• Some words about words: - The molecule is detected (signal).

- Molecules are only resolved if they are separated by a distance ~aperture size.

- The field profile of the tip is imaged.

• Sample is KTP with Rb-doped regions.

Raman spectra on a KTP sample:

• On and Off a Rb-doped region.

• C.L. Jahncke, H.D. Hallen, and M. A. Paesler, "Nano-Raman spectroscopy and imaging with the near-field scanning optical microscope," An invited contribution to the J. Raman Spectr. 27, 579-586 (1996).

• C.L. Jahncke, M. A. Paesler, and H.D. Hallen, APL 67, (17), 2483-2485 (1995).

Normalized to peak at 767 cm^-1. Both far-field measurements agree.

Normalized to peak at 767 cm^-1. Both far-field measurements agree.

• E. Betzig et al. Appl. Opt. 31, 22 (1992).

• P.J. Moyer and M.A. Paesler, SPIE 1855, 58-66 (1993).

Higher sensitivity can be obtained by oscillating the polarization:

• M. Vaez-Iravani and R. Toledo-Crow, APL 63, 138-40 (1993).

• E.B. McDaniel, S.C. McClain, J.W.P. Hsu, Appl. Opt. 37, 84 (1998).

• D.A. Higgins et al. J. Phys. Chem. 100 (32) 13794-803

• Some light polarized normal to the sample exists in the near-field region (theory verified).

• Any roughness on the coating will disrupt the tip polarization state or alter intensity vs. angle.

Metal samples with polarized light

• Boundary conditions are the same as for the metal coating on the tip -- the tangential component of the electric field must be zero.

• This gives strong polarization effects.

• Transmission:

- for a long metal strip, light polarized parallel to the strip will tend to be reflected back up the fiber.

- light perpendicular to the strip will be able to couple around the edge and be collected.

• Reflection - The new condition is that the light must make it way around the tip and up into the far-field.

- This changes the problem. Light levels are much smaller, and light polarized parallel to the strip are better able to couple out from under the tip and be reflected to the far-field.

• Reflection mode operation is much more susceptible to tip-induced artifacts than the transmission mode measurements.

- This is because the light must couple out from beneath the probe tip.

- One can get shadowing effects.

- Polarization data taken after a tip crash can show different behavior for the different polarization directions.

Dielectric samples with polarized light

• Less polarization dependence from small small structures.

• Birefringent samples: more.

• Light can be used to sense the magnetic field by use of the Faraday effect which rotates the polarization of the light.

• This can be done in either transmission or reflection.

• The polarization rotation can be small (~1°), but is observable (crossed polarizers without the sample).

• Image contrast can be reversed by rotating the analyzer (good check).

Early work -- magnetic bubbles and magneto-optic films

• E. Betzig, J.K. Trautman, J.S. Weiner, T.D. Harris and R. Wolfe, Applied Optics, 31, 4563-4568 (1992).

• E. Betzig, J.K. Trautman, R. Wolfe, E.M. Gyorgy and P.L. Finn, APL, 61, 142-144 (1992).

Recent magneto-optic imaging

• G. Eggers et al, Surf. and Inter. Anal. 75 (7-8) 483-7 (1997).

• C. Durkin, C. Lodder, I.V. Shvets, JAP 81 (8) 5019 (1997).

• M.R. Pufall, A. Berger and S. Schultz, JAP 81 (8) 5684-91 (1997).

Theory

• D. van Labeke, A. Vial and D. Barchiesi, SPIE 2782, 559-69 (1996).

A review of magnetic imaging with probe microscopes

• U. Hartmann, J. Magn. and Magn. Mater. 157-158, 545-9 (1996).

• A magnetic material is evaporated on a transparent substrate.

• The magnetic fields are all aligned in the same direction along the 'tracks'.

• The media is read by observing the rotation of the polarization of the NSOM signal.

• Bits are written by increasing the power input into the fiber probe.

• The tip of the probe heats up, and transfers energy to the sample locally. This raises the temperature of the magnetic film above the Curie temperature, and the direction of the field in the local region reverses (driven by the magnetic field from the neighboring areas).

• Read time is thus limited by the signal to noise for polarization detection (can be influenced by the topography).

• Write time is limited by the thermal transfer process.

• Seek time is limited by the speed of the feedback system to maintain the position of the probe in the near-field while avoiding a crash.

• Long term reliability is probably determined by the probe life, which is currently quite short even without the rapid raster rates.

• Density of bits is very high.

• To attain high enough rates, one may have to use several probes in parallel.

• NSOM holds much promise as many of the standard techniques developed for the far-field can be utilized by NSOM, including

- polarization contrast - index contrast - fluorescence (including all the dyes and methods for their attachment to cell structures). - luminescence - Raman spectroscopy - Infrared spectroscopy - Time-resolved measurements

• Fluorescence has been used to date.

• In addition, the topographic image provided by the force feedback provides additional information.

• NSOM is friendly in terms of imaging environment (water O.K.) and sample preparation (little required).

Early tissue slices, fibroblast cells.

• E. Betzig et al, Biophysics J. 49, 269-79 (1986).

• E. Betzig et al, Bioimaging 1 (3) 129-35 (1993).

• E. Betzig in Near Field Optics, D.W. Pohl and D. Courjon, eds. (Arc-et-Senans, France, Kluwer) 1993, 7.

Phospholipid monolayers

• Jeesong Hwang et al, Science 270 (5236) 610-44 (1995).

'Intact' myofibrils

• E.J. Seibel and G.H. Pollack, J. Microsc. 186 (3) 221-31 (1997).

Chromosomes

• M.H.P. Moers, W.H.J.Kalle, N.F. Van Hulst, J. Micr. 182 p1,40 (1996)

• N.VanHulst,M.Garcia-Parajo,A.Ruiter,J.Struct Bio.119(2)222(1997).

• W. Wiegrabe, et al. Surf. and Interf. Anal. 25 (7-8) 510-13 (1997).

In addition, much work has been done on organic films and

• Limitations for biological imaging:

- NSOM is a surface sensitive technique. Cell membranes Thin parts of cells such as moving cells (fibroblast cells work well).

- Cells can move. This is equivalent to microscope drift. Requires rapid imaging and a fast feedback loop.

Problem: many of the high power techniques require slow imaging to obtain adequate signal to noise.

Solution options: drug or kill the cells to slow them down, live with low signal to noise images, work with larger probes and sacrifice resolution.

- The effect of a possibly hot tip nearby has not been completely considered.

- Resolution may not be high enough for use on single molecules in an imaging sense. (although single molecules can be detected)

• To reduce dissipation in electro-optic devices, one wishes to reduce the threshold current, so builds very small lasers.

• Studying these lasers is difficult if only the far- field data is used.

• NSOM can bridge the gap between the lithography and the far-field radiation pattern by allowing one to study the light intensity profile in the near-field and transition regions.

• Dopant profiles can be investigated by observing the luminescence and lasing in the near field -- the functional forms of the intensity decay are different for luminescence and lasing

• Wave guide leakage can also be explored.

Early laser image, including a hot spot seen with topography

• S.K. Burratto et al. JAP 76, 7720 (1994) & APL 65, 2654 (1994).

Waveguides

• A.G. Choo et al, Ultramicroscopy 57, 124-9 (1995).

Aging of lasers

• A Richter, Ch. Lienan, J.W. Tomm, Surf & Interf. Anal. 25 (7-8) 573-82 (1997).

E-fields

• J.K. Leung, C.C. William and J.M. Olson, Phys Rev B56 (3) 1472-8 (1997).

Lasers and luminescence

• Lin Jutmy et al, APL 69 (23) 3519-21 (1996).

• I Fischer et al. Europhys Lett. 35 (8) 579-84 (1996).

• M. Ohtsu et al, JJAP 36 (7B) pt 2 L896-8 (1997).

• NSOM has been used to extend several characterization techniques to higher resolution, here is a sampling:

All-optical carrier lifetime measurements

• A. LaRosa, B. I. Yakobson, H.D. Hallen, APL 70 (13), 1656 (1997).

• A. LaRosa, C.L. Jahncke, and H.D. Hallen, SPIE 2384, 101 (1995).

• A. LaRosa, C.L. Jahncke, and H.D. Hallen, Ultramicroscopy 57, 303-308 (1995).

NOBIC (Near-field optical beam induced carriers)

• Xu Qin, M.H. Gray, J.W.P. Hsu, JAP 82 (2) 748-55 (1997).

Threading dislocations with polarization studies

• J.W.P. Hsu et al, APL 65 (3) 344-6 (1994); JAP 79(10) 7743 (1996).

Solar cells

• A.A. McDaniel, J.W.P. Hsu, A.M. Gabor, APL 70 (26) 3555-7 (1997).

SOI (silicon on insulator)

• A. LaRosa, B. I. Yakobson, H.D. Hallen, Proc of Diagn Tech for Semic Mater Proc II (Boston, MA, 27-30 Nov 1995) Mat. Res. Soc. Symp. Proc. 406, 189-194 (1996).

Spectroscopy

• W.M. Duncan, above MRS meeting, 183-8.

• B.B. Goldberg et al, above MRS meeting, 171-82.

• H.D. Hallen, A. LaRosa, C.L. Jahncke, Phys Stat Solidi (a) 152, 257-268 (1995).

• C. Coluzza et al, SPIE 2782, 591-601 (1996).

Surface passivation

• J. Liu and T. Kuech, APL 69 (5) 662-4 (1996).

• J. Liu and T. Kuech, above MRS meeting, 523-8.

Devices

• R.M. Cramer et al, Proc. 22nd Int. Symp for Testing and Failure Anal, 19-24 (Los Angeles, CA, 18-22 Nov 1996).

• J.P. Fillard, DRIP95, p. 195-200 (Boulder, CO, 3-6 Dec 1995).

Optical Measurements of Recombination Time Constants

-- The Experimental Set-Up --

Variation of the Visible Light Chopping Frequency

• The lifetime can be quantitatively measured from

the 'knee' position (2 samples shown).

• Images at different frequencies highlight the slower

lifetime process or the faster diffusion process.

Silicon-on -Insulator

• A. LaRosa, B. I. Yakobson, H.D. Hallen, Mat. Res. Soc. Symp. Proc. 406, 189-194 (1996).

• Some regions reflect carrier lifetime as above.

• Other regions, of less uniform thickness, also reflect

the ability of the carriers to diffuse away -- thickness

variations:

• Question:

- Why do we obtain high resolution when carrier diffusion is so large?

- The carriers, once formed locally by the visible light, rapidly diffuse.

- The diffusion profile reflects the local time constant.

- D is reflected in the contrast.