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Nanoptek’s Digital PTM™: Unparalleled Affordable upgrade enhances your optical microscope
Right: Nanoptek's Digital PTM upgrade comprises computer, monitor, 12-bit cooled CCD camera, PTM software, and near-field transducers--just add your optical microscope for high resolution photon tunneling near-field microscopy!
Nanoptek’s New Digital PTM builds on award winning and patented technology that resolves topographic heights that are a fraction of a nanometer— all in realtime with your optical microscope. No scanning probes, no vacuum, no high energy electrons, no sample coating, and no high price! Experience an immediacy with your sample that no other profiling microscope provides. To see something very small, you have to get very close... Obvious, perhaps, but the underlying optical physics is quite subtle. Objects that are very small with respect to the wavelength of the light scatter and diffract that light into angles that are very far from the perpendicular (normal). In fact, some of the diffraction angles are so large that the light is trapped, and never leaves the surface of the object. To see, or resolve, the object, however, requires all of that light to be collected and brought to a focus. Another way of thinking about this is that the light which is scattered into such large angles contains the information about the smallest features of the object. Without that critical information contributing to the focused image, the smallest features will not be seen.
Collecting that information requires the lens to be very close to the object. Further, to gather the light that is trapped at the object’s surface requires that the lens not only be close, but also that it is of a highly refractive material. The trapped light is an evanescent, or ghostlike, light field that cannot travel, or propagate or radiate, from the surface. However, the field can exist for up to a few hundred nanometers away from the surface, although it becomes weaker quickly with distance. If a material with high refractive index is brought into the field, the trapped light is converted into propagating light, and so can travel up to the focus and contribute to the image. Unique Integral Near-Field Imaging. Nanoptek has developed significant technology, based on pioneering work at Polaroid by the founder, which enables super-resolved imaging by retrieving the important information in the evanescent field, but in devices that can be used outside of the lab and in real-world applications. We do this by integrating the near-field optics, and hence the near-field itself, with the sample itself, so that the photons are the probes. It is quite difficult in practice to place a lens
within the hundred nanometers or so of the sample that near-field imaging
requires. Unless in a clean-room environment, most common dust is many
times larger than this distance. Further, there is real risk of contact
damage to either the lens, the sample, or both. And if the sample is
curved, the curvature will prevent the lens from getting close enough.
Right: Polystyrene spheres
(9 micron diameter) With Nanoptek’s PTM, conceptually, the surface of the near-field optic is physically separated from the lens, and is made flexible on a macro scale. Placed directly onto the sample (contact, yes, but non-sliding, low force, and soft contact– no sharp scanning probes) and made optically continuous with the remainder of the near-field lens with index matching fluid, any object of any shape can be imaged with super-resolution, and in real-world rather than cleanroom conditions. Any dust in the evanescent field interface simply causes the flexible surface to locally lift up and over the dust, returning back to the sample away from the dust location. Because our PTM images an entire sample area, rather than scanning it with a probe, it is faster, while eliminating the servos and piezos for lower noise, easier use, and lower cost Instead of smaller and sharper, we went larger and flatter. We call this thin flexible near-field component a transducer, in that it converts topographic height in the sample surface into light intensity variations, because of the local differences in coupling of the evanescent field to and from the object. It is disposable. PTM Customers. We are proud to have CMC Magnetics Corp., one of the largest producers of optical media in the world, and Avon Products Corp. as our customers. These highly respected companies indicate the breadth of use of PTM, from QC and QA of the new high density DVD optical masters, stampers, and substrates, to dermatology, respectively. In addition, older analog Photon tunneling microscopes are currently in use at the U.S. Army Materials Lab (Aberdeen), Motorola, U.S. Precision Lens (now Corning Precision Lens), Polaroid Corp., Olympus, and J. Schaeffer Associates (operating at Lawrence Livermore Lab). Award Winning Product. Our Digital PTM improves upon the analog PTM, which won an R&D 100 Award (often called the “Nobel Prize for Engineering”), the Photonics’ Circle of Excellence Award, the Optical Society of America’s Engineering Excellence Award, and the Polaroid Product Development Award. In addition, PTM is cited in numerous texts on near-field optics, and has been published in Science and Applied Optics. Patented Technology. In addition to our own proprietary technology, know-how, and patents pending, we have license to nine broad and deep U.S. and International Patents with over 248 claims. How PTM Works: Light incident from a denser medium to a rarer medium, such as in a diamond in a ring or a prism in a chandelier, will be reflected totally from the interface between the two if certain conditions are met, namely that the incident angle is greater than the critical angle T c defined as: Tc = sin-1 (n2 /n1 ) where n2 and n1 are the indices of refraction of air and glass, respectively. However, Sir Isaac Newton demonstrated some centuries ago that, though the light is totally reflected, it penetrates beyond the glass and into the air for a very small distance, and decays in intensity E exponentially with distance z from the glass as:
Where dp is the decay distance defined as:
Because of this rapid decay and non-propagating
nature, this light was later termed evanescent. Further, penetration
of the glass/air interface by light beyond the critical angle is the
photonic analog to the quantum phenomenon of electron tunneling through
an energy barrier, and so has been called photon tunneling. Most recently,
some group evanescent light with propagating light that is within a
wavelength or so in distance from a surface into the general term of
near-field. The figure at right shows the finite air gap (2) that remains when our flexible transducer (1) is placed on the sample (3). When optically connected to an objective of numerical aperture (N.A.) greater than 1, photons are incident to the transducer/air interface at greater than the critical angle qcrit . If no sample is present, total internal reflection (TIR) occurs, with all light returning to the microscope. However, in TIR photons actually “tunnel” into the air before returning, giving rise to an “evanescent” field, so called because its intensity decays exponentially with distance from the transducer. With the sample in place, the evanescent field couples into the topography to a degree proportional to the topographic height. A grayscale tunneling image results that is converted to quantitative 3D with our proprietary calibration method and software. The condition for photon tunneling just described is easily replicated in a reflected light microscope with an oil immersion objective having a numerical aperture greater than unity. If operated dry, all of the light entering the objective beyond N.A. 1 is totally reflected, and an evanescent field is created in the focus and sample plane. In the actual photon tunneling microscope, the total reflection surface is the bottom of the polymer transducer that faces the sample, and is in turn oil immersed to the objective. As the sample’s topography penetrates the evanescent field, the field couples into the sample and propagates away from the microscope, creating a grayscale image in which light is low topography and dark is high topography. Calibration of the grayscale image to a known topography reference allows quantitative metrology of the sample topography. Further, the vertical resolution is limited only by the detector, rather than the light wavelength. Sectioning the 400 nm vertical PTM range by the 4096 graylevel response in a cooled 12 bit camera indicates resolution of 0.1 nm. In addition to refraction beyond the critical angle, as described above, the evanescent field is also created under other conditions—in fact, under any condition in which propagating light becomes untenable. For example, tapering an optical fiber waveguide down to below the cutoff, forcing light transmission through an aperture that is less than a wavelength in diameter, and diffracting light with a grating period less than a wavelength, such that the sine of the diffraction angle becomes imaginary, are all ways to create and evanescent field. The first two are used in scanning photon tunneling microscopes (PSTM) and near-field scanning optical microscopes (NSOM), respectively. In principle, high vertical resolution is achieved in these microscopes via the evanescent or near-field at the probe, and the small probe tip also allows resolution in the lateral plane. However, the servo noise in the electronics and mechanics of scanning probe instruments reduces the signal to noise and prevents full use of the near-field information. In contrast, in PTM the probe is a large, flat, smooth, and flexible transducer that is placed in soft contact with the sample, thereby integrating the near-field optic, and hence the near-field, with the sample. There is no relative movement between the two, so that all of the inherent high resolution information in the near-field image so obtained can be fully used. Vertical resolution is higher than for scanning probe instruments, while lateral resolution approaches that of NSOM. Ref.: Guerra, J. M., et al, “Photon tunneling microscopy of polymeric surfaces,” Science, Vol. 262, pp. 1395-1400, 1993. Applications. The PTM was developed for dielectric homogenous samples such as polymers, but can also be used successfully on silicon, copper, brass, stainless steel, beryllium copper, and many other materials. Some of the myriad applications include:
PTM and the Competition. PTM’s topographic resolution is higher than SEM’s, is quantified, and requires minimal sample preparation— no coating or damaging vacuum or high energy electrons. PTM’s topographic resolution is equal to AFM or NSOM but faster— video refresh rate 3-D display of more than 150 micron diameter sample fields. PTM’s lateral resolution is better than confocal or phase shifted interference microscopes. PTM requires no infrastructure, is easy an inexpensive to operate, and is a fraction of the cost of the above to purchase. It can be used to compliment the above: survey your sample quickly with PTM, identify areas of interest to decrease AFM or SEM lab time costs. The learning curve for PTM is short, so engineers can use it directly with no technician go-between. PTM has a small footprint, and can operate outside of a cleanroom. PTM is even vibration tolerant, and so can operate on a desktop. Digital PTM Feature:
Benefit:
PTM System Specifications * The Digital PTM includes a cooled 12 bit camera, computer, calibration reference, 20 re-coatable 75 mm near-field transducers on silicon wafer carriers, all manuals and software CDs, and full customer support. All system components are chosen to meet our demanding specifications and our standards for quality and support. Vertical Resolution: Sub-nanometer Lateral Resolution: 150 nm or better Vertical range: 400 nm Field of View: 150 µm diagonal or more (optical specs are quoted for a diffraction-limited Nikon Eclipse microscope or equivalent with a 1.40 N.A. 100X objective and 4X camera adapter) Tunneling image acquisition speed: Visual is real time, digital is 40 µsec single frame and 30 FPS or more multiple frame (depends on ROI size). Image 3-D display speed: Video rate at full 12 bit resolution with ROI, or full-field with 2x2 binning and 8 bit Quantitative linear metrology: Sample-up total system calibration to NIST traceable reference provided. Camera: Peltier cooled 12 bit (4096 gray levels) monochrome progressive scan interline transfer CCD, 1.3 Mega pixels, 30 FPS full field with binning and 8 bit preview mode or with 12 bit and ROI, FireWire IEEE 1394 Digital Interface, 6.7µm square pixels for high dynamic range and high SNR, high speed low noise electronics, exposure/integration control 40 µsec to 15 minutes, real time image previewing even in 3-D Computer: Full tower, Intel™ Pentium 4™ Processor 2.53 GHz, 512 MB PC 1066 RDRAM, 533 clock, 80GB Ultra ATA Hard Drive, DVD-RAM/-R/CDRW Recorder, 128MB NVidia GForce4 MX440G AGP Graphics with TV out, 10/100 ethernet, Firewire ports, Windows XP, Microsoft Works Suite 2003, keyboard, optical mouse. Display: 18 inch viewable LCD flat panel high contrast display Near-field Transducer: Flexible, soft contact 75 mm diameter polymer, 15 to 20 microns thick. Transducer face is sealed to prime polished silicon wafer at the factory. Smooth to better than resolution of PTM. Hydrophobic for preservation of tunneling gap. Impervious to immersion oil. Wafers can be recycled. Software: Our PTM software provides a powerful scientific data acquisition and analysis environment that is also user-programmable. Features include: Auto exposure for best use of camera’s dynamic range Live histogram as well as x and y profile display for optimum focusing Video-rate 3-D topography display Real-time 3-D perspective control User-defined frame averaging Automatic X, Y, and Z calibration of photon tunneling image to actual topography with included reference and our high-order non-linear curve fitting with FFT analysis. Full 3-D roughness analysis: PV, RMS, Ra, autocorrelation Extensive image analysis including 2D FFTs, wavelet transformations, convolutions, line profiles, particle analysis, edge detection (eight methods, including Sobel), and thresholding (five methods, including fuzzy entropy) Intuitive generation of scientific publication quality graphs and page layouts Optical Microscope: Our PTM upgrade package is compatible with standard optical microscopes, including inverted, having these features: reflected-light (epi) Kohler illumination, C-mount camera port, and 1.25 to 1.40 N.A. oil immersion objective (the latter is required for tunneling in water). Such microscopes include the Nikon Eclipse series, Zeis Axiophot series, Olympus, and Leica. We can also provide you with a microscope of your choice if required. Options Complete PTM with our optical microscope our the scope of your choice Cameras from other manufacturers (SDK must be available) Application-specific near-field transducers– Call us Analytical PTM: Spectrophotometer with adapter mates to our camera and provides integrated micro-spectrophotometry with our software upgrade. Lithography package: Call us Three axis Piezo stage and controller *Specifications subject to change.
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