Silicon tips

It may be that in years to come, interatomic potentials can be estimated experimentally by the use of the atomic force microscope (Section 6.2.3). A first step in this direction has been taken by Jarvis et al. (1996), who used a force feedback loop in an AFM to prevent sudden springback when the probing silicon tip approaches the silicon specimen. The authors claim that their method means that force-distance spectroscopy of specific sites is possible - mechanical characterisation of the potentials of specific chemical bonds . 

Field emission displays are VFDs that use field emission cathodes as the electron source. The cathodes can be molybdenum microtips,33-35 carbon films,36,37 carbon nanotubes,38" 16 diamond tips,47 or other nanoscale-emitting materials.48 Niobium silicide applied as a protective layer on silicon tip field emission arrays has been claimed to improve the emission efficiency and stability.49 ZnO Zn is used in monochrome field emission device (FED) displays but its disadvantage is that it saturates at over 200 V.29... 

Fig. 2 OCM images of trichomes (shown by arrows) on the Urtica dioica L. leaf a - sting with silicon tip (edge) b - without tip (edge) c - ordinary trichome.

Nanotubes are being used as points in some SPM units. The ends of these nanotubes can be closed or functionalized offering even finer tips and tips that interact with specific sites allowing manipulation on an atom-by-atom basis. These nanotubes are typically smaller than silicon tips and are generally more robust. 

Fig. 4.16 (a) Computer simulated image of a silicon tip within a basic crystallographic triangle. In this image, no atomic reconstruction is assumed, (b) A map of the indices of the facets of the same surface. (c) A field ion image of the same triangular surface area. Note that all these surfaces are reconstructed. 

Figure 13.5(d) presents experimental stiffness measurements using differential UFM for three high modulus surfaces sapphire, Si(100) and LiF(lOO) (Dinelli et al. 2000b). The samples were probed with the same silicon tip on a V-shaped cantilever (nominally cantilever stiffness was kc - 2.8 nN nm 1,and radius of curvature R = 10 nm). The surface RMS roughness of the surfaces was less than 0.2 nm over a few square micrometres for all three samples. The relative difference between the three sets of data reveals that the elastic properties of these three materials can be distinguished by differential UFM the relative independence of the applied force may indicate the fact that the tip had been flattened by extended contact with such hard samples. 

Bale, M., and R.E. Palmer. 2002. Microfabrication of silicon tip stmetures for multiple-probe scanning tunneling microscopy. J. Vac. Sci. Technol. B 20 364-369. 

Micromasch, Estonia) was used. Radius of silicon tip was about 60 nm. 

Measurements by Atomic Force Microscopy (in tappingmode, using a standard silicon tip with a radius of 10 nm) of the surface topography of both the lower and the upper interface (the surface of the aluminum electrode and that of the polymer film, respectively) revealed a typical root-mean square roughness of 3 nm or less... 

All AFM measurements were carried out by means of a NanoScope Ilia - Multimode (Veeco, USA). The instrument was equipped with an electrically conducting cantilever with a silicon tip (Pointprobe EFM sensor, NanoSensors, Wetzlar, Germany). An overall metallic... 

A multimode AFM instrument and a NanoScope IV-D3100 (Digital Instruments, Santa Barbara) were operated in the tapping mode. Silicon tips with a radius of 10-20 nm, a spring constant of 30N/m and a resonance frequency of 250-300 kHz were used. 

The equipment and a method of research. Research was made on an atomic force microscope NTegra (NT-MDT, Russia). Silicon cantilever CSC 12(B) (Micromasch, Estonia) was used. Radius of silicon tip was about 60 nm. 

Fig. 16.3 Electric field distribution of a silver tip apex (30 run (()) excited by (a) p-polarized and (b) s-polarized light (K 532 nm). (c) and (d) are the field distribution of Si02 and silicon tip with...

Tarun A, Hayazawa N, Kawata S (2010) Site-selective cutting of carbon nanotubes by laser heated silicon tip. Jpn J Appl Phys 49 025003... 

Fullerene C(,o adsorbed onto STM tips has been reported to enhance atomic resolution images of highly oriented pyrolytic graphite [110]. Recently, Dai et al. [Ill] have demonstrated that multiwalled carbon nanotubes (MWNTs) attached to the silicon cantilever of a conventional atomic force microscope (AFM) can be used as well-defined tips with exceptionally high resistance to damage from tip crashes. The MWNT were attached by first coating the bottom 1 -2 mm section of the silicon tip with an acrylic adhesive by inserting them... 

SFM also enables us to measure specific interaction forces between a small silicon tip and the surface. The pull-off forces between the tip and the surface estimated from Force vs Distance Curves (FDC) can be correlated to the adhesive interactions between tip and surface [9]. Recording of FDCs line-by-line allows us to image surface topography and adhesive surface properties simultaneously [10]. This technique has some disadvantages, like the requirement for a large amount of data acquisition and analysis, which have been alleviated by the invention of the Pulsed Force Mode (PFM). The PFM simplifies and accelerates the measurements of adhesive properties with high lateral resolution [11, 12]. 

To simulate the toner-silica interactions, PS/PMMA blends were used as a model for polystyrene/acrylic toners. Silicon tips modified either with HMDS or with PDMS were applied to model surface-treated silica particles. The Pulsed Force Mode images of PS/PMMA films displayed... 

Fig. 2. Pulsed Force Mode images of PS/PMMA blend show no distinct changes in the tcqpography (upper row) when silylated tips are used but a clear dqiendence on the adhesive contrast (lower row). With a pure silicon tip (A), the elevated areas show higher adhesion after silylation, contrast is reversed. The HMDS-modified tip (B) shows a lower maximum force than the PDMS-treated tip (C).

Other Applications. Despite the ability of TED spectroscopy to detect surface states, comparatively little work has been done with semi-conductors. In a careful study of germanium Shepherd identified emission from the valence band and also from a band of surface states. Conduction band emission is negligible in the [100] direction but has been detected in emission from Ge (111). TED spectra from both field-evaporated and annealed 200 ohm-cm p-type silicon tips show electrons to be emitted from occupied surface states within the band gap which lie close to, and overlap, the valence band edge. TED spectra from CdS, PbTe, and GaP have proved to be broad and to contain tittle information. Weak unidentified features appear in the TED from TiC crystals and much stronger field-dependent peaks... 

Compare the contact areas in contact mode using Equation 5.5 (1) a silicon tip with an iron sample, and (2) a silicon tip with a polymer sample. Assume that the contact force is 10 nN and radius of the tip is 80 nm the Young s modulus of tip, iron and polymer are about 0.17 x 1012,0.2 x 1012 and 0.1 x 1012 Nm-2, respectively and their Poisson ratio is about 0.3. 

The results of various research groups show strong differences in the thickness of the QLL. Pittenger et al. calculated the thickness of the QLL assuming that it has the viscosity of supercooled water they estimated the QLL thickness to be about 1 nm at -1°C and 0.2 nm at -10°C for a silicon tip. For a hydrophobically coated tip, the layer thicknesses were slightly smaller. Several authors have used the jump-in distance to estimate the thickness of the QLL (gradient of the tip-sample forces becomes greater than... 

Hajra, M. Chubun, N.N. Chakhovskoi, A.G. Hunt, C.E. Liu, K. Murali, A. Risbud, S.H. Tyler, T. Zhirnov, V. Field emission characterization of silicon tip arrays coated with GaN and diamond nanoparticle clusters. Electrical and Computer Engineering Department, University of California, Davis, CA. J. Vacuum Sci. Technol. B Microelectron. Nanometer Struct.—Process. Meas. Phenom. 2003, 2/(1), 458-463. 

---