Yunseon Choi

Optimizing n-ZnO/p-Si heterojunctions for photodiode applications

Abstract N-ZnO/p-Si heterojunction photodiodes have been fabricated by sputter deposition of n-ZnO films on p-Si substrates. The substrate temperatures of 300, 400, 480 and 550°C were taken for the n-ZnO film deposition using an Ar/O 2 ratio of 6:1. All the diodes show typical rectifying behaviors as characterized by the current–voltage ( I – V ) measurement in a dark room and their photoelectric effects from the diodes have been observed under illumination using monochromatic red light with a wavelength of 670 nm. Maximum amount of photo-current or responsivity is obtained under reverse bias conditions from a n-ZnO/p-Si heterojunction when the ZnO film was deposited at 480°C while the ZnO films deposited at 550°C show the best stoichiometric and crystalline quality. Junction leakage or dark current is much higher in the diode with n-ZnO deposited at 550°C than in the other diodes. It is thus concluded that for a photodiode the quality of the diode junction is as important as that of the n-ZnO film deposited on p-Si.

Fabrication of p-pentacene/n-Si organic photodiodes and characterization of their photoelectric properties

We have fabricated p-pentacene/n-Si organic photodiodes by thermal evaporation of pentacene films at 25 (RT), 60, and 80u200a°C. Our pentacene films exhibit the main absorption peak (highest occupied molecular orbital-lowest unoccupied molecular orbital gap transition) at 1.82 eV and photoelectric effects were clearly observed from our p-pentacene/n-Si diodes when illuminated by a monochromatic red light of 1.85 eV (670 nm). Excellent photoresponsivity of 2.6 A/W and the photoresponse time of less than 40 ns have been demonstrated. The photodiodes exhibited typical rectifying behavior in the dark and the leakage current increases with the deposition temperature.

Characterization of films and interfaces in n-ZnO/p-Si photodiodes

We report on the fabrication of n-ZnO/p-Si heterojunction photodiodes. RF sputtering was performed to deposit ZnO films on p-Si substrates at various substrate temperatures of 300, 480 and 550 °C using Ar:O2 ratios of 6:1. Typical rectifying behaviors were observed from most of the diodes as characterized by the current–voltage (I–V) measurement. Some of the diodes exhibit photoelectric effects under illumination using monochromatic red light with a wavelength of 670 nm. Maximum quantum efficiency of 53% was obtained under a reverse bias condition from a diode with ZnO film deposited at 480 °C. Measuring photoluminescence, transmittance, sheet resistance from the ZnO films, and characterizing the n-ZnO/p-Si interface with X-ray photoelectron spectroscopy, it is concluded that the diodes with n-ZnO deposited at 480 °C conserve relatively a high film quality and good interface junction to exhibit the best photoelectric property.

Reirradiation to the pelvis for recurrent rectal cancer

This study investigated late toxicity and infield progression‐free survival in patients with locally recurrent rectal cancer (LRRC) who had previously received irradiation to the pelvis.

Effect of low-dose ketamine on inflammatory response in off-pump coronary artery bypass graft surgery.

BACKGROUNDnOff-pump coronary artery bypass graft surgery (OPCAB) is still associated with a marked systemic inflammatory response. The aim of this study was to investigate whether pre-emptive, low dose of ketamine, which has been reported to have anti-inflammatory activity in on-pump coronary artery bypass surgery, could reduce inflammatory response in low-risk patients undergoing OPCAB.nnnMETHODSnIn this prospective randomized-controlled trial, 50 patients with stable angina and preserved myocardial function undergoing OPCAB were randomly assigned to receive either 0.5 mg kg(-1) of ketamine (Ketamine group, n=25) or normal saline (Control group, n=25) during induction of anaesthesia. Inflammatory markers including C-reactive protein (CRP), interleukin (IL)-6, tumour necrosis factor-alpha (TNF-alpha), and cardiac enzymes were measured previous to induction (T1), 4 h after surgery (T2), and the first and second days after the surgery (T3 and T4).nnnRESULTSnThere were no significant intergroup differences in the serum concentrations of the CRP, IL-6, and TNF-alpha and cardiac enzymes. Pro-inflammatory markers and cardiac enzymes, except TNF-alpha, were all increased after the surgery compared with baseline values in both groups.nnnCONCLUSIONSnLow-dose ketamine administered during anaesthesia induction did not exert any evident anti-inflammatory effect in terms of reducing the serum concentrations of pro-inflammatory markers in low-risk patients undergoing OPCAB.

Dynamic and Static Photo-Responses of n-ZnO/p-Si Photodiodes

We report on the photo-response behavior of n-ZnO/p-Si photodiodes. Semiconducting n-ZnO films have been deposited on p-Si substrate by RF sputtering at 300, 480 and 550°C. An optimum static photo-response was achieved from the photodiode prepared at 480°C as characterized by photocurrent measurements using a continuous monochromatic red illumination. Temporal photo-response of 35 ns was obtained from the same n-ZnO/p-Si diode to which a high frequency modulation of 1.5 MHz was applied for the dynamic response measurements. It is concluded that the n-ZnO/p-Si photodiode has good detecting capabilities in both of the dynamic and static photo-responses.

The predictors for continuous renal replacement therapy in liver transplant recipients.

BACKGROUNDnAcute renal failure (ARF) after liver transplantation requiring continuous renal replacement therapy (CRRT) adversely affects patient survival. We suggested that postoperative renal failure can be predicted if a clinically simple nomogram can be developed, thus selecting potential risk factors for preventive strategy.nnnMETHODSnWe retrospectively reviewed the medical records of 153 liver transplant recipients from January 2008 to December 2011 at Severance Hospital, Yonsei University Health System, in Seoul, Korea. There were 42 patients treated with CRRT (20 and 22 patients received transplants from living and deceased donors, respectively) and 115 were not. Univariate and stepwise logistic multivariate analyses were performed. A clinical nomogram to predict postoperative CRRT application was constructed and validated internally.nnnRESULTSnHepatic encephalopathy (HEP; odds ratio OR, 5.47), deceased donor liver donations (OR, 3.47), Model for End-Stage Liver Disease (MELD) score (OR, 1.09), intraoperative blood loss (L; OR, 1.16), and tumor (hepatocellular carcinoma) as the indication for liver transplantation (OR, 0.11) were identified as independent predictive factors for postoperative CRRT on multivariate analysis. A clinical prediction model constructed for calculating the probability of CRRT post-transplantation was 1.7000 × HEP + [-4.5427 + 1.2440 × (deceased donor) + 0.0830 × (MELD score) + 0.000149 × the amount of intraoperative bleeding (L) - 2.1785 × tumor]. The validation set discriminated well with an area under the curve (AUC) of 0.90 (95% confidence interval, 0.85-0.95). The predicted and the actual probabilities were calibrated with the clinical nomogram.nnnCONCLUSIONSnWe developed a predictive model of postoperative CRRT in liver transplantation patients. Perioperative strategies to modify these factors are needed.

Role of Radiotherapy in the Multimodal Treatment of Ewing Sarcoma Family Tumors

Purpose The aim of this study was to evaluate the role of radiotherapy (RT) in the management of Ewing sarcoma family tumors (ESFT). Materials and Methods Retrospective analysiswas performed on 91 patientswith localized ESFT treated from 1988 to 2012. Primary tumor size was ≥ 8 cm in 33 patients. Surgery, RT, and combined surgery with RT were applied in 37, 15, and 33 patients, respectively. Results Median follow-up was 43.8 months. Forty-three patients (47.3%) showed recurrence or progressive disease. Twelve patients (13.2%) showed local failure after initial treatment. Thirty-nine patients (42.9%) experienced distant metastases. The 5-year overall survival (OS), progression-free survival, and local control (LC) were 60.5%, 58.2%, and 85.1%, respectively. According to treatment, 5-year LCwas 64.8% with RT and 90.2% with combined surgery and RT (p=0.052). Prognostic factors for OS were tumor size (≥ 8 cm, p < 0.001) and surgical resection (p < 0.001). In large tumors (≥ 8 cm), combined surgery and RT produced better LC compared to RT (p=0.033). However, in smaller tumors (< 8 cm), RT without surgery resulted in a similar LC rate as RT with surgery (p=0.374). Conclusion RT used for patients with unfavorable risk factors resulted in worse outcome than for patientswho received surgery. Smallertumors could be controlled locallywith chemotherapy and RT. For large tumors, combined surgery and RT is needed. Proper selection of local treatment modality, RT, surgery, or both is crucial in the management of ESFT.

Targeting ODC1 inhibits tumor growth through reduction of lipid metabolism in human hepatocellular carcinoma.

Ornithine decarboxylase 1 (ODC1), a metabolic enzyme critically involved in the polyamine biosynthesis, is commonly upregulated in hepatocellular carcinoma (HCC). Despite its altered expression in human HCC tissues, the molecular mechanism by which ODC1 alters the course of HCC progression and functions in HCC cell survival is unknown. Here we identified that silencing of ODC1 expression with small interfering (si) RNA causes inhibition of HCC cell growth through blockade of cell cycle progression and induction of apoptosis. Next, to obtain insights into the molecular changes in response to ODC1 knockdown, global changes in gene expression were examined using RNA sequencing. It revealed that 119 genes show same directional regulation (76 up- and 43 down-regulated) in both Huh1 and Huh7 cells and were considered as a common ODC1 knockdown signature. Particularly, we found through a network analysis that KLF2, which is known to inhibit PPARγ expression and adipogenesis, was commonly up-regulated. Subsequent Western blotting affirmed that the downregulation of ODC1 was accompanied by a decrease in the levels of PPARγ as well as of PARP-1, cyclin E1 and pro-caspase 9 delaying cell cycle progression and accelerating apoptotic signaling. Following the down-regulation of PPARγ expression, ODC1 silencing resulted in a strong inhibition in the expression of important regulators of glucose transport and lipid biogenesis, and caused a marked decrease in lipid droplet accumulation. In addition, ODC1 silencing significantly inhibited the growth of human HCC xenografts in nude mice. These findings indicate that the function of ODC1 is correlated with HCC lipogenesis and suggest that targeting ODC1 could be an attractive option for molecular therapy of HCC.

Dose escalation using helical tomotherapy improves local control in spine metastases from primary hepatic malignancies

This study was designed to reveal the prognostic significance of dose‐escalated radiotherapy with tomotherapy in local control for spine metastases of primary hepatic tumours.