Supervisors info:
Αθανάσιος Τσεκούρας Επίκ. Καθηγητής (Επιβλέπων), Εμμανουήλ Συσκάκης Επίκ. Καθηγητής, Ιωάννης Λελίδης Επίκ. Καθηγητής
Summary:
In this thesis we study the phenomenon of spontaneous polarization, according
to which polar compounds show polarization, and consequently, development of
voltage, when they are deposited at low temperatures, onto a metal substrate.
The compounds we examined were methanol, ethanol, 1-propanol, 1-butanol,
1-pentanol, tetrahydrofuran and diethyl ether. Depositions were carried out at
temperatures from 32 K to 120 K, onto a polycrystalline platinum foil. The
platinum foil was placed in a vacuum chamber, which was equipped with a
quadrupole mass spectrometer and a Kelvin probe. During the experimental
procedure the compound was condensed onto the metal substrate and then we
ramped the substrate’s temperature with simultaneous recording of the
developing voltage. The corresponding electric fields were of the order of 107
– 108 V/m. More specifically, alcohols, except for methanol, showed large
electric fields with negative voltage. In contrast, methanol and ethers showed
less intense electric fields and with different polarity. Tetrahydrofuran
showed positive voltage, while for methanol and diethyl ether there were
changes in polarity depending on deposition temperature. The percentage of
molecules showing alignment parallel to the surface normal was estimated at
most 10%.
Keywords:
Thin films, Low temperatures , Alcohols , Ethers , Electric field
