70 research outputs found
Investigation on oxygen vacancies influence on reduced WO3 sensing properties
Nowadays, the development of innovative and low-cost smart gas sensors is required in many applications,
including medical screening, environmental monitoring and precision farming. Chemoresistive gas sensors are
the most widely studied solid state gas sensors in this perspective, due to their small size, low production cost and
high sensitivity [1]. However, the lack of selectivity of the nanostructured metal oxides (MOX), i.e. the most
widely used class of sensing material so far, limited the effective and widespread adoption of these devices in
many applications. In the last few years, great attention has been paid on the development of innovative sensing
materials with advanced chemoresistive properties, able to overcome the shortcomings of the typical MOX,
seeking the optimization of the sensing performance. Modified MOX (doped or functionalised) proved to be good
candidates, owing to the right combination of typical MOX stability and improved selectivity due to surface
sensitisation [2]. Considering doping, the investigation of the influence of intrinsic dopants on the MOX sensing
properties has attracted considerable attention recently, particularly with regard to oxygen vacancies (Ov), which
have shown to have huge impact on the MOX electrical properties and surface reactivity.
In this work, a specific reducing treatment at high temperature has been investigated in order to develop reduced
WO3 with controlled Ov concentration. Nanostructured WO3 has been synthesised by using a simple sol gel
method. Then, a calcination treatment at 650ºC in air has been carried out in order to obtain a nanocrystalline and
stoichiometric WO3. A rapid thermal annealer (RTP) has been employed for the controlled reduction of the WO3
nanoparticles, by using H2 (4% in N2) as reducing agent. Different times (15 and 30 minutes) and temperatures
(from 300 to 800ºC) were investigated, in order to study their impact on the Ov formation. The Ov in the reduced
samples were characterized by using SEM-EDX, XRD and XPS. The XPS characterization has revealed a strong
increase in the 5+, 4+ and 3+ oxidation states of W as the treatment temperature rises, due to a strong increase in
the surface concentration of Ov. Both in-plane and bridging Ov were formed. An increase of the bulk Ov has been
observed as well by XRD analysis. On the other hand, the concentration of Ov did not change significantly with
treatment time. The reduced powders were deposited on silicon substrates and their sensing performances were
investigated vs. NH3. WO3 reduced at 700ºC showed the best sensing performance towards NH3 at near room
working temperature, showing an impressive increase of the sensitivity and selectivity compared to stoichiometric
WO3. The role of surface Ov in the sensing mechanism is under investigation
Oxidation of PIII (Plasma Immersion Ion Implanted)-doped Silicon: study of Arsenic redistribution by SIMS and XPS
The use of spin coated txrf reference samples for TOF-SIMS metal contaminants quantification on silicon wafers
Caratterizzazione SIMS ToF-SIMS e XPS di Ossidonitruri
L’obiettivo del presente lavoro è stato la caratterizzazione di ossidi sottili nitrurati tramite tecniche di microanalisi differenti e complementari. Lo sviluppo della tematica si è svolto attraverso tre linee guida la cui identificazione permette di esporre al meglio il lavoro svolto e definire in modo completo i risultati raggiunti: - Sviluppo di una metodologia necessaria a caratterizzare in modo completo ed accurato questa tipologia di campioni. - Caratterizzazione chimico-fisica di ossidonitruri al fine di definirne le proprietà fondamentali quali distribuzione dell’azoto, auqntificazione del contenuto di azoto, legami chimici. - Applicazione della metodologia sviluppata a campioni di produzione e impiego dei risultati ottenuti per monitorare ed aiutare a risolvere le problematiche di process
Characterization of RTP Oxynitrides by SIMS and XPS Analyses
Aim of this work is the characterization of oxynitride films grown by Rapid Thermal Processing (RTP) using nitrous oxide and nitric oxide precursors. The thickness of the oxynitrided layers is about 7nm. Secondary Ions Mass Spectrometry (SIMS) and X-rays Photoemission Spectroscopy (XPS) have been employed to obtain a complete chemical characterization. XPS analyses have been performed at different depths after removal of oxynitride layers by chemica etching. SIMS and XPS analyses have been also performed on the same samples after a reoxidation treatment. Depending on the precursors used, the oxynitrides show different characteristic
Characterisation of RTA Oxynitrides by SIMS and XPS Analyses
Aim of this work is the characterization of oxynitride films grown by Rapid Thermal Processing (RTP) using nitrous oxide and nitric oxide precursors. The thickness of the oxynitrided layers is about 7nm. Secondary Ions Mass Spectrometry (SIMS) and X-rays Photoemission Spectroscopy (XPS) have been employed to obtain a complete chemical characterization. XPS analyses have been performed at different depths after removal of oxynitride layers by chemica etching. SIMS and XPS analyses have been also performed on the same samples after a reoxidation treatment. Depending on the precursors used, the oxynitrides show different characteristic
Furnace and RTP Nitridation of Ultrathin Oxide Films by NO and N2O: SIMS and ToF-SIMS Characterisation
ALD growth, thermal treatments and characterisation of Al2O3 layers
Al2O3 films with thickness ranging from 20 to 300 nm are grown in a home-made reactor using atomic layer deposition with trimethylaluminum and water on different semiconductor substrates. The deposited films are investigated in terms of composition and electrical properties. Annealing treatments appear necessary in order to obtain films with good insulating properties, although the same treatments do not affect the stoichiometry of the main components
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