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Experimental study of illumination effects on the cathodic current-voltage curve on n-GaAs
215
J. Electroanal. Chem., 223 (1987) 215-221 Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands
EXPERIMENTAL STUDY OF ILLUMINATION EFFECTS CATHODIC CURRENT-VOLTAGE CURVE ON n-GaAs
H. HERRNBERGER,
R. SOURISSEAU
Sektion Chemie, Karl-Marx-Universitiir, (Received
ON THJ?
and W. LORENZ Leipzig (G.D.R.)
22nd October 1986; accepted 5th December
1986)
ABSTRACT
The cathodic current-voltage curve on n-GaAs electrodes has been investigated under illumination or after pre-ilhtmination. A possible majority carrier photoeffect is suppressed in both acidic and alkaline solution, presumably by light-driven chemisorption intermediates of hydrogen evolution. A minor illumination-dependent cathodic current peak in the pA range can be attributed to the re-reduction of dissolved As-oxidation products. The influence of pretreatment and of the crystal face has been studied.
(I) INTRODUCTION
While stationary anodic photocurrents on n-semiconductors of Group III-V have frequently been observed, much less data are available about illumination effects on cathodic currents. In the cathodic regime of n-semiconductors there is the possibility of a majority carrier photoeffect [l]; the conditions of observability have not yet been studied. In the anodic regime it is greatly surpassed by the common minority carrier photoeffect. Another related question concerns the influence of photo-oxidation products on the cathodic voltammetric behaviour (cf. ref. 2 for GaAs; also ref. 3 for CdSe). A marked cathodic current on n-GaAs (say, - 10 PA cm-*) is obtained already in the depletion regime: in acidic aqueous solution at E* = e - cFB = 0.3 V and in alkaline solution at e* = 0.4 V [4]. In Section (II), a more detailed investigation of the cathodic branch of the current-voltage curve, including the effects of illumination or pre-illumination, will be discussed. In Section (III), some calculations of the majority carrier photoeffect are presented for a cathodic process without chernisorption. The absence of this effect indicates interference of the chemisorbed intermediates of the main cathodic process-hydrogen evolution. 0022-0728/87/$03.50
0 1987 Elsevier Sequoia S.A.
216 (II) EXPERIMENTAL
OBSERVATIONS
n-GaAs samples in the donor density range 7 X 1014-1 X 10’8cm-3 were used. The low-doped samples with the epitaxial layer on a quasi-insulating substrate were contacted at the front; a homogeneous current density was guaranteed under this condition at frequencies 5 1 kHz, as well as at a slow voltage sweep. Samples were mostly prepared by H,SO, + H,O, + H,O etching (6 : 1: l, l-2 min at 25 o C) and rinsing. No significant influence of dissolved 0, on the current-voltage curves was found. Figure 1 shows the cathodic dark and photocurrent-voltage curves in the low current regime on n-GaAs (100) (about 4 X 10”cmP3 Te) in 0.5 M H,SO,(aq) for a single negative + positive sweep. A small cathodic current peak at - 0.4 to - 0.7 V (vs. SCE), which is considerably enhanced at illumination, and current-voltage hysteresis is observed. The dark peak is slightly enhanced when the H,SO, content of the etching solution is lowered. In Fig. 2, the cathodic dark and photocurrents are given for lower donor densities (7 x 10’4-1.5 X 10”cmW3 Si). The dependence of the current response on the donor density turns out to be not significant. This observation rules out the explanation of the photocurrent as a majority carrier photoeffect (see Section III). The current peak addressed is absent in alkaline solution (Fig. 2a). That the cathodic photocurrents in Figs. 1 and 2 do have a rather indirect cause is confirmed by the observation of similar behaviour of the dark currents obtained after pre-illumination at more positive potentials (strong photodissolution), which indicates that re-reduction of a photo-oxidation product is responsible for the illumination effects under discussion. Figure 3 shows the dependence of the cathodic
-0.5
0 E/Vtvs SCEI
Fig. 1. Current-voltage curves on n-GaAs (100) (4X 10” crnm3 Te)/O.5 M H,SO.,(aq) in the cathodic regime. Single negative+ positive sweep; sweep rate = 1 mV s-l. (1) Dark current; (2) photocurrent.
217
-1.4 -1,2 -1.0 -0,8
?
k ::
a ._
-0,0
-0.6 -0,L
o- dark -5. -10. -15. -20.
B photo
(Cl
I
id)
-25’__bi_
-0,8 -46
- 084
EA'(vs.SCE)
Fig. 2. Dependence of the cathodic current-voltage curves at n-GaAs (100) on the donor density. Sin@e negative+positive sweep between 0 V (vs. SCE) and flat-band potential; sweep rate = 1 mV s-l. (a) Donor density 3 X 10” cme3 Si, solution 1 M KOH(aq); (b) 7X1014 cmm3 Si, 0.5 M H$O,(aq); (c) 7~10”~ cme3 Si, 0.5 M H,SO,(aq); (d) 1.5~ 10’7cm-3 Si, 0.5 M H,SO,(aq).
current on pre-illumination and the sweep rate, at a GaAs (111A) surface (Ga surface). The time integral over the difference between the negative and the positive sweep (curves 2 and 3, Fig. 3) gives a measure of the reducible oxidation products, amounting to about 7 X 10e4 and 2 X 10m4C cm-* for curves 2 and 3, respectively. The decrease of this charge with increasing sweep rate indicates transport of the reducible species from the solution. A less significant decrease of the reduced charge is observed on the dark current peak, indicating reducible species at the surface, in the submonolayer range or in the form of islands. Freshly etched (111A) samples (curve 1, Fig. 3) show negligible hysteresis. The stronger photoetching which precedes curves 2 and 3 of Fig. 3 may partly destroy the Ga surface. In Fig. 4 it is verified, by the addition of As,O, to the solution, that an As-oxidation product is responsible for the current peak. The addition of Ga3+ to
218
0
-8
-12
-16 -1
-0.5
0 EIV(vs.SCE)
-1.0
-0.5
0
EIVlvs SCE)
Fig. 3. Cathodic dark current-voltage curves on n-GaAs (111A) (1 x 10” cmm3 Se)/05 M H,SO.,(aq). Single negative+positive sweep. (1) Freshly etched sample, scan rate = 1 mV s-‘; (2) 2 min pre-illumination at 0 V (vs. SCE), scan rate = 1 mV s -‘; (3) pre-illumination as before, scan rate = 10 mV s-‘. Fig. 4. Influence of As,03 added to the solution on the cathodic current-voltage curve on n-GaAs (100) (4 x 10” cme3 Te). Single negative+positive sweep, scan rate = 1 mV s-r. (1) 0.5 M H,SO,(aq); (2) as (l), with As203 added (saturated).
the solution had no effect on the current-voltage curve. This correlates with the strongly irreversible reduction of Ga3+ on mercury. (On the contrary, the easily reduced and oxidized In3+/In couple produces both cathodic and anodic current peaks on InP, as observed in ref. 5 and confirmed by our own measurements.) The observed current-voltage hysteresis can likewise be caused by irreversible oxidation of the reduced As product in the positive reverse sweep. Another possible reason can be a dispersed deposit which could render its re-oxidation difficult. Hydrogen evolution intermediates may contribute to a minor extent to hysteresis; the lack of any effect of Ga3+ addition supports the contention that there is no interference of a deposit of Ga oxide (improbable in strongly acidic or alkaline solution). Stirring of the solution enhances the cathodic current peak, already in the dark. The reason for this effect is, however, rather complex, since longer stirring (- lh) at 0 V (vs. SCE) in the dark shifts the cathodic current onset by up to 100 mV to more positive potentials, under partial disappearance of the peak. Similar behaviour is observed in higher acidic solutions. These effects again indicate participation of
219
As-oxidation products at the surface and an influence on the hydrogen evolution process, the details of which are still unknown. (II. I) Discussion The data reported show that the main cathodic process (hydrogen evolution) on n-GaAs is superposed in the low current regime by a reduction process of As-oxidation or photo-oxidation products. The observed dependences indicate that the reducible species are at least partly transferred by transport from the solution. In addition, an influence of surface structural properties on the reduction process can be inferred from the pretreatment effect indicated in the text on Fig. 1 and from the absence of current-voltage hysteresis on a freshly etched Ga surface (111A) (Fig. 3). Voltammetric measurements prove to be very sensitive. The small amount of reduced substance, together with partial transfer from the solution, indicates an upper bound of the chemisorbed reducible substance, below or even far below monolayer coverage. That rinsing can remove oxidation products from the GaAs surface, within the sensitivity of electron spectroscopy, has recently been supported in refs. 6 and 7. (III) CALCULATIONS
Here we look briefly at the possibility of a majority carrier photoeffect, larly in the cathodic regime of n-semiconductors. The non-equilibrium electron density is given by n,/&’ = [j&
+ B,, +
11exd-Mcp,)
particusurface
(1)
(cf. ref. l), where Acp,,= ‘p, - & A, = iV,(O)/en,D, and B, = I&(O)/n,D,. In contrast to irreversible anodic semiconductor dissolution, it is reasonable to choose here as the reference state (superscript “) the equilibrium potential of hydrogen evolution in the dark (I, = 0, B,, = 0, j, = 0), at a (fictive) hydrogen pressure equal to atmospheric pressure: e”(HJH+) = -0.24 V (vs. SCE). The charge-transfer kinetics following ref. 8 may be considered here for the idealized condition of a cathodic irreversible process, without taking into account light-driven chemisorption intermediates [9]. The kinetic equation of an irreversible cathodic charge-transfer process reads j,,=
-j,“(n,/rt,“)”
exp(-&#Acpu)
(2)
where j,” is the exchange current density and n,” is the equilibrium surface electron density, referred to the equilibrium hydrogen potential (see above). i& is the backward kinetic charge injection coefficient and d is the backward kinetic transfer coefficient related to the Helmholtz potential Acp,. Some computations are given in Fig. 5 for different donor densities or in turn different bulk electron densities nb appearing in the terms A, and B,, of eqn. (1). The j,” values have been roughly adjusted to experimental cathodic currents. The
220
dark
photo
7=-lb)
I ‘I
-0.8
-0.b
-0.4
- 08
EIH2/H* I
do.8
/
-0,6 -44
-0,2
EIV(vs.SCE)
Fig. 5. Theoretical cathodic dark and photocurrent-voltage curves for a one-step process without chemisotption, following eqns. (1) and (2). Parameters for n-GaAs; I,, = 0 (dark) or 5 X lOI photons cm-* s-l (photo); 01= 1 x lo4 cm-‘; D, = 3 cm* s-t. Potential division into Aqsc and A~J, calculated with negligible surface capacity. (a) Donor density No = 4X lOI cmm3: 6i = Z= 1 (curve 1) or 0.4 (curve 2); j,” =10-s (curve 1) or lo-‘* A cm-* (curve 2). (b) No = 2X1015 cmm3; 6 = h=l; j,0=10-9Acm-2.(c) N,=1x10’6cm-3; rE=E=l; JE=10-9Acm-2.
calculations reveal a strong increase of the cathodic photocurrent with decreasing donor density. This effect does not depend significantly on the value of ri?. The absence of majority carrier photoeffect in Fig. 2 has already been pointed out. The reason for this must primarily be sought in the obvious participation of chemisorbed intermediates in the hydrogen evolution mechanism. Light-driven chemisorption takes place under the concerted action of electron and hole currents [g-lo]. The connection of this effect with the stationary hydrogen evolution process will be further investigated separately.
(IV) SUMMARY
Stationary currents on n-GaAs electrodes have been investigated in the cathodic low-current (CIA) regime. Illumination effects and current-voltage hysteresis can be attributed to the reduction of at least partly dissolved As-oxidation products superposed to the main cathodic hydrogen evolution process. From the small turnover, one can infer a maximal in situ coverage of GaAs with oxidation products below a monolayer. A possible majority carrier photoeffect in the cathodic regime is suppressed, most probably by interference of light-driven chemisorbed intermediates of the hydrogen evolution process.
221 REFERENCES 1 2 3 4 5 6 7 8 9 10
W. Lorenz and M. Handschuh, J. Electroanal. Chem., 178 (1984) 197. P. Allongue and H. Cachet, Solid State Commun., 55 (1985) 49. R. Tenne and W. Giriat, J. Electroanal. Chem. 186 (1985) 127. W. Lorenz and B. Wolf, Electrcchim. Acta, 28 (1983) 191. S. Menezes, B. MiJler and K.J. Bachmann, J. Vat. Sci. Technol., Bl (1983) 48. J. Massies and J.P. Contour, J. Appl. Phys. 58 (1985) 806; Appl. Phys., Lett. 46 (1985)1150. P. Alnot, F. Wyczislc and A. Friedrich, Surf. Sci., 162 (1985) 708. W. Lorenz, J. Electroanal. Chem. 191 (1985) 31. W. Lorenz, M. Handschuh, C. Aegerter and H. Herrnberger, J. Electroanal. Chem., 184 (1985) 61. W. Lorenz, C. Aegerter and M. Handschuh, J. Electroanal. Chem., 221 (1987) 33.
J. Electroanal. Chem., 223 (1987) 215-221 Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands
EXPERIMENTAL STUDY OF ILLUMINATION EFFECTS CATHODIC CURRENT-VOLTAGE CURVE ON n-GaAs
H. HERRNBERGER,
R. SOURISSEAU
Sektion Chemie, Karl-Marx-Universitiir, (Received
ON THJ?
and W. LORENZ Leipzig (G.D.R.)
22nd October 1986; accepted 5th December
1986)
ABSTRACT
The cathodic current-voltage curve on n-GaAs electrodes has been investigated under illumination or after pre-ilhtmination. A possible majority carrier photoeffect is suppressed in both acidic and alkaline solution, presumably by light-driven chemisorption intermediates of hydrogen evolution. A minor illumination-dependent cathodic current peak in the pA range can be attributed to the re-reduction of dissolved As-oxidation products. The influence of pretreatment and of the crystal face has been studied.
(I) INTRODUCTION
While stationary anodic photocurrents on n-semiconductors of Group III-V have frequently been observed, much less data are available about illumination effects on cathodic currents. In the cathodic regime of n-semiconductors there is the possibility of a majority carrier photoeffect [l]; the conditions of observability have not yet been studied. In the anodic regime it is greatly surpassed by the common minority carrier photoeffect. Another related question concerns the influence of photo-oxidation products on the cathodic voltammetric behaviour (cf. ref. 2 for GaAs; also ref. 3 for CdSe). A marked cathodic current on n-GaAs (say, - 10 PA cm-*) is obtained already in the depletion regime: in acidic aqueous solution at E* = e - cFB = 0.3 V and in alkaline solution at e* = 0.4 V [4]. In Section (II), a more detailed investigation of the cathodic branch of the current-voltage curve, including the effects of illumination or pre-illumination, will be discussed. In Section (III), some calculations of the majority carrier photoeffect are presented for a cathodic process without chernisorption. The absence of this effect indicates interference of the chemisorbed intermediates of the main cathodic process-hydrogen evolution. 0022-0728/87/$03.50
0 1987 Elsevier Sequoia S.A.
216 (II) EXPERIMENTAL
OBSERVATIONS
n-GaAs samples in the donor density range 7 X 1014-1 X 10’8cm-3 were used. The low-doped samples with the epitaxial layer on a quasi-insulating substrate were contacted at the front; a homogeneous current density was guaranteed under this condition at frequencies 5 1 kHz, as well as at a slow voltage sweep. Samples were mostly prepared by H,SO, + H,O, + H,O etching (6 : 1: l, l-2 min at 25 o C) and rinsing. No significant influence of dissolved 0, on the current-voltage curves was found. Figure 1 shows the cathodic dark and photocurrent-voltage curves in the low current regime on n-GaAs (100) (about 4 X 10”cmP3 Te) in 0.5 M H,SO,(aq) for a single negative + positive sweep. A small cathodic current peak at - 0.4 to - 0.7 V (vs. SCE), which is considerably enhanced at illumination, and current-voltage hysteresis is observed. The dark peak is slightly enhanced when the H,SO, content of the etching solution is lowered. In Fig. 2, the cathodic dark and photocurrents are given for lower donor densities (7 x 10’4-1.5 X 10”cmW3 Si). The dependence of the current response on the donor density turns out to be not significant. This observation rules out the explanation of the photocurrent as a majority carrier photoeffect (see Section III). The current peak addressed is absent in alkaline solution (Fig. 2a). That the cathodic photocurrents in Figs. 1 and 2 do have a rather indirect cause is confirmed by the observation of similar behaviour of the dark currents obtained after pre-illumination at more positive potentials (strong photodissolution), which indicates that re-reduction of a photo-oxidation product is responsible for the illumination effects under discussion. Figure 3 shows the dependence of the cathodic
-0.5
0 E/Vtvs SCEI
Fig. 1. Current-voltage curves on n-GaAs (100) (4X 10” crnm3 Te)/O.5 M H,SO.,(aq) in the cathodic regime. Single negative+ positive sweep; sweep rate = 1 mV s-l. (1) Dark current; (2) photocurrent.
217
-1.4 -1,2 -1.0 -0,8
?
k ::
a ._
-0,0
-0.6 -0,L
o- dark -5. -10. -15. -20.
B photo
(Cl
I
id)
-25’__bi_
-0,8 -46
- 084
EA'(vs.SCE)
Fig. 2. Dependence of the cathodic current-voltage curves at n-GaAs (100) on the donor density. Sin@e negative+positive sweep between 0 V (vs. SCE) and flat-band potential; sweep rate = 1 mV s-l. (a) Donor density 3 X 10” cme3 Si, solution 1 M KOH(aq); (b) 7X1014 cmm3 Si, 0.5 M H$O,(aq); (c) 7~10”~ cme3 Si, 0.5 M H,SO,(aq); (d) 1.5~ 10’7cm-3 Si, 0.5 M H,SO,(aq).
current on pre-illumination and the sweep rate, at a GaAs (111A) surface (Ga surface). The time integral over the difference between the negative and the positive sweep (curves 2 and 3, Fig. 3) gives a measure of the reducible oxidation products, amounting to about 7 X 10e4 and 2 X 10m4C cm-* for curves 2 and 3, respectively. The decrease of this charge with increasing sweep rate indicates transport of the reducible species from the solution. A less significant decrease of the reduced charge is observed on the dark current peak, indicating reducible species at the surface, in the submonolayer range or in the form of islands. Freshly etched (111A) samples (curve 1, Fig. 3) show negligible hysteresis. The stronger photoetching which precedes curves 2 and 3 of Fig. 3 may partly destroy the Ga surface. In Fig. 4 it is verified, by the addition of As,O, to the solution, that an As-oxidation product is responsible for the current peak. The addition of Ga3+ to
218
0
-8
-12
-16 -1
-0.5
0 EIV(vs.SCE)
-1.0
-0.5
0
EIVlvs SCE)
Fig. 3. Cathodic dark current-voltage curves on n-GaAs (111A) (1 x 10” cmm3 Se)/05 M H,SO.,(aq). Single negative+positive sweep. (1) Freshly etched sample, scan rate = 1 mV s-‘; (2) 2 min pre-illumination at 0 V (vs. SCE), scan rate = 1 mV s -‘; (3) pre-illumination as before, scan rate = 10 mV s-‘. Fig. 4. Influence of As,03 added to the solution on the cathodic current-voltage curve on n-GaAs (100) (4 x 10” cme3 Te). Single negative+positive sweep, scan rate = 1 mV s-r. (1) 0.5 M H,SO,(aq); (2) as (l), with As203 added (saturated).
the solution had no effect on the current-voltage curve. This correlates with the strongly irreversible reduction of Ga3+ on mercury. (On the contrary, the easily reduced and oxidized In3+/In couple produces both cathodic and anodic current peaks on InP, as observed in ref. 5 and confirmed by our own measurements.) The observed current-voltage hysteresis can likewise be caused by irreversible oxidation of the reduced As product in the positive reverse sweep. Another possible reason can be a dispersed deposit which could render its re-oxidation difficult. Hydrogen evolution intermediates may contribute to a minor extent to hysteresis; the lack of any effect of Ga3+ addition supports the contention that there is no interference of a deposit of Ga oxide (improbable in strongly acidic or alkaline solution). Stirring of the solution enhances the cathodic current peak, already in the dark. The reason for this effect is, however, rather complex, since longer stirring (- lh) at 0 V (vs. SCE) in the dark shifts the cathodic current onset by up to 100 mV to more positive potentials, under partial disappearance of the peak. Similar behaviour is observed in higher acidic solutions. These effects again indicate participation of
219
As-oxidation products at the surface and an influence on the hydrogen evolution process, the details of which are still unknown. (II. I) Discussion The data reported show that the main cathodic process (hydrogen evolution) on n-GaAs is superposed in the low current regime by a reduction process of As-oxidation or photo-oxidation products. The observed dependences indicate that the reducible species are at least partly transferred by transport from the solution. In addition, an influence of surface structural properties on the reduction process can be inferred from the pretreatment effect indicated in the text on Fig. 1 and from the absence of current-voltage hysteresis on a freshly etched Ga surface (111A) (Fig. 3). Voltammetric measurements prove to be very sensitive. The small amount of reduced substance, together with partial transfer from the solution, indicates an upper bound of the chemisorbed reducible substance, below or even far below monolayer coverage. That rinsing can remove oxidation products from the GaAs surface, within the sensitivity of electron spectroscopy, has recently been supported in refs. 6 and 7. (III) CALCULATIONS
Here we look briefly at the possibility of a majority carrier photoeffect, larly in the cathodic regime of n-semiconductors. The non-equilibrium electron density is given by n,/&’ = [j&
+ B,, +
11exd-Mcp,)
particusurface
(1)
(cf. ref. l), where Acp,,= ‘p, - & A, = iV,(O)/en,D, and B, = I&(O)/n,D,. In contrast to irreversible anodic semiconductor dissolution, it is reasonable to choose here as the reference state (superscript “) the equilibrium potential of hydrogen evolution in the dark (I, = 0, B,, = 0, j, = 0), at a (fictive) hydrogen pressure equal to atmospheric pressure: e”(HJH+) = -0.24 V (vs. SCE). The charge-transfer kinetics following ref. 8 may be considered here for the idealized condition of a cathodic irreversible process, without taking into account light-driven chemisorption intermediates [9]. The kinetic equation of an irreversible cathodic charge-transfer process reads j,,=
-j,“(n,/rt,“)”
exp(-&#Acpu)
(2)
where j,” is the exchange current density and n,” is the equilibrium surface electron density, referred to the equilibrium hydrogen potential (see above). i& is the backward kinetic charge injection coefficient and d is the backward kinetic transfer coefficient related to the Helmholtz potential Acp,. Some computations are given in Fig. 5 for different donor densities or in turn different bulk electron densities nb appearing in the terms A, and B,, of eqn. (1). The j,” values have been roughly adjusted to experimental cathodic currents. The
220
dark
photo
7=-lb)
I ‘I
-0.8
-0.b
-0.4
- 08
EIH2/H* I
do.8
/
-0,6 -44
-0,2
EIV(vs.SCE)
Fig. 5. Theoretical cathodic dark and photocurrent-voltage curves for a one-step process without chemisotption, following eqns. (1) and (2). Parameters for n-GaAs; I,, = 0 (dark) or 5 X lOI photons cm-* s-l (photo); 01= 1 x lo4 cm-‘; D, = 3 cm* s-t. Potential division into Aqsc and A~J, calculated with negligible surface capacity. (a) Donor density No = 4X lOI cmm3: 6i = Z= 1 (curve 1) or 0.4 (curve 2); j,” =10-s (curve 1) or lo-‘* A cm-* (curve 2). (b) No = 2X1015 cmm3; 6 = h=l; j,0=10-9Acm-2.(c) N,=1x10’6cm-3; rE=E=l; JE=10-9Acm-2.
calculations reveal a strong increase of the cathodic photocurrent with decreasing donor density. This effect does not depend significantly on the value of ri?. The absence of majority carrier photoeffect in Fig. 2 has already been pointed out. The reason for this must primarily be sought in the obvious participation of chemisorbed intermediates in the hydrogen evolution mechanism. Light-driven chemisorption takes place under the concerted action of electron and hole currents [g-lo]. The connection of this effect with the stationary hydrogen evolution process will be further investigated separately.
(IV) SUMMARY
Stationary currents on n-GaAs electrodes have been investigated in the cathodic low-current (CIA) regime. Illumination effects and current-voltage hysteresis can be attributed to the reduction of at least partly dissolved As-oxidation products superposed to the main cathodic hydrogen evolution process. From the small turnover, one can infer a maximal in situ coverage of GaAs with oxidation products below a monolayer. A possible majority carrier photoeffect in the cathodic regime is suppressed, most probably by interference of light-driven chemisorbed intermediates of the hydrogen evolution process.
221 REFERENCES 1 2 3 4 5 6 7 8 9 10
W. Lorenz and M. Handschuh, J. Electroanal. Chem., 178 (1984) 197. P. Allongue and H. Cachet, Solid State Commun., 55 (1985) 49. R. Tenne and W. Giriat, J. Electroanal. Chem. 186 (1985) 127. W. Lorenz and B. Wolf, Electrcchim. Acta, 28 (1983) 191. S. Menezes, B. MiJler and K.J. Bachmann, J. Vat. Sci. Technol., Bl (1983) 48. J. Massies and J.P. Contour, J. Appl. Phys. 58 (1985) 806; Appl. Phys., Lett. 46 (1985)1150. P. Alnot, F. Wyczislc and A. Friedrich, Surf. Sci., 162 (1985) 708. W. Lorenz, J. Electroanal. Chem. 191 (1985) 31. W. Lorenz, M. Handschuh, C. Aegerter and H. Herrnberger, J. Electroanal. Chem., 184 (1985) 61. W. Lorenz, C. Aegerter and M. Handschuh, J. Electroanal. Chem., 221 (1987) 33.