Molecular quantum interference apparatus and applications of same

1. A molecular quantum interference device, comprising:

(a) at least one molecular quantum interference unit having a first terminal group and a second terminal group between which quantum interference affects electrical conduction;

(b) at least two molecular spacers, each having a first terminal group and a second terminal group, wherein a first one of the at least two molecular spacers is coupled to the molecular quantum interference unit through a chemical bonding between the first terminal group of the first molecular spacer and the second terminal group of the molecular quantum interference unit, and a second one of the two molecular spacers is coupled to the molecular quantum interference unit through a chemical bonding between the second terminal group of the second molecular spacer and the first terminal group of the molecular quantum interference unit, respectively;

(c) a first electrode electrically coupled to the second molecular spacer; and

(d) a second electrode electrically coupled to the first molecular spacer; ps wherein the at least two molecular spacers comprise at least one more spacer coupled between the molecular quantum interference unit and one of the first electrode and the second electrode.

2. The device of claim 1 , wherein at least one of the first electrode and the second electrode is electrically coupled to a corresponding molecular spacer through a chemical bonding.

3. The device of claim 1 , wherein at least one of the first electrode and the second electrode is electrically coupled to a corresponding molecular spacer through a non-chemical bonding.

4. The device of claim 1 , wherein a current source is electrically coupled to at least one of the first electrode and the second electrode for establishing a bias current or voltage across the first electrode and the second electrode.

5. The device of claim 4 , wherein when a bias current or voltage is established across the first electrode and the second electrode, a transmission spectrum is measurable between the first electrode and the second electrode and variable with the bias voltage.

6. The device of claim 1 , wherein each of the first and second electrodes comprises a material having a work function for electron tunneling between the first and second electrodes, respectively, through the molecular spacers and the molecular quantum interference unit.

7. The device of claim 6 , wherein each of the first and second electrodes comprises an electrically conducting or semi-conducting material.

8. The device of claim 7 , wherein each of the first and second electrodes comprises at least one of gold, copper, platinum, palladium, silver, silicon, graphene, carbon nanotubes, iridium, ITO and doped semiconductor materials.

9. The device of claim 1 , wherein the molecular quantum interference unit comprises one selected from the group of a cross-conjugated unit, a meta substituted phenyl ring, a substituted cyclic system that is not a phenyl ring, and a π-stacked unit.

10. The device of claim 9 , wherein the cross-conjugated unit comprises a cyclic or acyclic cross-conjugated unit.

11. The device of claim 9 , wherein each of the at least two molecular spacers comprises one selected from the group of a single bonded carbon unit, a double bonded carbon unit, a triple bonded carbon unit, a phenyl ring, a thiophene ring, an oxygen atom, a nitrogen atom, a sulphur atom, a silicon atom, a phosphorus atom, a boron atom and any combination of them.

12. The device of claim 11 , wherein each of the chemical bonding between the first terminal group of the first molecular spacer and the second terminal group of the molecular quantum interference unit, and the chemical bonding between the second terminal group of the second molecular spacer and the first terminal group of the molecular quantum interference unit comprises a carbon-carbon single bond.

13. A molecular quantum interference device, comprising:

(a) at least one molecular spacer having a first terminal group and a second terminal group;

(b) at least two molecular quantum interference units, each having a first terminal group and a second terminal group between which quantum interference affects electrical conduction, wherein a first one of the at least two molecular quantum interference units is coupled to the at least one molecular spacer through a chemical bonding between the first terminal group of the at least one molecular spacer and the second terminal group of the first molecular quantum interference unit, and a second one of the at least two molecular quantum interference units is coupled to the at least one molecular spacer through a chemical bonding between the second terminal group of the at least one molecular spacer and the first terminal group of the second molecular quantum interference unit, respectively;

(c) a first electrode electrically coupled to the first molecular quantum interference unit; and

(d) a second electrode electrically coupled to the second molecular quantum interference unit;

wherein the at least one molecular spacer comprises at least two molecular spacers coupled between the at least two molecular quantum interference units or between one of the first electrode and the second electrode and one of the at least two molecular quantum interference units.

14. The device of claim 13 , wherein at least one of the first electrode and the second electrode is electrically coupled to a corresponding molecular quantum interference unit through a chemical bonding.

15. The device of claim 13 , wherein at least one of the first electrode and the second electrode is electrically coupled to a corresponding molecular quantum interference unit through a non-chemical bonding.

16. The device of claim 13 , wherein a current source is electrically coupled to at least one of the first electrode and the second electrode for establishing a bias current or voltage across the first electrode and the second electrode.

17. The device of claim 16 , wherein when a bias current or voltage is established across the first electrode and the second electrode, a transmission spectrum is measurable between the first electrode and the second electrode and variable with the bias voltage.

18. The device of claim 13 , wherein each of the at least two molecular quantum interference units comprises one selected from the group of a cross-conjugated unit, a meta substituted phenyl ring, a substituted cyclic system that is not a phenyl ring, and a π-stacked unit.

19. The device of claim 18 , wherein the cross-conjugated unit comprises a cyclic or acyclic cross-conjugated unit.

20. The device of claim 18 , wherein the at least one molecular spacer comprises one selected from the group of a single bonded carbon unit, a double bonded carbon unit, a triple bonded carbon unit, a phenyl ring, a thiophene ring, an oxygen atom, a nitrogen atom, a sulphur atom, a silicon atom, a phosphorus atom, a boron atom and any combination of them.

21. The device of claim 13 , wherein each of the chemical bonding between the first terminal group of the at least one molecular spacer and the second terminal group of the first molecular quantum interference unit, and the chemical bonding between the second terminal group of the at least one molecular spacer and the first terminal group of the second molecular quantum interference unit comprises a carbon-carbon single bond.

22. The device of claim 13 , wherein each of the first and second electrodes comprises a material having a work function for electron tunneling between the first and second electrodes, respectively, through the at least one molecular spacer and the at least two molecular quantum interference units.

23. The device of claim 22 , wherein each of the first and second electrodes comprises an electrically conducting or semi-conducting material.

24. The device of claim 23 , wherein each of the first and second electrodes comprises at least one of gold, copper, platinum, palladium, silver, silicon, graphene, carbon nanotubes, iridium, ITO and doped semiconductor materials.

25. A molecular quantum interference device, comprising:

(a) at least one molecular spacer having a first terminal group and a second terminal group;

(b) at least two molecular quantum interference units, each having a first terminal group and a second terminal group between which quantum interference affects electrical conduction, wherein a first one of the at least two molecular quantum interference units is coupled to the at least one molecular spacer through a chemical bonding between the first terminal group of the at least one molecular spacer and the second terminal group of the first molecular quantum interference unit, and a second one of the at least two molecular quantum interference units is coupled to the at least one molecular spacer through a chemical bonding between the second terminal group of the at least one molecular spacer and the first terminal group of the second molecular quantum interference unit, respectively;

(c) a first electrode electrically coupled to the first molecular quantum interference unit; and

(d) a second electrode electrically coupled to the second molecular quantum interference unit;

wherein the at least two molecular quantum interference units comprise at least one more molecular quantum interference unit coupled between the at least one molecular spacer and one of the first electrode and the second electrode.