The light emission spectra of individual Au nanoparticles induced by a scanning tunneling microscope (STM) have been investigated. Two-dimensional ensembles of tunnel-coupled Au particles were prepared by thermal evaporation onto a native oxide silicon wafer in ultrahigh vacuum (10 – 9 mbar). Our STM measurements show a single peak at photon energy 1.6 eV in the tunneling mode and two peaks at 2.2 eV (connected with the Mie plasmon) and 1.45 eV (a new peak which was not discussed in literature before) in the field emission mode

Chernenkaya, A.

Chernov, S.V.

Ertl, G.

Medjanik, K.

Nepijko, S.A.

Odnodvorets, Larysa Valentynivna

Protsenko, Ivan Yukhymovych

Sapozhnik, A.A.

Schulze, W.

Schönhense, G.

Однодворец, Лариса Валентиновна

Однодворець, Лариса Валентинівна

Проценко, Иван Ефимович

Проценко, Іван Юхимович

SocioEconomic Challenges Journal (Sumy State University)

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ 
Vol. 8 No 2, 02039(3pp) (2016) Том 8 № 2, 02039(3cc) (2016) 
 
 
2077-6772/2016/8(2)02039(3) 02039-1  2016 Sumy State University 
Spectral Measurement of Photon Emission from Individual Gold Nanoparticles Using  
Scanning Tunneling Microscopy 
 
S.A. Nepijko1, A. Chernenkaya1, K. Medjanik1, S.V. Chernov1, A.A. Sapozhnik1,  
L.V. Odnodvorets2, I.Yu. Protsenko2, W. Schulze3, G. Ertl3, G. Schönhense1 
 
1 Institute of Physics, University of Mainz, 7, Staudingerweg, 55128 Mainz, Germany 
2 Sumy State University, 2, Rymskogo-Korsakova St., 40007 Sumy, Ukraine 
3 Fritz Haber Institute of the Max Planck Society, 4-6, Faradayweg, 14195 Berlin, Germany 
 
(Received 19 May 2016; revised manuscript received 10 June 2016; published online 21 June 2016) 
 
The light emission spectra of individual Au nanoparticles induced by a scanning tunneling microscope 
(STM) have been investigated. Two-dimensional ensembles of tunnel-coupled Au particles were prepared 
by thermal evaporation onto a native oxide silicon wafer in ultrahigh vacuum (10 – 9 mbar). Our STM 
measurements show a single peak at photon energy 1.6 eV in the tunneling mode and two peaks at 2.2 eV 
(connected with the Mie plasmon) and 1.45 eV (a new peak which was not discussed in literature before) in 
the field emission mode. 
 
Кeyworld: Electron-photon spectroscopy, Gold nanoparticle, Scanning tunneling microscope (STM). 
 
DOI: 10.21272/jnep.8(2).02039 
 
 
PACS numbers: 68.55.Nq, 71.20.Be, 71.20.Eh  
 
1. INTRODUCTION 
 
Spectroscopic measurements that allow characteri-
zation of nanoparticles as well as the study of their 
electronic structure (electron density of states near the 
Fermi level) can be performed in a scanning tunneling 
microscope (STM). One more possibility for electronic 
structure investigations corresponds to photon emis-
sion in such studies [1-16]. The light emission appears 
due to (i) inelastic tunneling of some electrons between 
the tip and the sample (at a tip voltage of a few volts of 
both polarities) or (ii) electron bombardment of the 
sample by field emission (when the negative voltage on 
the tip is about ten volts and higher). This light emis-
sion is characterized by a spectrum whose structure is 
caused mainly by the inter-band transitions, including 
surface states and the plasmons decay. At the same 
time the plasmon frequency is determined by the mate-
rial, size, shape of the nanoparticles and the distances 
between them as well as the dielectric surrounding. 
The electronic structure is also deformed by the parti-
cle size. The tip material and shape influence the spec-
trum [8,9]. Thus, measurements of the light emission 
spectra in research of nanoscale objects using a STM 
have a very high information content. The central point 
of this method is that it provides the results which are 
not averaged over a large number of particles with dif-
ferent sizes, i.e. measurements are not integral (like in 
most optical experiments), but give information about 
each individual particle [9-14], see also [15, 16]. 
 The measurements were performed on a gold (Au) 
nanoparticle film, namely a two-dimensional ensemble 
of tunnel-coupled Au nanoparticles on a dielectric sub-
strate. Au was chosen as an object of investigations due 
to its chemical inertness. In addition, there is a possi-
bility to compare our results of photon emission meas-
urements of Au nanoparticles induced by an STM with 
previously obtained results for bulk Au single crystals 
[2,3,7,8]. 
 
 
2. EXPERIMENTAL DETAILS 
 
Sample preparation, analysis and measurements 
were carried out in ultra-high vacuum (UHV) at 10 – 9 
mbar. Au nanoparticle films were prepared by thermal 
deposition on a silicon wafer (n-type Si,  ~ 0.01 Ω∙cm). 
The Volmer-Weber (3D) growth mechanism is imple-
mented in this system. The substrate cleaning (flash 
method) as well as Au deposition was performed in the 
preparation chamber. Resistance of the film was moni-
tored during the growth, deposition was stopped, when 
the resistance per square reached tens of megaohm, in 
this case, tunnel coupling is realized between the nano-
particles [17, 18]. Then the sample was moved into the 
STM in the main chamber using a transfer system. The 
STM tip was made of a polycrystalline tungsten (W) wire 
with diameter of 0.25 mm by electrochemical etching. In 
the experiment photon emission of individual Au nano-
particles was obtained using the STM in the tunnel and 
field emission modes. In order to obtain a large ac-
ceptance angle for the light collection, the STM was sur-
rounded by a parabolic mirror. Outside the vacuum 
chamber the light was focused onto the entrance slit of a 
spectrometer and detected with a liquid nitrogen cooled 
charge-coupled device (CCD) camera. Measurements 
were carried out in the spectral range from 200 to 
1050 nm (6.2-1.18 eV). To take spectra with high resolu-
tion, this spectral range was separated into several 
parts. Each part of the spectrum was projected onto a 
CCD matrix containing 1024  256 pixels. 
If the size of the nanoparticles is much smaller than 
the curvature radius of the tip, and their concentration 
is large, as in our case, the contrast of the STM image 
is not clear, i.e. gaps between individual nanoparticles 
couldn’t be fully resolved. Hence, the same Au nano-
particle film was also prepared on a copper transmis-
sion electron microscopy mesh with diameter of 3 mm 
with a carbon film with thickness of about 10 nm that 
is transparent to an electron beam with energy of 
200 keV for further studies in a transmission electron 
microscope "FEI Tecnai 20 F". 
 S.A. NEPIJKO, A. CHERNENKAYA, ET. AL. J. NANO- ELECTRON. PHYS. 8, 02039 (2016) 
 
 
02039-2 
3. RESULTS AND DISCUSSION 
 
Fig. 1 shows the photon emission spectrum in the 
STM experiment at the applied to the tip voltage of 
Vt  3 V and corresponding tunnel current I  1 nA. The 
light emission occurs due to inelastic tunneling of elec-
trons from the W tip to the Au nanoparticle. It is ac-
companied with excitation of a tip-induced plasmon 
[19, 20]. This is a result of the strong electromagnetic 
interaction between the tip and the nanoparticle caus-
ing collective electron oscillations of their coupled elec-
tron gases. The decay of the tip-induced plasmon gives 
a peak at 1.62 eV in Fig. 1, whose energy position is in 
a good agreement with the literature [7, 8, 14]. This 
peak remains when the voltage applied to the tip 
switches from negative to positive. 
 
 
 
Fig. 1 – Photon emission spectrum of Au particle (with size 
about 5 nm and spherical shape) taken at Vt
 
  3 V, I  nA 
 
The field emission mode of the STM sets in at in-
creasing of the negative voltage on the tip. The photon 
emission spectrum in this case is different (Fig. 2, up-
per curve). In this measurement Vt  10 V and 
I  10 nA. This spectrum disappears at a positive polar-
ity current on the tip in contrast to the spectrum in 
Fig. 1. The tip position was the same for measurements 
shown in Figs. 1 and 2 (upper curve). The lower curve 
in Fig. 2 shows the photon emission spectrum exclu-
sively from the pure substrate. This measurement was 
performed in the STM in the field emission mode at 
moving the tip to a substrate area that was not covered 
by nanoparticles. The spectra were decomposed (decon-
voluted) as shown in Fig. 2. The result is good enough 
when Gaussian curves are used for the decomposition. 
As one can see there are four peaks at energies 1.45, 
1.69, 1.98 and 2.22 eV on the upper curve, while the 
lower one consists only from two peaks at 1.69 and 
1.98 eV. The energy position of the 1.69 and 1.98 eV 
peaks are identical for the both curves. We assume that 
in the field emission mode, the electrons from the tip 
illuminate the investigated particles as well as partial-
ly the substrate. In the tunneling mode this cannot 
happen due to the protruding nanoparticles. It is possi-
ble when the curvature radius of the W tip is much 
larger than investigated the Au particles (R  r). After 
the spectral measurements radius of the tip and size of 
the Au nanoparticles were measured using scanning 
electron microscopy and transmission electron micros-
copy, respectively. It was obtained that the tip radius R 
was 60-100 nm in different cross-sections and the aver-
age size of the Au particles 2r was 5 nm. 
The peak at 2.22 eV corresponds to excitation and 
decay of the Mie plasmon in a mode polarized perpen-
dicular to the substrate [13, 14] (it was improperly as-
signed to inter-band transition in the early publications 
[2, 3]). Its position on the energy scale is determined by 
the material, size and shape of the nanoparticles, their 
concentration and the dielectric constant of the envi-
ronment. 
Another low-energy peak at 1.45 eV is clearly ob-
served but has not been discussed during the analysis 
of photon emission spectra in systems 
tip(W) / nanoparticle(Au) / substrate(TiO2 or -Al2O3), 
that were measured in the STM in the field emission 
mode (see Fig. 2 in Ref. [13] and Fig. 5 in Ref. [14]).  
 
 
 
Fig. 2 – Photon emission spectra of the same Au particle as in 
Fig. 1, that is situated on a native oxide covered silicon sub-
strate (upper curve), and of the substrate itself (lower curve) 
taken at identical experimental conditions (Vt
 
  10 V, 
I  10 nA) 
 
Due to the excitation electrons move to the energy 
levels of the electronic structure of Au nanoparticles 
that were unoccupied previously and then make a 
transition to a state near the Fermi level under the 
photon emission. This makes the present measure-
ments very informative for the investigation of the 
electron density of states above the Fermi level. 
 
4. CONCLUSIONS 
 
We present experimental evidence of photon emis-
sion from Au nanoparticles excited using the STM with 
W tip in the tunnel (Vt  5 V) and field emission modes 
(Vt  5 V). In the first case the tunnel current has an 
inelastic component connected with a tip-induced 
plasmon excitation. The corresponding photon emission 
is characterized by a maximum at 1.62 eV. In the se-
cond case the photon emission spectrum is more com-
plicated. The spectrum for an Au nanoparticle obtained 
after subtraction of photon emission from the substrate 
(a native oxide covered silicon wafer) is characterized 
 SPECTRAL MEASUREMENT OF LIGHT EMISSION… J. NANO- ELECTRON. PHYS. 8, 02039 (2016) 
 
 
02039-3 
by peaks at 2.22 and 1.45 eV connected with the Mie 
plasmon and the density of unoccupied states above the 
Fermi level, respectively. The low-energy peak at 
1.45 eV has not been discussed in the literature. It was 
more pronounced than in other publications (see Refs. 
[13, 14]) most likely due to the more blunt W tip in our 
experiment and consequently the larger applied voltage 
(the Au nanoparticle size was in the range of a few na-
nometers in all cases). 
The use of an STM in the field emission mode with 
the light signal detection allows to implement low-
energy electron-photon spectroscopy (inverse photoe-
mission spectroscopy). 
 
 
REFERENCES 
 
1. J.K. Gimzewski, B. Reihl, J.H. Coombs, R.R. Schlittler, 
Zeitschrift für Physik B 72, 497 (1988). 
2. R. Berndt, J.K. Gimzewski, P. Johansson, Phys. Rev. Lett. 
67, 3796 (1991). 
3. R. Berndt, J.K. Gimzewski, Surf. Sci. 269-270, 556 (1992). 
4. R. Berndt, J.K. Gimzewski, R.R. Schlittler, Ultramicrosco-
py 42-44, 355 (1992). 
5. N.L. Schneider, R. Berndt, Phys. Rev. B 86, 035445 (2012). 
6. G. Hoffmann, J. Kliewer, R. Berndt, Phys. Rev. Lett. 87, 
176803 (2001). 
7. Z.C. Dong, X.L. Zhang, H.Y. Gao, Y. Luo, C. Zhang, 
L.G. Chen, R. Zhang, X. Tao, Y. Zhang, J.L. Yang, 
J.G. Hou, Nat. Photonics 4, 50 (2010). 
8. T. Wang, E. Boer-Duchemin, Y. Zhang, G. Comtet, 
G. Dujardin, Nanotechnology 22, 175201 (2011). 
9. A. Olkhovets, S. Evoy, H.G. Craighead, Surf. Sci. 453, 
L299 (2000). 
10. A. Downes, M.E. Welland, Appl. Phys. Lett. 72, 2671 (1998). 
11. N. Nilius, N. Ernst, H.-J. Freund, Phys. Rev. Lett. 84, 3994 
(2000). 
12. N. Nilius, A. Cörper, G. Bozdech, N. Ernst, H.-J. Freund, 
Prog. Surf. Sci. 67, 99 (2001). 
13. N. Nilius, N. Ernst, H.-J. Freund, Surf. Sci. 478, L327 
(2001). 
14. N. Nilius, N. Ernst, H.-J. Freund, Phys. Rev. B 65, 115421 
(2002). 
15. R. Berndt, R. Gaisch, J.K. Gimzewski, B. Reihl, 
R.R. Schlittler, W.D. Schneider, M. Tschudy, Science 262, 
1425 (1993). 
16. N.L. Schneider, J.T. Lü, M. Brandbyge, R. Berndt, Phys. 
Rev. Lett. 109, 186601 (2012). 
17. P.G. Borziak, Yu.A. Kulyupin, S.A. Nepijko, 
V.G. Shamonya, Thin Solid Films 76, 359 (1981). 
18. S.A. Nepijko, D. Kutnyakhov, S.I. Protsenko, 
L.V. Odnodvorets, G. Schönhense, J. Nanoparticle Res. 13, 
6263 (2011). 
19. P. Johansson, R. Monreal, P. Apell, Phys. Rev. B 42, 9210 
(1990). 
20. B.N.J. Persson, A. Baratoff, Phys. Rev. Lett. 68, 3224 
(1992). 
 
 


Spectral Measurement of Photon Emission from Individual Gold Nanoparticles Using Scanning Tunneling Microscopy

https://essuir.sumdu.edu.ua/bitstream/123456789/45479/1/Nepijko_Chernenkaya_Medjanik.pdf

Spectral Measurement of Photon Emission from Individual Gold Nanoparticles Using Scanning Tunneling Microscopy

Abstract

Similar works

Full text

Available Versions

SocioEconomic Challenges Journal (Sumy State University)