Philipp Maydannik

Roll-to-roll atomic layer deposition process for flexible electronics encapsulation applications

At present flexible electronic devices are under extensive development and, among them, flexible organic light-emitting diode displays are the closest to a large market deployment. One of the remaining unsolved challenges is high throughput production of impermeable flexible transparent barrier layers that protect sensitive light-emitting materials against ambient moisture. The present studies deal with the adaptation of the atomic layer deposition (ALD) process to high-throughput roll-to-roll production using the spatial ALD concept. We report the development of such a process for the deposition of 20 nm thickness Al2O3 diffusion barrier layers on 500 mm wide polymer webs. The process uses trimethylaluminum and water as precursors at a substrate temperature of 105 °C. The observation of self-limiting film growth behavior and uniformity of thickness confirms the ALD growth mechanism. Water vapor transmission rates for 20 nm Al2O3 films deposited on polyethylene naphthalate (PEN) substrates were measured a...

Molecular layer deposition of polyethylene terephthalate thin films

Thin films of polyethylene terephthalate (PET) have been grown using sequential surface chemical reactions on silicon substrates. The surface has been sequentially exposed to terephthaloyl chloride (TC) and ethylene glycol (EG) in an ASM F-120 atomic layer deposition reactor. Precursor pulses were alternated with 30 s of N2 purge. The process has been studied as a function of temperature, precursor pulsing time, and number of cycles. The films were deposited in the temperature range 145–175 °C and the precursors were held at 130 °C (TC) and 70 °C (EG). Before deposition the silicon surface was functionalized using 3-aminopropyltriethoxysilane to ensure nucleation of the film. The film growth exhibits self-limiting behavior and linear growth rate dependence that confirms its molecular layer deposition nature. The deposited films have been identified as PET by means of attenuated total reflectance FTIR which reveals the presence of characteristic carbonyl and aromatic groups. Film thickness was measured by ...

Continuous atomic layer deposition: Explanation for anomalous growth rate effects

Spatial atomic layer deposition (ALD) on moving substrates has recently been the subject of increasing interest and development. Recent results of deposition on flexible substrates in a cylindrical rotating continuous ALD system showed that in certain regions of operation, deviations from ideal ALD behavior occurred showing excess deposition during the trimethylaluminium (TMA)/water process for aluminum oxide. It was speculated that this was due to boundary layer gas entrainment at the surface of the moving substrate and consequent drag-through of precursors between the different precursor vapor zones. In this paper a study has been made of these gas entrainment effects by using helium as a tracer gas to determine how the transport between zones takes place. A simple model of the process based on physical principles has been constructed which replicates the observed helium transport behavior in the boundary layer. Based on this, it has been shown that gas entrainment is not the reason for the anomalous ex...

Synthesis and application of polypyrrole coated tenorite nanoparticles (PPy@TN) for the removal of the anionic food dye ‘tartrazine’ and divalent metallic ions viz. Pb( ii ), Cd( ii ), Zn( ii ), Co( ii ), Mn( ii ) from synthetic wastewater

The present study deals with the synthesis of polypyrrole coated tenorite nanoparticles. The synthesized nanoparticles were characterized by XRD, TEM, SEM and EDS. TEM images showed the formation of nanoparticles with 26–30 nm diameter. The BET surface area of the nanoparticles was determined to be 425 m2 g−1 while the pore diameter of the nanoparticles was found to be 3.57 nm which showed the formation of mesoporous nanoparticles. The pHzpc of the nanoparticles was determined to be 4.4. The removal efficiency of the synthesized nanoparticles for an anionic food dye ‘tartrazine’ was investigated. Decreased removal was observed, when the dye concentration was increased from 100 to 200 mg L−1. It was observed that an acidic medium was favorable for tartrazine removal. A thermodynamic study suggested the endothermic nature of tartrazine adsorption. The value of Ea for the present system was found to be 26.97 kJ mol−1. The best suitable kinetic model was well explained by the pseudo second order model. Langmuir adsorption capacity was measured to be 42.50 mg g−1. Exhausted (dye loaded) nanoparticles were used as an efficient adsorbent for the removal of divalent metallic ions viz. Pb(II), Cd(II), Co(II), Mn(II), Zn(II) and were found to be efficient for the removal of metallic species from a single solute system as well as a multi-solute system. This study reveals that polypyrrole coated tenorite nanoparticles are very efficient for dye removal and the dye loaded exhausted adsorbent is equally good for metal removal because tartrazine loading on nanoparticles makes the surface suitable for metal interaction. Thus, the synthesized nanoparticles prove to be a good candidate for the treatment of dye and metal bearing wastewater.

Low temperature temporal and spatial atomic layer deposition of TiO2 films

Titanium dioxide films were grown by atomic layer deposition (ALD) using titanium tetraisopropoxide as a titanium precursor and water, ozone, or oxygen plasma as coreactants. Low temperatures (80–120 °C) were used to grow moisture barrier TiO2 films on polyethylene naphthalate. The maximum growth per cycle for water, ozone, and oxygen plasma processes were 0.33, 0.12, and 0.56 A/cycle, respectively. X-ray photoelectron spectrometry was used to evaluate the chemical composition of the layers and the origin of the carbon contamination was studied by deconvoluting carbon C1s peaks. In plasma-assisted ALD, the film properties were dependent on the energy dose supplied by the plasma. TiO2 films were also successfully deposited by using a spatial ALD (SALD) system based on the results from the temporal ALD. Similar properties were measured compared to the temporal ALD deposited TiO2, but the deposition time could be reduced using SALD. The TiO2 films deposited by plasma-assisted ALD showed better moisture barri...

Spatial atomic layer deposition: Performance of low temperature H2O and O3 oxidant chemistry for flexible electronics encapsulation

Water and oxygen were compared as oxidizing agents for the Al2O3 atomic layer deposition process using spatial atomic layer deposition reactor. The influence of the precursor dose on the deposition rate and refractive index, which was used as a proxy for film density, was measured as a function of residence time, defined as the time which the moving substrate spent within one precursor gas zone. The effect of temperature on the growth characteristics was also measured. The water-based process gave faster deposition rates and higher refractive indices but the ozone process allowed deposition to take place at lower temperatures while still maintaining good film quality. In general, processes based on both oxidation chemistries were able to produce excellent moisture barrier films with water vapor transmission rate levels of 10−4 g/m2 day measured at 38 °C and 90% of relative humidity on polyethylene naphthalate substrates. However, the best result of <5 × 10−5 was obtained at 100 °C process temperature with...

Photoelectrocatalytic activity of ZnO coated nano-porous silicon by atomic layer deposition

In the present study, ZnO thin film was grown on nano-porous silicon by atomic layer deposition (ALD) whereas porous silicon was prepared by a stain etching method for three different durations, 4 min (PS1), 8 min (PS2) and 12 min (PS3). SEM analysis shows that ZnO nanoparticles with a size of 20–50 nm were uniformly distributed on nano-porous silicon. AFM analysis shows that the surface roughness of the nanoporous silicon increases continuously with the increase of porous silicon etching time. In contradiction, the surface roughness is almost equal for ZnO/PS1, ZnO/PS2 and ZnO/PS3. XRD analysis shows that the ZnO nanoparticles exhibited a hexagonal wurtzite structure. XPS characterization was used to analyze the chemical composition and states present in the ZnO coated porous silicon. The DRS UV-Visible absorbance spectrum reveals that ZnO/PS3 very strongly absorbs visible light around 526 nm. ZnO coated porous silicon, especially ZnO/PS3, exhibited higher photocatalytic activity compared to ZnO coated glass towards methylene blue dye degradation. Likewise, the negative biased ZnO/PS3 exhibited superior photocatalytic activity compared to unbiased and positive biased ZnO/PS3. The enhanced solar photocatalytic and photoelectrocatalytic activity is attributed to the visible light absorption of ZnO/PS and the effective injection of photogenerated electrons from porous silicon to ZnO even if porous silicon is not directly involved in any redox reactions.

Atomic layer deposition of CuCl nanoparticles

We report the growth of copper (I) chloride by atomic layer deposition. CuCl was deposited as nanoparticle arrays whose size and density were controlled by the process conditions. The nanoparticles were deposited using the self-limiting reaction of [bis(trimethylsilyl)acetylene]-(hexafluoroacetylacetonato)-copper(I) and hydrogen chloride. UV absorption measurements showed the characteristic Z1,2 and Z3 exciton absorption bands of CuCl. A strong UV emission was observed at 5 K from the free exciton Z3 and bound exciton I1 at 386.7 and 390.6 nm, respectively. A previously unreported visible emission band at 408 nm was also observed and attributed to the acceptor level of Cu vacancies.

Atomic layer deposition of cerium oxide for potential use in diesel soot combustion

The particulate soot emission from diesel motors has a severe impact on the environment and peoples health. The use of catalytic convertors is one of the ways to minimize the emission and decrease the hazard level. In this paper, the activity of cerium oxide for catalytic combustion of diesel soot was studied. Thin films of cerium dioxide were synthesized by atomic layer deposition using tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)cerium [Ce(thd)4] and ozone as precursors. The characteristics of the films were studied as a function of deposition conditions within the reaction temperature range of 180–350 °C. Thickness, crystallinity, elemental composition, and morphology of the CeO2 films deposited on Si (100) were characterized by ellipsometry, x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy, and field emission scanning electron microscopy, respectively. The growth rate of CeO2 was observed to be 0.30 A/cycle at temperatures up to 250 °C with a slight increase to 0.37 A/...

Atomic layer deposition of nanocrystallite arrays of copper(I) chloride for optoelectronic structures

Zinc blende structure γ-copper(I) chloride is a wide bandgap semiconductor with high exciton and biexciton binding energies. γ-CuCl has applications in UV-wavelength optoelectronic structures which can exploit these characteristics, such as 4-wave mixing and optical bistability. For these purposes, a controllable method of achieving thin films and nanocrystallite arrays is necessary. Atomic layer deposition (ALD) of nanocrystallites and thin films of γ-CuCl under restricted conditions has previously been demonstrated. This paper greatly extends the previous work and unequivocally confirms that ALD growth takes place over a range of deposition parameters, as characterised by growth saturation with increasing precursor dose, deposition rate independent of temperature and linear growth rate once a complete film has been formed. Arrays of nanocrystallites of different sizes can be controllably deposited by varying the number of ALD cycles within the initial nucleation region. In this region two distinct growth regimes have been observed depending on the length of the post-chloride precursor purge pulse. Long purge time results in retarded nucleation whereas short pulse time shows enhanced nucleation compared to a strictly linear process. The zinc blende γ-CuCl phase was confirmed with both X-ray analysis and also the signature excitonic Z1,2 and Z3 peaks in optical absorption, with no evidence of other impurities. This demonstrates that ALD is a suitable technique for the controllable deposition of thin films and arrays of nanocrystallites of CuCl which may facilitate the use of CuCl in thin film or nanocluster form for further exploration in optoelectronic and photonic applications.