10980 DOI: 10.1021/la1015803 Langmuir 2010, 26(13), 10980–10984 Published on Web 06/15/2010 pubs.acs.org/Langmuir © 2010 American Chemical Society Dopant Enhanced Etching of TiSe 2 by Scanning Tunneling Microscopy Timothy E. Kidd,* ,† Brett I. Gamb, † Polina I. Skirtachenko, † and Laura H. Strauss ‡ † Physics Department and ‡ Chemistry and Biochemistry Department, University of Northern Iowa, Cedar Falls, Iowa 50614 Received April 20, 2010. Revised Manuscript Received June 3, 2010 The surfaces of pure and Mn doped TiSe 2 were etched using a scanning tunneling microscope. Both types of samples were found to etch easily when scanning was performed in ambient conditions. This process was enhanced at step edges or other surface defects. In pure samples, material was removed in a layer-by-layer fashion with a strong dependence on the scanning direction of the tip. Doped samples etched far more rapidly, to the point that stable scanning conditions were difficult to establish. Doped samples also showed a greater number of pits and other defects on their surface. A relatively small percentage of dopants was necessary to strongly impact the surface topography and stability. These results show that impurities can play a dominant role when using scanning tunneling microscopy to create surface nanostructures. 1. Introduction Scanning tunneling microscopy (STM) has evolved from a purely observatory technique to a powerful method for creating nanometer-scale features. Molecules and atoms can be mani- pulated to form novel surface structures in a variety of materials. 1-6 This form of surface modification is highly dependent on inter- actions between the tip and the sample. 7-9 For practical reasons, it is of interest to be able to manipulate surface structures in ambient conditions rather than under vacuum. However, under normal atmospheric conditions, a water layer of some thickness is always present on the surface of a given material. 10-13 This water layer can have a pronounced effect on tunneling conditions important for surface manipulation. TiSe 2 is a member of the transition metal dichalcogenides. These systems are a class of layered compounds with surfaces that can be readily modified at nanometer length scales by both STM 5,14,15 and atomic force microscopy (AFM). 16 Furthermore, dichalcogenides are sufficiently inert that atomic resolution can be obtained on many species even when measurements are per- formed in air. 17 This combination has enabled a variety of surface structures to be created in air or vacuum environments. 18,19 These materials have physical and electronic properties that are highly amenable to doping. 20 TiSe 2 is of special interest for its novel electronic character. Despite literally decades of research, there is still discussion over whether it is intrinsically a semimetal or small gap semiconductor. 21-23 The pure system has a charge density wave ground state linked to the formation of an excitonic insulator phase 24 and is in proximity to a superconducting ground state that can be induced either by doping 25 or by pressure. 26 Developing a technique for creating surface nanostructures would enable one to explore how quantum size effects and reduced dimensionality influence the complex electronic phase transitions seen in this system. STM has been used to remove material from dichalcogenide surfaces in a variety of ways. Voltage pulses can be used to create nanometer-scale features in a variety of dichalcogenides. 14,19,27-29 Voltage pulses induce surface modifications in both air and vacuum, although the voltage threshold is generally found to be lower for measurements performed in air. 30 Other methods for using an STM to induce etching also appear to be strongly influenced by the scanning environment. For example, in WSe 2 an electrochemical reaction can be induced using an STM or biased AFM tip between the sample and the surface water layer. 27,29,31 NbSe 2 also appears to readily undergo a chemical (1) Eigler, D. M.; Schweizer, E. K. Nature 1990, 344, 524. (2) Stroscio, J. A.; Eigler, D. M. Science 1991, 254, 1319. (3) Lyo, I.-W.; Avouris, P. Science 1991, 253, 173. (4) Foster, J. S.; Frommer, J. E.; Arnett, P. C. Nature 1988, 331, 324. (5) Parkinson, B. J. Am. Chem. Soc. 1990, 112, 7498. (6) Nyffenegger, R. M.; Penner, R. M. Chem. Rev. 1997, 97, 1195. (7) Csonka, S.; Halbritter, A.; Mihaly, G.; Jurdik, E.; Shklyarevskii, O. I.; Speller, S.; van Kempen, H. J. Appl. Phys. 2004, 96, 6169. (8) Flores, F.; Echenique, P. M.; Ritchie, R. H. Phys. Rev. B 1986, 34, 2899. (9) Persson, B. N. J.; Avouris, P. Chem. Phys. Lett. 1995, 242, 483. (10) Freund, J.; Halbritter, J.; H€ orber, J. K. H. Micros. Res. & Tech. 1999, 44, 327. (11) Asay, D. B.; Kim, S. H. J. Phys. Chem. B 2005, 109, 16760. (12) Hahn, J. R.; Hong, Y. A.; Kang, H. Appl. Phys. A: Mater. Sci. Proc. 1998, 66, S467. (13) Song, M.-B.; Jang, J.-M.; Bae, S.-E.; Lee, C.-W. Langmuir 2002, 18, 2780. (14) Akari, S.; Moller, R.; Dransfeld, K. Appl. Phys. Lett. 1991, 59, 243. (15) Schimmel, T.; Fuchs, H.; Akari, S.; Dransfeld, K. Appl. Phys. Lett. 1991, 58, 1039. (16) Delawski, E.; Parkinson, B. A. J. Am. Chem. Soc. 1992, 114, 1661. (17) Tanaka, M.; Mizutani, W.; Nakashizu, T.; Yamazaki, S.; Tokumoto, H.; Bando, H.; Ono, M.; Kajimura, K. Jpn. J. Appl. Phys. 1989, 28, 473. (18) Jaeckel, B.; Gassenbauer, Y.; Jaegermann, W.; Tomm, Y. Surf. Sci. 2005, 597, 65. (19) Park, J. B.; Jaeckel, B.; Parkinson, B. A. Langmuir 2006, 22, 5334. (20) Friend, R. H.; Yoffe, A. D. Adv. Phys. 1987, 36, 1. (21) Traum, M. M.; Margaritondo, G.; Smith, N. V.; Rowe, J. E.; Di Salvo, F. J. Phys. Rev. B 1978, 17, 1836. (22) Rasch, J. C. E.; Stemmler, T.; M€ uller, B.; Dudy, L.; Manzke, R. Phys. Rev. Lett. 2008, 101, 237602. (23) Kidd, T. E.; Miller, T.; Chou, M. Y.; Chiang, T. C. Phys. Rev. Lett. 2002, 88, 226402. (24) Cercellier, H.; Monney, C.; Clerc, F.; Battaglia, C.; Despont, L.; Garnier, M. G.; Beck, H.; Aebi, P.; Patthey, L.; Berger, H.; Forro, L. Phys. Rev. Lett. 2007, 99, 146403. (25) Morosan, E.; Zandbergen, H. W.; Dennis, B. S.; Bos, J. W. G.; Onose, Y.; Klimczuk, T.; Ramirez, A. P.; Ong, N. P.; Cava, R. J. Nat. Phys. 2006, 2, 544. (26) Kusmartseva, A. F.; Sipos, B.; Berger, H.; Forr o, L.; Tutia, E. Phys. Rev. Lett. 2009, 103, 236401. (27) Enss, C.; Winters, R.; Reinermann, M.; Weiss, G.; Hunklinger, S.; Lux-Steiner, M. Z. Phys. B. Cond. Matt. 1995, 99, 561. (28) Huang, J.-L.; Sung, Y.-E.; Lieber, C. M. Appl. Phys. Lett. 1992, 61, 1528. (29) Boneberg, J.; Lohrmann, M.; B€ ohmisch, M.; Burmeister, F.; Lux-Steiner, M.; Leiderer, P. Z. Phys. B.: Condens. Matter 1995, 99, 567. (30) Kondo, S.; Heike, S.; Lutwyche, M.; Wada, Y. J. App. Phys. 1995, 78, 155. (31) Bohmisch, M.; Burmeister, F.; Boneberg, J.; Leiderer, P. Appl. Phys. Lett. 1996, 69, 1882.