In-situ combined sensing of uniaxial nanomechanical and micromechanical stress with simultaneous measurement of surface temperature profiles by raman shift in nanoscale and microscale structures
Embodiments of the present disclosure include separating a measured Raman shift signal into mechanical and thermal components when a uniaxial compressive load is applied in situ. In some embodiments, in situ uniaxial compressive loads are applied on examined specimens from room temperature to 150° C. In alternate embodiments, Raman shift measurements are performed as a function of strain at constant temperature and/or as a function of temperature at constant strain levels. It was realized that the Raman shift measured at a given temperature under a given level of applied stress can be expressed as a summation of stress-induced Raman shift signal and temperature-induced Raman shift signal measured separately. Such a separation of Raman shift signal is utilized by various embodiments to measure localized change in thermal conductivity and/or mechanical stress of structures (e.g., semiconductor structures) under applied stress.
1. A method for measuring mechanical properties of a microscale or nanoscale structure, comprising:
supporting an elongate structure at one end, the opposite end being free;
heating the structure;
applying a load to the free end;
receiving energy reflected from the loaded structure while the loaded structure is being heated; and
measuring a Raman shift in the reflected energy;
determining a stress in the heated and loaded structure from the Raman shift.
2. The method of claim 1 , comprising:
illuminating the structure with a laser.
3. The method of claim 1 , which further comprises determining a temperature of the structure from the energy received from the structure, wherein said determining a stress and said determining a temperature of the structure is from the energy received from the heated and loaded structure.
4. The method of claim 1 , wherein said determining includes:
measuring the Raman shift difference Δω m ; and
calculating stress components σij.
5. The method of claim 1 , wherein said determining includes determining the stress distribution below the surface of the structure.
6. The method of claim 3 , wherein said determining includes determining the thermal conductivity of the structure.
7. An apparatus for measurement of stress and temperature of a nanoscale or microscale structure, comprising:
a load cell configured and adapted to impart an axial compressive load to a nanoscale or microscale structure;
an electronic heater adapted and configured to heat the nanoscale or microscale structure by conduction while the nanoscale or microscale structure is being axially loaded;
a receiver configured and adapted to receive reflected energy from the nanoscale or microscale structure while the structure is being illuminated with laser energy; and
a processor connected to said receiver, the processor configured and adapted to detect a Raman shift in the received reflected energy, and
determine a stress and a temperature of the nanoscale or microscale structure from the Raman shift.
8. The apparatus of claim 7 , comprising:
a laser, the laser configured and adapted to impart laser energy to the structure.
9. The apparatus of claim 7 , wherein the processor determines at least one stress and at least one temperature of the structure from the same reflected energy.
10. The method of claim 1 wherein the elongate structure has an axis extending from the one end to the opposite end, and said applying a load is a compressive load in the direction of the axis.
11. The method of claim 1 wherein said heating is with an electronic heater in contact with a surface of the elongate structure.
12. The method of claim 11 wherein the surface is an end of the elongate structure.
13. The method of claim 1 wherein said heating is with a pair of electronic heaters, each heater being in contact with a different end of the elongate structure.
14. The method of claim 1 which further comprises illuminating a surface of the elongate structure with a laser, and said receiving energy is energy from the laser.
15. The method of claim 1 wherein the applied load is more than about one-tenth of a milliNewton and less than about five hundred milliNewtons.
16. The method of claim 1 which further comprises determining a temperature of the loaded structure from the Raman shift.
17. The method of claim 1 wherein the applied load is a compressive load.
18. The method of claim 17 wherein said heating is with an electronic heater in contact with a surface of the elongate structure.
19. The method of claim 18 which further comprises determining a temperature of the loaded structure from the Raman shift.
20. The method of claim 1 wherein the applied load is less than about five hundred milliNewtons.
21. The method of claim 7 wherein the nanoscale or microscale structure has an axis extending from the one end to the opposite end, and said load cell imparts the axial load to the one end.
22. The method of claim 21 wherein the structure is supported in cantilevered manner, and the one end is the free end.
23. The method of claim 7 wherein said heater is a first heater, and which further comprises a second electronic heater adapted and configured to heat the nanoscale or microscale structure by conduction, said first heater and said second heater being located on opposite sides of the nanoscale or microscale structure.
24. The method of claim 7 which further comprises a laser configured and adapted to illuminate the structure.
25. The method of claim 7 wherein said load cell is configured and adapted to impart a load of more than about one-tenth of a milliNewton and less than about five hundred milliNewtons.
26. The method of claim 7 wherein said load cell is adapted and configured to impart the axial compressive load to the free end of a cantilevered nanoscale or microscale structure.
27. The method of claim 26 wherein said load cell is configured and adapted to impart a load less than about five hundred milliNewtons.
28. The method of claim 27 wherein said heater is a first heater, and which further comprises a second electronic heater adapted and configured to heat the nanoscale or microscale structure by conduction, said first heater and said second heater being located on opposite sides of the nanoscale or microscale structure.