DIET IN HIGHLY CHARGED ION INTERACTION WITH SILICON SURFACESDIET IN HIGHLY CHARGED ION INTERACTION WITH SILICON SURFACES

S. Takahashi1), K. Nagata1), M. Tona2), M. Sakurai3), N. Nakamura1), C. Yamada1), S. Ohtani1)

1) Institute for Laser Science, University of Electro-Communications Chofu, Tokyo 182-8585, Japan2) Japan Science and Technology Agency, Chofu, Tokyo 182-8585, Japan

3) Department of Physics, Kobe UniversityRokkodai 1-1, Nada, Kobe 657-8501, Japan

0.00001

0.0001

0.001

0.01

0.1

1

10

1 10 100

Charge State (q)

Spu

tterin

g Y

ield

(/X

e Io

n

HHCSi

K. Kuroki et al.：Nucl. Instrum. Meth. B 193 (2002) 804.

The present experiment (Xeq+, q=26, 44, 50)

Charge (q) dependence of potential energy of HCI

The structure of Tokyo-EBIT

Charge transfer occurs when HCI approaches to atom or surface at critical distance Rn

HCI

Atom/Surface

Hollow atom

Product ion

Characteristics of HCI

Principle of EBIS/TEBIS: electron beam ion sourceEBIT: electron beam ion trap

Using electron beam with the energy of 10 –100 keV and current density of the order of 1000A/cm2, atoms(ions) confined in the trap potential are ionized repeatedly by an electron impact.

Tokyo-EBIT

Abstract

We have observed mass spectra of desorbed ions from clean and hydrogen terminated silicon surfaces by the impact of highly charged ions (Xeq+, q=26, 44, 50) produced by the electron beam ion trap, ‘Tokyo-EBIT’ . The released ions mainly consist of proton for both surfaces, and the quantum yield of proton desorption for hydrogen terminated surface exceeds unity. Charge state dependence of ion yield roughly follows q 5 rule reported byKuroki et al. in the experiments for lower charge states.

HCI Beam

Si Substrate　(Sample bias 338V)MCP１

MCP2

Aperture(3 mm φ )

(Removable and Rotatable)

e-

e-

Position Sensitive Detector　(PSD)

Flight Tube(GND)

+

Multi-Stop Time Analyzer

Stop Pulse

Start Pulse

TOF Spectrum

PC

Lenses

MCP IN 800 V

70 V

GND

220 V

Setup of the TOF-SIMS

100 200 300

0

Electron Energy [eV]

Inte

nsity

[arb

. uni

ts] 0

(A)

(B)

CarbonSilicon

AES spectra from Si(111) substrate (A) before flushing, (B) after flushing.

LEED patterns of (a) clean Si(111) and (b) H-terminated Si(111) surfaces.

(a) (b)

Xe50+ - H-Si(111)

0.0001

0.001

0.01

0.1

1

0 2 4 6 8 10Time [µs]

(b)

TOF spectra of ions sputtered by the irradiation of Xe50+ on (a) clean Si(111) and (b) H-terminated Si(111).

Xe50+ - clean Si(111)

0.00001

0.0001

0.001

0.01

0 2 4 6 8 10

Time [µs]

H+

H2+

C+Si+

photon

(a)

Sputtering efficiencies of H+, H2+, C+ and Si+ from

Si(111) -H surfaces as a function of primary charge state q. The dashed line indicates q5 dependence.

2 3 4 5 60

1

2[×105]

Mass to Charge Ratio

Inte

nsity

[cps

]

Xe44+

Xe50+

Charge state distribution of Xe HCIsextracted from the Tokyo-EBIT.

Electron energy:20keV current:150mA

STM image of HOPG surface with the trace of incidence of single Xe44+ ion.

Potential energy dependence of the volume of swelled structure produced by the injection of HCIs

Electron energy : 300keV (max.)Electron current : 300mA (max.)Field strength of SC magnet : 4.5T

Helmholz coils

DYNAMICS OF PHYSISORBED MONOLAYER OF METHANE ON AG(111)DYNAMICS OF PHYSISORBED MONOLAYER OF METHANE ON AG(111)

M. SakuraiM. Sakurai1)1), C. Yamada, C. Yamada2)2)

1) Department of Physics, Kobe University, Rokkodai 1-1, Nada, Kobe 657-8501, Japan 2) Department Applied Physics and Chemistry, University of Electro-Communications, Chofu,

Tokyo 182-8585, Japan

Abstract

The adsorption, desorption and vibrational excitation dynamics of physisorbed methane monolayer was studied on a Ag(111) surface at cryogenic temperature by LEED and HREELS measurements. For LEED observation, electron stimulated desorption of adsorbed CH4 was obvious even at minimized incident electron current of 1nA, and the result suggests the possibility of leftover of electron stimulated reaction on the substrate that can not be identified nor desorb at raised temperature. Mode dependence of the width of energy loss peak was observed in the HREEL spectra. The excitation of the vibrational mode with sharper width is mainly associated with dipole scattering mechanism.

EEL spectra ofCH４/Ag(111)

measured at 20K

I‐V curves of elastic and vibrational loss peaks

Similar to elastic curve

⇒　dipole scattering is　dominant

ν４mode

Other modesIndependent from elastic feature

⇒　impact scattering

Width of ν４ peak is narrower than other modes

Mode dependence

Adsorption conditionvs. LEED pattern

CH4Ag

Adsorption scheme of methane and rare gas layers

Gas phase Intermediate phase 2D solid phase

structure 3

Methane

Rare gas

Xe/Graphite

Layer growth

Adsorption condition dependence of coverage derived from the LEED intensity

○　---　～１ML

△　---　＜１ML

×　---　～０ML

(a)

(b)

(c)

(d)

Apparatus

I-V curve at low electron-energy regionsMeasured using a HREEL spectrometer

LEED patterns of CH4 monolayer physisorbed on Ag(111) substrate measured at 2D-condensation

conditions

Diffraction spot from crystalline CH4 monolayer

The pressure dependence of dip structure is probably related with the CH4 crystal structure, which changes with ambient pressure at constant substrate temperature as proved by the present LEED observation.

The distinction of vibrational modes based on presence or absence of the tailing of vibrational loss peaks coincides with that on the dip in the IV plots. Thus it would be stated that the distinction comes not simply from the optical selection rules.

LEED spot intensity profiles of CH4physisorbed on Ag(111) after specific period of electron irradiation: (a) before irradiation, (b) 30 sec, (c) 90 sec, and (d) 150 sec at the current of 1 nA. If we assume the size of electron beam in the range of 0.3 to 1mm on the sample, the desorption yield is estimated at as high as 0.1-1.

0 100 200 300 400

Intensity [arb.units]

ECH4– ˚ 5L

E ¸ p 67CH4/Ag(111)

20

100

1×

14

9

7

6

4

Incident Electr Energy (E

i) [eV]

Energy Loss [meV]

ν１ν２ ν３ν４

Incident electron energy (eV)

Vibrational modes of CH4