asymmetric; the molecular weights of the PMMA block chains in the constituents were similar. A random copolymer brush was introduced and film thickness and composition of brush were adjusted to induce perpendicular orientation in thin film. As the blend composition of the long asymmetric block copolymer increased, the PS lamellar thickness increased from 15.8 to 25.1 nm, whereas the PMMA lamellar thickness remained constant at approximately 14 nm (the thickness decreased slightly from 14.0 to 13.3 nm). The domain spacing behavior in thin film was consistent in the bulk. These results were compared with the Birshtein, Zhulina, and Lyatskaya model and the theories for pure block copolymers in the strong segregation limit and in the intermediate segregation regime. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1393–1399     

Direct precursor conversion reaction for densely packed Ag2S nanocrystal thin films

Successful realization of highly crystalline and densely packed Ag2S nanocrystal (NC) films has been achieved by directly converting precursor molecules, Ag(SCOPh), on preheated substrates. When an aliquot of Ag(SCOPh) solution dissolved in trioctylphosphine (TOP) is applied on preheated solid substrates at 160 degrees C, such as SiO2/Si, H-terminated Si, and quartz. Ag2S NC thin films have been formed with instant phase and color changes of the precursor solutions from pale yellow homogeneous solution to black solid films. The average diameter of individual Ag2S NCs forming thin films is ca. 25 nm, as confirmed by examining both isolated Ag2S NCs from thin films and as-made thin film samples by using transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. Powder X-ray diffraction (XRD) pattern shows that the synthesized Ag2S NCs have well-defined monoclinic acanthite phase. Direct precursor conversion process has resulted in densely packed Ag2S NCs with reduced interparticle distances owing to efficient removal of TOP during the reaction. Compared to the devices fabricated by the drop-coating process, Ag2S thin film devices fabricated by direct precursor conversion process have shown a ca. 300-fold increased conductance. Such Ag2S NC devices have also displayed reliable photoresponses upon white light illumination with high photosensitivity (S approximately equal to 1).     

Nanostructure in energy conversion

Nanostructured and nanosized materials are widely applied to tackle the pressing challenges associated with energy conversion. In this conceptual review, rather than highlighting separate examples, we aim to give a general overview about where and how nanostructure design can be beneficial in the three major research fields(photo)thermal chemical energy conversion, electrochemical energy conversion, and solar energy conversion. It will be shown that in many cases the design of catalytically active nanostructures is the main task and that especially for catalysts nanostructure and activity are inseparably linked to each other. Moreover, electrochemical and photochemical processes are complicated by the overlap of multiple processes that all need to be optimized, including in particular light absorption, charge migration,recombination and trapping events and surface processes. It will also be shown how the development of materials for new challenges can often be based on our knowledge on existing materials for related applications.     

Synthesis of new lamellar materials by self-assembly and coordination chemistry in the solids

We report the preparation of a new class of lamellar hybrid organic–inorganic materials obtained by self-assembly of bridged organosilica precursors containing long alkylene chains during the sol–gel process. The self-assembly is induced by lipophilic van der Waals interactions. The introduction of –SS– bonds in the core of the alkylene chains permitted the functionalisation of lamellar materials, which were subsequently transformed into SH and –SO₃H groups. This methodology was extended to the formation of lamellar hybrid materials containing amino groups thanks to CO₂ as bridging groups as well as the formation of lamellar hybrid materials containing carboxylic groups. In this last case, the hydrolysis and polycondensation of cyanoalkyltrialkoxysilanes permitted the one pot synthesis of lamellar hybrid materials thanks to in situ hydrogen bonds formation between carboxylic acids groups. All these functional lamellar materials exhibit a very high chelating capability towards transition metal and lanthanide ions.     

Lithium inserted ZnSnN2 thin films for solar absorber: n to p-type conversion

ZnSnN₂ is a non-toxic and earth-abundant photoabsorber material for flexible photovoltaic devices because of its excellent optoelectronic behavior. However, theoretical studies show that the alkaline-earth metallic (Li, Na, K, Rb, Cs, and Fr) dopants in ZnSnN₂, particularly lithium (Li), display shallow-acceptor behavior and improve the performance of ZnSnN₂ semiconductors. Orthorhombic phase structure with (002) preferred orientation was observed for Li-doped films and the lattice parameters agree well with reported standards. Secondary ion mass spectroscopy (SIMS) analysis revealed the incorporation of Li in Li:ZnSnN₂ films. XPS, the density of states, and Born effective charge analysis revealed the chemical bonding states of Li–ZnSnN₂. In contrast to the pristine n-type ZnSnN₂, Li:ZnSnN₂ thin films showed conductivity with p-type hole concentrations varying between 1.14 × 10²⁰–9.47 × 10¹⁹ cm^?3 and the highest mobility of 20.03 cm²V^?1s^?1. Therefore, we obtained p-type conductivity by substituting an organolithium reagent (C?H?Li) on the Zn site, which highlights that Li:ZnSnN₂ can be effectively used as the photoanode layer for next-generation thin-film solar cell devices.     

Elemental composition analysis of silicon carbonitride thin films by energy dispersive spectroscopy

Specific features of elemental composition analysis of silicon carbonitride thin films by energy dispersive spectroscopy (EDS) are considered. The films were preliminarily examined by IR spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron (SEM) and atomic force microscopy (AFM), and X-ray diffraction analysis using synchrotron radiation (SR-XRD) to acquire data on their chemical and phase composition, crystalline structure and surface morphology. The effect of film thickness, substrate material and electron beam energy on the results of energy dispersive analysis was investigated.     

Growth and characterization of films containing fullerenes and water soluble porphyrins for solar energy conversion applications

Thin films consisting of two fulleropyrrolidine derivatives 1 or 2 and a water-soluble porphyrin, TPPS4, were prepared by the Langmuir-Sch?fer (LS, horizontal lifting) method. In particular, a solution of the fulleropyrrolidine in chloroform and dimethyl sulfoxide was spread on the water surface, while the porphyrin (bearing peripheral anionic sulfonic groups) was dissolved into the aqueous subphase. To the best of our knowledge, such a versatile method for film fabrication of fullerene/porphyrin mixed composite films has never been used by other researchers. Evidence of the effective interactions between the two components at the air-water interface was obtained from the analysis of the floating layers by means of surface pressure vs area per molecule Langmuir curves, Brewster angle microscopy, and UV-visible reflection spectroscopy. The characterization of the LS films by UV-visible spectroscopy reveals that in each case the two constituents behave as strongly interacting pi systems. The use of polarized light suggests the existence of a preferential direction of the TPPS4 macrocyclic rings with an edge-on arrangement with respect to the substrate surface, regardless which fulleropyrrolidine derivative is in the composite film. Atomic force microscopy investigations give evidence of morphologically flat layers even for LS transfer at low surface pressures. Photoaction spectra were recorded from films deposited by only one horizontal lifting onto indium-tin-oxide (ITO) electrodes, and the observed photocurrent increased notably with increasing transfer surface pressure for both 1/TPPS4 and 2/TPPS4 composite films. IPCE values are larger for 2/TPPS4 systems in comparison with 1/TPPS4 composite layers. Finally, a nonconventional approach to photoinduced phenomena is proposed by differential spectroscopy in the FT-IR attenuated total reflectance (ATR) mode.     

Single-crystal micro/nanostructures and thin films of lamellar molybdenum oxide by solid-state pyrolysis of organometallic derivatives of a cyclotriphosphazene

The solid-state pyrolysis of organometallic derivatives of a cyclotriphosphazene is demonstrated to be a new, simple and versatile solid-state templating method for obtaining single-crystal micro- and nanocrystals of transition and valve metal oxides. The technique, when applied to Mo-containing organometallics N₃P₃[OC₆H₄CH₂CN·Mo(CO)₅]₆ and N₃P₃[OC₆H₄CH₂CN·Mo(CO)₄ py]₆, results in stand-alone and surface-deposited lamellar MoO₃ single crystals, as determined by electron and atomic force microscopies and X-ray diffraction. The size and morphology of the resulting crystals can be tuned by the composition of the precursor. X-ray photoelectron and infrared spectroscopies indicate that the deposition of highly lamellar MoO₃ directly on an oxidized (400 nm SiO₂) surface or (100) single-crystal silicon surfaces yields a layered uniphasic single-crystal film formed by cluster diffusion on the surface during pyrolysis of the metal-carbonyl derivatives. For MoO₃ in its layered form, this provides a new route to an important intercalation material for high energy density battery materials.     

Characterization of self-assembled lamellar thermoresponsive silica-hydrogel nanocomposite films

Mesostructured lamellar nanocomposite films with alternating silica and organic layers containing poly(N-isopropropyl acrylamide) (PNIPAM) were prepared using evaporation-induced self-assembly. A suitable theoretical approach to analyze the small-angle X-ray scattering (SAXS) patterns of oriented lamellar two-phase systems was applied to the SAXS data of films of varying composition, providing details on the self-assembly process, the composition, and the polymerization. In particular, this approach allowed an accurate determination of the thickness of the silica and the organic layer. The applicability of the SAXS approach was carefully tested with simulated data and verified by thermogravimetric analysis (TGA). TGA and (13)C NMR were used to study the polymerization and linkage to the silica matrix. SAXS and time-resolved grazing incidence SAXS revealed that the phase transition of PNIPAM at ca. 32 degrees C leads to a reversible expansion/contraction perpendicular to the layers on a time scale of ca. 30 min.     

Membrane proteins in thin films

Molecular functions and structural changes of membrane proteins in an aqueous environment can be elucidated by reaction-induced FTIR difference spectroscopy upon photolysis of caged compounds. The achieved detection of IR band changes even due to single amino acid residues is, however, only possible in the presence of very high protein concentrations, implying that a low water content must be present. In general, the films are formed by controlled dehydration of membrane protein suspensions at reduced pressure and low temperature. For the retention of enzymatic activity of Na,K-ATPase, for example, a cosolvent such as glycerol is required. In order to interprete the results obtained by FTIR spectroscopy, it is important to know whether essential properties of the proteins such as hydration are changed upon film formation. Therefore, a differential scanning calorimetry (DSC) study has been carried out with purified Na,K-ATPase and Ca-ATPase in suspension, in form of pellets obtained by high-speed ultracentrifugation and in thin films. As relevant thermoanalytical properties, the endothermic denaturation transitions of the proteins have been studied. For Na,K-ATPase in the presence of 20% glycerol as cosolvent, a single, comparatively narrow endothermic and irreversible denaturation transition with a denaturation enthalpy of about 1.7 MJ mol⁻¹ and transition temperatures of about 65 and 70°C is found in concentrated suspension and in the state of the pellet, respectively. In the case of thin films suitable for IR spectroscopy, a characteristic change is observed in a reproducible manner. The enthalpy change of the remaining transition around 70°C is reduced but an additional transition at about 77°C is observed. Based on control experiments, the new high temperature transition is attributed to a partially dehydrated state of the protein. Furthermore, a comparatively broad endothermic transition around 20°C is found under conditions of high protein concentrations (film), which is tentatively assigned to a transition of the lipid environment of this integral membrane protein. Similar results are found for Ca-ATPase films. In the absence of glycerol, the deoxycholate treated enzyme in suspension exhibits a narrow endothermic main transition at 52°C with a denaturation enthalpy around 0.9 MJ mol⁻¹. For the film of this protein, two almost equally large endothermic transitions are found at 59 and 77°C. Also here, the data are characteristic of partial protein dehydration. These results show clearly that DSC can easily be applied in a sensitive manner to control and characterize the integrity and hydration properties of concentrated protein samples in thin films.