Different Number Of Bilayers Research Articles

Skew scattering dominated anomalous Hall effect in Si/Ni multilayers containing varying number of bilayers

A systematic study of the skew scattering dominated anomalous Hall effect (AHE) in Si/Ni multilayers has been carried out on several samples containing different number of bilayers. The investigation is performed by preparing a series of Si10Å/Ni30ÅN multilayers. When the number of bilayers (N) is decreased, structural analysis showed that the size of Ni nanocrystallites and the distance between them decreases whereas their count rises. As a result, the saturation magnetization lowers with N. Furthermore, the perpendicular magnetic anisotropy of the multilayers improves as N is reduced. The saturated AHE resistance (RHSA) is also found to decrease as N increases due to the decreases of the Si/Ni interface area and scattering effect from the Ni nanocrystallites. A maximum of about 28 times enhancement in RHSA is observed for the sample with N = 1 when compared with that for N = 24. It is seen that the skew scattering is the dominant mechanism which is responsible for the AHE in the Si/Ni multilayers.

Cathodic Vacuum ARC Multilayer Coatings (TiZrSiY)N/NbN: Structure and Properties Depending on The Deposition Interval of Alternate Layers

Two series of multilayer coatings with different numbers of bilayers (268 and 536, respectively) were synthesised using the cathodic vacuum-arc deposition (CVAD) with the simultaneous sputtering of two different cathodes. The first cathode was made of the multicomponent TiZrSiY material, and the second one was made of technical niobium. The coatings were condensed in a nitrogen atmosphere at a constant negative bias potential applied to the substrate. The resulting coatings have a distinct periodic structure composed of individual layers of (TiZrSiY)N and NbN with the thicknesses determined by the deposition interval (10 or 20 s, respectively). The total thicknesses of the coatings determined by the number of bilayers were 11 and 9 microns, respectively. The formation of polycrystalline TiN and NbN phases with grain size comparable to the size of the layers has been identified for both series of coatings. The layers exhibit a columnar structure growth with a predominant orientation (111). The hardness of the experimental coatings depends on the thickness of the layers and reaches 39.7 GPa for the coating with the smallest layer thickness. The friction coefficient of the obtained coatings varies from 0.512 to 0.498 and also depends on the thickness of the layers. A relatively large value of the friction coefficient is due to high roughness and the presence of a droplet fraction on the surface as well as in the volume of the coatings.

Development of Polyethersulfone Nanofiltration Membrane with Layer-by-Layer Method for Xylitol Purification

This work is aimed to develop polyethersulfone (PES) nanofiltration (NF) membrane with layer-by-layer (LBL) polyelectrolytes of chitosan (CHI) and poly(acrylic acid) (PAA) for xylitol purification from fermentation broth. Different number of bilayers and type of terminating layer were manipulated for producing more hydrophilicity, negatively charged with improved performance compared to pristine PES membrane. Successful deposition of polyelectrolyte layers onto PES membrane was able to be proven using various tests such as contact angle, Zetasizer and FT-IR. The results obtained have proven that LBL can develop PES membrane with higher resistance to fouling. From Zeta potential analysis, the value of pristine PES membrane's negativity confirmed the theory of negatively charged substrate for LDL. The negative value of PES membrane increased from -16.5 mV to -32.7 mV after being modified to PES (CHI/PAA)6. From FT-IR spectra, the formation of CHI/PAA complexes on the membrane's surface is confirmed through the presence of stretching peaks of -COOH, -NH3+ and -NH2+ groups The pure water flux reduces from 47.40 ±6.30 L⁄m2.h to 7.40 ±1.64 L⁄m2.h after being modified to PES (CHI/PAA)2. The rejection performance of xylitol for PES (CHI/PAA)2 is higher (84.95%) than pure PES membrane (66.17%), while (CHI/PAA)4 offered the lowest selectivity towards xylitol than arabinose and thus able to obtain higher purity of xylitol as retentate. LBL surface modification using CHI/PAA can develop PES membrane with higher hydrophilicity, negatively charge, and is able to give better xylitol rejection compared to pure PES.

Effect of Bilayer Thickness and Bias Potential on the Structure and Properties of (TiZr/Nb)N Multilayer Coatings as a Result of Arc-PVD Deposition.

This work is devoted to the study of the formation of nanostructured multilayer coatings (TiZr/Nb)N on the surface of an AISI 321 steel substrate depending on the deposition parameters of the Arc-PVD method. The results of the X-ray diffraction analysis showed the formation of solid solution (TiNb)N and ZrN in the multilayer coatings with an FCC structure, ε-NbN with a hexagonal structure, as well as with a small volume fraction of the ε-Ti2N and β-Nb2N phase. On the basis of phase composition data, it is possible to assume that an increase in the number of bilayers leads to a decrease in the nitrogen concentration in the bilayers and, consequently, to a decrease in the volume fraction of ε-NbN and β-Nb2N nitrides. In all investigated systems obtained at -100 V and -200 V bias potentials, ε-NbN is the main phase. The study of the element distribution over the thickness of the (TiZr/Nb)N coating confirms the results of the X-ray diffraction analysis. The use of the structure model in the form of alternating layers allows for significantly improving the adhesion characteristics of the protective coating, as well as ensuring their high hardness. Based on the experimental results, it is possible to analyze changes in the mechanical and tribological properties of multilayer coatings depending on the number of applied bilayers. The results of the study of the elastic modulus and hardness of multilayer coatings (TiZrNb)N with different numbers of bilayers showed that a large number of bilayers (small thickness of each individual layer) shows the lowest value of hardness. It is assumed that as the bilayer thickness decreases, the coating characteristics are closer to the monolayer alloy than to the multilayer structure.

Effect of bilayer numbers on structural, mechanical, tribological and corrosion properties of TiO2–SiO2 multilayer film-coated β-type Ti45Nb alloys

Protective films with excellent tribological performance and good corrosion resistance are needed in general because titanium implants are used in aggressive environments and always suffer from severe wear and corrosion. In this study, TiO2–SiO2 multilayer films were deposited with different numbers of bilayers (2, 4, and 8) on β-type Ti45Nb alloy substrates by physical vapour deposition. The influence of number of bilayers on microstructure, wettability, mechanical features, tribological performance and electrochemical behaviour of TiO2–SiO2 multilayer films were comparatively observed via XRD, XPS, SEM, AFM, nanoindentation tester, contact angle measurement system, reciprocating tribo-tester, and electrochemical corrosion media. The surface hardness, wear and corrosion resistance values of multilayer film-coated substrates were higher than the untreated substrate values. These properties and adhesion resistance and hydrophobicity of coated samples also increased with increase in number of bilayers due to the smaller grain size, increased layered interfaces and high structural density.

Thin film nanoarchitectonics of layer-by-layer assembly with reduced graphene oxide on intraocular lens for photothermal therapy of posterior capsular opacification

Due to development of surgical techniques and intraocular lens (IOL) implants, vision can often be restored in cataracts patients. However, posterior capsular opacification (PCO) has become the most common and challenging complication in cataracts surgery. While various approaches such as surface modification and drug prophylaxis have been investigated to prevent PCO development, there is no standard treatment that is sufficiently safe and effective to meet clinical demands. Near-infrared (NIR) light-triggered photothermal therapy is an attractive noninvasive treatment for PCO prophylaxis. We fabricated a new type of IOL with excellent biocompatibility, stability, and photothermal conversion property. Polyethyleneimine (PEI) and graphene oxide (GO) were layer-by-layer assembled on model polymethylmethacrylate and IOL substrates, and the thickness, surface roughness, and wettability of the substrates with different numbers of bilayers were evaluated. After the reduction of GO to reduced GO (rGO), a rGO/PEI multilayer thin film with good stability and photothermal conversion capability was obtained. The rGO/PEI multilayer coating was able to induce apoptosis in lens epithelium cells under 808-nm NIR laser irradiation in vitro. Finally, rGO@IOL was implanted into rabbit eyes, and the biocompatibility and ability to prevent PCO were evaluated for 5 weeks. The rGO@IOL implant exhibited excellent PCO prevention ability with the assistance of NIR irradiation and did not induce obvious pathological effects in surrounding healthy tissues. The rGO@IOL implant with good biocompatibility, good physicochemical stability, and excellent photothermal conversion property shows promise for clinical application in PCO prophylaxis.

Investigating the potential of ammonium retention by graphene oxide ceramic nanofiltration membranes for the treatment of semiconductor wastewater

Ceramic membranes with high chemical and fouling resistance can play a critical role in treating industrial wastewater. In the present study, we demonstrate the fabrication of graphene oxide (GO) assembled ceramic nanofiltration (NF) membranes that provide effective ammonium retention and excellent fouling resistance for treating semiconductor wastewater. The GO-ceramic NF membranes were prepared via a layer-by-layer (LbL) assembly of GO and polyethyleneimine (PEI) on a ceramic ultrafiltration (UF) substrate. The successful fabrication of the GO-ceramic NF membranes was verified through surface characterization and pore size evaluation. We also investigated the performance of GO-ceramic NF membranes assembled with different numbers of bilayers for the rejection of ammonium ions. GO-ceramic NF membranes with three GO-PEI bilayers exhibited 8.4- and 3.2-times higher ammonium removal with simulated and real semiconductor wastewater, respectively, compared to the pristine ceramic UF substrate. We also assessed flux recovery after filtration using real semiconductor wastewater samples to validate the lower fouling potential of the GO-ceramic NF membranes. Results indicate that flux recovery increases from 39.1 % in the pristine UF substrate to 71.0 % and 90.8 % for the three- and ten-bilayers GO-ceramic NF membranes, respectively. The low-fouling GO-ceramic NF membranes developed in this study are effective and promising options for the removal of ammonium ions from semiconductor wastewater.

Experimental realisation of tunable ferroelectric/superconductor ({text {B}} {text {T}} {text {O}}/{text {Y}} {text {B}}{text {C}} {text {O}})_{{text {N}}}/{text {S}}{text {T}}{text {O}} 1D photonic crystals in the whole visible spectrum

Emergent technologies that make use of novel materials and quantum properties of light states are at the forefront in the race for the physical implementation, encoding and transmission of information. Photonic crystals (PCs) enter this paradigm with optical materials that allow the control of light propagation and can be used for optical communication, and photonics and electronics integration, making use of materials ranging from semiconductors, to metals, metamaterials, and topological insulators, to mention but a few. Here, we show how designer superconductor materials integrated into PCs fabrication allow for an extraordinary reduction of electromagnetic waves damping, making possible their optimal propagation and tuning through the structure, below critical superconductor temperature. We experimentally demonstrate, for the first time, a successful integration of ferroelectric and superconductor materials into a one-dimensional (1D) PC composed of ({text {B}}{text {T}}{text {O}}/{text {Y}}{text {B}}{text {C}} {text {O}})_{{text {N}}}/{text {S}}{text {T}}{text {O}} bilayers that work in the whole visible spectrum, and below (and above) critical superconductor temperature T_C=80, {hbox {K}}. Theoretical calculations support, for different number of bilayers N, the effectiveness of the produced 1D PCs and may pave the way for novel optoelectronics integration and information processing in the visible spectrum, while preserving their electric and optical properties.

Effect of number of layers and deposition time on layer-by-layer (LbL) composite forward osmosis membrane

Forward osmosis (FO) refers to the osmotic process for water transfer through a semipermeable membrane that results in the separation of water from dissolved solutes. This method has been explored due to low fouling propensity and low energy requirement since the driving force is an osmotic pressure gradient between the feed and draw solutions. This research focused on determining the optimum FO membrane by controlling the number of polyelectrolyte bilayers and deposition time of membrane for seawater desalination. Poly(diallyl-dimethylammonium chloride), PDADMAC and poly(sodium 4-styrenesulfonate), PSS were used as active monomers to generate a thin layer on the ultrafiltration membrane support through layer-by-layer (LbL) deposition method. The FO lab-scale experiment was performed by using 1.75 M of sodium sulphate (Na 2 SO 4 ) as draw solution and deionised water (DI) as feed. This research was conducted based on the different number of bilayers (5, 10, and 15 bilayers) and deposition time (5, 10, and 15 min) which affected the water flux. After the best parameters were obtained, treatment on synthetic seawater (35 g/L of NaCl) was conducted, and the results were compared with that of real seawater. Among the modified membranes, it was found that the membrane 5FO15 with 5-bilayers of polyelectrolytes and 15 min of deposition time exhibited the highest water flux (4.75 L/m 2 ∙h). The membrane exhibited a lower water flux for seawater than synthetic seawater due to the existing of other solutes which may contribute to membrane fouling. From this research, the polyelectrolyte membrane exhibited a high potential of treating seawater in Malaysia by FO process which is a good option of water treatment.

Development of MWCNT thin film electrode transparent in the mid-IR range

In this research carbon nanotube-based thin film electrodes, with high transparency in mid-infrared range, were developed as a replacement for indium tin oxide electrodes. The thin film electrodes were prepared from polyelectrolyte and multi-walled carbon nanotubes by layer-by-layer assembly. Polyethyleneimine (PEI) and carboxylic multi-walled carbon nanotubes (MWCNT-COOH) were deposited alternately on glass substrates. Samples with different number of bilayers (PEI + MWCNT-COOH) were prepared. Thickness of the films varied between 80 and 240 nm, depending of the number of bilayers. After deposition of each bilayer, the samples were dried at 120 °C for 10 min. The fabricated films were characterized using Raman spectroscopy, high-resolution scanning microscopy (HRSEM) and transmission electron microscopy (TEM). Transparency of the films was measured in UV/Vis and IR ranges, utilizing UV/Vis spectrophotometer and FTIR spectrometer respectively. Sheet resistance of the films was measured with four-point probe method and the resistance values obtained were ranging from 6 kΩ/sq up to 23 kΩ/sq, depending on the number of layers.

MXene/chitosan nanocoating for flexible polyurethane foam towards remarkable fire hazards reductions

MXene/chitosan nanocoating for flexible polyurethane foam (PUF) was prepared via layer-by-layer (LbL) approach. MXene (Ti3C2) ultra-thin nanosheets were obtained through etching process of Ti3AlC2 followed by exfoliation. The deposition of MXene/chitosan nanocoating was conducted by alternatingly immersing the PUF into a chitosan solution and a Ti3C2 aqueous dispersion, which resulted in different number of bilayers (BL) ranging from 2, 5 and 8. Owing to the utilization of ultra-thin Ti3C2 nanosheets, the weight gain was only 6.9% for 8 BL coating of PUF, which minimised the unfavourable impact on the intrinsic properties of PUF. The Ti3C2/chitosan coating significantly reduced the flammability and smoke releases of PUF. Compared with unmodified PUF, the 8 BL coating reduced the peak heat release rate by 57.2%, alongside with a 65.5% reduction in the total heat release. The 8 BL coating also showed outstanding smoke suppression ability with total smoke release decreased by 71.1% and peak smoke production rate reduced by 60.3%, respectively. The peak production of CO and CO2 gases also decreased by 70.8% and 68.6%, respectively. Furthermore, an outstanding char formation performance of 37.2 wt.% residue was obtained for 8 BL coated PUF, indicating the excellent barrier and carbonization property of the hybrid coating.

Polysaccharide Coating of Gelatin Gels for Controlled BSA Release.

Self-assembly of natural polymers constitute a powerful route for the development of functional materials. In particular, layer-by-layer (LBL) assembly constitutes a versatile technique for the nanostructuration of biobased polymers into multilayer films. Gelatin has gained much attention for its abundance, biodegradability, and excellent gel-forming properties. However, gelatin gels melt at low temperature, thus limiting its practical application. With respect to the above considerations, here, we explored the potential application of gelatin gels as a matrix for protein delivery at physiological temperature. A model protein, bovine serum albumin (BSA), was encapsulated within gelatin gels and then coated with a different number of bilayers of alginate and chitosan (10, 25, 50) in order to modify the diffusion barrier. The coated gel samples were analyzed by means of Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) and confocal Raman spectroscopy, and it was found that the multilayer coatings onto polymer film were interpenetrated to some extent within the gelatin. The obtained results inferred that the coating of gelatin gels with polysaccharide multilayer film increased the thermal stability of gelatin gels and modulated the BSA release. Finally, the influence of a number of bilayers onto the drug release mechanism was determined. The Ritger-Peppas model was found to be the most accurate to describe the diffusion mechanism.

Hyaluronic acid/poly(ethylenimine) polyelectrolyte multilayer coatings for siRNA-mediated local gene silencing.

Local gene delivery systems utilizing RNA interference technology are a promising approach for therapeutic applications where site-specific release of agents is desired. Polyelectrolyte multilayers (PEMs) can be constructed using the layer-by-layer (LbL) technique and serve as a depot for bioactive substances, which can then be released in a controlled manner. Multilayers of hyaluronic acid/poly(ethylenimine) HA/PEI were built up with different numbers of bilayers and PEI-siRNA particles were embedded in bioactive layers for gene silencing. The increase of the bilayers and the release of siRNA particles were demonstrated by fluorescence intensity measurement with a fluorescence reader. Two different LbL techniques were tested for the reduction of ICAM–1 expression in EA.hy926: PEM build-up by dipping or drying steps, respectively. Herein, the drying technique of the bioactive layers with ICAM siRNA mediated a significant reduction of the ICAM–1 expression from 3 to 24 bilayers. The fluorescent siRNA release study and the re-culturing of the HA/PEI films demonstrated a release of the transfection particles within the first hour. The advantage of dried built-up PEMs compared to a dried monolayer of PEI-siRNA particles with the same siRNA concentration was a significant higher amount of viable cells.

Layer-by-layer assembled graphene oxide/polydiallydimethylammonium chloride composites for hydrogen gas barrier application

Poly(diallyldimethylammoium chloride) (PDDA)/acid or base modified graphene oxide (MGO) composite (PDDA/MGO)-based gas barrier films were prepared by layer-by-layer (LBL) assembly method on polyethylene terephthalate (PET) substrate using a spray coating assisted deposition. The effect of pH on the hydrogen gas permeability (H2GP) values of the different MGO-based films was investigated to determine the optimum pH value of the MGO solution for the preparation of PDDA/MGO-based LBL assembly. Accordingly, the different numbers of bilayers based LBL-assembled films were prepared using alternate deposition of PDDA and MGO solutions and the H2GP values were measured for those assemblies. The films were characterized by XRD, FT-IR, and Raman spectroscopy analyses. The morphology of the LBL-assembled film was observed by cross-sectional field emission scanning electron microscopy which confirms densely packed layered structure. The H2GP of six bilayers PDDA/MGO composite film is 5.7 cc/m2⋅d⋅atm, which is much lower than that of pure PET substrate (170.7 cc/m2⋅d⋅atm), indicating 96.7% decrease in H2GP. This result suggests that the PDDA/MGO composite film could be used as a potential candidate to fabricate hydrogen gas barrier coating material.

Modification of structural and magnetic properties in Fe/Pt (1 1 1)-oriented multilayers with ion beam irradiation

Abstract This paper reports on structural and magnetic properties changes that occur after irradiation of Fe/Pt (1 1 1) multilayers with Ne+ ions. Multilayer samples of Al 2 O 3 (0 0 0 1)/Pt 100 A/(Fe X A/Pt X A) n /Pt 100 A structure with different individual layer thickness X (5 or 10 A) and different number of bilayers n (5, 10 or 15) were irradiated with Ne+ ions of 10 to 25 keV energy and 1 × 10 14 ÷ 1 × 10 16 ions cm −2 dose range at room temperature. Irradiation parameters were estimated a priori using Tridyn software. As-deposited samples revealed presence of sharp interfaces. Structural properties changes were investigated using symmetrical and asymmetrical X-ray diffraction methods and magnetic properties changes were examined using vibrating sample magnetometer. Ion beam induced mixing of multilayers resulted in formation of disordered face centered cubic (fcc) FePt alloys of two different compositions (quasi-50:50 in the initial multilayer volume and Pt-rich in initial cover-layer volume). Non-regular changes in magnetic properties after ion irradiation were observed whilst retaining in-plane orientation of magnetization easy axis.

Chitosan-Recombinamer Layer-by-Layer Coatings for Multifunctional Implants.

The main clinical problems for dental implants are (1) formation of biofilm around the implant—a condition known as peri-implantitis and (2) inadequate bone formation around the implant—lack of osseointegration. Therefore, developing an implant to overcome these problems is of significant interest to the dental community. Chitosan has been reported to have good biocompatibility and anti-bacterial activity. An osseo-inductive recombinant elastin-like biopolymer (P-HAP), that contains a peptide derived from the protein statherin, has been reported to induce biomineralization and osteoblast differentiation. In this study, chitosan/P-HAP bi-layers were built on a titanium surface using a layer-by-layer (LbL) assembly technique. The difference in the water contact angle between consecutive layers, the representative peaks in diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray photoelectron spectroscopy (XPS), and the changes in the topography between surfaces with a different number of bi-layers observed using atomic force microscopy (AFM), all indicated the successful establishment of chitosan/P-HAP LbL assembly on the titanium surface. The LbL-modified surfaces showed increased biomineralization, an appropriate mouse pre-osteoblastic cell response, and significant anti-bacterial activity against Streptococcus gordonii, a primary colonizer of tissues in the oral environment.

Comparative study of polymeric matrices embedding oxygen-sensitive fluorophores by means of Layer-by-Layer nanosassembly

In this work, a comparative study of luminescent optical fiber oxygen sensors fabricated by means of Layer-by-Layer nanoassembly technique (LbL) has been carried out. The oxygen-sensitive fluorophore is the same in all the cases, the metalloporphyrin platinum tetrakis pentafluorophenylporphin (Pt-TFPP), which was deposited using LbL method by entrapping it into anionic micelles formed with a surfactant. As cationic counterpart to form the anionic-cationic bilayer, different polyelectrolytes acting as the polymeric matrices embedding the sensing material have been studied: poly(diallyldimethylammonium chloride) (PDDA), polyethyleneimine (PEI) and poly(allylamine hydrochloride) (PAH). Absorbance spectra, contact angle, Atomic Force Microscope and Scanning Electronic Microscope analysis were performed on the sensing films. The kinetics, resolution and sensitivity of the sensors for different number of bilayers were also determined. It has been found a remarkable difference on these characteristics depending on the polymer used.

The confinement of phonon propagation in TiAlN/Ag multilayer coatings with anomalously low heat conductivity

TiAlN/Ag multilayer coatings with a different number of bilayers and thicknesses of individual layers were fabricated by DC magnetron co-sputtering. Thermal conductivity was measured in dependence of Ag layer thickness. It was found anomalous low thermal conductivity of silver comparing to TiAlN and Ag bulk standards and TiAlN/TiN multilayers. The physical nature of such thermal barrier properties of the multilayer coatings was explained on the basis of reflection electron energy loss spectroscopy. The analysis shows that nanostructuring of the coating decreases the density of states and velocity of acoustic phonons propagation. At the same time, multiphonon channels of heat propagation degenerate. These results demonstrate that metal-dielectric interfaces in TiAlN/Ag coatings are insurmountable obstacles for acoustic phonons propagation.

Influence of electronic structure, plasmon-phonon and plasmon-polariton excitations on anomalously low heat conductivity in TiAlN/Ag nanoscale multilayer coatings

TiAlN/Ag multilayer coatings with different number of bilayers and thicknesses of individual layer were fabricated by DC magnetron sputtering. Thermal conductivity and electronic structure features were measured on a set of samples with different number of bilayers and individual layer thickness from a 5–150 nm for total coating thickness of ∼0.5 or 1 μm. It was found that thermal conductivity of the multilayer insulator/metal structure becomes lower than for monolithic TiAlN coatings with the same thickness when Ag layers are thinner than 25 nm. The physical nature of thermal barrier properties of the nanolaminate TiAlN/Ag films is studied using X-ray photoelectrons (XPS) and high-resolution electron-energy loss (HREELS) spectroscopies. Based on these results, a physical model for the anomalous decrease in heat conductivity for nanoscale multilayers was developed on base of analysis of plasmon and lattice vibrations inside the layers and at the interfaces. Anomalously low heat transfer is attributed to attenuation of longitudinal acoustic phonons vibrations, decreasing of plasmon-polariton penetration on interfaces, and plasmon states splitting in Ag nanolayers due to confinement effects at multilayer coatings nanostructuring.

Dynamics of creation photoinduced birefringence on (PAH/PAZO)n layer-by-layer films: Analysis of consecutive cycles

Reproducibility and reliability of data is an important subject in the development of organic devices for photonics applications. This work reports the analysis of successive photoinduced birefringence creation curves in layer-by-layer films of poly(allylamine hydrochloride) (PAH) and poly{1-(4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido)-1,2-ethanediyl, sodium salt} (PAZO) with different number of bilayers. The birefringence creation or writing curves are described by two processes: a faster one referring the contribution of trans–cis–trans photoisomerization cycles to the birefringence; and a slower one associated to the contribution of motion of the polymer chain to the birefringence. As the number of write–erase cycles increases, the characteristic times of these processes decreases, respectively, to values of 18 and 212s independently of the number of bilayers of films while for the magnitudes the fast process prevailed relatively to the slow, by 70% against 30%. The observed behavior is explained by the thermal treatment given by the laser beam in the irradiated area with increase of free volume which contributes for the chromophore mobility. This conclusion was achieved by measuring the surface temperature during and after irradiation and analyzing by optical microscopy the film surface where an increase of holes and aggregation as a result of irradiation was observed. Infrared spectra of films after and before irradiation showed changes in the CC absorbance indicating aggregation of azobenzene groups while changes in the protonated and deprotonated carboxylic acid groups are consistent with ionization degree diminishing which is explained by the removal of water molecules by heating caused by laser. The results presented in this paper indicates that an increase in the number of write–erase cycles contributes to reliable and reproducible birefringence characteristics of PAH/PAZO films – a good new from point of view of possible applications.