Using an atomic-force microscope* (AFM), we have studied the attractive and adhesive forces between a cantilever tip and sample surfaces as a function of sample surface energy. The measured forces systematically increased with surface energy. The AFM is very sensitive; changes in the surface forces (i.e., attraction and adhesion) of monolayer-covered samples could be clearly discerned when only the surface group of the monolayer film was changed from -CH3 to -CF3.PACS numbers: 68.35.Md, 62.20.PnThe atomic-force microscope 1 (AFM) has been used primarily to image the surfaces of insulating materials 2 " 6 with nanometer-scale resolution. The principal component of an AFM is a small cantilever which measures the force between a tip attached to the cantilever and the surface of interest. The force is determined by multiplying the measured cantilever deflection by the calibrated spring constant of the cantilever. Recording the deflection of the cantilever as a function of sample position generates a force map, or image, of the surface.Recently, the AFM has also been used to investigate the mechanical properties of materials including atomicscale friction, 7 elasticity, 8 and surface forces. 8,9 The dependence of the AFM surface-force measurement on tip-sample geometry and materials properties has not been studied systematically until now. In this study, cantilever tip size and shape are measured with a scanning electron microscope before and after use, and the composition, structure, and cleanliness of the sample surfaces are characterized using infrared reflectionabsorption spectroscopy. Sample surface energies are determined by contact angle measurements. We measure the attractive and adhesive forces between a tungsten tip and a variety of surfaces, and find the forces detected by AFM increase with sample surface energy. The attractive force results are compared to van der Waals forces calculated for a sphere approaching a flat surface. 10 Derjaguin-Muller-Toporov (DMT) adhesion theory 11,12 is used to analyze the adhesive forces. We estimate the contact area between tip and sample at zero applied load, and discuss the implications for tribology and imaging.Our instrument employs a "double cross" cantilever which constrains the motion of the tip to the z direction (normal to the sample surface). The cantilever has an effective spring constant of 50 ±10 N/m and its deflection is measured with a tunneling microscope. The tunneling microscope was operated in the constantcurrent mode, well below its maximum slew rate. Therefore, the force between the tunneling tip and cantilever was constant, and was ignored in our calculations. De-tails of the instrumentation are described elsewhere. The AFM measurements were done in a glove box under dry nitrogen. The partial pressure of water in the dry box was determined by dew-point measurements to be less than 1 /im of mercury. This is more than 3 orders of magnitude lower than the humidity required for nanometer capillary condensation. 10 As a result the measured attractive forc...

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A series of chemoselective polymers have been designed and synthesized in order to enhance the nitroaromatic sorption properties of coated acoustic wave devices. Acoustic wave (AW) devices coated with a thin layer of chemoselective polymer can provide highly sensitive transducers for the detection of vapors or gases. The sensitivity and selectivity of the sensor depends on several factors including the chemoselective coating used, the physical properties of the vapor(s) of interest, the selected transducer, and the operating conditions. To evaluate the effectiveness of the chemoselective coatings a polynitroaromatic vapor test bed was utilized to challenge polymer coated Surface Acoustic Wave (SAW) devices (@ 8mm2 active transducer area). Detection limits with the coated SAW sensors, as tested under laboratory conditions, are determined to be in the lower parts per trillion range. FTIR studies were undertaken to determine the nature ofthe polymer-polynitroaromafic interactions.

Nitrogen matrix reactions of alkaline earth metal atoms with ozone: Infrared spectra of the alkaline earth metal oxide molecules J. Chem. Phys. 62, 2320 (1975); 10.1063/1.430757Matrix reactions of alkali metal atoms with ozone: Infrared spectra of the alkali metal ozonide moleculesThe matrix reactions of copper atoms with ozone have been studied by infrared spectroscopy. Two products were found in the initial deposit: CuO,. which has a strong absorption at 802.3 cm -I, and CuO, which has its main feature, corresponding to the 6'CU l6 0 isotopic species, at 628.0 cm-I in solid argon. Copper atom reactions with oxygen-18,enriched ozone samples were used to obtain species identifications. The CuO J absorption was very similar in frequency and isotopic splitting behavior to alkali and alkaline earth metal ozonide species previously studied in matrices. The CuO frequency is in good agreement with gas phase measurements which put the ground state CuO vibrational fundamental at 631.3 cm-I • Temperature cycling of the Cu-O J matrices leads to CuO. formation by the secondary reaction of CuO with unreacted ozone.