CHNG 1

TNG QUAN***1. 1. CU TRC NANO1.1.1. NH NGHA Vt liu nano l vt liu trong c t nht mt chiu c kch thc nano mt (1nm = m). y l i tng nghin cu ca khoa hc nano v cng ngh nano, mt lnh vc mang tnh lin ngnh cao, bao gm vt l, ha hc, y dc sinh hc, cng ngh in t tin hc, cng ngh mi trng v nhiu cng ngh khc.

Tnh cht ca vt liu nano bt ngun t kch thc ca chng, vo c nano mt, t ti kch thc ti hn ca nhiu tnh cht ha l ca vt liu thng thng. V trng thi ca vt liu ngi ta phn ra thnh ba loi: rn, lng v kh. Vt liu nano c tp trung nghin cu hin nay ch yu l vt liu rn, sau mi n lng v kh.

1.1.2 Phn loi vt liu nano :

C nhiu cch phn loi vt liu nano, di y l mt s cch phn loi ph bin: Theo hnh dng vt liu, ngi ta phn ra cc loi sau:

Vt liu nano khng chiu ( c ba chiu u c kch thc nano), v d m nano, ht nano

Vt liu nano mt chiu l vt liu trong mt chiu c kch thc nano, v d dy nano, ng nano

Vt liu nano hai chiu l vt liu trong hai chiu c kch thc nano, v d mng mng

Ngoi ra, cn c vt liu c cu trc nano hay nanocomposite trong ch mt phn ca vt liu c kch thc nano mt, hoc cu trc ca n c nano khng chiu, mt chiu, hai chiu an xen ln nhau.

Theo tnh cht vt liu, th hin s khc bit kch thc nano:

Vt liu nano kim loi.

Vt liu nano bn dn.

Vt liu nano t tnh.

Vt liu nano sinh hc.

1.1.3 c trng ca vt liu nano:

Khi vt liu gim kch thc xung nano mt, t s gia s nguyn t nm b mt v s nguyn t tng cng ca vt liu nano ln hn rt nhiu. Th d, i vi mt ht nano hnh cu bn knh R cu to t cc nguyn t c kch thc trung bnh a, t s ny bng [4]:

eq \f(Nmtngoi,N) eq \f(3a,R)

(1.1)

Nh vy, nu nh vt liu thng thng, ch mt s t nguyn t nm trn b mt, cn phn ln cc nguyn t cn li nm su pha trong, b cc lp ngoi che chn th trong cu trc ca vt liu nano, hu ht cc nguyn t u nm trn b mt hoc b che chn khng ng k. Do vy, cc vt liu c kch thc nano mt, mi nguyn t c t do th hin ton b tnh cht ca mnh trong tng tc vi mi trng xung quanh. iu ny lm xut hin vt liu nano nhiu c tnh ni tri, c bit l cc tnh cht in, quang, t. Kch thc ht nh b cn l nguyn nhn lm xut hin vt liu nano ba hiu ng: hiu ng lng t, hiu ng b mt, hiu ng kch thc.

Hiu ng b mt

Din tch b mt ln l mt li th khi chng c ng dng tng tr kh hoc ng dng trong cc phn ng xy ra trn b mt ca cht xc tc. Mt khc, nng lng lin kt ca cc nguyn t b mt b h thp mt cch ng k v chng khng c lin kt mt cch y , kt qu l cc ht nano nng chy nhit thp hn nhiu so vi nhit nng chy ca cc vt liu khi tng ng.

Hiu ng lng t

i vi cc vt liu v m gm rt nhiu nguyn t (1m3 vt liu c khong 1012 nguyn t), cc hiu ng lng t c trung bnh ha cho tt c cc nguyn t, v th m ta c th b qua nhng khc bit ngu nhin ca tng nguyn t m ch xt cc gi tr trung bnh ca chng. Nhng i vi cu trc nano, do kch thc ca vt liu rt nh, h c rt t nguyn t nn cc tnh cht lng t th hin r hn v khng th b qua. iu ny lm xut hin vt liu nano cc hin tng lng t k th nh nhng thay i trong tnh cht in v tnh cht quang phi tuyn ca vt liu, hiu ng ng ngm....

Hiu ng kch thc

Cc vt liu truyn thng thng c c trng bi mt s cc i lng vt l, ha hc khng i nh dn in ca kim loi, nhit nng chy, nhit si, tnh axit....Tuy nhin, khi gim kch thc ca vt liu xung n thang nano (nh hn 100 nm) th cc i lng l, ha trn khng cn l bt bin na, ngc li chng s thay i theo kch thc. c bit, khi kch thc ht gim xung xp x bn knh Bohr exciton th cn xy ra hin tng kch thc lng t (quantum size effects) hay cn gi l hin tng giam gi lng t (quantum confinement effects). Trong , cc trng thi electron cng nh trng thi dao ng trong ht nano b lng t ha, quyt nh tnh cht vt l v ha hc ni chung ca cu trc [1, 4].

1.2. S HP TH TRONG TINH TH

Trong th tn ti nhiu c ch hp th khc nhau nh hp th ring, exciton, hp th bi cc ht ti in t do, hp th tp cht, hp th phonon, hp th plasma. y ch xt ti hai c ch c bn sau:1.2.1. Hp th ring

Khi hp th photon, 1 in t ca vng ha tr c kch thch ln vng dn, th hp th oc c gi l hp th ring hay hp th c bn [4]. hin tng ny xy ra, photon phi c nng lng ln hn vng cm, hin tng ny li mt l trng vng ha tr

Hnh 1.1: C ch hp th vng vngTrn quan im photon mang tnh cht ht, chuyn ng trong mi trng bn dn, h s hp th c tinh nh sau:

= eq \f(1,l) = g (h). eq \f(n,c)

(1.2)

Trong :

l : qung ng t do trung bnh ca photon

n: ch s khc x ca vt liu bn dn

g (h) : xc sut hp thu photon trong mt n v thi gian

h: nng lng photon

Xc sut hp th photon g(h) c nng lng trong khong h h + d(h) t l vi xc sut chuyn mc W()= W(h), s trng thi in t gn vng ha trtrong khong nng lng |dE| [1]. Vy

g(h) d(h) = 2.W(h)..(Ev E)1/2 |dE| (1.3)

Ta xt dng ph hp th trong bn dn vng cm thng. Gi s cc trng thi trong vng ha tr b lp y electron v trong vng dn cc mc u trng.Xt hp th vng vng.

Mt nng lng vng dn v vng ha tr c dng

E = Ec +

(1.4)

E = Ev -

(1.5)

Trong :

: khi lng hiu dng ca in t v l trng.

p dng bo ton nng lng

E = E + h

(1.6)

h = E E = Ec Ev + eq \f(k22,2) () = Eg + eq \f(k22,2m*) (1.7)

T cng thc (1.8), rt ra cc i lng thay th vo biu thc (1.4), ta c h s hp th photon trong chuyn mc thng l

.(h) = eq \f((2m*)3/2,23) . eq \f(n,c) . W (. (h Eg)1/2

(1.8)

i vi chuyn mc thng cn php, ta c xc sut chuyn mc in t l hng s W (h) = const = W ( [1]. Nh vy

.(h) = A. (h Eg)1/2

(1.9)

1.2.2. Hp th Exciton

Cc ph hp th thng th hin mt cu trc khi nng lng ca photon ti thp hn rng vng cm ca tinh th.Cu trc ny c gii thch bi s hp th mt photon v sinh ra mt cp in t l trng bi mt qu trnh chuyn thng hay chuyn nghing. in t l trng tng tc vi nhau bi lc Coulomb v to thnh trng thi lin kt exciton. Th nng tng tc Coulomb c to bi:

Vc = - eq \f(e2,4orre-h)

(1.10)

Trong r l hng s in mi ca bn dn ang xt re-h l khong cch gia in t v l trng.

Hnh 1.2: Cc mc exciton

Tng tc ny lm gim nng lng ca cp in t l trng mt lng bng [4, 12]. Nhng photon pht ra mt nng lng h = Eg Ta s nh ngha bn knh Bohr ca exciton ax. Vi nguyn t hydro, nng lng lin kt E0 v bn knh Bohr a0 c cho bi:

(1.11)

(1.12)

y, ch tnh n khi lng ca in t, v khi lng rt gn ca c proton v electron cng bng khi lng ca me (khi lng ca proton ln hn rt nhiu so vi khi lng in t).Vi exciton, khi lng hiu dng ca l trng v in t cng bc vi nhau. V th m phi tnh n khi lng rt gn:

(1.13)

Hn na, khi tnh n c hng s in mi ca bn dn ang nghin cu, s c nhng trng thi lin quan n h in t - l trng m vi cc trng thi , nng lng ton phn thp hn cc tiu ca vng dn. Cc mc nng lng ca exciton:

EX(n) = - eq \f(e4,8(0r)2h2) . eq \f(1,n2) = eq \f(,mer2) . eq \f(1,n2) .E0

(1.14)

Khong cch t mc nng lng ca trng thi c bn (n=1) n y ca vng dn gi l nng lng lin kt exction.

Bn knh Borh exciton:

(1.15)

Cc trng thi khi n = 2, 3, 4tng ng vi cc trng thi kch thch ca exciton.

1.3. S GIAM GI LNG T1.3.1. S giam gi trong hp lng t

Chuyn ng ca cc e v l trng trong tinh th gii hn t nht theo mt hay nhiu chiu, b lng t ha. iu kin c lng t ha l cc ht ti in chuyn ng trn mt khong cc L nh hn bc sng De Broglie :

B = eq \f(h,)

(1.16)

Trong : E l nng lng ca ht mang in.

Hnh 1.3, minh ha s lng t ha ca cc in t l trng khi chuyn ng trong mt khong khng gian b gii hn. C vng nng lng trong bn dn khi b tch ra thnh cc mc nng lng trong chm lng t.

Hnh 1.3: Cu trc vng nng lng trong bn dn khi

v trong chm lng t

S giam gi khng nhng lm gin on cc mc nng lng m cn lm thay i mt trng thi theo cc mc nng lng. Hnh 1.4 minh ha mt trng thi ca tinh th b giam gi theo c 3 chiu .

Hnh 1.4: S giam gi lng t theo c 3 chiu v mt trng thi.

Trong php gn ng khi lng hiu dng, nhng mc nng lng ca mt ht ti in c khi lng hiu dng m* chuyn ng trong mt hp lng t 3 chiu Lx, Ly, Lz, ph thuc vo 3 s lng t l, m,n:

(1.17)1.3.2. S giam gi lng t mnh

Khi to ra mt cp in tl trng, cn phi tnh n cc nh hng ca s giam gi lng t, tng tc Coulom gia hai ht ti in. Nu khong cch khng gian giam gi nh hn bn knh Borh th xy ra hiu ng giam gi mnh v ngc li khi khong cch khng gian giam gi ln hn bn knh Borh th gi l hiu ng giam gi lng t yu. Trong php gn ng bc mt, in t v l trng trong ch giam gi mnh c th coi nh khng ph thuc ln nhau.

Trong trng hp n gin ca mt in t giam gi trong mt ging th v hn, vic gii phng trnh Schodinger a ra mc nng lng u tin ca in t l:

(1.18)

Tng t vic gii phng trnh Schrodinger cho l trng, a ra biuthc ca mc nng lng u tin ca l trngl:

(1.19)

S dch chuyn cho php u tin gia cc mc 1S3/2 1Se gi l dch chuyn c bn, nhng dch chuyn khc gi l dch chuyn kch thch. Nng lng ca dch chuyn c bn xc nh gi tr ca vng cm hiu dng ca nano tinh th:

(1.20)

Biu thc ny cho chng ti bit rng rng vng cm hiu dng ca tinh th nano tng ln khi bn knh ca ht gim.

Cc php tnh trn nhn c khi cha tnh n nng lng lin kt exciton. Chnh xc hn, tnh n rng vng cm hiu dng nano trong tinh phi tnh n c nng lng lin kt exciton (Formule de Brus, Effros et Kayanuma):

(1.21)

Thnh phn th ba l nng lng tng tc Coulomb gia in t v l trng trong ch giam gi lng t mnh.

: rng vng cm ca tinh th nano bn knh a

Eg l rng vng cm ca tinh th khi

khi lng rt gn exciton

h l hng s Plank

khi lng hiu dng ca in t v l trng.

Khi kch thc ca PbS khong t 1-5 nm, c ngha l nh hn bn knh Borh (ax = 18 nm) n m bo iu kin giam gi lng t mnh.1.4 TINH TH NANO InP

Indi photphua (InP) l cht bn dn loi III-V. Cc vt liu bn dn III-V l cc tinh th hp kim ca phn t kim loi nhm 3 v mt phi kim nhm 5. Hp cht III-V c cu trc mng tinh th lp phng tm mt vi cc nguyn t nm cc nh hnh lp phng. V d, InP co cc nguyn t Indi nm cc nh hnh lp phng. hinh 1 : InP co cu truc lp phng tm mt. Trong s cc hp cht III-V, vt liu bn dn InP c quan tm nghin cu do s ph hp v nng lng vng cm (~1.35eV) v bn knh Bohr exciton tng i ln (11,3 nm).Khi kch thc cc tinh th nano nh hn bn knh Bohr exciton , hiu ng giam gi lng t s xy ra.2. Phng php ch to tinh th nano InP

2.1. Phng php.

Cc tinh th nano InP c ch to bng phng php phn ng ha hc gia cc nguyn t In mi sinh vi P trong h dung mi ethanol v toluene nhit thp (khong 600C ) trong iu kin khuy trn mnh v lin tc. Di y l s quy trnh ch to ht tinh th InP.2. 2. Ha cht v dng c Trong th nghim ny, chng ti s dng cc ha cht v dng c bao gm:Bng 2.1: Danh sch cc ha cht s dng

Ha chtCng thcVai tr

Kim loi khi InInCung cp ion In3+

Pht pho vngP4Cung cp ion P5-

Axit HClNng 36.5%HClCung cp ion Cl1-

Cht kh NaBH4NaBH4Cht kh

Bng 2.2: Cc dng c c s dng

Dng cTn

Cn in tAG245

B rung siu m

My khuy tKIA

My ly tmUniversal 320

T sy

Cc ng, bnh tam gic

2.3 .B tr th nghim:

Quy trnh tin hnh:

tng hp tinh th nano InP u tin ta iu ch mui InCl3 t 2.42 mmol In vi 0.63ml HCl 37%. Sau , ha tan lng mui InCl3 va iu ch c vo 25mml ethanol. Ha tan 7.25mmol photpho vng vo 25mml toluene. C hai dung dch s tr ln trong sut sau khi rung siu m 15 pht. Sau , ha ln hai dung dch trn vo bnh tam gic 200ml, ta c dung dch MS trong sut mu vng nht cha P v ion In3+. Dung dch A gm 15mmol NaBH4 ha tan trong 75ml ethanol. Dung dch MS c khuy t ti 600C th nh t t dung dch A vo vi tc nh l 1ml/pht. Phn ng tng hp InP s xy ra theo phn ng ha hc sau:

2In3+ + 6BH 2In + 3B2H6 + 3H2

In + P 4InP

Hay 4InCl + 12NaBH4 + P4 4InP + 12NaCl + 6B2H6 + 6H2

Sau khi nh NaBH4 c 15 pht ta thy dung dch bt u chuyn sang mu nu ri chuyn dn dn sang mu en. Tc nhn kh NaBH4 kh IN3+ thnh In mi sinh c hot tnh cao tc dng vi P to ra tinh th InP. Phn ng c t ti 600C trong 4h. Sau qu trnh phn ng ta thu c sn phm mu en. Sn phm ny s c ra li vi ln vi ethanol v toluene nng, dung dch HCl long loi b tp cht d sau phn ng nh P, NaCl, NaBH4, In. Cui cng, kt ta mu en c sy kh trong chn khng ti 600C trong 2h, ta thu c bt mn mu nu en.2.4. Phng php kho st.Dung dch trong sut, mu vng nht cha P v ion In3+

Kt ta mu en

75ml ethanol

Bt mn mu nu en

Dung dch mu en c cha cc tinh th nano InP

25ml ethanol

570mg NaBH4 NaBH4

25ml toluen

InCl3

0.93g P4

0.63ml HCl

0.278g In

t ti 600C trong 1h

Khuy t 4h,600C

Sy kh trong chn khng. 600C, 2h

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