Deposition techniques DOI: 10.1002/smll.200500479 Electrospray Ion Beam Deposition of Clusters and Biomolecules Stephan Rauschenbach,* Frank L. Stadler, Eugenio Lunedei, Nicola Malinowski, Sergej Koltsov, Giovanni Costantini, and Klaus Kern An ion beam source using electrospray ionization is presented for non- destructive vacuum deposition of mass-selected large organic molecules and inorganic clusters. Electrospray ionization is used to create an ion beam from a solution containing the nanoparticles or molecules to be deposited. To form and guide the ion beam, radio frequency and electro- static ion optics are utilized. The kinetic energy distribution of the particles is measured to control the beam formation and the landing process. The particle mass-to-charge ratio is analyzed by in situ time-of- flight mass spectrometry. To demonstrate the performance of the setup, deposition experiments with gold nanoclusters and bovine serum albumin proteins on graphite surfaces were performed and analyzed by ex situ atomic force microscopy. The small gold clusters are found to form three-dimensional agglomerations at the surface, preferentially decorating the step edges. In contrast, bovine serum albumin creates two-dimensional fractal nanostructures on the substrate terraces due to strong intermolecu- lar interactions. Keywords: · biomolecules · clusters · electrospray ionization · epitaxy · mass spectrometry 1. Introduction The surface deposition of organic molecules recently became an important topic due to technological develop- ments in biotechnology, organic electronics, and functional materials. Research in the field of proteomics [1] and the de- velopment of organic light-emitting diodes (OLEDs) [2] are good examples of the wide-ranging applications of organic molecules at surfaces. OLEDs are manufactured within the limitations of semiconductor technology implying that the production environment needs to be very clean and control- led. In order to achieve proper device performance, impuri- ty concentrations have to be in the order of 10 10 cm 3 . [3] Therefore the growth of the organic materials needs to take place in vacuum, where at present only small molecules can be deposited by means of organic molecular beam epitaxy (OMBE). Larger molecules typically exhibit lower vapor pressures and are unstable at elevated temperatures, with the consequence that they decompose before sublimation. The very same limitation concerns research on biological molecules, where no general vacuum deposition technique can be applied. In contrast, the study of fundamental inter- actions of biomolecules with surfaces and with each other would greatly profit from a precisely controlled environ- ment and from atomic-scale analytical techniques, both available only in ultrahigh vacuum. [4] Furthermore, the func- tionalization of surfaces with organic and biological mole- cules is of fundamental importance in molecular nanotech- nology, opening many new opportunities ranging from mo- [*] S. Rauschenbach, Dr. F. L. Stadler, Dr. E. Lunedei, Dr. N. Malinowski, Dr. G. Costantini, Prof. K. Kern Max-Planck-Institute for Solid State Research Nanoscale Science Department, Heisenbergstr. 1 70569 Stuttgart (Germany) Fax: (+ 49) 711-689-1662 E-mail: s.rauschenbach@fkf.mpg.de Dr. S. Koltsov Institute for Analytical Instrumentation Russian Academy of Science, 18813 St. Petersburg (Russia) 540 # 2006 Wiley-VCH Verlag GmbH & Co. KGaA, D-69451 Weinheim small 2006, 2, No. 4, 540 – 547 full papers S. Rauschenbach et al.