Khả năng ứng dụng các dây nano zno được chế tạo bằng phương pháp bốc bay nhiệt

DAI HOC QUOC GIA HA NOI
TRUONG OAI HOC KHOA HOC TU NHIEN
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V\

bl TA\l!

KHA NANG LTNG DUNG CAC DAY NANO ZnO Dl/OC
CHE TAO BANG PHl/ONG PHAP BOG BAY NHIET

MA SO:

I

QT - 06 - 09

CHU TRI DE TAI:

PCS. TS. Ta Dinh Canh

CAN

CN. Tran Thi Quynh Hoa

BO THAM

GIA:

CN. Nguyen Viet Tuyen

HA Ndi - 2006
^^Al H O C Q O O C GIA HA NQI
i^UN
DT/63^


Ket-noi.com kho tai lieu mien phi
hkO cAo TOM TAT
De tai:
KHA N A N G Q N G D U N G GAG DAY NANO ZnO DUOC
GHE TAO BANG P H U O N G PHAP B O G BAY NHIET

Ma so: QT - 06 - 09
Chii tri 66 thi:

PGS. TS. Ta Diiili Canh

Can bo tham gia:

CN. Tran Thi Quynh Hoa
CN. Nguyen Viet Tuyen

1. Muc tieu de tai:
Hien nay vat lieu cau true nano mot chieu (day nano, thanh nano,
bang nano) dang du-ffc quan tam dac biet vi tiem nang ung dung cua no
trong ITnh virc linh kien dien tir va quang dien tir co kich thu-ffc nano.
Vat lieu cau true nano mot chieu co the dune nhu* cac cau true thanh
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C3

phan de che tao cac linh kien dien tu va quang dien tir kfch thu'dc nano.
Cac vat lieu nay co the duae tong hop bang nhieu phu-ang phap khac
nhau nhu*: phuo'ng phap van chuyen tii' pha hoi [1-3], phu'O'ng phap lang
dong hoa hoc tir pha hoi [4], phuong phap ket tua bang dien [5], sol-gel
16]...
Trong so cac oxit ban dan, ZnO la chat ban dan viing cam thang, co
do rong vung cam o* nhiet do phong £g~ 3,37 eV va nang ino-ng lien ket
exciton co* 60 meV. Cac day nano, thanh nano ZnO la cac vat lieu co
nhieu trien vpng trong viec che tao cac lade, diot phat quang vung tii*
ngoai (sii- dung hieu ling exciton nhiet do phong), cac transit© hieu ung
tru-crng, chuyen mach quang va cac senso' khi...
Trong bai bao cao nay, chiing toi tr inh b ay cac ket qua che tao day
nano, thanh nano ZnO bang phuong phap van chuyen tir pha hai kh
ong V a CO chat xiic tac Au trong moi truong khi mang la Ar.

2, Noi dung nghien cihi:
De thirc hien dugc muc tieu neu a tren, de tai da giai quyet duae cac
van de sau:
+ xay dung he tao day nano ZnO
- Lo ong ((j) =40mm) tao nhiet do tren duori 1000^ co do on dinh
cao (16 CO sai so nho ca ± r va chay theo chuomg trinh)
- Khi mang Ar co do sach 99%
+ Tdng hop ca'u true nano ZnO 1-chieu tCr pha hai-ran (VS)
+ Tong hop cau true nano ZnO 1-chieu tir pha hai-long-ran (VLS)
bang each sir dung mang vang (chai xuc tac) nhu m6t dung moi tai nhiet
do cao.
+ Khao sat tinh chat cau true cua day nano ZnO
4- Khao sat tfnh chat huynh quang va khich thich huynh quang ciia day
nan6 ZnO
+Xfly dung thiinli cong he tlurc nghiem do sir phu thuoc dien tro'
ciia mau vao do am ciia moi truong
3. Cac ket qua dat dirac:
+ Che tao thanh cong day nano ZnO eo ducmg kinh nho tir 30-60nm
tren de Si bang 2 phirang phap VS va VLS co dung m6i trircmg thoi khi
tra Ar.
+ khao sat tinh chA'l cau true ciia ca'u triic nan6 ZnO phu thuoc vao
nhiet d6 de, th5i gian tao mSu, do day ciia cha't xiic tac vang.
-I- Khoa sat tinh chat huynh quang va kfch thich huynh quang ciia cac
day nan6 ZnO da che tao.
H-Birdc dau phat hien hieu ung nhay am ciia ZnO, ma ra kha nang
irng dung ZnO nano lam vat lieu sensor trong tirang lai.
+ Cong tac nghien cii'u: da cong bo 3 bai bao
1/ Tran Thi Quynh Hoa, Ta Dinh Canh, Nguyen Ngoc Long, Nguyen Viet

Tuyen, "Zinc oxide nanostructure for humidity sensor", VNU
Journal of Science, Mathematics - Physics, 2006 (in press).
2/ Ta Dinh Canh, Nguyen Ngoe Long, Nguyen Viet Tuyen, Tran Thi
Quynh Hoa, Cao Van Tuan, "Multiform ZnO nanostructures
fabricated by vapor-phase transport method without catalyst",
VNU Journal of Science, Mathematics - Physics, 2006 (in press).
3/ Tran Thi Quynh Hoa, Ta Dinh C anh, Nguyen Ngoc Long, Nguyen
Viet Tuyen and Nguyen Duy Phuong, "Photoluminescence of ZnO
nanostructure prepared by catalyst- assisted vapor-liquid-solid
technique", Tuyen lap bao cao IIQI nghj khoa hpc quang ph6 toan
(liioe hin (hiV IV, ('iiii llu), S/2()()(), (il;l iilifm in).


Ket-noi.com kho tai lieu mien phi
+ Cong tac dao tao :
* Da hiromg dan 2 khoa luan tot nghiep
-Vu Tien L6c"che tao mot sd cau triic nano ZnO bang phuang phap b6'c bay
nhiet" (2006)
-NguySn Viet Tuyen "Che tao va khao sat dTa nano dang I6i/v6 ciia Zn/ZnO
bang phuang phap boc bay nhiet" (2006)
* Da hu6ng dSn 2 luan van cao hoc:
-TrSn Thi Quynh Hoa, " Che tao va khao sat mot sd tinh cha't ciia day nano
ZnO duae che tao bang phuang phap bdc bay nhiet" (2006)
- Cao Van Tuah, "Che tao va khao sdt ca'u triic nan6 ZnO pha tap Co bang
phuang phcip bdc bay nhiel'\ (2006)
4. Tinh hinh su dung kinh phi:
Tong kinh phi thuc chi: 15.000.000 dong (mu5i lam trieu dong chan).
Trong do cac khoan da chi:
Thanh toan dich vu cong c6ng : 600.000 d (tien dien)
Thue mu6n : 6.000.000 d

Chi phi vat tu hoa chat: 7.800.000 d
Chi phi khac (QLCS): 600.000 d
Da th6ng qua chijng ttj* tai phong tai vu.

Xac nhan ciia ban chu nhiem Khoa
(Ky va ghi ro ho ten)

Chia tri de tai
(Ky va ghi ro ho ten)

?5
PGS.TS.NguyIn The Binh

Xiic nhAn ci'ui 'IVircnig DI IKI II'N
OHO HiEu I R U 6 N &

jblu/n/ c/IioLfiit

PGS.TS.Ta Dinh Canh


Brief of the Report

L The title of the project.
The possible applications of ZnO nanowires, prepared by vapor
phase transport method.
The code number: QT - 06 - 09.
2. Main responsible person: Assoc. Prof. Dr. Ta Dinh Canh.
3. Main implementation numbers
Bachelor: Tran Thi Quynh Hoa

Bachelor: Nguyen Viet Tuyen
4. The objects.
ZnO films composed of nanowires and nanorods were fabricated
on the Si substrates willi Pl "tape" electrodes by the vapor - phase
transport method. The humidity sensitive characteristics of the films
have been investigated. These nanoslructured films show humidity
sensitivity, good long-term stability. It was found that the resistance of
the films decreases with increasing relative humidity (RH). It is reliably
believed that the ZnO nanomalerial films will be used as efficient
humidity sensors.
5. The content of research.
ZnO has a direct bandgap of 3.37 eV and high mechanical and thermal
stabilities at room temperature. One-dimensional nanostructured ZnO
materials have recently stimulated great interest due to their importance in
basic scientific research and potential applications in numerous areas such as
nanoscale electronic and photonic. The traditional approaches to synthesize
one-dimensional ZnO nanostructures are the vapor - phase transport process
with the assistance of metal catalysis, thermal evaporation and template assisted growth [1].
The humidity control is essential for various fields of industry as well
as human life. In this work, ZnO films composed of nanowires and nanorods
were fabricated, respectively, on the Si substrate by the vapor - phase


Ket-noi.com kho tai lieu mien phi

transport process, and their humidity sensitivity characteristics have been
investigated.
6. Results:
1/Tran Thi Quynh Hoa, Ta Dinh Canh, Nguyen Ngoc Long, Nguyen Viet
Tuyen, "Zinc oxide nanostructure for humidity sensor", VNU Journal

ofScience, Mathematics - Physics, 2006 (in press).
2/Ta Dinh Canh, Nguyen Ngoc Long, Nguyen Viet Tuyen, Tran Thi
Quynh Hoa, Cao Van Tuan, "Multiform ZnO nanostructures
fabricated by vapor-phase transport method without catalyst", VNU
Journal ofScience, Mathematics - Physics, 2006 (in press).
3/ Tran Thi Quynh Hoa, Ta Dinh Canh, Nguyen Ngoc Long, Nguyen Viet
Tuyen and Nguyen Duy Phuong, "Photoluminescence of ZnO
nanostructure prepared by catalyst- assisted vapor-liquid-solid
technique",
Tuyen tap bao cao hoi nghi khoa hoc quang pho toan
qu6c \kn thu IV, Can Tho, 8/2006, (da nhan in).

7. Conclusion
* Obtaining the aims of the project,
* Training 2 graduate students, 2 master student.


MUC lUC
Mdddu:

1

Chuang 1: Phuang phap che tao cau triic nano mot chieu tijr pha khi

2

LI.

Cac phuang phap che tao ZnO nano
7.7./.

Phuang thuc top - down

7.7.2.

Phuang thiic bottom - up

1.2. Ca che phat trien day bang phuang phap boc bay nhiet dan gian
1.2.1

Ca che hoi - ran (VS)

L2.L

Co che hai - long - ran(VLS)

7.2.2

Hien tugng can bang nhiet dong

Ciurang 2: Thuc nghiOin

,

*^

7

Chuang 3: Ket qua va bien luan

12

Ket luan:

19

:.....

L5i cam an:

19

Tai lieu tham khao:

20


Ket-noi.com kho tai lieu mien phi
Md DAU
Hien nay tren the gidi da va dang hinh thanh mot nganh khoa hoc va cong nghe
mdi, CO nhieu trien vong va dir doan se co nhirng tac dong manh me den ta't ca cac ITnh
vuc khoa hoc, cong nghe, ky thuat cung nhu ddi song kinh te-xa hoi a the ky 21. Do la
Khoa hoc va Cong nghe nano.
Ky thuat nano la mot khdi dau quan trong ciia khoa hoc ky thuat the ky 21. Theo xu the
chung, ky thuSt nano da chd nen vucrt troi hem trong cuoc canh tranh khoa hoc. Linh virc
nay kham pha nhung vAl HCii vl\ li'nh chA'l cua nd khi kfchllurdc inftl chiCu nho cd tu inftl
idi vai iram nano met, che do kich thudc nay duae ndi tdi nhu la kich nano (nanoscale).
C) kfch thudc nano, hieu ung giam gui luong tu bdt dau anh hudng tdi tinh chat cua vat
Heu. Cai gi tao cho vat lieu nano su quan tSm dac biet, va cai gi da dan den su bung no
nhung nghien cuu trong linh vuc nay, nhung vat lieu nay cd the nSng cao va thay doi tinh

chat nhu do chung cd su giam gui lugng tu trong mot, hai, hoac ba chieu.
Nghien cuu trong linh vuc nay se cung ca'p hau het nhung phat minh trong ky
thucU, Kha nang de lam viec vdi nhirng nguyen tu d kich thudc nano, va vdi nguyen tu xac
dinh, huu hen md ra mot linh vuc mdi ciia su phat trien ky thuat. Tfnh cha't huynh quang
phu thuoc kfch thudc cua eham luoiig tu va do bdn ra't Idn cua ong nano cacbon la hai tfnh
chai cua vat Heu nano ma da cho tieng xau tren mot thap ky qua. Tuy nhien, nd khong bat
dau xam pham mot linh vuc rong Idn cua be mat va quan tam nhung ca'u true va nhiing
tfnh cha't da dugc kham pha. Linh vuc nay dugc hinh dung lam thay doi hiu het moi vat,
lam thd' nao chiing ta ch6' tao va liep can ky thuat. Nghien cuu vat lidu nano da thu dugc
Igi fch tir trandilo phat xa trudng (FETs) cho nhung thiet vi dien tii nhd ban, nhe han, va
nhanh hon. va cCing md ra m()t linh vuc mdi gidng nlur spintronic.
Tuy nhiCii, khoa ligc nano va ky thuAl nano vAn Hong giai doan clAu phat tridn.
Nhung khai ni6m co sd chi phdi linli vuc nay khdng dugc hic'u dAy du va cAn (Urge kiiam
plui xa hon. Trong thuc td', mot khdi lugng nghien cuu trong linh virc n^y hudng tdi viec
lao ra bfen canh nhung kham pha Idn trong tfnh cha't mdi, cA'u true rifing, hoac che tao thiei
bi thuong mai bang each su dung nhirng ca'u triic nano nay. Tuy nhien neu khoa hoc va ky
thuat nano bao gid tao ra mot anh hudng d^y y nghia trong khoa hoc cgng dong va the
gidi rdng Idn, nhung khai niem co ban va ly thuyei chi phdi mot ldp rieng cua nhung vat
lieu nay phai dugc phat hien.
Nghien cuu phai dugc tAp trung hon va ihAin dd trong ccrch^kiCm soat nhung tinh
chat va sir phat trien rieng biet cua nhirng cA'u true nay. Chung ta phai luu y kl dc' hieu
nhung phat hien dang kinh ngac nay; chiing ta phai khao sat, do, va md hinh, nhung quan
trgng hon, chiing ta phai cd khd nang du doan.


CHl/ONG I
PHirONG PHAP cut TAO CAU TRUC NANO
1-CHIlSUTirPHAKHI
1,1.Cac phirong phap che tao ZnO nano
Cdng nghe chS tao nano thudng dugc tiSn hanh theo hai phuong thuc la phuong

thuc "tu dudi len" (bottom - up) va phuong thuc "tir tren xudng" (top - down). Trong
phuang thuc bottom - up, ngudi ta lap ghep nhung hat cd kich thudc co nguyen tu, phan
tu hoac cd nano dk tao ra cac vat lieu kfch thudc nano. Trai lai, trong phuong thuc top down, ngudi ta chia nhd mot he thdng Idn de nham tao ra dugc cac vat lieu kich thudc
nano cd cau tnic va tfnh chat mong mudn.
Vat lieu cau true nano

i
^0
^

sap xep cac nguyen tir

Chia nho vat lieu

Dhan tu ca nano

khfti han rlan

Hmh 1.10: Phuang thuc bottom-up va top-down
/.2. /

Phuong thuc top - down

I)Ai vdi cdng nghv naiu>, dc \i\n\ dugc nhiYng kich tlnrdc nhd cd I nni -100 nm,
ngirdi ta phai khac nano bang chum electron, chum ion hdi lu, chum tia X... Cd nh&ng
trudng hgp can kich thudc cd nguyen tii*, ngudi ta phai dung bg quet d thiet bj hien vi de
quet dau dd dieu kien mui nhgn ve theo cac hinh mong mudn, diing dien trudng d dau dd
de lay di hoac them vao cac nguyen tii. Nhiing each khac hinh ndi tren khdng the dua vao
san xuat rdng rai vi ton thdi gian va gia thanh kha cao.
Ngoai ra, phuong phap nghien bi cung rat hieu qua trong mgt sd trudng hgp tao

bgt nano. Ngirdi ta chon ciic hdn bi cung, to va nSng cho vao mgt cai trdng hinh lri,i, cung.
Vdi tdc dp quay thich hgp, ta cd the thu dugc vat lieu vdi kich thudc mong mudn. Tuy
nhien thdi gian nghien bi cd the keo dai den hang chuc, hang tram gid. Hon niia, trong
phuong phap nghien bi vat lieu rat de bi bien dang va cd nhieu sai hdng nen sau khi thu
san pham phai cd qua trinh xu ly thich hgp.
1.2.2

Phirang thuc bottom - up

Phuong phap hien dai nhat cua viec sap xep lung phan tu nguyen lu la phuang
phap epitaxy. Phirong phap nay cd the khdng che chinh xac thanh phan hda hgc cung nhu
cau true vdi kich thudc cd vai nguyen tii. Epitaxy la phuong phap hieu qua rat cao nhung
ton kem do sir dung chan khdng sieu cao.
Ngoai ra, cac phuoiig phap hoa hoc khac ciing dugc coi la phuong thiic bottom up. Cac phuong phap hda hgc cd nhieu hiia hen vi gia re, che tao dugc sd lugng Idn va cd


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kho tai lieu mien phi
thS di6u khiSn kich thudc chinh xac. Ban chat ciia viec hinh thanh cac cau tnic nano theo
phuong phap bottom - up chinh la qua trinh tinh the hda thdng qua hai budc co ban: tao
mSm va phat triSn. Khi ndng do ciia cdc khoi vat chat (nguyen tir, ion hoac phan tu) dii
cao, chiing s6 lien tuc ket hgp lai thanh nhQug dam nhd (hay mam) thdng qua nhijng nhan
ddng nhat. Sau dd cac mam nay se ddng vai trd lam hat nhan cho cac qua trinh phat trien
tiep theo de hinh thanh cac cau tnic Idn hon. Mgt sd phuong phap hda hgc hay dugc sii
dung de che tao vat lieu cd cau tnic nano nhu: lang dgng tir pha hoi (CVD) hoac tu pha
hoi ciia cac hgp chat hiJu co kim loai (MOCVD), phuong phap bdc bay nhiet, bdc bay
bang laser, phuang phap sol - gel, aero - gel, phuong phap thuy nhiet (hydrothermal
method), dung mdi nhiet (solvothermal method)...
Mdi phuong phap deu cd nhiJng uu diem va nhugc diem rieng. Trong dd, lang
dgng tu pha hoi la phuong phap phd bien nhat trong viec lang dgng cac mang ZnO cau

tnic nano mgt chieu. LTU diem ciia phuang phap nay la co che don gian, tdc do lang dgng
cao, mang cd do day ddng deu, cd the dieu khien dugc kich thudc. De che tao hon hgp
hoi Zn va 0 trong phuang phap lang dgng tu pha hoi ngudi ta cd the thuc hien mgt sd
each sau:
Phuang phap phan hiiy true tiep ZnO rSn thanh hoi Zn va O
Z n O (ran)

> Z n (ho,) + O 2 (hai)

( 1 • 14)

Day la phuong phap dan gian, tuy nhien nd cd han che la nhiet dd che tao phai
cao (^1400 °C).
Phuong phap nung bdt Zn cd thdi khi oxy. Phuong phap nay la phuang phap true
tiap, rihiet do nung tuong ddi thAp (500 °C - 700 °C), nhirng ti sd giua ap suat hoi Zn va
oxy can phai dugc dieu chinh hel sue can than de cd the thu dugc cac cAu tnic ZnO nano
nhu mong muon. Ngirdi ta dA quan sat th/iy rAng s\r thay ddi ciia ti so nAy gdp phan lam
thay d6i Idn dkw mAu sAc ciia mAng cflng nhu dang hinh hgc ciia cac cau tnic nano.
Phuang phap gian tiep de tao ra hoi Zn bao gdm epitaxy tu pha hoi cua kim loai
hiju CO, ma trong dd hgp chat kim loai hiju co Zn, vi du nhu diethyl-zinc, dugc su dung
vdi luu lugng khi oxy hay N2O thich hgp.
Phuong phap hien nay dugc ap dung nhieu nhat la phuong phap nhiet cacbon, sir
d\nig bgt ZnO dirge Iron vdi bgt (' d5 lam v(it Ii$u nguon. U'u diem ciia phuang phap nay
la si,r xuat hi^n ciia C lam giam dang ke nhiet dp phan lu'iy ciia ZnO.
- Ngoai ra de tang hi?u suat cua phuang phap tren ngudi ta cdn cd th6 sir dung xiic
tac (Au, Pt, Ag, Ni...). Chat xiic tac nay se tac dung vdi hoi Zn tao thanh hgp kim. Khi
ndng do Zn trong hgp kim trd nen qua bao hda thi mam bat dSu dugc hinli thanh. DiSu
khien ldp xiic tac ta cd the dieu ki6n sir hinh thanh day nano ZnO. Co ch6 phat triSn day
nano ZnO cd xiic tac thudng la co ch^ hoi - Idng - ran (VLS). Trong khi co chg phat trign
day nano khdng cd xiic tac thudng la co chfi h(yi - rAn (VS).

I.2.C0 che pliAe trien dfiy hAii^ phuong phap hoc bay nhiyt don giiin
Tiiy thudc diSu kien che tao mau ma qua trinh phat triSn day se thdng qua 2 loai
CO che la co che hoi - rAn (VS) va co ch6 hoi - Idng - rAn (VLS).
7.2.5

Ca che hai - rdn (VS)


Trong CO ch^ VS, tinh thi cd the hinh thanh true tiep tir pha hoi ma khdng can sir
cd mat cua cac chat xiic tac.
Ban diu co chi nay dugc cho la do cac sai hdng mang, nhung vi?c xuat hi?n cac
day nano khdng sai hdng da chung minh dieu nguge lai. Them vao dd ngudi ta thay tdc
dg phat trien day cao hon loc dg ngung ty tu pha hoi. Co che nay cd the dugc giai thich la
do ZnO cd ciiu tnic dj hudng, \v\\c uu tien lA (0 0 2| - tryc mA dgc tiico nd iiAng lugng chu
de phat trien tinh the la thap nhat. Cac phan tii* khi Zn va ZnO|.x hap thu tir cac mSt khdng
phat trien day se khueeh tan len be mat (0 0 2). Tu day cau tnic nano 1 chieu ciia ZnO se
duoc hinh thanh.

00 I

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(b)
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Hinh 1.11: Mo hinh day nano ZnO phat trien theo co che VS
Trong CO che nay, do lugng hoi tdi vj trf ket tinh khdng ddng deu nen dudng kfnh
day nano khdng deu va giam dan ve phia dinh.
1.2.2 Ca che hai - long - ran(VLS)
Khac vdi VS, CO che VLS phat trien tinh the mgt each gian tiep thdng qua pha
Idng ciia kim loai xiic tac.
Kim loai xiic tac nay phai tro vdi vat lieu can che tao, cd ap suat hoi thap, ddng
thdi cd diem eclectic thap. Xiic tac nay cd the la cac chat nhu Au, Pt, Ag, Ni,... (trudng
hgp cd xiic tac) cung cd the la kim loai ciia chinh oxit (trirdng hgp tu xiic tac). Trong cac
mau khdng cd xiic lac, Zn ddng vai trd tir xiic tac. Hoi Zn dugc khi Ar dua tdi viing nhi^t
dp thap hon sg hda Idng. Cdn trong cac mau cd sir d\ing xiic tac (chAng h^n Au), hai Zn
vA /nOi.x tdi tAc d\ing vdi linh the Au (lining thai rAn) [[}o ihAnh hgp kim (cAc cau lu
khdng hda lan vAo nluui) va hoa long.
Gigt chat Idng trong ca hai trudng hgp se trd Ihanh dung mdi thich hgp dS bat cac
phan tu khf. ThS tich ciia cAc gigt chat Idng nay tang khi lugng hon hgp hoi tang. Tdi khi
chat Idng trd nen qua bao hda vdi hdn hgp hoi thi mam day bat dau hinh thanh qua phan
bien rAn - Idng. Trong qua trinh hinh thanh day, kich thudc gigt hgp kim khdng ddi, gigt
hgp kim ludn dugc day len phia trudc, phAn tinh the dugc hinh thanh dai dan ra vdi gigt
hgp kim d phfa cudi. Khi kcl Ihiic quA Irinh hinh thAnh day, gigt hgp kim dpng li;ii d cudi
day. Do qua trinh phat trien thdng qua pha Idng nen dudng kinh ciia cAc day nano phy
thudc vao kich thudc ciia giot chat long va khdng thay ddi trong sudt qua trinh ch6 tao.


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Hoi Zn vaZnOu,

1

Hoi Zn va ZnO|

w
O O O,

De Si cd phii vang

Gigt hgp kim
Au - Zn

^

P
Day nano,
thanh nano ZnO

Hinh 1.12: Ca che VLS phat trien day, thanh nano ZnO tren de co phu vang [3]
L2.4

Hien tirang can bang nhiet dgng

Tuong tu nhu ddi vdi day nano Si trong tai lieu [31] cd the md phdng qua trinh
hinh thanh day nano ZnO nhu sau:
cac nguyen tii* khi Zn va ZnOi.x bi khueeh tan vAo trong gigt chat long. Neu mau
khdng cd xiic tac vang, gigt chat long la hon hgp Zn va ZnO|.x. Neu mau cd xiic tac vang,
gigt chat Idng sg la hgp kim Au - Zn - ZnOi-x. Khi gigt chat Idng dat tdi trang thai qua
bao hda vdi nguyen tir Zn va ZnO|.x mam bat dau dugc hinh thanh. Trang thai can bang
nhiet dgng cua vat lieu cd the dugc md ta theo cdng thuc:

7rR'dL = —^Sdt

(] 16)

kT dx

^^^

trong dd D lA hC* so kluiyech lAii / n - ZnOi.x iren dc
R hi bAii kinh tifly nano
/J la the hda ciia cAc phan tir ZnO
S = IjrRa la dien tich khueeh tan
a la hang sd mang.
,_

IDa du

.

Mat khac do bien thien the hda hieu dung ciia cAc phan tir Zn - ZnOi.x trong day
nano va tren gigl chat Idng dugc tinh nhu sau:
A// = Aa-r^—'—

(M8)

A

trong dd ACT la irng suat trong ldp mang Zn - ZnOx
0) la the tich nguyen tir Zn, ZnOi.x
y la nang lugng mAl {v\\

Do bien thien the hda hieu dung A// chfnh bang tdng ciia hai phan nang lugng:
PhAn nang lugng.dan hdi tren mgt nguyen tir do su phuc hdi bi6n dang tren gigt chAt Idng
AOTy va phAn nang lirgng mat di tren mgt nguyen tir do su tAng dien tich hk mat ciia day


nano

- ^ . Ro rang khi b^a^lylr

(r la ban kinh gigt chdt long r « i ? ) thi A// = 0

day khdng phat trien niia.

iTm
p JUffflMi'ii
\
1
7 ^

Dl
>

r

///Az/z 7.75.- Md hinh day nano phat trien theo ca che VLS
IJ'ng sudt xuat hi?n chii yeu trong phan gan gigt vang. Do v^y khoang cAch ph\ic
hAi irng suAl lA X (hinh 1.13), khi dd:
di,i tS.^.L
(1.19)

dx

Cuoi Cling

IDa /ScTCO^

'lr"'Ti7

2r
AaR

(1.20)

Vay chieu dai day ty le thuan vdi thdi gian phat trien / va ty le nghieh vdi ban
kinh day R.
Thdng thudng Aaco I kT rAt nhd nen chieu dAi day bj han che dang ke khi khdng
sir dung xuc tac. De tang chieu dai day ngudi ta diing cac xiic tac vang. Chinh xuc tac nay
da tao ra hgp kim Au - Zn - ZnOi-x tao nen mgt pha Idng cd nang lugng hinh thanh mam
thAp dii dh phat trien cac day nano.


Ket-noi.com kho tai lieu mien phi
CHirONG II
THI/C NGHI$M
2.7

Phirtmg phap che tao vat li^u

Mau ZnO nano day da dugc che tao bang phuang phAp bdc bay nhi^t don gian.
Ban chAt ciia phuong phap nAy la sir lang dgng vat lieu tir pha hoi. LTu diem cua nd la co

chi dan giAn, tdc dg lAng dgng cao, mang cd dg day ddng deu, cd the dieu khien dugc
kich thudc.
2.7,7. Sa dd he boc bay nhiet dan gian [8]
Ld nung
o o o o o o o o o o o o

Ong thach

Khi

cap
nhiet

<

n^
nesi

B6t

tZZl CZI C=)
AT

t

O O O O O O O O O O O O

1

Ar

Hinh 2.1: Sa do he hoc bay va Id nung
He boc bay nhiet don gian gdm mgt Id nung hinh dng nam ngang dai 45 cm va
mgt he thdng diiu khiln. Thdng qua bd diiu khien ta cd the lap trinh san che do hoat
ddng ciia Id nhu nhiet do khdng chi, toe dg tang nhiet, tdc do ha nhiet, thdi gian dn dinh
nhi?t... Nhi?t dg cao nhat ma Id dat dugc la
1200 °C. Dd la nhi?t dp do dugc d
tam Id.
Thdng thudng Id dugc sir dung d nhiet do 1000 ^C. KhAo sAt sir phan bd nhiet
trong Id khi rihiet do dugc giCr dn dinh tai 1000 T cho thAy nhiet do phAn bd lech ve phia
trai, nhiet do tai tirng vi tri tren Id khA dn dinh theo thdi gian, sai sd nhiet do khdng qua
10 ^C.
NIU ehgn gdc tga dg tai tam Id thi s\r thay ddi nhi?t dp Id dpc theo tryc Id dugc
bilu dien bieu dien tren hinh 2.2 Ihco bAng s6 li^u lh\rc nghipm 2.1
chieu ddi U)
Hdng .:', /. I'hdnhd nhlC'l ci() Ihco

L (cm) T{°C)

L(cm)

T C'C) L(cm)

TC'C) Z.(cm)

r(°c)

L(cm)

r("c)

-22

330

-13

902

-4

1000

5

959

14

756

-21

458

-12

922

-3

1000

6

949

15

719

-20

570

-11

940

-2

1000

7

930

16

682

-19

655

-10

955

-1

998

8

912

17

640

-18

710

-9

969

0

996

9

891

18

600


-17

770

-8

977

1

991

10

869

19

549

-16

810

-7

984

2

984

11

842

20

490

-15

846

-6

991

3

979

12

815

21

415

-14

872

-5

996

4

971

13

785

22

330

1200

T

•

» • • — " 1

• "—

1 —

I

'

I

•

1

1

1
1

1000

I

U
m

800 -

^'

:

frfD
1
1

&

600

•

m
m

ffi
ffl

m

/

BB
200

ffl

1
1
1

m
400

•

1
1

m
m
ui

1

-24

.

N i r a 16 trai
1

-18

.

Nira 16 phai

1

1

I

1

-12

•6

0

1

1

6

•

1

12

a
1

1

18

1

L

24

Vi trf (cm)
Hinh 2.2. Phdn ho nhi^t do doc theo true cua Id
2.1.2. Quy trinh che tao
2.1.2.3.

Chuan hi

Vat lieu ngudn la bdt ZnO (99,9 %) va bdt C (99 %). Cac bdt ngudn dugc can
bang carl chfnh xAc. Ty le bdt ngudn ZnO:C tinh theo moi thay doi trong khoang tir
1:0,05 den 1:0,2. Hon hgp bdt ngudn dugc trdn ky trudc khi cho vao Id. Vat lieu ngudn
dugc cho vao Ihuyen sir rdi dAl vao giira Id (vi tri cAch tam 3 cm) noi cd nhiet dp cao nhAt.
Nhiet do Id dugc khdng chi tai To = 1000 T . Khi dd su biln ddi nhiet dp theo
tirng vi tri trong Id tuan theo quy luat tren hinh 2.2. Viec chpn nhiet dp dl phu thudc vao
each chpn vi tri dat de trong Id. Nhiet dp dl thudng dugc ehgn trong khoAng tir 500 °C

den 700 ""C. Nhu vay cac dl dugc dat d nira phAi ciia 16 each tam Id tir 15 din 20 cm.
Toan bd he thdng thuyen va de dugc dat trong dng thach anh hd hai dAu.
Dc la cac (am Silic (100) dirge rira .sa bo hAng con. Trudc khi lao man dc dirge
rung sicu am U'ong mdi Inrdng axcton khoAng 30 plit'il, roi say khd Uii W) "C trong Id say.
\^i!t iiAng cao hieu qiiA clic lao, sau khi ihAnh phan vai lieu nguon dugc chon phu hop, mdi
ldp vang xiic tac mdng dugc phiin xa len tren bl mat dl. Xiic tac dugc ehgn la vang (Au)
vi hoi vang cd ap suat thap va tro ve hda hgc so vdi vat lieu ZnO ban dAu. Xiic tac nay se
tao ra mdi trudng thuan Igi de hinh thanh va pRat trien cac day nano.
Trong qua trinh che tao mau cdn cd sir tham gia ciia khi mang Argon (Ar). Khi
dugc dua tir binh wen khi Ar cdng nghiyp vao mgl dau ong thach anh, dAu kia ciia ong
thach anh noi vdi mot binh dau nhdn. Dua vao the tich giot dau noi len tlieo thdi gian, la
cd the linh dugc luu lugng khi Ar qua dng. Tdc dp thdi khi dugc giir khdng ddi trong lAl
ca cac qua trinh che tao sao cho sd gigt dau xuat hien trong 1 phut la 60 gigt, ban kinh
mdi gigt la 0,5 cm. Vay luu lirgng khi thdi trong binh la:
8


Ket-noi.com kho tai lieu mien phi
(2.1)

v = 60.-;r.(0,5)^=3K4cmVphut
2.L2.3.

Chetqo

NhiC'l dg Id dugc dAl Ihco chuang trinh {\x ddng. QuA trinh nung dugc lhi,rc hi^n
iheo 3 giai doan bieu dien tren hinh 2.3.

1200

1

1

1

1

I

1

•

1

I

1000
/:

U

800
600

:^'

/ •

I

\

ill

400

III

s

m
m
m.ffl,

200

FU,
;

[!)

.J

'

L.

-

•

100

I

200

300

400

500

Thdi gian (phut)
Hinh 2.3. Che do nhiet do nung trong qua trinh che tao
Giai dogn 1: TAng nhi^^t lu nhi?t dp phdng len tdi 1000 ''C Toe dg tAng nhi?t lA 25
°C/ phut, d nhi?t dg cao, bgt carbon (C) trong dieu ki?n thilu oxy tAc dyng vdi oxy (O2)
sinh ra khf CO (chAt dgc, khdng mau, khdng miii).
(ran)

+ 02 (khi)

/ cao

(2.2)

> CO(khi)

Khi nhiet do tang len khoang 400 °C trong Id phat ra anh sang dd, khdi mau trAng
va miii hoi khet.
Cacbon va khi CO se ddng vai trd chat khir tAc dung vdi bgt ZnO sinh ra hoi Zn
va hai ZnOi.x (thieu oxy). CAc phan irng cd the xay rn hi |7 ,13|:
Z l l ( )(,fin)

'

^' (inn)

- > /^II (hin)

'' C O 2 (khi)

ZnO(rftn) "^ CO (kill) - > Zn (!,„,)

+ CO2 (khi)

ZnO(ran) "^ CO(khi) —> Z n O i - x (hoi) "^ C 0 2 ( k h i )

Z n (khi)

+ o2 (khi;

850"r

> ZnOi-x (hoi)

(2.3)
(2.4)

(2.5)

(2.6)

Trong qua trinh nay mam bat dau dugc hinh thanh.
Giai doqn II: On dinli nhivt, khdng chO nhivl dp d 1000 ''C trong 60 phiil. Trong
giai doan nAy loc do thdi khi Ar dugc khong che khoang 30 cm7phiit. Viec dieu khien
tdc do khi rat quan trgng vi qua trinh nay lien quan mat thiet tdi djnh hudng ciia cac dAy
nano. Cac phan irng (2.3) tiep tuc thuc hien. MAm dugc hinh thanh nhieu, qua trinh phAt
triln dAy vA oxy hda dAy bat dau xay ra.


Giai dogn 111: Ha nhiet, cho Id ngudi tu nhien tdi nhiet dg phdng. Trong giai doan
nay, day nano tiep tuc dugc hinh thanh va oxy hda cho tdi khi qua trinh phat trien dAy
dimg lai.
Sir hinh thanh day nano tren de dugc md ta tren hinh 2.4
Giai doan 1

Ddng Ar
«C)

• •••.

••

^300°C

o#«

^•^

^ 800 "C

<

Giai doan 2

Ddng Ar
«o

*

o**

•

.

•

^
•

^

•-. 'k-'^<^- ^
~300T

*

Giai doan 3

'Day ZnO

***** L6i

Zn

-V6^

ZnO

- ~800"C
Dong Ar
Day ZnO
L3i

Zn

'7..r\

~ 800 °C

~ 300 °C **

Hinh 2.4: Mo hinh mo td qua tnnh hinh thanh day nano [15].

10

-V6

Ket-noi.com kho tai lieu mien phi
2.1.2.3.
Thu san pham
Thdi gian de Id ngudi tu nhien tir 1000 °C tdi nhiet do phdng (30 °C) la khoAng 4 5 h. MAu thu dugc thudng cd be mat kha min. Mau cd mau anh den hoac trang due phu
thudc vao che do tao mau, cu the la khi nhiet do de cao mAu thu dugc cd mau trAng, khi
nhiet do de thap mAu cd anh den. Mau sac ciia mau dugc quyet dinh bdi do day ciia ldp
ZnO tren de.

I linh 2.5: Mau sau khi che tao


CHUONG III
KJ^T QUA VA BI$N LUAN
3.1.

Ket qua phan tich cau triic

ChAt lugng mgt mau phu thudc rAt nhieu vao cac thdng sd che tao nhu thanh phan
vat li^u ngudn, chat xiic tac, nhi^t dp,... Cac thdng sd ve ty 1^ moi giua cac v^it li?u
ngudn, dO dAy Idp vAng phii livn dc, nhitjt dO dl dugc thay ddi dl lim vi\ chi dd tAi uu cho
quA trinh tao mau ZnC) nano day. Dua vAo cAc kit qua phan tich cau tnic la cd the lim
dugc CO che hinh thanh va phAt trien cAc day nano ZnO.
Trong CO che VLS, hoi kim loai Zn se ddng vai trd tu xiic tac. Hoi kim loai nay
dugc khf Ar mang den vimg cd nhiet do thAp hon va ngung tu thanh gigt. Gigt chat Idng
Zn trd thanh dung mdi thfch hgp hAp thu hdn hgp hoi Zn va ZnO|.x, hinh thanh mAm va
phat trien thanh dAy ZnO. Tuy nhien kha nAng hinh thanh dAy nano theo co che VLS
trong trudng hgp [\r xiic tAc lA thap. MAm tinh the trong cA hai co che deu ty le vdi lugng
hoi Zn, ZnOi-x. Lirgng hoi nAy lai phu thupc vAo lugng carbon. Do vay sd lugng va hinh

dang ciia dAy phu thudc vao lugng carbon. Khi lugng carbon trong bdt ngudn nhd (hinh
3.1 a), sd lugng niAni quA it, sd lugng dAy tinh the dugc hinh thanh khdng dang ke, chung
phAn bd khdng deu tren de. Khi lugng carbon qua Idn, sd lugng vA kfch thudc mAm Idn
dAn den mat do va kich thudc cac tinh the Idn (hinh 3.1 d). Qua trinh oxy hda trong cac
thanh nano cd kfch thudc Idn nay xay ra khdng hoAn loan. Do dd trong loi thanh vAn Idn
tai kem. Thanh nano se cd cau tnic Idi vd vdi loi la Zn va vd la ZnO nhu cau triic thu
dugc trong [27, 29]. Dieu nay phii hgp vdi su xuat hien dinh nhieu xa dAc trung cho tinh
the Zn quan sat dugc tren hinh 3.2 d. Ngoai ra, lugng mAm Idn cdn gAy bat Igi cho qua
trinh tao tinh the. Bdi vi lugng mam Idn, Ap suat hoi tang, xac xuat hinh thanh sai hdng
tang, kha nang hinh thanh mam thir cap tang, day tinh the khdng cdn d dang don tinh the.
Vay thdng qua viec phan tich cau tnic, ta thay day nano trong cac mau khdng cd
xuc tAc vAng cd the hinh thanh theo 2 co che la VS va VLS. Ty le carbon trong vat lieu
ngudn cd mgt vai trd xiic tac rat quan trpng. Lirgng carbon tAng thi lugng day nano cung
lAng. Khi lugng carbon Idn, cAc mau thu dugc la cAc thanh nano da tinh the cd kich thudc
Idn, trong mau van cdn thanh phan Zn do chua oxy hda het. Ty le ZnO:C thich hgp nhat
cho viec hinh thAnh day nano ZnO IA 1:0,15.
3.1.1. Anh hwang ciia chieu day lop xiic tdc vang tren de
Tir ket qua khao sAl cau triic theo ty le bdt ngudn ta chpn thanh phan bdt ngudn
1:0,15 cho tat ca cac mau che tao. De dieu kien sir hinh thanh va phat trien day nano,
trudc khi che tao mau, de dugc plui Idp vAng vdi chieu day khac nhau lir 20 nm den 100
nm. CAc man ircn de plui vang deu dugc che li^io d che do nhi(Jl dd dl 7' - 600 "C, tdc dp
thoi khi V ' 31 A cm*/plnil \'A (rong thdi gian / ^= I h.
Anh SLM ciia cAc mau nAy dugc bieu dien trcMi hinh 3.3. Ddi vdi tat ca cAc mau,
cac dAy dugc sAp xep cd trat tu hon so vdi cac day trong mAu tren de khdng phii vang.
Tuy nhien chung chua dinh hudng dugc hoAn toan theo mot phuang xac dinh. Chieu day
cua mang Au tang thi dudng kinh ciia cac dAy cung tang theo, ddng thdi chieu dai ciia cAc
dAy giAm. Khi chieu day Idp mang la 20 nm va 25 nm thi day dai vai |im, cd dudng kinh
trung binh cd 36 nm va 40 nm tuxyng irng. Khi chieu day ldp vang len Idi 50 nni, cac cau
12

Ket-noi.com kho tai lieu mien phi
tnic nano thu dugc cd dang day dudng kinh Idn cd 60 nm. Chieu day ldp vAng Idn nhat
dugc khAo sat la 100 nm. Khi dd tren mau thu dugc cAc thanh ZnO ngan va cd dudng
kinh cd 130 nm.
D I tim hieu ky hon co che phat trien cac dAy nano, la se quan sat Anh SEM tai dAu
mill ciia cac day nano tren mau cd Idp vang lA 50 nm. I Mnh 3.4 lA Anh SEM ciia nipt day
nano Ifm ciing Ui mgl gigl chat Idng cd dirdng kinh
50 nm.

Hinh 3.4: Anh SEM cua mau ZnO che (ao vai d() day lop vdng 25 nm
Phd nhieu xa tia X ciia cac mau ZnO che tao tren de cd Idp vAng khac nhau dugc
chi ra tren hinh 3.5. Trong cac mau ngoai pha luc giAc ciia ZnO cdn xuAt hien them pha
vang vdi hai dinh ( I I I ) va (2 0 0). Chimg td trong mAu thuc sir cd vang. Trong phd
XRD ciia cAc mau cd Idp vang day cung thay xuAt hien dinh dac trung cho tinh the Zn.
Diiu nay cho thAy trong cac mau cd tinh the Idn vAn ton tai pha Zn.

Hinh 3.5: Pho XRD ciia cdc mau ZnO che tao tren de cd phu lap vdng
vdi d() ild\' khdc nhau: (a) 20 nm, (b) 25 nm, (c) 50 nm, (d) 100 nm
Cac kit qua phan tich cau tnic trcMi day vA dAc biet la sir xuAl hien giot hinh cau
tai cudi ciia day nano nAy la mot bAng chirng rd rang ve qua trinh phAt trien day dua tren
CO chi hoi - Idng - ran (VLS ) [29, 30]. Ban dau xiic tac vang d trang thai ran. Sau dd xiic
tac nAy lAc dung vdi hdn hgp hoi Zn vA ZnO^x d nhiet dp cao tao nen hgp kim Au - Zn ZnOi-x. Hop kim nay cd nhiet do ndng chAy thAp hon nhiet do ndng chay ciia vang. d
nhiet do cao, hgp kim hda Idng va trd thanh mdi trudng thuan Igi (dung mdi) hap thu hon
13


hgp hoi Zn va ZnOi.x. Khi lugng hoi hap thu tang, the tich gigt chAt Idng tAng. QuA trinh
nay dimg lai khi chAt gigt Idng trd nen qua bAo hda vdi hon hgp hoi Zn va ZnOi-x- Liic
nay mAm mdi bat dAu dugc hinh thanh va phat trien thanh day ZnO (the ran).

Trong sudt qua trinh phat trien, gigt hgp kim vang lien tuc bi day len. Do dd dinh
tinh the Au xuat hien trong tAt cA cac phd XRD (hinh 3.5). Hon the, the tfch gigt hgp kim
vang khdng bi thay ddi trong quA trinh phat trien dAy nen dudng kinh day hAu nhu khdng
thay ddi trong sudt quA trinh che tao. Vay kfch thudc va vi tri gigt hgp kim vAng se quyet
dinh kich thudc va vi trf cac dAy nano. Do day ldp vang eang Idn, kfch thudc gipt hgp
kim eang Idn dan tdi kich thudc dAy eang tang (hinh 3.3).
Khi dp day ldp vang la Idn nhat (hinh 3.3 d), mau thu dugc chi tdn tai cac thanh
ZnO nano vdi dudng kinh Idn va chieu dai nhd. Chieu dai ty le nghieh vdi ban kinh day.
Dieu nay hoan loan phii hgp vdi cdng thirc ly thuyet (1.20) da trinh bay trong chuong I.
Phd XRD ciia cac mau cd cac thanh nano dudng kinh Idn deu xuAt hi?n dinh dac trung
cho tinh the Zn chirng Id qua trinh oxy hda xay ra chua hoan loan.
Nhu vay ket qiia thuc nghiem mot lAn nira khang djnh rang co che phat trien day
nano tren de cd phii vang la co che VLS. Trong qua trinh hinh thanh mau, vang phu tren
dl tham gia vao gipt hgp kim va ddng vai trd xiic tAc. Dp day ldp vang quyet dinh kich
thudc tinh the ZnO. Dp day ldp vangcAng Icin, thiet dien day ZnO nano eang Idn va
chieu dai day eang nhd. Tinh the dAy ZnO kich thudc Idn thudng du kem do qua trinh
oxy hda khdng hoan loan. Vay chieu day tdi uu ciia ldp vang thich hgp cho day nano phat
trien la trong khoAng tir 20 nm den 25 nm.
Tdm Kii, thdng qua vi^c chpn ty 1$ bpl nguon thich hgp vA sir d^ing dl cd plui mpl
Idp vAng mdng, ta cd the dieu kicn dugc kich thudc day nano. Tuy nhien sir dinh hudng
vA djnh vj ciia cac day nano liii chua the dieu khien dugc bAng each sir dung dc phii vang
nay.
3.2.

Pho huynh quang nhiet do thap cua day ZnO nano

Mgt trong nhung irng dung ciia vat lieu ZnO cd cau tnic nano la cd the sir dung
chimg trong cac linh kicn quang dipn tir. Do do nghien ciru linh chat huynh quang ciia
cac mau nhan dugc la can ihict. Cac quy luat bien thien ciia nAn^ lugng huynh quang
Ihco nhiet dp do mfiu sO cho la nhieu thdng sd quy bau \\c\\ quan den cAu tnic vimg nAng

lugng ciia loai vat lieu nay. De hieu rd bAn chAt ciia cAc dinh huynh quang, mau ZnO tren
dl phii ldp Au day 20 nm da dugc do huynh quang tai nhiet do thAp. Cac phd huynh
quang dugc do trong dAi nhiet do tir 14,5 K den 300 K, sir dung budc sdng kfch thfch
X = 300 nm.
i.2.7. Cache tdi hap ciia huynh quang mien khd kien
Tren hinh 3.9 la tap hgp cAc phd huynh quang ciia mau. 6 mgi nhiet dp, trong phd
huynh quang deu quan sat dugc mot dai phAt xa rdng keo dai tir dai mau xanh da trdi din
xanh la cay vdi tam nam tai 2,5 eV va mot nhdm cac dinh tir ngoai (UV) hep. Dai huynh
quang xanh da trdi - xanh la cAy thudng dugc gAn vdi co che tai hgp hire xa qua cac mirc
sau (nut khuylt oxi, nguyen tir kem dien ke), cac trang thAi bay hoAc cAc trang thAi bl
mat. Cac gia thill ve cac co che dd thudng dua tren co sd ZnO la mgt oxit khdng hgp
thirc. Cac mirc nAng lirgng tao ra lidi cac loai sai hdng nhu mil khuylt oxi {V^^), nguyen
tir kem dien kS Zn,'\ mil khuyet oxi bj ion hda (KJ ), nguyen tir kgm diln ke bi ion hda
Zn ^' Zni'"". -. cd the ion tai trong vung cam ciia ZnO [20],
14


Ket-noi.com kho tai lieu mien phi
1.8x10

^

1 — I — f — I — I — 1 — 1 — I

1.5x10" -

1

r

^uvt

^ ^ - j
2.2

2.4

2.6

2.8

3.0

3.4

3.2

Nang lugng (eV)
Hinh 3.9: Pho huynh quang nhiet dg thap cua mau ZnO nano day
Tir hinh 3.9 cd the thAy ro dinh tai 2,5 eV rdng va hau nhu khdng thay ddi vi tri
khi nhiet dp thay ddi. Nhu vay dua theo quan diem ciia [21 ] cd the cho rAng day la td hgp
cua nhieu qua trinh chuyen mirc dugc chi ra tren gian dd nAng lugng hinh 3.10 nhu :
Vy~ -> V-^^ irng vdi 2,2 eV, Zn^ -> K;, irng vdi 2,32 eV, V^;; -> VB irng vdi 2.8 eV.

Vinui dan
1

I —

.y,

\ 2.:
2.8
r
:

3.13

3,3

1

2.2

113

IDA

3.3f
BF

D°}

1

t

•

Vime hda tri

Hinh 3.10: Mo hinh cdc mice dien tu trong ZnO
3.2.2. Ca che tdi hap cua huynh quang mien ti^ ngoai [15]

x7Q0

14.5 \L

X 190

37.1 K

x38

61.6 K

X 13

iiLLKNn.5 K

X 2.6

190.8 K

X 1.3

250.4 K300.0 K

3.0

3.2

3.4

3.6

3.8

Nang lugng (cV)
Hinh 3.11: Pho huynh quang nhiet do thap cua mau ZnO nano day
IS


,

r

«

*

Viec giai thich ngudn gdc cua cac dinh mien tir ngoai trong phd huynh quang ciia
ZnO dugc nhieu nha nghien cim quan tam, tuy nhien cd nhieu y kien khac nhau ve co
che phat quang. De khao sat ky han ve co che huynh quang mien cue tfm, dai phd tir 2,8
eV din 3,8 eV cua mau ZnO do trong dAi nhiet do tir 15 K din 300 K dugc chi tren hinh
3.11.
Cd the thay rang d nhi^t do thap, tai mien huynh quang tir ngoai, trong cac phd
deu xuAt hien 4 dinh. Tuy nhien do tuong quan cudng do phd nen cac dinh cd the ehdng
chap nhau. Tai nhiet dp 61,6 K sir tach phd tu nhien cd the quan sAt tdt nhat. Hinh 3.12
bieu dien phd huynh quang tai nhiet dp nay.
Phd huynh quang nhiet dp thAp vimg tir ngoai gdm 4 dinh: mot dinh tuong ddi

rpng tai 3,113 eV (dinh IV) va 3 dinh h?p (III, II, I) tai
3,243 eV, 3,316 eV,
3,362 eV tuong irng. Khi nhicl dp tang len, cAc dinh nAy bj djch ve phia nang lugng thap
Irong khi cudng dd ciia cluing giAm di. CAc dinh 1, II, 111 khA h(?p vA cd nAng lugng rat
gAn vdi nAng lugng viing cAm nen chung cd the dugc gan vdi co che tAi hgp exciton.
Dinh I bien mAt khi nhiet do xAp xi 166,1 K trong khi hai dinh (II, III) tdn tai tdi tan nhiet
do phdng.
I

5x10OX}

c
cr
j=

c
'>»
3

4x10

'

o

I

*

I

'

I

1

" Dirdng nt long Ix/p
Kit dinh I, II. III. IV

-

•

1

3.362 D'X
1
3.3 !6|
BF 1

3x10"

_

3.316 II
BF-LO

.

3.113
DAP
1

2x10' -

-O-

I

'

S0ll^ulhvcnghlCmtlolal6l,6K

1**1

Z'- -1

1x10

1

1

2.4

2.6

. . . . I

.''t.A.

2.8

3.0

3.2

3.4

Nang lugng (eV)
Hinh 3.12: Phd huynh quang ciia mau ZnO nano day do tai nhiet do 61,6 K
De lAm sang td ngudn gdc cua cAc dinh phAt xa nay, cAc sd lieu thirc nghiem dugc
fit bdi hAm ddi xirng Pearson Vll (vdi dg tin cay > 99.3 %) [14],
•m

y = A

2Vm.e^'^
nWe

-"

r(m-0.5)

1+4
W

: {X-Xr)
'- - ^

(3.1)

trong dd A lA cudng dp tfch phan, W lA ban do rdng (FWHM), m la he sd hieu chinh, xc la
Ipa dp dinh, and V la hAm dugc xAc djnh bdi:
\a)^\t"

\l(

{a

'{))

(3.2

Sir dung ham (it (3.1) cd the tach tirng phd thanh cac dai thanh phan vdi cAc dinh
tuong irng phii hgp. CAc phd thanh phan ciia dAi huynh quang cue tim tai 61,6 K cung
duoc bilu dien tren hinh 3.12.


Ket-noi.com kho tai lieu mien phi
Tir cAc kit quA fit la cd vi trf dinh, cudng dp tich phAn vA bAn dp rdng ciia cac
dinh UV. Dua vAo cAc sd lieu nay ta cd the xAc dinh dugc ngudn gdc cua cAc chuyen ddi
dien tir phat ra tin hieu huynh quang. Tren hinh 3.13 lA dd thi bieu dien sir phu thudc cua
nang lugng cac dinh pho I, II, III, IV vao nhiet do.
Cd the thAy rd rang cAc giA tri thirc nghiem ciia dinh I kha phii hgp vdi cdng thuc
Varshni [28]:
E{T)=I':{Q)-^—

(3.3)

trong dd £(0) la nSng lugng irng vdi vi tri dinh tai 0 K
a wk /3 la cAc tham sd thuc nghiem

100

160

200

250

300

350

Nhiet do (K)
Hinh 3.13: Sir phu thuoc cua ndng lirang dinh vdo nhiet do
Dua vao cAc sd lieu fit dugc ta cd the tinh toAn a = - 9 , 8 x 1 0 eV/K ,
J3 = - 8 0 0 K vA E(0) = 3,369 cV. Tir hinh 3.13 la thay vj tri dinh 1 cd nAng lugng Idn,
phii hgp khA tot vdi cdng Ihirc Varshni. Dinh I bj dap lAl d nhiet dp 166,1 K. Do vay dinh
I cd thi lA tai hgp ciia exciton lien ket vdi donor trung hda.
Dinh II va dinh III van tdn tai d nhiet dg phdng va vi tri dinh giAm theo nhiet dg
eham hon so vdi nang lugng viing cam. Dinh phat xa II da dugc nhieu cdng trinh bAo
cAo. Tuy nhien ngudn gdc ciia nd cdn lA vAn de phAi bAn luan. Mgt sd tAc giA cho rAng
dinh phAt xa nay lA exciton lien kit vdi acceptor trung hda [18, 19, 26, 32, 33]. Mgt sd tAc
giA khAc l^i cho rang dinh nAy lA do svr chuyen ddi hai di?n tir ciia exciton lien kit vdi
donor trung hda [18, 28], do lAi hgp ciia exciton lien ket vdi acceptor trung hda [19, 33]
hoac do cAc cap donor - acceptor [32]. Tuy nhien chiirig tdi ddng quan diem vdi cac tAc
giA [11] cho rang su phAt xa nay khdng the la su chuyen ddi hai dien tir ciia exciton lien

kit vdi donor trung hda, cung khdng the lA tai hgp cua exciton lien ket vdi acceptor trung
hda vi hai loai tai hgp nay bi dap tat d nang lugng thap, khdng tdn tai tdi nhiet dp phdng.
MsAl khac vi cac vach nay h<^p, vA giAm rAt eham theo nhipt dp nen khdng thi la pliAt xa
do tai hgp c^lp donor - acceptor (phan tich ve lAi hgp cAp donor - acceptor se dugc ndi rd
d phan sau). Cd the dua ra gia ihict rAng dinh II lA lAi hgp ciia hat lAi tren tap chAt vdi mpl
hsil lAi Ur do (Bound - I'rcc Bl'). Mau ZnO dugc che tao lA ban dan lo^ii n nen dinh II cd
thi la dien lir lien kit ircn doiu)r lai hgp vdi lo trdng lu do trong viing hda trj. Chuyen ddi
17
OAI HOC QUOC GiA HA N Q *
TRUNG TAM T N O N G TIN THQ V I E N

ZEZOZZ


nay ciing dugc nhieu tAc giA quan sat thay trong ZnO ca d nhiet do thap va nhiet do
phdng.
KhoAng each nAng lugng giOa hai dinh II va III ludn lA 73 meV. KhoAng cAc nay
xap xi dp dAi phonon quang dgc. Do dd dinh III cd the lA si,r l^p l*;ii phonon ciia dinh II
(BF-LO).
DAi phd rdng cudi ciing (dinh IV) giAm rAt nhanh khi nhiet dp tAng. Dinh nAy dugc
giAi thich lA do sir tAi hgp phAt xa ciia cAp donor - acceptor (DAP). Nang lugng irng vdi
vi tri ciia dinh nay dugc xAc dinh theo cdng thirc (1.9):
hco = AE -E^ -E^ + d nhi?t do thap cac hat lAi tren donor va acceptor vdi khoAng each r nhd s5 bj tai
hgp trudc, nAng lugng phAt xa Idn. Khi nhiet do tAng len cac hat tAi tren donor va
acceptor vdi khoAng cAch Idn hon se bi tAi hgp, nang lugng giam dan. Ket quA lA dinh
DAP djch nhanh ve phia nang lugng thap khi nhiet do tAng len.
Nhu vay bang viec phan tich dd thi sir phu thudc nAng lugng dinh huynh quan