Recently, we demonstrated the self-assembling of Au nanoparticles/ dielectric layer/ Ag mirror sandwiches, namely, the local plasmon resonator, by using a dynamic oblique deposition technique¹. Due to strong interference, their optical absorption can be controlled between 0.1% and 100% by changing the thickness of the dielectric layer. Although we focused our attention only on the local field enhancement in that work, now we notice that photothermal conversion efficiency can be spatially tuned by using the local plasmon resonators. This work is the feasibility study of application of the local plasmon resonator to the spatially controlled nanoheaters.

We prepared combinatorial local plasmon resonator chips which have different thicknesses of Au and the dielectric layers on a single substrate of 50×50 mm² by oblique deposition and measured the absorption spectrum on each element. In order to evaluate the heat generation from Au nanoparticles, we measured the temperature of the water, with which a small cell created on a local plasmon resonator was filled, irradiating the laser of the wavelength of 785 nm. The temperature of the water on the element with high absorption becomes higher than that on the element with low absorption. The change in temperature proportional to absorption of the element in the local plasmons resonator chips. This suggests that the photothermal conversion efficiency can be controlled by the interference. Consequently, local plasmon resonator can be applied to the nanoheaters, which can spatially control the heat generation.

This work was supported by KAKENHI 21656058 and by the Iketani Science Foundation.

1. M. Suzuki, et al., Journal of Nanophotonics, 3, 031502 (2009).

Multifrequency drive capabilities have recently been implemented on the atomic force microscope (AFM) to enhance imaging contrast and retrieve information about the material properties of the sample surface¹. Common to each technique is the use of a complex (amplitude-modulated) waveform to oscillate the cantilever tip in proximity to the substrate at two or more of its flexural resonances. Simultaneous measure of the amplitude and phase of the cantilever ac deflection is used to characterize the tip-sample coupling and may, for example, relay mechanical and chemical information through the separation of short- and long- range forces between distinct resonance modes^2,3. In this way, bimodal imaging has also advanced magnetic³ and electrostatic⁴ force mapping with the application of appropriate fields. Related techniques track spatial variations in the contact resonance by evaluating the cantilever response across either a frequency band (band excitation, BE) or at fixed limits bracketing the peak (dual ac resonance tracking, DART). Resonance tracking also reduces crosstalk between the surface topography and frequency-dependent material properties, and has been employed to measure energy dissipation⁵, as well as for piezoelectric domain characterization⁶ and local thermal analysis⁷ with drive signals modulating the local electrical bias and temperature gradient, respectively. This work focuses on the latter approach: the use of dual frequency excitation to resistively heat and actuate an AFM tip for thermomechanical imaging of sample surfaces. Evaluation of the ac deflection at two frequency limits provides the amplitude and phase data required to extract the quality factor (dissipation) by the simple harmonic oscillator model¹. The experimental procedure (thermal DART) has been demonstrated along with data post-processing to establish a temperature-dependent study of surface mechanical properties.

¹R. Proksch and C. Callahan, United States Patent Application Publication US 2009/0013770 A1 (2009).

²R. Proksch, Applied Physics Letters 89, 113121 (2006).

³J.W. Li, J.P. Cleveland, and R. Proksch, Applied Physics Letters 94, 163118 (2009).

⁴R. W. Stark, N. Naujoks, A. Stemmer, Nanotechnology 18, 065502 (2007).

⁵S. Jesse, S.V. Kalinin, R. Proksch, A.P. Baddorf, and B.J. Rodriguez, Nanotechnology 18, 435503 (2007).

⁶B. J. Rodriguez, C. Callahan, S. V. Kalinin, and R. Proksch, Nanotechnology 18, 475504 (2007).

⁷M.P Nikiforov, S. Jesse, A.N. Morozovska, E.A. Eliseev, L.T. Germinario and S.V. Kalinin, Nanotechnology 20, 395709 (2009).

It is known that ceramic coatings with substantial amounts of structurally incorporated carbon show low-friction behavior, in particular at intermediate temperatures. However, the mechanisms behind activation, formation and modification of the required free carbon in the friction contact are still not fully understood, especially in the case of Ti_xCN_y, a widely used commercial coating. In a previous study the importance of the presence of water vapor for the formation of a friction-reducing layer has been revealed by tribological tests at different water vapor pressures in the surrounding atmosphere. In the present work, water adsorption studies on titanium nitride (TN) and titanium carbon nitride (TiCN) coatings are carried out in order to gain a new insight about the active chemical processes on the coating surface.

The TiN and TiCN coatings were prepared by dc magnetron sputtering of a TiN and Ti₂CN compound target, respectively, in an lab-scale deposition system. X-ray diffraction was used to study the crystal structure and the obtained patterns show a face-centered cubic structure with a [111] texture for TiCN and a [200] texture for TiN . Both X-ray Photoelectron Spectroscopy (XPS) and Temperature Program Desorption (TPD) experiments in the range 110-700 K were conducted in an Ultra High Vacuum chamber with a base pressure of ~ 3 x 10^-10 Torr. Also, the water adsorption on the coatings as a function of % relative hu midity was measured using a quartz crystal microbalance.

XPS measurements reveal the presence of a surface oxide, with the composition of the coatings being Ti_2.0N and Ti_1.73CN_1.35. TPD experiments show that water adsorption has a zero-order desorption mechanism. After low coverage and temperature of exposure of 110 K, the spectra yield calculated desorption energies of 22.96 ± 4.17 kJ/mol and 18.42 ± 4.73kJ/mol for the TiN and TiCN surfaces, respectively, based on a leading-edge analysis. Measurements from higher coverage indicate the strength of the water-water attractive interactions which cause clustering of H₂O into 2-D islands and then multilayers. The desorption energies from this regime are calculated to be 47.45 ± 2.31 kJ/mol and 41.73 ± 4.06 kJ/mol for the TiN and TiCN surfaces, respectively. These values are higher than the water’s combined heats of vaporization and fusion: ΔH_v + ΔH_f= 9.72 kcal/mol + 1.44 kcal/mol. The water adsorption results can be correlated to the microstructure, composition and tribological properties.