DOI: 10.3897/aldj.1.105146

Authors: Albert Santoso, Bart J. van den Berg, Saeed Saedy, Eden Goodwin, Volkert van Steijn, J. Ruud van Ommen

Abstract: Polydimethylsiloxane (PDMS) has been widely employed as a material for microreactors and lab-on-a-chip devices. However, in its applications, PDMS suffers from two major problems: its weak resistance against common organic solvents and its chemically non-functional surface. To overcome both issues, atmospheric pressure atomic layer deposition (AP-ALD) can be used to deposit an inorganic nanolayer (TiOx) on PDMS that, in turn, can be further functionalized. The inorganic nano layer is previously communicated to durably increase the organic solvent resistance of PDMS. In this study, we investigate the possibility of this TiOx nano layer providing surface anchoring groups on PDMS surfaces, enabling further functionalization. We treat PDMS samples cured at three different temperatures with AP-ALD and measure the hydrophilicity of the treated samples as an indicator of the presence of surface anchoring groups. We find that all the treated PDMS samples become hydrophilic right after the AP-ALD treatment. We further find that the AP-ALD-treated PDMS samples cured at 150 °C and 200 °C maintain their hydrophilicity, while the samples cured at 70 °C become less hydrophilic over time. The presence of surface anchoring groups through TiOx nano layer deposition on PDMS is further demonstrated and utilized by depositing gold nanoparticles (AuNPs) on the AP-ALD-treated samples. The samples exhibit visible light absorbance at 530 nm, a typical absorbance peak for AuNPs. In conclusion, this study demonstrates the use of nano layers grown by AP-ALD to solve the two major problems of PDMS simultaneously, widening its applicability, especially for use in high-end applications such as catalysis and bio-sensing.

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DOI: 10.3897/aldj.1.101651

Authors: Jie Shen, Fred Roozeboom, Alfredo Mameli

Abstract: Atmospheric-pressure plasma-enhanced spatial atomic layer deposition (PE-spatial-ALD) of SiNx is demonstrated for the first time. Using bis(diethylamino)silane (BDEAS) and N2 plasma from a dielectric barrier discharge source, a process was developed at low deposition temperatures (≤ 250 °C). The effect of N2 plasma exposure time and overall cycle time on layer composition was investigated. In particular, the oxygen content was found to decrease with decreasing both above-mentioned parameters. As measured by depth profile X-ray photoelectron spectroscopy, 4.7 at.% was the lowest oxygen content obtained, whilst 13.7 at.% carbon was still present at a deposition temperature of 200 °C. At the same time, deposition rates up to 1.5 nm/min were obtained, approaching those of plasma enhanced chemical vapor deposition and thus opening new opportunities for high-throughput atomic-level processing of nitride materials.

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DOI: 10.3897/aldj.1.101276

Authors: Jamie P. Wooding, Shawn A. Gregory, Amalie Atassi, Guillaume Freychet, Kyriaki Kalaitzidou, Mark D. Losego

Abstract: Background: We report on the fundamental crystallization kinetics of atomic layer deposited (ALD) TiO2 thin films undergoing a post-deposition anneal (PDA) at low temperatures to probe differences in the as-deposited film microstructure. Methods: The system of study is ALD TiO2 thin films prepared from tetrakis(dimethylamino)titanium(IV) (TDMAT) and water at 120 °C, 140 °C and 160 °C followed by ex situ low temperature annealing at temperatures ranging from 140 °C to 220 °C. All as-deposited TiO2 thin films are amorphous by X-ray diffraction (XRD). Post-deposition annealing (PDA) produces large grain anatase crystals, confirmed by XRD and top-view scanning electron microscopy (SEM). A detailed SEM study is performed to quantify the nucleation and growth kinetics by fitting microstructural data to the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. Finally, a time-temperature-transformation (TTT) diagram is constructed to summarize the differences in crystallization behavior at different ALD deposition temperatures. Results and conclusions: Fitting microstructural data to the JMAK equation reveals an Avrami exponent close to 3 with continuous nucleation, suggesting two-dimensional, plate-like crystal growth. Applying an Arrhenius relationship to the phase transformation data, the combined activation energy for nucleation and growth is found to be 1.40–1.58 eV atom-1. Nucleation rates are determined, and an Arrhenius relationship is used to calculate the critical Gibbs free energy for nucleation (~1.3–1.4 eV atom-1). As such, nucleation is the rate-limiting step for the amorphous to anatase phase transformation. ALD growth temperature is found to dictate film microstructure with lower deposition temperatures reducing the nucleation rate and leading to larger grain sizes irrespective of PDA conditions. The nucleation rate pre-exponential frequency factor increases with increasing deposition temperature, thereby increasing the likelihood for nucleation. Interestingly, it is this difference in the vibrational modes of the amorphous structure, as indicated by the variation in the nucleation rate pre-exponential frequency factor, that alters the phase transformation rates and not a change in the activation energies for the transformation.

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