Retention of surface structure causes lower density in atomic layer deposition of amorphous titanium oxide thin films

Abstract

Size effects and structural modifications in amorphous TiO2 films deposited by atomic layer deposition (ALD) were investigated. As with the previously investigated ALD-deposited Al2O3 system we found that the film’s...

Maxwell–Wagner Relaxation-Driven High Dielectric Constant in Al2O3/TiO2 Nanolaminates Grown by Pulsed Laser Deposition

“…The activation energies ( U ) for the corresponding processes are derived from the slopes of the linear fits as shown in Figure . Lower activation energies obtained for set-2 (i.e., for TiO 2 layers) compared to set-1 (i.e., for Al 2 O 3 layers) (Figures a,b) further corroborate the higher conductivity of TiO 2 layers compared to Al 2 O 3 layers, possibly due to a higher concentration of charge carriers at the surface/subsurface region of TiO 2 sublayers. − This observed conductivity contrast between TiO 2 and Al 2 O 3 sublayers promotes charge accumulation across interfaces and further supports M–W interfacial polarization in the subnanometric regime . Because the calculated activation energies of conduction for both the layers lie in a range from ∼0.11 to 0.21 eV, electron hopping via oxygen vacancies (OVs) can be assigned as the conduction mechanism in ATA NLs. , For TiO 2 layer conduction processes, the decrease in the activation energy from 0.16 to 0.11 eV with t s decreasing from ∼1 to 0.8 nm suggests an increased hopping probability of charge carriers in TiO 2 .…”

“…Hence, the linear increase in tan δ toward a low-frequency side is due to long-range electron hopping-driven dc conductivity (σ 0 ) across the NL structure. Additionally, the relaxation peaks (marked by arrows) observed in the tan δ versus f plot (Figure b) are found to shift toward a higher-frequency side with t s decreasing from ∼2 to 0.7 nm, which further indicates a decrease in the relaxation time with a decrease in the sublayer thickness, probably due to an enhanced concentration of surface/interface states. − Furthermore, the maximum tan δ (∼0.9) observed for 0.5A-0.5T NL is probably due to enhanced intermixing of TiO 2 and Al 2 O 3 layers, thereby forming a composite layer of AlTiO x or TiAlO x . ,, …”

“…Furthermore, an important aspect of device performance is cut-off frequency ( f c ), which is referred to the inflection point of the tan δ versus ε r curve, as shown by arrow marks in Figure b . As can be seen, the cut-off frequency of ATA NL increased from ∼3.1 to ∼63 kHz as t s reduced from ∼2 to 0.7 nm, which may be due to the decrease in separation between interfaces and an increase in conductivity of the TiO 2 layer with decreasing t s . Although the cut-off frequency for 0.8A-0.8T NL ( f c ∼ 50 kHz) is slightly less than that for 0.7A-0.7T NL ( f c ∼ 63 kHz), a huge difference in the dielectric constant observed between 0.7A-0.7T NL (ε r ∼ 370) and 0.8A-0.8T NL (ε r ∼ 670) clearly suggests that 0.8A-0.8T NL may be more suitable for practical applications requiring high dielectric constants and low loss.…”

“…52 As can be seen, the cut-off frequency of ATA NL increased from ∼3.1 to ∼63 kHz as t s reduced from ∼2 to 0.7 nm, which may be due to the decrease in separation between interfaces 53 and an increase in conductivity of the TiO 2 layer with decreasing t s . 48 Although the cut-off frequency for 0.8A-0.8T NL (f c ∼ 50 kHz) is slightly less than that for 0.7A-0.7T NL (f c ∼ 63 kHz), a huge difference in the dielectric constant observed between 0.7A-0.7T NL (ε r ∼ 370) and 0.8A-0.8T NL (ε r ∼ 670) clearly suggests that 0.8A-0.8T NL may be more suitable for practical applications requiring high dielectric constants and low loss. The high dielectric constant (∼670), low loss (∼0.16), and high cut-off frequency (∼50 kHz) reported in this work, for PLD-grown 0.8A-0.8T NL, compare favorably with the best reported values for ALD-grown ATA NLs.…”

Specific capacitance of graphene oxide–metal interfaces at different deoxygenation levels

“…The GO/Ti samples are distinct from the B-type samples for the following main reason: the Ti-rich oxides grown electrochemically (see below) on Ti, including Ti 6 O, are reported to be conductive. [86][87][88] This is veried by observing two orders of magnitude higher currents passing through the Ti/rGO/Ti samples than the analogous B-type samples under the same biasing conditions (the max current level in Fig. 6d should Fig.…”