Combinatorial Thin Film Libraries

The design of a combinatorial catalyst library refers to the act of composing a sequence of synthesis steps such that the desired portion of a compositional or process parameter space will be mapped onto the final materials (catalyst) library. 

The design of libraries is generally preceded by the selection of some rational catalyst concept, yet may include some degree of serendipity. Library Studio [31] served as the principal library design tool. To design a thin film library, the substrate or destination for the materials array is selected, in this case an 8x8 electrode array, as described above. The set of chemical sources (e.g., metals or metal 

---

Friebe C, Wild A, Perelaer J, Schubert US (2012) Inkjet printing of zinc(II) bis-2,2 6, 2"-terpyridine metallopolymers printability and film-forming studies by a combinatorial thin-film library approach. Macromol Rapid Commun 33 503-509... 

An exciting new area of materials research that has begun to evolve in recent years is the application of combinatorial chemistry to the creation of thin-film libraries. By using masks (grids with separate squares), thousands of distinct combinations of materials can, in principle, be deposited onto a single substrate in order to greatly accelerate the screening of the resultant compounds for certain properties. This is part of a broad approach... 

Chang, H. Gao, C. Takeuchi, I. Yoo, Y. Wang, J. Schultz, P. G. Xiang, X.-D. Sharma, R. P. Downes, M. Venkatesan, T., Combinatorial synthesis and high throughput evaluation of fer-roelectric/dielectric thin-film libraries for microwave applications, Appl. Phys. Lett. 1998, 72, 2185-2187... 

Three techniques have been described in the literature to prepare combinatorial libraries of fuel cell electrocatalysts solution-based methods [8, 10-14], electrodeposition methods [15-17] and thin film, vacuum deposition methods [18-21]. Vacuum deposition methods were chosen herein for electrocatalyst libraries in order to focus on the intrinsic activity of the materials, e.g., for ordered or disordered single-phase, metal alloys. 

Although they have not yet been applied to the production and screening of photoelectrolysis materials, we will briefly mention some other approaches to produce metal oxide libraries using well-established thin film deposition techniques (meant here to include physical vapor deposition, sputtering, pulsed laser deposition, and molecular beam epitaxy). These techniques have been used for the production of combinatorial metal oxide libraries in the search for more effective luminescent materials [90,91], transparent conducting oxides [92,93], and dielectrics [94,95]. It would presumably be straightforward to apply the same techniques to the production of material libraries to be screened for photoelectrolysis activity. 

Preparation of catalyst libraries for the discovery phase can be broadly divided into two categories (1) solution-based methods, and (2) thin-film deposition/based methods. The solution-based methods include those that utilize (1) multi-tasking robotic workstations [14-16] (2) inkjet printhead technology [17], and (3) microjet technology [18]. The thin-film deposition-based methods employ electron beam and thermal evtqroration, sputtering, pulsed laser ablation, and chemical vapor deposition (see [60] in [13] for a list of references). A detailed discussion of how these have been applied is provided elsewhere [13]. Web sites provide links to various aspects of combinatorial chemistry (www.combichem.net and www.5z.com). Here, the hardware aspects are lightly sketched. 

Lu G, Cooper JS, McGinn PJ (2006) SECM characterization of Pt-Ru-WC and Pt-Ru-Co ternary thin film combinatorial libraries as anode electrocatalysts for PEMFC. J Power Sources 161(1) 106-114... 

Figure 12.9. Schematic drawing of an assembled electrochemical cell for combinatorial screening catalyst libraries prepared by sputter deposition [22], (Reprinted from Joiunal of Power Sources, 163(1), Cooper JS, McGinn PJ. Combinatorial screening of thin film electrocatalysts for a direct methanol fuel cell anode, 330-8, 32006, with permission from Elsevier.)...

Black, M., Cooper, J., McGinn, P. Scanning electrochemical microscope characterization of thin film combinatorial libraries for fuel cell electrode applications. Meas. Sci. Technol. 2005, 16, 174—182. 

One of the major requirements related to combinatorial material research is, however, the preparation of thin films and dots from solution in a fast and reproducible manner. Furthermore, the parallel investigation of the physical properties of these films is required to develop a more detailed understanding and new structure-property relationships. Ink-jet printing can bridge the gap between polymer synthesis and solid-state or surface property evaluation, since the technique opens the way to the automatic preparation of libraries of polymers, polymer blends, and composites, with a systematic variation of parameters such as chemical composition or thickness." ... 

---