An electrohydrodynamic iom source with a reservoir and an emitter tip heated by electron bombardment

15

International Journal of Mass Spectrometry and Ion Physics. 46 (1983) 15-18 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

AN

ELECTROHYDRODYNAMIC

AND T.

NODA

AN

EMITTER

1

ION

TIP

1

, T. OKUTANI , K. 2 2 TAMURA , H. O&AN0 and

SOURCE

HEATED 1

YAGI

BY

WITH

A RESERVOIR

ELECTRON

BOMBARDMENT

,

2

H. H. WATANABE 1 Toyohashi University of Technology, 2. Hitachi Central Research Laboratory,

Tempaku,

Toyohashi

Kokubunji,

Tokyo

440,

Japan

185,

Japan

ABSTRACT An electrohydrodynamic (EHD) ion source equipped with a reservoir and an emitter tip heated by electron bombardment was constructed. Owing to the heating method and reservoir, this source can produce various ion including melting point species high materials stably for a long time. Operated with metals such as indium and gold, an intense and stable ion beam was obtained from each material. This ion source can also be operated as a surface ionization source which produce ions at a very small area of the emitter tip heated by electron bombardment.

INTRODUCTION The with

development

a good

interest

focusing

because

microprobe been

sharpened

other

to

is

coil for

a

the

a narrow

posed This ing

to

vacuum

makes

the

a much

an

constxuction,

emitter

a

temperature rapidly

fairly type heated

the

same

ion

source

electron

hardware

shortens type

the

point

a of

heating with

be

0

1983 Elsevier

Scientific

Publishing

the

the extip.

operat-

reservoir the

metaL

method.

bombardment. also

In

the

with

By

Company

We

a reservoir devising

employed

source.

OOZO-7381/83/0000-OOOO/$OS.OO

source

and

of

a

the

heating

ion

shank

that

equipped

could

to and

remained:

than and

of

is

a

the

emitter

melting

because

emitter

and

as

still

capillary the

needle

the

higher

but

low

by

on

far

spot-welded

known

evaporate The

EHD

well

so

(ref.l-3),

hollow

problems

held

lifetime,

be

tip

ionization

some

metal

source.

a new

and

surface

are

are

beam

ion

have

whose

and

.filament a

ion

considerable

sources

type

radius

with

the

microfabrication,

EHD

needle

in

these

there

longer

its

the

for

collected

to of

types

hairpin

type

liquid

the

to

is

tungsten

material of

is constrained designed

Two

first

has

has

applicability

Although

the

source

ion

metals

micrometers

a

beam,

lifetime

gives

its

capillary

type,

EHD

liquid

etc.

few

as

(ref.4,5).

needle

thus

of

The

such

bright

with

analysis,

reported:

heater

a

of

as

a

16 CONSTRUCTION First so

as

of

to

all,

satisfy

(1)

Ion

(2)

Long

the

of

figure

1.

the

power,

a of

In

the

ID

ter

tip

time

and

owing

nun is

to

provision

placed

by

tip the

tip

was

settled

the

as

of

reservoir

is

illustrated

allows

one

with

small

be

produced

to

easily

electric for

made

of

through

0.5mm

quartz which

a long

tungsten

micrometers

in

pipe the

wire

ring

filament

electron

emitter

for

of

emitelm-

radius

A tungsten the

with

ionized.

reservoir. is

few

the be

OC

a hole,

as

materials.

(ref.61

stably

made

and

of

0.12

heating.

Tip/

Construction

1.

3000

of

holder.

Emitter

Fig.

is

and to

source

reservoir

sharp

point

system

can

with

tip

as

a

around

the

The

polished

tip

than

bottom

placed.

chucked

heating

species

study,

source

replenishment.

material ion

ion

cone-shaped

is

the

higher

of

present

trolytically simply

this

ion

melting

emitter

of

present

Since

high without

the

the

this

reqirements:

lifetime

temperature variety

period

6mm

of

for

from

a choice

construction

in

even

replacing at

goal

following

operating

others

raise

design

production

Ease

(3)

The

our

of

the

EHD

ion

source.

RZSULTS We

examined

gold.

Figure

indium

ions,

extraction half

angle

characteristics 2(a) where

shows the

electrode of

20

mrad

probe

voltage

of

this

ion

current

vs

was

and

the

probe

was

monitored

applied current by

source

with

extraction to

the

within

a Faraday

tip the

cup.

indium

and

voltage

for

agains.t

the

acceptance It

is

shown

17

that

ion

the

extraction

current

and

steeply in

varies

half

angle-which

is

set

This

corresponds

to

a

traction ions. the

case

ior

in

voltage Also

found

of

indium

the

I-V

understood

liquid

gold

density gold ty

of

ions.

of

at

and

kV.

20,

a

steep

but

it

on

the

needle

apex.

several

tens

to

typical

gold be

a

The

to

needle

active

as

the

not

yet

phenomenon

reported

unit

in

behav-

have

shows

per

any

We

also

fluctuation

exgold

current

in

figure

the

two-stage

change

current

without

probe

ions.

certain

respectively.

results-for

see

due

emitter

to

the

of

acceptance

)_IA/sr at

the

can

voltage

the

mrad,

100

microampere

probe

hour

of we

may

the

of

2.0

shows

increase

or

al

2(b)

of

t_hreshold

of

addition,

III

(ref.71,

et

A

6.7

a

square

density

Figure

ions.

formation

5% per

ca_

is

to

current

origin,

cusps

Clumpitt

10

at

proportion

characteristics

its

multiple by

of

rises

on the

flow

a

solid shows

of

cesium of

current

angle the

for

stabili-

stabilization. 100

. .

(b)

(a)

*

r

. .

;sI x

In c- J P&I_

X X

“a

a..=2on-G

x

F

$3

*xx

~_,,&“Fiq.

VERSION

FOR

Probe current and gold ions

2.

SURFACE

Primary

ions

secondary

for

purpose

this

opment We new

of

thus

schema

ion

the

ion at

type of

Cs

ion

this

cesium

is

aimed

L

10 VoltageC kV 1

variations of indium ions (a) (b) with extraction voltage.

mass

now gun

have

been

with

source source

with

used

spectrometry

commercially

conversion

Cs

8

Va f Extraction

IONIZATION

of

negative

o-,-

10 8 Voltagec kV)

6 Va : Extraction

a

small of

the

a high

using

CsCl.

for

the

high

(SIMS).

available, source

A Cs but

size

has

abovementioned brightness. This

sensitivity

system

ion

further been

awaited.

source Figure is

source devel-

into

3(a) the

is

same

a a as

18

r 3.

Fig.

that

shown

the

setting

only

the

the

3(b)

electron

The his

of

extracted

ampere

per

1

in

the shows

CS

the ions

relationship

the for

express

position

3t a),

where

the

solid

assistance

the

Figure

within

unit

but

tip,

current

authors

devoted

Figure

shown

end

Figure ions

in

Construction (a) and characteristics of the present Cs ion source.

acceptance

heating.

angle

can

their on

the

of

sincere drafting

emitter

electron are

half

be

bombardment

the

In heats

intensity

angle

of

density

of

20

of

mrad

a few

Cs and

micro-

obtained.

thanks as

tip.

produced.

between

Current easily

the

(b)

well

to as

Mr. the

M.

Fukuda

for

experiment.

REFERENCES 1 2 3 4 5 6 7

and G. H. Robertson, Appl. Phys. R. J. Culbertson T. Sakurai, Lett. 34(l), ll(1979). and H. Kawakatsu, J. Appl. Phys. 52(4), 2642(1981). M. KomGo K, Gamo, Y.Ochiai,.Y_Inomoto and S.Namba, PGc. 28th. Intern. 198h)p83. (Oregon, Field Emission Symp. 27(9),479(1975). Appl. Phys. Lett. V.E. Krohn and G,R.Ringo, Seliger, J-W. Ward, V. Wang and R.L. Kubena, Appl. Phys. R.L. 34(5),310(1979). Lett. and H-Watanabe, H.Okano H.Tamura, K.Yagi, T.Okutani, T.Noda, Rev. Sci. Instrum. (to be published, 19821. Low-Energy Ion beam 1977. Jefferies, Clampitt and D. K. R. Inst. Phys. Conf. Ser. ~0.38 ch 1.