Elemental Analysis of European Coins Using Photoelectric SpectroscopyN. Turpin, W. Chen, M. Mezher, D. Hanks

Department of Chemistry, University of Nevada, Las Vegas

IntroductionNew techniques were employed to determine the make up of two different types of European coins that are worth more than the US Dollar (according to current exchange rates) to ensure the integrity of each. These new techniques, XPS, UPS, and SEM, were able to analyze each coin without defacing the legal tender. Each element in the sample could be identified by its corresponding, ejected electron. Databases have been compiled extensively with data for these types of spectroscopy.(4) The experimental findings were compared with the reported make up of each coin.

Methods and Materials

http://photonicswiki.org/index.php?title=Photoelectron_Spectrometer_XPS_and_UPS

Key points to understand for this experiment:

*X-ray Photoelectric Spectroscopy sends photon in and a core electron comes out.*UV Photoelectric Spectroscopy sends a photon in and a valence electron comes out.*Scanning Electron Microscope sends a focused beam of electrons onto surface of sample, detects back-scattered and secondary electrons along with x-rays.These detected and measured electrons were identified to their host atom by their binding energy confirmed by references.

The instrument used for the XPS and UPS was an amalgam of components from different manufactures. Such components included, but not limited to: Specs XR 50 X-ray source, VG Scienta R4000 spectrometer, Stanford Research Systems residual gas analyzer 300. Due to the mixed family of devices from different manufacturers this device was wittily referred to as “The Brady Bunch.” Thus reaffirming the “indisputable truth that PHYSICAL CHEMISTRY IS FUN.” (2) The SEM used was a Joel JSM-5600.

References[1] European Central Bank. https://www.ecb.europa.eu/euro/coins/1euro/html/index.en.html (accessed Oct 29, 2014).[2] Mezher, M., Hanks, J. CHEM 423L Syllabus, Chem. Dept. UNLV, 2014.[3] Moulder, J.F., et al. Handbook of X-ray Photoelectron Spectroscopy , Perkin-Elmer: Eden Prairie, 1992[4] National Institute of Standards and Technology. NIST X-ray Photoelectron Spectroscopy Database; http://srdata.nist.gov/xps/Default.aspx, (accessed Oct 29, 2014).[5] The Royal Mint. http://www.royalmintmuseum.org.uk/coins/british-coinage/current-coins/one-penny-coin/index.html (accessed Oct 29, 2014)

Data British Penny 1 € National CoinGoal: To determine the elemental make up of each coin.

British Penny 1st Sweep with Al Kα

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

100.

00

250.

00

400.

00

550.

00

700.

00

850.

00

1000

.00

1150

.00

1300

.00

1450

.00

Binding Energy

Cou

nts

Per

Sec

ond

O 1sCu Auger

L3M45M 45Satellite

Satellite

Cu 2p1/2O Auger KL1L1

C 1s

Euro XPS

0

20000

40000

60000

80000

100000

120000

140000

160000

100.

0

250.

0

400.

0

550.

0

700.

0

850.

0

1000

.0

1150

.0

1300

.0

1450

.0

KE (eV)

Coun

ts p

er S

econ

d

SEM Surface Img

XPS

SEM

XPS

SEM

SEM Surface Image

Inner part / Outer ring

ResultsBoth coins were cleaned by sonication in acetone. The 1€ had to be trimmed in order to fit into the holder for XPS. It was cut with a silicon carbide blade but not cleaned properly. As a result, peaks for silicon and carbon in the form of carbide were detected.

XPS was performed with non-monochromated x-ray. This was why many unidentifiable peaks were present in spectra. UPS was performed with monochromated UV light from excited He. The advantage of UPS was that it was more surface-sensitive, thus produced narrower line peaks.

SEM confirmed the identified peaks from the XPS/UPS spectra. Relative concentrations of elements were identified as well by the SEM. The British Penny was coated with mostly copper and a little of oxygen from the oxide form of the copper. The Euro’s center was 67:31:2 Cu-Ni-Zn alloy. Its outer ring consisted of 67:22:11 Cu-Zn-Ni alloy. The actual composition of the coin was not listed. Simply stated: copper-nickel alloy for the center and copper-zinc alloy for the ring (1).

DiscussionPhotoelectric spectroscopy was a useful tool for verifying the contents of the two coins. XPS did a good job at identifying the elements on the surface (3,4). This included contaminants such as NaCl from sweaty fingers and SiC from the cutting disc used on the Euro. Satellite and shake off peaks in the XPS spectrum made it somewhat confusing for the identification. The NIST database(4) proved especially useful for peak identification. A much better spectrum could have been obtained had a monochromated x-ray source been used. Due to time limitations that was skipped and SEM was used to verify elements. UPS was not used fully in this experiment. UPS did verify the presence of copper with the lone “bump” in the spectrum.

SEM was the most user-friendly. The beam was easily focused on specific locations of the coins in order to analyze the specific location. SiC was verified using SEM but omitted form the images because of the delocalization of the contaminant.

All in all, these two currencies proved valid and legit based on the published information from both mints.

C 1s

O 1s

Cl Alkali

Si 2s

Cu 2p3/2

Cu 2s

Cu 2p1/2

Ni 2p3/2

Ni 3p

Zn 2p3/2

British Penny UPS

0.00E+00

2.00E+04

4.00E+04

6.00E+04

8.00E+04

1.00E+05

1.20E+05

1.40E+05

-34.8 -32.3 -29.8 -27.3 -24.8 -22.3 -19.8 -17.3 -14.8 -12.3 -9.8 -7.3 -4.8 -2.3

Kinetic Energy (eV)

Coun

ts p

er S

econ

d

UPS

(5)

(1)