In this paper we present the results of the resistances changes of carbon-palladium films under the influences of gas like
hydrogen, ammonia and methane. Our research has shown that carbon-palladium films (C-Pd films) according to the
form and the structure in which they appear, they can respond to a variety of gases. The C-Pd film obtained by Physical
Vapor Deposition (PVD) method is sensitive to hydrogen and do not respond to the ammonia. Thermal modification of
the C-Pd film in Chemical Vapor Deposition (CVD) process affects the morphology of the film, increases its resistance
and it causes that this film begins to react to the ammonia. This change causes that this film stops responding on
hydrogen. Film sensitive to methane was obtained by changing the technology conditions of the PVD process. The
reaction of C-Pd film on the hydrogen and the ammonia is increase resistance, while film sensitive to methane reacts by
decrease of initial resistance value. In both cases, the changes are reversible after cleaning by air atmosphere. Different
varieties of C-Pd films can be used to build selective sensors for hydrogen, ammonia and methane.
Nanocomposite carbonaceous-palladium (C-Pd) films are promising materials for hydrogen and hydrogen compounds sensors. It is connected with highly selective hydrogen absorption by palladium nanocrystallites. Nanostructural C-Pd films were deposited on alundum substrate with silver electrodes. These C-Pd films were prepared in physical vacuum deposition (PVD) process and were characterized by scanning electron microscope (SEM). A special measurement set-up was built to study the changes of C-Pd film resistance in gas presence.
KEYWORDS: Palladium, Hydrogen, Chemical vapor deposition, Scanning electron microscopy, Resistance, Sensors, Transmission electron microscopy, Carbon, Temperature metrology, Nanostructures
Structural, topographical and morphological changes of carbonaceous-palladium (C-Pd) films obtained by physical
vapor deposition /chemical vapor deposition (PVD/CVD) method were studied. Effect of changes in these properties
under the influence of CVD process temperature on the hydrogen sensitivity of these films is discussed. Scanning
electron microscopy (SEM) observations were used to investigate the topography and morphology of an initial
(PVD) film and the film modified in CVD process (PVD/CVD film) at different temperatures. The changes of film’s
morphology after modification performed at various temperatures (500, 550, 600, 650, 700 and 750°C) caused
changes in their resistance. The electrical measurements carried out in the presence of gas containing 1vol % of
hydrogen showed different sensing characteristics for various films. The highest hydrogen sensitivity and the fastest
response were observed for films modified at the temperature of 500°C and 550°C. In SEM images on surface of
these films palladium nanograins with different sizes were observed. For films modified at the temperatures higher
than 600°C Pd nanograins placed under superficial very thin carbonaceous layer were found.
In this paper we present studies of hydrogen sensors based on nanostructural C-Pd films deposited on alundum substrate
with silver or titanium electrodes. These C-Pd films were prepared by PVD method. Films were characterized by SEM
and EDS. Sensitivity of films toward hydrogen were measured in specially prepare experimental set-up with small
chamber (50ml). Response time was also registered for different percentage of hydrogen / nitrogen mixture (up to 1% of
hydrogen).
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