The MAX-phases are ternary compounds with the general composition M_n+1AX_n (n=1-3), where M is an early transition metal, A an element mainly from the groups IIIA-VA and X is nitrogen or carbon. They can be described as nanolaminates with MX slabs interleaved with single layers of the A-element. This special structure gives these compounds very interesting properties. Hitherto, Ti₃SiC₂ has attained most research interest since it is elastically stiff, electrically and thermally conductive, chemically very inert, but also easily machinable and with self-lubricating properties. Other MAX compounds have been reported to exhibit similar properties. Due to the large number of possible elements that can be included in the MAX-phases, these compounds can be designed to exhibit special properties in different applications.

We have recently demonstrated that epitaxial thin films of MAX-phases in the Ti-Si-C system can be deposited by magnetron sputtering using elemental targets. In this study, we present results from the Ti-Al-C system. We have deposited single-crystalline and epitaxial films of Ti₂AlC and Ti₃AlC₂ on Al₂O₃(0001) at 900°C. At lower temperatures, the phase composition changes into cubic TiC with a solid solution of Al. The films have been characterized by XRD, XPS and high-resolution TEM. Mechanical and electrical properties have been studied with nanoindentation and four-point-probe measurements. The materials chemistry of the MAX-phases in the Ti-Al-C and Ti-Si-C systems will be compared and the differences in physical properties are discussed. Furthermore, the influence of Si substitution of Al, i.e. Ti_n+1(Al_xSi_1-x)C_n, has been investigated.

Recently, micro and nano fluidic devices have been developed and applied to wide fields. Highly sensitive molecular sensing techniques are necessary for much wider application, in particularly to biomedical field. Here we report a novel molecular sensing technique based on the photothermal detection of molecules by using a nano metal thin-film grating structure.

Nano gratings of chromium evaporated on fused silica substrates were patterned by electron beam lithography and selective etching of windows. The typical period of a grating was 1000 nm, in which a window of 600 nm is etched from the blank. Periods of bright and dark stripes are thus formed on the sample solution when irradiated by a pump beam pulse, cast through the metal grating. Then, the solution was spatially modulated in accord with the grating pattern along with many of its properties. These changes can be detected by the probe beam output which went through the diffraction of the metal grating and the modulated liquid combined.

We obtained time-profiles of the diffracted signals of nitrobenzene in 2-propanol. Nanosecond pulsed UV beam (355nm) of a Nd:YAG laser and a red beam (633 nm) of a cw He-Ne laser were used as pump and probe beams, respectively. By the theoretical analysis, we assume that the signal attributed to the spatial modulation was due to temperature and density variation. Also we found that the signal intensity and decay rate/time were proportional to the molecular concentration and thermal diffusion coefficient of 2-propanol.

This sensing technique has many advantages compared with traditional optical techniques; such as: (1) simple setting, easy alignment, (2) high sensitivity, low noise, (3) high speed (high modulation frequency) detection, and (4) ease in analysis. This molecular sensing technique should be a very powerful and useful tool for nano and microfluidic devices indeed.

A comparative study of the characteristics exhibited by the nanocomposite copolymer films with self-assembled ZnO nanoclusters on Si and SiO₂/Si substrates, when using two different diblock copolymers - polystyrene-acrylic acid (PS-b-PAA) and polystyrene-methacrylic acid (PS-b-PMAA)with block repeat unit ratios of 16500 to 4500 and 33000 to 6700, respectively, is reported. These block ratios allowed the formation of nanosized spherical domains, due to microphase separation of the minority blocks in solid phase. The methodology for the self-assembly process of ZnO involved the doping of the copolymers with ZnCl₂ precursor in liquid phase at room temperature, followed by the ZnCl₂ nanocluster formation within the spherical domains on Si and SiO₂/Si surfaces and subsequent conversion into ZnO. Two conversion methods, a wet chemical process using weak base, NH₄OH and a new dry chemical process using Ozone, were investigated. The study showed that the treatment with ozone provided better conversion rate with minimal loss of ZnO than the wet chemical process. The conversions of ZnCl₂ to ZnO nanoclusters were verified and evaluated using x-ray photoelectron spectroscopy (XPS). The comparisons of the two nanocomposite films showed poor solvent evaporation with poly(styrene-acrylic acid) and shorter wet chemical treatment time with poly(styrene-methacrylic acid) while the new dry technique was equally effective for conversion on both Si and SiO₂/Si surfaces. Morphological characteristics of the nanocomposite films were obtained using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The AFM and SEM images showed the spherical morphology of the ZnO nanoclusters within the polymer matrix and provided an evaluation of the nanocluster sizes between the two copolymers as the domain sizes are tunable with the change in the molecular length of the block.

The support of NSF grants ECS#9980794 and ECS#0302494 are greatly acknowledged.

Properly functionalized and structurally ordered mesoporous materials such as MCM-type silicas and aluminas, with tunable pore size and narrow pore-size distributions have attracted much attention for their potential applications in adsorption, catalysis, separation and sensing^1,2. These materials allow for a bottoms-up molecular design strategy to their synthesis³ thus making them attractive candidates for tailored nanotribological films. For example, organo-functionalized MCM-type silicas could function as synthetic thin lubricant films for adaptive tribological applications via careful and selective functionalization of the exterior and interior surfaces of these ordered structures. Such films would possess the structure and order that provides beneficial contact properties to minimize friction and wear and exhibit the reactivity required for adaptive characteristics. However investigations of tribological properties of such films appear to be lacking.

In this study, the nanotribological behavior of mesoporous silica nanosphere (MSN) films with different external functional layers that exhibit different reactivity levels to moisture - Polylactic acid (PLA), Polyamidoamine (PAMAM) and Polyglutamic acid (PG) are investigated using scanning probe microscopy. The tribological behavior of these films are compared to that of alkane-thiol self-assembled monolayer films that have similar end groups (-COOH). The affect of varying humidity on the nanoscale friction behavior of the MSN films is also studied to evaluate the feasibility of using these films as tribologically adaptive films.

¹A. Stein, et al. Adv. Mater. (Weinheim, Ger.) 2000, vol 12, pp. 1403-1419.

²A. Sayari, S. Hamoudi, Chem. Mater. 2001, vol 13, pp. 3151-3168.

³C-Y. Lai et al. J. Am. Chem. Soc. 2003, vol 125, pp. 4451-4459.

Today, controlled modification of polymeric surface properties induced by the interaction of energetic photons and plasmas has become a field of considerable technical importance. It can be used to improve adhesion properties of metal coatings on polymers by changing the morphology and the chemical properties of the polymer surface.

In most cases, it is necessary to use nonthermal plasmas at low gas pressures, i. e. in a pressure range of a few 0.1 Pa to a few 102 Pa, because high gas temperatures can destroy the polymeric sample. A special type of nonthermal discharge at atmospheric pressure is the dielectric barrier discharge (DBD). Because no expensive vacuum equipment is required, the DBD can be advantageous from the technical point of view. Furthermore, one of the promising new applications of the DBD are novel excimer lamps of UV and vacuum UV radiation.

This paper reports on experiments concerning the plasma- and UV-induced surface treatment of polymers by using the DBD and the DBD driven excimer lamps. As a further example of surface modification, selective-area electroless metal plating on pre-activated polymers by using DBD and excimer lamps are described. The results are compared to those obtained with conventional excimer lasers.