Presentation Title

Studying the Interface Between Croconic Acid Thin Films and Substrates Using Slow Positron Beam

Faculty Mentor

Dr. Renwu Zhang

Start Date

17-11-2018 10:00 AM

End Date

17-11-2018 10:15 AM

Location

C335

Session

Oral 2

Type of Presentation

Oral Talk

Subject Area

physical_mathematical_sciences

Abstract

Croconic acid (CA) is the first organic ferroelectrics with a spontaneous polarity of 20 μC/cm2. Which is comparable with its inorganic counterparts in bulk samples, such as potassium di-hydrogen Phosphate (KDP)2and Barium Titanate (BaTiO3)3. As the natural extension of study, ultrathin CA films (~500nm) are investigated to reveal the effect on the ferroelectricity from substrates for both fundamental and industrial significance. However, the void defect on the interface between the films and substrates is presumed to have the interference on such surface effect. In order to study this void defect a slow positron beam was used as a non-invasive and non-destructive technique. The slow positron beam was coupled with the Doppler broadening energy spectroscopy (DBES), which allows us to observe the void defects between the CA thin film and the two substrates Si and SiO2. The effect of external electric field, approximately 800 V/mm, on the defect formation is also investigated and the underlying mechanism is proposed.

Summary of research results to be presented

Thin croconic acid films were fabricated using physical vapor deposition with or without in situ electric field guidance on two substrates, Si and SiO2. The surface topography of the films was characterized via atomic force microscopy and the interfacial defect concentration of the films was studied via slow positron beam coupled with Doppler broadening energy spectroscopy. It was found that surface of the films prepared with electric field have more uniform morphologies, indicating better molecular alignment. It was also found that the interface of the film and SiO2 substrates has lower defect concentrations than on Si substrates. In addition, the application of an electric field during deposition significantly reduced the defect concentration in the interface of the CA film on Si with no effect observed for the SiO2 substrate. These phenomena were explained by the strong H-bond interaction between the CA molecule and SiO2 substrate.

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Nov 17th, 10:00 AM Nov 17th, 10:15 AM

Studying the Interface Between Croconic Acid Thin Films and Substrates Using Slow Positron Beam

C335

Croconic acid (CA) is the first organic ferroelectrics with a spontaneous polarity of 20 μC/cm2. Which is comparable with its inorganic counterparts in bulk samples, such as potassium di-hydrogen Phosphate (KDP)2and Barium Titanate (BaTiO3)3. As the natural extension of study, ultrathin CA films (~500nm) are investigated to reveal the effect on the ferroelectricity from substrates for both fundamental and industrial significance. However, the void defect on the interface between the films and substrates is presumed to have the interference on such surface effect. In order to study this void defect a slow positron beam was used as a non-invasive and non-destructive technique. The slow positron beam was coupled with the Doppler broadening energy spectroscopy (DBES), which allows us to observe the void defects between the CA thin film and the two substrates Si and SiO2. The effect of external electric field, approximately 800 V/mm, on the defect formation is also investigated and the underlying mechanism is proposed.