Observation of Landau levels on nitrogen-doped flat graphite. surfaces without external magnetic fields

Transcription

1 Supplemetary Iformatio Observatio of Ladau levels o itroge-doped flat graphite surfaces without exteral magetic fields Takahiro Kodo,, oghui Guo, Taishi Shikao, Tetsuya Suzuki, Masataka Sakurai, Susumu Okada, ad Juji Nakamura, * * orrespodig author: akamura@ims.tsukuba.ac.jp Faculty of Pure ad pplied Scieces, Uiversity of Tsukuba, -- Teodai, Tsukuba, Ibaraki 5-57, Japa. Tsukuba Research eter for Iterdiscipliary Materials Sciece (TIMS) & eter for Itegrated Research i Fudametal Sciece ad Egieerig (irfse), Uiversity of Tsukuba, -- Teodai, Tsukuba, Ibaraki 5-57, Japa. S. How to estimate the itroge cocetratio o the surface S. Examples of STS with may peaks S. Peak aalysis method S. LLs of graphee observed o the itroge-doped graphite surface S5. XPS Ns ad s core level spectra

2 S. How to estimate the itroge cocetratio o the surface The itroge cocetratio was estimated by coutig the dark ad bright spots visible i each STM image. The eightee STM images used for the estimatio are show i Figure S. I each case, the origial STM image is show o the left, while the STM image with pik circles, used to cout the spots i STM image is show o the right. The itroge cocetratio was estimated assumig that a sigle itroge atom is represeted by oe pik circle with a diameter of m. The desity of the circles i the STM image was divided by the desity of carbo atoms per uit area (. 5 (atoms/cm )) to determie the cocetratio. a f k o b g l p c h m q d i r e j Figure S STM images used for the estimatio of itroge cocetratio. STM images of the itroge-doped graphite surface. I each figure, the image o the left is the raw STM image, ad image o the right is the STM image with pik circles used to cout the spots i the image (see text) a, mv, p, 5 5 m, b, mv, p, m, c, mv, p, 5 5 m, d, mv, p, m, e, 5 mv, p, m, f, mv, p, m, g, mv, p, m, h, mv, p, 5 5 m, i, mv, p, 5 5 m, j, -5 mv, p, 5 5 m, k, mv, p, 5 5 m, l, 5 mv, 9 p, 5 5 m, m, 5 mv, 9 p, m,, 5 mv,.7 p, m, o, -5 mv, 9. p, 5 5 m, p, 5 mv, 9 p, m, q, 5 mv, 9 p, m, ad r, 5 mv, 97. p, m.

3 S. Examples of STS with may peaks I additio to those show i Figure i the mai text, we obtaied STS spectra with may distict peaks reproducibly at differet positios o the itroge-doped graphite surface at over poits. Examples are show i Figures S S5. I Figure S, the STS spectra labelled were take at the positios labelled i the STM image. May peaks appear i the STS spectra, except for spectra labelled ad 7. I Figure S, the STS spectra labelled P were take at the positios labelled P i the STM image. ll of the STS spectra exhibit may distict peaks, idepedet of the measuremet positio. Figures S ad S5 show STS results together with atomic resolutio STM images. The surface was foud to be atomically flat i each case. The STS spectra labelled were take at the positios labelled i the STM image. I every case, the STS peaks i Figures S ad S5 were foud to correspod to the LLs of bilayer graphee, based o the fittig aalysis (Figures Sd ad S5g-S5j), as i the case of Figure i the mai text.

4 x x x x x x - x - x x x x - x - x - x - x - x x - x - x x x - x - x - x - x - x x - x - x - x - x - x - x - x x - x - x - x di/dv (arb.uits) x - x Figure S STS spectra o the itroge-doped graphite show may peaks. STM curret image at 5 K ( mv, p, m ) ad STS spectra. STS spectra of were take at the correspodig positios i the STM image.

5 5 - - di / dv (arb.uits) E F G H I J K L M N O P E F G H I J K L M N O P Figure S STS spectra o the itroge-doped graphite show may peaks. STM curret image at 5 K ( mv, p, 5 5 m ) ad STS spectra. STS spectra at P were take at the correspodig positios i the STM image.

6 a c di/dv (arb. uits) m b m d STS peak eergy (mev) T 7 T T T - - sg() Figure S STS spectra at the atomically flat area of the itroge-doped graphite shows Ladau levels of bilayer graphee (ifferet example from Figure ). a, STM image (same image as i Figure c, -5 mv, 9. p, 5 5 m ). b, STM image at the positio idicated by the white square i a (-5 mv, 97. p, 5 5 m ), c, STS obtaied at the positios labelled,,, ad i b. d, Liear scalig betwee the peak positios i STS ad sg( ) ( + ). The estimated pseudo-magetic fields are also show i the figure. We assumed that the effective mass m* of the bilayer graphee was..5 m 7 e. Error bars idicate the variatio i te measuremets at each positio.

7 a c di/dv (arb. uits) e di/dv (arb. uits) m STS at STS at b d di/dv (arb. uits) f di/dv (arb. uits) m STS at STS at g STS peak eergy (mev) STS peak eergy (mev) STS peak eergy (mev) STS peak eergy (mev) h i j V Pr = sg() V Pr = sg() V Pr =.99 - sg() V Pr = sg() at T at 7 7 T at 7 7 T at 7 7 T Figure S5 STS spectra at the atomically flat area of the itroge-doped graphite show Ladau levels of bilayer graphee (ifferet example from Figure ). a, STM image (same image as i Figure c, -5 mv, 9. p, 5 5 m ). b, STM image at the positio idicated by the white square i a (-5 mv, 9. p, m ). c-f, STS obtaied at the positio labelled,,, ad i b. g-j, Liear scalig betwee the peak positios i the STS ad sg( ) ( + ). The estimated pseudo-magetic fields are also show i the figure. We assumed that the effective mass m* of the bilayer graphee was..5 m 7 e. Error bars idicate the variatio i te measuremets at each positio. 7

8 S. Peak aalysis method We coducted a fittig aalysis of the STS peak eergies usig equatios ()-() followig the procedure described i our previous report. riefly, values of Pearso s r obtaied for every possible peak assigmet was compared after fittig the results with equatios ()-(). The best fittig results, i.e. the most probable peak assigmets (idicated by the largest Pearso s r value) were idetified. Figure S shows a compariso of Pearso s r for each fittig case, e.g., Pearso s r for the fittig results for i Figure f are plotted i of Figure S. I the case of i Figure S, the largest Pearso s r was.999, idicated by the solid gree circles at - o the horizotal axis. The Ladau idex from the left of the STS spectrum (-79.9 mv) i Figure f was the assiged a value of = - i equatio (). The error bar for each STS peak eergy positio was determied as the amout of variatio i te measuremets. For example, i the case of STS spectrum i Figure f, the peak at -7 mv has a rage of variatio of mv, as show i Figure S7, ad thus the size of the error bar was set as mv.

9 .. Pearso s r Pearso s r Pearso s r ssumed Ladau idex of the st peak from the left i STS ssumed Ladau idex of the st peak from the left i STS Pearso s r ssumed Ladau idex of the st peak from the left i STS ssumed Ladau idex of the st peak from the left i STS Figure S ompariso of Pearso s r i fittig aalysis of STS peak eergies. Pearso s r is plotted as a fuctio of assumed Ladau idex of the st STS peak from the left i each of the spectra i Figure f. 9

10 di/dv (arb.uits) a mv Fig.f di/dv (arb.uits) b Fig.f mv c.. Fig.f d.. Fig.f di/dv (arb.uits) mv di/dv (arb.uits)..... mv Figure S7 Raw data sets of STS spectra i Figure f. Te STS spectra obtaied at the positios labelled,,, ad i Figure d are show. The averaged spectrum for te spectra is show for each case i Figure f. There is a fiite variatio of approximately 5 mv i the peak. The variatio is represeted by a error bar aroud the peak positio i Figure g. S. LLs of graphee observed o the itroge-doped graphite surface s described i the mai text, STS peaks obtaied at the itroge-doped graphite surface were foud to be correspod primarily to the LLs of the bilayer graphee. However, a few STS spectra were foud to correspod to the LLs of graphee. Two examples are show i Figure S. The best fittig results for the STS peak eergies were obtaied for the case i which we used equatio () (LLs for graphee), ad the first peak from the left i the STS spectrum was assumed to correspod to = -5 ad = - for Figs. Sb ad Sf, respectively, as idicated by the values of Pearso s r i Figs. Sd ad Sh.

11 a e b f m di/dv (arb uits.) K.5 K di/dv (arb uits.) c Peak positio eergy (mev) d Pearso s r Pearso's r.99 s =. T sg() / g Peak positio eergy (mev) Pearso's r sg() / h Pearso s r sg() s =.9 T ssumed Ladau idex of the st peak from the left i STS ssumed Ladau idex of the st peak from the left i STS Figure S STS spectra of the itroge-doped graphite showig LLs of graphee. a, e, STM image take at K (- mv, p). b, f, STS obtaied at the positio idicated by arrow i a. c, g, Liear scalig betwee the peak positios i STS ad. d, h, Pearso s r for the fittig aalysis of STS peaks show i c ad g (see S).

12 S5. XPS Ns ad s core level spectra Figure S9 shows XPS s core level spectra used for the estimatio of itroge cocetratios. orrespodig XPS Ns core level spectra (which are the same spectra show i Fig. ) are also show. s peaked at. ev,.5 ev,. ev, ad.5 ev for the samples with itroge cocetratio of.9 at %,. at %,.7 at %, ad 9. at%, respectively. Except for the sample with the itroge cocetratio of.9 at %, the bidig eergy of s shifted slightly to higher eergy, compared to the s of the pristie graphite (. ev). This is most likely due to the charge trasfer from itroge to carbo, which raises the Fermi level.

13 N s N 9. at% fter 9 K N s N.7 at% fter 9 K Pass eergy 5 ev Pass eergy 5 ev s N 9. at% fter 9 K Pass eergy 5 ev s N.7 at% fter 9 K Pass eergy 5 ev N s N. at% fter 9 K Pass eergy 5 ev s N. at% fter 9 K Pass eergy 5 ev N s N.9 at% fter 9 K Pass eergy ev s N.9 at% fter 9 K Pass eergy ev Figure S9 XPS Ns ad s core level spectra. XPS Ns ad s core level spectra of itroge-doped graphite with differet itroge cocetratio (9.,.7,., ad.9 at %) are show. ll Ns spectra show here are the same with Figure a. Oly for the.9 at %, the pass eergy is selected as ev to clearly resolve the differet itroge species.