금(111) 표면 위에서 트라이페닐포스핀의 흡착 및 분자 자기조립 = Adsorption and molecular self-assembly of triphenylphosphine on Au(111) surface

다국어 초록 (Multilingual Abstract)

The phosphine-capped gold nanoparticles (Au NPs) have been widely studied for decades. Generally, these studies require for the investigation of surface behavior of TPPs on the 2-dimensional metal surface, revealing the kinetic and thermodynamic mechanism of diffusion and packing behaviors. Recently, the formation and packing structure of TPP adlayer on face-centered cubic lattice of Au(111) surface was revealed by scanning tunneling microscopy (STM) at low temperature in ultrahigh vacuum condition. On the other hand, there have been few studies regarding the adsorption and surface structure of TPP adlayer on Au(111) formed in solution. In this study, to understand these issues, the adsorption and self-assembly phenomena of TPP on Au(111) surface formed in solution were examined by STM at room temperature after the immersion in the solution, as a function of immersion time. Regardless of solution concentration and immersion time, we found that TPP adlayer has only randomly oriented structure with darkened pits on the Au(111) surface. To examine the adsorption behavior and affinity of TPP molecules on Au(111) surface, we monitored the formation and structure of binary self-assembled momolayers (SAMs) from TPP and 1-octanethiols (OTs) with different molecular ratio and the displacement process of pre-covered TPP adlayer by 1-decanethiols (DTs) as a function of displacement time or vice versa. It was revealed that the dominant phase of OT SAMs was formed with increasing the fraction of OT molecules or increasing with displacement time by DTs. The formation of OT SAMs from toluene solution containing binary mixture was confirmed by the existence of the lying-down striped phase with (5 × √3) unit cell structure corresponding to the chain length of carbons. In addition, the cyclic voltammetry measurements gave an insight that the TPPs would exist on the Au(111) surface adsorbed as the chemisorption. From our study, we found that the combined interaction of adsorbate-adsorbate and adsorbate-substrate drives the stability of SAMs, and TPPs could have less interactive force with metal surface and lateral species than alkanethiols. Further verification, the displacement process was analyzed by the X-ray photoelectron spectroscopy (XPS). The normalized XPS intensity of close-packed DT SAMs formed in ethanol medium shows the most intensified signal, 0.0068 and after transferred to TPP solution, the drastic change is not shown. The relative XPS intensity of the transferred sample is 0.0062. In the case of DT SAMs formed by the displacement of TPP, the results of XPS are fitted with the tendency of displacement, because the relative intensity of S 2p region of each sample is measured as 0.0032 and 0.0055 in the displaced SAMs for 30 min and 24 h, respectively. Interestingly, the intensity of displaced SAMs for 24 h has almost same quantity of fabricated SAMs by single DT compound in toluene medium. The measured intensity is 0.0054. This implies the TPP adlayers are fully substituted after the displacement for 24 h by DTs.

국문 초록 (Abstract)

수십 년간, 포스핀에 싸여진 금 나노입자 (Au nanoparticles, Au NPs)는 널리 연구되어왔다. 일반적으로, 이런 연구는 확산과 밀집 경향의 속도론적, 열역학적 기제를 알기 이해하기 위해서 트라이페닐포스핀(triphenylphosphine, TPP)의 2 차원 금속 표면 위에서의 현상을 규명하는 것을 요구한다. 최근에, 초고진공에서 저온 주사 터널 현미경(scanning tunneling microscopy, STM)으로 금(111)의 면심 입방 격자에서의 TPP 흡착층의 형성과 그 밀집 구조가 밝혀졌다. 반면에, 금(111)에서 용액상에서 형성된 TPP 흡착층의 흡착과 표면 구조에 대해서는 거의 연구가 없었다. 이 연구에선, 이런 문제를 이해하기 위해, 금(111) 표면 위에서 용액상에서 형성된 TPP의 흡착과 자기-조립 현상을 상온에서 담금 시간의 조절에 따라 용액상 증착 후 STM으로 설명하였다. 농도와 담금 시간과 관계 없이, 우리는 TPP 흡착층이 어두운 영역과 함께 무작위적으로 배향되어있는 구조만이 금(111) 위에 있는 것을 관측했다. 금(111) 표면 위에서 TPP 분자의 흡착 거동과 친화도를 설명하기 위해서, 분자 비율을 변경하며 TPP와 옥탄싸이올(1-octanethiol, OT)로부터, 또는 미리 처리한 TPP 흡착층을 치환 시간 조절에 따라 데칸싸이올(1-decanethiol, DT)에 의한 치환 과정으로, 혹은 그 반대로 두 화학종의 자기-조립 단분자막(self-assembled monolayers, SAMs)의 형성과 구조가 관찰되었다. OT SAMs의 지배적인 상은 OT 분자의 비율을 증가시켜주거나 DT에 의한 치환 시간 증가로 볼 수 있다. 두 화학종의 혼합물을 포함하는 톨루엔 용액에서의 OT SAM의 형성은 탄소열의 길이와 같은 (5 ×√3) 단위 세포 구조의 누워있는 스트라이프 페이즈의 존재로 확인할 수 있다. 게다가, 전극의 순환 전위법 측정은 TPP가 화학적 결합으로 금(111) 위에 붙어 존재한다는 것을 알게 해주었다. 본 연구에서, 흡착질-흡착질과 흡착질-기판의 종합적 힘이 SAMs의 안정성에 기여하는 것과 TPP는 알칸싸이올보다 금속 표면과 이웃한 종과의 약한 힘을 갖는 것으로 밝혀졌다. 증명을 위해 치환 과정을 X-선 광전자 분광학(X-ray photoelectron spectroscopy, XPS)으로 분석하였다. 에탄올 매개로 최밀-충전된 DT SAMs의 정규화된 XPS 세기가 0.0068로 가장 강하게 나타났고, TPP 용액에 담고 난 후에도 큰 변화가 나타나지 않았다. 그 표본의 상대적인 XPS 세기는 0.0062이다. 각 표본의 S 2p 영역에서의 세기가 30 분 치환 표본은 0.0032, 24 시간 치환 표본은 0.0055로 측정되었으므로, TPP를 치환한 DT SAMs의 경우에도 XPS 결과는 치환 경향에 맞게 나타났다. 흥미롭게도, 24 시간 치환한 SAMs의 세기는 톨루엔 매개에서 DT 만으로 제작된 SAMs와 거의 같은 양을 갖는다. 그 측정된 세기는 0.0054이다. 이것은 TPP 흡착막이 DT에 의하여 24 시간 후에는 완전히 치환되었음을 의미한다.

목차 (Table of Contents)

• Table of Contents
• Abstract ·····························································································i
• Table of Contents ·················································································iii
• List of Tables ······················································································vi
• List of Figures ····················································································vii
• 1. Introduction ···················································································1
• 1.1 Phosphine as a Useful Material for Well-Controlled Small Au NPs ··············1
• 1.2 Lack of Studies about the Assembly Behavior of Phosphines on Au(111) ·······4
• 1.3 Binary Mixture: Thermodynamically Competitive System ·······················6
• 2. Experimental Section ········································································8
• 2.1 Materials and Preparation of Au(111) Substrate ····································8
• 2.2 Preparation of SAMs on Au(111) ·····················································8
• 2.2.1 Concentration Effect on the Formation of TPP Adlayers in Toluene Solution ··········································································9
• 2.2.2 Co-Adsorption of Binary Mixture ·············································9
• 2.2.3 Displacement Process ·························································10
• 2.3 Characterization Method ·····························································14
• 2.3.1 Scanning Tunneling Microscopy ·············································14
• 2.3.2 Contact Angle Goniometry ···················································14
• 2.3.3 Cyclic Voltammetry ···························································15
• 2.3.4 X-Ray Photoelectron Spectroscopy ·········································15
• 3. Results and Discussion ·····································································16
• 3.1 Effect of Concentration on the Formation of TPP Adlayers on Au(111) Surface ···························································································16
• 3.2 Effect of Immersion Time on the Adlayers of TPP on Au(111) Surface ········18
• 3.2.1 Change of Morphology Formed after Long Term Deposition of TPP Adlayers ········································································18
• 3.2.2 Wettability of TPP Adlayers Regardless of Immersion Time ·············22
• 3.2.3 Electrochemical Behavior of TPP Adlayers ································24
• 3.3 Co-Adsorption of OT and TPP on Au(111) Surface ·······························28
• 3.3.1 Structural Evolution with Increasing the Ratio of OT ·····················28
• 3.3.2 Wettability Change Depending on the Molecular Ratio ···················31
• 3.3.3 Analysis of Redox Profile and Cathodic Desorption According to the Fitted Results ··································································33
• 3.4 Displacement of TPP by DT on Au(111) Surface ··································38
• 3.4.1 Displacement Process of TPP by DT as a Function of Time ··············38
• 3.4.2 Confirmation of Importance of Lateral Stability by Close-Packed DT SAMs Transferred into TPP Solution ·······································45
• 3.4.3 Supporting Evidence of Displacement of TPP by XPS ····················51
• 4. Conclusion ·····················································································59
• References ························································································61
• Abstract in Korean ···············································································68