.TRNG I HC KHOA HC T NHIN TP HCM

KHOA VT LB MN VT L NG DNG

BI TIU LUN

NGHIN CU CH TO MNG SnO2BNG PHNG PHP

PHN X MAGNETRON

GVHD: TS. L Trn

HVTH: L Ngc Thy Tin

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Tp.HCM Thng 5/2010

I. Tng quan v vt liu SnO2 :1) Cu trc tinh th v tnh cht ca SnO2

a) Cu trc:- L tinh th phn cc bt ng hng, c cu trc rutile nh

TiO2, GeO2- n v cha su nguyn t, hai thic, bn oxi. Bao quanh mi

nguyn t thic c su nguyn t oxi.Cc nguyn t oxi tothnh hnh bt din c tm l nguyn t thic.

- Hng s mng tinh th: a = b = 4,737Ao, c = 3,186Ao

- T tr ng 300oK l 6.95g/cm3

- im nng chy: 1630oC- H s dn n nhit: 0.02oC-1

b) Tnh cht:Tnh cht khi:

- L loi bn dn loi n, trong sut, rng vng cm 3,6 - 4,3eV.

- Trong mng tinh th tn ti nhiu sai hng. SnO2 c bit nnh bn dn loi n do s hin din ca nhng nt khuyt oxitrong mng tinh th, chnh cc nt khuyt ny to iu kin cho2 in t trong nguyn t Sn tr thnh in t t do, t hnhthnh hai mc donor ED1 v ED2. ED1 cch y vng dn 0.03eV,

C u trc tinh th SnO2

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trng thi oxi ha t c ti nhit khong 200oC. ED2 cchy vng dn 0.15 eV, trng thi oxi ha t ti nhit 400oC.

- Thic oxit c kh nng bn ha hc, bn c hc rt cao, n chb n mn bi kim nng m c.

Tnh cht in:- dn in ca tinh th bn dn b l tng dn ca electron

(e) v l trng (p).b = e+ p

- in tr ca vt liu khi Rb c tnh theo cng thc:Rb = l / (b.A) , vi b = e+p = n. e .e + p.p.e

l linh ng, l: chiu di vt liu, A: din tch b mt.- Nng ht ti in uc tnh:

n = Nc exp ( ); Nc = 2 ( )3/2

p = Nv exp ( ); Nv = 2 ( )3/2

- SnO2 l bn dn loi n , l do tn ti cc nt khuyt oxi trongmng tinh th SnO2. Trong tinh th SnO2 ng thi cha hailoi ht: Sn4+ ( b oxi ha hon ton) v Sn2+. Tn ti ca hailoi ht ny mang li cho SnO2 tnh dn in. Cc ion nm cnhnhau c th trao i cc cp in t cho nhau dn n s dichuyn cc in t t ni ny sang ni khc tng ng vi stng linh ng ht ti in, lm tng tnh dn in ca mng.

2) ng d ng c a SnO2:Vt liu SnO2 c ng dng rng ri trong i sng hinnay:

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- Mt lp mng SnO2 c ph ln ca knh my bay c tcdng gia nhit ca knh v lm tan bng hoc lm bc hisng m.

- Lm in cc trong sut trong n pht quang v n hnh mytnh.

- Dng lm d kh: nu b mt SnO2 tip xc vi khng kh, oxic hp th trn b mt. Ty vo nhit , n thay i trngthi oxi ha thnh O2- hoc O-. Khi tip xc vi kh cn d, Oxihp ph s phn ng vi kh d v lm thay i in tr cavt liu.

- Dng ch to pin mt tri: do truyn qua cao v dn in caom vt liu SnO2 pha tp F c s dng lm in cc trongsut pin mt tri

- Dng lm lp ph bo v chng n mn: hu ht cc chai thytinh c sn xut ngy nay u c ph mt lp SnO2 dy t10 n 100nm. nhng v chai ny c bn cao hn 20% sovi v chai bnh thng v c th c ti ch.

3) Phng php to mng SnO2:- C nhiu phng php to mng SnO2: bc bay, bn chm in

t, phn x magnetron.- Trong mng SnO2 c ch to bng phng php

Magnetron s cho nhy kh cc i nhit thp, v nhykh ethanol cao th ch hp cho vic ng dng cc cm bin dn.

II. C ch to mng SnO2 bng phng php phn xa Magnetron:1) L do to mng bng phng php Magnetron:

Trc s pht trin ca cng nghip th mt yu cu c t rai vi cc thit b kim tra nng cc kh chy n (CH4, H2,C3H7) v cc kh c hi (CO, NO, H2S, CH3OH) l mt vn cn thit.

Trong cc loi cm bin d kh th cm bin d kh c ch tot mng mng bn dn SnO2 c nhiu quan tm do SnO2 c tnhtr ha hc, tnh n nh nhit cao, v gi thnh r.

Mng SnO2 c ch to bng phng php Magnetron s cho nhy kh cc i nhit thp, v nhy kh ethanol cao th ch hpcho vic ng dng cc cm bin dn.2) Cc qu trnh xy ra trn b mt vt liu:

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Qu trnh hp ph vt l v hp ph ha hc trn bmt mng SnO2:

- Hp ph vt l: l mt dng lin kt yu trn b mt. khi xy rahp ph vt l, cu trc hnh hc v cu trc in tch b mtkhng b thay i. hp ph vt l da trn lc tng tc tnhin gia cc phn t vi nhau, cn gi l lc lin ktVanderwaals.

- Hp ph ha hc: l loi lin kt mnh gia cc nguyn t hpph vi b mt vt liu, loi lin kt ny s lm thay i cutrc ca b mt. hp ph ha hc thng xy ra sau qu trnhhp ph vt l khi c cung cp nng lng hot ha (thngl nhit nng).

Khi nng lng hot qu t n mt gi tr no th qu trnhhp ph ha hc xy ra. Sau khi hp ph ha hc, trng thi linkt O-O tr nn yu i v mt trng thi lin kt Sn-O c hnhthnh. Nh vy, lin kt gia Sn-O c hnh thnh t lin kt hahc ca phn t Oxi vi b mt SnO2.

C ch gii hp:- L qu trnh ngc vi qu trnh hp ph, qu trnh gii hp xy

ra khi lin kt ha hc gia nguyn t hp ph vi b mt b bgy v nguyn t ny ri khi b mt. iu ny xy ra khi kchthch nhit n nhit gii hp.

- Qu trnh gii hp gip ta tnh c ph b mt ca mngSnO2.

C ch nhy kh . Cc yu t nh hng n nhy khca mng:

+ C ch nhy kh:Tnh cht nhy kh ca cm bin kh ha hc dng mng mngc gii thch qua hai giai on:

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Giai on u, cc phn t oxi trong khng kh s b hpph vt l trn b mt mng , di tc ng ca nhit n chuyn sang hp ph ha hc v by nhng in ttrn b mt mng lm dn ca mng gim.

- Do b mt SnO2 c hin tng khuyt oxi nn tn ti cc ionSn2+ cha b oxi ha hon ton (ion Sn4+ b oxi ha hon ton) .Cc phn t O2 sau khi hp ph vt l c xu hng ion Sn2+

bng cch ly i cp in t ca chng, to thnh Sn4+. Qutrnh ly i cc in t lm thay i cu trc nng lng v intch b mt mng.

giai on tip theo, khi t mng trong mi trng khcn d, cc nguyn t oxi hp ph s tng tc vi kh dlm dn ca mng tng ln. S thay i dn introng c hai giai on th hin nhy kh ca mng, nu dn in thay i cng nhiu, nhy mng cng cao.

Trong giai on ny, oxi hp ph thc hin qu trnh oxi hakh vi cc cht kh vi mi trng xung quanh. Ty thuc vocc cht kh khc nhau, phn ng ca oxi hp ph ha hc vichng s khc nhau.Cc kh kh khi tng tc vi oxi hp ph str li cho mng cc electron, lm mng tng tnh dn in.

CO + O- CO2 + e-

C2H5OH + O- CH3CHO + H2O + e-

Trong khi kh c tnh oxi ha rt cc electron c a oxi hp , cc oxihp ph li rt cc electron ca mng lm mng gim dn in.

NO + O2- + e- NO2- + O-

Cc yu t nh hng n nhy kh:- Nhit : nhit lm nh hng n cc qu trnh xy ra trn bmt, cc qu trnh hp ph, gii hp- m: cc nhm OH- hay H+c th phn ng vi kh d. Mtkhc khi t mng trong mi trng kh d, cc oxi hp ph cngc th tng tc vi gc OH- lm tng hay gim dn in cacm bin. m c th to ra cc sai s cho php o, do trongqu trnh o phi kim sot c m.- Cu trc mng b cht hay cu trc mng xp:+ i vi mng c cu trc xp cht : th qu trnh nhy kh chyu da trn b mt, nng kh d hp ph ln mng khng cao, nhy km.

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+i vi mng c cu trc xp: ngoi s tng tc ca oxi hp phvi kh d th cn c thm hin tng khuch tn, chy thm thuca kh d vo bn trong mng, tng din tch tip xc mng vikh d, lm nhy tng ln.- Vi cu trc mng: kch thc ht c nh hng rt ln i vi nhy kh:Nu kch thc ht nh th mt oxi b hp ph trn b mt tngln, v lng electron b rt i cng tng, hnh thnh mt vngngho ti b mt tip xc. Nu kch thc cc ht c kch thc htnano th ton b in t bn trong th tch ht s b rt ht, lc nyb mt tr thnh mt ng th, nhy mng tng ln ng k theocng thc:

= o exp ( )

- S pha tp: tng nhy ca b mt v tng tnh lc la kh i vi b mt,ngi ta a thm vo b mt cc kim loi qu.Mt vi cht ph gia ca mng SnO2 lm tng nhy i vi mts kh d:

Cht xc tc Kh d Cht xc tc Kh dCeO2 Methane Os CH4La2O3 CO2 Cd H2Pd CO,CH4 Rh AcetaldehydePt CO Au COTh2O CO,trimethylamine Ag H2,H2S,propane

III. Thc nghim ch to mng SnO2 bng phng php phn xMagnetron:

1) c im mng SnO2:- L mng mng trong sut c tnh truyn qua, dn in tt, bn

ha hc, bn c hc cao.- Mng c cu trc tinh th nh hng u tin cc mt (110), (101),

(211)- Mng c cu trc xp v g gh cao- Nhy kh ethanol.

2) Thit b:a) C bn v phn x Magnetron:

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- Cu to: h gm cc b phn:+ Anode (v tr t cn ph mng): c th t song song hocvung gc vi cathode+ Cathode ( v tr ca bia lm bng vt liu to mng) c cp thm t 200V n 500V+ H nam chm (to t trng) c b pha sau cathode to ttrng khp kn. T trng ny to nn do s i cc gia cc namchm bn ngoi vi nam chm gia v c khp kn nh tmst ni t gia cc nam chm vi nhau.

- Nguyn l hot ng:+ Khi th m cc c cp vo h, bia tr thnh cathode v trthnh anode+ Khi tn ta bn trong mt h mt in trng c tc dng nhhng v gia tc cho cc ion hoc electron s cp ban u.+ Cc ion dng di tc dng ca in trng, tin v phacathode p vo b mt bia lm gii phng cc in t th cptrong khi in trng E gia tc cho cc electron th cp va sinh rath t trng B (do h nam chm to ra) ng vai tr nh mt byin t, lm cc electron th cp chuyn ng trong vng gn bmt cathode theo qu o cycloid. Qu o ny lm tng thi giansng ca in t ln rt nhiu ln trc khi n n c anode.+ Trong lc chuyn ng, electron th cp s va chm vi ccnguyn t, phn t kh bn trong h to ra cc ion cn gi l qutrnh ion ha.+ Qu trnh din ra lin tc cho n khi lng in t sinh ra bnglng in t ti hp, khi qu trnh phng in c duy tr, khpht sng trn b mt bia, th phng in gim v dng tng nhanh.nhng in t c nng lng cao sinh ra nhiu ion dng mangnng lng ln tng tc vi b mt bia lm phn x vt liu biav bt ra cc in t th cp phng in c duy tr . Lc nykhi th tng mt lng nh dng s tng ln ng k.

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b) Thit b:H chn khng gm:

- Bm s cp: to mi trng chn khng ban u cho h, duy tr psut lm vic cho bm khuch tn.Cng sut bm 1.5 kW, vn tc 760 lit/pht, vn tc quay 950vng/pht, p sut ti hn 10-2 torr

- Bm th cp: to mi trng chn khng su cho hDng bm khuch tn du vi cng sut 1.9 kW, vn tc ht 3000lit/s, th tch cha du 0.82 lt, p sut ti hn 5.10-7 torr

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- Bung chn khng.- H phn x.

- T in iu khin h chn khng

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- H o nhy kh

IV. Kt qu thc nghim- Cc mu SnO2 c kho st c dy mng t 120nm n

500nm, kch thc ht t 5nm n 12nm, mu c nung nng nnhit 350oC v trong 5gi sau s tin hnh o c.

- Qu trnh lng ng mng iu kin 6mtorr, I =0.3A, t l khO2/(O2+Ar) = 0.5, t = 70 pht.

1. nh hng ca nhit hot ng n nhy kh ca mng:Tin hnh kho st nhit hot ng ca mng ti cc nhit 200oC, 250oC, 300oC

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Kt qu kho st cho thy:+ 200oC-250oC: b mt hp th ch yu l O2- nn nhy thp.

+ 300oC qu trnh hp ph O- chim u th, nhy mng tngln.+ Nhit >300oC: qu trnh gii hp bt u xy ra, nhy gim.

2. nh hng ca p sut to mng n nhy khChn kho st cc p sut khc nhau: 6 mtorr, 9 mtorr, 13 mtorr+ Hnh thi b mt

- Ti p sut 6 mtorr trn b mt xut hin cc vt en l cc h sub mt, nguyn nhn l do p sut thp, ht n vi nnglng ln do t b va chm nn chng d kt t li vi nhau dn nmng c cu trc b cht. Nhng h su trn b mt l do s bnph ca cc ion, lm cho g gh ca b mt tng ln.

- Ti p sut 9 mtorr, 13 mtorr mng ng u do ht n cnng lng thp hn. Tuy nhin mng 9 mtorr c lng ht n ln hn nn kch thc m ht ln hn.

+ nhy kh:

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- Mng 13 mtorr nhy kh hn v c kch thc m ht nh hn sovi cc mng cn li.

- Tuy nhin mng 9 mtorr li c nhy km hn so vi mng 6mtorr do g gh ca mng 9 mtorr km hn.

3. nh hng ca thi gian phn x n nhy kh:Kho st dng phn x 0.3A, 0.2A, 0.4 A

- Khi dng phn x tng th kch thc ca m ht cng tng dn,do khi tng dng phn x th ht n c nng lng ln nn ktt li cho m ht c kch thc ln.

+ nhy kh:

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- Mu 0.3A c nhy cao nht- Mng 0.4 A c nhy km nht l do kch thc m ht ln nht- Mng 0.2 A c nhy thp hn so vi 0.3A do trong qu trnh

phn ht Sn bn ra t bia c nng lng thp , ht Sn s khng nng lng phn ng hon ton vi Oxi, dn n nguyn t kimloi b phn x nhiu hn nguyn t kim loi b oxi ha, nn nhy ca 0.2A thp hn so vi 0.3A.

4. nh hng ca thi gian phn x n nhy khKho st thi gian t 70 pht, 50 pht, 30 pht- Khi thi gian phn x tng th nhy tng, v khi nhit tng

dn n cu trc mng dn n nh , dn n nhy tng.

5. Ngoi ra mng cn chu nh hng ca t l kh n nhy kh.6. nh hng ca cc cluster Ag thm vo n nhy kh :

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- Cc cm bin kh c ch to t cc oxit kim loi th c kh nngnhy vi rt nhiu kh khc nhau (H2, CO, CH4, C3H8, H2S, NO,NO2, ethanol, methanol, axeton.). Vic ch to mt loi cmbin ch nhy vi mt loi kh no v khng nhy nhiu vi cckh cn li th da vo phng php to mng v tp cht pha tpvo mng.

- i vi mng SnO2 c ch to bng phng php Magnetron scho nhy kh cc i nhit thp, v nhy kh ethanol cao.Khi thm vo mng cc ht kim loi xc tc th b mt mng SnO2s c tnh lc la i vi ethanol.

+ Cu trc mng SnO2/Ag:- Trn b mt mng SnO2 c ph bi cc cluster Ag phn b ng

u trn b mt.Ph nhiu x tia X ca mu SnO2/Ag c xut hin nh ph (111) caAg .

+ nhykh ethanol ca mng SnO2/Ag so vi mng SnO2:

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nhy kh ethanol ca SnO2/Ag ln hn rt nhiu ln so vi mngSnO2.Nguyn nhn lm cho mng SnO 2/Ag c nhy ln hn l do c chnhy kh ca chng khc nhau.Mng SnO2/Ag nhy kh da trn c ch cn bng mc Fermi caSnO2 vi mc Fermi ca Ag v Ag+.Trong mng SnO2 nhy kh da vo c ch hp ph ion O- trn bmt SnO2Khi ph thm lp Ag, nhy kh ethanol tng ln gp 25 ln so vimng SnO2 thun.

V. Kt lun:Mng SnO2 c to bng phng php phn x Magnetron c nhy ln nht l:

p sut phn x 13 mtorr dng phn x 0.3A thi gian phn x 70 pht khong cch bia l 7cm

tng nhy ca mng SnO2 ngi ta pha thm cc cluster Ag, ktqu l nhy tng ln 25 ln so vi mng thun.

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TI LIU THAM KHO:1.Ch to mng SnO2, SnO2/Ag c tnh nhy kh bng phng php phnx Magnetron - lun vn thc s Tr n Quang Trung.2.Tng hp vt liu SiO2 v SnO2 SiO2 bng phng php Sol Gel - lunvn thc s Bi Thanh S