National Institute Of Materials Physics - Romania
Atomic Structures and Defects in Advanced Materials Laboratory
Domains of competence / Scientific interests
- Fundamental research in the field of solid state physic, semiconductors and surface physic;
- Experimental research in the field of gas sensors based on metal oxide semiconductors (MOS);
- Complex phenomenological investigations (electrical conductivity, work function, impedance spectroscopy) in controlled gas atmosphere;
- Analyse, statistics and modelling of the experimental results;
The main objective of the group is the fundamental comprehension of the role of the morphology of the metal oxide semiconductors (MOS) nanostructures on the surface reactivity, or more exactly on the gas-sensitive proprieties.
More specific will attempt to bring clarifications on :
The quantitative or qualitative nature of the effect
due to crystallite dimension;
It is intended to establish the dependence of sensor-performances upon the nano- character of the MOS structure, either as a result of the increasing specific surface, either as a result of the physical proprieties induced by the decrease in the crystallite dimensions. In the first case, the increase of the surface/volume ratio due to decreasing the crystallite dimension increases the material reactivity owing to the surface phenomena as the dominant component. In the second case, the qualitative effects are taken into account, namely the quantum proprieties induced by the decrease of the crystallite dimensions under 10 nm.
The identification of the reaction partners in MOS
interaction with the molecules of the test gas;
We aim to understand: what are the elementary steps, what is responsible for the surface reaction with the gas molecules, what is the role of the pre-adsorbed molecules, what are the changes induced by the crystallite’s dimensions. This fact implies the identification of the adsorbed species, monitoring of the changes induced by gas exposure, monitoring the reaction products both on the surface and in the gas phase.
Understanding the charge transfer mechanism associated
with the surface reactions and their connection with the
respectively with the changes of the macroscopic parameters
We aim to understand: which is the electrical effect of different components from the sensor. We are concerned with the charge transfer process between the gas and solid molecules- especially in the distinction between the localized and non-localized interactions – and the mode that the crystallite’s dimensions may affect them. Also, it is interesting to establish the influence of the crystallite’s dimension on the transducer effect of a charge transfer process onto changes of an electrical parameter (macroscopic) of the sensitive layer.
||Flow system is used to dose different target gas concentrations under dynamic regime. It consists of eleven individual channels (dry synthetic air, humid synthetic air, NO2, CO, CH4, NH3, H2S, SO2). Every channel is equipped with one mass flow controller (MFC) and two solenoid valves which are computer controlled via D/A cards. Desired gas concentrations (from ppb to ppm level) are obtained by appropriate adjustment of carrier/target gases. In order to avoid any possible channel contamination, corrosion, or outgassing, high quality materials (Swagelock stainless steel tubing and fittings, Kalrez, Teflon, glass tubing) are used.|
|Sensors measurement chamber||Description|
|Within the sensors chambers up to four gas sensors with different electrodes configurations can be simultaneously exposed to the gas atmosphere. Subsequent Teflon sockets and stainless steel electrical contacts are used for DC measurements and sensor’s temperature control. The two parts of the chamber, the main body and the cover are sealed using Viton to avoid outgassing.|
|Alltech Digital Flow Check + Testo 625 thermo hygrometer|
Precise gas flow control is crucial for acquiring accurately gas concentrations.
Therefore mass flow controllers must be periodically calibrated using Alltech DFC.
Calibrated Testo 625 thermo hygrometer is used to check the relative humidity accuracy through the flow system.
|Keithley 6517A electrometer / Keithley 2000 multimeter||Description|
Keithley 6517A specifications:
Keithley 2000 specifications:
|Keithley 6517A electrometer / Keithley 2000 multimeter are used for real time DC measurements (electrical resistance or current), being fully computer controlled. Keithley 2000 is used for lower resistance values (up to 100 MΩ), whilst Keithley 6517A is used for larger r esistance values (up to hundreds of TΩ using proper shielding setups).|
|Photoacustic analyser INNOVA 1314|
Appropriate optical filters can be installed in the Photoacoustic multi-gas monitor INNOVA 1314 filter carousel so that it can selectively measure the concentration of up to 5 component gases and water vapor.
It is used for evaluation of the catalytic activity exhibited by the substrate, electrodes, and sensitive material. By subtracting the first two components one can gain solely information about the catalytic activity of the sensitive material.
|Kelvin Probe KP6500 McAllister|
Specifications: High surface sensitivity response: < 1 meV, which corresponds to 10-3 of an adsorbate layer. The reference electrode has been both chemical and electrical passivated. Automatic tracking system can be activated in order to compensate the sample position changes which may occur during the measurements runtime.
Description: The Kelvin Method measures the contact potential difference (CPD) between the sample and reference electrode and not the absolute work function. It is, therefore, used to monitor the change in work function or ΔCPD over time. Many factors can influence CPD, including temperature, stress, strain, adsorption or desorption of molecules (including moisture) and, depending on the sample material, even photo excitation. By using simultaneous electrical resistance and relative work function measurements (McAllister Kelvin Probe KP6500) in different test gas conditions, one can understand the way in which a gas-surface interaction is translated into a variation of a physical parameter. Using this technique one can get insights about the changes of the surface adsorbed species which may or may not exchange free charge carriers with the sensitive layer. More specific, the work function (Φ) contains three contributions: the surface band bending (qVs), the difference between the conduction band and Fermi level (EC-EF)bulk and the electron affinity (χ). All three contributions can change due to gas atmosphere shift inside the Kelvin Probe.
|LumaSense IN 5-L plus pyrometer|
Specifications: IN 5-L plus model is designed for non-contact temperature measurements on non-metallic surfaces and also on painted, coated or anodized metals. The sensitive spot is 2mm.
Description: This instrument is used for determining the Temperature = f (voltage) dependence for different types of heaters.
|PC IV Program INCO-Copernicus / EASTGAS (Environmental control with the Aid of Sensor Technologies for GAS sensing)||Scientific Responsible||09.1999
|PC V Program INCO-Copernicus / GASMOH (Gas sensors based on a new gas detection principle: Gas Sensing of Metal Oxides Hetero-junctions)||Scientific Responsible||12.2000
|Corint MCT / Proiect aditional GASMOH||Project Director||05.2002
|533,061 mil. Lei|
|PNCDI Matnantech / SENGAZ (Senzor de gaze)||Project Director||11.2003
|2.166,500 mil. Lei|
|PNCDI Ceres / Materiale semiconductoare si supraconductoare studiate prin spectroscopia pozitronilor anihilati||Scientific Responsible||11.2002
|380 milioane Lei|
|Program Eureka / ADVANCED PLD (Pulsed laser deposition – a new technique for coating sheet materials and three dimensional industrial components at low temperature)||Scientific Responsible||09.2003
|200 milioane Lei|
|PNCDI-Calist / PROGAZ (Procedura de evaluare a senzorilor chemorezistivi de gaze utilizati in aplicatii de monitorizare a mediului)||Project Director||11.2004
|650 milioane Lei|
|CEEX-Ceres / NANOPOLIR-LP (Studiul unor noi materiale nanocompozite de tip Polimer-Fier obtinute prin piroliza laser: sinteza, analiza structurala si proprietati senzoriale)||Scientific Responsible||07.2006
|CEEX-Matnantech / SONDAG (Senzori optici nanostructurati pentru detectia avansata de gaze)||Scientific Responsible||07.2006
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