The Detection of Doped Cr

Presence in Sr0.6Ba0.4Nb2O3

by SIMS

ARL-TN-132 May 1999

Unchul Lee

Approved for public release; distribution unlimited.
The findings in this report are not to be construed as an

official Department of the Army position unless so

designated by other authorized documents.

Citation of manufacturer’s or trade names does not

constitute an official endorsement or approval of the use

thereof.

Destroy this report when it is no longer needed. Do not

return it to the originator.
ARL-TN-132 May 1999

Army Research Laboratory

Adelphi, MD 20783-1197

The Detection of Doped Cr

Presence in Sr0.6Ba0.4Nb2O3

by SIMS

Unchul Lee 

Sensors and Electron Devices Directorate

Approved for public release; distribution unlimited.
Photorefractive materials like SrBaNb (SBN) have optical properties that

can have several military applications. To improve the figures of merit for

these materials, it is very important to have better control of Cr dopant

in the SBN. Since the amount of Cr dopant is so small, the usual

analytical techniques are not adequate to analyze this material. In this

report, the incorporation of Cr into SBN using secondary ion mass

Abstract

spectrometry (SIMS) measurement with an electron gun is confirmed.

ii
iii

Contents

1. Introduction ........................................................................................................................................ 1

2. Experiment .......................................................................................................................................... 2

2.1 Equipment ....................................................................................................................................... 2

2.2 Depth Profiling ................................................................................................................................ 3

3. Results and Discussion ..................................................................................................................... 4

3.1 Presence of Cr .................................................................................................................................. 4

3.2 Uniformity....................................................................................................................................... 4

4. Summary .............................................................................................................................................. 6

References .................................................................................................................................................. 6

Distribution ............................................................................................................................................... 7

Report Documentation Page................................................................................................................... 9

Figures

1. Secondary ion mass spectrometry (SIMS) .......................................................................................... 2

2. SIMS data for nominal value samples of 0.005%, 0.010%, and 0.025% Cr .................................... 5

Tables

1. Average and normalized counts for three nominally doped Cr samples...................................... 4

2. Counts for spots A, B, and C for three nominally doped Cr samples ............................................ 5
1

1. Introduction

Photorefractive (PR) materials are used for optical beam fanning, beam

coupling, optical storage, and optical image processing [1]. These optical

applications are critical for military purposes, such as protecting optical

sensors. To maximize the protection capability, it is very important to

increase the coupling coefficient and maintain a fast response time.

The control of the protection capability, i.e., the speed of response and

coupling efficiency, requires a specific donor/acceptor ratio that is very

difficult to realize using only a single dopant species. For this reason, the

Rockwell Science Center introduced the double-doping concept and tried

Cr3+, which showed considerable promise in maintaining a fast response

and a sufficiently high coupling coefficient.

SBN (Sr, Ba, Nb) crystals are grown along the (001) direction at the

Rockwell Science Center using the Czochralski pulling technique from

platinum crucibles in an oxygen atmosphere. To confirm the soundness of

using Cr as a dopant, the Rockwell Science Center grew samples with

different amounts of Cr dopant in the melts. In this study, we chose the

materials doped with chromium only in the amounts of 0.005, 0.010, and

0.025 wt.% in the melts. The size of the samples was 6 × 6 × 6 mm [2].

Analyzing these materials poses a challenge because the dopant concentration is too low for XPS/AES (x-ray photoelectron spectroscopy)/(auger

electron spectroscopy), EDX/WDX (energy dispersive x-ray)/(wavelength dispersive x-ray) analytical techniques and because sample preparation for the AAS (atomic absorption spectroscopy) technique is very

difficult. Therefore, we used the SIMS (secondary ion mass spectrometry)

technique to prove the presence of Cr as a dopant as well as the amount

by weight percent of Cr dopants. SIMS is the one of the most powerful

techniques for the surface and depth profile analysis of materials.

SIMS typically provides detection limits between 1 ppm (part per million)

and 1 ppb (part per billion), depending on instrumental transmission

efficiency, detector efficiency, mass resolution, primary beam density, and

matrix-related effects. SIMS instrumentation also provides a dynamic

range of about nine orders of magnitude for secondary ion signal

intensities.

This report details the dopant analyses conducted at the Army Research

Laboratory of these photorefractive samples grown by the Rockwell

Science Center.
2

2. Experiment

2.1 Equipment

The SIMS technique is widely used to investigate trace-level impurities

and dopant distributions throughout the sample and to provide interface

analysis for device fabrication. Many different kinds of SIMS exist,

depending on the primary source and mass spectrometer, and pros and

cons exist for each different type of SIMS instrument.

In this analysis, we used an ATOMIKA Ionprobe A-DIDA 3000 SIMS

instrument with a quadruple mass filter as a mass analyzer for the secondary ions (see fig. 1). The primary source is the magnetically confined

hot cathode oscillating electron bombardment type. We extracted positive

argon gas from the discharge using a two-level electrostatic immersion

system and accelerated the primary ion beam to energies between 1 and

15 keV. In addition to this, the machine is equipped with cold cathode

mode, which can produce O2

+ ions as well. The source lens arrangement

was designed as a telefocus system, providing a beam spot with current

densities continuously variable between 10–10 and 10–4 A/cm2 and with

good homogeneity across a 5-mm-diam sample spot at a distance of about

55 cm from the source exit hole. We used a unipotential lens to focus the

space-charge-broadened telefocus beam into a 100-μm spot at the target

surface. Two pairs of perpendicular deflection plates on the downstream

side of the unipotential lens were used for beam scanning. Raster scanning of the primary beam, in conjunction with an electronic aperture, was

used to reduce edge effects in depth profiling [3].

Ion source

Primary

ion beam

Target

(sample)

Secondary

ion beam

Mass

analyzer Detector

Recorder/

oscilloscope

X–Y

recorder

Computer

Mass number

Time (depth)

Data processing

Counts/s Counts/s

1. Mass spectrum

2. Depth profile

3. Data analysis

Figure 1. Secondary

ion mass

spectrometry (SIMS).
3

Proper selection of a narrow energy band pass for the secondary ions is

essential for achieving good mass resolution in the quadruple mass

spectrometer. In the ATOMIKA SIMS instrument, this energy selection is

performed in a modified parallel-plate condenser. Some of the secondary

ions emitted from the sample enter the condenser through an entrance

diaphragm mounted off-axis with respect to the condenser centerline and

the quadruple axis.

During SIMS analysis of samples with electrically insulating materials, a

local charge builds up when samples are bombarded with a primary ion

beam. This charge deflects the primary ion beam and accelerates the

secondary ions in an undetermined manner. A simple but effective solution to this problem is to compensate this charge with an intense electron

beam. Without charge compensation, no signal could have been obtained

for the SBN samples analyzed in this study. Therefore, charge compensation was used for all the measurements we made during this study.

2.2 Depth Profiling

The three SBN samples were doped with Cr at nominal values of 0.005,

0.025, and 0.010 wt.%. For each sample at least three depth-profiling

measurements were taken from different spots (A, B, and C). The primary

oxygen ion beam energy was 6 keV with ~200 nA current on the sample

surface. Since these samples were excellent insulators, it was not possible

to collect any secondary ion signal because of the charging effect on the

sample surface. When we bombarded the sample with a 1-keV electron

beam of 2.7 A (filament), we then were able to obtain a measurable secondary ion signal. It would have been impossible to obtain the data

without an electron gun.
4

3. Results and Discussion

3.1 Presence of Cr

With electron beam bombardment, we were able to obtain chromium and

the major substrate constituents (Sr, Ba, Nb) ion signals from all three

samples. For each depth profile, we took 50 layers of data points. Among

the chromium isotopes, mass number 52 was chosen because Cr 52 is

most abundant and there is no possibility of mass interference with other

secondary ions.

We selected Sr counts as a benchmark. The average signal counts of Cr

dopant were then normalized against Sr counts from the A spot of the

0.005 wt.% Cr-doped sample. As the data in table 1 show, these values are

not proportional to the nominal values. One disadvantage of SIMS analysis is that it is not possible to get quantitative numbers unless standard

samples with known dopant concentrations are available. It appears that

the samples were either mislabeled or the gravimetric dopant quantity

was incorrect.

3.2 Uniformity

To determine the uniformity of Cr dopant throughout the sample, at least

three different spots (A, B, and C) were chosen from which to obtain

depth-profile measurements. A difficulty was associated with the readjustment of the SIMS instrument whenever the measuring spot was

changed. To make a reliable comparison, we needed a benchmark. For

this reason, we included ions of three major constituents (Sr, Ba, Nb) as

well as Cr counts for depth profiling. In each case, we normalized Cr

counts against Sr counts for the A spot of the 0.005 wt.% sample, since the

composition of the major constituents was identical for all the samples.

Comparing the three graphs in figure 2, we note that the beginning of the

0.010 wt.% data points is different from the other two graphs. At the start

of data collection for the SIMS measurement, there is an idiosyncrasy we

must take into account, i.e., that the first few data points are always

unstable. For this reason, the first few data points for figures 2(b) and (c)

were not collected.

Average values were obtained from the compiled data. All the values

were normalized against the 0.005 wt.% spot A Cr counts using Sr counts

as a benchmark. From table 2, we conclude that there are variations in the

uniformity of Cr dopant concentration throughout the surface and that

the contents are not proportional as expected.

Average Normalized

Sample counts counts

0.005% Cr 50 50

0.010% Cr 70 32

0.025% Cr 150 114

Table 1. Average and

normalized counts

for three nominally

doped Cr samples.
5

Cr

Sr

Ba

Nb

0 20 40 60

100,000

10,000

1,000

100

Depth (layers)

Counts

Cr

Sr

Ba

Nb

0 20 40 60

10,000

1,000

100

Depth (layers)

Counts

Cr

Sr

Ba

Nb

0 20 40 60

10,000

1,000

100

10

1

Depth (layers)

Counts

Cr counts

Sample Spot A Spot B Spot C

0.005% 50 30 30

0.010% 32 21 21

0.025% 114 105 210

Table 2. Counts for

spots A, B, and C for

three nominally

doped Cr samples.

(a)

(b)

(c)

Figure 2. SIMS data

for nominal value

samples of (a) 0.005%,

(b) 0.010%, and

(c) 0.025% Cr.
6

4. Summary

First, we confirmed that Cr dopants had been incorporated into the SBN

samples during the crystal growth process, a finding that was not possible using any other technique to date. We cannot say that the dopant

proportionality is close to the proposed values. To calculate the absolute

quantity of Cr dopant incorporated into the samples, we need standard

samples that have exactly the same SBN matrix with a known quantity of

dopants.

References

1. R. R. Neurgaonkar, W. K. Cory, J. R. Oliver, E. J. Sharp, M. J. Miller, W. W.

Clark III, G. L. Wood, and G. J. Salamo, “Cr3+Sr0.6Ba0.4Nb2O6 Single

Crystals for Photorefractive Applications,” Mat. Res. Bull. 24, 589 (1989).

2. R. R. Neurgaonkar, Technical Report SC5550.FR, Rockwell Science Center

(January 1996).

3. A. Benninghoven, F. G. Rudenaur, and H. W. Werner, Secondary Ion Mass

Spectrometry, John Wiley & Sons, New York (1987).
7

Distribution

Admnstr

Defns Techl Info Ctr

Attn DTIC-OCP

8725 John J Kingman Rd Ste 0944

FT Belvoir VA 22060-6218

Ofc of the Dir Rsrch and Engrg

Attn R Menz

Pentagon Rm 3E1089

Washington DC 20301-3080

Ofc of the Secy of Defns

Attn ODDRE (R&AT)

Attn ODDRE (R&AT) S Gontarek

The Pentagon

Washington DC 20301-3080

OSD

Attn OUSD(A&T)/ODDR&E(R) R J Trew

Washington DC 20301-7100

AMCOM MRDEC

Attn AMSMI-RD W C McCorkle

Redstone Arsenal AL 35898-5240

Army Rsrch Ofc

Attn AMXRO-GS Bach

PO Box 12211

Research Triangle Park NC 27709

CECOM

Attn PM GPS COL S Young

FT Monmouth NJ 07703

Dir for MANPRINT

Ofc of the Deputy Chief of Staff for Prsnnl

Attn J Hiller

The Pentagon Rm 2C733

Washington DC 20301-0300

Hdqtrs Dept of the Army

Assist Secy of the Army for RD&A

Attn SARD-DOV H Fallin Rm 3E411

The Pentagon

Washington DC 20301-0103

Night Vsn & Elect Sensors Dirctrt

Attn AMSEL-RD-NV-STD B Ahn

FT Belvoir VA 22060-5677

TECOM

Attn AMSTE-CL

Aberdeen Proving Ground MD 21005-5057

US Army Armament Rsrch Dev & Engrg Ctr

Attn AMSTA-AR-TD M Fisette

Bldg 1

Picatinny Arsenal NJ 07806-5000

Director

US Army CECOM Rsrch, Dev, & Engrg Ctr

FT Monmouth NJ 07703-5201

US Army Edgewood RDEC

Attn SCBRD-TD G Resnick

Aberdeen Proving Ground MD 21010-5423

US Army Info Sys Engrg Cmnd

Attn ASQB-OTD F Jenia

FT Huachuca AZ 85613-5300

US Army Natick RDEC Acting Techl Dir

Attn SSCNC-T P Brandler

Natick MA 01760-5002

Director

US Army Rsrch Ofc

4300 S Miami Blvd

Research Triangle Park NC 27709

US Army Simulation, Train, & Instrmntn

Cmnd

Attn J Stahl

12350 Research Parkway

Orlando FL 32826-3726

US Army Tank-Automtv Cmnd Rsrch, Dev, &

Engrg Ctr

Attn AMSTA-TA J Chapin

Warren MI 48397-5000

US Army Train & Doctrine Cmnd

Battle Lab Integration & Techl Dirctrt

Attn ATCD-B J A Klevecz

FT Monroe VA 23651-5850
Distribution (cont’d)

8

US Military Academy

Mathematical Sci Ctr of Excellence

Attn MDN-A MAJ M D Phillips

Dept of Mathematical Sci Thayer Hall

West Point NY 10996-1786

Nav Surface Warfare Ctr

Attn Code B07 J Pennella

17320 Dahlgren Rd Bldg 1470 Rm 1101

Dahlgren VA 22448-5100

DARPA

Attn B Kaspar

3701 N Fairfax Dr

Arlington VA 22203-1714

Univ of West Virginia Physics Depart

Attn Abdul-Razzaq

Morgantown WV 26506

Hicks & Associates, Inc

Attn G Singley III

1710 Goodrich Dr Ste 1300

McLean VA 22102

Nat Inst of Stand & Techl

Attn P Amirtharaj

Semiconductor Bldg

Gaithersburg MD 20899

Palisades Inst for Rsrch Svc Inc

Attn E Carr

1745 Jefferson Davis Hwy Ste 500

Arlington VA 22202-3402

US Army Rsrch Lab

Attn AMSRL-DD J Rocchio

Attn AMSRL-CI-LL Techl Lib (3 copies)

Attn AMSRL-CS-AS Mail & Records Mgmt

Attn AMSRL-CS-EA-TP Techl Pub (3 copies)

Attn AMSRL-SE-EM U Lee (10 copies)

Adelphi MD 20783-1197
1. AGENCY USE ONLY

8. PERFORMING ORGANIZATION

 REPORT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

12a. DISTRIBUTION/AVAILABILITY STATEMENT

10. SPONSORING/MONITORING

 AGENCY REPORT NUMBER

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

6. AUTHOR(S)

REPORT DOCUMENTATION PAGE

2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

11. SUPPLEMENTARY NOTES

14. SUBJECT TERMS

13. ABSTRACT (Maximum 200 words)

Form Approved

OMB No. 0704-0188

(Leave blank)

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources,

gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this

collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson

Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503.

12b. DISTRIBUTION CODE

15. NUMBER OF PAGES

16. PRICE CODE

17. SECURITY CLASSIFICATION

 OF REPORT

18. SECURITY CLASSIFICATION

 OF THIS PAGE 19. SECURITY CLASSIFICATION

 OF ABSTRACT

20. LIMITATION OF ABSTRACT

NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. Z39-18

298-102

The Detection of Doped Cr Presence in Sr0.6Ba 0.4Nb2O3

by SIMS

May 1999 Final, 12/1/98 to 1/15/99

Photorefractive materials like SrBaNb (SBN) have optical properties that can have several military

applications. To improve the figures of merit for these materials, it is very important to have better

control of Cr dopant in the SBN. Since the amount of Cr dopant is so small, the usual analytical

techniques are not adequate to analyze this material. In this report, the incorporation of Cr into SBN

using secondary ion mass spectrometry (SIMS) measurement with an electron gun is confirmed.

Cr dopant, SIMS, SBN

Unclassified

ARL-TN-132

9NE6B1

622705.H94

AH94

62705A

ARL PR:

AMS code:

DA PR:

PE:

Approved for public release;

distribution unlimited.

15

Unclassified Unclassified UL

2800 Powder Mill Road

Adelphi, MD 20783-1197

U.S. Army Research Laboratory

Attn: AMSRL-SE-EI ulee@arl.mil

U.S. Army Research Laboratory

9

Unchul Lee

email:

2800 Powder Mill Road

Adelphi, MD 20783-1197
DEPARTMENT OF THE ARMY

U.S. Army Research Laboratory2800 Powder Mill RoadAdelphi, MD 20783-1197

An Equal Opportunity Employer