University of Illinola Urbane, Illinois Department of Physics. Principal Investigator Robert J» Bauror. June 1953

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$7 T Cntract K6nr-07l29 CZ5 HR 017-1*12 f~\ r/*\ Physics f the Slid$ Stats ' v University f Illinla Urbane, Illinis Department f Physics

1 ^ Technical Reprt i.'. 7 T Cntract K6nr-07l29 CZ5 HR 017-1*12 f~\ r/*\ Physics f the Slid Stats ' v University f Illinla Urbane, Illinis Department f Physics Principal Investigatr Rbert J» Baurr June 1953 U. 3. Department f the Nary Offie f Naval Research Washingtn, D. C.

2 J p V. ; ELECTRONIC HALL EFFECT IN NaCl Alfred G. Rdfield 17. S. Atmic Energy Cmmissin prdctral Fellw University f Illinis 0

I Dy applying the pulsed light methd f Phl and his c- wrkers t the measurement f electrnic Hall effect in insulating phtnductrs it has been pssible t avid the space charge diffi- 2 3 ulties present

sets up a ptential gradient n the lwer surface f the crystal, and thus an inhmgenius field in the crystal which is, n the average, in the x-diretin.

3 I Dy applying the pulsed light methd f Phl and his c- wrkers t the measurement f electrnic Hall effect in insulating phtnductrs it has been pssible t avid the space charge diffi- 2 3 ulties present in previus wrk ' The electrde arrangraent is shwn in Figure 1. The battery V. sets up a ptential gradient n the lwer surface f the crystal, and thus an inhmgenius field in the crystal which is, n the average, in the x-diretin. The upper plate is held at grund ptential by the electrmeter circuit; the ptential f the entire lwer plate can be changed with the ptentimeter, and mving the ptentimeter tap rtates the electrl field in the crystal. The electrmeter respnds nly t the cm- pnent f charge flw which is in the y directin. In making a measurement, a magntic fild is applied in f*) the % directin, th rystal is illuminated with pulses f light a few secnds in duratin, and the ptentimeter is adjusted until th electrmeter jives zer deflectin during illuminatin. This means that th average charge flw in the rystal is in the z direc- tin parallel t the electrdes, but the average electrl field is at an angle, the Hall angle, t the electrdes. T eliminate spae charge, the batteries are turned ff between each bservatin f the electrmeter and the crystal is illuminated with a strng light. The magnetic field is then reversed and the ptentimeter is again adjusted as befre, s that the avera-e charge flw is again in the x dirctin but the average lctric fild has been rtated thrugh twice th Hall angle. Using a therem f Shckley } it can then be shwn rigrusly that (fr small 8) 1 I I

' i. 0 0 rdv wher u is th mbility, H tb magnetic fild, e the velcity f lijht, th Ilall angle, D the thicknss f the crystal, n the number f electrns pr unit vlume released by the light, T the mean

First, it is a transient methd* Secnd, the electric field Inside the crystal is rtated by external electrdes, rather than by the electrns under study.

4 ' i. 0 0 rdv wher u is th mbility, H tb magnetic fild, e the velcity f lijht, th Ilall angle, D the thicknss f the crystal, n the number f electrns pr unit vlume released by the light, T the mean electrnic lifetime, and fi the x cmpnent f electric field in the crystal. The integratins are ver the vlume f the crystal* This methd differs frm the cnventinal ne in several ways. First, it is a transient methd* Secnd, the electric field Inside the crystal is rtated by external electrdes, rather than by the electrns under study. Finally, n attempt is made t in* Jct r eject lectrns thrugh the surface f the crystal. The methd cannt be applied directly t crystals having finite dark cnductivity* It has already been applied t dla.ind.-* Dtli additively clred and x-rayd Ilarshaw UaCl crystals have been studld and the charge rlasd frm F cnters in these crystals gives a Hall vltage plarity characteristic f elctrns. At 62 t 2 K the mbility is 2$0 t $ ca^/vlt sec, and at 200 K the mbility is f the rder f frty* The experimental errr is due t nise in the cnducting plates, F center bleaching, temperature variatins, r pssibly crystal imperfectins. By vilently quenching the crystal its mbility an be reduced t as lw as 150 m/vu sec* at 82 K. These bservatins are in reasnable agreement with bth the thery f Frhlich and Mtt and the mre recent calculatin f Lw and Pines'. Wrk is under way t imprve and extend these measurements* The help f many peple in this wrk is gratefully acknwledged; the authr wishes particularly t thank Dr. fi. J*

5 M. aeaciatd fr the usa f their nagnct.

A, Redfield, papr presented at the 1955 --rth Carlina meeting f the American Physical Sciety. 6.

6 References 1. R. W. Phl, Prc. Phys. Sc. (Lndn) l (Extra part), 5 (1937). 2. J. Evans, Phys. Rev,, kl (19^0). 3. C. C. Kllck and R. J. Haurer, Phys. Rv. 81, 12l. (1951) I*. W. Shckley, J. Appl. Phys. <L, 635 (1953). 5. A, Redfield, papr presented at the rth Carlina meeting f the American Physical Sciety. 6. PVhlih, Pelser, and Zlenau, Phil. Uag. l, 221 (1950). 7. P. E. Lw and D. Pinee, letter t be published in the Physical Review.

7 Y -*-X O - Figure! SLsetrd* a WBpwt fp il i dag Iftetrat Mil afffwt is C

11. DUAL NATURE OF RADIATION AND MATTER

11. DUAL NATURE OF RADIATION AND MATTER Very shrt answer and shrt answer questins 1. Define wrk functin f a metal? The minimum energy required fr an electrn t escape frm the metal surface is called the