Perihan Durmuş

Reactions of small Ni clusters with a diatomic molecule : MD simulation of D2 + Nin (n = 7-10) systems

The kinetics of the reactions of nickel clusters with a deuterium molecule are studied. Dissociative chemisorption probabilities of the D{sub 2} molecule on the small Ni{sub n} (n=7-10) clusters are computed by a quasi-classical molecular dynamics computer simulation technique. Structures of the clusters are obtained by an embedded-atom potential, and the interaction between the D{sub 2} and Ni{sub n} is modelled by an LEPS (London-Eyring-Polanyi-Sato) function (energy surface). This analysis includes the chemisorption probabilities as functions of the impact parameter and of the relative translational energy of the D{sub 2}. The corresponding reactive cross-sections for the ground state of the molecule are calculated as functions of the collision energy and the size of the cluster. The role of the size of the clusters is examined. An indirect mechanism to the reaction, which involves formation of molecular adsorption as precursors to dissociative adsorption in the low collision energy region (less than 0.1 eV), is observed. Results are discussed by comparing with the other similar theoretical and experimental studies.

Analyses of temperature-dependent interface states, series resistances, and AC electrical conductivities of Al/p?Si and Al/Bi4Ti3O12/p?Si structures by using the admittance spectroscopy method

In this study, Al/p—Si and Al/Bi4Ti3O12/p—Si structures are fabricated and their interface states (Nss), the values of series resistance (Rs), and AC electrical conductivity (σac) are obtained each as a function of temperature using admittance spectroscopy method which includes capacitance—voltage (C—V) and conductance—voltage (G—V) measurements. In addition, the effect of interfacial Bi4Ti3O12 (BTO) layer on the performance of the structure is investigated. The voltage-dependent profiles of Nss and Rs are obtained from the high-low frequency capacitance method and the Nicollian method, respectively. Experimental results show that Nss and Rs, as strong functions of temperature and applied bias voltage, each exhibit a peak, whose position shifts towards the reverse bias region, in the depletion region. Such a peak behavior is attributed to the particular distribution of Nss and the reordering and restructuring of Nss under the effect of temperature. The values of activation energy (Ea), obtained from the slope of the Arrhenius plot, of both structures are obtained to be bias voltage-independent, and the Ea of the metal-ferroelectric-semiconductor (MFS) structure is found to be half that of the metal—semiconductor (MS) structure. Furthermore, other main electrical parameters, such as carrier concentration of acceptor atoms (NA), built-in potential (Vbi), Fermi energy (EF), image force barrier lowering (Δ Φb), and barrier height (Φb), are extracted using reverse bias C−2—V characteristics as a function of temperature.

Influence of interfacial layer thickness on frequency dependent dielectric properties and electrical conductivity in Al/Bi4Ti3O12/p-Si structures

Three Al/Bi4Ti3O12/p-Si structures were fabricated with different interfacial layer thickness values (10, 25, and 53 nm) and admittance measurements of the structures were carried out between 1 kHz and 1 MHz in order to investigate the influence of interfacial layer thickness on dielectric properties of these structures. For the structure with thicker interfacial layer, higher dielectric constant (e′) and dielectric loss (e″) values were obtained at low frequencies. At high frequencies, these parameters tend to be saturated and become almost constant. Loss tangent versus frequency plots exhibit a peak and magnitude of the peak weakens with increasing frequency and shifts toward high frequency region. The dispersion in e′ and e″ with varying thickness at low frequencies was ascribed to interfacial polarization. In addition, obtained e″ values indicated higher energy dissipation in the structure with thicker interfacial layer. Admittance data of the structures were also considered in terms of modulus formal...

Effects of Frequency and Bias Voltage on Dielectric Properties and Electric Modulus of Au/Bi4Ti3O12/n-Si (MFS) Capacitors

In this work, a metal-ferroelectric-semiconductor (MFS) type capacitor was fabricated and admittance measurements were held in a wide frequency range of 1 kHz-5 MHz at room temperature for the investigation of frequency and voltage dependence of complex dielectric constant, complex electric modulus and electrical conductivity of the MFS capacitor . Bismuth titanate (Bi 4 Ti 3 O 12 ) with high dielectric constant was used as interfacial ferroelectric material and the structure of MFS capacitor was obtained as Au/Bi 4 Ti 3 O 12 /n-Si. Experimental results showed that dielectric, modulus and conductivity parameters are strong functions of frequency and voltage especially in depletion and accumulation regions due to the existence of surface states (N ss ), series resistance (R s ), interfacial polarization and interfacial layer. It was found that R s of the structure and interfacial ferroelectric layer are efective in accumulation region whereas surface states (N ss ) and interfacial polarization are efective in depletion region. Also the changes in dielectric, modulus and conductivity parameters become considerably high particularly at low frequencies due to high values of R s and N ss . The observed anomalous peak in voltage dependent plots of capacitance and dielectric constant was atributed to the particular density distribution of N ss , R s and minority carrier injection. Moreover, the value of conductivity at low and intermediate frequencies is almost independent of frequency thus low frequency data was used to extract d.c. conductivity. This work showed that the use of high-dielectric Bi 4 Ti 3 O 12 as ferroelectric interfacial layer in a MFS capacitor is preferable due to high values of its dielectric constant compared with traditional insulator layer materials such as SiO 2 and SnO 2 . Therefore, a MFS capacitor with Bi 4 Ti 3 O 12 interfacial layer can store more energy thanks to its high dielectric constant.

D2 +Nin(T), n=7 and 9, Collision System

In this study the kinetics of reactions of Nin n=7 and 9, clusters with a deuterium D2 molecule are studied via quasiclassical molecular dynamics. Dissociative chemisorption probabilities as functions of impact parameters, collision energies, and a rovibrational state of a molecule are calculated. And the corresponding reactive cross sections are evaluated. Resonance formation in the low collision energy region is discussed.