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The formation and morphological evolution of germanides formed in a ternary Ni/Ta-interlayer/Ge system were examined by ex situ and in situ annealing experiments. The Ni germanide film formed in the Ni/Ta-interlayer/Ge system maintained continuity up to 550°C, whereas agglomeration of the Ni germanide occurred in the Ni/Ge system without Ta-interlayer. Through microstructural and chemical analysis of the Ni/Ta-interlayer/Ge system during and after in situ annealing in a transmission electron microscope, it was confirmed that the Ta atoms remained uniformly on the top of the newly formed Ni germanide layer during the diffusion reaction. Consequently, the agglomeration of the Ni germanide film was retarded and the thermal stability was improved by the Ta incorporation.
In this study, we synthesized ZnO nanowires using Au catalytic particles formed on a ZnO seed layer. We modulated the microstructure of the ZnO seed layer by changing the sputtering power to investigate how the underlying ZnO film microstructure affects the distribution of ZnO nanowires. Examining the samples after each of the three key steps of the growth process (ZnO seed layer deposition, Au catalytic particle formation, and nanowire growth) using various characterization methods such as scanning electron microscopy, transmission electron microscopy, and x-ray diffraction helped us illuminate the profound impacts of the grain size of the seed layer on the nanowire density.
This study examined the performance of poly(3-hexylthiophene-2,5-diyl)(P3HT)- and [6,6]-phenyl C61 butyric acid methyl ester (PCBM)-based organic solar cells (OSCs) with a pyromellitic dianhydride (PMDA) cathode interfacial layer between the active layer and cathode. The effect of inserting the cathode interfacial layer with different thicknesses was investigated. For the OSC samples with a 0.5 nm thick PMDA layer, the power conversion efficiency (PCE) was approximately 2.77% under 100 mW/cm2 (AM1.5) simulated illumination. It was suggested that the PMDA cathode interfacial layer acts as an exciton blocking layer, leading to an enhancement of the OSC performance.
This study examined the degradation of the device performance of InGaZnO4 (IGZO)-based thin-film transistors after annealing at high temperatures in air ambient. Using various characterization methods including scanning electron microscopy, x-ray diffraction, and transmission electron microscopy, we were able to disclose the details of a two-stage phase transformation that led to the device performance degradation. The Mo electrodes first succumbed to oxidation at moderate temperatures (400∼500 °C) and then the Mo oxide further reacted with IGZO to produce an In–Mo–O compound with some Ga at higher temperatures (600∼700 °C). We analyzed our results based on the thermodynamics and kinetics data available in the literature and confirmed that our findings are in agreement with the experimental results.
Rapid thermal annealing (RTA) processing under N2 and O2 ambient is suggested and characterized in this work for improvement of SiCOH ultra-low-k (k = 2.4) film properties. Low-k film was deposited by plasma-enhanced chemical vapor deposition (PECVD) with decamethylcyclopentasiloxane and cyclohexane precursors. The PECVD films were treated by RTA processing in N2 and O2 environments at 550 °C for 5 min, and k values of 1.85 and 2.15 were achieved in N2 and O2 environments, respectively. Changes in the k value were correlated with the chemical composition of C–Hx and Si–O related groups determined from the Fourier transform infrared (FTIR) analysis. As the treatment temperature was increased from 300 to 550 °C, the signal intensities of both the CHx and Si–CH3 peaks were markedly decreased. The hardness and modulus of the film processed by RTA have been determined as 0.44 and 3.95 GPa, respectively. Hardness and modulus of RTA-treated films were correlated with D-group [O2Si–(CH3)2] and T-group [O3Si–(CH3)] fractions determined from the FTIR Si–CH3 bending peak. The hardness and modulus improvement in this work is attributed to the increase of oxygen content in (O)x–Si–(CH3)y by rearrangement.
Area selective HfO2 thin film growth through atomic layer deposition (ALD) has been achieved on octadecyltrichlorosilane (ODTS) patterned Si substrates. Patterned hydrophobic self-assembled monolayers (SAMs) were first transferred to Si substrates by micro-contact printing. Using hafnium-tetrachloride or tetrakis(dimethylamido) hafnium(IV) and water as ALD precursors, amorphous HfO2 layers were then grown selectively on the SAM-free regions of the surface where native hydroxyl groups nucleate growth from the vapor phase. The HfO2 pattern was readily observed through scanning electron microscopy and scanning Auger imaging, demonstrating that soft lithography is a simple and promising method to achieve area selective ALD. To evaluate the selectivity, the resolution of the soft lithography based method was compared with that of area selective ALD of HfO2 by selective surface modification of patterned silicon oxide obtained using long-time SAM exposure. It was found that the selective surface modification showed much higher spatial resolution and selectivity, an observation consistent with previous studies indicating that highly ordered and densely packed ODTS films were important to achieve complete deactivation.
Ultra-thin ZrO2 and HfO2 dielectric films grown by atomic layer deposition (ALD) are quite promising materials for gate dielectric applications in future transistors, and they exhibit significantly different as-grown microstructures: polycrystalline and amorphous phases, respectively. However, under the identical deposition conditions, both metal oxides show surprisingly similar capacitance–voltage (C–V) characteristics as a function of film thickness, implying that the identities and densities of fixed charge and bulk trapping charge are similar. Factors other than the film microstructure, such as concentration of impurities incorporated during the film deposition, are believed predominantly to control important C–V characteristics. Only the dielectric constant appears to depend significantly on the identity of the dielectric material. It is found that the dielectric constant of ALD-HfO2 (∼20) is significantly lower than that of ZrO2 (∼30) due to the differences in microstructure and also atomic density of the film. In terms of the leakage current characteristics, the effective potential barrier heights between Pt and these two dielectric films are identical (∼2.3 eV) within the experimental uncertainty. Implications for the electrode/dielectric interface electronic structure are discussed.
We investigated the discrepancy between the significant 18O isotope motion observed after bipolar voltage cycling used to induce ferroelectric fatigue in unannealed Pt/Pb(Zr,Ti)O3/Ir (PZT) capacitors and the lack of any observable oxygen tracer motion in annealed capacitors. We found that while unannealed Pt electrodes are permeable to oxygen, annealed Pt electrodes are oxygen impermeable. Further, when the initial oxygen tracer profile does not vary strongly with depth, the ability to detect oxygen motion during fatigue voltage cycling depends critically on the oxygen permeability of the capacitor’s top electrode. Our results indicate that oxygen exchange between the PZT film and external oxygen sources and sinks during voltage cycling is not necessary for ferroelectric fatigue to be manifest. In addition, studies of the dependence of ferroelectric materials properties on ambient gases should be accompanied by analysis of the permeability of exposed surfaces to the gases of interest.
Zirconia–hafnia (ZrO2–HfO2) nanolaminate structures were grown using the atomic layer deposition (ALD) technique with different stacking sequences and layer thickness layer thicknesses. The microstructural evolution and surface roughness were compared with those of single-layer ZrO2 or HfO2 films using transmission electron microscopy and atomic force microscopy. Thin single-layer ALD-ZrO2 films were polycrystalline and composed of the tetragonal ZrO2 phase as-deposited, whereas thicker (>14 nm) films were composed mainly of the monoclinic phase. HfO2 films were amorphous as-deposited and crystallized into primarily monoclinic during subsequent anneals at temperatures over 500 °C. All the nanolaminate structures having individual layer thicknesses greater than approximately 2 nm were crystalline (mixture of tetragonal and monoclinic phases) independent of layer sequence and also exhibited a layer-to-layer epitaxy relationship within each grain. However, the identity of the starting layer determined the final grain size and surface roughness of the nanolaminates. A qualitative model for the observed microstructure evolution of the laminate films is proposed.
A series of self-assembled molecules have been investigated as deactivating agents for the HfO2 atomic layer deposition (ALD). Three important factors of self-assembled monolayers (SAMs) deactivating efficiency towards ALD--chain length, reactivity and steric effect--have been investigated and discussed as well as the initial blocking mechanism of this process. This investigation shows that in order to achieve satisfactory deactivation, it is crucial to choose high reactivity, low steric effect molecules with certain chain length to form condensed, high hydrophobic organic monolayers.
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