In situ spectroscopic ellipsometry for atomic layer deposition

The application of in situ spectroscopic ellipsometry during thin film synthesis by atomic layer deposition (ALD) is examined for results obtained on Al2O3, TaN2, and TiN films with thicknesses ranging from 0.1 to 100 nm. By analyzing the film thickness and the energy dispersion of the optical constants of the films, the layer-by-layer growth and material properties of the ALD films can be studied in detail. The growth rate per cycle and the nucleation behavior of the films can be addressed by monitoring the thickness as a function of the number of cycles. It is shown that from the energy dispersion relation, insight into the conductive properties of metallic films can be derived. Moreover, the shape of the dispersion relation can be used to discriminate between different material compositions

Film properties and in-situ optical analysis of TiO2 layers synthesized by remote plasma ALD

TiO2 is a widely studied material due to its optical and photocatalytic properties and its hydrophilic nature after prolonged UV exposure. When synthesized by atomic layer deposition (ALD) the TiO2 can be deposited with ultimate growth control with a high conformality on demanding topologies and even at room temperature when e.g. using a plasma based process. We report on the deposition of TiO2 films using remote plasma ALD with titanium (IV) isopropoxide as precursor and O2 plasma as oxidant. Stochiometric TiO2 films with carbon and hydrogen levels below the detection limit of Rutherford backscattering/elastic recoil detection (<2 at.%) have been deposited within the temperature range of 25°C to 300°C. Depending on the ALD conditions and film thickness amorphous films turn anatase for temperatures higher than 200°C as revealed by X-ray diffraction. It is demonstrated that this change in crystal phase can also be observed by spectroscopic ellipsometry revealing an increase in growth rate per cycle (from typically 0.45 Å/cycle to 0.7 Å/cycle) and change in bandgap (from 3.4 eV to 3.7 eV) when the TiO2 becomes anatase. An accompanying change in surface topology is clearly observed by atomic force microscopy. The hydrophilicity of low temperature TiO2 films is studied by contact angle measurements for adhesion purposes revealing that the amorphous films are super-hydrophilic after UV exposure

OLED Encapsulation by Room Temperature Plasma-Assisted ALD Al2O3 Films

Organic light emitting diodes (OLEDs, both small molecule and polymer LEDs) require excellent gas and moisture permeation barrier layers to increase their lifetime. The quality of the barrier layer is ultimately controlled by the presence of defects in the layer. Although a barrier layer may be intrinsically excellent (water vapor transmission rate, WVTR = 10-6 g·m-2·day-1) the protected device may fail in the presence of defects that lead to preferential diffusion pathways for H2O (e.g., defects caused by particles from the environment and/or production process). The state-of-the-art barrier coatings are micrometer-thick multi-layer structure, in which organic interlayers are alternated with inorganic barrier layers with the purpose of decoupling the above-mentioned defects. Recently, atomic layer deposition (ALD) has been successfully tested for the deposition of very thin (<50 nm) single layer permeation barriers on pristine polymer substrates [1,2], showing the potential of this highly uniform and conformal deposition technique in the field of moisture permeation barriers. In this contribution the encapsulation of OLEDs by plasma-assisted ALD of thin (20-40 nm) Al2O3 layers is addressed. The layers are synthesized at room temperature by sequentially exposing the substrate to Al(CH3)3 vapor and a remote inductively coupled O2 plasma in Oxford Instruments FlexALTM and OpALTM reactors. The intrinsic quality of the deposited ALD layers was determined by monitoring the oxidation of a Ca film encapsulated by the Al2O3 film: WVTR values as low as 2·10-6 g·m-2·day-1 have been measured. The potential of ALD layers in encapsulating OLEDs, and therefore in successfully covering the defects present on the device, has been investigated by means of electroluminescence measurements of polymer-LEDs (effective emitting area of 5.8 cm2). The black spot density and area growth were followed as a function of the time under standard conditions of 20°C and 50% relative humidity. Within a 500 h test ALD-encapsulated OLEDs show approximately half the black spot density compared to devices encapsulated by plasma deposited a-SiNx:H (300 nm thick). The black spot density is further reduced by combining the a-SiNx:H and ALD Al2O3 layers. These results point towards a very promising application of ALD Al2O3 layers in the field of OLED encapsulation and will be interpreted in terms of possible mechanisms related to film growth in multi-layer structures

Young men are at higher risk of failure after ACL hamstring reconstructions:a retrospective multivariate analysis

Background: Results of ACL reconstruction are influenced by both patient and surgical variables. Until now a significant amount of studies have focused on the influence of surgical technique on primary outcome, often leaving patient variables untouched. This study investigates the combined influence of patient and surgical variables through multivariate analysis. Methods: Single-center retrospective cohort study. All patients who underwent primary ACL hamstring reconstruction within a 5-year period were included. Patient characteristics (gender, age, height, weight, BMI at time of surgery) and surgical variables (surgical technique, concomitant knee injury, graft diameter, type of femoral and tibial fixation) were collected. Patients were asked about Tegner Activity Scale (TAS), complications and revision surgery. Multivariate logistic regression was used to study risk factors. First graft failure and potential risk factors (patient and surgical) were univariately assessed. Risk factors with a p-value ≤ 0.05 were included in the multivariate model. Results: Six hundred forty-seven primary ACL hamstring reconstructions were included. There were 41 graft failures (failure rate 6.3%). Patient gender, age, height and preoperative TAS had a significant influence on the risk of failure in the univariate analysis. The multivariate analyses showed that age and sex remained significant independent risk factors. Patients with a failed ACL reconstruction were younger (24.3 vs 29.4 years, OR 0.937), with women at a lower risk for failure of their ACL reconstruction (90.2% males vs 9.8% females, female OR 0.123). ACL graft diameter and other surgical variables aren’t confounders for graft failure. Conclusion: This study shows that patient variables seem to have a larger influence on the failure rate of ACL hamstring reconstructive surgery than surgical variables. Identification of the right patient variables can help us make more informed decisions for our patients and create patient-specific treatment protocols. Young men’s higher risk of failure suggests that these patients may benefit from a different reconstruction technique, such as use of a patellar tendon or combined ligament augmentation. Level of evidence: Retrospective cohort III

Spelling in adolescents with dyslexia: errors and modes of assessment

In this study we focused on the spelling of high-functioning students with dyslexia. We made a detailed classification of the errors in a word and sentence dictation task made by 100 students with dyslexia and 100 matched control students. All participants were in the first year of their bachelor’s studies and had Dutch as mother tongue. Three main error categories were distinguished: phonological, orthographic, and grammatical errors (on the basis of morphology and language-specific spelling rules). The results indicated that higher-education students with dyslexia made on average twice as many spelling errors as the controls, with effect sizes of d ≥ 2. When the errors were classified as phonological, orthographic, or grammatical, we found a slight dominance of phonological errors in students with dyslexia. Sentence dictation did not provide more information than word dictation in the correct classification of students with and without dyslexia