Marek Godlewski

2-D Finite-Element Modeling of ZnO Schottky Diodes With Large Ideality Factors

In this paper, we complement our previous work on the study of low-temperature rectifying junctions based on Ag/ZnO Schottky barriers. Diodes characterized by very high ION/IOFF ratio and ideality factors considerably higher than unity, in disagreement with the thermionic emission model, are modeled with a 2-D finite-element simulator. We could discard tunneling and inhomogeneous barrier-height distribution as sources for this anomalous value. A new interface charge layer model was therefore introduced, which is able to reproduce the electrical behavior in devices with large ideality factors without decreasing the rectifying properties.

Tuning properties of long-period gratings by atomic layer deposited zinc oxide nano-coating

This work presents an application of thin zinc oxide (ZnO) films obtained using atomic layer deposition (ALD) for effective tuning of spectral response and the refractive-index (RI) sensitivity of long-period gratings (LPGs). The technique allows for an efficient and well controlled deposition at monolayer level of excellent quality nano-films as required for optical sensors. The effect of ZnO deposition on spectral properties of the LPGs is discussed. We correlated the increase in ZnO thickness with the shift of the LPG resonance wavelength and proved that similar films are deposited on fibers and silicon reference samples in the same process run. The thin overlay effectively changes the distribution of the cladding modes and thus also tunes the device’s RI sensitivity. The tuning can be simply realized by varying number of cycles, which is proportional to thickness of the high-refractive-index (n<1.9 in infrared spectral range) ZnO film. The advantage of this approach is precision in determining the film thickness resulting in RI sensitivity of the LPGs.

Refractive index sensitivity of optical fiber lossy-mode resonance sensors based on atomic layer deposited TiOx thin overlay

This work presents an optical fiber refractive index sensors based on lossy–mode resonance (LMR) effect supported by titanium oxide (TiOx) thin overlay. The TiOx overlays of different thickness were deposited on core of polymer-clad silica (PCS) fibers using atomic layer deposition (ALD) method. Based on numerical simulations, a number of structures differing in the location of exposed core area and the thickness of TiOx coatings were designed. For fabricated structures the spectral response to external refractive index (next) was measured. The maximum sensitivity reaches 634.2 nm/RIU (next range: 1.357 - 1.402 RIU; TiOx coating thickness: 260.9 nm; investigated spectral range: 500-800 nm) and it highly depends on the thin-film thickness.

Modified PV structures with a nanostructured top electrode

Structured Silicon layers are used to improve light harvesting by Si-based solar cells. Microstructure of Si is obtained by a selective Si etching using aggressive solvents (acids like HF). In the approach discussed in this work a simplified architecture of solar cells is discussed. A structured electrode is formed by deposition of ZnO nanorods on top of p-type Si. This modification eliminates energy consuming and environmental unfriendly technological steps, as discussed. The so-obtained 3D top electrode consists of n-type ZnO:Al (AZO) layer grown on ZnMgO coated zinc oxide nanorods. AZO and ZnMgO films are deposited by Atomic Layer Deposition method (ALD). Advantages of this technique are first discussed. Several possible applications of the ALD are reviewed.

Multimodal non-gadolinium oxide nanoparticles for MRI and fluorescence labelling

Magnetic Resonance Imaging (MRI) is considered a useful non-invasive method for cancer detection. However, MRI still has some limitations: low specificity for early-stage cancers as well as toxicity of Gadolinium ions, which were reported to accumulate in the nerve tissue and kidneys. Early cancer development and metastases monitoring are still difficult, because of the issues with permeability of contrasting agents through the blood-organ barriers. Nowadays, studies are being conducted to find the new contrasts with high magnetic moment, yet without gadolinium-induced toxicity. We propose an innovative, multimodal, high-k oxide-based contrasting nanoparticles (NPs), combining fluorescent properties of lanthanides with contrast in T1 and T2 spin relaxations. This material can facilitate both in-situ screening and visualization of tumour for fluorescence assisted biopsy or surgery. NPs used in our study were developed in the Institute of Physics, PAS. The NPs core was based on HfO2, doped with Eu ions, while Gd was used for positive control. Fluorescence was induced at 619nm, while emission was detectable at 630-650nm. The T1 and T2 relaxation times have been assessed using phantoms. Statistically significant changes were observed in T2 relaxation time. We used old rats, patients of the oncology clinic as an animal model. Prior to oral application of NPs (1mg/ml, 1ml/rat, LEC No 13/2015) the initial MRI screening of rats was performed. Weighted images T2 (3D FSE), SWI and SS-FSE were performed twice, 24 and 48 hours after IG. After imaging, tumours were surgically removed, for cytometric and pathomorphology evaluation.

Novel fluorescent oxides provide insight into the dynamics of nanoparticle mediated drug uptake from the gastro-intestinal tract

In recent years nanotechnology gathered much attention due to promising applications in biomedicine. Using nanoparticles as drug carriers could allow for more effective and efficient therapy in treating cancer or neurological diseases. This is due to their unique properties such as enhancement of drug bioavailability or the ability to protect the drug from degradation. In this study we performed in vivo (BALB-c mice) and in vitro (Caco-2 cell line) experiments with Y2O3:Tb_lectin conjugates as well as pure lectin to characterize the dynamics of nanoparticles mediated drug uptake from gastro-intestinal tract. Mice were given 0.3ml of Y2O3:Tb_lectin conjugates or pure lectin suspension and were sacrificed after 3h, 24h and 1 week (Y2O3:Tb_lectin conjugates) or 3h and 24h (pure lectin). Cell cultures were incubated for 24h with increasing concentration (0.001mg/ml; 0.01mg/ml; 0.1mg/ml; 1mg/ml) of Y2O3:Tb_lectin or pure lectin. After analysing gathered data we concluded that our nanoparticles successfully conjugated with lectin and allowed for its transport through physiological barriers. NPs_Lectin conjugates undergo absorption, distribution and redistribution similarly as free nanoparticles do, although it decreased the efficiency of absorption compared to free nanoparticles. Lastly after reaching the tissue conjugates dissolved leading to lectin deposition in the tissue.

Novel nanomaterials for applications in cancer imaging

Enormous potential of nanoparticles in medicine is a rapidly growing research field. Hereby, we focused on the applications of biocompatible oxide nanoparticles in the field of cancer diagnosis and therapy. This work was focused on the development of fluorescent Tb-doped ZrO2 nanoparticles (NPs) for application in lung cancer diagnostics. Obtained, hydrothermally created NPs were below 100 nm with very low influence of Tb concentration on size. Mice received suspension of nanoparticles (10 mg/ml, 0.3 ml/mouse) via gastric gavage. All protocols were according to the EU guidelines and approved by LEC agreements No 2/2012 and 13/2015. At 3h and 24h mice were sacrificed and all tissues collected for analyses under confocal microscope and scanning cytometry. Following oral administration, ZrO2:Tb nanoparticles were passively targeted to all tumour loci via the enhanced permeation and retention (EPR) effect. Due to the very tight endothelial barrier in the lungs NPs in this organ were targeted specifically to the areas of metastases rendering them a highly specific diagnostic tool for cancer diseases with high potential applications as a carrier of therapeutic factors.

Regeneration of titanium oxide nano-coated long-period grating biosensor

This work presents an application of sodium hydroxide (NaOH) as an effective method for regeneration of titanium oxide (TiOx) nano-coated long-period grating (LPG) biosensor. Below 100 nm in thickness TiOx coating was deposited with atomic layer deposition (ALD) method on LPGs for enhancing their refractive index sensitivity up to 2912 nm/RIU in RI range 1.33-1.36 RIU. Next, the sensors were biofunctionalized in order to immobilize receptor (biotin) on their surface and used for selective avidin detection. After successful biofunctionalization process and avidin detection the sensors were washed in NaOH and biofunctionalized again. The proposed method for recovering the sensor does not cause decrease in its functional properties. As a result of the applied procedure the biosensor was fully regenerated.

P2.7.4 Zinc oxide nanostructures obtained by hydro-thermal method for sensor application

We have developed a new and inexpensive method for preparation of ZnO nanostructures (nanorods) for sensor applications. We use hydro-thermal method and fairly low growth temperature of 50°C. As a substrate gallium arsenide and silicon wafers were selected with gold eutectic mixture prepared on their surface. We used deionized water and zinc acetate as an oxygen and zinc precursors, respectively. The eutectic mixture nucleates growth of ZnO nanorods. These structures show sensor behavior when different chemical solvents and gases are applied. Importantly, the so-obtained sensor works at room temperature and heating and processing is not required to reset them to initial resistivity.