We investigated the negative differential resistance (NDR) property of self-assembled 4,4-di(ethynylphenyl)-2'-nitro-l-(thioacetyl)benzene ('nitro-benzene'), which has been well known as a conducting molecule [1], Self-assembly monolayers (SAMs) were prepared on Au (111), which had been thermally de...
We investigated the negative differential resistance (NDR) property of self-assembled 4,4-di(ethynylphenyl)-2'-nitro-l-(thioacetyl)benzene ('nitro-benzene'), which has been well known as a conducting molecule [1], Self-assembly monolayers (SAMs) were prepared on Au (111), which had been thermally deposited onto pre-treated $(H_2SO_4: H_2O_2=3:1)$ Si, The Au substrate was exposed to a 1mM solution of 1-dodecanethiol in ethanol for 24 hours to form a monolayer. After thorough rinsing of the sample, it was exposed to a $0.1{\mu}M$ solution of nitro-benzene in dimethylformamide (DMF) for 30 min and kept in the dark during immersion to avoid photo-oxidation. Following the assembly, the samples were removed from the solutions, rinsed thoroughly with methanol, acetone, and $CH_2Cl_2$, and finally blown dry with $N_2$. Under these conditions, we measured the electrical properties of SAMs using ultra high vacuum scanning tunneling microscopy (UHV-STM) and scanning tunneling spectroscopy (STS) [2]. As a result, we confirmed the properties of NDR in between the positive and negative region.
We investigated the negative differential resistance (NDR) property of self-assembled 4,4-di(ethynylphenyl)-2'-nitro-l-(thioacetyl)benzene ('nitro-benzene'), which has been well known as a conducting molecule [1], Self-assembly monolayers (SAMs) were prepared on Au (111), which had been thermally deposited onto pre-treated $(H_2SO_4: H_2O_2=3:1)$ Si, The Au substrate was exposed to a 1mM solution of 1-dodecanethiol in ethanol for 24 hours to form a monolayer. After thorough rinsing of the sample, it was exposed to a $0.1{\mu}M$ solution of nitro-benzene in dimethylformamide (DMF) for 30 min and kept in the dark during immersion to avoid photo-oxidation. Following the assembly, the samples were removed from the solutions, rinsed thoroughly with methanol, acetone, and $CH_2Cl_2$, and finally blown dry with $N_2$. Under these conditions, we measured the electrical properties of SAMs using ultra high vacuum scanning tunneling microscopy (UHV-STM) and scanning tunneling spectroscopy (STS) [2]. As a result, we confirmed the properties of NDR in between the positive and negative region.
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문제 정의
The purpose of this research is to study the application of molecules as a device using the NDR property. Expressly, analyze the electric property (I-V) of the nitro benzene molecule to define the NDR property by STM.
가설 설정
3. (a) The characteristics of current-voltage (I-V) and (b) dl/dV (c) UV/visible spectrophotometer data, energy gap (Eg) of nitro-benzene is 3.3 eV.
3. (a) The characteristics of current-voltage (I-V) and (b) dl/dV (c) UV/visible spectrophotometer data, energy gap (Eg) of nitro-benzene is 3.3 eV.
5 shows the mechanism of tunneling current and NDR. A: In the case of zero voltage, being equilibrium, there is no electron transfer, because the energy level of the other part is closed and the current is zero. B: highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the organic molecule exist over than Fermi level of tip and gold electrode.
In this case, if positive bias is applied on the gold electrode, molecular energy state inclines toward the state of the gold electrode. C: Current reaches to peak value (Vpeak) by tunneling in resonant state between tip and molecule. Resonant state means that local density of state (LDOS) of the tip and molecular energy state are piled up.
D: After resonant ends, current decreases until the applied voltage is increased enough to make thermal electron emission. E: This is the flow of conductive current by the thermal electron emissions.
제안 방법
Because it blocks the aggregation of the nitro benzene molecule, we used 1-dodecanethiol as the base material and measured intrinsic properties of nitro-benzene SAMs [2], Nitro-benzene is also known as a conducting molecule [1]. Therefore, we used nitro-benzene to measure the property of NDR using a self-assembly method in STM In addition, this study produced the vertical junction structure of a STM tip/SAMs/Au (111) substrate using a STM tip. We used the Au (111) substrate as the base substrate and the surface morphology was investigated at the STM mode.
대상 데이터
1. Materials used in this experiment are nitro-benzene that is composed in the Korea Research Institute of Chemical Technology (KRICT) [9]. This material could fabricate a SAMs easily because it contained a thioacetyl functional radical, which could perform a self-assembly onto the surface ofAu(lll).
이론/모형
The STM measurement was performed at room temperature using a UHV-STM (UNISOKU, USM-1200). The vacuum condition is 6x10-8 Torr.
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