Periodic semiconductor nano-structures for the enhanced photovoltaic devices

Department of Chemical EngineeringThe photovoltaic devices which convert the solar energy to the electrons or chemical materials become very important clean energy devices due to the environmental pollution from the fossil energy. The Dye-sensitized Solar cell (DSSC) which generates the electron-hole pairs using solar light and photoelectrochemical cell (PEC), one of the promising clean energy solar cells for capturing and storing solar energy by splitting water into a hydrogen and oxygen gas have received extensive attention because of high performance and low price. Enhancing optical property is the one of the fascinate strategy for the increasing the properties of photovoltaic devices. Interference lithography (IL) is a very convenient and fast method to fabricate the two/threedimensional polymer template in a submicrometer scale. By combining an IL technique and hydrothermal growth, the high crystalline periodic semiconductor nanowires such as ZnO, TiO2 and Fe2O3 can be fabricated. The 2D patterned semiconductor nanowires can be considered as a diffraction grating layer which can enhance the optical property for increasing the overall performance of photovoltaic devices such as DSSC and PEC. In this thesis, I studied on the synergetic effects of the IL technique and the hydrothermal growth method for enhancing the optical properties. The patterned nanowires with a subwavelength scale that act as the diffraction grating layer can increase the optical path in the photovoltaic devices. Especially, the absorption of visible wavelength of solar light (400nm ~ 800nm), a major source to generate the electron-hole pairs in the photovoltaic cells can be enhanced by the pattern nanowires. The outstanding properties of the 2D patterned nanowires suggest the great potential in energy-related devices such as DSSCs, PEC cells and sensor devices such as SERS.ope

Band gap and morphology engineering of hematite nanoflakes from an ex situ Sn doping for enhanced photoelectrochemical water splitting

In this article, we report a simple ex situ Sn-doping method on hematite nanoflakes (coded as MSnO2-H) that can protect the nanoflake (NF) morphology against the 800 degrees C high-temperature annealing process and activate the photoresponse of hematite until 800 nm wavelength excitation. MSnO2-H has been fabricated by dropping SnCl4 ethanol solution on hematite nanoflakes homogeneously grown over the conductive FTO glass substrate and annealed at 500 degrees C to synthesize the SnO2 nanoparticles on hematite NFs. The Sn-treated samples were then placed in a furnace again, and the sintering process was conducted at 800 degrees C for 15 min. During this step, structure deformation of hematite occurs normally due to the grain boundary motion and oriented attachment. However, in the case of MSnO2-H, the outer SnO2 nanoparticles efficiently prevented a shape deformation and maintained the nanoflake shape owing to the encapsulation of hematite NFs. Furthermore, the interface of hematite/SnO2 nanoparticles became the spots for a heavy Sn ion doping. We demonstrated the generation of the newly localized states, resulting in an extension of the photoresponse of hematite until 800 nm wavelength light irradiation. Furthermore, we demonstrated that SnO2 nanoparticles can effectively act as a passivation layer, which can reduce the onset potential of hematite for water splitting redox reactions. The optimized MSnO2-H nanostructures showed a 2.84 times higher photocurrent density and 300 mV reduced onset potential compared with a pristine hematite nanoflake photoanode.Web of Scienc

Retrospective Analysis of Peripheral Blood Stem Cell Transplantation for the Treatment of High-Risk Neuroblastoma

Disease relapse after autologous peripheral blood stem cell transplantation (APBSCT) is the main cause of treatment failure in high-risk neuroblastoma (NBL). To reduce relapse, various efforts have been made such as CD34+ selection and double APBSCT. Here the authors reviewed the clinical features and outcomes of high-risk NBL patients and analyzed their survival. The medical records of 36 patients with stage III or IV NBL who underwent APBSCT at Seoul National University Children's Hospital between May 1996 and May 2004 were reviewed. Total 46 APBSCTs were performed in 36 patients. Disease free survival (DFS) and overall survival of all patients were 47.7% and 68.8%, respectively. The patients were allocated to three groups according to the APBSCT type. The DFS of CD34+ non-selected single APBSCT patients (N=13), CD34+ selected single APBSCT patients (N=14), and CD34+ selected double APBSCT patients (N=9) were 55.6%, 40.6%, and 50.0%, respectively, which were not significantly different. Thus the survival was not found to be affected by CD34+ selection or transplantation number. To improve long-term survival, various efforts should be made such as chemotherapy dose intensification, more effective tumor purging, and control of minimal residual disease via the use of differentiating and immune-modulating agents

Akt1-Inhibitor of DNA binding2 is essential for growth cone formation and axon growth and promotes central nervous system axon regeneration.

Mechanistic studies of axon growth during development are beneficial to the search for neuron-intrinsic regulators of axon regeneration. Here, we discovered that, in the developing neuron from rat, Akt signaling regulates axon growth and growth cone formation through phosphorylation of serine 14 (S14) on Inhibitor of DNA binding 2 (Id2). This enhances Id2 protein stability by means of escape from proteasomal degradation, and steers its localization to the growth cone, where Id2 interacts with radixin that is critical for growth cone formation. Knockdown of Id2, or abrogation of Id2 phosphorylation at S14, greatly impairs axon growth and the architecture of growth cone. Intriguingly, reinstatement of Akt/Id2 signaling after injury in mouse hippocampal slices redeemed growth promoting ability, leading to obvious axon regeneration. Our results suggest that Akt/Id2 signaling is a key module for growth cone formation and axon growth, and its augmentation plays a potential role in CNS axonal regeneration

Improved survival in patients with recurrent Wilms tumor: the experience of the Seoul National University Children's Hospital

The survival in cases with relapsed Wilms tumor is dismal. Recently, however the introduction of new therapeutic agents and experimental strategies has improved the survival. We analysed the survival of patients with relapsed Wilms tumor according to the treatment period. During the early period 1983-1993, patients who had received two drugs were treated with doxorubicin and the others were treated with cisplatin and etoposide, whereas during the late period 1994-2004, patients were treated with combinations of cyclophosphamide/etoposide and carboplatin/etoposide. During the early period, 8 of 57 experienced relapse, and 8 of 41 relapsed during the late period. Only 2 patients treated during the early period survived in complete response (CR), whereas during the late period, 5 patients remained alive in CR, and 3 of those received high-dose chemotherapy (HDC) with autologous peripheral stem cell rescue (SCR). The estimated 5 yr event-free survival rate was 37.5% in the entire study group, 50% for patients in the late period, and 25% for patients in the early period (p=0.38). The survival in patients with relapsed Wilms tumor dramatically improved during the late period and HDC with SCR was one of the effective salvage strategies

Three-dimensional nano-foam of few-layer graphene grown by CVD for DSSC

We report a robust and direct route to fabricate a three-dimensional nano-foam of few-layer graphene (3D-NFG) with large area coverage via a chemical vapor deposition (CVD) technique. Pyrolysis of polymer/nickel precursor film under a hydrogen environment, simply prepared by spin-coating, leads to the creation of nano-foam in the film and the reduction process of nickel ions. Carbonized-C and the nickel nano-frame formed from the pyrolysis are used as a solid carbon source and as a catalyst for the growth of graphene under CVD conditions, respectively. We investigate the use of 3D-NFG, with the advantage of large surface area and high conductivity, as an alternative to the Pt counter electrode material in dye sensitized solar cells. The excellent properties of 3D-NFG, fabricated in this simple and direct manner, suggest a great potential for interconnected graphene networks in electronic devices and photocatalytic sensors as well as in energy-related materials.close221

Interaction and ordering of vacancy defects in NiO

By using a first-principles method employing the local density approximation plus Hubbard parameter approach, we study point defects in NiO and interactions between them. The defect states associated with nickel or oxygen vacancies are identified within the energy gap. It is found that nickel vacancies introduce shallow levels in the density of states for the spin direction opposite to that of the removed Ni atom, while the oxygen vacancy creates more localized in-gap states. The interaction profiles between vacancies indicate that specific defect arrangements are strongly favored for both nickel and oxygen vacancies. In the case of nickel vacancies, defect ordering in a simple-cubic style is found to be most stable, leading to a half-metallic behavior. The ionized oxygen vacancies also show a tendency toward clustering, more strongly than neutral pairs. The microscopic origin of vacancy clustering is understood based on overlap integrals between defect states. © 2008 The American Physical Society.open343

Effect of collagen endometrial patch loaded with adipose-derived mesenchymal stem cells on endometrial regeneration in rats with a thin endometrium

BackgroundThis study aimed to investigate the effects of a collagen endometrial patch (EM patch) loaded with adipose-derived mesenchymal stem cells (ADSCs) on endometrial regeneration in a rat model with thin endometrium.Materials and methodsThin endometrium was induced in female rats and divided into treatment groups as outlined: control, group 1(G1), local injection of ADSCs into the uterus, group 2 (G2), an EM patch without ADSCs, group 3 (G3), and an EM patch loaded with ADSCs, group 4 (G4). The rats were euthanized at either two weeks or four weeks after modeling and treatment followed by histological and biochemical analyses to examine the regenerative effects on the injured endometrium.ResultsTransplantation of the ADSC-loaded EM patch significantly promoted endometrial proliferation and increased the luminal epithelial area. Two weeks after treatment, the mean number of von Villebrand factor (vWF)+ or cluster of differentiation (CD) 31+-stained blood vessels was significantly higher in G4 than in G1 and G2. The mRNA and protein expression levels of TGF-β and FGF2 were significantly upregulated in G4 compared to those in the control. G4 exhibited significantly increased LIF mRNA levels and immunoreactivity compared with the other groups at both two weeks and four weeks after treatment. Cell tracking after ADSCs treatment revealed the presence of a substantial number of ADSCs grafted in the uterine tissues of G4, whereas a low number of ADSCs that were focally clustered were present in G2.ConclusionTransplantation of EM patches loaded with ADSCs resulted in the histological and biochemical restoration of an injured endometrium. The strategic integration of EM patches and ADSCs holds significant promise as an innovative therapeutic approach for effectively treating impaired endometrial conditions