Κατεύθυνση Φυσικοχημεία
Library of the School of Science

2017-10-30

2017

Adamopoulos Sotirios-Alexandros

Αθανάσιος Τσεκούρας, Επίκουρος Καθηγητής, Τμήμα Χημείας, ΕΚΠΑ

Μελέτη της αυθόρμητης πόλωσης λεπτών υμενίων ακετόνης, βουτανάλης και τολουολίου και η εξάρτησή της από τη θερμοκρασία.

Greek

Study of spontaneous polarization of thin films of acetone, butanal and toluene and its dependence on temperature

Spontaneous polarization phenomena occurred when thin films of acetone, butanal and toluene were deposited at low temperatures, ranging between 31 and 120 K, under high vacuum conditions. These phenomena are perceived through the detection of surface potentials which arise in the deposited thin films. A Kelvin probe is used in order to measure the film voltages. The voltage magnitude of each organic thin film appeared to be strongly dependent on both deposition temperature and film thickness. A heat ramp took place after each deposition, which showed a different voltage behavior for each organic compound. Usually, the surface potentials would vanish upon reaching temperatures beyond 120 K, during the sample heating, with some notable exceptions of acetone thin films, deposited at higher temperatures, where the potential was sustained until 150 K. An attempt to recool the sample midway through the heating process, left the voltages unaffected, proving that spontaneous polarization is, indeed, an irreversible effect. Toluene films developed the highest recorded voltage and were the only case where the calculated degree of polarization would go as high as 10%. Results showed that no simple model could replicate the peculiar, non-linear, dependence between surface voltage and deposition temperature, for all three compounds. Further investigation of possible causes that shape certain voltage characteristics, such as sign changes or steep declines, unique for each compound, as deposition temperature varies or during the heating process, led to the conclusion of a possible correlation with phase transitions that occur at similar temperature ranges.

Science

spontaneous polarization, low temperatures, acetone, butanal, toluene, Kelvin probe, surface potential

Yes

2

Yes

38

134

File access is restricted only to the intranet of UoA.

https://pergamos.lib.uoa.gr/uoa/dl/object/2075237