412 Brazilian Journal of Physics, vol. 36, no. 2A, June, 2006 Characterization and Properties of CdO Nanocrystals Incorporated in Polyacrylamide P. A. Radi1, A. G. Brito-Madurro1, J. M. Madurro1, and N. O. Dantas2 1Laboratorio´ de Filmes Polimericos´ (LAFIP), Instituto de Qu´ımica and 2Laboratorio´ de Novos Materiais Isolantes e Semicondutores (LNMIS), Fac. de F´ısica, Universidade Federal de Uberlandia,ˆ 38400-902, Uberlandia-MG,ˆ Brazil Received on 4 April, 2005 CdO quantum dots (QDs) incorporated in polyacrylamide were synthesized adding aqueous suspension of cadmium oxide in acrylamide:bisacrylamide copolymer. Optical properties of CdO nanocrystals were studied by optical absorption. The size ranges (2-3 nm) were calculated by the effective mass approximation. Keywords: CdO quantum dots (QDs); Polyacrylamide; Optical properties I. INTRODUCTION the O2/Ar stream at 400 ˚ C [18]. In this present work CdO quantum dots (QDs) incorporated Nanoparticles have attracted great interest in recent years in polyacrylamide have been synthesized in which electrons because of their unique chemical and physical properties, are confined in all three spatial directions. Due to the in- which are different from those of either the bulk materials or creased quantum confinement, these QDs exhibit new physics single atoms [1]. properties that are strongly dependent upon nanocrystal size. The sizes of the particles were calculated by the effective mass In recent years, researchers have focused on cadmium oxide model approximation [19-20]. (CdO) due to its applications, specifically in the field of opto- electronic devices such as solar cells [2-3], photo transistors [4] and diodes [5], transparent electrodes [6], gas sensors [7], etc. These applications of CdO are based on its specific opti- II. EXPERIMENTAL DETAILS cal and electrical properties. For example, CdO films show a high transparency in the visible region of the solar spectrum, All employed chemicals were used as received. The chem- as well as a high ohmic conductivity. The intensity of optical icals were purchased from different companies: acrylamide and electrical effects of CdO depends on the deviations from 99.9% (Bio-Rad), bisacrylamide 98% (Sigma), cadmium ox- the ideal CdO stoichiometry, as well as on the size and shape ide (Nuclear), ammonium persulfate 98% (Invitrogen), and of the particles [8]. Bulk CdO is an n-type broad band gap TEMED (N,N,N’,N’-tetramethylenediamine) 99% (Sigma). (2.3 eV) semiconductor, with an indirect band gap of 1.36 eV The gel material was did with aqueous suspension of cad- [9]. mium oxide in acrylamide:bisacrylamide copolymer. The Some researchers try to modify the synthesis procedure cadmium oxide suspension was prepared using distilled wa- for CdO with the aim to improve chemical and physi- ter with concentration of 1.0x10¡4, 2.0x10¡4, 5.0x10¡4, cal properties of this material. Some examples of this 10.0x10¡4, 20.0x10¡4and 40.0x10¡4mol/L. The suspension are: Gulino et al. [10] that investigated the formation was immersed in ultrasound bath during 30 min for homoge- of CdO thin films by thermal decomposition of cadmium nization. For the copolymerization reaction 10 mL of a mix- hexafluoroacetylacetonate dehydrate [Cd(C5F6HO2)2.H2O]. ture containing 0.098 g of acrylamide and 3.6g of bisacry- The Cd(C5F6HO2)2.CH3OCH2OCH3 complex was used as lamide was prepared. The CdO solution was added slowly to a ligand MOCVD (metal-organic chemical vapor deposition) the jelly monomer mixture. Ammonium persulfate (10%) and precursor in the preparation of thin CdO films [11]. The TEMED were added to the jelly matrix, allowing the copoly- thermal decomposition of cadmium itaconate monohydrate merization reaction to take place at room temperature. The (C5H4O4Cd.H2O) in N2,H2 or air was also investigated polymerization was carried at presence of light at room tem- [12].Uplane et al. [13] reported the preparation of CdO thin perature. films onto the hot glass substrate at 400 ˚ C by spray pyroly- Were did two groups of samples: the first was stored at sis of the aqueous cadmium acetate solution. Varkey and Fort room temperature and aqueous atmosphere for 5 days (120h) [14] prepared transparent CdO thin films on glass substrate and the second was stored under vacuum to dry for 5 days. using the aqueous solution of soluble cadmium amine com- The Optical Absorption (OA), of the first group (gel material) plexes as a precursor of CdO. Cd(OH)2 deposited on the glass was done just after the polymerization and after 2, 4, 24, 48, substrate was transformed into CdO after heating. Matsuura et and 120h to observe the stability of the synthesized material. al. [15] prepared CdO thin films using the Langmuir–Blodgett The second group had this optical properties analyzed only deposition technique. Aletru´ et al. [16] prepared Cd(OH)2 gel after totally dried. by mixing cadmium acetate and sodium hydroxide solutions. Using the values of AO the nanoparticules sizes were deter- Peng et al. [17] reported on the formation of CdO nanowires mined from the absorption onset by the effective mass model by oxidation of mixed Cd/Te film on aluminium substrate in approximation. P. A. Radi et al. 413 III. RESULTS AND DISCUSSION µ ¶ (Invitrogen), and TEMED (N,N,N’,N’- In the second group~ (solid)2π2 the1 best result1 was observed » -4 tetramethylenediamine) 99% (Sigma). in the concentrationE = Ebulk + of 1.0x102 mol/L+ Fig. 2.. In bigger The obtained materials are transparent and the solid mater- 2er mem0 mhm0 The (Invitrogen),gel material was anddid with TEMEDaqueous suspension(N,N,N’,N’- of concentrationsIn the second the group band (solid) of theCdO best resultnanocrystals was observed was not ial looks like glass, presenting a good transparency and rigid- tetramethylenediamine) 99% (Sigma). in the concentration of 1.0x10-4 mol/L Fig. 2.. In bigger ity. cadmium oxide in acrylamide:bisacrylamide copolymer. whereobserved,E is theindicating band gap the of formation the nanoparticles, of bulkyE CdO.bulk is the band The gel material was did with aqueous suspension of concentrations the band of CdO nanocrystals was not The cadmium oxide suspension was prepared using gap ofThe the size bulk range material, of CdO r is thenanoparticles particle radius, is about meand 2-3 m nmh are in The best result in the first group (gel material) was observed distilledcadmium water withoxide concentration in acrylamide:bisacrylamide of 1.0x10-4, 2.0x10copolymer.-4, effectivetheobserved, two massesgroups. indicating of the the electrons formation and of bulky holes, CdO. respectively, and in the sample with CdO concentration of 2.0x10¡4 mol/L and -4The cadmium-4 oxide suspension-4 was -4 prepared using The size range of CdO nanoparticles is about 2-3 nm in 5.0x10 , 10.0x10 , 20.0x10 and 40.0x10 mol/L.-4 The-4 m is the free electron mass. the result of the OA spectroscopy of this material in different distilled water with concentration of 1.0x10 , 2.0x10 , 0the two groups. suspension was-4 immersed-4 in ultrasound-4 bath during-4 30 min times of store can be observed in Fig. 1. The narrow peaks 5.0x10 , 10.0x10 , 20.0x10 and 40.0x10 mol/L. The 0.14 7 for homogenization.suspension was For immersed the copolymerization in ultrasound bath reactionduring 30 10 min indicate that the size distribution is very homogenous. 0.120.14 7 mL of afor mixture homogenization. containing For 0.098 the copolymerizationg of acrylamide reactionand 3.6g 10 6 A batocromic effect (red-shift) was observed with the time, 0.12 of bisacrylamidemL of a mixture was containingprepared. 0.098 The g CdOof acrylamide solution and was 3.6g 0.10 6 indicating an increase of the particle’s size, and an absorbance added slowlyof bisacrylamide to the jelly was monomer prepared. mixture.The CdO Ammonium solution was increase with time shows that the primary particles growth. 0.10 5 added slowly to the jelly monomer mixture. Ammonium 0.08 persulfate (10%) and TEMED were added to the jelly 5 The samples with other concentrations presented similar re- persulfate (10%) and TEMED were added to the jelly 0.08 sults but in less absorbance intensity for less concentrations matrix, allowing the copolymerization reaction to take 0.06 4 matrix, allowing the copolymerization reaction to take 0.06 place at room temperature. The polymerization was carried Absorbance 4 3 and biggest red-shift for higher concentrations. place at room temperature. The polymerization was carried Absorbance 0.04 2 3 at presence of light at room temperature. 0.04 2 In the second group (solid) the best result was observed in at presence of light at room temperature. ¡ Were did two groups of samples: the first was stored at 0.02 1 the concentration of 1.0x10 4 mol/L Fig. 2. In bigger con- Were did two groups of samples: the first was stored at 0.02 1 room temperatureroom temperature and aqueousand aqueous atmosphere atmosphere for for 5 5days days centrations the band of CdO nanocrystals was not observed, 0.000.00 (120h) and(120h) the and second the second was storedwas stored under under vacuum vacuum to todry dry for for indicating the formation of bulky CdO. 5 days. 5The days. Optical The Optical Absorption Absorption (OA), (OA), of theof thefirst first group group 300 320 320 340 340 360 360 380 380 400 400 420 420 440 440 460 460 480 480500 500 The size range of CdO nanoparticles is about 2-3 nm in the (gel material)(gel material) was done was donejust afterjust after the thepolymerization polymerization and and Wavelengh,Wavelengh, nm nm two groups. after 2, after4, 24, 2, 4,48, 24, and 48, 120h and 120hto observe to observe the thestability stability of ofthe the Fig.1.Fig.1.