산화물/질화물 복합구조를 이용한 유연한 전자 및 광전소자 응용

학위논문 (박사) -- 서울대학교 대학원 : 자연과학대학 물리학과, 2020. 8. 이규철.물리적으로 강하고 유연한 그래핀과 같은 2차원 소재위에 성장된 무기물 나노소재로 구성된 복합차원 나노소재는 유연한 대면적 전자 및 광전소자로의 응용에 적합한 형태의 소재 구조이며, 실제로 이를 기반으로 한 유연한 수직형 전계효과 트랜지스터 및 발광다이오드 등을 포함한 많은 소자들이 개발되고 있다. 하지만, 처리된 정보를 저장하고 이를 사용자에게 전달하는 기능을 수행하기 위해선 보다 다양한 소자들이 개발되어야 할 필요가 있다. 본 학위논문은 이러한 수요를 충족시키기 위해, 복합차원 나노소재 기반 유연한 대면적 차세대 비휘발성 메모리 및 유연한 대면적 다파장 발광 다이오드의 개발에 대하여 다루고 있다. 복합차원 나노소재를 기반으로 차세대 비휘발성 메모리를 구현하기 위해 니켈 산화물 및 질화갈륨 이종구조로 구성된 마이크로디스크 형태의 소재를 그래핀 위에 성장하고, 본 소재의 상부 및 하부에 전극을 증착하여 전극/산화물/전극으로 구성된 형태의 산화물 기반 저항변화 메모리를 제조할 수 있었다. 마이크로디스크 형태의 소재의 사이가 떨어져있기 때문에 본 소자를 유연한 형태에서 구현하거나 1,000 회 이상의 구부림 뒤 소자의 특성을 파악할 때 소자 특성의 큰 변화 없이 정보가 안정적으로 저장되는 특성을 확인할 수 있었다. 뿐만 아니라, 니켈 산화물 기반 저항변화메모리를 동작할 때, 산화물 내부에 전도성이 높은 니켈 산화물이 필라멘트 형태로 구성되는데, 이를 발광다이오드의 나노전극으로 사용하여 저항변화메모리 내부의 필라멘트 역학에 대해서도 연구할 수 있었다. 한편, 저장된 정보를 사용자에게 정확하게 전달하기 위해선 발광다이오드의 한 픽셀 (pixel) 의 크기가 수 마이크로미터 이하로 작아야하고, 빨강, 초록, 파랑색의 빛을 발광할 수 있어야 하는데 이는 현재 이용되고 있는 픽 앤 플레이스 (pick and place) 기술을 이용하여 제조할 때 소자 제조의 효율성 및 재현성에 한계를 보이고 있다. 본 학위논문에서는 이를 극복하기 위한 방법의 하나로, 다양한 색을 발광할 수 있는 발광다이오드를 하나의 그래핀 기판위에 동시에 성장하는 방법을 제시하고 이를 유연한 다파장 발광다이오드로 구현하는 방법에 대해 기술하고 있다. 본 소자를 구현하기 위해 다양한 모양의 질화갈륨 및 산화아연 이종구조를 그래핀 위에 성장하는 방법을 개발하였는데, 산화아연 나노튜브의 간격을 다르게 설정하여 성장하고 이 위에 질화갈륨을 성장하면 질화갈륨의 성장률이 나노튜브의 간격에 따라 다르게 형성되어 다른 모양의 마이크로 발광다이오드가 성장되는 것을 이용하였다. 각기 다른 발광다이오드에 같은 전압을 가해줬을 때 성장률의 차이로 인한 다중 양자 우물 조성의 변화 및 소재 내부의 결함으로 인해 각기 다른 파장의 색이 발광되는 특성을 확인하였고, 유연한 형태에서도 안정적으로 발광특성이 유지되는 것을 확인할 수 있었다.The hybrid dimensional nanostructrures composed of high-quality inorganic nanostructures grown directly on two-dimensional (2D) materials such as graphene offers a novel material system for flexible electronics and optoelectronics. Indeed, the hybrid dimensional nanostructures have been fabricated to flexible electronics/optoelectronics and attracted many attentions with their excellent performances. Despite of the demonstration of flexible devices using the hybrid dimensional nanostructures, there remains a lot of devices that need to be further investigated in order to realize future electronics/optoelectronics such as wearable devices. This thesis presents the hybrid material system composed of oxide/nitrid heterostructures grown on graphene films and their applications on flexible non-volatile memory and flexible multi-color LEDs.Abstract Chapter 1. General Introduction 1 1.1. Motivation: Potentials of hybrid dimensional nanomaterials for flexible electronic/optoelectronic device applications 1 1.2. Thesis objective and approach 3 1.3. Thesis outline 4 Chapter 2. Literature survey 6 2.1. Oxide-based flexible electronics 6 2.1.1. Current status of oxide-based electronics 8 2.1.2. Next generation oxide-based electronics: ReRAM 12 2.1.3. Flexible ReRAM 17 2.1.3.1. ReRAM on plastic substrates 17 2.1.3.2. Transfer of ReRAM layers on flexible substrates 20 2.2. Nitride-based flexible optoelectronics 23 2.2.1. Current status of nitride-based optoelectronics 23 2.2.2. Next generation nitride-based optoelectronics: flexible & high-resolution LED 29 2.3. Hybrid dimensional material systems for flexible electronics and Optoelectronics 34 2.3.1. Growth of oxide & nitride nano-/micro-structures on graphene layers35 2.3.2. Functional devices using hybrid dimensional material Systems 45 2.3.2.1. Electronics 47 2.3.2.2. Optoelectronics 50 Chapter 3. Experimental Techniques 53 3.1. Growth techniques 53 3.1.1. Metalorganic vapor-phase epitaxy system 53 3.1.1.1. Gas delivery system 53 3.1.1.2. Reactor and temperature controller 55 3.1.1.3. Exhaust disposal system and low pressure pumping System 56 3.2. Structural characterization 57 3.2.1. Morphology inspection 57 3.2.2. Crystallographic and microstructural investigations 57 3.2.2.1. Transmission electron microscopy 57 3.3. Optical characterization 58 3.3.1. Photoluminescence & electroluminescence spectroscopy 58 3.4. Electrical characterization 59 3.4.1. Current-Voltage measurement 59 Chapter 4. Flexible ReRAM based on hybrid dimensional material systems 60 4.1. Introduction 60 4 .2. Growth of oxide/nitride hybrid structures on graphene layers 61 4.2.1. ZnO nanowall growth CVD-graphene films 62 4.2.2. Growth of GaN microdisk arrays 62 4.2.3. Growth of resistive switching layers 65 4.4. Fabrication of flexible ReRAM 65 4.5. Resistive switching characteristics 69 4.6. Discussion for the mechanism of resistive switchings using oxide/nitride hybrid structures 78 4.6.1. Fabrication of ReRAM/LED hybrid device 80 4.6.2. Real-time imaging of resistive switching dynamics 85 4.7. Summary 99 Chapter 5. Monolithic integration of morphology controlled GaN microstructures on graphene films for flexible & multi-color LEDs 101 5.1. Introduction 101 5.2. Morphology control of GaN microstructures on graphene films 103 5.2.1. Growth parameter: spacing & time 103 5.2.2. Growth behavior analysis 109 5.3. Fabrication of LEDs on graphene films 115 5.4. EL and electrical characteristics 118 5.5. High temperature operations of flexible LEDs 125 5.6. Summary 134 Chapter 6. Conclusion and Outlook 136 6.1. Conclusion 136 6.2. Future works and outlook 141 References 143 Abstract (Korean) 151Docto

Prosthetic graft interposition of the brachiocephalic veins or superior vena cava combined with resection of malignant tumours: Graft patency and risk factors for graft occlusion

BACKGROUND: We aimed to assess graft patency in patients undergoing prosthetic graft interposition of the brachiocephalic veins (BCVs) or the superior vena cava (SVC) combined with resection of malignant tumours. METHODS: A retrospective analysis was conducted on 16 patients who underwent prosthetic graft interposition of the BCVs or the SVC between 1998 and 2012. RESULTS: Among a total of 20 grafts in 16 patients (unilateral graft interposition in 12, bilateral graft interposition in 4), 8 grafts were occluded in 8 patients. Overall graft patency rate was 64.6%, 42.4% at the 2- and 5-year follow-up. Graft patency rate of the left BCV was significantly lower than that of the right BCV or the SVC (2-year patency, 38.1% vs. 81.8%, P=0.024). In univariate analysis, the superior anastomosis site [left BCV vs. right BCV; hazard ratio (HR) =2.312; 95% confidence interval (CI), 1.015-5.265; P=0.046], the inferior anastomosis site (right atrial appendage vs. SVC; HR =2.409; 95% CI, 1.124-5.161; P=0.024), and interruption of warfarin (HR =5.015; 95% CI, 1.106-22.734; P=0.037) were significant risk factors for graft occlusion. Graft occlusive symptoms were identified in 4 patients who underwent unilateral graft interposition. CONCLUSIONS: Prosthetic graft interposition between the left BCV and the right atrial appendage resulted in a significant rate of graft occlusion. Prosthetic graft interposition of the bilateral BCVs and long-term warfarin therapy may be necessary to prevent graft occlusive symptoms.ope

Comparisons of the clinical outcomes of thoracoscopic sympathetic surgery for palmar hyperhidrosis: R4 sympathicotomy versus R4 sympathetic clipping versus R3 sympathetic clipping

BACKGROUND: Thoracoscopic sympathetic surgery is regarded as a definitive treatment for palmar hyperhidrosis. However, the optimal surgical strategy remains unclear. The aim of this study was to compare outcomes based on the level and type of sympathetic disconnection in patients with palmar hyperhidrosis. METHODS: From January 2009 to December 2014, 101 patients with palmar hyperhidrosis underwent thoracoscopic sympathetic surgery at Gangnam Severance Hospital. Complete follow-up information was obtained from 59 patients. We retrospectively analyzed the results of operation, degree of palmar sweating (%), grade of compensatory sweating (none, mild, moderate, severe, very severe), grade of satisfaction (very satisfied, satisfied, moderate, dissatisfied, very dissatisfied), and recurrence/failure. RESULTS: R4 sympathicotomy, R4 sympathetic clipping, and R3 sympathetic clipping were performed in 16, 20, and 23 patients, respectively. The mean degree of palmar sweating after sympathetic surgery was not significantly different between these three groups (17.50% vs. 27.00% vs. 29.78%; P=0.38). The rate of life-bothering compensatory sweating was lower in the R4 sympathicotomy group compared with those of other two groups (0% vs. 25%, 47.8%; P=0.09). The rate of very satisfied to moderate grades of satisfaction were lower in the R3 sympathetic clipping group compared with those of other two groups (93.8%, 100% vs. 73.9%; P=0.07). The rate of recurrence/failure rates were lower in the R4 sympathicotomy group compared with those of other two groups (12.50% vs. 35.00%, 34.8%; P=0.25). Sympathetic surgery at the R3 level was the only significant risk factor for patient dissatisfaction (odd ratio =12.353, 95% confidence interval =1.376-110.914; P=0.025). CONCLUSIONS: Our data support that R4 sympathicotomy had lower grades of compensatory sweating, higher grades of satisfaction, and lower rates of recurrence/failure. We therefore consider R4 sympathicotomy as an optimal surgical treatment for palmar hyperhidrosis.ope

Phlegmonous Esophagitis Treated with Internal Drainage and Feeding Jejunostomy

We report the case of a 67-year-old woman presenting with epigastric pain. Computed tomography identified diffuse phlegmonous esophagitis. Esophagogastroduodenoscopy revealed multiple perforations in the mucosal layer of the esophagus. A large amount of pus was drained internally through the gut. The patient was treated with antibiotics and early jejunostomy feeding. Although phlegmonous esophagitis is a potentially fatal disease, the patient was successfully treated medically with only a minor complication (esophageal stricture).ope

Minimally Invasive Repair of Pectus Carinatum in Patients Unsuited to Bracing Therapy

Background : We used an Abramson technique for minimally invasive repair of pectus carinatum in patients who preferred surgery to brace therapy, had been unsuccessfully treated via brace therapy, or were unsuitable for brace therapy because of a rigid chest wall. Methods : Between July 2011 and May 2015, 16 patients with pectus carinatum underwent minimally invasive surgery. Results : The mean age of the patients was 24.35±13.20 years (range, 14?57 years), and all patients were male. The percentage of excellent aesthetic results, as rated by the patients, was 37.5%, and the percentage of good results was 56.25%. The preoperative and postoperative Haller Index values were 2.01±0.19 (range, 1.60?2.31), and 2.22±0.19 (range, 1.87?2.50), respectively (p-value=0.01), and the median hospital stay was 7.09±2.91 days (range, 5?15 days). Only one patient experienced postoperative complications. Conclusion : Minimally invasive repair is effective for the treatment of pectus carinatum, even in adult patients.ope

Outpatient Treatment for Pneumothorax Using a Portable Small-Bore Chest Tube: A Clinical Report

Background : For treatment of pneumothorax in Korea, many institutions hospitalize the patient after chest tube insertion. In this study, a portable small-bore chest tube (Thoracic Egg; Sumitomo Bakelite Co. Ltd., Tokyo, Japan) was used for pneumothorax management in an outpatient clinic. Methods : Between August 2014 and March 2015, 56 pneumothorax patients were treated using the Thoracic Egg. Results : After Thoracic Egg insertion, 44 patients (78.6%) were discharged from the emergency room for follow-up in the outpatient clinic, and 12 patients (21.4%) were hospitalized. The mean duration of Thoracic Egg chest tube placement was 4.8 days, and the success rate was 73%; 20% of patients showed incomplete expansion and underwent video-assisted thoracoscopic surgery. For primary spontaneous pneumothorax patients, the success rate of the Thoracic Egg was 76.6% and for iatrogenic pneumothorax, it was 100%. There were 2 complications using the Thoracic Egg. Conclusion : Outpatient treatment of pneumothorax using the Thoracic Egg could be a good treatment option for primary spontaneous and iatrogenic pneumothorax.ope

A Case of Symptomatic Tracheal Diverticulum and Surgical Resection as a Treatment Modality

Tracheal diverticulum is often diagnosed incidentally and, due to its rarity, there is no standard treatment. It is a benign entity, but has the potential to cause specific symptoms, such as chronic upper respiratory infection and chronic cough. Symptomatic tracheal diverticulum can be medically treated, but likelihood of recurrence is high. We report a case of surgical resection of symptomatic tracheal diverticulum to prevent recurrence.ope

Effectiveness of Ambulatory Tru-Close Thoracic Vent for the Outpatient Management of Pneumothorax: A Prospective Pilot Study

OBJECTIVE: This study aimed to assess the technical feasibility, procedural safety, and long-term therapeutic efficacy of a small-sized ambulatory thoracic vent (TV) device for the treatment of pneumothorax. MATERIALS AND METHODS: From November 2012 to July 2013, 18 consecutive patients (3 females, 15 males) aged 16-64 years (mean: 34.7 ± 14.9 years, median: 29 years) were enrolled prospectively. Of these, 15 patients had spontaneous pneumothorax and 3 had iatrogenic pneumothorax. A Tru-Close TV with a small-bore (11- or 13-Fr) catheter was inserted under bi-plane fluoroscopic assistance. RESULTS: Technical success was achieved in all patients. Complete lung re-expansion was achieved at 24 hours in 88.9% of patients (16/18 patients). All patients tolerated the procedure and no major complications occurred. The patients' mean numeric pain intensity score was 2.4 (range: 0-5) in daily life activity during the TV treatment. All patients with spontaneous pneumothorax underwent outpatient follow-up. The mean time to TV removal was 4.7 (3-13) days. Early surgical conversion rate of 16.7% (3/18 patients) occurred in 2 patients with incomplete lung expansion and 1 patient with immediate pneumothorax recurrence post-TV removal; and late surgical conversion occurred in 2 of 18 patients (11.1%). The recurrence-free long-term success rate was 72.2% (13/18 patients) during a 3-year follow-up period from November 2012 to June 2016. CONCLUSION: TV application was a simple, safe, and technically feasible procedure in an outpatient clinic, with an acceptable long-term recurrence-free rate. Thus, TV could be useful for the immediate treatment of pneumothorax.ope

High versus low attenuation thresholds to determine the solid component of ground-glass opacity nodules.

OBJECTIVES: To evaluate and compare the diagnostic accuracy of high versus low attenuation thresholds for determining the solid component of ground-glass opacity nodules (GGNs) for the differential diagnosis of adenocarcinoma in situ (AIS) from minimally invasive adenocarcinoma (MIA) and invasive adenocarcinoma (IA). METHODS: Eighty-six pathologically confirmed GGNs < 3 cm observed in 86 patients (27 male, 59 female; mean age, 59.3 ± 11.0 years) between January 2013 and December 2015 were retrospectively included. The solid component of each GGN was defined using two different attenuation thresholds: high (-160 Hounsfield units [HU]) and low (-400 HU). According to the presence or absence of solid portions, each GGN was categorized as a pure GGN or part-solid GGN. Solid components were regarded as indicators of invasive foci, suggesting MIA or IA. RESULTS: Among the 86 GGNs, there were 57 cases of IA, 19 of MIA, and 10 of AIS. Using the high attenuation threshold, 44 were categorized as pure GGNs and 42 as part-solid GGNs. Using the low attenuation threshold, 13 were categorized as pure GGNs and 73 as part-solid GGNs. The sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy for the invasive focus were 55.2%, 100%, 100%, 22.7%, and 60.4%, respectively, for the high attenuation threshold, and 93.4%, 80%, 97.2%, 61.5%, and 91.8%, respectively, for the low attenuation threshold. CONCLUSION: The low attenuation threshold was better than the conventional high attenuation threshold for determining the solid components of GGNs, which indicate invasive fociope

Birt-Hogg-Dube syndrome prospectively detected by review of chest computed tomography scans

PURPOSE: Birt-Hogg-Dube syndrome (BHD) is a rare disorder caused by mutations in the gene that encodes folliculin (FLCN) and is inherited in an autosomal dominant manner. BHD is commonly accompanied by fibrofolliculomas, renal tumors, multiple pulmonary cysts, and spontaneous pneumothorax. The aim of this study was to detect BHD prospectively in patients undergoing chest computed tomography (CT) scans and to evaluate further the characteristics of BHD in Korea. METHODS: We prospectively checked and reviewed the chest CT scans obtained for 10,883 patients at Gangnam Severance Hospital, Seoul, Korea, from June 1, 2015 to May 31, 2016. Seventeen patients met the study inclusion criteria and underwent screening for FLCN mutation to confirm BHD. We analyzed the characteristics of the patients confirmed to have BHD and those for a further 6 patients who had previously been described in Korea. RESULTS: Six (0.06%) of the 10,883 patients reviewed were diagnosed with BHD. There was no difference in demographic or clinical features between the patients with BHD (n = 6) and those without BHD (n = 11). Pneumothorax was present in 50% of the patients with BHD but typical skin and renal lesions were absent. The maximum size of the cysts in the BHD group (median 39.4 mm; interquartile range [IQR] 11.4 mm) was significantly larger than that in the non-BHD group (median 15.8 mm; IQR 7.8 mm; P = 0.001). Variable morphology was seen in 100.0% of the cysts in the BHD group but in only 18.2% of the cysts in the non-BHD group (P = 0.002). Nine (95%) of the total of 12 Korean patients with BHD had experienced pneumothorax. Typical skin and renal lesions were present in 20.0% of patients with BHD. CONCLUSIONS: Our findings suggest that BHD can be detected if chest CT scans are read in detail.ope