578
Langmuir 1988,4, 578-579
that TMCS ligands react with isolated silanols to a greater degree than with paired silanols. Therefore, with the addition of 3PPS, a majority of the isolated silanols have been deactivated and the 3PPS ligands must cluster into regions of high local density. If the present work is indicative of the distribution of C1, ligands, it appears that thermal pretreatment of silica does not change the overall distribution of C18 monofunctional silane ligands. The effect of heat pretreatment may be more pronounced when considering the deactivation of surfaces when highly active solutes, e.g., basic solutes, are separated rather than altering the distribution of surface bound ligands. Although an analogous surface-bound probe is not readily available to mimic C8 and chlorodimethylbutylsilane(C,) bonded phases, the smaller molecular size of these silanes would indicate that thermal pretreatment of the silica surface should affect the n-alkyl
chain distribution and surface coverage to a greater degree than C18phases. The deactivation of silica surfaces toward solutes, which may interact with residual silanols by partially reacting the surface with TMCS and then with C18 ligands, as demonstrated by Lochmuller and Marshall,14may be a more reproducible method to make less reactive, more homogeneous chromatographic surfaces.
Acknowledgment. This work was supported, in part, by a grant from the National Science Foundation, Grant NO. CHE85-00658 (to C.H.L.). Registry No. TMCS, 75-77-4; 3PPS, 86278-57-1; Si02, 7631-86-9. (14)Lochmuller, C. H.; Marshall, D. B. Anal. Chim. Acta 1982,142, 63.
A Simple Method for the Production of Controlled Electroplated Designs on a Metal Surface Ewa S. Kirkor, Donald E. David, Thomas F. Magnera, and Josef Michl* Center for Structure and Reactivity, Department of Chemistry, The University of Texas, Austin, Texas 78712-1167 Received September 14, 1987. In Final Form: November 19, 1987 A procedure for the imaging of an adsorbate macroscopic island on a metal surface covered elsewhere by a single molecular layer of another adsorbate has been developed. Carbon monoxide and iodine were utilized as the adsorbents. The latent image of the islands was created by laser ablation of the original adsorbate (carbon monoxide or iodine) from the illuminated part of the surface in the presence of the vapor of the other adsorbate (iodine or carbon monoxide, respectively). The image can be developed by silver electroplating.
Introduction We report a simple procedure for the production of electrodeposited images on a metal surface. Macroscopic islands of an adsorbate (A) in the layer of another adsorbate (B) were produced by first covering all of the surface with B and then desorbing it in the atmosphere of the adsorbate A by a laser beam passing through a mask defining a spatial pattern. Adsorbates A and B need to adsorb to the support surface strongly enough to prevent exchange with other potential adsorbates and to prevent mutual scrambling before the image is developed by selective electroplating. The latter is induced by choosing one of the adsorbates so that it passivates the surface with respect to metal deposition and the other adsorbate so that it does not interfere with metal deposition. For initial demonstration, we have chosen carbon monoxide and iodine for adsorbates A and B, platinum as the primary metal surface, and silver for the plating metal. Iodine and carbon monoxide are known to interact strongly with many metal surfaces, and each one has the ability to hinder the adsorption of certain other adsorbates.'$ Silver is known to electroplate on a surface covered with iodine but does not deposit on a surface covered with C0.3 It is known that iodine or CO adsorbates on platinum are
stable a t silver electrodeposition potentials in oxygen-free ele~trolytes.~,~ It is also known that an iodine adsorbate on platinum can be exposed to AgClO, electrolyte without damage although restructuring of the adsorbed layer occurs during ele~troplating.~-'
Results and Discussion Two ways of preparing the images were tested, in which either CO or iodine was utilized as an initial adsorbate. The desorption from the irradiated area was performed in the atmosphere of the other adsorbate in order to stabilize the image immediately. The latent image was then developed by silver plating (Figure 1). The irradiation resulted in a desorption as demonstrated by the observation of a short-lived RGA signal of the initial adsorbate. The signal intensity was the highest after the first laser flash and decreased to zero after the fifth. The nature of the adsorbates a t various stages of the process was characterized by XPS spectroscopy. Since the spatial resolution of the available spectrometer was low, we have formed only one large island on the surface in this series of experiments and did not attempt to follow the (4)Breiter, M. W. J. Electroanal. Chem. Interfacial Electrochem. 1981, 127, 157 and references therein.
(1) Katekaru, J. Y.; Garwood, G. A., Jr.; Hershberger, J. F.; Hubbard, A. T. Surf. Sci. 1982, 121, 396. (2) Sherman, M. G.; Kingsley, J. R.; Dahlgren, D. A.; Hemminger, J. C.; McIver, R. T., Jr. Surf. Sci. 1985, 149(1), L-25. (3) Hubbard, A. T., personal communication.
(5) Stickney, J. L.; Rosasco, S. D.; Song, D.; Soriaga, M. P.; Hubbard, A. T. Surf. Sci. 1983, 130, 326. (6) Salaita, G. N.; Lu, F.; Laguren-Davidson, L.; Hubbard, A. T. J. Electroanal. Chem. Interfacial Electrochem. 1987, 229, 1. (7) Lu, F.; Salaita, G. N.; Baltruschat, H.; Hubbard, A. T. J. Electroanal. Chem. Interfacial Electrochem. 1987, 222, 305.
0743-7463/88/2404-0578~01.~0l0 0 1988 American Chemical Societv
Controlled Electroplated Designs on a Metal
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9
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Longmuir, Vol. 4, No. 3,1988 579
u t i the surface-differentiating electroplating technique employed here.
Experimental Section
Figure I. Image of CO replacement pattern on iodide-coverad platinum surface developed hy silver plating (magnification2X). boundaries. There was some carbonaceous contamination even on the cleaned initial surface, but this did not interfere with the experiment. The shape of the XPS carbon peak indicated that the primary contaminant on the "clean" surface was hydrocarbons (-65%) and oxygencontaining organic compounds, with less than 10% of CO?.g The XPS C O ratio corrected for detection sensitivity was 3.25 f 0.15 regardless of the method of surface cleaning. Exposure of a 'clean" surface, or laser irradiation of a contaminated surface in the presence of CO, reduced the C O ratio to 2.0 i 0.4. After attempted electroplating, such a CO-covered surface showed no XPS signals for Ag. XPS signals for iodine were not found after exposure to 1, vapor at room temperature in the dark, but they were clearly seen when the exposure was accompanied by laser irradiation. After exposure of a %lean" surface to iodine or the iodide ion, XPS signals for I were obeerved and the C O ratio was 4.1 f 0.4. It was insensitive to exposure to CO without light or heat but decreased to 2.0 i 0.4 if the exposure was accompanied by Laser irradiation. The iodine W S signals also disappeared in the process. Electroplating on an iodine-covered surface proceeded smoothly and was apparent visually. An example of a developed image is shown in Figure 1. The mechanism of ablative adsorbate exchange might be a mixture of thermal and possibly photodesorption processes,1° since the exchange took place on both the irradiated and the unirradiated side of the thin Pt foil.
Conclusions It is possible to use single molecular layers for electrochemical imaging. Our observations leave no doubt that the mechanism of the observed image production is the one that was intended. We were able to produce a series of positive images, starting with a surface totally covered with carbon monoxide, and of negative images, starting with a surface totally covered with iodine. The laser-desorption technique is only capable of relatively low spatial resolution. Our ultimate goal, production of submicroscopic images, will have to rely on other methods of initial image recording but can presumably (8) Norton, P. R. Surf.Sei. 1974,44,624. (9) pilks, k In Electron Spectroscopy, Theory, Techniquesand Applkotiona: Drunde, C. R.,BaLer, A. D., Eds.; hdemic Nem York, 1981,
Vol. 4.
(IO) Chuaag, T.J. J . Vu. Sei. Technol. B 1985,83,1408.
Carbon monoxide (99.95% Matheson), iodine, sodium iodide, potassium carbonate, perchloric acid, and ammonia (dlanalytical grade) were used without purification. Water was triply distilled from an all-quartz apparatus. AgC10, was prepared by precipitation of AgzC08.Hz0with potassium carbonate from AgNOs solution, rinsing with dilute ammonia and then water until no NO3- anions could be detected, and disaolution of the precipitate in 1M HClO,. The concentration of silver was estimated by eleetrogravimetry. Acidity was adjusted to pH 1with HC104. A cyclic voltammogram scanned from +1.2 to 0 V showed only expected silver oxidation and reduction peaks and Pt oxidation starting at +0.9 V. A 10 X 10 X 0.025 m m Pt foil from AESAR (99.99%) was cleaned after Pt wire electrode leads were spotwelded to it. The foil was either boiled in concentrated nitric acid and then rinsed with triply distilled water or resistively heated for 2 h at -1200 K in a stream of oxygen at 10+ Torr (background pressure 5 X lo4 Torr) and then annealed and cooled. The cleaned surface was covered hy the desired coating hy exposure to CO, iodine vapor, or a saturatad aqueous solution of NaI. An adlattice of iodine forma spontaneously on a Pt surface upon immersion in aqueous iodide solution?' CO or iodine vapor were applied in a vacuum chamber at Torr. The Pt foil to he covered by iodine in NaI solution was deaned in nitric acid, rinsed 10 times with water, and then boiled for 5 min in saturated NaI solution. The salt was removed with 1M HCIO, and then excess water. The sample covered with primary deposit was placed in a miniature vacunm chamher equipped with quartz windows, the mask was placed in front of the window, and the chamber wan tilled with the island-filling second adsorbate at Torr and irradiated with unfocused 248- or 308-nm laser light (LambdaPhysik, -120 mJ, 20 Hz)for approximately 1 min. The sample wan then transferred to the electroplating bath without any special precautions. Silver deposited on the iodine-covered areas, where coverage with CO prevented Ag electrodeposition, so that a mask image appeared on the surface. The plating solution was a 0.02 M solution of AgCIO, in 1M HCIO,? Silver was deposited either at +0.27 V (bulk) for developing images6 or at +0.44 V (underpotentialdeposition yielding two monolayers of Ag on the plated surface') for XPS analysis. The potential was measured against an SCE, and it was lower than the oxidative desorption potentials of CO' and I and lower than that of the oxidation of Pt.'3 The charge passed was measured. The foils were immersed in the electrolyte under polarized open circuit conditions. The solutions were deareated hy passing oxygen-freenitrogen for 10min before immersion of the latent image containing foil. After plating, the foil was rinsed, dried,and surface analyzed. The XPS analysis wan done on an HP 5950B electron spectrometer, and MS w&5 measured hy using the residual gas analyzer on a home-built instrument?'
Acknowledgment. This work was supported by the
US.Army Research Office. We are indebted to Prof. A. T. Hubbard for a useful discussion, to Prof. B. S. Pons for permission to use his electrochemical equipment, and to P. Dryden for XPS measurements. Registry No. Ag. 7440-22-4; CO, 630-08-0;I,, 7553-56-2;Pt, 7440-06-4. (11) Stickmy, J. L.; Rasaseo, S. D.:Salaim, G. N.: Hubbard, A. T. Lorylmuir 1986, 1.66. (12) Felm, T. E.:Hubbard. k T. J . Elpefmanol.C h " 197% IW,473. (13) Tindd. G. W.: Bruckenstein, S.Elecfroehim.A m 1971,16.245. (14) Mwera,T. F.: David, D. E.: Orth! R, Sculik, D.; Jonkman. H. T.: Michl, J . . u) be submrtred for publrcatron.
