Non-porous Thin Films Research Articles

Effect of particle size on optical and electrical properties of thin films – a simulation approach

This paper presents a simulated investigation of the relationship between surface roughness and particle size as well as the resulting impact of the both on the thin film’s physical and optical properties. Non-porous thin films are created through computer simulation for a range of particle sizes following the random deposition with a surface relaxation approach. For the deposited thin films different fundamental parameters like transmittance, reflectance, absorption coefficients, frequency dependent dielectric constants, loss angle, refractive indices, optical band gap have all been calculated and in this process of calculation the fundamental values of two different materials; zinc oxide (ZnO and cadmium selenide (CdSe) are taken. It has been seen that when the particle sizes are comparable the calculated values of optical band gap of both ZnO and CdSe matches well with the experimental values of the same reported by others. This is probably the first effort to develop a direct relation between the particle size with different fundamental optical properties of different materials through simple simulation which agrees well with the experimental result. This would definitely help the experimental researchers in the field of material science to design their experiments as per the desired requirements.

Comparative studies on thin polycaprolactone-tricalcium phosphate composite scaffolds and its interaction with mesenchymal stem cells

BackgroundHybrid scaffolds combining biodegradable polymers and ceramic particles for control of cell adhesion and proliferation are interesting materials for tissue engineering applications. Combinations of biodegradable polymers and ceramics are to provide higher beneficial functionalities to tissue engineering scaffolds with addition of different cell specific bio-factors. Many such hybrid combinations have been reported by several researchers around the world by using various methods and solvents as well as bioactive matrix polymers to fabricate such biomaterials. However, thin hybrid scaffolds with high porosity, cell adhesion factors and biodegradability, as well as the ability to support stem cells often require tedious processes like electrospinning, freeze drying, etc. A simple method to develop porous biodegradable hybrid scaffolds with proper cell adhesion factors is still the need of the hour in tissue engineering and regenerative medicine.MethodThin biodegradable poly(ε-caprolactone) (PCL) based hybrid scaffolds were developed in combination with α-tricalcium phosphate (TCP) particles, gelatin and fibronectin separately and the fabricated scaffolds were evaluated systematically using human mesenchymal stem cells (hMSCs) for tissue engineering applications. A simple modified solvent casting method combined with gas foaming process was used to develop porous thin hybrid structures and compared their properties with those of corresponding non-porous hybrid scaffolds. The TCP particles distribution, morphology, biodegradability and functional groups of the different hybrid scaffolds were analyzed using energy-dispersive X-ray spectroscopy (EDX), light microscopy/scanning electron microscopy (SEM), buffer solutions and Fourier-transform infrared spectroscopy (FTIR), respectively The cellular and tissue regeneration behaviors such as in vitro cell attachment (live/dead assay), cell proliferation (CCK-8 assay) and histological studies were performed using hMSCs.ResultsThin PCL-based hybrid scaffolds were fabricated using modified solvent casting method. Homogeneous distribution of TCP particles in the scaffolds were confirmed by EDX. Cellular interactions of the hybrid scaffolds demonstrated overall higher cell adhesion, proliferation and tissue regeneration on the non-porous thin films of PCL-TCP, PCL-TCP-gelatin and PCL-TCP-fibronectin. Coating of fibronectin was remarkable in induction of cell adhesion and proliferation.ConclusionsThe experimental results revealed that diversely designed PCL-TCP thin hybrid films showed high cell interaction and proliferation with hMSCs. From the results of the cell viability, attachment, proliferation and histological analyses as well as their biodegradation and coating effects, we conclude that these thin PCL-TCP hybrid films are suitable for tissue engineering applications.

Comparison of Bonds Existing Between C60 Fullerene and Polyamide Molecules in Various Nanocomposite Materials

Fullerene–polymer composites may find applications in different areas, particularly, in membrane technology. The formation of bonds between molecules of C60 fullerene and poly(phenylene isophtalamide) (PA) in PA-C60 composites was investigated. Powder-like PA-C60 mixtures, ultrafiltration membranes and nonporous thin films were studied by extracting C60 from the samples with various solvents. It was found that two types of fullerene coexist in the studied composites: the free (easily extractable) fullerene and the bound molecules. The percentage of extractable C60 in a given sample depends on sample composition and the method used for obtaining this nanocomposite material. An important factor in increasing the C60-PA bond strength is the duration of the material formation procedure. The quantitative processing of digital photographs of membranes, scanning electron microscopy (SEM), and electron spectroscopy for chemical analysis (ESCA) data showed that the free C60 is mainly located close to the active membrane surface. The bound C60 molecules are distributed throughout the membranes and films.

Water Absorption and Diffusion Characteristics of Nanohydroxyapatite (nHA) and Poly(hydroxybutyrate‐co‐hydroxyvalerate‐) Based Composite Tissue Engineering Scaffolds and Nonporous Thin Films

Water uptake characteristics of poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV‐) based composite tissue engineering (TE) scaffolds incorporating nanosized hydroxyapatite (nHA) have been investigated. The water absorption of these composite scaffolds obeyed the classical diffusion theory for the initial period of time. The diffusion coefficients of the composite scaffolds during the water absorption were much faster than those for the nonporous thin films, suggesting that the water uptake process depends on the presence of porosity and porous microstructure of the composite scaffolds. The incorporation of nHA increased the water uptake of both the composite scaffolds and thin films. It was also observed that the equilibrium uptake increased with the incorporation of nHA. This increase in the water uptake was largely due to the nHA particle aggregates in the microstructure of both composite scaffolds and thin films. The activation energy for diffusion was also determined using the Arrhenius equation for both porous scaffolds and thin films and the results suggested that the activation energy for scaffolds was lower than that for thin films.

Structure of hydrogenated diamond like carbon by Micro-Raman spectroscopy

The first-, second- and higher order Raman spectra of hydrogenated diamond like carbon (HDLC) are analyzed considering the effect of partial hydrogenation of hexagonal sp 2 (C C) carbons on the characteristic G and D bands of graphitic materials. That coherency of sp 3 C H and sp 2 C C carbons in HDLC can produce a continuous, non-porous thin film having atomically smooth surface is reported as a new result.

Study of in vitro degradation of biodegradable polymer based thin films and tissue engineering scaffolds

This paper reports the in vitro degradation of three-dimensional, highly porous tissue engineering scaffolds and non-porous thin films based on poly (L-lactide) (PLLA) biopolymers. The tissue engineering scaffolds were produced through the emulsion freezing/freeze-drying technique. The nonporous thin films were produced using solvent casting technique. In vitro degradation experiments in terms of water uptake, water diffusion and weight loss were performed for various period of time. Results show that the scaffolds had more water uptake than the thin films at the same experimental condition. After 6 weeks, the weight loss of scaffolds was much greater than the films.

Characterisation of chemical bath deposited CdS thin films on different substrates using electrolyte contacts

Aqueous electrolyte contacts have been used to characterize CdS thin films grown using chemical bath deposition (CBD) on 4 different fluorine-doped tin oxide (FTO) coated conducting glass substrates (identified by the supplier Pilkington Group Limited as TEC-15, TEC-7, NSG low-E, and NSG Solar). The porosity of CdS layers prepared on different substrates was evaluated by voltammetry using the oxidation of hexacyanoferrate (II) to probe residual electrochemical activity arising from the underlying conducting substrate. Using a simple model, it can be concluded that thin films deposited on NSG substrates at 85 °C are probably nanoporous with a porosity of up to ~ 20% of the coverage of the CdS surface. The porosity appears to depend on the nature of the substrate rather than the physical parameters of the deposition. In the case of non-porous films deposited on TEC substrates, analysis of the impedance gave values of the space charge capacitance from which the doping density and flat band potential were derived. The doping densities for CdS were found to be in the order of 10 17 cm −3–10 20 cm −3 depending on the substrate. The transmission spectra, recorded in the UV–visible range, reveal a relatively high transmission coefficient in the obtained films. The transmittance data further indicate that the optical band gap is closely related to the deposition conditions. Micro-Raman analysis showed structural similarity and differences between porous and non-porous thin films.

Capacitive Field-effect (bio-)chemical Sensors Based on Nanocrystalline Diamond Films

AbstractCapacitive field-effect electrolyte-diamond-insulator-semiconductor (EDIS) structures with O-terminated nanocrystalline diamond (NCD) as sensitive gate material have been realized and investigated for the detection of pH, penicillin concentration, and layer-by-layer adsorption of polyelectrolytes. The surface oxidizing procedure of NCD thin films as well as the seeding and NCD growth process on a Si-SiO2 substrate have been improved to provide high pH-sensitive, non-porous thin films without damage of the underlying SiO2 layer and with a high coverage of O-terminated sites. The NCD surface topography, roughness, and coverage of the surface groups have been characterized by SEM, AFM and XPS methods. The EDIS sensors with O-terminated NCD film treated in oxidizing boiling mixture for 45 min show a pH sensitivity of about 50 mV/pH. The pH-sensitive properties of the NCD have been used to develop an EDIS-based penicillin biosensor with high sensitivity (65-70 mV/decade in the concentration range of 0.25-2.5 mM penicillin G) and low detection limit (5 μM). The results of label-free electrical detection of layer-by-layer adsorption of charged polyelectrolytes are presented, too.

Towards nanoporous polymer thin film-based drug delivery systems

A nanoporous polymer thin film has been developed as a potential platform for drug delivery. The film was fabricated by a light-induced polymerization process in which non-reactive solvent was first separated from photopolymer (dipentaerythritol penta-/hexa-acrylate as the monomer) and then removed from polymer via evaporation, yielding pores with diameters between 20 and 40 nm. Loading and release of Rhodamine B (drug model molecules) on both porous and non-porous thin films proved that nanopores enhanced the film's effectiveness in encapsulating and releasing the drug model molecules, which was attributed to the high surface-to-volume ratio of nanoporous film. Ultrasound-enhanced cumulative and pulsatile release revealed the advantages of ultrasound in controlled drug delivery.

Evaluation of response characteristics of resistive oxygen sensors based on porous cerium oxide thick film using pressure modulation method

In order to reduce the response time of resistive oxygen sensors using porous cerium oxide thick film, it is important to ascertain the factors controlling response. Pressure modulation method (PMM) was used to find the rate-limiting step of sensor response. This useful method measures the amplitude of sensor output ( H( f)) for the sine wave modulation of oxygen partial pressure at constant frequency ( f). In PMM, “break” response time, which is minimum period in which the sensor responds precisely, can be measured. Three points were examined: (1) simulated calculations of PMM were carried out using a model of porous thick film in which spherical particles are connected in a three-dimensional network; (2) sensor response speed was experimentally measured using PMM; and (3) the diffusion coefficient and surface reaction coefficient were estimated by comparison between experiment and calculation. The plot of log f versus log H( f) in the high f region was found to have a slope of approximately −0.5 for both porous thick film and non-porous thin film, when the rate-limiting step was diffusion. Calculations showed the response time of porous thick film was 1/20 that of non-porous thin film when the grain diameter of the porous thick film was the same as the thickness of non-porous thin film. At 973 K, “break” response time ( t b) of the resistive oxygen sensor was found by experiment to be 109 ms. It was concluded that the response of the resistive oxygen sensor prepared in this study was strongly controlled by diffusion at 923–1023 K, since the experiment revealed that the slope of plot of log f versus log H( f) in the high f region was approximately −0.5. At 923–1023 K, the diffusion coefficient of oxygen vacancy in porous ceria ( D V) was expressed as follows: D V (m 2s −1) = 5.78 × 10 −4 exp(−1.94 eV/ kT). At 1023 K, the surface reaction coefficient ( K) was found to exceed 10 −4 m/s.

Response behaviour of tin oxide thin film gas sensors grown by MOCVD

Tin oxide is the most widely studied semiconducting oxide for use in gas sensor applications. However, the majority of previous study has been centred around porous media produced as thick films or thin sputtered films. This paper concerns the behaviour of relatively non-porous thin films grown by metal-organic chemical vapour deposition (MOCVD) and presents their response behaviour to the hazardous gases H 2S, CH 4 and NO 2. The films were produced from tetratertiarybutoxytin at 350°C. They were found to act as selective H 2S sensors at room temperature and show sensitive responses to all three gases above 200°C. The response to all gases is a reduction in resistance and the effect of water vapour on the response is small.