Patent Publication Number: US-2006003594-A1

Title: Molecules for langmuir-blodgett deposition of a molecular layer

Description:
BACKGROUND  
      The present disclosure relates generally to molecular electronics, and more particularly to molecular layers formed using Langmuir-Blodgett methods.  
      Molecular devices having two electrodes (for example, a bottom electrode and a top electrode) and a molecular switching layer or film at the junction of the two electrodes are known. Such devices may be useful, for example, in the fabrication of devices based on electrical switching, such as molecular wire crossbar interconnects for signal routing and communications, molecular wire crossbar memory, molecular wire crossbar logic employing programmable logic arrays, multiplexers or demultiplexers for molecular wire crossbar networks, molecular wire transistors, and the like. Such devices may further be useful, for example, in the fabrication of devices based on optical switching, such as displays, electronic books, rewritable media, electrically tunable optical lenses, electrically controlled tinting for windows and mirrors, optical crossbar switches (for example, for routing signals from one of many incoming channels to one of many outgoing channels), and the like.  
      Typically, the molecular switching layer or film has an organic molecule that, in the presence of an electrical (E) field, switches between two or more energetic states, such as by an electro-chemical oxidation or reduction (redox) reaction or by a change in the band gap of the molecule induced by the applied E-field.  
      It is important to form a good electrical contact between the electrode and the molecular switching layer in order to fabricate operative molecular devices. Molecules with special chemical end groups are able to form direct chemical bonds with metal or semiconductor electrodes to form a self-assembled monolayer (SAM), which may have a good electrical contact with an electrode(s). However, this self-assembled molecular layer formed on the surface of the electrode may generally be prone to a high density of defects. If a second electrode is formed on the molecular layer, then an electrical short may occur between the first and second electrode through the defects in the self-assembled molecular layer.  
      The formation of Langmuir-Blodgett (LB) layers or films employing switching molecules has been attempted because such layers or films are generally much denser than SAM films. Further, LB layers or films have relatively low defect densities compared to SAM films. However, it has proven to be a significant challenge to effectively bond LB films to the electrode substrate. As such, if the LB film is not sufficiently bonded to the electrode(s), then poor electrical contact may result.  
      As such, there is a need for providing a high density molecular switching layer on an electrode(s), which layer also bonds well with the electrode.  
     SUMMARY  
      A molecule for Langmuir-Blodgett (LB) deposition of a molecular layer is disclosed. The molecule includes at least one switching moiety, a hydrophilicity-modifiable connecting group attached to one end of the moiety, and a hydrophilicity-non-modifiable connecting group attached to the other end of the moiety. The hydrophilicity-modifiable connecting group is transformable to a temporary end group upon adjustment in pH of the aqueous environment containing the molecule. The temporary end group is more hydrophilic than the hydrophilicity-modifiable connecting group and the hydrophilicity-non-modifiable connecting group. The difference in hydrophilicity between the temporary end group and the hydrophilicity-non-modifiable connecting group causes formation of a substantially well-oriented, uniform LB film at a solvent surface.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Objects, features and advantages will become apparent by reference to the following detailed description and drawings, in which like reference numerals correspond to similar, though not necessarily identical components. For the sake of brevity, reference numerals having a previously described function may not necessarily be described in connection with subsequent drawings in which they appear.  
       FIG. 1A  is a schematic representation of two crossed wires, with at least one molecule at the intersection of the two wires;  
       FIG. 1B  is a perspective elevational view, depicting the crossed-wire device shown in  FIG. 1   a;    
       FIG. 2  is a schematic representation of a two-dimensional array of switches, depicting a 6×6 crossbar switch;  
       FIGS. 3A-3D  is a schematic flow diagram depicting an embodiment of a method of the present invention;  
       FIGS. 4A-4D  is similar to  FIG. 3 , but depicts an alternate embodiment of a method of the present invention; and  
       FIGS. 5A-5B  is similar to  FIG. 3 , but depicts yet a further alternate embodiment of a method of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
      Embodiments of the present invention advantageously use a novel concept of hydrophilicity modification. This concept takes advantage of the advantageous qualities of self-assembly techniques (e.g. good electrical contact due to chemical bonding) and Langmuir-Blodgett (LB) deposition (e.g. low defect density). The concept further substantially eliminates problems that may in some instances be associated with both methods. The method according to embodiments of the present invention provides a good Langmuir-Blodgett film(s), orienting the connecting groups at the ends of the molecule forming the film(s), such that chemical bonding and the formation of good electrical contact with the crossbar electrodes at either end of the molecule is promoted (described in further detail below, also for example with reference to  FIGS. 5A-5B ).  
      Referring now to  FIGS. 1A-1B , a crossed wire switching device  10  includes two wires  12 ,  14 , each either a metal or semiconductor wire, that are crossed at some substantially non-zero angle. Disposed between wires  12 ,  14  is a layer  16  of molecules, molecular compounds, or mixtures thereof, denoted R. The particular molecules  18  that are sandwiched at the intersection (also interchangeably referred to herein as a junction) of the two wires  12 ,  14  are identified as switch molecules R S .  
      There are generally two primary methods of operating such switches  10 , depending on the nature of the switch molecules  18 . The molecular switching layer  16  includes a switch molecule  18  (for example, an organic molecule) that, in the presence of an electrical (E) field, switches between two or more energetic states, such as by an electrochemical oxidation or reduction (redox) reaction or by a change in the band gap of the molecule induced by the applied E-field.  
      In the former case, when an appropriate voltage is applied across the wires  12 ,  14 , the switch molecules R S  are either oxidized or reduced. When a molecule is oxidized (reduced), then a second species is reduced (oxidized) so that charge is balanced. These two species are then called a redox pair. One example of this device would be for one molecule to be reduced, and then a second molecule (the other half of the redox pair) would be oxidized. In another example, a molecule is reduced, and one of the wires  12 ,  14  is oxidized. In a third example, a molecule is oxidized, and one of the wires  12 ,  14  is reduced. In a fourth example, one wire  12 ,  14  is oxidized, and an oxide associated with the other wire  14 ,  12  is reduced. In such cases, oxidation or reduction may affect the tunneling distance or the tunneling barrier height between the two wires, thereby exponentially altering the rate of charge transport across the wire junction, and serving as the basis for a switch. Examples of molecules  18  that exhibit such redox behavior include rotaxanes, pseudo-rotaxanes, and catenanes; see, e.g., U.S. Pat. No. 6,459,095, entitled “Chemically Synthesized and Assembled Electronic Devices”, issued Oct. 1, 2002, to James R. Heath et al, the disclosure of which is incorporated herein by reference in its entirety.  
      Further, the wires  12 ,  14  may be modulation-doped by coating their surfaces with appropriate molecules—either electron-withdrawing groups (Lewis acids, such as boron trifluoride (BF 3 )) or electron-donating groups (Lewis bases, such as alkylamines) to make them p-type or n-type conductors, respectively.  FIG. 1B  depicts a coating  20  on wire  12  and a coating  22  on wire  14 . The coatings  20 ,  22  may be modulation-doping coatings, tunneling barriers (e.g., oxides), or other nano-scale functionally suitable materials. Alternatively, the wires  12 ,  14  themselves may be coated with one or more R species  16 , and where the wires cross, R S    18  is formed. Or yet alternatively, the wires  12 ,  14  may be coated with molecular species  20 ,  22 , respectively, for example, that enable one or both wires to be suspended to form colloidal suspensions, as discussed below. Details of such coatings are provided in above-referenced U.S. Pat. No. 6,459,095.  
      In the latter case, examples of molecule  18  based on field induced changes include E-field induced band gap changes, such as disclosed and claimed in patent application Ser. No. 09/823,195, filed Mar. 29, 2001, published as Publication No. 2002/0176276 on Nov. 28, 2002, which application is incorporated herein by reference in its entirety. Examples of molecules used in the E-field induced band gap change approach include molecules that evidence molecular conformation change or an isomerization; change of extended conjugation via chemical bonding change to change the band gap; or molecular folding or stretching.  
      Changing of extended conjugation via chemical bonding change to change the band gap may be accomplished in one of the following ways: charge separation or recombination accompanied by increasing or decreasing band localization; or change of extended conjugation via charge separation or recombination and π-bond breaking or formation.  
      The formation of micrometer scale and nanometer scale crossed wire switches  10  uses either a reduction-oxidation (redox) reaction to form an electrochemical cell or uses E-field induced band gap changes to form molecular switches. In either case, the molecular switches typically have two states, and may be either irreversibly switched from a first state to a second state or reversibly switched from a first state to a second state. In the latter case, there are two possible conditions: either the electric field may be removed after switching into a given state, and the molecule will remain in that state (“latched”) until a reverse field is applied to switch the molecule back to its previous state; or removal of the electric field causes the molecule to revert to its previous state, and hence the field must be maintained in order to keep the molecule in the switched state until it is desired to switch the molecule to its previous state.  
      Color switch molecular analogs, particularly based on E-field induced band gap changes, are also known; see, e.g., U.S. application Ser. No. 09/844,862, filed Apr. 27, 2001.  
      Referring now to  FIG. 2 , the switch  10  may be replicated in a two-dimensional array to form a plurality or array  24  of switches  10  to form a crossbar switch.  FIG. 2  depicts a 6×6 array  24 . However, it is to be understood that the embodiments herein are not to be limited to the particular number of elements, or switches  10 , in the array  24 . Access to a single point, e.g.,  2   b , is done by impressing voltage on wires  2  and b to cause a change in the state of the molecular species  18  at the junction thereof, as described above. Thus, access to each junction is readily available for configuring those that are pre-selected. Details of the operation of the crossbar switch array  24  are further discussed in U.S. Pat. No. 6,128,214, entitled “Molecular Wire Crossbar Memory”, issued on Oct. 3, 2000, to Philip J. Kuekes et al., which is incorporated herein by reference in its entirety.  
       FIG. 3A  depicts an embodiment of a molecule suitable to form a molecular layer(s) attachable to a substrate. An aqueous environment contains a molecule  18  with a molecular switching moiety (MD)  26  having a hydrophilicity-modifiable connecting group (HSCG)  30  attached to one end of the moiety  26 , and a hydrophilicity-non-modifiable connecting group (HNSCG)  28  attached to an opposed end of the moiety  26 .  
      In an embodiment of the present invention, the molecule  18  is an organic molecule, and the molecular switching moiety  26  is an optically switchable molecular functional unit or an electrically switchable molecular functional unit. It is to be understood that the switching moiety  26  may be any suitable moiety, however, in an embodiment, the moiety  26  includes at least one of saturated hydrocarbons, unsaturated hydrocarbons, substituted hydrocarbons, heterocyclic systems, organometallic complex systems, or mixtures thereof.  
      In an embodiment, the switching moiety  26  is a moiety that, in the presence of an electric field, undergoes at least one of oxidation or reduction, and/or experiences a band gap change. In one embodiment, the switching moiety  26  undergoes at least one of oxidation or reduction and is at least one of rotaxanes, pseudo-rotaxanes, catenanes, and mixtures thereof. An example of a switching moiety  26  that undergoes a band gap change in the presence of an external electrical field is described in U.S. Pat. No. 6,674,932 granted to Zhang et al. on Jan. 6, 2004, the specification of which is incorporated herein by reference in its entirety.  
      It is to be understood that any suitable hydrophilicity-non-modifiable connecting group (HNSCG)  28  may be used as desired or necessitated by a particular end use. In an embodiment of the present invention, the hydrophilicity-non-modifiable connecting group (HNSCG)  28  is at least one of multivalent hetero atoms selected from the group consisting of C, N, O, S, and P; functional groups containing the hetero atoms and selected from the group consisting of SH, OH, SiCl 3 , NH, and PH; saturated hydrocarbons; unsaturated hydrocarbons; substituted hydrocarbons; heterocyclic compounds; carboxylic acids; derivatives thereof (non-limitative examples of which include carboxylic esters, amides, nitrites, or the like); and mixtures thereof.  
      In a further embodiment of the present invention, the hydrophilicity-non-modifiable connecting group (HNSCG)  28  functional groups are at least one of S-alkyl, S-aryl, S—S-alkyl, S—S-aryl, S-acyl, O-aryl, O-alkyl, O-acyl, NH 2 , NH-alkyl, NH-aryl, NH-acyl, N-(alkyl) 2 , N-(aryl) 2 , N-(alkyl)(aryl), PH 2 , PH-alkyl, PH-aryl, PH-acyl, P-(alkyl) 2 , P-(aryl) 2 , P-(alkyl)(aryl), and mixtures thereof.  
      It is to be understood that any suitable hydrophilicity-modifiable connecting group (HSCG)  30  may be used as desired or necessitated by a particular end use. In an embodiment of the present invention, the hydrophilicity-modifiable connecting group (HSCG)  30  is at least one of multivalent hetero atoms selected from the group consisting of C, N, O, S, and P; functional groups containing the hetero atoms and selected from the group consisting of SH, OH, SiCl 3 , NH, and PH; saturated hydrocarbons; unsaturated hydrocarbons; substituted hydrocarbons; heterocyclic compounds; carboxylic acids; derivatives thereof; and mixtures thereof.  
      In a further embodiment of the present invention, the hydrophilicity-modifiable connecting group (HSCG)  30  functional groups are at least one of NH 2 , NH-alkyl, NH-aryl, N-(alkyl) 2 , N-(aryl) 2 , N-(alkyl)(aryl), PH 2 , PH-alkyl, PH-aryl, P-(alkyl) 2 , P-(aryl) 2 , P-(alkyl)(aryl), pyridine, and mixtures thereof.  
      Referring now to  FIG. 3B , as the pH of the aqueous environment is adjusted, the hydrophilicity-modifiable connecting group (HSCG)  30  is transformed into a temporary end group (IPEG)  32 , wherein the temporary end group  32  is more hydrophilic than the hydrophilicity-modifiable connecting group (HSCG)  30  and the hydrophilicity-non-modifiable connecting group (HNSCG)  28 .  
      Referring now to  FIG. 3C , a Langmuir-Blodgett (LB) film of the molecule  18  is formed on an interface  34  between an organic solvent(s)/air and water, the film being depicted by the plurality of molecules  18  shown. The organic solvent(s) is above the water, and in some instances may volatilize quickly; as such what was an interface  34  between water and organic solvent(s) may become an interface  34  between water and air. Thus, it is to be understood that interface  34  as defined herein may be a water/solvent interface  34  and/or a water/air interface  34 . Without being bound to any theory, it is believed that the difference in hydrophilicity between the temporary end group  32  and the hydrophilicity-non-modifiable connecting group  28  causes formation of a substantially well-oriented, uniform LB film at the interface  34  of the organic solvent(s)/air and the water.  
      The pH of the aqueous environment is then re-adjusted so as to transform the temporary end group  32  back to the hydrophilicity-modifiable connecting group  30 , as shown in  FIG. 3D . The substrate is then passed through the Langmuir-Blodgett film to form the molecular layer chemically bonded on the substrate (not shown in  FIGS. 3A-3D ).  
      Embodiments of the present invention are advantageously suitable for fabricating molecular devices with molecules containing two or more substantially asymmetric, connecting end-groups  28 ,  30 . In an embodiment, it is desirable that both of the connecting end-groups  28 ,  30  be capable of forming good electrical contact with electrodes  38 ,  40  (as shown in  FIGS. 5A and 5B ) made of noble metals (e.g. Au, Pt, Ag, Cu, alloys of these metals, or the like) via chemical bonding.  
      In an embodiment, one of the hydrophilicity-modifiable connecting group  30  or the hydrophilicity-non-modifiable connecting group  28  is a connecting unit between the organic molecule  18  and the substrate ( 38 ,  40 ,  42  as shown in  FIGS. 5A and 5B ). The other of the hydrophilicity-modifiable connecting group  30  or the hydrophilicity-non-modifiable connecting group  28  is a connecting unit between the organic molecule  18  and an other substrate ( 38 ,  40 ,  42  as shown in  FIGS. 5A and 5B ). It is to be understood that the substrate and the other substrate is a solid substrate, and may be either an electrode or a non-electrode, depending on the application. It is to be further understood that the substrate and the other substrate may each be hydrophilic, hydrophobic, or one may be hydrophilic and the other may be hydrophobic. As such, connecting group  30  or connecting group  28  will be more attracted to the substrate or other substrate, depending upon the hydrophilicity/hydrophobicity of the substrate or other substrate and of the group  30 ,  28 . The substrates will be discussed in further detail below in relation to  FIGS. 5A and 5B .  
      The method of the embodiment outlined above will be discussed in more detail herein. The hydrophilicity of one of the end groups  30  may be modified by changing the pH of the aqueous environment, for example the subphase of an LB trough, within a range under which the other end group  28  of the molecule  18  remains inert. This change in hydrophilicity of the one end group  30  is due to the formation of a temporary end group  32  following the pH adjustment. It is to be understood that the temporary end group  32  may be any suitable end group. However, in an embodiment, the temporary end group  32  is an ion pair (IPEG)  32 . It is to be further understood that the ion pair  32  may be any suitable ion pair. A non-limitative example of such an ion pair  32  is H + X − , wherein X— is at least one of Br − , Cl − , I − , CH 3 CO 2   − , HCO 2   − , NO 3   − , H 2 PO 4   − , HPO 4   2− , HSO 4   − , SO 4   2− , other organic acids, or mixtures thereof.  
      The conversion of the one end-group  30  to an ion pair  32  makes it more hydrophilic than the inert end-group  28 , causing the molecule to orient itself such that the ion pair (temporary end group)  32  preferentially resides at the solvent/water interface  34  of the LB trough. After forming this film, the pH of the subphase in the LB trough is then carefully readjusted. The pH change converts the ion pair  32  at the solvent-air interface  34  back to the original reactive end-group  30  for a subsequent bonding reaction with the metal electrodes  38 ,  40 .  
      It is to be understood that any solvent suitable for an LB process may be used. In an embodiment, the solvent is water, organic solvents, or mixtures thereof. Suitable organic solvents include, but are not limited to chloroform, dichloromethane, benzene, toluene, ethyl acetate, hexane, pentane, heptane, ethyl ether, or the like.  
      In carrying out embodiments of the method, it is desirable to consider the following guidelines. The hydrophilicity-modifiable connecting group (HSCG)  30  may be sensitive to pH changes; whereas the hydrophilicity-non-modifiable connecting group (HNSCG)  28  may be substantially inert to pH change. It would be desirable that both the hydrophilicity-modifiable connecting group (HSCG)  30  and the hydrophilicity-non-modifiable connecting group (HNSCG)  28  be reactive enough to react with a noble metal electrode substrate to form a stable chemical bond. It would be desirable that both the hydrophilicity-modifiable connecting group (HSCG)  30  and the hydrophilicity-non-modifiable connecting group (HNSCG)  28  be substantially hydrophobic, but soluble in selected organic solvents. It is desirable that the molecular switching moiety (MD)  26  be stable to pH change and substantially hydrophobic. Further, the LB process and thin film transfer may desirably be carried out in a substantially inert atmosphere to aid in preventing the highly reactive connecting end-groups  28 ,  30  from being deleteriously affected or destroyed by oxidation.  
      A non-limitative embodiment is shown in  FIGS. 4A-4D . In this embodiment, the hydrophilicity-non-modifiable connecting group (HNSCG)  28  is an S—COR group, and the hydrophilicity-modifiable connecting group (HSCG)  30  is a pyridine group. Both of these end-groups  28 ,  30  are very reactive towards the noble metals (e.g. Au, Cu, Ag, Pt, alloys of these metals, or the like) and are able to form good chemical bonds to these metals. The pyridine group is a mild base, which may be protonated under a weakly acidic environment (pH greater than about 5), and the S—COR is a neutral unit that is stable under pH regimes ranging from about pH 4 to about pH 9. The letter R designates any suitable hydrophobic end-group. In an embodiment, R may be selected from any alkyl group, aryl group, or combinations thereof. Some examples of suitable R groups include, but are not limited to CH 3 , C 2 H 5 —, C 3 H 7 —, C 6 H 5 —, C 6 H 5 —CH 2 —, or the like.  
      After carefully adjusting the pH of the water solution in the LB trough, an ion pair H + X −  is formed at the pyridine end-group  32 . The formation of the ion pair H + X −  greatly enhances the hydrophilicity of the pyridine end-group  32 , tethering it more strongly to the air-water interface than the S—COR end-group  28 , thereby resulting in a preferential orientation of the molecules  18  that helps to form a good, substantially uniform LB thin film.  
      After this good, substantially uniform thin film is formed in the LB trough, the pH environment of the LB trough is carefully readjusted. The pH change converts the ion pair H + X −  back to the non-protonated pyridine end-group  30  that is able to chemically bond with metal electrodes (not shown in  FIGS. 4A-4D ).  
      A further non-limitative embodiment is shown in  FIGS. 5A-5B . In this embodiment, as shown in  FIG. 5A (I), an OH group is the hydrophilicity-non-modifiable connecting group (HNSCG)  28  and an NH 2  group is the hydrophilicity-modifiable connecting group (HSCG)  30  of the molecule  18 . Both of these groups  28 ,  30  are reactive toward the noble metals (e.g. Au, Cu, Ag, Pt, etc), and are able to form good chemical bonding with electrode material.  
      The —OSi(CH3) 2 R group is an example of a trialkyl silyl type of hydrophobic temporary protecting group  36  (one non-limitative example of a temporary protecting group  36 ) generated by treating —OH with (CH3) 2 RSiCl under a mild base condition (Et 3 N) to form a mono-capped molecule (see  FIG. 5A (II)). This group  36  is stable during the preparation of the X − NH3 +  ion pair (the water soluble cationic form of the —NH 2  group) temporary end group  32 , and during the L-B thin film preparation process (see FIGS.  5 A(III) and  5 A(IV)). It is to be understood that the temporary protecting group  36  may be hydrophobic or hydrophilic, as desired or necessitated by a particular embodiment(s). The highly water-soluble X − NH 3+  ion pair is generated from the —NH 2  group by carefully adjusting the pH to acidic (pH ranging between about 2 and about 4). This ion pair on the temporary end group  32  will help the end group  32  stay in the interface  34  of water and organic solvent during the Langmuir-Blodgett monolayer thin film preparation (which, as stated hereinabove, enables preparation of a high quality LB thin film). Further, the temporary end group  32  will be stable during the LB thin film preparation.  
      It is to be understood that R in the temporary protecting group  36  may be any suitable alkyl group, including, but not limited to, —CH 3 , —C 2 H 5 , —C 3 H 7 , —C 4 H 9 , —C 5 H 11 , —C 6 H 13 , —C 7 H 15 , —C 8 H 17 , —C 9 H 19 , —C 10 H 21 , —C 11 H 23 , substituted hydrocarbons (e.g. —(CH 2 ) n —Ar; —(CH 2 ) n -Het; where n&gt;0, the —Ar may be any suitable aromatic hydrocarbon, and the Het may be any suitable heterocyclic system; or the like), or combinations thereof. A generic representation of a trialkyl silyl type of temporary protecting group  36  is —OSiR 1 R 2 R 3 . It is to be understood that the R 1 , R 2 , R 3  may each be the same type of alkyl group, may each be a different alkyl group, or may be any combination of similar and different alkyl groups. The non-limitative examples of R groups listed above may also serve as suitable non-limitative examples of R 1 , R 2 , R 3  groups.  
      The temporary protecting group  36  may also advantageously aid in orienting the molecule  18  such that the temporary protecting group  36  remains in the air, and the ion pair end group  32  remains at the water/solvent interface  34 .  
      Referring now to FIGS.  5 A(IV) and  5 A(V), the highly water-soluble X − NH 3   +  ion pair may be selectively reconverted back to —NH 2  by carefully readjusting the pH of the water phase to basic (for example, a pH greater than about 10) with a sodium hydroxide (NaOH) solution after the thin film is formed.  
      In any of the embodiments described herein, there are at least two non-limitative embodiments for constructing crossbar devices  10  with good electrical contact. A first embodiment, direct linking to the electrode substrate, may be desirable if the end-group  30  is reactive enough to form a chemical bond quickly with the bottom electrode  38  (it is to be understood that an annealing at a mild elevated temperature under an inert environment may be advantageous in order to facilitate the solid-solid interaction).  
      In this first embodiment, the L-B thin film ( FIG. 5A (V)) is transferred and chemically bonded onto the bottom electrode  38  to form a semi-device ( FIG. 5A (VI)). At this time, the protecting group  36  may be removed by a treatment with hydrofluoric acid (HF), followed by vacuum evaporation of volatile by-products to render a complete un-protected semi-device ( FIG. 5A (VII)). A chemically bonded top metal electrode  40  may then be formed by, for example, a sputtering process or an evaporative metal deposition process to yield the desired crossbar device  10  ( FIG. 5B (VIII)).  
      A second non-limitative embodiment for constructing crossbar devices  10  with good electrical contact may be desirable if the end-group  30  is not reactive enough toward the electrode substrate  38  in the bonding reaction among the solid-solid interface. In this second embodiment, the LB thin film ( FIG. 5A (V)) is transferred onto a non-electrode solid substrate  42  to form a temporary intermediate device ( FIG. 5B (IX)). At this time, the protecting group  36  may be removed by a treatment with hydrofluoric acid (HF), followed by vacuum evaporation of volatile by-products to render an uncapped molecule  18  (FIG.  5 B(X)). A chemically bonded top metal electrode  40  is then formed by an evaporative metal deposition, a sputtering process, or the like to yield a semi-device ( FIG. 5B (XI)). The device is then flipped vertically about the electrical contact to yield the device as shown in  FIG. 5B (XII). Non-electrode solid substrate  42  is removed, and a bottom electrode  38  is then formed by an evaporative metal deposition process, a sputtering process, or the like to finish the final desired crossbar device  10  ( FIG. 5B (XIII)).  
      It is to be understood that non-electrode solid substrate  42  may be formed from any suitable material, including but not limited to at least one of inorganic materials (e.g. glass, silicon, metal oxides (e.g. silicon oxides, aluminum oxides, etc.) and the like), organic materials (e.g. polycarbonates and the like), or combinations thereof.  
      An embodiment of a crossed wire molecular device  10  includes a plurality of bottom electrodes  38 , a plurality of top electrodes  40  crossing the bottom electrodes  38  at a non-zero angle, and a molecular layer formed from a plurality of organic molecules  18 , each of the molecules  18  having at least one molecular switching moiety  26 . The molecular layer is operatively disposed in at least one junction formed where one electrode  38 ,  40  crosses another electrode  40 ,  38 . A non-limitative embodiment of a method of forming the crossed wire molecular device  10  is as follows. The pH of the aqueous environment is adjusted as described hereinabove in a manner sufficient to transform the hydrophilicity-modifiable connecting group  30  to a temporary end group  32 . A Langmuir-Blodgett (LB) film of the molecule  18  is formed on the solvent/water interface  34 . The pH is re-adjusted in a manner sufficient to transform the temporary end group  32  back to the hydrophilicity-modifiable connecting group  30 . Each of the plurality of bottom electrodes  38  is passed through the Langmuir-Blodgett film to form the molecular layer chemically bonded, via the hydrophilicity-modifiable connecting group  30 , on a surface of the bottom electrode  38 . The method may further include forming one of the plurality of top electrodes  40 , crossing the one of the plurality of bottom electrodes  38  at the non-zero angle, thereby forming the junction therebetween. The molecular layer is thereby chemically bonded, via the hydrophilicity-non-modifiable connecting group  28 , on a surface of the top electrode.  
      While several embodiments have been described in detail, it will be apparent to those skilled in the art that the disclosed embodiments may be modified. Therefore, the foregoing description is to be considered exemplary rather than limiting.