Fe3O4/γ-Fe2O3 nanoparticles (NPs) based thin films were used as active layers in solid state resistive chemical sensors. NPs were synthesized by high temperature solution phase reaction. Sensing NP ...monolayers (ML) were deposited by Langmuir–Blodgett (LB) techniques onto chemoresistive transduction platforms. The sensing ML were UV treated to remove NP insulating capping. Sensors surface was characterized by scanning electron microscopy (SEM). Systematic gas sensing tests in controlled atmosphere were carried out toward NO2, CO, and acetone at different concentrations and working temperatures of the sensing layers. The best sensing performance results were obtained for sensors with higher NPs coverage (10 ML), mainly for NO2 gas showing interesting selectivity toward nitrogen oxides. Electrical properties and conduction mechanisms are discussed.
•AlN structural switch from (002) to (101) was obtained by tuning total pressure.•The total pressure was tuned by changing the throttle valve opening.•This result is explained in terms of growth ...units formation at different pressures.
Reactively sputtered aluminum nitride (AlN) is a piezoelectric material, largely used for technological applications, ranging from sensors to energy harvesting. The structural properties of AlN are crucial for its integration in piezoelectric devices. The preferential orientation of the film discriminates its applicability in devices, where the excitation of the longitudinal rather than the shear mode is required. In order to tune the film crystallographic orientation, a fine control of the sputtering parameters is required. In this paper, a structural switch, from (002) to (101) preferential orientation was obtained by increasing the total pressure in the deposition chamber with the only use of the throttle valve, while keeping constant all the other deposition parameters. This structural change was interpreted on the basis of the growth kinetics, which explains how deposition parameters control the energy of the species impinging on the substrate.
This study reports on the fabrication and characterization of an event detection subsystem composed of a flexible piezoelectric pressure sensor and the electronic interface to be integrated into an ...implantable artificial pancreas (IAP) for diabetic patients. The developed sensor is made of an AlN layer, sandwiched between two Ti electrodes, sputtered on Kapton substrate, with a preferential orientation along c-axis which guarantees the best piezoelectric response. The IAP is made of an intestinal wall-interfaced refilling module, able to dock an ingestible insulin capsule. A linearly actuated needle punches the duodenum tissue and then the PDMS capsule to transfer the insulin to an implanted reservoir. The device is located at the connection of the needle with the linear actuator to reliably detect the occurred punching of the insulin-filled capsule. Finite Element Analysis (FEA) simulations were performed to evaluate the piezoelectric charge generated for increasing loads in the range of interest, applied on both the sensor full-area and footprint area of the Hamilton needle used for the capsule punching. The sensor-interface circuit was simulated to estimate the output voltage that can be obtained in real operating conditions. The characterization results confirmed a high device sensitivity during the punching, in the low forces (0-4 N) and low actuator speed (2-3 mm/s) ranges of interest, meeting the requirement of the research objective. The choice of a piezoelectric pressure sensor is particularly strategic in the medical field due to the request of self-powered implantable devices which do not need any external power source to output a signal and harvest energy from natural sources around the patient.
Antibacterial coatings on catheters for acute dialysis were obtained by an innovative and patented silver deposition technique based on the photo-reduction of the silver solution on the surface of ...catheter, with consequent formation of antibacterial silver nanoparticles. Aim of this work is the structural and morphological characterization of these medical devices in order to analyze the distribution and the size of clusters on the polymeric surface, and to verify the antibacterial capability of the devices treated by this technique against bacterial proliferation. The structure and morphology of the silver nanoparticles were investigated by using scanning and transmission electron microscopy. The antimicrobial capability of the catheters after silver deposition was confirmed by antibacterial tests with
Escherichia coli
. Both scanning electron microscopy analysis and antibacterial tests were performed also after washing catheters for 30 days in deionized water at 37°C, relating these data to thermogravimetric analysis and to energy dispersive spectroscopy, in order to check the resistance of coating and its antimicrobial capability after the maximum time of life of these devices.
Matrix assisted pulsed laser evaporation (MAPLE) is a new promising laser-based technique thought for polymer or biomaterial thin films deposition. In this work, the MAPLE technique has been used for ...the deposition of titania (TiO2) nanoparticle thin films to be used for gas sensor applications. For this purpose, an aqueous solution of TiO2 nanoparticles, synthesized by a novel chemical route, was frozen at the liquid nitrogen temperature and introduced in a vacuum chamber to be irradiated with a pulsed ArF excimer laser. The volatile solvent was pumped away while the TiO2 nanoparticles were deposited on Si and Al2O3 substrates. A uniform distribution of TiO2 nanoparticles with an average size of about 10nm was obtained, as demonstrated by high resolution scanning electron microscopy (SEM-FEG) inspection. We realized gas-sensing devices based on resistive transduction mechanism by using the TiO2 nanoparticles thin films deposited by the MAPLE technique onto suitable rough alumina substrates equipped with interdigitated electrical contacts (IDC) and heating elements. Electrical characterization measurements were carried out in controlled environment. The results of the gas-sensing tests towards low concentrations of ethanol and acetone vapors are reported. Typical gas sensor parameters (gas responses, response/recovery time, sensitivity, and low detection limit) towards ethanol were extracted and compared with to the corresponding parameters towards acetone.
The surface of a detector grade CVD polycrystalline diamond sample (5×5×0.05mm3) was irradiated by an ArF excimer laser (λ=193nm, τ=20ns) to produce graphitic conductive layers.
In particular, two ...sets of four parallel graphitic strip-like contacts, with 1mm pitch, were created along the whole sample on the top and on the rear surfaces of the sample respectively. The two series of stripes lie normally to each other. Such a grid allows to obtain a segmented all-carbon device capable of giving bi-dimensional information on particle detection processes in nuclear applications.
Afterwards, an extensive characterization of the samples was performed: SEM and micro-Raman investigations to study the morphological and structural evolution of the irradiated areas, EDS measurements to individuate any absorption phenomena from environment associated to laser treatment, and nanoindentation mapping to understand how the hard-soft transformation occurred depending on the locally transferred energy. Finally, current-voltage analyses were carried out checking the ohmic behavior of the diamond-graphite contact. By comparing the results of the different characterization analyses, a strong periodicity of the modified surface properties was found, confirming the reliability and reproducibility of the laser-induced graphitization process.
The results demonstrate that the laser-writing technique is a good and fast solution to produce graphitic contacts on diamond surface and therefore represents a promising way to fabricate segmented all-carbon devices.
Hardness and reduced elastic modulus mappings of a graphitic strip induced by laser on diamond surface. Display omitted
•The manufacturing of strip-like graphitic contacts on diamond surface by laser-writing was carried out.•The contacts were created on diamond surface of both sides, with orthogonal orientation, to obtain a segmented all-carbon device capable to give bi-dimensional information during detection processes.•SEM and micro-Raman Spectroscopy analyzes allowed understanding the physical evolution of the graphitization process, and how the morphological and structural changes depend on laser processing.•Phenomena of chemical modifications were found by EDS: oxidation reactions were present on all the irradiated areas, with increasing intensity values for the most damaged zones.•Nano-indentation investigations were performed showing that hard-soft transformation occurred depending on the locally deposited energy and in agreement with the changes of hybridization (sp3→sp2) of carbon atoms.•Current-voltage analyses allowed to verify the ohmic behavior of the contacts and to evaluate the resistivity values of every strip, which range from 2.5 × 10-5 Ωm up to 3 × 10-5 Ωm.
The paper deals with the role of the oxygen contamination, coming from residual gas atmosphere in the deposition chamber, on the physical properties of AlN thin films, sputtered in Ar + N2 working ...gas, at different values of nitrogen flux percentages, and without substrate heating. Contaminant concentration varies with the nitrogen partial pressure in the working gas mixture. Oxygen atoms are incorporated into the growing films due to their higher affinity towards Al atoms compared to N atoms. Oxygen inclusion produces important modifications in the structural, chemical, optical and electrical properties of the AlN thin films. Therefore, contamination can play a crucial role for the tuning of the physical characteristics of sputtered materials.
Display omitted
•AlN thin films were produced by RF magnetron sputtering.•The role of oxygen contamination was investigated.•Oxygen incorporation can be varied by changing N2 content in the reactive mixture.•Oxygen influences structural, morphological, optical and electrical properties.•Contamination plays a nodal role for tuning films physical characteristics.
Brookite titanium dioxide (TiO₂) nanorods, synthesized by a surfactant-assisted aminolysis route, were used as precursors for the fabrication of thin films by using the matrix-assisted pulsed-laser ...deposition (MAPLE) technique. Thin films with controllable thickness were grown on a variety of substrates for different characterizations. High-resolution scanning and transmission electron microscopy investigations evidenced the formation of rough TiO₂ films incorporating individually distinguishable nanocrystals with different shapes. Suitable alumina substrates equipped with interdigitated electrical contacts (IDC) and heating elements were used to fabricate gas-sensing devices based on resistive transduction mechanism. Electrical characterization measurements in controlled environment were carried out. Typical gas sensor parameters (such as gas response, sensitivity, stability and detection limit) towards selected oxidizing and reducing gases, namely NO₂ and CO, respectively, were extracted in dark condition. Very interesting optically activated enhancement of the response towards NO₂ oxidizing gas was achieved in controlled atmosphere upon irradiating the sensing layer with UV light with low energy close to the TiO₂ sensing layer band-gap width.
MAPLE deposition of nanomaterials Caricato, A.P.; Arima, V.; Catalano, M. ...
Applied surface science,
05/2014, Letnik:
302
Journal Article, Conference Proceeding
Recenzirano
•The MAPLE deposition of nanoparticles and nanorods is reported.•MAPLE deposition of nanomaterials requires carful control of deposition parameters.•The influence of the deposition parameters on the ...physical mechanisms which govern the deposition process is discussed.
The matrix-assisted pulsed laser evaporation (MAPLE) has been recently exploited for depositing films of nanomaterials by combining the advantages of colloidal inorganic nanoparticles and laser-based techniques. MAPLE-deposition of nanomaterials meeting applicative purposes demands their peculiar properties to be taken into account while planning depositions to guarantee a congruent transfer (in terms of crystal structure and geometric features) and explain the deposition outcome. In particular, since nanofluids can enhance thermal conductivity with respect to conventional fluids, laser-induced heating can induce different ablation thermal regimes as compared to the MAPLE-treatment of soft materials. Moreover, nanoparticles exhibit lower melting temperatures and can experience pre-melting phenomena as compared to their bulk counterparts, which could easily induce shape and or crystal phase modification of the material to be deposited even at very low fluences. In this complex scenario, this review paper focuses on examples of MAPLE-depositions of size and shape controlled nanoparticles for different applications highlights advantages and challenges of the MAPLE-technique. The influence of the deposition parameters on the physical mechanisms which govern the deposition process is discussed.
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