23
Bull. Soc. Photogr. Imag. Japan. (2016) Vol. 26 No. 2: 23–27

Original Paper

Analysis of gold and silver content in particles formed by gold deposition development
Ken’ichi Kuge, Hidetaka Tomimatsu, Fumiyuki Shiba

Abstract: e content of gold and silver atoms in the particles formed by gold deposition development on silver halide grains was investigated.
Th
An increase in the amounts of gold and silver with development time was observed using atomic absorption spectroscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. While silver atoms formed by photolysis already existed before
development, only the amount of gold increased and that of silver did not. The gold deposition development was intensified by theaddition of ascorbic acid (AA) to the developer, and in this case, the amount of silver increased slightly with development time. The
amount of gold increased more, but the size of the particles was smaller than the case without AA. It was suggested that the reduction of silver halide by AA proceeded, but it was still unclear that this reduction affected the acceleration of development rates or not.

Key words:

Silver-salt photographic materials, Gold particles, Gold-deposition development, Photolysis of silver halide, Reduction by ascorbic acid

1. Introduction
We have reported the formation of gold particles on exposed silver-salt photographic materials by gold-deposition
development1~7). This method is a modification of the gold
development process, which forms gold atoms on latent image specks composed of photolytic silver atoms8~10). In thisprocess, gold atoms are deposited by the decomposition of
the Au (I) thiocyanate complex [Au (I) (SCN)2−], and the latent image specks act as a catalyst for this reaction. As thephotolytic silver atoms remain in the gold particles, the particles should include some silver atoms. However, theamount of silver contained in the gold particles has not yet
been investigated.
Because the minimum number of silver atoms in a developable latent image speck is estimated as four atoms for anormal development process11), the amount of silver will bevery little in this case. On the other hand, Tasaka observed
latent image specks directly using an electron microscopeand reported that they were several nm in size12). In thiscase, percent level of silver atoms is included in a minuteparticle with a size of about 10 nm. Hereafter, we call thelatent image specks as photolytic silver particles, because
we also observed them with an electron microscope as described later and they have enough size to be called particles.
This gold deposition development is greatly accelerated
when ascorbic acid (AA) is added to the developer7). It isconsidered that this is because of the reduction of gold (I)ions by AA. However, as AA is a reductant used as a develReceived: 13th, September 2016; Accepted: 1st, November 2016.

Graduate School of Advanced Integration Science, Chiba University
1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

oping agent13, 14), it may be possible that it reduces a part ofthe silver halide to silver atoms directly by the catalytic
action of the photolytic silver particles, similar to the normal
development process. Usually, such a reduction reaction depends on the pH and proceeds faster under alkaline conditions. Photographic developers using AA is also at a highpH14). However, as developers for the gold deposition development do not contain alkaline reagents and are strongly
acidic, the reduction ability of AA may be weak.
When the reduction of silver ions proceeds on a photolytic
silver particle and silver atoms are deposited on it, the number of silver atoms in the particle will increase. Previously,
we reported that the rate of gold deposition without AA
increased with the exposure value and this could be explained as follows; photolytic silver particles formed at alarger exposure value had a larger particle size, and larger
ones had a higher catalytic activity of the disproportionation
reaction to deposit gold5). In this case, AA reacts to intensify
this reaction. However, it has not yet been confirmed whether
or not the reduction from silver halide to silver actuallyproceeds during the gold-deposition process with AA.
This solution can be obtained by analyzing the content ofgold and silver in the particles. However, as the content ofsilver in the particles will change with the size of the particles, it is necessary to measure the content considering theparticle size.
We quantitatively analyzed the content of gold and silver
using atomic absorption spectroscopy. At the same time,these particles were observed using transmission electron
microscopy (TEM), and the content of gold and silver was

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Bull. Soc. Photogr. Imag. Japan. Vol. 26 No. 2 (2016)

2. Experimental
A silver iodobromide ultra-fine grain emulsion (diameter
40–50 nm), the same as used in our previous reports15), wasused for the preparation of photographic materials. It wascoated on a glass plate. The plates were exposed uniformly
for several microseconds to a high-intensity white light froma xenon flash lamp. The exposure was enough to ensurethat almost all silver halide grains could be developed eventhough the emulsion was not sensitized.
The formula of the developer for gold-deposition development is shown in Table 1. In the case of the developer withAA, the AA solution was added to the developer just before
development. The final concentration of AA was 2×10−3
mol/L and the concentration of other reagents was the sameas shown in Table 1. The development temperature was 293
K. Development times without AA were 5 min~48 h, andwith AA were 5~240 min. Because the development rateincreases with the addition of AA to the developer7), thedevelopment times in the latter case were shortened to obtain similar optical density after development. Every sample
was fixed with a photographic fixer F-5 after development
to remove the silver halide grains, and the gold particles
were dispersed in the gelatin layer. The optical density ofthe developed plates was measured using a photographic
densitometer.
The amount of gold and silver deposited on the plate wasmeasured using atomic absorption spectroscopy (Varian,SpectrAA). We prepared the sample solutions by dissolving
the particles on the plate on a certain area with aqua regia.
The particle size was measured using TEM (HITACHI,
H-7650). We observed the particles on sample grids andmeasured their size from the electron micrographs. The
sample grids for microscopy were prepared using the following suspension technique. The gelatin layer containing
the particles was scraped from the plate and decomposed in
an enzyme solution. The suspension containing the particles
was then dropped onto a grid covered with a collodion layerand dried.

The gelatin gel capsule method12,16,17) was also used for theobservation of photolytic silver particles on each silver halide grain. The exposed emulsion layer, which contains thesilver halide grains, was scraped from the plate without development and dissolved in warm water. The suspension of
the grains in gelatin solution was then dropped onto grids
and dried. The grid was immersed in a glutaraldehyde solution to harden the gelatin layer, and then, immersed in the
fixer solution to remove the silver halide. In this method, thesilver particles were kept in a gelatin gel capsule formed bydissolving the silver halide grains. Consequently, the position relationship between the silver particles and a silver
halide grain is defined clearly.
We analyzed the composition of the particles using an
EDX attached on the TEM at the same time as the TEM
observation. Because the intensity of the X-rays emitted
from one particle was insufficient, we analyzed an area witha few particles, all of which were of average diameter. Analysis of the atomic ratio between gold and silver was performed using the intensity of the L-lines in the EDX spectra.
We measured different areas several times and estimatedthe average ratio.

3. Experimental Results
The increase in the optical density of the developed plateswith the development time is shown in Fig. 1. Open circles
with a solid line and closed circles with a dashed line represent the sample treated with the developers without andwith AA, respectively. A rapid increase and subsequent saturation in the optical density at around 60 min was observed
for the sample treated with the developer with AA, whereas the density for the sample without AA shows a slow but
continuous increase. This acceleration of the increasing ratewith AA was the same behavior reported previously7).
The amounts of gold and silver in the particles measured
using atomic absorption spectroscopy are shown in Fig. 2

3

2
OD

analyzed using an energy-dispersive X-ray spectroscope(EDX) attached to the electron microscope after the measurement of particle size. Then, we analyzed the relationships between the ratio of gold to silver and the size ofparticles, and report the results.

: with AA: without AA
1

Table 1 Formula of developer for gold deposition development
Reagent

KSCN
NaAuCl4・2H2O
KBr
Ascorbic acid

Concentration(mol/L)
4×10−3
1×10−38×10−3
2×10−3

Ascorbic acid solution was added just before development to obtain this concentration.

0

100

200

300

400

500

600

Development Time / minFig. 1. The rate of increase of optical density (OD) of layers with gold particles as a function of development time.

ken’ichi kuge, hidetaka tomimatsu, fumiyuki shiba

25

Analysis of gold and silver content in particles formed by gold deposition development

Amount /10 7mol cm-2

108

without AAwith AA: gold: silver

6
4
2

0

100

200

300

400

500

600 0

50

100

150

200

250

300

Development Time / minFig. 2. The rate of increase in the amount of gold or silver in the layer as afunction of development time, as measured using atomic absorption
spectroscopy. Left: developer without ascorbic acid (AA), right : with
AA.

200nm

200nm

Fig. 4. Electron micrograph of gold particles formed by the developer with
AA at a higher magnification. Development time : left = 10 min,right = 180 min.
150
without AAwith AA

Diameter /nm

100

50

500nm

500nm

Fig. 3. Electron micrograph of gold particles formed by the developer without AA at a lower magnification. Development time : left = 4 h, right= 48 h.

for each development period. The left figure shows the result with AA and the right shows the result without AA.
The amount of gold increased with the development time
and this suggested the formation of gold atoms. This figure
also shows an acceleration of the rate for the developers
with AA, but the increase in the amount of gold saturated
at around 60 min. On the other hand, this amount increased
continuously for the developer without AA. A small amountof silver was observed even before the development, andthis silver should be photolytic silver atoms. The amount ofsilver was nearly the same for all development times for thedeveloper without AA, whereas this amount gradually increased with the development time and then saturated ataround 10 min for the sample with AA.
Electron micrographs for the developed particles for several development times are shown in Fig. 3 and Fig. 4. The
former shows the particles developed without AA for development times of 4 h (left) and 48 h (right) at a lower magnification. The latter shows the particles with AA for shorter
development times of 10 min (left) and 180 min (right) at ahigher magnification. The average size of both particles increased with the development time, although the particles
had a size distribution. Particles in Fig. 3 were nearly spherical and had a smooth surface. On the other hand, the particles in Fig. 4 had an indeterminate form and a rough surface
with protrusion.
Both figures show that the addition of AA accelerated therate of size increase. This increase in size is shown in Fig. 5,

0
0

10

20

30

Development Time /h

40

50 0

50

100

150

200

Development Time /minFig. 5. Rate of increase in the diameter of gold particles as a function ofdevelopment time, measured using TEM. Left: developer without
ascorbic acid (AA), right : with AA. The bar on each circle shows thestandard deviation of the particle size.

as shown in the scale of abscissa. The left figure for the developer without AA shows a continuous increase in size,
while the right figure for the one with AA shows that theincrease in size saturated at around 60 min. Therefore, thefinal size of the gold particles without AA is larger than thatwith AA, although the deposited amount of gold with AA
was much larger than that without AA. This suggests thatthe number of deposited particles with AA was significantly
more than that without AA.
Electron micrographs of the photolytic silver particles observed using the gelatin gel capsule method are shown in
Fig. 6. This method can be used to observe the particles oneach silver halide grain. The white circles indicate the envelope of the silver halide grains and the black points on thecircle are the photolytic silver particles. The average size ofthe silver particle was 7±3.5 nm.
EDX spectra are shown in Fig. 7. The silver L lines at 3.3
keV and gold at 9.7 keV were used for the analysis. Other
peaks for carbon, oxygen, copper, and aluminum were alsopresent, but they originated from the grid or holders supporting the sample. This analysis did not give the absoluteamounts of gold and silver, but we could obtain the atomic
ratio of gold and silver in each particle, which were compared with these L lines.
We also calculated the ratio of gold and silver from the26

Bull. Soc. Photogr. Imag. Japan. Vol. 26 No. 2 (2016)

Table 2 Atomic ratio of gold and silver in the particles

Developer
without AA
Developerwith AA

AtomicEDX on TEM
Development Absorption
Atomic Ratio
Average particle
timesize /nm
Au：Ag
Au：Ag
4h
9h

82：18
91：9

75：25
98：2

29
62

5 min
180 min

82：18
89：11

72：28
87：13

23
45

4. Discussion

100 nmFig. 6. Electron micrograph of photolytic silver particles before gold-deposition development measured using the gelatin-gel capsule method.
The white circles are the gelatin-gel capsules of silver halide grains
and the black points are the silver particles.

Without AA 9h dev.
CuK

AuM

AuL

AlK

AgL

CuK

Intensity (arb.unit)

CuL
0K

With AA 180 min dev.

CuK
CuL
AlK
AuM
0K
AgL

AuL
CuK

2

4

6

8

10

E /keV
Fig. 7. EDX spectra of gold particles. Arrows indicate the peak positions of
the Au L-line and Ag L-line used for analyzing the atomic ratio.
Top: developer without AA, 9 h development, bottom : developer
with AA, 180 min development.

atomic absorption spectroscopy results in Fig. 2. Both ratios
are shown in Table 2. At a shorter development time, theratio of silver is high, but this ratio decreases and the ratioof gold increases with the development time. At longer development time the ratio of silver with AA is higher thanthat without AA.

Both atomic absorption and EDX revealed that theamount of silver was not zero before development, and theparticles prepared by the gold-deposition method included
silver atoms. This silver should be the photolytic silver atoms that catalyze the gold-deposition reaction. The average
size of these silver atom particles observed with TEM wasabout 7 nm. This value is fairly larger than the value reported by Tasaka12). This was considered that the exposure value used here was much larger than that used by Tasaka
and this caused the formation of larger silver particles.
This amount of silver for the developers without AA was
kept the same along with the development time, and sothese silver atoms were covered with the depositing gold
atoms. On the other hand, the amount of silver increased
gradually for the developer with AA. This suggests that the
reduction of silver halide by AA proceeded simultaneouslywith gold deposition. As the formation rate of silver atoms
was not so large because of the low pH and low concentration of AA in the developer, the ratio of silver atoms decreased and these silver atoms would also be covered withthe gold phase. Therefore, the gold layer in the gold-layer
photographs reported recently18–23) should be composed ofan alloy with a large amount of gold and a smaller amountof silver. There is the possibility that this small amount ofsilver somewhat affects the property of the layer of thesegold-layer photographs. Anyway, the reduction of silver halide to silver atoms occurs with AA, and the amount of silver in the gold particles increases slightly.
In many cases, the relative content of silver measured
with EDX was larger than that measured using atomic absorption spectroscopy. Perhaps, the accuracy of the former
was not enough and included significant noise because the
EDX peak was not large enough to estimate the amount ofgold and silver. These would make the values apparently
larger.
The growth rate of gold particles with AA saturated withthe development time. This saturation started around 60
min of development for the optical density (Fig. 1), theamount of gold (Fig. 2), and the particle diameter (Fig. 4).
One possible reason is the consumption of AA or gold ions.
As the amount of AA is 2 times that of gold ions, it is moreken’ichi kuge, hidetaka tomimatsu, fumiyuki shiba

Analysis of gold and silver content in particles formed by gold deposition development

probable that the consumption of gold ions causes the saturation. On the other hand, the amount of silver with AA
saturated much faster, around 10 min. As mentioned before,
the silver particles were gradually covered with gold atoms,
and would lose their catalytic activity for the reduction ofsilver halide.
Addition of AA decreased the average size of the particles, but increased their numbers. At the same time, theaddition of AA increased the sensitivity, and this suggeststhat the photolytic silver particles of smaller size become
developable7). Then, the number of developable specks increases and this brings about the competition of gold ions
between the photolytic silver particles to form particles ofsmaller size.
It is not obvious that this formation of silver atoms affects
the acceleration of gold deposition by AA. The formation ofgold particles without AA proceeds through the disproportionation reaction of Au(I)2), although the reaction rate isvery slow. Addition of AA to this system accelerates thedeposition of gold atoms, and there are two possibilities forthis acceleration. One is the direct reduction of Au(I) by AA
and the other is the intensification of the disproportionation
reaction. In the former case, the photolytic silver particles or
the growing gold particles catalyze the reaction between
the gold ions and AA effectively.
Formation of silver atoms proceeds at the same time asgold deposition. As mention above, we reported that therate of gold deposition increased with the exposure value,and explained that photolytic silver particles formed at alarger exposure value had a larger particle size and they
had higher catalytic activity of gold deposition5). In the latter
case, increase in the size of silver particles intensifies thedisproportionation reaction.
However, it is still uncertain whether this increase in thesize of silver particles intensifies the disproportionation reaction or not. This will be clarified by an analysis of thequantitative relationships between the amounts of AA andAu(I), a subject of future study.

27

Acknowledgment
This work was supported by the JSPS KAKENHI Grant
Numbers 26287037 and 15K13476.

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