JP2008021685A - Molecular element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel molecular element which can be switched by applying an electric field externally while avoiding thermal rotation of metal-including fullerene leading to blockage of switching even under a high temperature of 13 K or above. <P>SOLUTION: The molecular element 10 comprises a first electrode 1, a self-organization monomolecular film 2 arranged on the first electrode 1, a metal-including fullerene 3 arranged on the self-organization monomolecular film 2, and a second electrode 4 arranged on the metal-including fullerene 3 while spaced apart by a predetermined distance wherein the self-organization monomolecular film has a thickness of 1.2 nm or less. The self-organization monomolecular film 2 consists of a first functional group chemisorbed to a metal atom becoming a first electrode 1, and a second functional group bonding to the first functional group. The molecular element 10 operates as a switching element or a memory element at 65.1 K. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electronic device and an optical device having a size of a nanometer (nm) unit, and more particularly to a molecular element useful as a switching element or a memory element.

  Technology for miniaturizing semiconductor elements has been developed, but the miniaturization has physical limitations. As a next-generation device for overcoming the limit of miniaturization of semiconductor devices, research on molecular devices using so-called functional molecules is underway. Carbon nanotubes and fullerenes are known as materials for such molecular elements. Metal-encapsulated fullerene is a functional molecule in which a metal atom is encapsulated inside a fullerene shell made of carbon. Many researchers have confirmed the operation of switches using metal-encapsulated fullerenes because of the polarization and polarity of the electronic state in the molecule due to charge exchange between the fullerene shell and the encapsulated metal atoms, that is, the dipole moment. Have tried.

In the nonpatent literature 1, the present inventors reported the switching phenomenon of the molecular element using metal inclusion fullerene for the first time in the world. In the molecular device using metal-encapsulated fullerene, a self-assembled monomolecular film (SAM) composed of octanethiol is formed on Au (111), and Tb @ C ₈₂ is disposed as the metal-encapsulated fullerene on the film structure. It is. Scanning tunneling spectroscopy (STS) results measuring was performed, switching phenomenon due to the orientation of the dipole moment of Tb @ C ₈₂ was observed for the first time at 13K cryogenic. In the observed current-voltage characteristics, hysteresis and negative differential conductance due to differences in the voltage sweep direction were also observed. The novel molecular device using the metal-encapsulated fullerene of Non-Patent Document 1 is cited as a candidate for a new logic device in place of a semiconductor device in ITRS (International Technology Roadmap for Semiconductors) 2005.

  As self-assembled monolayers that can be formed on metal films, dithiocarbamate groups and derivatives thereof are described in Non-Patent Document 2, β-cyclodextrin thiol (Thiolated β-chyclodextrins) is described in Non-Patent Document 3, and viologen-terminated. Thiol (Viologen-terminated thiol) and ferrocene-terminated thiol are described in Non-Patent Document 4, N- (2-mercaptoethyl) -4-phenylazobenzenezamide (N- (2-mercaptoethyl) -4- phenylazobenzamide) is described in Non-Patent Document 5, dithio-bis-succinimidyl-terminated thiol is described in Non-Patent Document 6, and 4′-methyl-1,1′-biphenyl-4-butane (4 '-methyl-1,1'-biphenyl-4-butane) is described in Non-Patent Document 7, and mercaptoalkanol and mercaptoalkanoic acid are described in Non-Patent Document 8. Non-Patent Document 9 includes amide-terminated thiol, amino-terminated thiol, and 3-aminothiolphenol, and methyl xanthate and ethyl xanthate. ) And self-assembled monolayers having xanthate groups such as butyl xanthate have been reported in Non-Patent Document 10, respectively.

Y. Yasutake, Z. Shi, T. Okazaki, H. Shinohara, and Y. Majima, “Single Molecular Orientation Switching of an Endohedral Metallofullerene”, Nano Letters, 5, pp.1057-1060, 2005 Y. Zhao, 3 others, Journal of the American Chemical Society, 127, pp. 7328-7329, 2005 J.-Y. Lee, 1 other, Journal of Physical Chemistry B, 102, pp. 9940-9945, 1998 R. A. Wassel, 3 others, Nano Letters 3, pp. 1617-1620, 2003 S. Yasuda, 3 others, Journal of the American Chemical Society, 125, pp. 16430-16433, 2003 P. Wagner, 4 others, Biophysical Journal 70, pp.2052-2066, 1996 B. Lussem, 5 others, Langmuir, 22, pp.3021-3027, 2006 D. A. Hutt, 1 other, Langmuir, 13, pp.2740-2748, 1997 A. E. Hopper, 3 others, Surface and Interface Analysis, 31, pp.809-814, 2001 P. Talonen, 4 others, Phys. Chem. Chem. Phys., 1, pp. 3361-3666, 1999

  The molecular element in Non-Patent Document 1 operates only at an extremely low temperature of 13 K, and it is estimated that the cause is the interaction between the electrode and the metal-encapsulated fullerene and the disturbance due to heat to the metal-encapsulated fullerene, that is, rotation. ing. Thus, the conventional molecular device using metal-encapsulated fullerene has a problem that it cannot be operated at a temperature of 13K or higher.

  In view of the above problems, the present invention provides a novel molecular element capable of avoiding thermal rotation of metal-encapsulated fullerene, which is a hindrance to switching, even at a high temperature of 13K or higher, and capable of switching operation by applying an electric field from the outside. It is intended to provide.

  As a result of intensive studies focusing on the self-assembled monomolecular film of the molecular device, the present inventors have avoided the thermal rotation of the metal-encapsulated fullerene and applied an electric field from the outside even at a high temperature of 13K or higher. As a result, the inventors have found that a novel molecular element can be realized by switching operation, and the present invention has been completed.

In order to achieve the above object, the molecular device of the present invention includes a first electrode, a self-assembled monolayer disposed on the first electrode, and a metal disposed on the self-assembled monolayer. An endohedral fullerene and a second electrode disposed on the metal endohedral fullerene at a predetermined distance are provided, and the thickness of the self-assembled monolayer is 1.2 nm or less.
In the above configuration, preferably, the self-assembled monolayer includes a first functional group chemically adsorbed on a metal atom serving as a first electrode and a second functional group bonded to the first functional group, The first functional group is any group of a thiol group, a dithiocarbamate group, and a xanthate group.
The second functional group of the self-assembled monolayer is preferably any one of alkane, alkene, alkane or alkene in which part or all of hydrogen molecules are substituted with fluorine, amino group, nitro group, or amide group. It has the following group. The molecular element can be preferably used as a switching element capable of performing a switching operation.

  According to the above configuration, when a voltage higher than the threshold value is applied to the first and second electrodes of the molecular element in a high temperature region of 13K or higher, a tunnel current flows and the switching element can be operated. According to the molecular device of the present invention, the voltage is swept from a high voltage equal to or higher than the positive threshold value to a high voltage equal to or higher than the negative threshold value, and again swept from the negative high voltage to the positive high voltage. In some cases, hysteresis and negative differential conductance occur in the current-voltage characteristics.

  In the above configuration, the molecular element can be preferably used as a memory element capable of performing a memory operation. According to the present invention, the molecular element can be operated as a memory element by utilizing the fact that the direction of the dipole moment of the metal-encapsulated fullerene changes along the electric field direction from the outside.

  According to the present invention, by controlling the thickness of the self-assembled monolayer, it is possible to provide a molecular device that is thermally stable, capable of switching operation, and useful as a memory device that can store data. it can.

  According to the memory element using the molecular element of the present invention, since the memory can be stored according to the direction of the dipole moment of the metal-encapsulated fullerene, it is thermally stable and can be written / erased. Data can be read by destruction.

Hereinafter, preferred embodiments of the molecular device of the present invention will be described with reference to the drawings. In each figure, the same or corresponding members are denoted by the same reference numerals.
FIG. 1 is a diagram schematically showing the structure of the molecular device of the present invention. As shown in FIG. 1, a molecular device 10 of the present invention includes a first electrode 1 as a lower electrode, a self-assembled monolayer 2 disposed on the first electrode 1, a self-assembled monolayer. The fullerene 3 encapsulating the metal disposed on the molecular film 2 and the second electrode 4 as the upper electrode disposed at a predetermined distance 5 from the fullerene 3 encapsulating the metal. The molecular element 10 includes a first tunnel junction formed between the metal-encapsulated fullerene 3 and the lower metal 1 via the self-assembled monolayer 2, and the upper metal 4 via the metal-encapsulated fullerene 3 and the gap 5. And a second tunnel junction formed between the two.

  A first electrode (hereinafter also referred to as a lower electrode as appropriate) 1 as a lower electrode is made of a metal substrate or a metal layer formed on a single crystal substrate. The lower electrode 1 is preferably made of a single crystal such as gold (Au).

  The self-assembled monomolecular film 2 is a film made of a monomolecule formed on the lower electrode 1 and self-assembled, that is, a nanostructure is spontaneously formed in the formation process. The self-assembled monolayer 2 has a first functional group 2A bonded to the metal atom of the electrode layer 1 serving as the lower electrode by chemical adsorption, and a second functional group 2B chemically bonded to the functional group 2A. is doing.

  Examples of the first functional group 2A bonded to the metal atom of the lower electrode 1 by chemical adsorption include any of a thiol group, a dithiocarbamate group, and a xanthate group.

  As the second functional group 2B chemically bonded to the first functional group 2A, alkane, alkene, alkane and alkene hydrogen molecule partially or entirely substituted with fluorine, amino group, nitro group, amide group It can be any group.

  The thickness of the self-assembled monolayer 2 is preferably 1.2 nm or less, which is the thickness of hexanethiol, and more preferably 1 nm or less in order to increase the tunnel current flowing through the molecular element. is there. If the thickness is greater than 1.2 nm, the molecular element 10 does not perform a switching operation at a temperature of 13K or higher.

  As the self-assembled monolayer 2, diethyldithiocarbamate can be used. FIG. 2 is a diagram showing the molecular structure of diethyldithiocarbamate. As shown in FIG. 2, it can be seen that the functional group 2A under the diethyldithiocarbamate, that is, two thiol groups are bonded (chemically bonded) to the metal electrode layer by chemical adsorption.

3 to 15 are diagrams showing chemical structures of self-assembled monolayers that can be used in the present invention.
FIG. 3 is a diagram showing a general formula of a dithiocarbamate group as a chemical structure of a self-assembled monolayer that can be used in the present invention, and (B) to (N) showing derivatives thereof. . In the dithiocarbamate group shown in FIG. 3A, R ₁ and R ₂ are different alkyl groups. FIG. 3 (B) shows dimethyldithiocarbamate, FIG. 3 (C) shows diethyldithiocarbamate, FIG. 3 (D) shows dibutyldithiocarbamate, and FIG. 3 (E) shows diisopropyldithiocarbamate. Fig. 3 (F) shows piperidine dithiocarbamate, Fig. 3 (G) shows morpholine dithiocarbamate, and Fig. 3 (H) shows bis-2-phyridylmethyl. Dithiocarbamate (Bis (2-pyridylmethyl) dithiocarbamate) is shown, and FIG. 3 (I) shows metaphetadithiocarbamate.
3 (J) to 3 (N) show R ₁ or R ₂ alkyl groups that can be used, and (J) is tert-butyl, and (K) is isobutyl (R). (isobutyl), (L) is sec-butyl, (M) is neo-pentyl, and (N) is isopentyl.

FIG. 4 shows β-cyclodextrin thiol (Thiolated β-chyclodextrins), and the number n of alkylene groups (—CH ₂ —) in the structural formula can be 6 or 7. FIG. 5 shows a viologen-terminated thiol, and the number of alkylene groups n can be 1-11. FIG. 6 shows a ferrocene terminated thiol, and the number of alkylene groups n can be 1-11.

  FIG. 7 shows N-2- (mercaptoethyl) -4-phenylazobenzamide, and trans and cis isomers can be used. FIG. 8 shows dithio-bis (succinimidylundecanoate), and the number of alkylene groups n can be 1-11. FIG. 9 shows 4'-methyl-1,1'-biphenyl-4-butane.

  FIG. 10 shows mercaptoalkanol, and the number n of alkylene groups can be 1-11. FIG. 11 shows mercaptoalkanoic acid, and the number n of alkylene groups can be 1-11.

  12 to 14 are examples of self-assembled monolayers containing an amide group, an amino group, and a nitro group, and show an amide-terminated thiol, an amine-terminated thiol, and 3-aminothiolphenol, respectively. Can be 1-11.

FIG. 15 is a diagram showing (X) xanthate and (B) to (E) showing specific examples of the chemical structure of a self-assembled monolayer that can be used in the present invention. In the xanthate shown in FIG. 15A, R ₁ is an alkyl group. FIGS. 15B to 15E show methyl xanthate, ethyl xanthate, propyl xanthate, and butyl xanthate, respectively. The alkyl group _{R 1,} tert-butyl shown in FIG 3 (I) ~ (M) , can be isobutyl, sec- butyl, neo-pentyl, also be isopentyl.

  In the molecular element 10 of the present invention, the first functional group 2A of the self-assembled monolayer and the metal-encapsulated fullerene 3 are bonded. In the metal-encapsulated fullerene 3 (hereinafter, appropriately referred to as a metal-encapsulated fullerene), one metal atom 3B is inserted inside the fullerene 3A made of a carbon element. This metal-encapsulated fullerene 3 will be expressed as M @ Cn. Here, M is a metal atom included in fullerene, and Cn is fullerene. n is the number of carbon atoms, and n = 60, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94.

The metal M is preferably a trivalent metal atom, and any of Sc (scandium), Y (yttrium) and lanthanoid can be used. As lanthanoids, La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Pm (promethium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (Dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), Lu (lutetium). As such metal inclusion fullerene, Lu @ _C82 , Er @ _C82 , Tb @ _C82, etc. can be used.

  The upper second electrode 4 (hereinafter appropriately referred to as the upper electrode) disposed at a predetermined distance L from the metal-encapsulated fullerene 3 can be an electrode made of a needle having a dimension on the order of nm, for example. This distance L may be set to about 0.3 to 1.5 nm in order to increase the tunnel current flowing through the molecular element 10. The space 5 separating the predetermined distance can be a layer made of a vacuum or a self-assembled monomolecular film.

In the molecular element 10, the electrode layer 1 serving as the lower electrode is an Au crystal having a (111) plane, the self-assembled monomolecular film 3 is diethyldithiocarbamate, the metal-encapsulated fullerene 4 is Lu @ C ₈₂ , Er @ C ₈₂ , It can be configured using Tb @ C ₈₂ .

Next, the operation of the molecular device of the present invention will be described.
FIG. 16 is a diagram schematically showing current-voltage characteristics of the molecular element 10 of the present invention. In FIG. 16, the vertical axis indicates the tunnel current (arbitrary scale) flowing through the molecular element 10, and the horizontal axis indicates the voltage applied to the molecular element 10 (arbitrary scale). A voltage is applied between the upper electrode 4 and the lower electrode 1. The positive side is the case where the upper electrode 4 is the positive electrode and the lower electrode 1 is the negative electrode. In the figure, the metal-encapsulated fullerene 3 is Lu @ C ₈₂ , and its dipole moment 3C is indicated by an arrow.
As shown in FIG. 16, the voltage is indicated by a solid line when it is changed from the positive side to the negative side, and is indicated by a dotted line when it is changed from the negative side to the positive side. Current voltage characteristics are different, that is, hysteresis characteristics are obtained. When the voltage is higher than a sufficiently high positive voltage and negative threshold voltage (V _th ), a tunnel current flows through the molecular element 10. Therefore, according to the molecular element 10 of the present invention, it is possible to transition from the off state to the on state by applying a voltage of ± _Vth from the state where no voltage is applied. From the on state, if the voltage is less than ± V _th , for example, 0 V, the transition to the off state can be made again.

At this time, the direction of the external electric field applied to the molecular element 10 is the direction from the upper part of the paper to the lower part of the paper when the upper electrode 4 has a positive voltage (see the downward arrow (↓) in FIG. 16). In the case of a negative voltage, the direction is from the bottom of the page to the top of the page (see the downward arrow (↑) in FIG. 16). In Lu @ C ₈₂ , the inclusion metal atom Lu is positively charged to trivalent, the fullerene shell 3A is negatively charged to trivalent, and the position of the Lu atom 3B in the fullerene shell 3A is shifted from the center. Since it is fixed, the appearance is symmetric but electrically asymmetrical, and has a dipole moment 3C. Therefore, the electrical properties differ depending on the orientation of the metal-encapsulated fullerene 3.

As shown in FIG. 16 (a), in the region within _{-V th} voltage from positive high voltage side and 0V (see (b) of FIG. 16), the orientation of the dipole moment 3C metal endohedral 3 The direction is from the upper electrode 4 to the lower electrode 1, that is, the direction of the downward arrow (↓). When the voltage is −V _th or more (see FIG. 16C), the negative high voltage side (see FIG. 16D), and the region from 0 V to the positive voltage (see FIG. 16E), bipolar The direction of the child moment 3C is the direction from the lower electrode 1 to the upper electrode 4, that is, the direction of the upward arrow (↑) because the electric field direction is opposite. The voltage further increases to the positive side, and in the vicinity of the threshold value _Vth , the direction of the dipole moment 3C of the metal-encapsulated fullerene 3 is again from the upper electrode to the lower electrode, that is, in the direction of the downward arrow (↓), and current begins to flow. .

When the voltage is changed from the negative side through 0V to the positive high voltage, a negative differential conductance occurs immediately before _Vth . That is, a region where the current decreases as the voltage increases (see a region surrounded by a dotted line in FIG. 4), that is, dI / dV <0. Negative differential conductance may occur even on a negative voltage. These negative differential conductances are presumed to be caused by the reversal of the direction of the dipole moment 3C in the metal-encapsulated fullerene 3.

  According to the molecular element 10 of the present invention, the first tunnel junction formed between the metal-encapsulated fullerene 3 and the lower metal 1 via the self-assembled monolayer 2, the metal-encapsulated fullerene 3 and the gap 5 are formed. The second tunnel junction formed between the upper metal 4 and the inner metal fullerene 3 prevents thermal rotation of the metal-encapsulated fullerene 3 and applies an electric field from the outside to make it difficult for current to flow. Or can be operated as a switching element that switches from a state in which current does not easily flow to a state in which current easily flows.

  The molecular element 10 of the present invention can be operated at a high temperature of 10K or higher, for example, 60K or higher, with the thickness of the self-assembled monomolecular film 2 in the first tunnel junction being 1.2 nm or less. If the first functional group 2A chemically bonded to the lower electrode 1 is two thiol groups, such as the self-assembled monolayer 2 is dithiocarbamate, the surface of the Au (111) substrate or the like as the lower electrode 1 Since the close-packed structure is formed, the flowing tunnel current can be increased as compared with the case where alkanethiols having the same chain length are used as the self-assembled monolayer. That is, the conductance of the molecular element 10 can be increased, the amount of tunnel current can be increased, and a stronger electric field can be applied to the metal-encapsulated fullerene 3, so that molecular orientation control at a higher temperature than before can be realized.

FIG. 17 is a time chart schematically showing the operation of the memory element using the molecular element 10 of the present invention, in which (A) shows the applied voltage and (B) shows the read current. Each horizontal axis in FIG. 17 represents time, the vertical axis in FIG. 17A represents a voltage pulse train, and the vertical axis in FIG. 17B represents a current pulse train.
In FIG. 17, writing or erasing is performed by applying a pulse voltage of about ± 3 V to the molecular element 10 and controlling the initial orientation of the metal-encapsulated fullerene 3, that is, the direction of the dipole moment 3C. For example, in the case of a voltage of + 3V, the direction of the dipole moment 3C of the metal-encapsulated fullerene 3 is a downward arrow (↓), and in the case of a voltage of −3V, the direction is an upward arrow (↑). Digital storage is possible by corresponding to “0” and “1”, respectively. In this writing state, the voltage before and after the switching is used for reading, and the change in current is observed using the voltage value at which the negative differential conductance or hysteresis occurs, so that the direction of the dipole moment 3C of the metal-encapsulated fullerene 3 Can be detected. As shown in FIG. 17B, the erase state or the write state can be determined using the fact that the magnitude of the read current in the erase and write states is different from the small current and the large current, respectively. With the read voltage before and after the above switching, the direction of the dipole moment 3C in the metal-encapsulated fullerene 3 does not change, so that data can be read without destruction.

Next, the manufacturing method of the molecular element 10 of this invention is demonstrated.
The metal crystal that becomes the lower electrode 1 can be formed by vapor-depositing a metal material or the like on a crystal substrate. As such a vapor deposition method, so-called chemical vapor deposition (CVD) or physical vapor deposition (PVD) can be used. In order to increase the orientation of the crystal plane, heat treatment may be performed after the metal film is formed. The self-assembled monolayer 2 formed on the lower electrode 1 can be formed by a known method such as Non-Patent Documents 2 to 10.
The metal-encapsulated fullerene 3 is obtained by performing direct current arc discharge using a graphite rod kneaded with the metal to be encapsulated, and purifying and separating the obtained soot. Liquid chromatography can be used for this purification and separation step. The metal-encapsulated fullerene 3 thus produced is deposited on the self-assembled monomolecular film 2 by physical vapor deposition. Finally, the upper electrode 4 is disposed on the metal-encapsulated fullerene 3 at a predetermined distance. As the upper electrode 4, a metal wire needle having a tip on the order of nm can be used.

Next, the present invention will be described in more detail with reference to examples.
The molecular device of Example 1 was manufactured as follows.
First, the cleaved mica was heat-treated at 500 ° C. for 2 hours in a vacuum to obtain a clean surface, and then Au was deposited by evaporation while heating the mica to 450 ° C. The mica substrate on which gold was deposited was heat-treated at 450 ° C. for 8 hours to obtain a gold layer having a (111) plane.
Next, a diethyldithiocarbamate film having a thickness of 0.9 nm was formed as a self-assembled monomolecular film 2 on the electrode 1 made of gold. The diethyldithiocarbamate film was formed by immersing the electrode 1 for 48 hours in 10 ml (cm ⁻³ ) of a mixed solution (concentration: 10 mmol / liter) obtained by dissolving diethyldithiocarbamate (manufactured by Aldrich) in ethanol.
As the metal-encapsulated fullerene 3, Lu @ C ₈₂ prepared by a vacuum arc discharge method and purified by liquid chromatography was used, and after degassing at 120 ° C. for 12 hours in a vacuum, on the diethyldithiocarbamate film By sublimating at 550 ° C., the film thickness was equal to or less than the monomolecular layer. As the upper electrode 4, the molecular element 10 of Example 1 was manufactured by using a PtIr line whose tip was sharpened to the nano order by mechanical polishing.

Next, a comparative example will be described.
(Comparative Example 1)
A molecular element was produced in the same manner as the molecular element of Example 1 except that the metal-encapsulated fullerene 3 was not provided.

Next, the measurement result of the molecular element 10 of Example 1 will be described.
18A and 18B are plan views of the molecular element 10 of Example 1 observed with a scanning tunneling microscope. FIG. 18A is a diagram showing a scanning tunneling microscope image, and FIG. 18B is an explanatory diagram thereof. The observation area is 40 nm square. In the measurement, the upper electrode 4 was used as a probe of the scanning tunneling microscope. As can be seen from FIG. 18, one molecule of Lu @ C ₈₂ , which is metal-encapsulated fullerene 3, is observed as a white circle.

FIG. 19 is a view showing a scanning tunneling microscope image of the molecular element of Comparative Example 1. The observation area is 30 nm square. As can be seen from FIG. 19, in the molecular device of Comparative Example 1, Lu @ C ₈₂ observed in the case of Example 1 shown in FIG. 18 does not exist. Note that the black square region in the figure is generated on the Au of the lower electrode 1 and is a defect of the Au monoatomic layer called an etch pit.

FIG. 20 is a diagram showing current-voltage characteristics at 65.1 K of the molecular element 10 of Example 1. In FIG. 20, the horizontal axis indicates the applied voltage (V), and the vertical axis indicates the current (pA) flowing through the molecular element 10. The solid line in the figure indicates a voltage sweep from 3V to -3V, and the dotted line indicates a voltage sweep from -3V to + 3V.
As can be seen from FIG. 20, the tunnel current flows and switches at +1.7 V or more and −1.2 V or more. In the voltage sweep from 3V to -3V, it can be seen that negative differential conductance occurs on the negative voltage side (see arrows A and B in FIG. 20). In the voltage sweep from −3 V to +0 V, it has been found that a current-voltage characteristic, that is, a hysteresis characteristic different from the voltage sweep from 0 V to −3 V is obtained (see arrows D and E in FIG. 20). It can be seen that in the voltage sweep from 0 V to +3 V, negative differential conductance occurs at a voltage lower than _Vth (see arrow F in FIG. 20).

  FIG. 21 is a diagram showing current-voltage characteristics of the molecular element shown in Comparative Example 1 at 65.1K. The horizontal and vertical axes in FIG. 21 are the same as those in FIG. 20, and the solid line in the figure indicates a voltage sweep from 3 V to −3 V, and the dotted line indicates a voltage sweep from −3 V to +3 V. As is clear from FIG. 21, the molecular element of Comparative Example 1 has one tunnel junction composed of the lower electrode 1, the self-assembled monolayer 2 and the upper electrode 4, so that the positive side and the negative side It was found that hysteresis occurs when a positive voltage is applied. However, it was found that the negative differential conductance observed in Example 1 did not occur at all.

Next, a memory element using the molecular element 10 of Example 1 will be described.
FIG. 22 is a time chart obtained by measuring the operation of the memory element using the molecular element 10 of the present invention. (A) shows the applied pulse voltage, and (B) shows the tunnel pulse current flowing through the molecular element 10. Show. The horizontal axis in FIG. 22 represents time (seconds, s), the vertical axis in FIG. 22A represents voltage (V), and the vertical axis in FIG. 22B represents tunneling current (pA). Based on the current-voltage characteristics of the molecular element 10 of Example 1 observed in FIG. 20, a pulse voltage of ± 3 V is applied as a writing and erasing voltage, and +1.3 V indicating a negative differential conductance of +1.3 V is read voltage. Used as.
As shown in the region (1) in FIG. 22 (write → read), when a -3V pulse is applied and then a + 1.3V voltage pulse is applied, a current due to negative differential conductance is observed.
On the other hand, when a pulse voltage of +3 V is applied as shown in the region (2) of FIG. 22 (erase → read), a large positive current flows, and the dipole moment 3C of the metal-encapsulated fullerene 3 in the molecular element 10 Can be inverted with respect to the orientation on the −3V side. Thereby, the information written at -3V can be erased. In this erased state, when a pulse voltage of +1.3 V is next applied as a read voltage, negative differential conductance does not occur. Therefore, the read current in the erased state can be easily distinguished from a large current based on the negative differential conductance when the write voltage is read. Thereby, it can be seen that the molecular element 10 of the present invention operates as a memory element.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention described in the claims, and it goes without saying that these are also included in the scope of the present invention.

  The molecular device 10 of the present invention is expected to expand to nm-scale memories and logic circuits, which are expected to increase in the future, and is expected to play an important role in the field of molecular nanoelectronics.

It is a figure which shows typically the structure of the molecular element of this invention. It is a figure which shows the molecular structure of diethyl dithiocarbamate which can be used as a self-assembled monomolecular film in the molecular device of the present invention. (A)-(N) are figures which show the chemical structure of the self-assembled monolayer which can be used for this invention. It is a figure which shows the chemical structure of the self-assembled monolayer which can be used for this invention. It is a figure which shows the chemical structure of the self-assembled monolayer which can be used for this invention. It is a figure which shows the chemical structure of the self-assembled monolayer which can be used for this invention. It is a figure which shows the chemical structure of the self-assembled monolayer which can be used for this invention. It is a figure which shows the chemical structure of the self-assembled monolayer which can be used for this invention. It is a figure which shows the chemical structure of the self-assembled monolayer which can be used for this invention. It is a figure which shows the chemical structure of the self-assembled monolayer which can be used for this invention. It is a figure which shows the chemical structure of the self-assembled monolayer which can be used for this invention. It is a figure which shows the chemical structure of the self-assembled monolayer which can be used for this invention. It is a figure which shows the chemical structure of the self-assembled monolayer which can be used for this invention. It is a figure which shows the chemical structure of the self-assembled monolayer which can be used for this invention. (A)-(E) are figures which show the chemical structure of the self-assembled monolayer which can be used for this invention. It is a figure which shows typically the current-voltage characteristic of the molecular element of this invention. 3 is a time chart schematically showing the operation of a memory element using the molecular element of the present invention, wherein (A) shows an applied voltage and (B) shows a read current, respectively. It is the top view observed with the scanning tunneling microscope of the molecular element of Example 1, (A) shows a scanning tunneling microscope image, (B) is the explanatory drawing. 4 is a view showing a scanning tunneling microscope image of the molecular element of Comparative Example 1. FIG. 6 is a graph showing current-voltage characteristics at 65.1 K in the molecular element of Example 1. FIG. 6 is a graph showing current-voltage characteristics at 65.1 K in the molecular device of Comparative Example 1. FIG. It is the time chart which measured operation | movement of the memory element using the molecular element of this invention, (A) is an applied pulse voltage, respectively, (B) is a figure which shows the tunnel pulse current which flows into a molecular element.

Explanation of symbols

1: First electrode (lower electrode)
2: self-assembled monolayer 2A: first functional group 2B: second functional group 3: metal-encapsulated fullerene 3A: fullerene 3B: metal atom 3C: dipole moment 4: second electrode (upper electrode) )
5: Crevice (self-assembled monolayer)
10: Molecular device

Claims (5)

A first electrode, a self-assembled monolayer disposed on the first electrode, a metal-encapsulated fullerene disposed on the self-assembled monolayer, and a predetermined distance on the metal-encapsulated fullerene. A second electrode spaced apart, and
A molecular element, wherein the self-assembled monolayer has a thickness of 1.2 nm or less. The self-assembled monolayer includes a first functional group that is chemisorbed on a metal atom serving as the first electrode and a second functional group that is bonded to the first functional group,
2. The molecular device according to claim 1, wherein the first functional group is any one of a thiol group, a dithiocarbamate group, and a xanthate group.   The second functional group of the self-assembled monolayer is an alkane, alkene, alkane or alkene in which part or all of hydrogen molecules are substituted with fluorine, an amino group, a nitro group, or an amide group The molecular device according to claim 1, wherein the molecular device is characterized by comprising:   The molecular element according to claim 1, wherein the molecular element is a switching element.   The molecular element according to claim 1, wherein the molecular element is a memory element.