Poly Methyl Methacrylate Layer Research Articles

Temperature measurement of Joule heated silicon micro/nanowires using selectively decorated quantum dots

We developed a novel method to measure local temperature at micro/nano-scale regions using selective deposition of quantum dots (QDs) as a sensitive temperature probe and measured the temperature of Joule heated silicon microwires (SiMWs) and silicon nanowires (SiNWs) by this method. The QDs are selectively coated only on the surface of the SiMWs and SiNWs by a sequential process composed of selective opening of a polymethyl methacrylate layer via Joule heating, covalent bonding of QDs, and lift-off process. The temperatures of the Joule-heated SiMWs and SiNWs can be measured by characterizing the temperature-dependent shift of photoluminescence peak of the selectively deposited QDs even with far-field optics. The validity of the extracted temperature has been also confirmed by comparing with numerical simulation results. The proposed method can potentially provide micro/nanoscale measurement of localized temperatures for a wide range of electrical and optical devices.

A triboelectric charge top-gated graphene transistor

A graphene channel with polymer polymethyl methacrylate (PMMA) or Polydimethylsiloxane (PDMS) passive layer were fabricated on a Si/SiO2 substrate. The gate-effect of triboelectric charges on a foreign stimulator and in situ generated triboelectric charges on the passive layer are tested by controlling the foreign stimulator (PDMS or Acrylic plate) touch or not with the passive layer. When the negatively charged PDMS (positively charged Acrylic) stimulator approach and leave the device without touching the passive layer, the channel resistance shows a pulsed decrease (increase) with amplitude less than 1%. When the stimulator has a temporary touch with the passive layer, the in situ generated triboelectric charges on the PMMA (PDMS) passive layer cause stepwise increase (decrease) of the channel resistance. The amplitude of the resistance change steps of the device with PMMA passive layer (2μm in thickness) is about one order larger for than that of the device with PDMS passive layer (about 60μm in thickness). The significant different response of the device depending on whether the stimulator touches or not with the passive layer suggests two possible operation models for the tribo-charge top-gated graphene channel. It may enable diverse design of tactile sensors and pressure sensors based on the tribotronic effect.

Highly concentrated phenanthrenequinone – polymethylmethacrylate composite for thick reflection holograms recording at 532 nm

The formation of stable phase reflection holograms in highly-concentrated phenanthrenequinone - polymethylmethacrylate (PQ-PMMA) layers with a thickness of about 100 µm at 532 nm recording wavelength has been investigated. In spite of the low absorbance of the photosensitive material at the long wave edge of the absorption spectrum, a refractive index modulation of 4.2·10−4 close to the practically reachable limit was achieved during the optical recording. Quantitative investigation of thermal and light treatment of the recorded holograms has demonstrated a tenfold increase of the diffraction efficiency (up to 60%) without disturbing the angular selectivity profile.

Mechanical Transfer of Large-Scale Two-Dimensional Materials Onto Arbitrary Substrates Via Water-Penetration-Assisted Method

Recently, two-dimensional (2D) materials have emerged as an important research topic. Single layer molybdenum disulfide (MoS2) is one of the most widely investigated 2D materials, and possesses outstanding properties with applications in band gap engineering, optical and electrical devices, and spin-orbit research. Large-area and uniform single layer MoS2 can be synthesized by performing chemical vapor deposition (CVD) on various substrates. The full exploitation of the potential of CVD MoS2 requires a method for the clean transfer of the as-grown MoS2 from the growth substrate to the target substrate without degeneration of its properties. The current approach to the transfer of CVD MoS2 usually involves coating a polymer carrier film on top of the CVD MoS2 as a supporting layer and the chemical etching of the growth substrate to separate MoS2 from its surface. However, this etching process causes serious damage to the 2D material due to the harsh corrosivity of the etchant, usually hydrogen fluoride (HF) or a strong base (NaOH or KOH), and the removal of polymer carrier film leaves a residue. Thus the development of a gentle transfer approach that is highly efficient, repeatable, and environmentally friendly is required. In this work, we report a method that with the assistance of water penetration enables the mechanical transfer of MoS2 from the growth substrate to a target substrate without any etching of the growth substrate or leaving any polymer residue on the MoS2 layer. The whole transfer process is as below: After CVD growth of MoS2 on SiO2, a thin Cu carrier film (50–100 nm) is prepared with e-beam deposition on top of the MoS2 layer. Then a layer of polymethyl methacrylate (PMMA) is spin-coated onto Cu/MoS2/SiO2, then baking process is performed, and a layer of polydimethylsiloxane (PDMS) is attached onto PMMA/Cu/MoS2/SiO2. Next, PDMS/PMMA/Cu/MoS2/SiO2 is immersed in deionized (DI) water (We also carried out peeling off out of water under ambient conditions as in other mechanical transfer processes as a contrast experiment). Once the peeling off process starts, water will immediately flood into the space generated by the separation of PDMS/PMMA/Cu/MoS2 because of this natural tendency and the hydraulic pressure. The penetrated water mechanically supports the upper PDMS/PMMA/Cu/MoS2 with buoyancy force, which prevents physical damage. After separation of PDMS/PMMA/Cu/MoS2, it is dried under ambient conditions, and then PDMS/PMMA/Cu/MoS2 is placed and pressured onto a target substrate. The whole sample is heated at 130°C on a hotplate. Once PDMS has lost adhesion, it can easily be peeled off leaving PMMA/Cu/MoS2 on top of the target substrate. In the next step, the PMMA/Cu/MoS2/target substrate is dipped in acetone to remove PMMA and then in Cu etchant to remove Cu. In contrast to the residue left on the MoS2 layer after the removal of the polymer contact material in previous studies, the Cu layer is completely removed by the Cu etchant due to the de-wetting of metals on 2D materials. We also experimentally demonstrated that Cu, which has a strong adhesion force with MoS2, is an ideal contact material for the clean peeling off of the carrier film and MoS2. Finally, perfectly uniform, large-area CVD MoS2 with a clean surface is obtained on the target substrate with our transfer process. The morphology of MoS2 before and after transfer under or out of water were observed with optical microscopy (OM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The MoS2 before and after transfer under water both appear to be uniform, continuous, and clean without any wrinkles, cracks or polymer residue. However, many holes were observed in the sample transferred out of water which were generated by the abrupt forces generated by the peeling off process; the absence of support by water means that the MoS2 layer, which is just one atomic layer thick, can easily be damaged. Samples were also studied with Raman and photoluminescence (PL) spectroscopy. Raman spectra and PL peak positions are same for all three samples. But the PL peak intensity of the MoS2 sample transferred out of water is much weaker than the other two samples due to the physical damage generated by the transfer process without water support. All above results confirmed the important role of water penetration in our mechanical transfer process. Our transfer method protects the original quality and morphology of large area MoS2 without leaving any polymer residue, and enables the reuse of the growth substrate. This clean transfer approach is expected to facilitate the realization of industrial applications of MoS2 and other 2D materials.

Impact of nucleation of carbonaceous clusters on structural, electrical and optical properties of Cr+-implanted PMMA

Specimens of polymethylmethacrylate (PMMA) have been implanted with 400 keV Cr+ ions at different ion fluences ranging from 5 × 1013 to 5 × 1015 ions/cm2. The possible chemical reactions involved in the nucleation of conjugated carbonaceous clusters in implanted PMMA are discussed. Furthermore, impact of formation of carbonaceous clusters on structural, optical, electrical and morphological properties of implanted PMMA has been examined. The structural modifications in implanted PMMA are observed by Raman spectroscopy. The variation in optical band gap and Urbach energy is measured using UV–visible spectroscopic analysis. The effects of Cr+ ion implantation on electrical and morphological properties are investigated by four-probe apparatus and atomic force microscopy, respectively. The Raman spectroscopic analysis confirmed the formation of carbonaceous clusters with the transformation of implanted layer of PMMA into amorphous carbon. Simultaneously, the optical band gap of implanted PMMA has reduced from 3.13 to 0.85 eV. The increase in Urbach energy favors the decline in band gap together with the structural modification in implanted PMMA. As a result of Cr+ ion implantation, the electrical conductivity of PMMA has improved from 2.14 ± 0.06 × 10−10 S/cm (pristine) to 7.20 ± 0.36 × 10−6 S/cm. The AFM images revealed a decrease in surface roughness with an increment in ion fluence up to 5 × 1014 ions/cm2. The modification in the electrical, optical and structural properties makes the PMMA a promising candidate for its future utilization, as a semiconducting and optically active material, in various fields like plastic electronics and optoelectronic devices.

Dynamic Fracture of Layered Plates Subjected to In-Plane Bending

Layered structures typically used in applications such as windshields, thermal protection systems, heavy armor, etc., have property jumps at the layer interfaces. Present study focuses on understanding crack initiation and propagation in such systems under dynamic loading particularly when the property jumps are across the crack front. Layered plates were fabricated by joining polymethylmethacrylate (PMMA) and epoxy sheets using an epoxy-based adhesive (Araldite). Single-edge notched (SEN) specimens were subjected to dynamic loading using a modified Hopkinson bar setup. High-speed imaging coupled with dynamic photoelasticity was used to record the crack-tip isochromatic fringes from which the stress intensity factor (SIF) history was obtained. In selected experiments, a pair of strain gages installed on surfaces of specimen was used to record the strain history in the layers, from which the SIF in each layer was obtained. The results indicated that, prior to crack extension, the strain in both layers was identical. The crack tips in the layers start extending at different time instants with the one in the relatively brittle epoxy layer extending first followed by the one in the PMMA layer. At low impact velocity, the delay obtained was significantly higher than that at high impact velocity. The speed of epoxy crack was lower initially due to the bridging of the crack by the uncracked portion of the PMMA layer till initiation of the crack in the PMMA layer. This effect reduced at higher impact velocity for which the delay was much lower and the cracks propagated at a higher-speed.

All-semiconductor plasmonic gratings for biosensing applications in the mid-infrared spectral range.

We propose 1D periodic, highly doped InAsSb gratings on GaSb substrates as biosensing platforms applicable for surface plasmon resonance and surface enhanced infrared absorption spectroscopies. Based on finite-difference time-domain simulations, the electric field enhancement and the sensitivity on refractive index variations are investigated for different grating geometries. The proposed, optimized system achieves sensitivities of 900 nm RIU-1. A clear red shift of the plasmon resonance as well as the enhancement of an absorption line are presented for 2 nm thin adlayers in simulations. We experimentally confirm the high sensitivity of the InAsSb grating by measurements of the wavelength shift induced by a 200 nm thin polymethylmethacrylate layer and demonstrate an enhancement of vibrational signals. A comparison to a gold grating with equivalent optical properties in the mid-infrared is performed. Our simulations and experimental results underline the interest in the alternative plasmonic material InAsSb for highly sensitive biosensors for the mid-infrared spectral range.

Tailoring the Dielectric Layer Structure for Enhanced Performance of Organic Field-Effect Transistors: The Use of a Sandwiched Polar Dielectric Layer.

To investigate the origins of hydroxyl groups in a polymeric dielectric and its applications in organic field-effect transistors (OFETs), a polar polymer layer was inserted between two polymethyl methacrylate (PMMA) dielectric layers, and its effect on the performance as an organic field-effect transistor (OFET) was studied. The OFETs with a sandwiched dielectric layer of poly(vinyl alcohol) (PVA) or poly(4-vinylphenol) (PVP) containing hydroxyl groups had shown enhanced characteristics compared to those with only PMMA layers. The field-effect mobility had been raised more than 10 times in n-type devices (three times in the p-type one), and the threshold voltage had been lowered almost eight times in p-type devices (two times in the n-type). The on-off ratio of two kinds of devices had been enhanced by almost two orders of magnitude. This was attributed to the orientation of hydroxyl groups from disordered to perpendicular to the substrate under gate-applied voltage bias, and additional charges would be induced by this polarization at the interface between the semiconductor and dielectrics, contributing to the accumulation of charge transfer.

Giant Anisotropic Raman Response of Encapsulated Ultrathin Black Phosphorus by Uniaxial Strain

The giant anisotropic Raman response of encapsulated ultrathin black phosphorus (BP) is reported by uniaxial strain. A modified bending technique is employed to apply precise uniaxial tensile strain along the zigzag or armchair direction of the ultrathin BP encapsulated by a layer of polymethyl methacrylate. The Raman shift rates of the A 1 g, B 2g, and A 2 g modes are significantly distinct for strain applied along different directions. For the strain applied along zigzag direction, the Raman shift rate of the B 2g mode can reach a remarkable value of ≈−11 cm−1/% strain. In addition, the Grüneisen parameter is as high as ≈2.5, which is the largest among all the reported common 2D materials. Density functional perturbation theory calculations are performed to understand the exceptional anisotropic strain response discovering that not only the bond lengths but also the bond angels are changed in the strained ultrathin BP, which lead to the giant anisotropic Raman response. Furthermore, an alternative method based entirely on the strained ultrathin BP and nonpolarized Raman spectroscopy is demonstrated to determine the crystallographic orientations of ultrathin BP. This work paves a way to study the strain‐induced anisotropic electrical conductance and magnetotransport properties of BP.

3D homogeneity study in PMMA layers using a Fourier domain OCT system

Micro-metallic particles embedded in polymers are now widely used in several industrial applications in order to modify the mechanical properties of the bulk. A uniform distribution of these particles inside the polymers is highly desired for instance, when a biological backscattering is simulated or a bio-framework is designed. A 3D Fourier domain optical coherence tomography system to detect the polymer's internal homogeneity is proposed. This optical system has a 2D camera sensor array that records a fringe pattern used to reconstruct with a single shot the tomographic image of the sample. The system gathers the full 3D tomographic and optical phase information during a controlled deformation by means of a motion linear stage. This stage avoids the use of expensive tilting stages, which in addition are commonly controlled by piezo drivers. As proof of principle, a series of different deformations were proposed to detect the uniform or non-uniform internal deposition of copper micro particles. The results are presented as images coming from the 3D tomographic micro reconstruction of the samples, and the 3D optical phase information that identifies the in-homogeneity regions within the Poly methyl methacrylate (PMMA) volume.

Photo-stability of the photons converter applied in the photovoltaic conversion systems

In this work we develop the idea of using a poly methyl methacrylate (PMMA) polymer doped with optically active molecules such as photovoltaic encapsulation materials. The effect of this encapsulation system on the incident solar spectrum has been obtained from direct allowed transition after the samples have been exposed to sunlight. A resulting, the incident solar spectrum at the interface is red-shifted for a better fit with the spectral response of SiO2/Si solar cell structures. The simulation results showed that the short-circuit current density increased by 7%. Therefore the mechanism of the photo-degrading by UV illumination of an LDS has been studied to identify molecular changes that occur in the organic dye when exposed to UV light. The photo-degrading effect of the PMMA layer was measured by CONICA-MINOLTA spectrometer, as a function of increasing exposure time to UV light. The UV Photo-degrading studies revealed that the more photo-stable dye doped in value.

(Invited) 2D Transport and Velocity Modulation in Black Phosphorus Field Effect Transistors

Black phosphorus (bP) is an elemental allotrope with a layered crystal structure of puckered honeycombs that can be mechanically exfoliated down to atomic layer thickness. First synthesized over a century ago, bP has been previously studied as a bulk semiconductor [1,2] and is subject to a resurgence of interest as a 2D semiconductor with properties complementary to the 2D semi-metal graphene [3]. bP is the most thermodynamically stable allotrope of phosphorus but is nonetheless subject to photo-oxidation in the presence of water, oxygen and visible light with a reaction rate that increases as bP layer thickness decreases [4]. We have fabricated bP quantum wells in both back-gated and dual-gated field effect transistor (FET) geometries with bP thicknesses ranging from 6±1 nm to 47±1 nm. Stability under ambient conditions was achieved in back-gated FETs by encapsulation with a layer of poly methyl methacrylate (PMMA), while dual-gated FETs were additionaly protected by a combination of Al2O3 deposited by atomic layer deposition and optically opaque gold metallization. Charge transport measurements reveal ambipolar conduction, field effect mobilities of up to 900 cm2/Vs for holes at low temperatures ( T< 100 K ), current saturation as expected of a bona fide semiconductor, and on/off current ratios exceeding 105 at room temperature [5]. Shubnikov-de Haas (SdH) oscillations were observed in bP FETs at 300 mK to 30 K and magnetic fields of up to 35 T. Lifshitz-Kosevich analysis of the SdH oscillations indicates the presence of a 2-D hole gas with Schrödinger fermion character in an accumulation layer at the bP surface. A simple Schrödinger-Poisson analysis predicts accumulation of holes in a single 2-D sub-band at 300 mK over the range of applied electric fields used in our experiments. Analysis of the thermal activation of SdH oscillations yields a hole effective mass of m*=0.36±0.03m0. Improvements to bP device quality by the independent Y. Zhang group has led to the observation of the quantum Hall effect [6].The top gate of dual-gate bP FETs was found to be effective at modulating both carrier mobility and contact resistance [7]. The mobility modulation effect enables operation of the dual-gate bP FET as a velocity modulated transistor (VMT), first proposed by Sakaki [8] to overcome the limitation on transistor switching frequency imposed by the channel transit time of charge carriers. The mobility of charge carriers within an assymetric bP FET structure is dependent upon the charge carrier density distribution, and is thereby dependent upon the externally applied electric field of the top gate. A two-fold mobility modulation and a two-fold contact resistance modulation leads to a four-fold modulation of transconductance at a fixed hole density. The observation of mobility modulation effects in dual-gate bP FETs demonstrates the capacity for bP to function as a room temperature VMT. Charge density distribution plays an important role in the charge transport properties of 2D atomic crystals, where the exposed surfaces of naked quantum well structures can lead to a strong spatial dependence of charge carrier scattering rates. The recent observation in angle resolved photo-emission spectroscopy of bandgap tuning and a semiconductor to semi-metal transition in K-doped bP via a giant Stark effect [9] suggests the possibility of electric field tuning of bP bandgap in bP FETs. Further work is required to improve the quality of bP/dielectric interfaces and to increase the applied electric field strength to access electric field tunable bandgap devices with bP.

Experimental research on shear-slip characteristics of simulated fault with zigzag-type gouge

We sheared layers of polymethyl methacrylate (PMMA) by traditional double-direct shear tests, and synchronously measured the acoustic emissions (AE) generated by shear-slip and friction. Laboratory observations of simulated fault by PMMA materials with zigzag-type gouge showing repetitive, shear-slip events that are reminiscent of earthquakes were verified. In addition, the influencing rules of zigzag size and normal force on shear-slip process and intensity, as well as AE were revealed. Especially, prior to final failure of zigzag, the duration among shear-slip events gradually decreases and shows significant steadiness, which may prove the probability of the obvious foreshock effect to a larger earthquake. Maybe, this work can interpret the shear-slip mechanism of earthquakes and even provide warnings of failure and instability of fault.

On the influence of a high-power ion beam on thin polymer layers deposited onto dielectric substrates

The effect of a nanosecond high-power ion beam on thin polymer layers of chlorinated polyvinyl chloride and polymethyl methacrylate containing ferrocene as an additive is investigated. Arrays of carbon nanofibers with a characteristic diameter of 30–160 nm and lengths of up to 15 m are formed on the surface of the chlorinated polyvinyl chloride. The same effect on polymethyl-methacrylate layers leads to intense cavitation of the surface layer. The possible mechanisms of the formation of carbon nanofibers in chlorinated polyvinyl chloride with ferrocene additive under the action of a high power ion beam are discussed.

Fiber‐Optic Probes for Small‐Scale Measurements of Scalar Irradiance

A new method for producing fiber-optic microprobes for scalar irradiance (=fluence rate) measurements is described. Such fine-scale measurements are important in many photobiological disciplines. With the new method, it is possible to cast spherical 30-600 μm wide light integrating sensor tips onto tapered or untapered optical fibers. The sensor tip is constructed by first casting a clear polymethyl methacrylate (PMMA) sphere (~80% of the size of the final probe tip diameter) onto the optical fiber via dip-coating. Subsequently, the clear sphere is covered with light diffusing layers of PMMA mixed with TiO2 until the fiber probe exhibits a satisfactory isotropic response (typically ±5-10%). We also present an experimental setup for measuring the isotropic response of fiber-optic scalar irradiance probes in air and water. The fiber probes can be mounted in a syringe equipped with a needle, facilitating retraction of the spherical fiber tip. This makes it, e.g. possible to cut a hole in cohesive tissue with the needle before inserting the probe. The light-collecting properties of differently sized scalar irradiance probes (30, 40, 100, 300 and 470 μm) produced by this new method were compared to probes produced with previously published methods. The new scalar irradiance probes showed both higher throughput of light, especially for blue light, as well as a better isotropic light collection over a wide spectral range. The new method also allowed manufacturing of significantly smaller scalar irradiance microprobes (down to 30 μm tip diameter) than hitherto possible, and such sensors allow minimally invasive high-resolution scalar irradiance measurements in thin biofilms, leaves and animal tissues.

Preparation of core–shell attapulgite particles by redox-initiated surface reversible addition–fragmentation chain transfer polymerization via a “graft from” approach

Polymethyl methacrylate layer was grown uniformly from attapulgite by using surface-initiated reversible addition–fragmentation chain transfer polymerization via redox initiation system.

Electrical Instability in Pentacene Transistors with Mylar and PMMA/Mylar Gate Dielectrics Transferred by Lamination Process

This study deals with electrical instability under bias stress in pentacene-based transistors with gate dielectrics deposited by a lamination process. Mylar film is laminated onto a polyethylene terephthalate (PET) substrate, on which aluminum (Al) gate is deposited, followed by evaporation of organic semiconductor and gold (Au) source/drain contacts in bottom gate top contact configuration (Device 1). In order to compare the influence of the semiconductor/dielectric interface, a second organic transistor (Device 2) which is different from the Device 1 by the deposition of an intermediate layer of polymethyl methacrylate (PMMA) onto the laminated Mylar dielectric and before evaporating pentacene layer is fabricated. The critical device parameters such as threshold voltage (VT), subthreshold slope (S), mobility (μ), onset voltage (Von) and Ion/Ioff ratio have been studied. The results showed that the recorded hysteresis depend on the pentacene morphology. Moreover, after bias stress application, the electrical parameters are highly modified for both devices according to the regimes in which the transistors are operating. In ON state regime, Device 1 showed a pronounced threshold voltage shift associated to charge trapping, while keeping the μ, Ioff current and S minimally affected. Regardless of whether Device 2 exhibited better electrical performances and stability in ON state, we observed a bias stress-induced increase of depletion current and subthreshold slope in subthreshold region, a sign of defect creation. Both devices showed onset voltage shift in opposite direction.

Mixed-mode fracture of layered plates subjected to in-plane bending

Layered architecture is being widely used in applications such as thermal protection systems, windshields, body and vehicle armor etc. In layered materials, properties vary in a discrete manner from layer to layer, leading to property jumps across the interfaces. The focus of this study is to understand the mixed mode fracture behavior of cracked layered plates in which elastic and fracture properties vary along the crack front. Layered plates were prepared by joining polymethylmethacrylate (PMMA) and Epoxy sheets using an Epoxy based adhesive (Araldite). Between the two materials, Epoxy has higher elastic modulus and lower fracture toughness. Single edge notched specimens were subjected to asymmetric four point bending. The failure was observed to be progressive in nature with the crack in Epoxy layer extending first followed by crack growth in PMMA layer. Inspection of fractured surfaces indicated twisting of crack during crack extension. Results of three-dimensional finite element analysis (FEA) indicated variation of SIF and mode mixity along the crack front and also presence of mode-III SIF. The load corresponding to extension of crack and angle of crack propagation in the Epoxy layer was reasonably predicted by the maximum tensile stress criteria. The interaction between the two layers once the crack in the Epoxy layer starts growing is explained using results of FEA.

Resistive switching in polymethyl methacrylate thin films

The origin of the resistive switching in Polymethyl methacrylate (PMMA) films is studied in this work, analysing the switching mechanism of Ag/PMMA/FTO devices. Significant improvement in the performance occurs upon annealing the sample, indicating that the evaporation of the solvent plays a significant role in the memory behaviour of the devices. The shift in the space-charge-limited conduction regime after the set process shows that the electron mobility has been enhanced by two orders of magnitude upon switching. Voltage stress analyses show that the switching from high-resistive phase to low resistive phase occurs only when the silver electrode is positively biased, which confirms that the origin of switching is Ag+ filament formation through PMMA. The performance of the devices at different temperatures shows that the set and reset voltages increase with temperature. This observation is explained based on the vitrification of the PMMA layer as a result of the increased evaporation of the solvent at higher temperatures.

Controlling surface adsorption to enhance the selectivity of porphyrin based gas sensors

This study reports an enhancement in the selectivity of the vapor sensing properties of free base porphyrin 5,10,15,20-tetrakis[3,4-bis(2-ethylhexyloxy)phenyl]-21H,23H-porphine (EHO) Langmuir–Schaefer (LS) films. These sensors respond by changing color upon adsorption of the analyte gas to the sensor surface. The enhanced selectivity is achieved by adding selective barrier layers of 4-tert-Butylcalix[4]arene, 4-tert-Butylcalix[6]arene and 4-tert-Butylcalix[8]arene embedded in PMMA (Poly(methyl methacrylate)) on top of the porphyrin sensor films to control the gaseous adsorption onto the sensor surface. The Langmuir properties of EHO, PMMA and calix[n]arene monolayers were investigated by surface pressure–area (Π–A) isotherms in order to determine the most efficient transfer pressure. Six layer EHO films were transferred onto glass and silicon substrates to investigate their optical and structural characteristics. The three different calix[n]arenes were embedded within PMMA layers to act as the selective barrier layers which were deposited on top of the six layer EHO films. The different calix[n]arene molecules vary in size and each was mixed with PMMA in specific ratios in order to control the selectivity of the resulting barrier layers. Spectroscopic Ellipsometry (SE) and Atomic Force Microscopy (AFM) measurements were carried out to analyze the structure of the porous barrier layers. It was found that the orientation of the calix[8]arene molecules was well controlled within the Langmuir layers such that molecular ring lies flat on the EHO layers when deposited. However, the calix[6]arene and calix[4]arene molecules were quite not so reliably oriented. The sensor films (with and without the addition of the different selective barrier layers) were exposed to various carboxylic acid vapors. More specifically, acetic acid, butyric acid and hexanoic acid were chosen due to their different molecular sizes. The uncovered EHO films were highly sensitive to all the carboxylic acids. The porosity of the barrier layers which influences their selectivity was investigated by changing the size of the acid molecules. Upon deposition of a barrier layer on top of EHO film the sensing response rate and magnitude were changed depending on both the barrier layer structure and molecular size of the analyte vapor. The optical sensing results show that by controlling the size of the pores in the barrier layer it can be used as a size selective layer which limits the diffusion of analyte molecules into the sensor and in extreme cases stopping the diffusion completely. Therefore the selectivity of this sensor system has been enhanced by adding a controllable barrier layer. The enhanced sensors have been used to differentiate between acetic, butyric and hexanoic acids.