tions between the beam electrons conducted by a piezoelectric and weakly bound electrons in the tube scanner which scans the tip conduction band of the sample. in a raster pattern with respect Some energy from the beam to the sample (or scans to the electrons is transferred to the sample with respect to the tip). conduction band electrons in the The tip-sample interaction is sample,providing enough energy monitored by reflecting a laser for their escape from the sample off the back of the cantilever surface as secondary electrons. into a split photodiode detector. Secondary electrons are low By detecting the difference in energy electrons (<50eV),so only the photodetector output those formed within the first few voltages,changes in the cantile- nanometers of the sample surface ver deflection or oscillation NCSU have enough energy to escape and amplitude are determined.A Hit Zero Crossing Stopband Eneest be detected.High energy beam schematic of this can be seen in b electrons which are scattered back Figure 1. out of the sample(backscattered electrons)can also form secondary The two most commonly used electrons when they leave the modes of operation are contact surface.Since these electrons mode AFM and travel farther into the sample than TappingModeTM AFM,which the secondary electrons,they can are conducted in air or liquid emerge from the sample at a much environments.Contact mode larger distance away from the AFM consists of scanning the impact of the incident beam probe across a sample surface which makes their spatial distribu- while monitoring the change in tion larger.Once these electrons cantilever deflection with the escape from the sample surface, split photodiode detector.A Figure 5:(a)SEM image of rugged polysilicon thin they are typically detected by an feedback loop maintains a film.100,000x,Bar=0.1um;(b)TappingMode AFM Everhart-Thornley scintillator- constant cantilever deflection by image of the same with roughness measurement. photomultiplier detector.The vertically moving the scanner to 1um scan. SEM image formed is the result of maintain a constant photodetec- the intensity of the secondary tor difference signal.The electron emission from the sample distance the scanner moves at each x,y data point during the vertically at each x,y data point rastering of the electron beam is stored by the computer to across the surface. form the topographic image of the sample surface.This Atomic Force Microscopy feedback loop maintains a constant force during imaging, AFM consists of scanning a sharp which typically ranges between tip on the end of a flexible 0.1to100nN. cantilever across a sample surface while maintaining a small, TappingMode AFM consists of constant force.An integrated oscillating the cantilever at its silicon tip and cantilever can be resonance frequency(typically seen in Figure 3.The tips -30okHz)and lightly“tapping” typically have an end radius of on the surface during scanning. 2nm to 20nm,depending on tip The laser deflection method is type.The scanning motion is used to detect the root-mean- 33 tions between the beam electrons and weakly bound electrons in the conduction band of the sample. Some energy from the beam electrons is transferred to the conduction band electrons in the sample, providing enough energy for their escape from the sample surface as secondary electrons. Secondary electrons are low energy electrons (<50eV), so only those formed within the first few nanometers of the sample surface have enough energy to escape and be detected. High energy beam electrons which are scattered back out of the sample (backscattered electrons) can also form secondary electrons when they leave the surface. Since these electrons travel farther into the sample than the secondary electrons, they can emerge from the sample at a much larger distance away from the impact of the incident beam which makes their spatial distribu￾tion larger. Once these electrons escape from the sample surface, they are typically detected by an Everhart-Thornley scintillator￾photomultiplier detector. The SEM image formed is the result of the intensity of the secondary electron emission from the sample at each x,y data point during the rastering of the electron beam across the surface. Atomic Force Microscopy AFM consists of scanning a sharp tip on the end of a flexible cantilever across a sample surface while maintaining a small, constant force. An integrated silicon tip and cantilever can be seen in Figure 3. The tips typically have an end radius of 2nm to 20nm, depending on tip type. The scanning motion is conducted by a piezoelectric tube scanner which scans the tip in a raster pattern with respect to the sample (or scans to the sample with respect to the tip). The tip-sample interaction is monitored by reflecting a laser off the back of the cantilever into a split photodiode detector. By detecting the difference in the photodetector output voltages, changes in the cantile￾ver deflection or oscillation amplitude are determined. A schematic of this can be seen in Figure 1. The two most commonly used modes of operation are contact mode AFM and TappingModeTM AFM, which are conducted in air or liquid environments. Contact mode AFM consists of scanning the probe across a sample surface while monitoring the change in cantilever deflection with the split photodiode detector. A feedback loop maintains a constant cantilever deflection by vertically moving the scanner to maintain a constant photodetec￾tor difference signal. The distance the scanner moves vertically at each x,y data point is stored by the computer to form the topographic image of the sample surface. This feedback loop maintains a constant force during imaging, which typically ranges between 0.1 to 100nN. TappingMode AFM consists of oscillating the cantilever at its resonance frequency (typically ~300kHz) and lightly “tapping” on the surface during scanning. The laser deflection method is used to detect the root-mean￾Figure 5: (a) SEM image of rugged polysilicon thin film. 100,000x, Bar=0.1µm; (b) TappingMode AFM image of the same with roughness measurement. 1µm scan. (a) (b)