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The growth mode and electronic structure of copper overlayers on Pd(100) AND Pt(100)
Surface Science 152/153 (lYX5) ZhO- 261 North-Holland. Amsterdam
260
THE GROWTH MODE AND ELECTRONIC OVERLAYERS ON Pd(100) AND Pt(100) C.J. BARNES
*, M. LINDROOS
OF COPPER
and M. PESSA
L)qpartmentof Ph_vsm Tumperr Ur~~~wsrt~ of Technolqy. Received
STRUCTURE
SF- _?3/0/ Tumpcw
10, F~tdrrtrd
3 April 1984
Low energy electron diffraction (LEED), Auger electron spectroscopy (AES). angle resolved photoemission spectroscopy (ARPES) and work function measurements have been used to deduce the growth mode and follow the evolution of electronic structure of thin Cu films on Pd(lOO) and Pt(lOO) single crystal substrates. Auger signal versus time (AS-r) plots were constructed using the peak-topeak heights of the differentiated Cu MVV (60 eV) and Pd M,,,N,.,N,,, (330 eV) AES lines. In the case of Pd(lOO), a series of linear sections of differing gradients have been detected for the Cu MVV peak, indicating that the Cu overlayer is initially growing in a layer-by-layer (Frank van der Merwe) fashion. Corresponding linear sections and breaks could not he definitely detected for the Pd 330 eV peak. presumably due to the greater escape depth. hence lower surface sensitivity of this peak. Similar consideration of Pt AES features suggest that the growth mode on this substrate is also initially layer-by-layer. LEED results indicate that growth is pseudomorphic on both substrates up to coverages of - 2 ML, both surfaces exhibiting a sharp p(1 x 1) pattern in this coverage range. The characteristic 5 x 20 reconstruction observed for the clean Pt(100) surface is lifted by submonolayer coverages of Cu. For Cu coverages > 3 ML, an increase in background intensity could be observed, although we note that even at coverages as high as 10 ML diffuse spots were still visible. We associate the increase in background with possible relaxation of the Cu film towards its own lattice constant, as both Pt and Pd have lattice constants 8% greater than bulk Cu. The evolution of electronic structure of Cu films in the coverage range 0- IO ML has been monitored using ARPES and work function measurements (determined from the full width of He 1 UPS spectra). Large changes in the electronic structure of pseudomorphic overlayers from those expected based on * Present address: L69 3BX. UK.
The Donnan
Lahoratorvs.
Uniwrsitb
of Liverpool.
0039-6028/85/$03.30 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
B.V.
P.O. Box 147. LIverpool
C.J. Barnes et al. / Copper overlayers on Pd(lO0) and Pt(100)
261
the known electronic structure of bulk Cu(100) single crystals have been observed. Changes in electronic structure are however expected due to the much expanded lattice constant of the film. We particularly note an intense peak at a binding energy 4.6 eV with respect to the Fermi level, seen at normal emission with He I radiation. This peak exhibits a large dispersion. We tentatively assign this feature to emission from the Cu sp band, the intensity being much enhanced relative to that from a bulk Cu(100) single crystal. A full account of this work will be published elsewhere.
260
THE GROWTH MODE AND ELECTRONIC OVERLAYERS ON Pd(100) AND Pt(100) C.J. BARNES
*, M. LINDROOS
OF COPPER
and M. PESSA
L)qpartmentof Ph_vsm Tumperr Ur~~~wsrt~ of Technolqy. Received
STRUCTURE
SF- _?3/0/ Tumpcw
10, F~tdrrtrd
3 April 1984
Low energy electron diffraction (LEED), Auger electron spectroscopy (AES). angle resolved photoemission spectroscopy (ARPES) and work function measurements have been used to deduce the growth mode and follow the evolution of electronic structure of thin Cu films on Pd(lOO) and Pt(lOO) single crystal substrates. Auger signal versus time (AS-r) plots were constructed using the peak-topeak heights of the differentiated Cu MVV (60 eV) and Pd M,,,N,.,N,,, (330 eV) AES lines. In the case of Pd(lOO), a series of linear sections of differing gradients have been detected for the Cu MVV peak, indicating that the Cu overlayer is initially growing in a layer-by-layer (Frank van der Merwe) fashion. Corresponding linear sections and breaks could not he definitely detected for the Pd 330 eV peak. presumably due to the greater escape depth. hence lower surface sensitivity of this peak. Similar consideration of Pt AES features suggest that the growth mode on this substrate is also initially layer-by-layer. LEED results indicate that growth is pseudomorphic on both substrates up to coverages of - 2 ML, both surfaces exhibiting a sharp p(1 x 1) pattern in this coverage range. The characteristic 5 x 20 reconstruction observed for the clean Pt(100) surface is lifted by submonolayer coverages of Cu. For Cu coverages > 3 ML, an increase in background intensity could be observed, although we note that even at coverages as high as 10 ML diffuse spots were still visible. We associate the increase in background with possible relaxation of the Cu film towards its own lattice constant, as both Pt and Pd have lattice constants 8% greater than bulk Cu. The evolution of electronic structure of Cu films in the coverage range 0- IO ML has been monitored using ARPES and work function measurements (determined from the full width of He 1 UPS spectra). Large changes in the electronic structure of pseudomorphic overlayers from those expected based on * Present address: L69 3BX. UK.
The Donnan
Lahoratorvs.
Uniwrsitb
of Liverpool.
0039-6028/85/$03.30 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
B.V.
P.O. Box 147. LIverpool
C.J. Barnes et al. / Copper overlayers on Pd(lO0) and Pt(100)
261
the known electronic structure of bulk Cu(100) single crystals have been observed. Changes in electronic structure are however expected due to the much expanded lattice constant of the film. We particularly note an intense peak at a binding energy 4.6 eV with respect to the Fermi level, seen at normal emission with He I radiation. This peak exhibits a large dispersion. We tentatively assign this feature to emission from the Cu sp band, the intensity being much enhanced relative to that from a bulk Cu(100) single crystal. A full account of this work will be published elsewhere.