Synthesis and Reactivity in Inorganic, Metal-Organic ...

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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lsrt20

Chemical Vapor Deposition of β-HgS Nanoparticles From a Precursor, bis(cinnamylpiperazinedithiocarbamato) Mercury(II) a

b

M. Govindaraj , M. Arivanandhan & C. Vedhi a

c

Department of Chemistry, Agni College of Technology, Chennai, Tamil Nadu, India

b

Nanodevices and Nanomaterial Division, Research Institute of Electronics, National University Corporation, Shizuoka University, Hamamatsu, Japan c

Department of Chemistry, V. O Chidambaram College, Tuticorin, Tamil Nadu, India Accepted author version posted online: 03 Sep 2014.Published online: 01 Oct 2014. To cite this article: M. Govindaraj, M. Arivanandhan & C. Vedhi (2015) Chemical Vapor Deposition of β-HgS Nanoparticles From a Precursor, bis(cinnamylpiperazinedithiocarbamato) Mercury(II), Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 45:2, 217-224, DOI: 10.1080/15533174.2013.831884 To link to this article: http://dx.doi.org/10.1080/15533174.2013.831884

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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, (2015) 45, 217–224 Copyright © Taylor & Francis Group, LLC ISSN: 1553-3174 print / 1553-3182 online DOI: 10.1080/15533174.2013.831884

Chemical Vapor Deposition of b-HgS Nanoparticles From a Precursor, bis(cinnamylpiperazinedithiocarbamato) Mercury(II) M. GOVINDARAJ1, M. ARIVANANDHAN2, and C. VEDHI3 1

Department of Chemistry, Agni College of Technology, Chennai, Tamil Nadu, India Nanodevices and Nanomaterial Division, Research Institute of Electronics, National University Corporation, Shizuoka University, Hamamatsu, Japan 3 Department of Chemistry, V. O Chidambaram College, Tuticorin, Tamil Nadu, India

Downloaded by [Marimuthu govindaraj] at 04:47 04 October 2014

2

Received 11 May 2013; revised 13 June 2013; accepted 27 July 2013

Chemical vapor deposition method for the synthesis of b-HgS (meta cinnabar) nanoparticles is reported with bis (cinnamylpiperazinedithiocarbamato)mercury(II) as the single source precursor. Crystalline structure, size, morphology and composition of the products are characterized by X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) analysis. PXRD shows (111), (220), (200), (311), (222), (400), (331), (420) reflections characteristic of b-HgS nanoparticles. SEM micrographs display the spherical nature of the b-HgS nanoparticles. EDX analysis showed the presence of Hg and S.HRTEM images confirm the spherical nature of the nanoparticles with their size in the range of 5–10 nm. The results are in agreement with those estimated from the XRD pattern. XPS signals observed at 162.6, 162.8, 222.3, 99.9, and 104.1 eV are due to S2p (3/2, 1/2), S2s (1/2), and Hg4f (7/2, 5/2) respectively. The precursor [Hg (cpzdtc)2] was synthesized and characterized by IR and NMR (1H and 13 C). Single crystal X-ray crystallography of precursor shows the presence of HgS4 distorted tetrahedral coordination environment, with a distinct Hg–S bond asymmetry. Keywords: dithiocarbamate, thioureide, precursor, chemical vapor deposition, powder diffraction, transmission electron microscope, semiconductor nanoparticles

Introduction Dithiocarbamates of zinc, cadmium, and mercury have continued to attract attention in recent years on account of their industrial applications[1] and biological profiles.[2,3] Nanoparticles have drawn interest and attention due to their special characteristics that differ from the bulk solids. Semiconductor nanoparticles have been widely studied because of their interesting properties and wide range of applications.[4–8] The interest stems from various special properties of materials in the nano scale regime, including photocatalytic,[9] mechanical,[10] electrical, and optical applications.[11,12] Semiconductor sulfides have already found applications as sensors or laser materials,[13] solar cells,[14] biological imaging,[15,16] therapeutics,[17] and in many other devices.[18,19]

Address correspondence to M. Govindaraj, Department of Chemistry, Agni College of Technology, Chennai- 603103, Tamil Nadu, India. E-mail: [email protected] Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsrt.

Dithiocarbamate complexes of formulation [M(S2CNR1R2)n] (M D transition metal, R1 and R2 D alkyl group, and n D 2 or 3) have been reported as single source precursors for both the synthesis of metal sulfide nanoparticles[4] and the chemical vapor deposition (CVD) of thin films.[5] Mercury sulfide is a technologically interesting material in quantum electronics[20] and is widely used in many fields such as ultrasonic transducers,[21,22] electrostatic image materials,[23] photoelectric conversion devices,[21,22] and infrared sensor.[23] HgS crystallizes in three different polymorphic structures, among which, a–HgS (cinnabar, hexagonal) and b–HgS (meta cinnabar, zinc-blende type, cubic) have been most extensively explored. a–HgS is a wide band gap semiconductor (Eg D 2.0 eV), but it converts to the zincblende modification (b–HgS) with temperatures above 344 C and becomes a narrow band gap semi-metal (Eg D 0.5 eV).[24] Recently attempts have been made to isolate reasonably pure forms of HgS by procedures that have been relatively cumbersome.[25] In this article, we report the synthesis of Hg(II) dithiocarbamate complex, [Hg(cpzdtc)2], and its subsequent use as a single source precursor for the synthesis of b–HgS nanoparticles. The single-crystal X-ray

218 structural studies of complexes have been documented elsewhere.

Experimental

Govindaraj et al. (Model No.1077). The aerosol droplets of the precursor thus generated were transferred in to the hot wall zone of the reactor by carrier gas. The reactor was placed in a Carbolite furnace. Decomposition of the precursor took place resulting in deposition of particles on the glass plate.

Materials and Methods Cinnamylpiperazine, carbondisulfide, and mercuric chloride were purchased from Sd Fine Chemicals and were used as purchased.


Physical Measurements IR spectra were recorded on an ABB Bomem MB 104 spectrometer (range 4000–500 cm¡1) as KBr pellets. NMR spectra were recorded as saturated CDCl3 solution at room temperature on a Bruker AV400 spectrometer. The powder XRD spectrum was collected in the 2u range of 5–80 using a Bruker-D8 X-ray diffractometer equipped with Cu-Ka radiation at fixed current and potential. The scan speed and step size were 0.05 min¡1 and 0.00657 respectively. Transmission electron microscopic (TEM and HRTEM) measurements were obtained by employing a JEOL 2100 transmission electron microscope, using an accelerating voltage of 200 kV. The surface of the products was analyzed on Shimadzu ESCA 3400 X-ray photoelectron spectrometer, using nonmonochromatized MgKa X-ray as the excitation source. SEM and EDX were obtained on a JEOL JSM6360A instrument with W filament. Preparation of [Hg(cpzdtc)2] Cinnamylpiperazine (2 mmol) and carbon disulphide (2 mmol) in ethanol (10 mL) were mixed under ice-cold condition (5 C) to form a yellow solution of dithiocarbamic acid. An aqueous solution of HgCl2 (1 mmol) was then added with continuous stirring. A colorless precipitate was obtained, which was washed with ethanol and was then dried in air. Single crystals suitable for X-ray diffraction analysis were obtained by slow evaporation of acetonitrile and chloroform (1:1 v/v) solution of the compound. (Yield: 59%; dec.: 170–174 C). Synthesis of b-HgS Nanoparticles by Chemical Vapor Depoisition Method Using [Hg (cpzdtc)2] as a Single-Source Precursor In a typical deposition, 0.100 g of the precursor was dissolved in 10 mL toluene in a round-bottom flask. Argon at flow rate of 240 sccm was used as a carrier gas. The argon flow rate was controlled by a Platon flow gauge. Six glass substrates (approximately 1.60 cm) were placed inside the reactor tube and they were heated at the desired temperature for 15 min before carrying out the deposition. The temperature of the evaporator was set in the 180–270 C and that of the substrate in the 241–352 C range. The precursor solution, in a round-bottom flask, was kept in a water bath above the piezoelectric modulator of a PIFCO ultrasonic humidifier

Results and Discussion Infrared Spectral Studies For [Hg(cpzdtc)2], the characteristic transmittances due to the nC-N (thioureide) band appears at 1477 cm¡1 and the nC-S at 1020 cm¡1 without any split supporting the bidentate coordination of the dithiocarbamate to the metal center.[26] The nC-H bands of aliphatic and aromatic hydrogens appear at 2920, 2862, 2807, and 2762 cm¡1 respectively. Indicating loss of water molecules by crystallization.

NMR Spectral Studies 1

H and 13C NMR spectra of [Hg (cpzdtc)2] are shown in Figures 1 and 2.

1

H NMR: A triplet observed around 2.61–2.63 ppm is due to methylene protons at C5 and C50 . Similarly, another triplet around 4.06–4.09 ppm is assigned to protons (methylene) attached to C4 and C40 . The observed deshielding of the –CH2 protons in all the compounds is attributed to the shift of electron density towards the nitrogen of the NR2 groups, forcing high electron density on the sulfur (or the metal) through the thioureide p-system. However, the CH2 (C7), CH (C8), and CH (C9) protons present in the cinnamyl part of the dithiocarbamate group resonate around 3.19–3.21 (d), 6.19–6.26 (m), and 6.52–6.56 (d) ppm. The signals around 7.24–7.39 ppm due to phenyl ring protons present in cinnamylpiperazinedithiocarbamate. 13

C NMR: The most important 13C NMR signal of the thioureide carbon are observed at 203.3 ppm for complex [Hg(cpzdtc)2] with very weak intensity associated with thioureide carbon signals. The mesomeric shift of electron density from dithiocarbamate moiety towards the metal center contributes to the downfield shift from the normal chemical shift of parent complexes. Generally, higher nC–N (thioureide) correlates with lower NCS2 chemical shifts d (N13CS2). The methylene carbons [(C4, C40 ), (C5, C50 ), and (C7)] appeared in the region of 52.3–60.4 ppm. Similarly, the olefinic carbons [C8 and C9] are observed in the higher frequency region of 125.5– 126.4 ppm. These carbon signals are not greatly affected on complexation due to their relative distance from the thioureide p-system and the metal center. Aromatic carbon signals are observed in the downfield region of 127.8–136.6 ppm for the synthesized complex.


CVD for the Synthesis of b-HgS Nanoparticles

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Fig. 1. 1H NMR spectrum of [Hg(cpzdtc)2].

Structural Analysis An ORTEP diagram of precursor, [Hg (cpzdtc)2],[27] shown in Figure 3 along with the atom-numbering scheme. The crystal structure of [Hg(cpzdtc)2] contains four discrete monomeric molecules per unit cell. The central mercury is in a distorted tetrahedral environment of four sulfur atoms from the two chelating cinnamylpiperazinedithiocarbamate groups (MS4 coordination). In the short thioureide crystal structure of [Hg(cpzdtc)2] the C–N distances [1.314(7), 1.322(7) A] indicate that the p-electron density is delocalized over the S2CN moiety and the bond has strong double bond character. This is also confirmed by the fact that the S–C–N angles [123.1 (5), 118.9(5) ] are greater than those of S–C–S angles [118.0(4) ]. Very small bite angles [68.93(6), 70.21(5) ] of dithiocarbamate leads to a distorted tetrahedral geometry. The significant asymmetry in the pairs of Hg–S [2.787(2), 2.3955(18), 2.4498(18), 2.6944(17) A] indicates that the negative charge is localized on one of sulfur atoms of the dithiocarbamate. The phenyl and alkyl groups attached to the cinnamylpiperazinedithiocarbamate, show normal bond parameters. It also shows intermolecular S3¢¢¢S3 nonbonded interaction at a distance of 3.231 A, which is responsible for the stabilization of the molecule in the solid state. In addition, noncovalent interactions such as S2¢¢¢C19 (3.485 A) and S2¢¢¢N3 (3.330 A) prevail in the

complex. A short H2A¢¢¢H26 (2.3893.485 A) also adds strength to the solid structure. Characterization of the b-HgS Nanoparticles Powder XRD Measurement: Powder XRD measurements were carried out at room temperature. Figure 4 shows the XRD pattern of the product. All the diffraction peaks in the XRD can be indexed to the pure cubic phase (zinc-blende structure) b-HgS. The peaks correspond to (111), (220), (200), (311), (222), (400), (331), and (420) planes, which are in good agreement with the JCPDS-pattern (JCPDS file No.: 73-1593) for b-HgS.[28] Broadened signals indicate diminished dimensions of the b-HgS nanoparticles and average crystal diameter of the b-HgS nano particles are estimated to be 20 nm using the Scherrer formula from the XRD pattern.[29] SEM-/EDX Analysis: The elemental composition of b–HgS nanoparticles is determined using SEM energy-dispersive analytical X-ray (EDX) spectroscopy by performing the spot measurements on nanoparticles. Figure 5 is a SEM micrograph of b–HgS nanoparticles. Majority of the particles are uniformly spherical in nature within the size range of 10–15 nm. However, a very small number of particles are relatively of bigger size due to


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Govindaraj et al.

Fig. 2. 13C NMR spectrum of [Hg(cpzdtc)2].

agglomeration of smaller particles due to aging. Figure 6, shows a typical EDX pattern of b–HgS nano particles. The major peaks are due to the presence of Hg along with sulfur and negligible amount of oxygen. The predominant low energy peak in the EDX spectrum is due to carbon tape, which was used to fix the material. The elemental ratio of Hg to S in the HgS nanoparticles is 51:49, which is in good agreement with the XPS results.

TEM Observation: The size and morphologies of the b–HgS nanoparticles were probed by TEM measurements. The HTEM images (Figure 7) of b–HgS clearly show that they are of spherical morphology. The diameter is observed to be 5–10 nm. The

Fig. 3. ORTEP diagram of [Hg(cpzdtc)2].[27]

Fig. 4. XRD pattern of b–HgS nanoparticles.



Fig. 5. The SEM micrograph of b-HgS nanoparticles.

results are in agreement with those estimated from the XRD patterns.

221 XPS Analysis: Survey scans were carried out showed the presence of S2s, S2p and Hg4f core level signals. High-resolution XPS(HRXPS) spectra of Hg4f (7/2, 5/2), S2p (3/2, 1/2) and S2s (1/2) core levels of nanoparticles of HgS are shown in Figure 8 and the FWHM for the signals are less than 1 eV for all the signals and the Bes have been referred to C1s. The Hg4f spectrum has a doublet feature due to spin orbit splitting resulting in 4f7/2 and 4f5/2 peaks at 99.9 and 104.1 eV, respectively. The peaks measured in the S energy region detected at 162.6 and 162.8 eV are attributed to the S(2p3/2 and 2p1/2) transition and S(2S1/2) appeared at 222.3 eV. Earlier EPS investigations on a–HgS and b–HgS have shown that the two forms sho similar binding energies and it has not been possible to differentiate between them based on XPS. Measurement of the Hg4f and S2p peak areas show the ratio of Hg to S to be 1.1:1, which is very close to the expected ratio of 1:1 for HgS. The observation is in keeping with the EDX measurement. No peaks of impurities such as those of oxide or metallic mercury are observed in the spectrum, indicating the high purity of the b–HgS product.

Fig. 6. The EDX pattern of b–HgS nanoparticles (the predominant low energy peak in the EDX spectrum is due to carbon tape, which was used to fix the material).


222

Fig. 7. HRTEM images of b–HgS nanoparticles.

Govindaraj et al.


223 a large variety of metal sulfide nanoparticle and thin films by CVD synthesis. This paper presents atmospheric pressure chemical vapor deposition using [Hg(cpzdtc)2] at 241–352 C produced b–HgS nanoparticles on glass substrates. The nanoparticles have regular shape, narrow size distribution, and high purity. PXRD analysis showed the sample to be b–HgS nanoparticles. EDX pattern of HgS showed major peaks due to the presence of Hg along with sulfur in the ratio 51:49. HRTEM measurement indicated the size of the spherical b–HgS nanoparticles to be in the range of 10–15 nm. XPS signals observed at 162.6 and 162.8 are due to S2p3/2 and 2p1/2 binding energies and the S2S1/2 was appeared at 222.3 eV.


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Fig. 8. High-resolution XPS spectra for the Hg and S region of b-HgS nanoparticles: (a) Hg (4f); (b) S (2p); (c) S (2s).

Conclusions We demonstrated that [M(cpzdtc)2] (M D Zn, Cd, Hg, Cu, Pb) complex compounds can be used as precursors to prepare

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