Gravure Printed and Solution-Processed Polymer Semiconductor Devices

The idea of printing optoelectronic devices has been developed over the last decade by various printing techniques such as screen printing, transfer printing, and inkjet printing, attributed to the advent of soluble organic semiconducting (OSC) materials. Printing of optoelectronic devices provides economical advantages for its fast and simple processing stages which is conceptually similar to the graphical printing. The advantage is expected to overcome the relatively low performance of organic materials where its charge transport is occurred by hopping process which is limited by its hopping distance and conformation of molecular chains. Printing techniques currently available should be optimized further to attract a huge impact. For example, the inkjet printing has a drawback of its low printing speed although it offers the printing of high definition pixels with its width around 60 μm. In this Thesis, gravure printing, a high throughput printing technique, is discussed to experimentally demonstrate its feasibility as a production method of optoelectronic devices. The targeted device structures are organic light-emitting diodes (OLEDs) and field-effect transistors (OFETs). Both printed OFETs and OLEDs have reached device performance similar to reference devices with the same materials and structures fabricated by spin-coating. Unlike the graphic art printing, such as is used to fabricate newspapers, magazines and posters, the printing of OSC optoelectronic devices is very sensitive to processing conditions attributed to a thickness of very thin layers, usually less than 100 nm. Therefore, the surface uniformity of the printed layers must be very planar, with a surface roughness root mean square (RMS) value typically less than 3 nm. It is found that controlling hydrodynamic forces during the thin film formation, such as the coffee stain convection flow and the surface tension driven Marangoni flow, offer a clear opportunity for achieving devices with high performance in gravure contact printed thin films. Chapter 2 and 3 discuss background theory related to experiments in this thesis. Chapter 4 is an experimental chapter explaining materials used and experimental techniques. In Chapter 5, gravure printing of OLEDs with printed poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) hole injection and LUMATION Green 1300 (LG1300) light emissive layers is developed with discussions of wetting of printing formulations and fluidic movements observed during film formation. A mixture of solvent method provides the circulation of hydrodynamic flows inside the printed formulation providing a deposition of highly uniform thin film after solvent evaporation. As a result, high performance of OLEDs with its performance of 8.8 cd/A and 5.4 lm/W with a maximum brightness of 66,000 cd/m2 is reported in OLEDs where both PEDOT: PSS and LG1300 are gravure printed. The performance is the highest up to date among the OLEDs printed by the same printing method. Chapter 6 introduces an inverted structure type OLED where its high work function anode is placed on the top of the device so that it consequently improves device stability as high work function metals such as Au or Ag are less sensitive to ambient dopants. The use of carbonate or oxide layers on the top of a high work function metal at the bottom of the device induced efficient injection of electrons to the device. A very thin layer of caesium carbonate (Cs2CO3) around 5-10 nm was gravure printed onto the ITO electrode. The printed Cs2CO3 layer showed that the surface roughness is highly improved owing to molecular ordering is affected and improved by the mechanical forces such as pressure and thermal energy engaged during the printing. The inverted OLEDs with the printed Cs2CO3 layer recorded the device performance of 10 cd/A and 3 lm/W with a maximum brightness of around 7,500 cd/m2. This is a first report showing that a very thin and inorganic layer can also be gravure printed. Chapter 7 describes charge balancing and position of recombination zone in inverted OLEDs using poly (9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) and poly (9,9-dioctylfluoreneco- N-(4-butylphenyl)-diphenylamine) (TFB) bilayer structure. The two layers are either hole or electron transporting materials and can form a large energy offsets between the HOMO levels and the LUMO levels of the two materials at the interface which confines a large number of injected charge carriers there. It is shown that a position of recombination zone and the charge carrier confinement effect are dependent with the thicknesses of the two polymer layers. The confined charged carriers induce the recombination zone to be positioned close to the interface where charge carrier tunnelling and Föster energy transfer occur more frequently than the bulk. The experimentally optimized thicknesses of the two layers record the highest efficiency of 36 cd/A and 23 lm/W with a bright emission of 51,200 cd/m2 at a low voltage around 4 V. The efficiency is the highest efficiency reported so far to the best of our knowledge using fluorescence materials. Chapter 8 explains gravure printing of OFETs using a thiophene polymer. Poly(3- hexylthiophene)-2,5-diyl (P3HT) OSC, two dielectric layers, and top Ag gate electrode are sequentially gravure printed. The annealing condition of P3HT, choice of dielectric layer and issues related to printing P3HT are discussed. Fully gravure printed OFETs on the pre-patterend ITO source and drain pattern report a high mobility of 3 × 10-2 cm2/Vs and an on/off current ratio of 104.62. The performance is the highest among the printed OFETs using P3HT

Electronic and spintronic devices using two-dimensional materials

179 p. El contenido del capítulo 8 está sujeto a confidencialidadEver since in 2004 atomically-thin two-dimensional van der Waals materials became available to the scientific community, at the reach of manual microexfoliation techniques, their implementation in novel device structures and concepts promised disruptive new applications and motivated research in a vast range of fields.Confined to the thinnest possible thickness, electrons in these materials exhibit a plethora of electronic properties, from semiconducting MoS2, to superconductor NbSe2, dielectric BN, and, jack-of-all trades, graphene.In this thesis, we explore fundamental and applied aspects of chemical vapor deposition (CVD) graphene, MoS2, and WSe2 using electronic device structures that use them as transporting channel, namely field-effect transistors (FETs), Hall bars, and diodes.MoS2 is a n-type semiconducting 2D vdW that complements one of the weak aspects of graphene-based transistors, which is the small ratio between the maximum current output and of the minimum current output of the transistors. Using MoS2 we identify an electron doping constraint for performing stable magnetotransport measurements, and we investigate the origins of the strong current fluctuations of the FETs. We study the low-frequency noise (LFN) of the current output of devices made with different layer thicknesses, and use the strong light-matter interactions of MoS2 to employ photodoping techniques together with the electrostatic gating to dope the channel. By converging all these conditions, we are able to discern the mechanism behind the different types of LFN noise reported in literature for MoS2, while at the same time identifying a LFN crossover driven by photodoping.With p-type semiconducting WSe2 we optimize the electron and hole transport properties of ambipolar FETs by considering BN as a top and bottom interface substrate and encapsulation layer, respectively. By doing so, we areable to address to some extent the strong hysteretic effects that adversely affect the operation of WSe2 FETs on oxide substrates, and improve the overall device performance.The versatility of CVD graphene allows us to do both applied and fundamental studies, both related to spintronics and electronics.The unique properties of graphene make it a core material in the search of full-electrical approaches to generate, transport, and detect spin currents without the use of magnetic elements. Using a Hall-bar shaped sample, non-local signals in graphene have been demonstrated to be associated with spin transport. In our case, we use the large area availability of CVD graphene to study non-local effects in an unlikely scenario for the transport of spins. We study the non-local signals of millimeter sized Hall-bars of CVD graphene, and by doing a systematic study as a function of device scale, from macro-to-microscale we identify a mechanism that cannot be connected with spin diffusion that also leads to large signals. By evaluating the microscopic details of the samples, and the different effects observed, we propose a mechanism mediated by grain boundaries to drive such effects.In a more applied manner, we use CVD graphene for two other types of devices. First, we study the use of graphene as an electrode material for lateral and vertical field-effect transistors that operate using organic channels, and determine that the low density of states of graphene allows for unscreened electric fields to reach the organic layer and enable the transistor operation in the vertical geometry.The second applied study is the large-scale fabrication of diodes using CVD graphene. Benefiting from the ultra-thin cross section of graphene, and using a lateral geometry we demonstrate the reliable fabrication of lateral metal/insulator/graphene diodes. The time constants determined from the direct-current analysis place the operation of the fabricated devices in the THz range. Additionally, the material combination considered enabled large current densities based on field-emission processes.CICnanoGUNE : nanoscience cooperative research cente

Photodiodes based in La0.7Sr0.3MnO3/single layer MoS2 hybrid vertical heterostructures

The fabrication of artificial materials by stacking of individual two-dimensional (2D) materials is amongst one of the most promising research avenues in the field of 2D materials. Moreover, this strategy to fabricate new man-made materials can be further extended by fabricating hybrid stacks between 2D materials and other functional materials with different dimensionality making the potential number of combinations almost infinite. Among all these possible combinations, mixing 2D materials with transition metal oxides can result especially useful because of the large amount of interesting physical phenomena displayed separately by these two material families. We present a hybrid device based on the stacking of a single layer MoS2 onto a lanthanum strontium manganite (La0.7Sr0.3MnO3) thin film, creating an atomically thin device. It shows a rectifying electrical transport with a ratio of 103, and a photovoltaic effect with Voc up to 0.4 V. The photodiode behaviour arises as a consequence of the different doping character of these two materials. This result paves the way towards combining the efforts of these two large materials science communities.Comment: 1 table, 4 figures (+9 supp. info. figures

Evaporative printing of organic materials and metals and development of organic memories

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004.Includes bibliographical references (p. 125-132).The advantages of directed printing make it the ideal fabrication tool for the ubiquitous electronic technologies of the future. However, direct printing techniques such as ink-jet technology, are currently limited to materials that can be processed in solution. We developed a novel micro-machined print head capable of expanding the capabilities of inkjet printing to metals and molecules that are suited for evaporative deposition. Deposition of metals is particularly desirable advantage of the proposed printer. We demonstrate arbitrary organic and metal patterns by printing, with the line width modulated by controlling the micro-machined shutter. With the challenges and solutions for ambient pressure printing are also studied. Additionally, the printer can be used for organic crystal formation, and controlled doping. In the second part of the thesis we examine charge trapping and storage in organic thin film devices. We demonstrate that by controlled doping, we can engineer charge storage in active organic electronic devices. Charge trapping in organic hetero-junction structures results in two distinct phenomena that both manifest as a memory behavior. Trapped charge can (1) increase the carrier mobility in organic structures, (2) generate current during the de-trapping process. Both processes are demonstrated in practical structures.by Sung Hoon Kang.S.M

Energy Transport in Organic Photovoltaics.

Organic photovoltaics (OPV) have the potential to be a flexible and low-cost form of carbon-neutral energy production. However, many of the underlying physical mechanisms that dictate the behavior of OPVs remain frustratingly obscure in comparison to the well-understood physics of inorganic semiconductors. This dissertation centers around the development of new techniques to characterize the behavior of excitons in organic semiconductors, both in the bulk and at interfaces. We first examine the method of spectrally-resolved photoluminescence quenching (SR-PLQ), the most convenient and powerful current technique for measuring the exciton diffusion length (LD) of organic semiconductors, and extend it to work with optically thin films. This allows for its application to a much wider range of materials and physical systems. The second part of the dissertation presents a further extension of the method of PL quenching to characterize non-ideal interfaces, those which block or quench only a fraction of incident excitons. This is used to understand the operation of a novel fullerene:wide energy gap material buffer in OPVs. In combination with charge transport and morphological studies, it is shown that the mixed buffer shows disproportionate benefits from the two materials; blocking excitons superlinearly with wide energy gap material concentration and still conducting charges efficiently even at very small (10%) fullerene concentration. Finally, we extend the principles of PL quenching to characterize arbitrary interfaces, including those between materials with identical energy levels but different LD and exciton lifetime, and those between materials with small (~20 meV) energy offsets. These techniques allow us to finally resolve the ambiguity in the spin state of the exciton which serves as the primary source of photocurrent in C60, one of the most important materials in current efficient OPVs.PhDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/113547/1/kjberg_1.pd

Electronic and spintronic devices using two-dimensional materials

179 p. El contenido del capítulo 8 está sujeto a confidencialidadEver since in 2004 atomically-thin two-dimensional van der Waals materials became available to the scientific community, at the reach of manual microexfoliation techniques, their implementation in novel device structures and concepts promised disruptive new applications and motivated research in a vast range of fields.Confined to the thinnest possible thickness, electrons in these materials exhibit a plethora of electronic properties, from semiconducting MoS2, to superconductor NbSe2, dielectric BN, and, jack-of-all trades, graphene.In this thesis, we explore fundamental and applied aspects of chemical vapor deposition (CVD) graphene, MoS2, and WSe2 using electronic device structures that use them as transporting channel, namely field-effect transistors (FETs), Hall bars, and diodes.MoS2 is a n-type semiconducting 2D vdW that complements one of the weak aspects of graphene-based transistors, which is the small ratio between the maximum current output and of the minimum current output of the transistors. Using MoS2 we identify an electron doping constraint for performing stable magnetotransport measurements, and we investigate the origins of the strong current fluctuations of the FETs. We study the low-frequency noise (LFN) of the current output of devices made with different layer thicknesses, and use the strong light-matter interactions of MoS2 to employ photodoping techniques together with the electrostatic gating to dope the channel. By converging all these conditions, we are able to discern the mechanism behind the different types of LFN noise reported in literature for MoS2, while at the same time identifying a LFN crossover driven by photodoping.With p-type semiconducting WSe2 we optimize the electron and hole transport properties of ambipolar FETs by considering BN as a top and bottom interface substrate and encapsulation layer, respectively. By doing so, we areable to address to some extent the strong hysteretic effects that adversely affect the operation of WSe2 FETs on oxide substrates, and improve the overall device performance.The versatility of CVD graphene allows us to do both applied and fundamental studies, both related to spintronics and electronics.The unique properties of graphene make it a core material in the search of full-electrical approaches to generate, transport, and detect spin currents without the use of magnetic elements. Using a Hall-bar shaped sample, non-local signals in graphene have been demonstrated to be associated with spin transport. In our case, we use the large area availability of CVD graphene to study non-local effects in an unlikely scenario for the transport of spins. We study the non-local signals of millimeter sized Hall-bars of CVD graphene, and by doing a systematic study as a function of device scale, from macro-to-microscale we identify a mechanism that cannot be connected with spin diffusion that also leads to large signals. By evaluating the microscopic details of the samples, and the different effects observed, we propose a mechanism mediated by grain boundaries to drive such effects.In a more applied manner, we use CVD graphene for two other types of devices. First, we study the use of graphene as an electrode material for lateral and vertical field-effect transistors that operate using organic channels, and determine that the low density of states of graphene allows for unscreened electric fields to reach the organic layer and enable the transistor operation in the vertical geometry.The second applied study is the large-scale fabrication of diodes using CVD graphene. Benefiting from the ultra-thin cross section of graphene, and using a lateral geometry we demonstrate the reliable fabrication of lateral metal/insulator/graphene diodes. The time constants determined from the direct-current analysis place the operation of the fabricated devices in the THz range. Additionally, the material combination considered enabled large current densities based on field-emission processes.CICnanoGUNE : nanoscience cooperative research cente

Effects of Dielectric Stoichiometry on the Photoluminescence Properties of Encapsulated WSe2 Monolayers

Two-dimensional transition-metal-dichalcogenide semiconductors have emerged as promising candidates for optoelectronic devices with unprecedented properties and ultra-compact performances. However atomically thin materials are highly sensitive to surrounding dielectric media, which imposes severe limitations to their practical applicability. Hence for their suitable integration into devices, the development of reliable encapsulation procedures that preserve their physical properties are required. Here, the excitonic photoluminescence of WSe2 monolayer flakes is assessed, at room temperature and 10 K, on mechanically exfoliated flakes encapsulated with SiOx and AlxOy layers employing chemical and physical deposition techniques. Conformal flakes coating on untreated - non-functionalized - flakes is successfully demonstrated by all the techniques except for atomic layer deposition, where a cluster-like oxide coating is observed. No significant compositional or strain state changes in the flakes are detected upon encapsulation by any of the techniques. Remarkably, our results evidence that the flakes' optical emission is strongly influenced by the quality of the encapsulating oxide - stoichiometry -. When the encapsulation is carried out with slightly sub-stoichiometric oxides two remarkable phenomena are observed. First, there is a clear electrical doping of the monolayers that is revealed through a dominant trion - charged exciton - room-temperature photoluminescence. Second, a strong decrease of the monolayers optical emission is measured attributed to non-radiative recombination processes and/or carriers transfer from the flake to the oxide. Power- and temperature-dependent photoluminescence measurements further confirm that stoichiometric oxides obtained by physical deposition lead to a successful encapsulation.Comment: 30 pages, 6 figure

낮은 표면 에너지와 확산 방지층으로 코팅된 하이브리드 도장의 개발 및 유기전자소자 제작에 대한 그 응용

학위논문(박사)--서울대학교 대학원 :융합과학기술대학원 융합과학부(나노융합전공),2019. 8. 김창순.Since the pioneering work by Whitesides et al., termed soft lithography, poly(dimethylsiloxane) (PDMS) has been very widely used as a material composing a stamp from which various materials are transferred onto a target substrate. However, even more than 20 years after the first paper reporting this work, applications of PDMS-stamp-based materials transfer have been rather limited to simple cases where materials transfer alone is sufficient for their success and/or the quality of the transfer-bonded interfaces and the cleanliness of the transferred layers do not matter significantly. This is in part due to the following adverse properties of the PDMS stamp: absorption of small molecules by PDMS free volumes and contamination of the transferred layers by uncured oligomers in PDMS. Here, I develop a hybrid stamp comprised of a PDMS bulk and a perfluoropolyether (PFPE) coating induced by a condensation reaction between not only PDMS and PFPE molecules but also adjacent PFPE molecules. A key role of the PFPE coating layer on the PDMS stamp is effective to prevent organic small molecules from being absorbed into the stamp and the uncured siloxane oligomers of the PDMS from migrating on a layer to be transferred. I prove the effectiveness and versatility of the PFPE-coated PDMS stamp by fabricating an organic light emitting diode whose organic-organic interface is formed by a transfer process and an organic hole-only device with a bottom electrode composed of a graphene bilayer transferred from the stamp. As a result, the mechanically bonded interfaces are sufficiently intimate at the molecular level compared to those of the same interface formed by thermal evaporation. Furthermore, the top surface of the transferred layer that was in contact with the stamp is enough to clean for injecting and extracting charge carriers. The PFPE-coated stamp demonstrated in this work is expected to be widely used in fabricating devices or systems that are especially difficult to realize using high-temperature or wet processes. An exciting example is full-color organic light-emitting device (OLED) displays with a resolution much higher than that of the current displays in smartphones, which is required for virtualreality applications but is difficult to fabricate using the current shadow maskbased patterning.폴리디메틸실록산(PDMS)은 다양한 재료를 최종 기판으로 옮길 때 사용하는 소재로써 매우 널리 사용되어 왔다. 그러나 많은 연구자들이 오랫동안 이와 관련된 많은 연구들을 진행했음에도 불구하고, PDMS 도장 기반의 층 또는 패턴 전사 공정은 기계적으로 접합된 계면과 전사된 물질의 청결이 중요하지 않은 응용분야에서만 제한적으로 진행되었다. 이는 다음과 같은 PDMS 도장의 불리한 성질에 기인한다: (i) PDMS의 내부로 유기소분자의 흡수, (ii) PDMS의 경화되지 않은 올리고머에 의한 이동된 층의 오염. 이러한 문제가 해결된다면, 도장을 이용한 패턴된 물질 증착은 기존의 쉐도우 마스크 공정과 진공증착 공정으로 제작되는 유기전자소자 분야에서 다양하고 새로운 구조 및 소자를 제작할 수 있을 것이다. 본 연구에서는 PDMS와 퍼플루오르폴리에테르(PFPE) 분자뿐만 아니라 인접한 PFPE 분자들 사이의 응축 반응에 의해 유도된 PDMS 벌크 및 PFPE 코팅 층으로 구성된 하이브리드 도장을 개발하였다. PDMS 도장 위에 있는 PFPE 코팅 층의 핵심 역할은 PDMS의 경화되지 않은 실록산 올리고머가 전사 될 층 위로 이동하는 것을 막고 전사 될 층의 물질이 도장 내부로 흡수되는 것을 방지하는 것이다. 박막전사 과정에서 가지는 PFPE로 코팅된 PDMS 도장의 효율성과 다 기능성은 전사 공정으로 형성된 유기—유기 계면이 포함된 유기발광 다이오드와 상기 도장으로부터 전사된 그래핀 이중층으로 구성된 하부 전극을 갖는 유기 hole-only 소자를 제작함으로써 증명되었다. 그 결과 기계적으로 결합된 계면의 품질은 열 증발에 의해 형성된 동일한 계면의 품질과 비교하여 비슷한 수준이었다. 또한, 도장과 접촉한 전사 층의 상부 표면은 전하 캐리어를 주입 및 추출하기에 충분하였다. 본 연구에서 개발된 PFPE가 코팅된 도장은 고온 또는 습식 공정을 사용하여 구현하기 가 특히 어려운 전자장치 또는 전자소자 제작에 널리 사용될 수 있을 것으로 예상된다. 가장 흥미로운 예는 가상 현실 어플리케이션에 필요하지만 현재의 쉐도우 마스크 기반 패터닝을 사용하여 제조하기 어려운 스마트 폰의 현재 디스플레이보다 훨씬 높은 해상도를 갖춘 풀 컬러 유기발광소자 (OLED) 디스플레이이다.Contents Chapter 1 Introduction..........................................................................................1 1.1 Overview ........................................................................................................1 1.1.1 Limitations of PDMS as a stamp in a contact transfer process……………………1 1.1.2 Previous studies to overcome problems with PDMS ............3 1.2 Common elements to understand a contact transfer process...........5 1.2.1 Conditions for a reliable contact-transfer process.................5 1.2.2 Stamp materials for a contact transfer process......................7 1.3 Scope of this thesis........................................................................10 1.3.1 Development of a process for transferring of graphene patterns and the motivation for the need to coat a PFPE layer on PDMS……………………...……………………………………….12 1.3.2 Overcoming limitation of PDMS as a stamp in a contact transfer process .................................................................................12 1.3.3 Application of the PFPE-coated PDMS stamp to the fabrication of organic electronic devices..........................................13 1.4 References .....................................................................................15 Chapter 2 Low-Temperature, Dry Transfer-Printing of a Patterned Graphene Monolayer ...................................................................................19 2.1 Introduction ...................................................................................19 2.2 Results and discussion...................................................................22 2.2.1 The low-temperature and dry transfer process for a CVDgrown graphene monolayer...............................................................22 2.2.2 Effect of surface on the quality of transfer-printed graphene monolayers........................................................................................27 2.2.3 Characterizations of graphene monolayer patterns transferprinted on materials that can be damaged by a wet process .............36 2.2.4 Morphological characterizations of transfer-printed graphene monolayers........................................................................................39 2.3 Conclusions ...................................................................................44 2.4 Methods.........................................................................................45 2.4.1 Low-temperature, dry transfer-printing process..................45 2.4.2 Transfer-printing of patterned graphene layers ...................46 2.4.3 Sample preparation for the elemental analysis....................48 2.4.4 Preparation of PDMS stamps ..............................................48 2.5 References .....................................................................................51 Chapter 3 Polydimethylsiloxane (PDMS) Stamp Coated with a LowSurface-Energy, Diffusion-Blocking, Covalently Bonded Perfluoropolyether (PFPE) Layer ......................................................................................58 3.1 Introduction ...................................................................................58 3.2 Results and discussion...................................................................60 3.2.1 Dip-coating process for depositing a PFPE layer on a PDMS stamp………………………………………………………………. 60 3.3 Conclusions ...................................................................................64 3.4 Methods.........................................................................................66 3.4.1 Preparation of PDMS stamps ..............................................66 3.4.2 PFPE dip-coating of PDMS stamps.....................................66 3.5 References .....................................................................................69 Chapter 4 Application of the PFPE-coated PDMS Stamp to the Fabrication of Organic Electronic Devices by Layer Transfer ................71 4.1 Introduction ...................................................................................71 4.2 Results and discussion...................................................................74 4.2.1 Transfer-printing of a patterned layer composed of organic small molecules from the PFPE-coated stamp to a target substrate .74 4.2.2 Fabrication of green fluorescent OLEDs by organic-layer transfer .…………………..……………………………..………….85 4.2.3 Characteristics of a transferred graphene monolayer using the PFPE-coated PDMS stamp ...............................................................89 4.2.4 Organic hole-only device with a graphene bottom electrode deposited by using the PFPE-coated PDMS stamp ..........................95 4.2.5 Characteristics of red phosphorescent OLEDs fabricated by patterns transfer...............................................................................100 4.2.6 Organic patterns formed by a transfer-printing process ....107 4.3 Conclusions .................................................................................107 4.4 References ...................................................................................109 Chapter 5 Conclusions..........................................................................115 5.1 Summary......................................................................................115 5.2 Further studies .............................................................................117 5.2.1 Further applications of a contact-transfer process using PFPEcoated PDMS stamps......................................................................117 5.2.2 Further modification of a PFPE-coated PDMS stamp.......118 5.3 References ...................................................................................121 요 약 (국문초록)........................................................................................123Docto