• KIEE International Transactions on Electrophysics and Applications
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• 제5C권3호
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• pp.115-118
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• 2005

Currently, molecular devices are reported utilizing active self-assembled monolayers (SAMs) containing the nitro group as the active component, which has active redox centers [1]. SAMs are ordered molecular structures formed by the adsorption of an active surfactant on a solid surface. The molecules will be spontaneously oriented toward the substrate surface and form an energetically favorable ordered layer. During this process, the surface-active head group of the molecule chemically reacts with and chemisorbs onto the substrate In this paper, the electrical properties of the 4'4- di(ethynylphenyl)-2'-nitro-1-benzenethiolate was confirmed. This material is well known as a conducting molecule having possible application to molecular level negative differential resistance (NDR) device. To deposit the self-assembly monolayers onto the gold electrode, the prefabricated Au(1 l l) substrates were immersed into 0.5[mM/l] self-assembly molecule in THF solution. Then, the electrical properties and surface morphologies of 4' 4-di(ethynylphenyl)-2' -nitro-1-benzenethiolate were measured by using the ultra-high vacuum scanning tunneling microscopy (UHV-STM).

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 추계학술대회 논문집 전기물성,응용부문
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• pp.139-141
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• 2005

It is possble to study charge transfer property which is caused by height variation because we can see the organic materials barrier height and STM tip by organic materials energy band gap. Here, we investigated the negative differential resistance(NDR) and charge transfer property of self-assembled 4,4-Di(ethynylphenyl)-2'-nitro-1-(thioacetyl)benzene, which has been well known as a conducting molecule. Self-assembly monolayers(SAMs) were prepared on Au(111), which had been thermally deposited onto pre-treatment($H_{2}SO_{4}:H_{2}O_{2}$=3:1) Si. The Au substrate was exposed to a 1 mM/l solution of 1-dodecanethiol in ethanol for 24 hours to form a monolayer. After thorough rinsing the sample, it was exposed to a $0.1{\mu}M/1$ solution of 4,4-Di(ethynylphenyl)-2'-nitro-1-(thioacetyl)benzene in dimethylformamide(DMF) for 30 min and kept in the dark during immersion to avoid photo-oxidation. After the assembly, the samples were removed from the solutions, rinsed thoroughly with methanol, acetone, and $CH_{2}Cl_{2}$, and finally blown dry with $N_2$. Under these conditions, we measured electrical properties of self-assembly monolayers(SAMs) using ultra high vacuum scanning tunneling microscopy(UHV-STM). The applied voltages were from -1.50 V to -1.20 V with 298 K temperature. The vacuum condition is $6{\times}10^{-8}$ Torr. As a result, we found that NDR and charge transfer property by a little change of height when the voltage is applied between STM tip and electrode.

• Journal of Electrochemical Science and Technology
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• 제14권1호
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• pp.21-30
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• 2023

This work presents a correlation between the behavior of formic acid oxidation (FAO) on various Bi-modified Pt(poly) disk electrodes and their morphologies observed on Bi-modified Pt(111) disk electrodes using electrochemical scanning tunneling microscopy (EC-STM) to understand the effects of Bi on Pt. To distinguish the FAO activities of Bi on Pt and plain Pt around Bi, additional Pt was intentionally deposited using two different routes: direct route and iodine route. In direct route, Pt was directly deposited on Bi islands and plain Pt sites around Bi islands, while in iodine route, Pt was exclusively deposited on Bi islands by protecting plain Pt sites with adsorbed iodine. Thus, a comparison of FAO performances on the two Bi-modified Pt electrodes with additional Pt (deposited in the different ways) disclosed a difference in FAO performances on plain Pt sites and Bi islands. When Bi coverage was ~0.04, the Bi deposits were scattered Bi islands enhancing FAO on Pt(poly). The additional Pt deposits using direct route increased FAO efficiency, while the ones using iodine route slightly decreased FAO current. The EC-STM observations indicated that Pt deposits around Bi islands, not on Bi islands, were responsible for the FAO current increase on Bi-modified Pt(poly). The FAO efficiency on Bi-modified Pt(poly) with a Bi coverage of ~0.25 increased by a factor of 2. However, the additional Pt deposits using the two Pt deposition routes notably decreased the FAO current. The dependency of FAO on Bi coverage was discussed in terms of electronic effect and ensemble effect.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.205-205
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• 2011

The self-assembly of ${\gamma}$-phenylalanine on Au(111) at 150 K was investigated using scanning tunneling microscopy (STM). Phenylalanine can potentially form two-dimensional (2D) molecular networks through hydrogen bonding (through the carboxyl and amino groups) and ${\pi}-{\pi}$ stacking interactions (via aromatic rings). We found that ${\gamma}$-phenylalanine molecules self-assembled on Au(111) surfaces into well-ordered structures such as ring-shaped clusters (at low and intermediate coverages) and 2D molecular domains (intermediate and monolayer coverages), whereas ${\alpha}$-phenylalanine molecules formed less-ordered structure on Au(111). The self-assembly of ${\gamma}$- but not ${\alpha}$-phenylalanine may be related to the flexibility of the carboxyl and amino groups in the molecule. Moreover, as expected, the 2D molecular network of ${\gamma}$-phenylalanine on Au(111) was mediated by a combination of hydrogen bonding and ${\pi}-{\pi}$ stacking interactions.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.26-26
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• 2011

Self-assembled monolayers (SAMs) prepared by sulfur-containing organic molecules on metal surfaces have drawn much attention for more than two decades because of their technological applications in wetting, chemical and biosensors, molecular recognition, nanolithography, and molecular electronics. In this talk, we will present self-assembly mechanism and two-dimensional (2D) structures of various organic thiol SAMs on Au(111), which are mainly demonstrated by molecular-scale scanning tunneling microscopy (STM) observation. In addition, we will provide some idea how to control 2D molecular arrangements of organic SAMs. For instance, the formation and surface structure of pentafluorobenzenethiols (PFBT) self-assembled monolayers (SAMs) on Au(111) formed from various experimental conditions were examined by means of STM. Although it is well known that PFBT molecules on metal surfaces do not form ordered SAMs, we clearly revealed for the first time that adsorption of PFBT on Au(111) at $75^{\circ}C$ for 2 h yields long-range, well-ordered self-assembled monolayers having a $(2{\times}5\sqrt{13})R30^{\circ}$ superlattice. Benzenethiols (BT) SAMs on gold usually have disordered phases, however, we have clearly demonstrated that the displacement of preadsorbed cyclohexanethiol self-assembled monolayers (SAMs) on Au(111) by BT molecules can be a successful approach to obtain BT SAMs with long-range ordered domains. Our results will provide new insight into controlling the structural order of BT or PFBT SAMs, which will be very useful in precisely tailoring the interface properties of metal surfaces in electronic devices.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.355-355
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• 2010

The epitaxial growth of MgO film on Fe(001) has been investigated by scanning tunneling microscopy (STM). After confirming the clean Fe(001)-c($2{\times}2$) substrate by STM, Mg was deposited at room temperature (RT) under $O_2$ partial pressure of $10^{-7}\;Torr$. The MgO was grown as clusters, not as an epilayer even after postannealing at $400^{\circ}C$, as shown in Figure (a). On the contrary, when Mg was deposited on Fe(001)-c($2{\times}2$) at RT and post-oxidized through exposing $O_2$ at partial pressure $10^{-7}\;Torr$, the thin-layered film with some clusters was formed. Extended-annealing at $400^{\circ}C$ reduced the cluster density, and finally the single and epitaxial MgO-c($2{\times}2$) film was formed on Fe(001)-c($2{\times}2$) as shown in Figure (b). This ultrathin MgO film formed on Fe is expected to be applied to many technological applications, such as catalysis, microelectronics, and magnetic devices.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.367-367
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• 2010

The adsorption configurations of S-proline on Ge(100) were studied using scanning tunneling microscopy (STM), density functional theory (DFT) calculations, and high-resolution core-level photoemission spectroscopy (HRCLPES). We identified three adsorption structures of S-proline on Ge(100) through analysis of the STM images, DFT calculations, and HRCLPES results: (i) an 'intrarow O - H dissociated and N dative bonded structure', (ii) an 'O - H dissociation structure', and (iii) an 'N dative bonded structure'. Moreover, because adsorption through the N atom of S-proline produces a new chiral center due to symmetry reduction by N dative bonding, the adsorption configurations have either (R,S) or (S,S) chirality, yielding an (R,S)-'intrarow O - H dissociated and N dative bonded structure' and an (R,S)-'N dative bonded structure', with a preference for reaction at the Re face. This work presents a novel method for generating stereoselective attachment using S-proline molecules adsorbed onto a Ge(100) surface.

• 한국진공학회지
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• 제22권6호
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• pp.285-290
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• 2013

금속 기판 위에 성장한 그래핀은 원자구조와 전자구조 연구에 우수한 기반이 된다. 그래핀은 금소 기판에서 탄소의 surface segregation 이나 chemical vapor deposition으로 성장할 수 있는데, 이 두 방법의 성장 양상에 대한 비교 연구는 아직까지 없었다. 본 연구에서는 surface segregation, 흡착된 에틸렌의 post-annealing, 에틸렌의 high-temperature dose 등 3 방법으로 성장한 그래핀의 성장구조를 주사형 터널링 현미경으로 연구했다. 처음 2종류의 방법에서는 $100nm^2$ 수준의 작은 그래핀 영역이 나타났고, 3 번째 방법에서는 $10^4nm^2$ 보다 큰 그래핀이 육각형 무아레 무늬와 함께 타나났다. 본 연구에서는 에틸렌의 high-temperature dose 방법이 추가적인 분자성장 등에 필요한 넓은 그래핀을 성장하기에 가장 좋은 방법임을 보였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.270-270
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• 2013

We have investigated the self-assembled structures of glutaric acid (HOOC-(CH2)3-COOH) on the Cu(110) surface as a function of coverage using Scanning Tunneling Microscopy (STM). At low coverage, glutaric acid molecules diffuse freely on Cu(110) surface at room temperature, thus they can't form ordered structures at this coverage. However, when we scanned the same area several times, novel structures have been created during scanning due to the field-induced self-assembly. Also, the induced structures are quite stable during continuous scanning process. At 0.25 ML, glutaric acid adsorbs as a bi-glutarate (-OOC(CH2)3-COO-) after annealing to 450 K producing a racemic conglomerate of coexisting mirror domains. Although the molecule is achiral, it forms chiral domains on the surface from adsorption-induced asymmetrization. At 0.5 ML coverage, zigzag structure is observed, and still gltutaric acid adsorbs as a bidentate configuration. This bi-glutarate structure is stable until 650. Finally, at 1ML, glutaric acid adsorbs as a mono-glutarate at room temperature forming close packed structures.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 춘계학술대회 논문집 센서 박막재료 반도체재료 기술교육
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• pp.24-26
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• 2002

In this paper, we discuss the electrical properties of self-assembled (2'-amino-4,4-di(ethynylphenyl)-5'-nitro-l-(thioacetyl)benzene), which has been well known as a conducting molecule having possible application to molecular level NDR device. The phenomenon of negative differential resistance (NDR) is characterized by decreasing current through a junction at increasing voltage. also fabrication of MIM-type molecular electronic and the Molecular Level Using Scanning Tunneling Microscopy