플랑크 흑체복사공식을 이용한 광원의 온도 측정 탐구활동의 개발

이미섭 한국교원대학교 교육대학원 2013 국내석사

고등학교 물리의 흑체복사 탐구활동에 사용할 목적으로 2 W pilot lamp에 인가전압을 높여가며 방출하는 파장별 빛의 세기를 측정하였다. 전압이 증가할수록 2 W pilot lamp의 온도가 증가하여 피크 파장이 감소함을 확인하였다. 2 W pilot lamp에서 방출되는 복사의 분산 스펙트럼을 스테핑 모터를 이용하여 파장 분해능 10 nm 로 스캔하였다. 전기회로의 미세 전류를 측정하기 위해 분해능 10 fA의 Keithley 피코 암페어 전류계를 사용하였다. 결과적으로 플랑크상수 J·s를 얻었다.

Electroluminescence of 2D materials and van der Waals heterostructures from near UV to visible light range

서동제 Graduate School, Yonsei University 2020 국내박사

Graphene, widely known as two-dimensional (2D) material, has been studied in various applications due to its uniq electrical, thermal and mechanical properties. However, since graphene does not have an energy bandgap, there are fundamental limitations in the electronic and optoelectronic device applications such as FETs, LED, and solar cells. As a result, the interest in other 2D materials is exponentially increasing. In nature, there are a large number of 2D materials, including various electrical and optical properties. Typical materials include hexagonal boron nitride (hBN), which is an insulator with a large bandgap, and transition metal dichalcogenide (TMDC), which is a semiconductor having a bandgap in the visible light region, have recently been actively studied. Among them, the 2D semiconductors TMDC have unique optical properties such as a direct transition semiconductor, light absorption, and high exciton binding energy. Also, hBN shows the possibility as an extremely bright and polarized emitter of non-classical light at room temperature by local point defect. More importantly, 2D materials with different physical properties can be combined to realize optical and optoelectronic device such as charge transfer, diffusion, detection, recombination process. Besides, 2D materials have high expectations for future applications such as nano-electronics and optoelectronics devices due to its atomically thin, flexibility, and tunable band-gap. The development of a 2D light source enables the development of a high-performance light-emitting device with nanoscale, and it is possible to realize most of the optical elements required for the processing of high-speed optical information and atomic layer light emitter. Next-generation light-emitting devices based on 2D materials will play an important role in the future industrial revolutions such as the development of optical communication and display. In this dissertation, we focus on 2D material-based optical properties with atomic layer thickness and application of optoelectronic devices. To utilize the merits and potential of 2D materials for optoelectronics application, the experimental demonstration of light-emitting of 2D materials and systematic investigation of luminescence through structural modulation were carried out. The thesis aims to study the electroluminescence based on 2D materials from near UV to visible range of light in order to make efficient optoelectronics devices with a new approach. Therefore, we discuss the issues of the new optical properties of 2D materials with semiconducting transition metal dichalcogenide (TMDC), graphene, and hexagonal boron nitride (hBN) for optoelectronics. We chosed TMDC as the first optoelectronic material because most of the monolayer TMDCs are direct bandgap semiconductor. We experimentally demonstrate high performance MoS2 device to reduce contact resistance with electron doped graphene electrode and monolayer hBN/Co contact as tunneling contact. As a way to reduce contact resistance, we present a novel strategy for the achieving the high performance and Ohmic contact to monolayer MoS2 FET under the modest gate voltage using the nitrogen-doped graphene, which has an intrinsic high electron carrier density. Nitrogen doped graphene and monolayer MoS2 hybrid FET platform exhibits a small threshold voltage and barrier-free Ohmic contact under zero gate voltage compared to the pristine graphene electrodes platform. The possibility of using highly electron doped graphene to 2D semiconductors as electrodes opens the way to achieve the next generation high performance transistor. To address the second challenge, we demonstrated that monolayer hBN and transition metal (Co) provide robust Ohmic contact. For the purposes of the two advantages, the single-layer hBN insulator reduces the work function by more than 1 eV and contributes to the metal-MoS2 interaction to eliminate the interfacial condition causing the Fermi level pinning. We estimated a flat-band Schottky barrier and confirmed the Ohmic contact at low tempearture. In order to study TMDC applications and intrinsic properties, Ohmic contact and fabrication of high-performance devices are important. Through research on contacts to TMDC, we demonstrate electroluminescence in bilayer WSe2 induced using a thin hBN as a tunnel barrier with transparence graphene electrode. The WSe2 has high optical quality product in electroluminescence with 10 times smaller linewidth than other 2D semiconductors used in LEDs, such MoS2. Optical properties of the Gr/hBN/WSe2/hBN/Gr heterostructure with top and bottom hBN encapsulation device are studied using electroluminescence spectrum. By applying bias voltage between the bottom and top graphene electrodes, charge carriers allow the tunnel current to pass through the hBN tunnel barrier to the WSe2 active layer. We observed electroluminescence of bilayer WSe2 as well in the tunnel current, which is similar to photoluminescence. And We demonstrated van der Waals heterostructure with embedded WSe2 highly promising materials for thin light source. Secondly, graphene is receiving attention in the field of photonics and optoelectronics. To form a bandgap of graphene, we present the observation of electrically driven in-situ deformation to change color from two different graphenes (pristine and nitrogen-doped graphene). We have successfully demonstrated that efficient electroluminescence and electrical characteristics of pristine and nitrogen-doped graphene. At the high electric field, we have found thermal radiation by hot electrons scattered by surface phonon emission. At the estimated electron temperature of ~ 1,500 K, which is high enough to deform graphene to reduced graphene oxide to adhere surface of graphene. Pristine graphene and nitrogen-doped graphene reacts with oxygen and decompose. Deformation occurs only on one side from the center of the graphene channel by the electric field direction. After deformation, green emission (pristine graphene) and blue emission (nitrogen-doped graphene) are observed. When the graphene is deformed to the graphene oxide, it has bandgap corresponding to light emission. A specific understanding of electroluminescence due to the deformation of graphene will provide the foundation for studying 2D-based green and blue light sources. Finally, hBN shows the possibility as an extremely bright and polarized emitter of non-classical light at room temperature by local point defect. Defects play an important role in determining the nature and technical application of 2D materials, and it is particularly important to characterize defects. We observe strong light emission with a peak in the near-ultraviolet regime (3.14 eV, 394 nm) and broad peak (668 nm, 1.85 eV), which is likely the result of emission by electrically induced defect state in hBN. The light emission from the insulating hBN is that the defect state is formed inside hBN when the voltage is applied to the hBN using transparent graphene electrode. In a vacuum environment, we observed a stable and reproducible bright visible light emission from hBN. Emission occurs in an overlap area of two graphene electrode and stars from the edge of the graphene to the entire surface because the edge has strong electric field densities. At high current densities, we observed a remarkably bright visible light emission from a micron-scale structure that can be observed by the naked eyes. We can observe different spectra depending on the direction of the applied voltage. Defects appear to reversibly switch between charged and neutral states, as well as between states with opposite charge. This is considered to be a change in spectrum depending on the charged state of the defect. Furthermore, we have shown that hBN is capable of the photodetector application where low noise and high sensitivity are a need and has the potential for atomically thin light sources. Moreover, what we have demonstrated here, defect creation and color development will be required more progress in the future, and the optical source and photodetector of 2D materials are expected to have many applications. The results of this study show that 2D materials are promising materials in optoelectronics. It is proved that industrially application for light-emitting devices based on 2D materials can be applied to displays. This suggests a new direction for future research of 2D light-emitting device.

은닉된 카메라 색출을 위한 적외선 광학계 설계

강민수 명지대학교 대학원 2021 국내석사

The crime rate of hidden camera has been increasing rapidly since 2011, and the size of the small camera module market has been increasing every year. As camera modules become smaller, the types and functions of hidden cameras are becoming increasingly diverse, and to prevent such crimes, I study hidden camera detection methods and design infrared optical systems. The most common way to detect hidden cameras is by using red-eye effect. This method detects hidden cameras by shining a strong light source towards the lens of the hidden camera and detecting light reflected from the lens of the hidden camera. Other methods include detecting radio frequency emitted from wireless hidden cameras. Unlike the aforementioned methods, this study uses methods to detect heat emitted from hidden cameras. Any object above absolute temperature emits light from a specific wavelength band depending on the temperature of the object. The purpose of this study is to design a thermal imaging optical system that uses this phenomenon to detect hidden cameras. We also design a high-magnification zoom system to detect remote or inaccessible hidden cameras. As a result, we design an infrared zoom optical system that can detect infrared in wavelength bands and has approximately 12x zoom magnification. 2011년 이후로 몰래카메라 범죄율이 급증하고 있으며 해마다 소형 카메라 모듈 시장 규모가 증가하고 있다. 카메라 모듈이 소형화됨에 따라 몰래카메라의 종류와 기능이 점점 다양해지고 있는 가운데 이러한 범죄를 예방하고자 몰래카메라 탐지 방법을 연구하고 적외선 광학계 설계를 하였다. 몰래카메라를 탐지하는 가장 보편적인 방법은 적목현상을 이용한 방법으로 몰래카메라의 렌즈에 강한 광원을 비추어 몰래카메라의 렌즈를 맞고 반사되는 빛을 탐지함으로써 몰래카메라를 탐지한다. 그 외에는 무선 몰래카메라에서 방출되는 radio frequency를 탐지하는 방법이 있다. 본 연구는 이 방법들 외에 몰래카메라에서 방출되는 열을 탐지하는 방법을 사용한다. 절대온도가 넘는 모든 물체는 물체의 온도에 따라 특정한 파장대역의 빛을 방출한다. 이러한 현상을 이용하여 열화상 광학계를 설계하여 몰래카메라 탐지기를 만드는 것이 본 연구의 목적이다. 또한 멀리 있거나 접근하기 어려운 몰래카메라를 탐지하기 위하여 고배율 줌 시스템을 도입하였다. 그 결과 파장 대역의 적외선을 탐지할 수 있고 약 12배의 줌 배율을 가지는 적외선 줌 광학계를 설계하였다.