I n d . Eng. Chem. Res. 1989, 28, 877-880
Table I. ComDuted Resultsa 2
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00
A1
A2
X1
x2
H
0.2775 0.2667 0.2538 0.2384 0.2212 0.2034 0.1851 0.1663 0.1469 0.1261 0.1036
-0.5275 -0.4971 -0.4635 -0.4264 -0.3889 -0.3546 -0.3226 -0.2923 -0.2634 -0.2334 -0.2017
0.8350 0.7991 0.7661 0.7357 0.7085 0.6850 0.6642 0.6455 0.6285 0.6123 0.5969
0.1088 0.1391 0.1653 0.1878 0.2068 0.2227 0.2364 0.2483 0.2590 0.2685 0.2772
0.049 95 0.049 95 0.049 95 0.049 95 0.049 94 0.049 94 0.049 94 0.049 94 0.049 93 0.049 93 0.049 93
T 825 825 825 825 554 431 364 321 300 300 300
877
Nomenclature F = fresh feed rate, M T = absolute temperature, K W = recycle rate of flow, M Y = integrand of the objective function H = Hamiltonian function f = right-hand sides of (3) and (4) s = separation factor y = objective function x = mole fraction z = independent variable (fractional distance down the reactor)
Feed rate: 1.0. Recycle rate: 0.6. Feed mole fractions: 0.98, 0.01, 0.01. Separation factors: 1, 1. Maximum temperature: 825 K. Minimum temperature: 300 K.
Greek Symbols X = adjoint function { = value of the artificial objective function
variables. The artificial objective function is created from the boundary conditions on the adjoint functions, (7) and (8), and the material balances, (2). This result is
Subscripts f = reactor feed p = product w = recycle 0 = reactor inlet 1 = chemical species A 2 = chemical species B
r = [~,,e/~,,o
W / ( F + W/S1)l2 + [X,,O/X,,OW/(F + W/s2)12 + [xi,o/xi,e - xi,fF/((F + W)xi,e) W / ( F + W/S1)12 + [ x z , o / x 2 , 0 - x,,,F/((F + WIx2,e) - W / ( F + W/s2)I2 (11) -
r
At the solution, will be zero or sufficiently close to zero and positive at other points. The computed results for the example along with other parameters are shown in Table I. The amount of nonlibrary code that had to be written for this example was about 75 lines. For this example, 154 evaluations of the objective function were required; the amount of CPU time was 26.6 s. This technique has been successfully tested with a variety of reactor problems. The above requirements are typical provided the usual precautions are taken in formulating the objective function. It is desirable-thatthe objective function be formed so that perturbations in the search variables yield roughly the same changes in the objective function.
6 = exit of reactor
Literature Cited Beveridge, G. S. G.; Schechter, R. S. Optimization: Theory and Practice; McGraw-Hill: New York, 1970. Carnahan, B.; Luther, H. A.; Wilkes, J. 0. Applied Numerical Methods; Wiley: New York, 1969. Kuester, J. L.; Mize, J. H. Optimization Techniques with Fortran; McGraw-Hill New York, 1973.
Clayton P.Kerr Department of Chemical Engineering Tennessee Technological University Cookeville, Tennessee 38505 Received for review September 8, 1988 Revised manuscript received March 2, 1989 Accepted March 29, 1989
Preparation of Copper Sulfide Powders and Thin Films by Thermal Decomposition of Copper Dithiocarbamate Complexes Copper dialkyldithiocarbamates 2a-d (Cu(S2CNk),, where R = ethyl (Et), 2a; butyl (Bu), 2b; hexyl (Hex), 2c; 2-ethylhexyl (Oct), 2d) decomposed up to 320 "C into Cu2S. In contrast, (P-hydroxyethy1)methyldithiocarbamate 2e ( C U ( S & N M ~ ( C H ~ C H ~ O Hinitially ))~) released 3-methyloxazolidine-2-thione and gave CuS up to 230 "C. CuS thus formed was further converted into Cu2S between 300 and 400 "C. Although 2d and 2e gave pure Cul&3 phase, the sulfide mixture phase consisting of &Cu2S and Cu1.&3 was obtained from 2a-c. The preparation of Cu2S thin films on glass substrate also became possible via solution pyrolysis of 2e a t 250 and 300 "C for 1 h under Ar atmosphere, using DMSO solution (5 w t %). Copper sulfide is widely used as a semiconductor device material, especially for optoelectronics and photovoltaics, and several thin film processes have already been established (Yoshikawa et al., 1980; Rastogi and Salkalachen, 1982; Iborra et al., 1987). In general, large-area copper sulfide layers for terrestrial solar cells were prepared by chemical methods such as spray pyrolysis (Gadgil et al., 1987; Orban de Xivry et al., 1987), electrochemical deposition (Garcia-Camarero et al., 1986; Engelken and McCloud, 1985, and chemical bath deposition (Pramanik et al., 1987; Fatas et al., 1985). However, the yields of the target sulfide thin films still remain low in such chemical processes with respect to the precursor material fed 0888-5885/ 8912628-0877$O1.50/0
amounts. In particular, large proportions of the spray solution were exhausted from the chamber unused in spray pyrolysis, and the deposition efficiency decreased with a lowering of the concentration of the precursors in electrochemical deposition. In our continuous studies on the preparation and utilization of metal dithiocarbamate complexes, we have proposed a new and facile preparation procedure for certain metal dithiocarbamate complexes via direct condensation using metal oxides together with dithiocarbamic acids as starting materials (Nomura et al., 1986, 1987a). Since metal dithiocarbamates are soluble materials, the copper dithiocarbamate complexes prepared by the direct 1989 American
Chemical Society
878 Ind. Eng. Chem. Res., Vol. 28, No. 6, 1989 Table I. Yields and Analytical Data of Prepared 2a-en analytical data/ %
2a 2b 2c 2d 2e
t/h
yield/%
mp/'C
C
found H
N
C
calcd H
5 5 5 2
81 57 46 37b 8aC
200 58-59 49
33.31 45.73 53.50 58.50 26.38
5.60 7.73 8.99 9.86 4.42
7.80 5.91 4.76 3.93 7.71
33.36 45.77 53.43 58.60 26.40
5.60 7.70 8.97 9.86 4.43
2
oil 158
N
formula C,~H&UN~S~ CI~H~~CUN~S~ C~~H&UN~S~ C~H&UN~S~ C~H~~CUN~S~
7.80 5.93 4.79
4.02 7.70
"CuO (5 mmol) and 1 (10 mmol) were stirred in CH3CN (30 mL) at room temperature. bThis condensation was carried out at 60 "C. CH30H was used in place of CH3CN.
Scheme I
CUO + 2RR'NCSzH 1
a
b C
d e Hex denotes n-hexyl.
R Et Bun Hex" OCtb Me
+
Cu(S2CNRR' )z 2
+ HzO
R' Et Bun Hex Oct CHZCHZOH
I
t
I
I
t
* Oct denotes 2-ethylhexyl.
condensation process might be useful as precursors for the copper sulfide thin films through a solution pyrolysis method (Nomura et al., 1987b, 1988, 1989), which is expected to be the most effective thin film process for the preparation of copper sulfide layers (Croitoru and Jakobson, 1979). In the present communication, we will describe our investigation of the thermal properties of copper dithiocarbamates 2 and the preparation of copper sulfide thin films via thermal decomposition of 2 (Scheme I).
Experimental Section General. UV-vis spectra were recorded on a Shimadzu UV-BOOS spectrophotometer. Thermal analysis was performed with a SEIKO TG/DTA 30 model. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were obtained by a Hitachi S-405-type microscope and a Rigaku Rota-flex X-ray diffractometer (Cu K,, 40 kV), respectively. Surface composition was observed by using of a Shimadzu ESCA 650B and a Rigaku 0600 ultratrace X-ray fluorescence microanalyzer. Copper oxide (CuO) was used without further purification (Aldrich,pure grade). Preparation of Copper Dithiocarbamate Complexes (2). A detailed preparative operation was described in our previous reports (Nomura et al., 1987a, 1988). Dialkyldithiocarbamates were purified by repeated recrystallization several times (solvent: acetonitrile) (2a-c) or washing with methanol and acetonitrile (2d,e). The yields and analysis data of 2 are summarized in Table I. Preparation of Copper Sulfide Powders. Pyrolysis of 2 (0.5 g) was conducted in a 30-mL porcelain crucible set into a quartz tube under Ar atmosphere for 1 h. Preparation of Copper Sulfide Thin Films. About 40 pL of a solution of 2 in p-xylene or dimethyl sulfoxide (DMSO) was dropped onto a glass substrate (Pyrex) and spread over the whole surface of the substrate by tipping. The substrates were heated in a quartz tube at 100 "C for 1 h and then at 250 or 300 "C for 1 h to obtain the final copper sulfide films. Results and Discussion Thermal analyses of 2 were performed under Nz flow (heating ratio: 10 "C/min), and the typical thermograms (TGA and DTA curves) are shown in Figure 1. Thus, it was found that the weight loss of dialkyl derivatives of 2
100
200
300
LOO
500
100
200
330
LOO
500
Temperature I 'C
Figure 1. Typical thermograms of copper dithiocarbamates. Pyrolysis products, estimated from the % weight loss and confirmed by X-ray fluorescence analysis, are also indicated. Scheme 11. Thermal Decomposition Path of 2e
cu---s
-F)
300-4OO'C
)2
P I
l-7 - 0 NMe
22
2,
started at about 230 "C and ended at about 320 "C to give CuzS as a final pyrolysate, which was confirmed by X-ray fluorescence analysis and ESCA, and that the main thermal decomposition process produced endothermic DTA peaks. In contrast, the decomposition of (P-hydroxyethy1)dithiocarbamate 2e started and ended at lower temperatures (159 and 230 "C, respectively), and the primary pyrolysate was cupric sulfide, which further released sulfur to give Cu,S between 300 and 400 "C. In our previous reports (Nomura et al., 1985,1987a), we preliminarily stated that the dithiocarbamate complexes containing w-hydroxyl groups easily eliminate most of the ligand moieties via a cyclocondensation-elimination path as shown in Scheme 11. Thus, the formation of stable five-membered-ring heterocycles was considered to lower the decomposition temperature and accelerate the formation of metal sulfide species which possessed relatively large sulfur contents. Preparation of Copper Sulfide Powders. On the basis of the above-mentioned thermal analysis data, we attempted to prepare copper sulfide powders by thermal decomposition of 2 in a crucible, and the typical X-ray diffraction patterns of the copper sulfide powders obtained are displayed in Figure 2. Coking the dithiocarbamate complexes was done under Ar atmosphere and gave grey-to-black fine powders (50-100 pm in diameter). However, there are some additional phases observed in the copper sulfide X-ray powder diffraction patterns, as shown in Figure 2. Thus, 2a-c gave the sulfide mixture consisting of Cu1,&3 and /3-Cu2Sas shown in Figure 2b. Similar multiphase de-
Ind. Eng. Chem. Res., Vol. 28, No. 6, 1989 879 Table 11. Preparation of Copper Sulfide Thin Films" composi- resistivisolventb T/"C tione tvd/Qcm remarks 2b p-xylene 300 Cuz$ black' black-to-brown 2e DMSO 250 C U S ~ . ~2.0 ~ X 300 C U ~ . ~ S3.2 X black-to-brown DMSO
(a) I
O
a Substrate, 20- X 20-mm Pyrex glass; heating sequence, 100 "C for 1 h and 300 "C for 1 h, under Ar atmosphere. b 5 wt ?& solutions were used. Obtained by X-ray fluorescence analysis. Estimated by a four-probe apparatus. 'Poorly adhesive film deposited as islands.
10
20
30
LO
50
60
2 8 I degree
20
30
40
50
60
2 8 /degree
Figure 2. X-ray powder diffraction patterns of copper sulfide powders obtained in the pyrolysis of copper dithiocarbamate under Ar atmosphere. Precursor dithiocarbamates and pyrolysis temperatures are as follows: (a) 2d, 300 "C; (b) 2c, 300 "C; (c) 2e, 300 "C; (d) 2e, 200 "C. Marks located over each peaks indicate that the peak is Cul& (JCPDS 29-577), ( 0 )&CuZS(JCPDS 26-1115), assigned (0) and (A)CuS (JCPDS 6-0464).
position was also reported for sputtered and ion-exchanged films (Engelken and McCloud, 1985), while 2d afforded pure Cul.&3 phase unexpectedly. We believe such differences arise from a difference in the number of carbon atoms in the ligand moieties. We tentatively assume that the traces of carbonous residues existing in the pyrolysates affect the reduction of excess sulfur. The quantitative measurement of the carbon content of the pyrolysates is now in progress. 2e could supply both uniform CuS and C U ~ .powders ~S at 200 and 300 "C, respectively. Such a drastic change of the pyrolysates can be explained as follows: 2e should decompose via a cyclocondensation-elimination path to give CuS as the sole pyrolysate, which undergoes a thermal transformation into C U ~ . effectively, ~~S as indicated in Figure 1. Preparation and Characterization of Copper Sulfide Thin Films. The printing technique (solution pyrrolysis) contained two successive operations. The first step is to form a homogeneous solution film on the substrate. Next, the solution films are converted into solid films in the main pyrolysis step. Thus, the preparation of the solution of the precursor materials is a critical step. Dialkyl derivatives of 2 are generally soluble in most organic solvents, and we tried to prepare copper sulfide films using p-xylene as reported earlier (Nomura et al., 1987a, 1988). However, the solution was essentially repelled from the surface of the substrate, and poorly adhesive copper sulfide layers are obtained. Further it could not be improved by the use of other organic solvents such as chloroform, acetonitrile, and DMSO. Although 2e is soluble in a very limited number of solvents, such as DMSO and higher alcohols, we could prepare copper sulfide films using a DMSO solution of 2e ( 5 wt %), and the results obtained are summarized in Table 11. Deposited cuprous sulfide films are brown-toblack in color and relatively conductive (3.2 X fl cm).
Figure 3. X-ray diffraction patterns of copper sulfide film deposited on a glass substrate via solution pyrolysis of 2e in DMSO solution (5 wt %) at 300 "C for 1 h under Ar. The main peaks appearing between 10" and 60" (20) could be assigned to those for Cu,S (JCPDS 23-957).
Typical X-ray diffraction patterns are shown in Figure 3, and it was found that the main structure consisted of the Cu,S (1.96 > 2 > 1.86, metastable hexagonal form of digenite, JCPDS 23-957) phase. The composition of the film was almost homogeneous, and the Cu/S ratio turned out to be 1.88, which was determined by X-ray fluorescence analyses. The surface morphology was also observed by SEM, and we found that many cracks existed on the surface. Further, the direc gap energy was estimated as 2.10 eV, which is a similar value to that of Cu1&3prepared by chemical bath deposition (2.1 eV) (Pramanik et al., 1987). In addition, the solution pyrolysis of 2e operating at 250 "C could also give curpic sulfide layers, but no X-ray diffraction peak was detected. In conclusion, copper dithiocarbamate complexes, especially 2e, which have w-hydroxy groups in the ligand moiety are good precursors for copper sulfide powders and thin films using pyrolysis at 300 "C. Registry No. 2a, 13681-87-3;2b, 13927-71-4;2c, 62637-60-9; 2d, 120085-60-1;2e, 52672-76-1; CuS, 1317-40-4; Cu2S,22205-45-4; CU1.&3, 107499-48-9.
Literature Cited Croitoru, N.; Jakobson, S. Properties of Cadmium Sulfide Films and Copper(1) Sulfide-Cadmium Sulfide Junctions Prepared by Chemical Printing. Thin Solid Films 1979, 56, L5. Engelken, R. D.; McCloud, H. E. Electrodeposition and Material Characterization of Cu,S Films. J. Electrochem. SOC.1985,131, 567. Fatas, E.; Garcia, T.; Montemayor, C.; Medina, A.; Garcia-Camarero, E.; Arjona, F. Formtion of Copper Sulfide (Cu,S) Thin Films Through a Chemical Bath Deposition Process. Mater. Chem. Phys. 1985,12, 121. Gadgil, S. B.; Thangaraj, R.; Agnihotri, 0. P. Optical Properties and Solar Selectivity of Flash-Evaporated Copper Sulphide Films. J. Phys. D 1987,20, 112. Garcia-Camarero, E.; Arjona, F.; Leon, M.; Nunez, M. J.; Fatas, E.; Garcia, T. Formation of CuzS Thin Films by an Electrochemical Procedure. J. Mater. Sci. 1986, 21, 4169. Iborra, E.; Santamaria, J.; Martil, I.; Gonzalez-Diaz, G.; SanchezQuesada, F. Thin Cu,S Sputtered Films in Ar/H2 Atmosphere. Vacuum 1987,37,437. Nomura, R.; Kori, M.; Matauda, H. Preparation and Reactions of Novel p-OxobisantimonyAminoalkoxide. Chem. Lett. 1985,579. Nomura, R.; Takabe, A.; Matsuda, H. Catalytic Oxidation of Thiols by Triphenylstibine Oxide. Chem. Express 1986, I , 375.
880 Ind. Eng. Chem. Res., Vol. 28, No. 6, 1989 Nomura, R.; Takabe, A,; Matsuda, H. Facile Synthesis of Antimony Dithiocarbamate Complexes. Polyhedron 1987a, 6 , 411. Nomura, R.; Inazawa, S.-J.;Matsuda, H.; Saeki, S. Thermal Decomposition of Organoindium Compounds and Preparation of Indium-tin-oxide Films. Polyhedron 1987b,6, 507. Nomura, R.; Kanaya, K.; Matsuda, H. Preparation of Copper-indium-sulfide Thin Films by Solutions Pyrolysis of Organometallic Sources. Chem. Lett. 1988, 1849. Nomura, R.; Kanaya, K.; Matsuda, H. Preparation of Transparent and Conducting Indium Oxide Films by Solution Pyrolysis of Dibutylindium Thiolate. Thin Solid Films 1989, 167, L27. Orban de Xivry, E.; Streydio, J. M.; Berote, G. Chemical Spray Technology Adapted to Their Film Semiconductor Growth. Mater. Sci. Monogr. B 1987, 38, 1709; Chem. Abstr. 1988, 107, 137533~. Pramanik, P.; Akhter, M. A.; Basu, P. K. Modified Chemical Method for the Decomposition of Copper Sulfide (Cu1.&3)Thin Film. J . Mater. Sci. Lett. 1987, 6, 1277.
Rastogi, A. C.; Salkalachen, S. Optical Absorption Behaviour of Evaporated Cu,S Thin Films. Thin Solid Films 1982,97, 191. Uppal, P. N.; Burton, L. C. X-Ray and XPS Studies of Evaporated Cu,S Thin Films. J. Vac. Sci. Technol. A 1983, I , 479. Yoshikawa, A.; Yoshihara, S.; Kasai, H.; Nishimaki, M. A New Apparatus for Multilayer Growth by Chemical Vapor Deposition. The Slidingboat Close-spaced Technique. Appl. Phys. Lett. 1980, 37, 732.
Ryoki Nomura,* Kouichi Kanaya, Haruo Matsuda Department of Applied Chemistry Faculty of Engineering Osaka University Yamada-Oka, Suita, Osaka 565, Japan Received for review August 12, 1988 Revised manuscript received February 27, 1989 Accepted March 20, 1989
ADDITIONS AND CORRECTIONS Cinematic Modeling of Dynamics of Solids Mixing in Fluidized Beds [Volume 26, Number 2, page 2921. Chandrasekharan C. Lakshmanan and Owen E. Potter* Page 293. In Table I, the entry in the first column, sixth row should be ea. Page 2%. In the Nomenclature section, u, = linear velocity of the main dense phase, (m3 of phase/m2 of phase)/s; and u, = linear velocity of the wall phase, (m3 of phase/m2 of phase)/s.
