Nanoporous Thin Films Research Articles

Nanoporous gold-palladium: A binary alloy with high catalytic activity for the electro-oxidation of ethanol

Abstract Nanoporous gold (NP–Au) is a promising versatile material that can be used in many fields due to its high conductivity, large surface area, and excellent stability. NP-Au is commonly functionalized by adding or doping other materials. However, difficult functionalizing procedures are oftentimes obstacles towards catalyst development. Herein, a simple method for alloying nanoporous gold with palladium (NP–AuPd) with a tunable Au/Pd ratio is developed. Ternary alloy films of Au–Pd–Mg are prepared by sputter deposition and Mg is dissolved from the alloy to make nanoporous alloy structures. The Au and Pd in NP-AuPd are evenly distributed over the entire structure. The catalytic activity of the developed NP-AuPd is evaluated by oxidizing ethanol in alkaline media. The optimized NP-AuPd shows remarkable catalytic activity and excellent stability. The nanoporous structure not only increases the number of reaction sites and mass transfer, but it also enhances the durability of the catalyst. The developed method can be extended to the preparation of binary nanoporous thin films with controlled compositions and desired catalytic activities.

Oxide Coated Nano-Porous Ag Thin Film for Chemical Sensing By Gas Flow Sputtering

A completely non-destructive analytical method is one of the great advantages of Raman spectroscopy. However, low efficiency of Raman signals should be improved to be widely used for detecting less than ppm of chemicals. Surface enhanced Raman scattering (SERS), which is a valuable technique for detecting the target substance very sensitively, is a method of amplifying Raman signals by the plasmon coupling effect at the gap between the nanoparticles. For this reason, materials and the nano-structure such as particle size, shape, gap and density were major factors for determining the performance of the SERS substrate.In this study, gas flow sputtering (GFS) was used for fabricating SERS substrates. The nano-porous structure was observed using scanning electron microscope (SEM) and crystal structures were also analyzed by X-ray diffraction (XRD). The density of the nano-porous structure was calculated using the thickness of the film and the mass difference before and after deposition.Silver (Ag) was widely studied as SERS substrate, due to excellent SERS effect and lower price than that of other noble metals. However, Ag has a significant degradation in SERS effect with time which appears to be a problem caused by oxidation of the Ag surface. Owing to this problem, fabricating a highly reproducible SERS substrate is a challenging issue and many researchers are conducting study.To solve this problem, Ag dense film and oxide film were sequentially deposited. Then, Ag nano-porous thin film was deposited on the oxide film to form a dielectric nano-gap between Ag dense film and Ag nano-porous thin film. Also, to protect from oxidation, Ag nano-porous thin film was coated with a thin oxide film using in-situ co-sputtering. The structure of nano-porous thin film was controlled by varying the sputtering power, time, process pressure.As a result, rhodamine 6G of less than 0.5 uM was successfully detected and it showed much improved Raman signal compared with single Ag nano-porous thin film. In addition, the aging problem, which was the most important issue, also reduced noticeably.

Graphitic Nanoporous Carbon Thin Films: Fabrication Method, Structural, Electrical and Gas Sensor Properties

Carbon nanoporous thin films are very attractive for application in fields of supercapacitors, fuel cells, gas sensors and others. However due to it very high resistance an employment of this material for resistance gas sensor is problematic. At the same time graphene based materials are very sensitive to different gas ambient and have a resistivity suitable for testing. In this work the new method of formation of high porous graphite-like thin films by RF magnetron plasma enhanced chemical vapor deposition (MPECVD) from argon-methane/argon-acetylene gas mixture followed by annealing at 650ºC, is suggested. A comparative study of transformation of nanoporous carbon film produced in different carbon-hydrogen atmosphere into graphitic one, their structural and electrical properties are presented. The films of nanoporous carbon were fabricated on silicon or SiO2/Si wafers. To clarify chemical structure of the film FTIR spectroscopy and XPS were used. Micro-Raman spectroscopy and AFM were applied to determine of structure and surface morphology correspondingly. X-ray refraction (XRR) method allows us to determine a density and a thickness of the films. Four point probe method and transmittance line (TSL) technique were used for the analysis of electrical properties. Additionally, electrical conductivity at different temperature and frequency was examined by measurement of resistance between two nearest Ni contacts. The same contacts were used to estimate of the gas sensitivity.It was shown that initial deposited films have mainly sp3 C-H bonds without appearance of silicon bonds. AFM demonstrates nanostructured surface morphology with size of the surface fluctuation about 3 nm; a density of the films is about 1.3 g/cm3 for both carbon films, that corresponds to nanoporous carbon; resistivity is about 108 Ohm×cm. After thermal annealing at 650°C for 30 min in N2 atmosphere the sp3 C-H bonds are disappeared, and C=C sp2 bonds are formed. Besides the resistivity the films synthesized in argon-methane gas mixture decreases to 104 Ohm×cm whereas the films synthesized in argon-acetylene gas mixture decreases their resistivity up to 102 Ohm×cm. The density of the C films synthesized in in argon-methane gas mixture reaches about 1.5 g/cm3 that corresponds to 34% of porosity, and material shows layered structure. The density of the C films synthesized in in argon-acetylene gas mixture falls to 1.01 g/cm3 that corresponds to 55% of porosity. Graphitized films synthesized in argon-methane gas mixture appears sensory sensitivity to moisture and ammonia whereas the films synthesized in argon-acetylene gas mixture show low sensitivity to these gases. The nature of the gas sensor resistor sensitivity is discussed.

Block-Copolymer Derived Nanoporous Thin Films for the Development of a L-BMAA Aptamer-Based Electrochemical Biosensor

Produced by diverse cyanobacteria, b-N-methylamino-l-alanine (L-BMAA) is a non-protein neurotoxic cyanotoxin that has been linked to an elevated incidence of neurodegenerative diseases such Parkinson’s and Alzheimer’s disease and Multiple Lateral Sclerosis. The continuing rising of water temperatures and eutrophication of the water bodies propitiate the increment and size of harmful algal blooms, subsequently increasing the production of L-BMAA and other cyanotoxins. This toxin is known to bioaccumulate in plants, animals and humans. Currently, the detection of L-BMAA in water is limited by its hydrophilicity, absence of ultraviolet and fluorescent properties, and the isomers that cause false positives. Given the threat that this cyanotoxin could represent to the long-term human health, it is imperative to develop new analytical techniques for its detection in water. Therefore, this project proposes the development of an impedimetric aptamer-based biosensor, using block-copolymer (BCP’s) derived nanoporous thin films as the electrode, for the detection of L-BMAA. Our hypothesis is that the development of such aptasensor will lead to the advancement of an innovative device for a sensitive, portable, economic and flexible way to achieve the detection of the cyanotoxin in water. To achieve this, we used BCP polystyrene-poly(methylmethacrylate) (PS-b-PMMA), known to form cylinder-like structures, to create recessed nanodisk-array electrodes (RNEs). These cylindrical nanostructures provide primary mass transport pathways for ionic and redox active species which changes upon analyte binding, making them ideal to use in biosensing applications. The nanoporous electrodes were prepared by spin-coating a PS-b-PMMA solution in toluene over gold-coated silicon wafers, followed by thermal annealing and UV etching. Different annealing times, temperatures and UV exposure has been used in order to produce the alignment of the cylindrical polymer microdomains in a vertical fashion over the surface of the electrode. The prepared films were characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), to confirm the formation of RNE’s. Under specific sets of conditions, CV data shows sigmoidal curves at high scan rates characteristic of RNE’s, suggesting the formation of this type of nanopores with a sufficiently large distance among them to attain radial diffusion. Atomic force microscopy (AFM) images of the samples evidence the formation of vertical nanopores but mixed with horizontal alignments. Furthermore, grazing incident small angle x-ray scattering (GISAXS)11 suggests that the polymer was well-dispersed among the surface although the expected scattering profile for RNEs is missing. Future work includes the optimization of the electrode preparation methods and the selection of a L-BMAA specific aptamer through graphene oxide-assisted selection evolution of ligands by exponential enrichment (GO-SELEX).

(Invited) Electrolytic Metal Atoms Enabled Manufacturing of Nanoporous Structures

Nanostructuring surface layers of a metallic electrode is of particular interest for a wide range of potential applications because the nanostructures can not only increase the active area accessible to liquid or gaseous media and reactants but also improve electron mobility in the solid ligaments. In the past two decades, several strategies have been developed to design and fabricate nanostructured electrodes with highly ordered networks and high surface area [1]. Template synthesis is a popular approach for preparing nanoporous metals ranging from microporous to macroporous, and further to hierarchical porous structures. The control over the nanostructures enables systematically experimental and theoretical studies of the electrode structure-activity relationship. Despite the great success of the template syntheses, they are limited to producing nanoporous thin films or macroparticles with irregular morphologies. Since the shape and size distribution of nanostructures are critical parameters of their function and utility for specific applications, the preparation of porous metal nanostructures with a well-defined shape is highly desirable and technologically important. For this purpose, surfactant mediated synthesis has received considerable attention in the fabrication of nanoporous metal structures. A seeding reduction method has been developed to synthesize nanoporous platinum and other metals. The nanoporous structures exhibit remarkable surfactant-dependent morphological properties. The above techniques provide a formidable toolkit for nanostructuring electrode materials and have been dramatically utilized in the manufacturing of electrochemical systems. However, the high cost of the manufacturing of nanostructures is still a barrier to their commercial implementation into the advanced systems. The cost-reduction of the manufacturing techniques is one crucial target for continued research.For the above purposes, a unique electrochemical method based on one-pot electrochemical deposition and dissolution of metal atoms onto a target electrode substrate is a front-runner technology. Based on this method, metal atoms deposit from their corresponding metal ions and are directed to “attack” the substrate electrode in the electrodeposition mode, and they are removed from the substrate in the subsequent electro-dissolution mode. Moreover, the electrochemical deposition and dissolution of metal atoms can be conveniently manipulated through simple potential modulation such as potential cycles. In principle, no net consumption of chemicals such as metal salts, can be achieved. A range of metallic and alloy electrodes have been successfully nanostructured using different electrolytic metal atoms by this method [2, 3]. Some of them have demonstrated impressive performance for several different application in electrocatalysis, energy storage, and sensors.In this presentation, we will introduce the thermodynamic and kinetic fundamentals of this manufacturing technique, the characterization of resulting nanostructures, the analysis of their electrochemical behavior, the implementation of this technique for the development of advanced electrodes, and a preliminary economic analysis of this technique.

Sustainable and selective formic acid production from photoelectrochemical methanol reforming at near-neutral pH using nanoporous nickel-iron oxyhydroxide-borate as the electrocatalyst

Industrial production of formic acid requires a highly energy-intensive process involving carbonylation of methanol with fossil fuel-based CO to methyl formate and subsequent hydrolysis of methyl formate to formic acid. In this study, we present a sustainable and selective production of formic acid from methanol-reforming using electro-synthesized nanoporous nickel-iron oxyhydroxide-borate thin film (nanoFe:Ni-Bi) as the electrocatalyst at near-neutral pH. We found that the incorporation of a suitable amount of iron not only facilitated the formation of active Ni3+ species but also improved the kinetics of methanol oxidation with active Ni3+ species, resulting in the significant enhancement in the formate production. Notably, nanoFe:Ni-Bi with optimal Fe content exhibited a turnover frequency (TOF) of 152.71 ± 9.95 h−1 with Faradic efficiency for formate production (FEformate) of 66.3 ± 1.7%, whereas nanoporous nickel oxyhydroxide-borate only showed a TOF of 56.65 ± 12.68 h−1 with FEformate of 30.5 ± 5.6%. In addition, a highly efficient and selective photoelectrochemical methanol-reforming system using nanoFe:Ni-Bi modified BiVO4 photoanode was established. In contrast to the negligible activity of the pristine BiVO4 photoanode, nanoFe:Ni-Bi modified BiVO4 photoanode exhibited formate production rate of 5.7 ± 1.0 μmole cm−2h−1 with a FEformate of 94.6 ± 12.3% at an applied potential of 0.55 V vs. RHE under light illumination. This study provides a sustainable and less-energy intensive alternative route for the production of formic acid.

Design and characterization of mechanically stable, nanoporous TiO2 thin film antimicrobial coatings for food contact surfaces

To improve food safety during food processing, we developed a titanium dioxide, photocatalytic coating that can be applied to standard stainless-steel food contact surfaces (FCS) via a sol-gel method. These thin, self-assembled, porous coatings have the potential to reduce surface cross-contamination in food processing environments when used in combination with oxygen, water, and ultraviolet (UV) light through photocatalytic processes. Under these conditions, the coating releases reactive oxidative species (ROS), the amount of which is directly related to the coating's photocatalytic activity; ROS are responsible for killing microorganisms. In this study, a quadratic mathematical model is used to optimize the relationships among synthetic parameters, including sol-gel aging time and sintering temperature, and the resulting photocatalytic activity of the coatings. Using statistical analysis, the coatings synthesized using 223 h aging time and 507 °C sintering temperatures were predicted to yield maximized photocatalytic activity within the experimental range. We verified this prediction experimentally, and compared the relationships between photocatalytic activity and the areal porosity of the photocatalytically-optimized coatings to determine how the porosity of the coatings impacted their photocatalytic activity. Lastly, in an effort to assess real-life applications, the mechanical stability of the photocatalytically-optimized coatings was evaluated using nanoindentation and pencil hardness testing. By tailoring the coatings' physicochemical properties to optimize for photocatalytic performance and mechanical stability, we can create photocatalytic coatings for food contact surfaces that have the potential to prevent or minimize cross-contamination during food processing.

Porous Ultra-Thin Films from Photocleavable Block Copolymers: In-Situ Degradation Kinetics Study of Pore Material.

On the basis of the major application for block copolymers to use them as separation membranes, lithographic mask, and as templates, the preparation of highly oriented nanoporous thin films requires the selective removal of the minor phase from the pores. In the scope of this study, thin film of polystyrene-block-poly(ethylene oxide) block copolymer with a photocleavable junction groups based on ortho-nitrobenzylester (ONB) (PS-hν-PEO) was papered via the spin coating technique followed by solvent annealing to obtain highly-ordered cylindrical domains. The polymer blocks are cleaved by means of a mild UV exposure and then the pore material is washed out of the polymer film by ultra-pure water resulting in arrays of nanoporous thin films to remove one block. The removal of the PEO materials from the pores was proven using the grazing-incidence small-angle X-ray scattering (GISAXS) technique. The treatment of the polymer film during the washing process was observed in real time after two different UV exposure time (1 and 4 h) in order to draw conclusions regarding the dynamics of the removal process. In-situ X-ray reflectivity measurements provide statistically significant information about the change in the layer thickness as well as the roughness and electron density of the polymer film during pore formation. 4 H UV exposure was found to be more efficient for PEO cleavage. By in-situ SFM measurements, the structure of the ultra-thin block copolymer films was also analysed and, thus, the kinetics of the washing process was elaborated. The results from both measurements confirmed that the washing procedure induces irreversible change in morphology to the surface of the thin film.

Two-step modification of phonon mean free paths for thermal conductivity predictions of thin-film-based nanostructures

As one simple metamaterial, nanopatterns are often fabricated across a thin film so that the thermal transport can be manipulated. The etched sidewalls for these nanostructures are usually rough due to surface defects introduced during the nanofabrication, whereas the top and bottom film surfaces are smoother. In existing analytical models, the contrast between these surfaces has not been addressed and all boundaries are assumed to be diffusive for phonon reflection. In this paper, a new two-step approach to address this issue is proposed for phonon transport modeling of general thin-film-based structures. In this approach, the effective in-plane phonon mean free paths (ΛFilm) are first modified from the bulk phonon MFPs to account for the influence of the top/bottom film surfaces, with possibly enhanced probability of specular phonon reflection at cryogenic temperatures. This ΛFilm is further modified to include the scattering by etched sidewalls with almost completely diffusive phonon scattering. Such a two-step phonon mean free path modification yields almost identical results as frequency-dependent phonon Monte Carlo simulations for etched nanowires and representative nanoporous thin films. This simple yet accurate analytical model can be applied to general thin-film-based nanostructures to combine the phonon size effects along orthogonal directions.

Morphology study and threshold measurement of laser induced damage of nano-porous antireflective silica thin films in nano- and femtosecond pulse regimes

Laser induced damage threshold (LIDT) of nano-porous antireflective silica thin films is measured using 10 ns laser pulses at λ = 532 nm. The thin films are prepared by dip-coating of BK7 substrates and then drying them by three different heating methods, to see how their LIDT and transmission are affected. Furthermore, using SEM imaging, the morphology of the laser induced damages is inspected and compared to those of similar samples, previously irradiated by femtosecond laser pulses at λ = 800 nm. The images evidently show that in the regions damaged by nanosecond pulses, the silica nanoparticles are melted and fused to each other, while in the samples irradiated by femtosecond pulses, the silica nanoparticles are sputtered and dispersed around, in the damaged area. The SEM images clearly demonstrate the different damage mechanisms involved in the nanosecond and femtosecond regimes of interaction.

Synthesis of amphiphilic poly(ethylene glycol)-block-poly(methyl methacrylate) containing trityl ether acid cleavable junction group and its self-assembly into ordered nanoporous thin films

Abstract A strategy for the synthesis of well defined poly(ethylene glycol)-block-poly(methyl methacrylate) diblock copolymers containing trityl ether acid cleavable junctions is demonstrated. This approach is achieved by using a combination of poly(ethylene glycol) macroinitiator containing a trityl ether end group, which is susceptible to acid cleavage, and atom transfer radical polymerization technique. The trityl ether linkage between blocks can be readily cleaved in solution or in solid phase under very mild acid condition, which has been confirmed by 1H NMR. These diblock copolymers have been used to successfully fabricate nanoporous thin films by acid cleavage of trityl ether junction followed by complete removal of poly(ethylene glycol) block. The fabricated nanoporous thin films may have a wide range of application such as Recessed Nanodisk-array electrode (RNE) or as a template to fabricate nanoelectrode array for senor applications.

Synthesis and characterization of nanoporous copper thin films by magnetron sputtering and subsequent dealloying

Nanoporous copper (NPC) films with ligament sizes ranging from 18 to 46 nm were synthesized by dealloying CuxAl100-x (x = 22–37 atomic percent) precursor films with thickness from 0.5 to 1.2 μm in 0.01–1 M NaOH. The precursor alloy films were deposited on silicon (100) via magnetron co-sputtering. Effects of precursor alloy and dealloying conditions on the morphology of NPC films were investigated by the use of scanning electron microscopy and energy-dispersive X-ray spectroscopy, while the cross-sectional areas were characterized using focused ion beam. The yield strengths of NPC films were measured by the nanoindenter. The morphology of NPC films transformed from well-distributed to aggregated clusters with the increase of Cu concentration from 22 to 37 atomic percent. Limited residual Al and oxidation can be detected in NPC films, regardless of dealloying conditions. The ligament size of NPC films shows no significant difference with the change of NaOH concentrations, while cracks observed in NPC films seem to be mitigated with extended dealloying time. The yield strengths of NPC thin films are higher than those predicted by bulk Cu or pure Cu films.

Nanoporous WO3 films synthesized by tuning anodization conditions for photoelectrochemical water oxidation

Morphology engineering is of prime significance in designing semiconductor photoelectrodes for efficient photoelectrochemical (PEC) fuel generation. Herein, we report a strategy to fabricate nanostructured tungsten oxide films using anodic oxidation of tungsten and their performance as photoanodes for PEC water splitting. A solution of an organic compound, dimethyl sulfoxide, with hydrofluoric acid was used as the electrolyte. The anodization parameters such as voltage and electrolyte temperature were found to have a critical influence in determining the porous nature and dimensions of the resulting oxide film. Anodization conducted at a voltage ~10 V and a temperature ~40 °C led to the formation of compact tungsten oxide films due to the low strength of the electric field partially responsible for the porous morphology development. The surface of the film became porous at elevated temperatures. At higher voltages, a thin nanoporous film atop a thicker compact layer was formed; however, the structure became more disordered and less porous when the electrolyte temperature was increased. The study demonstrated that by adjusting the voltage and temperature, the oxide film morphology could be varied from a compact layer to a porous structure resembling nanotubes. The films heat treated at 500 °C attained the monoclinic phase of WO3. The PEC performance was influenced strongly by the morphology of the films. The films with nanotube like morphology yielded incident photon to current conversion efficiency values of over 40%. This study would provide a practical basis for developing optimal WO3 nanostructures for efficient PEC fuel generation.

Differential processing of high-molecular-weight kininogen during normal pregnancy.

Studies identified kininogen as a potential biomarker of preeclampsia, a major cause of adverse maternal outcomes. High-molecular-weight kininogen (HK) and its activated form participate in numerous pathways associated with establishing and maintaining pregnancy. However, dynamic changes in HK and naturally occurring HK-derived peptides during the natural course of pregnancy are largely unknown. Longitudinal serum samples during the course of normal pregnancy (trimesters T1, T2, T3) from 60 pregnant women were analyzed by western blot with an anti-HK antibody. Circulating peptides in longitudinal serum specimens derived from 50 participants were enriched using nanoporous silica thin films. Peptides were identified by liquid chromatography/tandem mass spectrometry (LC/MS/MS) and database searching. Relative quantification was performed using MaxQuant and in-house scripts. Normality was evaluated by either ANOVA or Friedman tests with p < 0.05 for statistical significance. Western blotting revealed that HK significantly decreased during normal pregnancy (T1 vs T2, p < 0.05; T1 vs T3, p < 0.0001). A 100 kDa intermediate increased during pregnancy (T1 vs T2, p < 0.005; T1 vs T3, p < 0.01). Moreover, the heavy chain (T1 vs T2, p < 0.0001; T1 vs T3, p < 0.0001; T2 vs T3, p < 0.01) and light chain (T1 vs T2, p < 0.0001; T1 vs T3, p < 0.0001; T2 vs T3, p < 0.05) significantly increased during pregnancy. LC/MS/MS analysis identified 180 kininogen-1 peptides, of which 167 mapped to domain 5 (D5). Seventy-three peptides with ten or more complete data sets were included for further analysis. Seventy peptides mapped to D5, and 3, 24, and 43 peptides showed significant decrease, no trend, and significant increase, respectively, during pregnancy. This study demonstrates dynamic changes in HK and naturally occurring HK-derived peptides during pregnancy. Our study sheds light on the gestational changes of HK and its peptides for further validation of them as potential biomarkers for pregnancy-related complications.

Development of highly performing TiO2 complex thin films by novel combined physico-chemical process for enhanced photo-catalytic applications

Structural, morphological, optical, photoresponse and photo-catalytic properties of TiO2 nanostructured thin films, prepared through novel combined physico-chemical (GLADOX) process by varying the electrolyte ratio have been investigated. TiO2 nanoporous structured thin films were prepared by anodization of Ti thin films, prepared on FTO substrate by using DC magnetron sputtering equipped with the glancing angle arrangement and by varying electrolyte ratio of anodization. The structural studies show that the TiO2 nanostructured thin films have a crystal structure of tetragonal with a crystalline phase of rutile with an appreciable secondary phase; monoclinic TiO. The morphological studies reveal the nanoporous structure of the GLADOX deposited TiO2 thin films. The optical studies show that the absorbance and band gap of the optimized TiO2 thin films prepared at optimized electrolyte ratio are ideal for photo-catalytic applications. The photo-catalytic properties of TiO2 nanostructured thin films were investigated by the degradation of methylene blue (MB) dye in the presence of visible light and the influence of secondary phase on the photo-catalytic performance is also investigated with the support of photoresponse studies.

Controlling the Electronic Properties of a Nanoporous Carbon Surface by Modifying the Pores with Alkali Metal Atoms.

We investigate a process of controlling the electronic properties of a surface of nanoporous carbon glass-like thin films when the surface pores are filled with potassium atoms. The presence of impurities on the surface in the form of chemically adsorbed hydrogen and oxygen atoms, and also in the form of hydroxyl (OH) groups, is taken into account. It is found that even in the presence of impurities, the work function of a carbon nanoporous glass-like film can be reduced by several tenths of an electron volt when the nanopores are filled with potassium atoms. At the same time, almost all potassium atoms are ionized, losing one electron, which passes to the carbon framework of the film. This is due to the nanosizes of the pores in which the electron clouds of the potassium atom interact maximally with the electrons of the carbon framework. As a result, this leads to an improvement in the electrical conductivity and an increase in the electron density at the Fermi level. Thus, we conclude that an increase in the number of nanosized pores on the film surface makes it possible to effectively modify it, providing an effective control of the electronic structure and emission properties.

Thermal studies of nanoporous thin films with added periodic nanopores—a new approach to evaluate the importance of phononic effects

Phonon transport within periodic nanoporous materials has been intensively studied for its potential applications in thermoelectrics, heat waveguides, thermal diodes, and heat imaging. It is now acknowledged that wave effects of lattice vibrations, i.e., phononic effects, are only important for ultrafine nanoporous structures and/or at cryogenic temperatures. Experimental evidence is usually found by comparing the thermal conductivities of periodic and aperiodic nanoporous Si films, or by measuring the specific heat to check the phonon dispersion variation. In this work, a new approach is used to evaluate the impact of possible wave effects, simply by comparing the thermal conductivity of the same Si thin film with increased rows of nanopores as drilled with a focused ion beam. In the temperature range of 85–300 K, it is found that the total thermal resistance of the thin film increases almost linearly with the number of rows, indicating dominant incoherent phonon transport or negligible wave effects. For nanopores with small spacing, the amorphous regions around pore edges can largely overlap so that the whole region can be treated as a homogeneous amorphous material with nanoporosity. When the pore spacing is larger, the amorphous pore edges expand the effective pore diameter that is used in the data analysis based on frequency-dependent phonon Monte Carlo simulations. A better understanding of these nanoporous films can benefit their applications in thermoelectrics and thermal management of thin-film-based electronic devices.

Nanopore-Enhanced Drop Evaporation: When Cooler or More Saline Water Droplets Evaporate Faster.

The evaporation of water droplets on surfaces is a ubiquitous phenomenon in nature and has critical importance in a broad range of technical applications. Here, we show a substantial enhancement of liquid evaporation rate when droplets are on nanoporous thin film surfaces. We also reveal how this nanopore-enhanced evaporation leads to counterintuitive phenomena: cooler or more saline water droplets evaporate faster. We find indeed that, contrary to typical evaporation behavior of sessile droplets on nonporous surfaces, the droplets placed on nanoporous thin films evaporate more rapidly when salt concentration increases or when the temperature decreases. This peculiar droplet evaporation behavior is related to the key role of the steady wetted annulus that is self-generated into the nanopore network in the drop periphery, which leads to an effectively enhanced evaporation area that controls the overall evaporation process. Our results provide the prospect of conceiving fresh scenarios in the evaporation of drops on surfaces in both relevant applications and fundamental insights.

Increased power conversion efficiency of dye-sensitized solar cells with counter electrodes based on porous polypyrrole

The porous polypyrrole (PPPy) was synthesized with zeolitic imidazolate framework-8 (ZIF-8) used as template by simple hydrothermal. The resultant PPPy was employed as counter electrode (CE) in dye-sensitized solar cell (DSSC). The 5% Cu(ClO4)2 and 2% ZIF-8 ratio in PPPy at 100 °C by simple hydrothermal method demonstrates comparable performance with traditional Pt in DSSC as CE, 8.63% and 9.05% energy conversion efficiency (η), respectively. The electrochemical and photo-electrochemical as well as impedance spectra measurements revealed that ZIF-8 as template by simple hydrothermal method is a effective way for preparing PPPy at 100 °C as CE in DSSC, which may open up an alternative choice for the future industrial application. In DSSC, PPPy at 100 °C is one of the most promising material used for nano-porous thin film when, it serves as CE due to its appropriate low cost, and easy preparation method. The template polymerization of PPPy on zeolytes is interesting method for DSSC and as electro-catalyst, it can be big perspective in polymer membrane fuel cells, Zn air battery, Li ion battery and also useful for hydrogen production from water. So, this article will broaden the application of conductive polymers in DSSCs as well as above described fields.

Arrayed nanopore silver thin films for surface-enhanced Raman scattering.

Active substrates are crucial for surface-enhanced Raman scattering (SERS). Among these substrates, large uniform area arrayed nanoporous silver thin films have been developed as active substrates. Arrayed nanoporous silver thin films with unique anisotropic morphologies and nanoporous structures can be fabricated onto the nanoporous anodic aluminum oxide (AAO) of controlled pore size and interspacing by precisely tuning the sputtering parameters. These thin films preserve locally enhanced electromagnetic fields by exciting the surface plasmon resonance, which is beneficial for SERS. In this study, nanoporous silver thin films were transferred into polymethylmethacrylate (PMMA) and polydimethylsiloxane (PDMS) substrates using our recently invented template-assisted sol–gel phase inverse-imprinting process to form two different nanopore thin films. The as-formed Ag nanoporous thin films on PMMA and PDMS exhibited intensively enhanced SERS signals using Rhodamine 6G (R6G) as the model molecule. The two nanopore thin films exhibited opposite pore size-dependent SERS tendencies, which were elucidated by the different enhancement tendencies of the electric field around pores of different diameters. In particular, the Ag nanoporous thin film on PMMA exhibited an R6G detection limit of as low as 10−6 mol L−1, and the SERS enhancement factor (EF) was more than 106. The low detection limit and large EF demonstrated the high sensitivity of the as-prepared SERS substrates for label-free detection of biomolecules. Compared with conventional smooth films, this nanopore structure can facilitate future application in biomolecular sensors, which allows the detection of single molecules via an electronic readout without requirement for amplification or labels.