Molecular thermoelectric device comprising self-assembled monolayer formed on double metal electrode, and method for manufacturing same by using underpotential deposition

Abstract

The present invention relates to a molecular thermoelectric device comprising a self-assembled monolayer formed on a double metal electrode in which a heterogeneous metal single atom adsorption layer is formed on a metal by using underpotential deposition (UPD). According to the present invention, a Seebeck coefficient of a saturated hydrocarbon-based monolayer can be improved by up to four times or more while excellent current density can be implemented, and thus can be a basis for implementing excellent thermoelectric performance in a saturated hydrocarbon-based molecular thermoelectric device and, based thereon, additional research and development and industrial applications of the molecular thermoelectric device can be expected.

Description

A molecular thermoelectric device comprising a self-assembled monolayer formed on a double metal electrode and a method for manufacturing the same using a low-potential deposition method

[0001] The present invention relates to a molecular thermoelectric device comprising a self-assembled monolayer formed on a dual metal electrode and a method for manufacturing the same. More specifically, the invention relates to a molecular thermoelectric device comprising a self-assembled monolayer formed on a dual metal electrode in which a heterogeneous metal monolayer adsorption layer is formed on a metal using an underpotential deposition (UPD) method, and a method for manufacturing the same.

[0002] The thermoelectric phenomenon, a physical phenomenon that converts thermal energy into electricity, is receiving significant attention as a field of new and renewable energy research.

[0003] In research on molecular thermoelectric devices using organic compounds, most studies are based on unsaturated / conjugated molecules rich in pi electrons, and saturated hydrocarbons, which have low electrical conductivity, generally exhibit very poor thermoelectric performance. Many plastics used in daily life are also based on saturated hydrocarbon structures; because they lack pi electrons, electricity does not flow, and therefore they do not serve as good thermoelectric materials. However, if a structure with repeating unsaturated hydrocarbon structures is introduced into the material, it is possible to make plastics conduct electricity just like metals, which forms the basis for good thermoelectric materials.

[0004] As such, saturated molecular materials exhibit very low thermoelectric performance, which generally limits their application in organic molecular thermoelectric devices; furthermore, existing research on the thermoelectric voltage of saturated molecules has sometimes misdefined the thermoelectric mechanism. Research and development in molecular thermoelectric device technology can contribute not only to verifying charge transport mechanisms across molecular junctions under different temperature gradient conditions but also to the development of molecular-scale devices with thermoelectric performance.

[0005] Furthermore, the thermoelectric performance evaluation system for liquid metal-based monomolecular films is the first technology researched and developed by the inventors (Nano Lett. 2018, 18 (12), 7715-7718). Using this system, the thermoelectric performance of monomolecular films with various chemical structures can be easily and rapidly tested. Based on this, the thermoelectric performance of monomolecular films was verified, and the results showed that the thermoelectric performance of monomolecular films based on saturated hydrocarbons was not very good. Therefore, performance improvement is urgently needed for future industrial applications. In particular, a common problem faced in the field of molecular thermoelectric devices is that increasing the Seebeck coefficient leads to a decrease in electrical conductivity.

[0006] Underpotential deposition (UPD) is a technique for introducing a single atomic layer of a different type of external metal onto a metal electrode. This technology is utilized in the development of heterogeneous catalysts and various sensors, and it allows for the control of energy at the electrode interface.

[0007] The inventors of the present invention confirmed that the two problems mentioned above can be solved simultaneously by using underpotential deposition (UPD) technology and came to complete the present invention.

[0008] In order to solve the above-mentioned problems, the present invention aims to provide a molecular thermoelectric junction capable of improving thermoelectric performance while simultaneously achieving excellent electrical conductivity in saturated molecular materials such as saturated hydrocarbons, and a molecular thermoelectric device using the same.

[0009] To solve the above problem, the present invention provides a molecular thermoelectric junction comprising a metal substrate, a metal monolayer deposited on the metal substrate, and a self-assembled monolayer (SAM) formed on the metal monolayer.

[0010] According to the present invention, the monomolecular assembly layer (or also expressed as "self-assembled monomolecular layer") may be a monomolecular assembly layer formed by self-assembling molecules comprising an anchor group capable of forming a coordination bond or a chelate bond with the metal single atom layer.

[0011] According to the present invention, the anchor group may be a functional group comprising sulfur (S), oxygen (O), phosphorus (P), carbon (C), nitrogen (N), selenium (Se), or a combination thereof.

[0012] According to the present invention, the anchor group may be one or more selected from the group consisting of thiol (-SH), selenol (-SeH), carboxylic acid or carboxylate (-COOH / -COO), phosphonic acid or phosphonate (-PO3H₂ / -PO₃), siloxy (-Si-O-), carbene (-C:), and amine (-NH2 / -NR2).

[0013] According to the present invention, the molecule may include a molecular backbone composed of a saturated hydrocarbon, an unsaturated hydrocarbon, an aromatic, or a mixture thereof.

[0014] According to one embodiment of the present invention, the monomer assembly layer is n-alkanethiol (HSC n ) molecule or n-alkanic acid (HO2CC n-1 It may be a monomolecular assembly layer formed by self-assembly.

[0015] According to the present invention, the metal monolayer is characterized by being formed on a metal substrate through an underpotential deposition (UPD) method.

[0016] According to one embodiment of the present invention, the metal substrate is an atomic-level ultrathin template of gold or silver (Au) made by template-stripping (TS). TS or Ag TS It can be.

[0017] According to the present invention, the metal monolayer may be composed of Cu, Ag, Au, Pd, Pt, Ni, Co, Fe, Mn, or an alloy thereof.

[0018] According to one embodiment of the present invention, the metal single atomic layer may be a copper (Cu) single atomic layer.

[0019]

[0020] In addition, the present invention provides a molecular thermoelectric element comprising a first electrode, a second electrode, and a self-assembled monolayer.

[0021] The first electrode is characterized as being a bimetallic (BE) electrode composed of a metal substrate and a metal monolayer deposited on the metal substrate.

[0022] The above self-assembled monolayer is characterized by being composed of a molecule comprising an anchor group capable of coordination bonding or chelation bonding with the metal single atom layer.

[0023] According to the present invention, the anchor group may be a functional group comprising sulfur (S), oxygen (O), phosphorus (P), carbon (C), nitrogen (N), selenium (Se), or a combination thereof.

[0024] According to the present invention, the anchor group may be one or more selected from the group consisting of thiol (-SH), selenol (-SeH), carboxylic acid or carboxylate (-COOH / -COO), phosphonic acid or phosphonate (-PO3H₂ / -PO₃), siloxy (-Si-O-), carbene (-C:), and amine (-NH2 / -NR2).

[0025] According to the present invention, the molecule may include a molecular backbone composed of a saturated hydrocarbon, an unsaturated hydrocarbon, an aromatic, or a mixture thereof.

[0026] In addition, the self-assembled monolayer is n-alkanethiol (HSC n ) molecule n-alkanic acid (HO2CC n-1 It is characterized by being a monomolecular assembly layer formed by self-assembly.

[0027] According to the present invention, the metal monolayer is formed on a metal substrate through an underpotential deposition (UPD) method to form a bimetallic (BE) electrode.

[0028] According to one embodiment of the present invention, the second electrode is liquid metal eutectic gallium-indium (EGaIn), and is characterized by having a conductive thin gallium oxide (Ga2O3) film layer formed on its surface by a self-passivating reaction.

[0029] According to one embodiment of the present invention, the metal substrate is an atomic-level ultrathin template of gold or silver (Au) made by template-stripping (TS). TS or Ag TS It can be.

[0030] According to one embodiment of the present invention, the -S or -COOH of the self-assembled monolayer is characterized as an anchor group that binds to the metal monolayer.

[0031] According to the present invention, the metal monolayer may be composed of Cu, Ag, Au, Pd, Pt, Ni, Co, Fe, Mn, or an alloy thereof.

[0032] According to one embodiment of the present invention, the metal single atomic layer may be a copper (Cu) single atomic layer.

[0033] According to the present invention, the molecular thermoelectric element is characterized by implementing thermoelectric properties in which the Seebeck coefficient (S) and electrical conductivity (J) are simultaneously improved.

[0034] In addition, the above thermoelectric properties are characterized by being attributed to an energy level alignment mechanism induced by a gateway orbital (GWO) formed by hybridization between the anchor group and the orbitals of the metal single atomic layer.

[0035] The present invention can provide a molecular thermoelectric junction and a molecular thermoelectric device having excellent current density, in which the Seebeck coefficient of a saturated hydrocarbon-based monolayer is improved by up to four times or more using an electrode (UPD electrode) formed using low-potential deposition technology.

[0036] According to the present invention, a foundation is established to realize excellent thermoelectric performance in a saturated hydrocarbon-based molecular thermoelectric device, thereby enabling further research and development and industrial application of the molecular thermoelectric device.

[0037] FIG. 1(a) is a schematic diagram comparing the structures of a large-area molecular junction according to the present invention, wherein the self-assembled monolayer (SAM) formed on a monometallic (ME) electrode and the self-assembled monolayer (SAM) formed on a bimetallic (BE) electrode, respectively, and (b) is an alkyl derivative used to test the thermoelectric effect of the molecular junction according to one embodiment of the present invention, wherein the alkyl derivatives are an n-alkanethiol having a thiol or a carboxylic acid fixation group (HSC n ) and n-alkanes (HO2CC n-1 )am.

[0038] Here, ME is an ultrathin template made of gold or silver (Au) using TS (template-stripping). TS / Ag TS ) and BE is Au covered with a Cu single-atom adsorption layer via underpotential deposition (UPD). TS EGaIn / Ga2O3 is a eutectic Ga-In metal in which a thin film layer of conductive gallium oxide (Ga2O3) is formed on the surface through a self-passivating reaction.

[0039] FIG. 2(a) is an Au according to one embodiment of the present invention TS This is the current-voltage graph result observed when forming a Cu single-atom adsorption layer via Underpotential Deposition (UPD), and if a voltage higher than the UPD is applied, the bulk Cu becomes Au TS It is formed on the surface and is called overpotential deposition (OPD). (b) is Au TS The scheme for the formation of a Cu monolayer formed via the UPD method shown above demonstrates that it can also be removed via an electrochemical method. (c) High-resolution spectrum of the Cu 2p energy region of the Cu UPD monolayer confirmed by photoelectron spectroscopy (XPS), with a gap of approximately 20.2 eV between the two peaks.

[0040] FIG. 3(a) shows the SC of BE at various temperature differences (ΔT, K) according to one embodiment of the present invention. n (n=8) and O2CC n-1 (n=8) This is a representative histogram of the thermovoltage (ΔV, μV) for SAM. (b) is a graph showing the change in thermovoltage according to the applied temperature difference (ΔT, K). (c) is a graph of the Seebeck coefficient (S, μV / K) calculated from the thermovoltage measurement, showing (O2CC of BE and ME). n-1 and SC n SAM (AgTS and Au TS ) respective Seebeck coefficient values), it can be confirmed that the Seebeck coefficient changes depending on the change in the chain length of the molecule. (d) is a graph showing that the Seebeck coefficient is improved by up to 4 times when using a BE electrode compared to ME according to the present invention.

[0041] FIG. 4(a) is a molecular junction setup used for DFT quantum calculation according to one embodiment of the present invention, wherein each electrode 1 (Au / SC n / Au), electrode 2 (BE / SC n / Au), Electrode 3 (BE / O2CC n-1 / Au) (n is the number of carbon atoms in the alkyl skeleton, with different lengths). (b) to (d) are graphs of transmission functions that vary depending on the molecular junction setup, i.e., the presence or absence of a Cu monolayer (ME, BE) and whether the fixed group is a thiol or a carboxylic acid. (e) is E at 0.5 eV. F This is a graph comparing the average Seebeck coefficient values ​​of the above electrodes 1 to 3.

[0042] The present invention will be described in more detail below.

[0043] The present invention relates to a molecular thermoelectric device capable of realizing excellent thermoelectric performance based on saturated hydrocarbons, wherein (i) in terms of configuration, the main feature is the use of a UPD electrode, and (ii) in terms of effect, the Seebeck coefficient of a monomolecular film based on saturated hydrocarbons is improved by up to 4 times or more and the current density is also improved by using a UPD electrode.

[0044]

[0045] In terms of structure, the present invention is as shown on the left side of (a) of FIG. 1 below, Au TS / SC nIt is composed of / Ga2O3 / EGaIn, and compared to conventional thermoelectric junctions, Au is produced by underpotential deposition (UPD). TS A dual electrode (Au) further comprising a Cu single atomic layer deposited on the surface TS - It is characterized by being a Cu single atomic layer, Cu UPD electrode (right side of Figure 1 (a) below), and is characterized by applying such a thermoelectric junction as a molecular thermoelectric element.

[0046]

[0047] <Manufacture of UPD electrode according to the present invention>

[0048] To form a Cu UPD electrode according to the present invention, a template-stripped gold (Au) is formed using an underpotential deposition (UPD) method. TS It was manufactured by forming a single Cu atomic layer on )

[0049] Gold (Au TS A three-electrode system consisting of copper wire and platinum wire was used as the working electrode, reference electrode, and counter electrode, respectively, and electroplating was performed in a saturated N2 solution containing 1 mM CuSO4 and 0.1 M H2SO4(aq). Before use, the copper wire was sanded and its surface cleaned by immersing it in diluted nitric acid, and the potential was set to the bulk deposition peak (approx. 0.02 V vs. Cu) for 60 seconds. +2 The value was maintained at a positive value. The bimetallic electrode (BE) obtained through this process was removed from the solution under potential control, rinsed with a large amount of ethanol, and then dried with an N2 stream.

[0050] In the present invention, a template-stripped Au substrate (Au TS The reason for using ) is that the surface is very flat compared to commonly used Au substrates, so it is possible to secure high-quality Cu UPD electrodes.

[0051] Cu UPD enables the fabrication of a Cu single-atom layer surface. Although Cu generally oxidizes very easily in air, which can cause problems when depositing molecular layers on metal surfaces, the Cu single-atom layer surface fabricated with UPD according to the present invention does not oxidize easily, unlike bulk Cu, and thus has the advantage of stably fixing molecular layers onto electrodes.

[0052] In order to confirm the effect of the Cu UPD electrode according to the present invention in a molecular thermoelectric device, the structure of the molecular layer and the upper electrode, etc., and the respective thermoelectric junction structure were made identical (Fig. 1).

[0053] In addition, the Cu UPD electrode was prepared by electrochemical method as shown in Fig. 2(b), and the formation of Cu UPD was confirmed by checking the current peak generated when removing Cu UPD by electrochemical method (Fig. 2(a)) or by X-ray photoelectron spectroscopy (XPS, Fig. 2(b)).

[0054]

[0055] <Preparation of a molecular thermoelectric junction according to the present invention>

[0056] Cu UPD is an Au substrate (Au TS It is an electrode composed of two metal components in that it is formed on the surface. Therefore, the Cu UPD electrode according to the present invention is referred to as a bimetallic electrode, BE, whereas an electrode composed only of gold or silver is referred to as a monometallic electrode, ME.

[0057] As shown in Fig. 1(b) below, a monolayer was formed on a Cu UPD electrode. In this case, the molecules used according to one embodiment of the present invention each have two anchor groups, thiol and carboxylic acid.

[0058] The inventors of the present invention fabricated a thermoelectric junction molecular junction containing a monomolecular film formed on a Cu UPD electrode and measured the Seebeck coefficient using a Seebeck coefficient measurement method utilizing a system using a gallium-indium eutectic alloy (EGaIn) first developed by the inventors of the present invention (Fig. 1 (b)).

[0059] Figure 3 shows the results of such thermoelectric measurements, and it is confirmed that the Seebeck coefficient is improved by up to 2 times when a thiol anchor is present and by up to 4 times or more when a carboxylic acid anchor is present in the thermoelectric assembly according to the present invention that introduces BE, i.e., Cu UPD electrodes, compared to ME.

[0060] In the present invention, after the above UPD process, the substrate modified by UPD was immediately transferred to a solution containing an acid or thiol derivative (1 mM; ethanol and n-hexadecane for alkanethiols and alkanates, respectively), and all samples were performed in the solution under an N2 atmosphere for at least 12 hours. The generated SAMs of alkanethiols and alkanates were rinsed with ethanol and hexane, respectively, and all samples were dried by gently blowing Na before characterization.

[0061]

[0062] <Mechanism for Improving the Seebeck Coefficient in a Molecular Thermoelectric Device Using a UPD Electrode According to the Present Invention>

[0063] The mechanism of the improvement in the Seebeck coefficient following the introduction of UPD electrodes was identified through Density Functional Theory (DFT) calculations.

[0064] When a molecule forms a chemical bond with an electrode surface, the molecule's orbitals undergo orbital hybridization with atoms on the electrode surface, thereby creating a new energy level. This is called a Gateway orbital (GWO).

[0065] Figures 4(b) to 4(d) show the results of quantum calculations of the GWO depending on the presence or absence of the Cu UPD electrode and the type of the molecular anchor group, respectively, and the peak indicated by the dotted line in the figure represents the energy resonance corresponding to the GWO. It can be confirmed that the GWO energy level becomes sharper upon the introduction of the Cu UPD. In particular, it can be observed that the sharpness of the GWO energy level is greater in the carboxylic acid anchor than in the thiol anchor, which is because the bond between the carboxylic acid and the Cu monolayer is relatively weaker. According to the Mott formula, the sharper the shape of the energy level of the molecular orbital located near the Fermi level, the greater the Seebeck coefficient increases. The trend of the Seebeck coefficient inferred by DFT (Figure 4(e)) is similar to the trend of the experiment according to the present invention. Therefore, the cause of the high Seebeck coefficient in the Cu UPD electrode is explained.

[0066]

[0067] Characterization of the low-voltage thermoelectric joint according to the present invention

[0068] First, when a molecule is adsorbed onto a substrate, orbital mixing occurs between the molecule and surface atoms, creating new energy states within the gap. In molecular electronics, understanding the characteristics of these new energy states induced by adsorption is crucial for investigating charge transport behavior and developing functions. The Seebeck coefficient (S) is closely related to the shape of transport resonances resulting from molecular orbitals accessible at the Fermi level. Generally, for molecular junctions where a single energy level controls charge transport and there is a bond between the molecule and the electrode, S can be estimated using the Mott formula (Equation 1) coupled with a Lorentz-shaped transfer function (Equation 2).

[0069] Equation (1)

[0070] (2)

[0071]

[0072] Here, E MO is the frontier molecular orbital energy, Γ1 and Γ2 are molecular orbital expansions resulting from the top and bottom contact of the junction, respectively, and k B ε is the Boltzmann constant, T is the junction temperature, e is the electron charge, and E F is the Fermi level.

[0073]

[0074] Molecular thermotransfer primarily changes the chemical structure of active molecules to E F and E MOWhile some studies focus on molecular approaches that control the energy offset (ΔE) between Γ and enhance S, a few studies adopt non-molecular approaches that focus specifically on the identity of the electrode. In previous studies, changes in the S value of fullerene molecules were observed as the top electrode of a single-molecule junction changed from gold to silver to platinum, and these observations indicated that the ΔE value changed due to the different Fermi levels of the metals. Additionally, another study reported that the S value of benzenedithiol changed from 7.4 to -12.1 μV / K after replacing the gold electrode with nickel. Changes in the magnitude and polarity of S can be explained by strong spin-splitting hybridization between the HOMO and the d-band of nickel, which caused a change in ΔE and a shift in identity of accessible orbitals from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO).

[0075]

[0076] In addition to single-metal materials, bimetal materials (electrode materials composed of two different metals in the form of a layer or alloy) can provide insights into how to engineer energy structures at molecular junctions. Undefined voltage deposition (UPD) is an electrochemical process in which an entire single layer of two different metal materials is deposited onto a substrate at a potential lower than predicted by the Nernst equation due to the difference in work functions. This technique serves as a powerful means for creating bimetal materials and investigating the influence of the adsorption layer of the second metal. Changes in the electronic structure of the molecular-electrode interface via UPD have been used to control molecular adsorption affinities, heterocatalytic properties, and plasmonic properties. Recently, UPD-based bimetal electrodes have also been used to enhance the electrical conductivity of junctions. Furthermore, modifying a gold electrode into a silver or copper UPD resulted in a 40–60-fold increase in the conductivity of alkanes compared to the unmodified electrode, which is attributed to a smaller ΔE induced by the d-band shift and stronger bonding between the molecule and the electrode.

[0077] The inventors of the present invention confirmed how a UPD-based bimetallic electrode (BE) affects the thermoelectric properties of a self-assembled monolayer (SAM)-based junction (Fig. 1).

[0078] BE is Cu-UPD / Au TS As gold (Au TS A UPD Cu adsorption layer was introduced on the surface. In addition, n-alkanethiol (HSC n ; n = 4, 6, 8, 10 or 12) and n-alkanic acid (HO2CC n-1 ; n = 8, 10, 12 or 14) using BE and single metal electrode (ME), Au TS or Ag TS SAM was formed on the surface (Fig. 1 (b)).

[0079] Measurements of the junction using eutectic Ga-In (EGaIn) technology (Fig. 1(a)) showed that S increased by more than four times when ME was replaced with BE. First-principles quantum transport calculations indicated that the presence of the Cu UPD layer E F This means that it significantly changes the shape and / or location of the transmission resonance corresponding to the nearby gateway orbital (GWO).

[0080] In addition, the inventors of the present invention conducted experiments focusing on n-alkanethiols and n-alkanes for the following reasons: (i) n-alkanes are Cu-UPD / Au TS BE and Ag TS Forming layers in all ME, and n-alkanethiols are Cu-UPD / Au TS BE and Au TS This is because the effect of UPD on thermoelectric properties can be simply isolated by forming a layer in all MEs. (ii) In addition, the Seebeck coefficient of SAM in MEs is already widely known from prior research as well as from the inventors' previous research results, and (iii) their transport mechanism is well defined.

[0081] Figure 2(a) shows Au in an N2-saturated solution containing 1 mM CuSO4 and 0.1 M H2SO4. TS These are cyclic voltammetry (CV) curves for UPD and overvoltage deposition (OPD) of the Cu adsorption layer on the substrate.

[0082] Distinct peaks corresponding to UPD (A1 and A2 for deposition, and D1 and D2 for removal) and OPD (B1 and C1 for deposition and removal, respectively) were observed, which is consistent with previously known research results and literature.

[0083] Figure 2(b) illustrates the deposition and removal processes during reduction and oxidation, respectively. The presence of a single-atom Cu adsorption layer was confirmed via X-ray photoelectron spectroscopy (XPS). The Cu 2p spectrum exhibited doublet peaks at 931.9 and 951.8 eV, which correspond to Cu 2p, respectively. 3 / 2 and Cu 2p 1 / 2 Corresponds to (Fig. 2(c)). Cu 2P for the Cu adsorption layer on gold 3 / 2 The binding energy of was about 0.7 eV lower than that of bulk Cu (932.6 eV), which is consistent with previous research results regarding Cu UPD, and the Cu 2p region represents the Cu(0) or Cu(I) species. In addition, the relative atomic ratios of Cu and Au atoms were 15% and 85%, respectively, which is also consistent with previous research results.

[0084]

[0085] In addition, the inventors of the present invention formed a SAM using a conventionally known method and characterized it with XPS.

[0086] After SAM is formed in BE, Cu 2P 3 / 2 and Cu 2p 1 / 2 The binding energy of the peak shifts slightly to a positive value, and in the case of the SC8 molecule, the S 2p signal is identified by doublet peaks observed at 162.1 and 163.3 eV, which are S 2p, respectively. 3 / 2 and 2p1 / 2 This is attributed to. This binding energy is similar to the binding energy for a similar SAM on a bulk copper substrate.

[0087] The C 1s XP spectrum of HO2CC7SAM in BE was confirmed to show two peaks at 284.5 and 287.3 eV, assigned to the alkyl carbon and the bonded carboxylate group, respectively. No signal characteristics of the free carboxylic acid (~288.5 eV) were detected, indicating that the SAM of the alkanic acid was well formed on the surface of BE. The single bond energy of O 1s was observed at 531.3 eV, suggesting symmetric bonding of the carboxylate group to BE, which is similar to the case of silver.

[0088]

[0089] The inventors of the present invention used an EGaIn system method to form a junction of a substrate / SAM / Ga2O3 / EGaIn structure (substrate = ME or BE, where / and / represent covalent bonds and van der Waals interfaces, respectively) and obtained thermal voltage (ΔV, μV) data at various temperature differences (ΔT = 4, 8, 12, 15, or 20 K).

[0090] All SAMs tested in this invention exhibit positive S values ​​(Fig. 3(c)), which means that HOMOs dominate transport. The SAMs of alkyl backbones generally exhibit a linear regression of S as molecular length increases.

[0091] Similar trends were observed in SAM regardless of electrode type (ME vs. BE) and anchor group (-COOH vs. -SH). BE / O2CC -1 and BE / SC n The S values ​​of are in the range of 13.3 to 6.4 μV / K and 8.6 to 5.0 μV / K, respectively. The S values ​​of BE are up to approximately 4.3 times and 1.8 times higher than the S values ​​of ME for alkanic acid and alkanethiolate SAM, respectively (Fig. 3(d)).

[0092] It was confirmed that the slope of the length dependence plot changed at the point near n = 10, similar to the trend of alkanethiolate SAM above gold.

[0093]

[0094] The work function of the Cu-UPD / Au substrate is 5.2 eV, which is between the work functions of gold (5.5 eV) and copper (4.6 eV). As the work function is lower, ΔE becomes smaller and consequently S decreases, which is in contrast to the present invention.

[0095] When alkyl molecules are adsorbed onto a metal, a new gap state called a chemisorbence-induced gap state or GWO appears. This new state depends primarily on the structure of the metal and the anchor group. To investigate the interaction between the single-atom Cu adsorption layer and the new state, theoretical simulations were performed using density functional theory (DFT) and quantum transport calculations.

[0096] In molecular junctions formed by the parallel arrangement of molecules, different molecules may have different contact configurations with the electrodes, so the T(E) values ​​may differ. In a SAM where N molecules are connected in parallel, T for molecule j j In the case of (E), the mean S is explained as follows.

[0097] Equation (3)

[0098] Here And, is, is the Fermi-Dirac probability distribution function and T is the temperature. In Equation (3), the electrical conductivity G and the Seebeck coefficient S of each molecule with different electrode / molecular configurations must all be calculated to obtain the average S (S = SG / G) for parallel molecular arrangements. Therefore, a series of junctions with different contact configurations were constructed, and T(E) for each junction was calculated, and then S was obtained using Equation (3).

[0099] FIG. 4(a) shows 1 (Au / SC) with different lengths (n = 2, ..., 18). n It shows the average T(E) for a set of structures consisting of an alkanethiol wire sandwiched between two electrodes denoted as / Au). As can be seen in Fig. 4(b), n-alkanethiolate exhibits a relatively wide energy gap, ~9 eV, between the HOMO and LUMO, consistent with previous research results. Due to the interaction between the contact sulfur atoms within the molecule and the electrode atoms at the Au / alkanethiol / Au junction, the DFT Fermi energy (E F An additional state was formed within the HOMO-LUMO gap at -0.5 eV (black dashed line in Fig. 4(b)) compared to -0.5 eV (= 0 eV). This state is mainly attributed to the presence of sulfur atoms and is called GWO. To investigate the origin of this transport function, we also performed T(E) calculations for three different junctions: Au / C4 / Au, Au / SC4 / Au, and Au / SC4S / Au.

[0100] Clearly, a new transport resonance was formed in the energy gap of the Au / C4 / Au junction when a sulfur atom was present at the terminal. Furthermore, calculations of the local density of states (LDOS) around this resonance for all junctions of different lengths showed that the charge density was localized to the terminal sulfur atom, and that the GWO due to this atom E F It was confirmed that it was in a nearby transport resonance.

[0101]

[0102] The average S of molecules of different lengths was calculated using Equation (3) from the DFT T(E) values. The S of the alkanethiolates decreased with length. This is because the width of the GWO state increases with the length of the alkane chain. Since the Seebeck coefficient is proportional to the slope of T(E), the increase in the width of the GWO state with length reduces the slope of T(E) and thus reduces S.

[0103] As shown in Fig. 3(c), there is a transition in the length-dependent gradient at n = 10, and calculations show that the resonance due to the GWO state becomes wider as the junction length increases. Consequently, the decrease in S with length is faster when the resonance is sharp, and slower when the resonance is wider. Additionally, the resonance approaches the Fermi energy as the molecular length increases. This further reduces the rate of decrease in S with length.

[0104] These two effects combine, so S initially decreases at a faster rate, but at longer junctions, the rate of decrease slows down, causing Au TS SC of n The two different length dependencies observed in SAM can be understood. An investigation into the intermolecular packing effect for S revealed that the permeability plots of alkanethio-based junctions with different intermolecular distances were nearly identical over a broad energy range around the Fermi level, indicating that the role of intermolecular interactions in the thermal power of these molecules is negligible.

[0105] In addition, as a result of calculating the DFT T(E) value for the junction formed by the Cu-coated bottom gold electrode as shown in Fig. 4(c), the GWO state is BE / SC n It was also formed in the / Au junction. The energy around the GWO resonance energy showed that the charge density was localized to both the terminal sulfur atom and the Cu atom, which implies that this GWO state is due to hybridization between the orbitals of the terminal sulfur atom and the Cu layer. The width of the resonance due to this GWO state was smaller than that of the corresponding n-alkanethiolate with a similar length in Au without the Cu layer.

[0106] Consequently, the slope of T(E) was steeper in the Au / Cu BE, and Au / SC n BE / SC rather than / Au junction n It led to a higher S at the / Au junction.

[0107] Furthermore, in the case of the carboxylic acid anchor system, a steep slope of T(E) close to the GWO state occurred due to the weak interaction between -COO- and the Cu layer (Fig. 4(d)), resulting in a high S. Fig. 4(e) shows E for the various junctions shown in Fig. 4(a). F Compare the S values ​​at -0.5 eV (black dashed lines in Figs. 4 (b) to (d)). BE / O2CC n-1 While the / Au junction showed the highest S value, the Au / SC n The / Au junction showed the lowest S, which is consistent with (c) of Fig. 3.

[0108]

[0109] In addition, the inventors of the present invention verified the existence of a GWO state occurring in the interaction between two anchor groups and BE by measuring the current density (J).

[0110] DFT calculation is BE / SC n and Au ME / SC n GWO and E in the system F Since there was no significant difference in the energy offset between them, BE / SC n The conductivity of the system is ME / SC n Assuming that the system would be identical, to verify this, log|J|-V was determined for the thioleate (HSC8) and alkanic acid (HO2CC7) SAMs of the same alkyl backbone in BE and ME, respectively, and the SAM in BE (0.51 ± 0.46 A / cm²) 2 ) and ME (0.58 ± 0.24 A / cm 2 It was confirmed that the loglJl values ​​at 0.5 V for ) were indistinguishable from each other.

[0111] Furthermore, in contrast to the results for thiolet SAM, when Ag ME was replaced with BE, the loglJl values ​​of HO2CC7SAM at 0.5 V ranged from -0.54 ± 0.95 to 0.73 ± 0.94 A / cm. 2It increased. Ultimately, for alkanes, both S and J values ​​increased in BE compared to ME.

[0112]

[0113] As examined above, the present invention confirms and derives the influence of UPD on the thermoelectric properties of alkyl SAM-based junctions, wherein Au TS It can be confirmed that the Seebeck coefficient S is improved by up to 4 times or more by introducing a single-atom Cu layer into the substrate through UPD.

[0114] Furthermore, in the additional analysis of the present invention, DFT calculations confirm that the resonance peak of the GWO resulting from hybridization between the anchor group and the Cu atomic layer orbital plays a significant role in enhancing the thermoelectric power of the molecular junction, and that this effect is largely dependent on the selection of the anchor group (thiol versus carboxylic acid).

[0115] According to the present invention, a foundation is established to realize excellent thermoelectric performance of a saturated hydrocarbon-based molecular thermoelectric device, thereby enabling further research and development and industrial application of the molecular thermoelectric device.

Claims

1. A metal substrate; a metal monolayer deposited on the metal substrate; and A molecular thermoelectric junction comprising: a self-assembled monolayer (SAM) formed by self-assembling the above-mentioned metal single-atom layer into a molecule comprising an anchor group capable of forming a coordination bond or a chelate bond.

2. In Paragraph 1, A molecular thermoelectric junction characterized in that the metal monolayer is formed on a metal substrate through an underpotential deposition (UPD) method.

3. In Paragraph 1, A molecular thermoelectric conjugate characterized in that the above anchor group is a functional group comprising sulfur (S), oxygen (O), phosphorus (P), carbon (C), nitrogen (N), selenium (Se), or a combination thereof.

4. In Paragraph 3, A molecular thermoelectric conjugate characterized in that the above anchor group is one or more selected from the group consisting of thiol (-SH), selenol (-SeH), carboxylic acid or carboxylate (-COOH / -COO), phosphoic acid or phosphonate (-PO3H₂ / -PO₃), siloxy (-Si-O-), carbene (-C:), and amine (-NH2 / -NR2).

5. In Paragraph 1, A molecular thermoelectric junction characterized by comprising a molecular backbone composed of a saturated hydrocarbon, an unsaturated hydrocarbon, an aromatic, or a mixture thereof.

6. In Paragraph 1, A molecular thermoelectric junction characterized in that the above-mentioned metal single atomic layer is composed of Cu, Ag, Au, Pd, Pt, Ni, Co, Fe, Mn, or an alloy thereof.

7. In Paragraph 6, A molecular thermoelectric junction characterized in that the metal single-atom layer is a copper (Cu) single-atom layer.

8. The metal substrate is an atomic-level ultrathin template of gold or silver (Au) made by template-stripping (TS). TS or Ag TS A molecular thermoelectric junction characterized by being ).

9. A molecular thermoelectric element comprising: a first electrode; a second electrode; and a self-assembled monolayer; wherein The first electrode is characterized as being a bimetallic (BE) electrode composed of a metal substrate and a metal monolayer deposited on the metal substrate, and A molecular thermoelectric element characterized in that the self-assembled monolayer comprises a molecule having an anchor group capable of coordination bonding or chelation bonding with the metal single-atom layer.

10. In Paragraph 9, A molecular thermoelectric device characterized in that the second electrode is liquid metal eutectic gallium-indium (EGaIn) and a conductive gallium oxide (Ga2O3) thin film layer is formed on the surface by a self-passivating reaction.

11. In Paragraph 9, A molecular thermoelectric element characterized in that the above anchor group is a functional group comprising sulfur (S), oxygen (O), phosphorus (P), carbon (C), nitrogen (N), selenium (Se), or a combination thereof.

12. In Paragraph 11, A molecular thermoelectric element characterized in that the above anchor group is one or more selected from the group consisting of thiol (-SH), selenol (-SeH), carboxylic acid or carboxylate (-COOH / -COO), phosphoic acid or phosphonate (-PO3H₂ / -PO₃), siloxy (-Si-O-), carbene (-C:), and amine (-NH2 / -NR2).

13. In Paragraph 9, The metal substrate above is an atomic-level ultrathin template of gold or silver (Au) made by template-stripping (TS). TS or Ag TS A molecular thermoelectric device characterized by being ).

14. In Paragraph 9, A molecular thermoelectric element characterized in that the above-mentioned metal single atomic layer is composed of Cu, Ag, Au, Pd, Pt, Ni, Co, Fe, Mn, or an alloy thereof.

15. In Paragraph 14, A molecular thermoelectric junction characterized in that the metal single-atom layer is a copper (Cu) single-atom layer.

16. In Paragraph 9, The above molecular thermoelectric element is characterized by exhibiting thermoelectric properties in which the Seebeck coefficient (S) and electrical conductivity (J) are simultaneously improved.

17. In Paragraph 16, A molecular thermoelectric device characterized in that the above thermoelectric properties are attributed to an energy level alignment mechanism induced by a gateway orbital (GWO) formed by hybridization between the anchor group and the orbitals of the metal single atomic layer.

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