The use of plasmonic inclusions in heterojunction solar cells promises increase of solar-to-electric energy conversion efficiency. Recently, solar cells with ZnO nanorods attracted a lot of attention due to improved efficiency provided by highly scattering ZnO nanostructures on silicon or perovskite. N-type ZnO nanorods are grown on p-Si monocrystalline 180 μm thick substrates among others by means of a hydrothermal technique which requires prior seeding by deposition of thin film of ZnO or noble metals. In the latter case, naturally formed metal islands can also act as plasmonic nanoparticles (NPs). Excitation of plasmonic resonance on the NPs leads to directional scattering of light towards Si layer and electromagnetic field enhancement at their vicinity, close to the ZnO-Si junction, what results in improved energy absorption in the semiconductor layer and thus energy conversion efficiency. In this study, we investigate optimal conditions at which plasmonic phenomenon further improves light trapping in the Si-ZnO solar cells. In simulations performed by means of 3D FDTD method, we calculate light absorption enhancement in the system due to plasmonic NPs used as a seed layer at the ZnO/Si. In the calculations Ag, and Al NPs of different size and geometry close to that achievable in the experiment are analyzed. Finally, numerical results taking into account the granulometry of metal NPs achieved in the experiment are compared with the efficiency of fabricated cells.
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.
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.
Nanotechnology as a new field of science is broadly exploited in a plethora of commercial uses. Biocompatible nanomaterials are also attractive for medical applications. However, an exact processes related with their biodistribution within the body needs to be examined. This study deals with future perspectives for biodegradable nanoparticle on the example of fluorescent ZnO NPs (zinc oxide nanoparticles), doped with europium (Eu) ions. The aim of the study was to evaluate distribution processes of biodegradable ZnO:Eu NPs within the living organism. ZnO:Eu NPs were administered intra-gastric (IG) (10 mg/ml, 0.3 ml/mouse) to adult Balb-c mice (n=35) and following 3h, 24h, 7d, 14d and 1m mice were sacrificed and internal organs were collected, as was described before [1]. For determination the excretion patterns of these nanostructure, ZnO NPs were orally administered to mice (n=24) with further measurement of zinc content in the feces of tested animals. All procedures were conducted according to local and EU regulations and approved by the LEC 44/2012. No pathological/behavioral changes were observed in mice. Biodegradable ZnO:Eu NPs revealed ability to overcome majority of physiological barriers in the organism, which renders them invaluable tool for biomedical applications. After 3h the presence of fluorescent NPs was already observed in key tissues and the peak of NPs distribution was observed at 24 h after IG in majority of tissues, including brain. Moreover, obtained results revealed fast and efficient clearance of ZnO NPs from the living organism, even following multiple administration of nanostructures (up to 4d after IG).
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.
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.
Thin films of wide band-gap oxides grown by Atomic Layer Deposition (ALD) are suitable for a range of applications. Some of these applications will be presented. First of all, ALD-grown high-k HfO2 is used as a gate oxide in the electronic devices. Moreover, ALD-grown oxides can be used in memory devices, in transparent transistors, or as elements of solar cells. Regarding photovoltaics (PV), ALD-grown thin films of Al2O3 are already used as anti-reflection layers. In addition, thin films of ZnO are tested as replacement of ITO in PV devices. New applications in organic photovoltaics, electronics and optoelectronics are also demonstrated Considering new applications, the same layers, as used in electronics, can also find applications in biology, medicine and in a food industry. This is because layers of high-k oxides show antibacterial activity, as discussed in this work.
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.
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.
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.
KEYWORDS: Metamaterials, Scanning electron microscopy, Reflectivity, Silicon, Photovoltaics, Amorphous silicon, Crystals, Electron beams, Optical properties, Chemical species
A new class of ordered structures that exhibit exceptional properties not readily observed before in nature or in the
laboratory is called metamaterials. Their properties arise from qualitatively new response functions that are not observed
in the constituent materials and result from the inclusion of artificially fabricated, intrinsic and extrinsic, lowdimensional
components. Low-dimensional or nanostructured Si materials as, for example, nanoscale Si-layered systems
combined with an active interface with its crystalline defects show new PV behavior never observed before in nature and
in engineering. To observe such nanolayers buried within a Si single-crystal one has to conserve a local strain that plays
an important role in the metamaterial formation. To do this, one uses techniques based on X-ray spectroscopy or more
recently proposed SEM and EDS images of just cleaved edges. The microscopy results of layered structures have been
compared with those obtained from reflectivity simulations from our code based on Lorentz-Drude theory and
experimental reflectivity measured in integrated hemispheres. An excellent agreement can be observed.
The nowadays quite indispensable enhancement of PV conversion efficiency cannot be obtained without new
mechanisms. The most useful of these mechanisms have to appear in the front face of the device, i.e. in the emitter, so
as to allow exploitation of the energetic photons of the solar spectrum. Such an improvement can be realized through a
multistage PV conversion starting by primary generation (photon absorption) followed by secondary generations (hot
carrier collisions with low-energy generation centers). This cascade-like process is possible, for example, in
multiinterface devices containing several emitter strata. Some of these strata assume the primary free-carrier generation
while others do the secondary free-carrier generation.
In this work we report investigations of new mechanisms based on I(V) curves measured on test samples with
different multiinterface architectures, electronic passivations, front grids, collecting electrodes and so on. The
measurements have been performed under a variable intensity incident light beam conserving always its spectral (solar)
composition, except for analogous measurement cycle without a UV component. The same beam intensities with a
filtered UV component complemented these investigations. The measurements have been compared with those of a
weak excitation from a typical halogen lamp (relatively stable flux without a UV component). The test structures show
a clear improvement of the PV conversion in the UV range induced by impact ionization within the superficial
nanostratum.
Nanoparticles of wide band gap II-VI compounds doped with transition metal (TM) and rare earth (RE) ions show fairly
efficient light emission. Mechanisms of enhancement of 3d-3d (TM ions) and 4f-4f (RE ions) intra-shell transitions are
discussed. It is demonstrated that quantum confinement, imposed on free carriers in nanoparticles, enhances spin
dependent interactions of free carriers with TM and RE impurities. These interactions relax parity and spin selections
rules for intra-shell transitions. We also show that host-to-impurity energy transfer is increased in nanoparticles, as
compared to situation found in bulk samples.
Shallowly formed InAs quantum dots (QDs) embedded in GaAs are investigated by Optically Detected Microwave
Resonance (ODMR) technique. The low temperature (1.6 K) photoluminescence (PL) spectrum reveals a two-peak
structure which is attributed to two different classes of QDs: smaller and larger in size. V-band (60 GHz) ODMR is
selectively detected in each of the peaks and depending on the PL detection energy, a different ODMR spectrum is
obtained. Detection in the high-energy band reveals a low-field negative signal which is ascribed to cyclotron resonance
of the electron in the two-dimensional wetting layer, corresponding to an effective mass of 0.067 m0. The microwave-induced
signal at higher fields (~1.1 T) is tentatively attributed to magnetic resonance transitions between spin states of
the holes confined in the smaller QDs. When monitoring the emission of the larger QDs, the obtained microwave-induced
signal is negative while the resonance line at low field, associated with the cyclotron resonance, is no longer
present. The V-band ODMR spectra are compared with W-band (94 GHz) measurements obtained for the same QD structure.
Properties of strongly localized excitons in heterostructures of CdTe/CdMnTe are described. Strong localization effects, which modify properties of excitons, are related to micro- structure characteristics of the sample studied. We demonstrate that at low temperatures excitons in the structure with 68% Mn fraction in the CdMnTe barriers are quasi-zero- dimensional.
Strong localization effects are observed in epilayers of GaN and InGaN. We relate them to microstructure characteristics of samples studied. The same mechanism of localization is shown to be the dominant in GaN and in InGaN. Influence of strong localization effects on light emission properties is discussed.
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