Forensic Science

8 Examples of SEM Analyses in Forensic Evidence Applications JOHN SABO, New York State Police Scientific Laboratory, Albany, N. Y. 12226 GARY JUDD, Materials Division, Rensselaer Polytechnic Institute, Troy, N. Y. 12181

Downloaded by UNIV LAVAL on March 3, 2015 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/bk-1975-0013.ch008

STARK FERRISS, New York State Police Scientific Laboratory, Albany, N. Y. 12226

The scanning e l e c t r o n microscope (SEM) has been shown t o be an e f f e c t i v e instrument f o r the a n a l y s i s o f p h y s i c a l evidence m a t e r i a l s . Both t o p o g r a p h i c a l , i . e . surface c h a r a c t e r i z a t i o n , and compositional, i . e . elemental c o n s t i t u t i o n , analyses have been s u c c e s s f u l l y reported in s e v e r a l recent s t u d i e s (1-8). The utilization of this instrumentation has widely increased. S e v e r a l f o r e n s i c l a b o r a t o r i e s in the United States and in other c o u n t r i e s have SEM facilities, many o f which are equipped f o r energy d i s p e r s i v e compositional a n a l y s i s (EDA). This paper will describe s e l e c t e d a c t u a l recent a p p l i c a t i o n s o f SEM-EDA techniques performed at the New York State P o l i c e Scientific Laboratory and E l e c t r o n M i c r o a n a l y s i s Laboratory a t Rensselaer Polytechnic I n s t i t u t e . Experimental Procedure P h y s i c a l evidence obtained from c r i m i n a l i n v e s t i g a t i o n was introduced i n t o the scanning e l e c t r o n microscopel. The topography o f the samples was i n i t i a l l y examined i n the SEM t o determine areas o f i n t e r e s t and whether or not EDA would be r e q u i r e d . For conductive samples and a l s o f o r samples i n which charging was minimal, SEM t o p o g r a p h i c a l and EDA compositional 2

1. 2.

AMR 1000 Scanning E l e c t r o n Microscope, AMR, B u r l i n g t o n , Mass. Edax TOOA Energy D i s p e r s i v e Analyzer, EDAX, P r a i r i e View, 111.

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In Forensic Science; Davies, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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a n a l y s e s were p e r f o r m e d s i m u l t a n e o u s l y . F o r samples d i s p l a y i n g c h a r g i n g , t h e e n e r g y d i s p e r s i v e a n a l y s i s was p e r f o r m e d f j r s t . These s a m p l e s were t h e n c o a t e d w i t h a t h i n l a y e r o f g o l d a n d v i e w e d i n t h e SEM f o r t o p o g r a p h i c a l a n a l y s i s . A l l images w e r e r e c o r d e d u s i n g P o l a r o i d P/N Type 55 f i l m a n d t h e n e g a t i v e s were u s e d i n t h o s e c o m p a r i s o n p r o c e d u r e s where t h e h i g h e s t r e s o l u t i o n images were r e q u i r e d . For r e p o r t i n g convenience t h e r e s u l t s were c a t a l o g u e d i n terms o f t o p o g r a p h i c a l a n a l y s i s , c o m p o s i t i o n a l a n a l y s i s , and coupled a n a l y s i s .


R e s u l t s and D i s c u s s i o n A. T o p o g r a p h i c a l A n a l y s e s . The SEM a l l o w e d f o r t h e a n a l y s i s o f s e v e r a l cases by v i r t u e o f t o p o g r a p h i c a l i n f o r m a t i o n t h a t c o u l d n o t h a v e b e e n a c q u i r e d as r e a d i l y , o r w i t h as c o n v i n c i n g an o p i n i o n , u s i n g o t h e r a v a i l a b l e t e c h n i q u e s i n t h e c r i m e l a b o r a t o r y . Examples a r e p r e s e n t e d i n t h e p a r a g r a p h s that follow. I n a n a u t o t h e f t c a s e , t h e v e h i c l e i n f o r m a t i o n number t a b (VIN) h a d b e e n removed a n d a s e c o n d one w e l d e d o n t o r e p l a c e i t . The V I N t a b was e x a m i n e d i n t h e SEM a n d t h e w e l d , t h e r e m a i n i n g f r a c t u r e s u r f a c e s , t h e g r i n d i n g marks a n d t h e s w a r f remnant f r o m t h e g r i n d i n g were e a s i l y i d e n t i f i e d a n d p h o t o g r a p h e d . These f e a t u r e s a r e shown i n F i g u r e 1. M e t a l l o g r a p h i c p r o c e d u r e s were a l s o u s e d a f t e r t h e SEM a n a l y s i s t o c o n f i r m t h e f a c t t h a t a w e l d i n g o p e r a t i o n had been performed. The f i r i n g p i n i m p r e s s i o n on t w o c a r t r i d g e c a s i n g s , one c a s i n g t h a t h a d b e e n t a k e n f r o m t h e s c e n e o f a h o m i c i d e , a n d one c a s i n g t h a t h a d b e e n f i r e d f r o m t h e s u s p e c t weapon a t t h e l a b o r a t o r y , a r e shown i n F i g u r e 2. The u n u s u a l a s p e c t o f t h i s c a s e i s t h a t a f t e r t h e h o m i c i d e , t h e weapon was t h r o w n i n t o a river. U n t i l i t was r e t r i e v e d b y p o l i c e d i v e r s , s u f f i c i e n t t i m e had e l a p s e d t o a l t e r t h e compression o f t h e f i r i n g p i n . This r e s u l t e d i n a v a r i a t i o n i n depth between t h e evidence f i r i n g p i n i m p r e s s i o n and t h e l a b o r a t o r y t e s t f i r i n g p i n i m p r e s s i o n . This made c o m p a r i s o n u s i n g o p t i c a l t e c h n i q u e s n e a r l y i m p o s s i b l e . However, u s i n g t h e s i g n i f i c a n t l y l a r g e r d e p t h o f f i e l d o f t h e SEM, a p o s i t i v e c o m p a r i s o n c o u l d b e made e m p l o y i n g p e r s i s t e n t f e a t u r e s i n t h e f i r i n g p i n impression and t h e angular spacings b e t w e e n them ( F i g u r e 3 ) . B. Composition A n a l y s i s . Comparison o f e l e m e n t a l c o m p o s i t i o n p r e s e n t i n p h y s i c a l e v i d e n c e has been f a c i l i t a t e d w i t h t h e a d v e n t o f SEM-EDA i n s t r u m e n t a t i o n . A p a i n t c h i p comparison between a minute c h i p t a k e n from t h e c l o t h i n g o f a h i t - a n d - r u n v i c t i m a n d t h e s u s p e c t s c a r i s shown i n F i g u r e U. The a n a l y s i s o f s a f e i n s u l a t i o n t a k e n f r o m t h e s c e n e o f a s a f e 1

1.

F i l m V a c EMS-Ul M i n i C o a t e r , F i l m - V a c I n c . , E n g l e w o o d , N . J .


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Figure 1. SEM photomicrographs of the filler metal and grinding swarf on a Vehicle Information Number (VIN) Tab (275X)

Figure 2. from (a)

Firing pin impressions evidence (b) control firings

Figure 3. Schematic and angular representation of selected details observed in the firing pin impressions shown in Figure 2. (a) evidence (b) control.


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breaking, the c l o t h i n g o f a suspect, and from a t o o l (crow b a r ) taken from the suspect car i s shown i n Figure 5 . The spectra from paper used t o wrap marijuana and from paper taken from a suspect's "workshop" i s shown i n Figure 6 . In a d d i t i o n t o the EDA o f the paper other standard p h y s i c a l paper analyses were performed ( f i b r i l l a t i o n t e s t s , d e n s i t y , t h i c k n e s s , b a s i s weight, and i n f r a r e d a n a l y s i s ) which a l s o confirmed that the papers were from the same batch. C. Coupled Analyses. In a malicious m i s c h i e f case, an unknown substance was found i n the gas tank o f a f l e e t o f t r u c k s . The topography revealed that the substance had a c h a r a c t e r i s t i c cube-like shape. The chemical spectrum i n d i c a t e d t h a t elemental make up o f the p a r t i c l e was sodium and c h l o r i n e (Figure 7). The same examination was performed on t a b l e s a l t and the r e s u l t s showed that the f o r e i g n substance was indeed common s a l t . In a grand t h e f t case a c r i t i c a l aspect o f the case i n v o l v e d the matching o f lacquered wood which was an i n t e g r a l p a r t o f the s t o l e n merchandise with wood found at the suspect's work area. The composition comparison o f the lacquer i s shown i n Figure 8. The t o p o g r a p h i c a l comparison o f the wood (coniferous) i s shown i n Figure 9 . The p o s i t i v e comparison obtained i n both independent analyses was confirmed by IR techniques. Conclusions The SEM has proved t o be an i n v a l u a b l e instrument i n i t s a p p l i c a t i o n t o f o r e n s i c evidence m a t e r i a l s . S e v e r a l widely d i f f e r e n t s u c c e s s f u l a p p l i c a t i o n s o f the SEM-EDA instrumentation to a c t u a l c r i m i n a l cases have been presented. Acknowle dgment The work i n t h i s paper was supported by a F e d e r a l grant (FORSEM I I - NYSP C-55708) d i s t r i b u t e d by the New York State O f f i c e o f C r i m i n a l J u s t i c e . The studies were conducted at the New York State P o l i c e S c i e n t i f i c Laboratory and i n the E l e c t r o n M i c r o a n a l y s i s Laboratory i n the NASA I n t e r d i s c i p l i n a r y M a t e r i a l s Research Center at Rensselaer P o l y t e c h n i c I n s t i t u t e . Literature Cited 1. 2. 3.

MacQueen, H. R., Judd, G., and F e r r i s s , S., J o u r n a l o f F o r e n s i c Science, (1972), 17, 645-658. Wilson, R. and Judd, G., Advances o f X-ray A n a l y s i s , (1972), 17, 19-26. Grove, C. A., Judd, G., and Horn, R., J o u r n a l o f F o r e n s i c Science, (1972), 17, 659-667.



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Figure 4. EDA spectra comparison of paint chips. The solid spectrum is from the evidence, the dotted is from the control. The major peaks are Al, Si, S, CI, K, and Fe.

Figure 5. EDA spectra comparison of safe insulation. The upper comparison is between contaminant particles on the clothing and the control specimen. The bottom comparison is between contaminants on a tool and the control specimen. The dotted spectrum in both cases is the control and the solid spectrum is the evidence. Major peaks are S and Ca.



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Figure 6. EDA spectra comparison of paper used to wrap marijuana (dotted spectrum) and, paper found at the suspects workshop (solid spectrum). Major peaks are Al, Si, S, CI, K, Ca, and Ti.

Figure 7. (a) Sodium chloride crystals, SEM photomicrographs (155X)(h) EDA analysis of crystals showing major Na and CI peaks.


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Figure 8. EDA spectra comparison of lacquer found on evidence (dotted spectrum) with lacquer found in the suspect's possession (solid spectrum)

Figure 9. SEM comparison of wood samples, (a) evidence (h) wood in suspect's possession.


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4. Grove, C. A., Judd, G., and Horn, R., to be published in the Journal of Forensic Science. 5. W i l s o n , R., J u d d , G., a n d Ferriss, S., Journal of Forensic Science, (1974), 19, 3 6 3 - 3 7 1 . 6. Williams, R. L . , "An Evaluation of the SEM with X - r a y Microanalysis A c c e s s o r y for Forensic Work", 537-544, F o u r t h I I T R I Symposium, 1971. 7. S i e g e s m u n d , R. A. a n d H u n t e r , G. M., " S c a n n i n g Electron M i c r o s c o p y o f Selected C r i m e L a b o r a t o r y S p e c i m e n s " , 577-584, F o u r t h I I T R I Symposium, 1 9 7 1 . 8. J u d d , G., S a b o , J., H a m i l t o n , W. J., Jr., Ferriss, S., a n d H o r n , R., to be published in the Journal of Forensic Science.


Forensic Science

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