Aerosol-assisted metallo-organic chemical vapour deposition of Bi 2 Se 3 films using single-molecule precursors. The crystal structure of bismuth(III) dibutyldiselenocarbamate Olinda C. Monteiro, a Tito Trindade,* a Filipe A. Almeida Paz, b Jacek Klinowski, b John Waters c and Paul O’Brien c a Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal. E-mail: ttrindade@dq.ua.pt; Tel: 1351-234-370726; Fax: 1351-234-370084 b Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, UK CB2 1EW c The Manchester Materials Science Centre, Department of Chemistry, University of Manchester, Oxford Road, Manchester, UK M13 9PL Received 11th June 2003, Accepted 7th October 2003 First published as an Advance Article on the web 24th October 2003 The complexes [Bi{Se 2 CN(C 2 H 5 ) 2 } 3 ], [Bi{Se 2 CN(C 4 H 9 ) 2 } 3 ], [Bi{Se 2 CN(CH 3 )(C 4 H 9 )} 3 ] and [Bi{Se 2 CN(CH 3 )(C 6 H 13 )} 3 ] have been synthesized and characterized structurally using IR, 1 H and 13 C NMR. In addition, the crystal structure of [Bi{Se 2 CN(C 4 H 9 ) 2 } 3 ] was determined by single-crystal X-ray diffraction, showing the bismuth centre coordinated to three dialkyldiselenocarbamate ligands through the selenium donor atoms. The Bi(III) compounds were used as precursors for the deposition of Bi 2 Se 3 films on glass substrates through aerosol-assisted metallo-organic chemical vapour deposition (AA-MOCVD). Introduction Single-molecule precursors have been widely used to prepare metal chalcogenides as thin films or nanopowders. 1–4 Thus, both elements needed for the final product come from a single molecule, allowing one-step preparation of the metal chalco- genide phase and avoiding the use of hazardous compounds such as hydrogen sulfide or hydrogen selenide. Compounds used as sources of metal selenides include metal diseleno- carbamates (ZnSe, CdSe, PbSe), 5–8 (CH 3 ) 2 InSe(C 6 H 5 ) and In{Se(C 6 H 5 )} 3 (InSe and In 2 Se 3 ), 9 bulky selenolate complexes of the type M(SeC 6 H 2 R 3 -2,4,6) 3 , 10 and diselenoimidodiphos- phinate compounds (CdSe, As 2 Se 3 , Sb 2 Se 3 , Bi 2 Se 3 ). 11,12 The paper by Crouch et al. 12 is the only report of chemical vapour deposition (CVD) of Bi 2 Se 3 films using a single source approach. Bi 2 Se 3 , a narrow band gap semiconductor with E g ~ 0.24 eV, 13 crystallizes with a rhombohedral lattice and, together with the analogous isomorphic compounds Bi 2 Te 3 and Sb 2 Te 3 , is of interest for solid-state thermoelectric devices. These narrow band-gap semiconductors and their alloys have been used for cooling and for power generating devices operating near room temperature (e.g., Peltier coolers). 14 The aim of the present work is to assess the potential of Bi(III) dialkyldiselenocarbamato complexes as single sources for the preparation of Bi 2 Se 3 films using the AA-MOCVD method. We report the synthesis and characterization by IR, 1 H and 13 C NMR of a series of Bi(III) dialkyldiselenocarbamato complexes, [Bi(Se 2 CNRR’) 3 ] [where R ~ C 2 H 5 (Et), n C 4 H 9 (Bu n ) or CH 3 (Me), and R’ ~ C 2 H 5 (Et), n C 4 H 9 (Bu n ) or n C 6 H 13 (Hex n )], with the crystal structure of [Bi{Se 2 CN(C 4 H 9 ) 2 } 3 ]. This is the first reported Bi(III) diselenocarbamate, confirmed by a search of the Cambridge Structural Database. 15 As observed for the analogous Bi compound containing S 2 CNBu n 2 , 16,17 [Bi(Se 2 CN- Bu n 2 ) 3 ] has three diselenocarbamate anions coordinated to the Bi 31 centre in a bidentate-chelating fashion, leading to a coordination environment best described as a distorted triangular antiprism. Experimental Preparation and identification of the compounds [Bi(Se 2 CNRR 1 ) 3 ] All chemicals were of at least reagent grade and were used as supplied by Aldrich. CSe 2 was prepared following reported methods. 18 CAUTION: carbon diselenide is a malodorous and very toxic liquid which should only be handled in a well- ventilated fume hood under strict safety conditions. All the [Bi(Se 2 CNRR’) 3 ] compounds were prepared in a similar way, with CSe 2 reacting with the respective secondary amine in a methanolic solution and also in the presence of Bi 2 O 3 in suspension. [Bi{Se 2 CN( n C 4 H 9 ) 2 } 3 ] was typically obtained as follows. Dibutylamine (5.17 g, 40 mmol) and then CSe 2 (4 g, 50 mmol) were added to a stirred suspension of Bi 2 O 3 (2.80 g, 6 mmol) in methanol (20 cm 3 ). The mixture was stirred at room temperature for 48 h, and the orange precipitate collected by vacuum filtration. Recrystallization from a hot mixture of chloroform and methanol (3 : 1) followed by mechanical centrifugation yielded an orange solid which was manually harvested and kept in a flask under a nitrogen atmosphere. Single-crystals suitable for X-ray studies were obtained by recrystallization from acetone. All the compounds were characterized by elemental analysis (theoretical values are given in parentheses), IR, 1 H and 13 C NMR spectroscopy. The elemental analyses were performed twice for the recrystallized compounds. The difference between the calculated and experimental values observed for [Bi{Se 2 - CN(C 4 H 9 ) 2 } 3 ] may be due to slight degradation of the analyzed sample. [Bi{Se 2 CN(C 2 H 5 ) 2 } 3 ]. 1 H NMR: d 1.38 (6H, t, CH 2 CH 3 ), 3.91 (4H, q, CH 2 CH 3 ); 13 C NMR: d 12.04 (CH 2 CH 3 ), 51.56 (CH 2 CH 3 ), 191.95 (Se 2 CN); selected IR data (cm 21 ): 1493 n(C–N), 820 n(C–Se); mp 176 uC; elemental composition: C 19.31 (19.13), H 3.29 (3.21), N 3.64 (4.47)%. 3006 J. Mater. Chem., 2003, 13, 3006–3010 DOI: 10.1039/b306662m This journal is # The Royal Society of Chemistry 2003