유기 셀레늄 분자에 의한 자기조립단분자막의 형성과 구조

Abstract

금속 기판 위에 싸이오펜 치환체와 다양한 유기 셀레늄 물질의 자기조립단분자막의 특성을 scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), contact angle (CA)와 cyclic voltammetry (CV) 장비로 측정하였다. 연구는 3-hexylthiophene (3-HTP)의 hexyl 체인의 영향과 아로마틱 링의 2-D 자기조립단분자막의 형성과 thiophene (TP), selenophene (SeP), diethylselenide (DESe)와 diethylsulfide (DES)의 자기조립단분자막의 형성을 통한 헤드 그룹의 효과에 대해 조사해보았다. 또한, 헤드 그룹이 한 개인 셀레나이드와 둘인 셀레나이드 형태의 diphenylselenide (DPSe), diphenyldiselenide (DPDSe), diethyldiselenide (DEDSe)와 DESe 물질들의 자기조립단분자막 형성을 통한 비교 연구룰 진행하였다. 그 결과 hexyl 체인 사이의 인력 때문에 3-HTP 자기조립단분자막의 환원 탈착되는 값이 TP보다 높게 나왔다. XPS 피크를 통해 TP 와 3-HTP의 자기조립단분자막 모두 화학적인 결합 피크인 S1 (161 eV)과 S2 (162 eV)를 갖는 것을 확인하였다. 하지만 3-HTP 자기조립단분자막에서는 hexyl치환체의 영향으로 인해 물리적인 결합 피크인 S3 (163 eV) 또한 가지는 것을 확인하였다. 골드 기판 위 SeP 자기조립단분자막의 분자 패킹 구조와 흡착 조건이 일반적인 알켄싸이올의 경우와는 달리 증기 조건, 온도와 담그는 시간의 영향을 많이 받는다는 것을 발견했다. 특히 매우 잘 배열된 SeP 자기조립단분자막은 사각형의 Vis와 길고 큰 도메인을 갖는다는 것은 확인하였다. DPSe 자기조립단분자막은 어떠한 조건에서도 비정상적으로 많은 Vis와 잘 배열되지 않는 구조를 보이지만 75 ˚C에서1 mM의 용액 농도 하에서 여섯 시간 동안 담가 만든 DPDS의 자기조립단분자막 경우에는 매우 높게 패킹된 도메인을 갖는 잘 배열된 구조를 형성한다. 비록 골드 위에서 DPSe 물질이 잘 배열된 자기조립단분자막을 형성하지 못하지만, DESe 자기조립단분자막의 경우 비교적 덜 단단한 구조인 짧은 ehtyl 치환체를 가지기 때문에 증기 상태의 조건에서 잘 배열된 표면 구조를 얻을 수가 있었다. 게다가 DESe 자기조립단분자만은 75 ˚C 조건 하에서 담그는 시간이 길수록 매우 높은 상태의 표면 구조를 보였다. 그리고DESe 자기조립단분자막의 (2√6 × √3)R5˚의 2-D 배열된 구조를 얻었다. 반면 DES와 DEDSe 자기조립 단분자막의 경우 잘 배열된 라인 형태와 잘 배열되지 않은 구조를 동시에 갖는 두 가지의 상분리상태 도메인을 갖는다. 골드 기판 이외에도, 자기조립단분자막 기술을 전자 소자 시스템에 적용시키기 위해 indium-tin oxide (ITO)기판에 적용시켜 보는 연구를 진행하였다. 우리는 phenylphosphonic-acid (PPA), 4-chlorophenylphosphonic-acid (Cl-PPA), 4-methoxyphenylphosphonic-acid (Me-PPA) 와 4-ethylphenylphosphonic-acid (Ethyl-PPA) 물질의 자기조립단분자막을 형성시켜 유기발광 다이오드 (OLED) 소자의 정공 주입 층으로 적용시켜 보았다. 결과적으로 Cl-PPA 자기조립단분막에서 자기조립단분자막을 형성시키지 않은 OLED 소자에 비해 24.76 %의 구동 전압을 낮추는 상당한 효과를 보았다. 결과적으로 이 연구는 아로마틱 싸이오펜 치환체 물질들과 다양한 셀레늄을 기반으로 한 물질들의 자기조립단분자막의 표면 구조, 전기적인 거동, 흡착하는 조건을 이해하는 데에 있어서 매우 의미있는 정보가 될 것이라고 믿는다. |Self-assembled monolayers (SAMs) of thiophene derivative and various selenium-based molecules on Au(111) were characterized by means of scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), contact angle (CA), and cyclic voltammetry (CV). This study examined the effect of hexyl chain of 3-hexylthiophene (3-HTP) and the aromatic ring for the formation of 2D SAMs and the head group effect through formation of thiophene (TP), selenophene (SeP), diethylselenide (DESe) and diethylsufide (DES) SAMs. Also, we studied the formation of SAMs compared with monoselenides and diselenides such as diphenylselenide (DPSe) , diphenyldiselenide (DPDSe), diethyldiselenide (DEDSe) and DESe. Reductive desorption value of 3-HTP SAMs is higher than TP because of stronger intermolecular interaction. Through the XPS peaks, both of TP and 3-HTP SAMs have bound sulfur peaks (S1, S2). However, 3-HTP SAMs have an unbound peak (S3) due to effect of substituted hexyl chain. It was found that the molecular packing structures and adsorption conditions of SeP SAMs on Au(111) was influenced by vapor condition, temperature and immersion time, unlike the case of alkanethiol. Especially, well-ordered SeP SAMs have tetragonal vacancy islands and long-range domain. The DPSe SAMs show irregular a number of vacancy islands and disordered structure any conditions, whereas the DPDSe SAMs formed by 1 mM solution at 75 ºC for 6 hours have ordered structure with the higher packing density domains. Although DPSe on gold generally does not form ordered SAMs, the well ordered DESe SAMs were formed by vapor condition because of short chain on less rigid molecular structure. In addition, DESe SAMs show high quality of surface structure when SAMs were formed at 75 ºC for longer times. And this study can be obtained 2-D ordered structures as a (2√6 ⅹ √3)R5˚ of DESe SAMs. On the other hand, DES and DEDSe SAMs formed by same condition of DESe SAMs have two phase-separated domains composed of ordered paired rows and the disordered phase. In addition to gold substrate, SAMs technique on indium-tin-oxide (ITO) substrate was studied in order to apply electronic device system. Phenylphosphonic-acid (PPA), 4-chlorophenylphosphonic-acid (Cl-PPA), 4-methoxyphenylphosphonic-acid (Me-PPA) and 4-ethylphenylphosphonic-acid (Ethyl-PPA) SAMs on ITO substrates were prepared in order that SAMs layer could use the hole-injection layer of organic light emitting diode (OLED) device. As a result, Cl-PPA SAMs significantly reduced the operating voltage of OLED by 24.76 % compared with OLEDs without SAMs. Our results obtained here will provide meaningful information for understanding surface structure, electrochemical behavior, and adsorption condition, of thiophene derivative and various selenium-based SAMs.; Self-assembled monolayers (SAMs) of thiophene derivative and various selenium-based molecules on Au(111) were characterized by means of scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), contact angle (CA), and cyclic voltammetry (CV). This study examined the effect of hexyl chain of 3-hexylthiophene (3-HTP) and the aromatic ring for the formation of 2D SAMs and the head group effect through formation of thiophene (TP), selenophene (SeP), diethylselenide (DESe) and diethylsufide (DES) SAMs. Also, we studied the formation of SAMs compared with monoselenides and diselenides such as diphenylselenide (DPSe) , diphenyldiselenide (DPDSe), diethyldiselenide (DEDSe) and DESe. Reductive desorption value of 3-HTP SAMs is higher than TP because of stronger intermolecular interaction. Through the XPS peaks, both of TP and 3-HTP SAMs have bound sulfur peaks (S1, S2). However, 3-HTP SAMs have an unbound peak (S3) due to effect of substituted hexyl chain. It was found that the molecular packing structures and adsorption conditions of SeP SAMs on Au(111) was influenced by vapor condition, temperature and immersion time, unlike the case of alkanethiol. Especially, well-ordered SeP SAMs have tetragonal vacancy islands and long-range domain. The DPSe SAMs show irregular a number of vacancy islands and disordered structure any conditions, whereas the DPDSe SAMs formed by 1 mM solution at 75 ºC for 6 hours have ordered structure with the higher packing density domains. Although DPSe on gold generally does not form ordered SAMs, the well ordered DESe SAMs were formed by vapor condition because of short chain on less rigid molecular structure. In addition, DESe SAMs show high quality of surface structure when SAMs were formed at 75 ºC for longer times. And this study can be obtained 2-D ordered structures as a (2√6 ⅹ √3)R5˚ of DESe SAMs. On the other hand, DES and DEDSe SAMs formed by same condition of DESe SAMs have two phase-separated domains composed of ordered paired rows and the disordered phase. In addition to gold substrate, SAMs technique on indium-tin-oxide (ITO) substrate was studied in order to apply electronic device system. Phenylphosphonic-acid (PPA), 4-chlorophenylphosphonic-acid (Cl-PPA), 4-methoxyphenylphosphonic-acid (Me-PPA) and 4-ethylphenylphosphonic-acid (Ethyl-PPA) SAMs on ITO substrates were prepared in order that SAMs layer could use the hole-injection layer of organic light emitting diode (OLED) device. As a result, Cl-PPA SAMs significantly reduced the operating voltage of OLED by 24.76 % compared with OLEDs without SAMs. Our results obtained here will provide meaningful information for understanding surface structure, electrochemical behavior, and adsorption condition, of thiophene derivative and various selenium-based SAMs.