Nghiên cứu chế tạo chuyển mạch nhiệt quang và ứng dụng

Noi dung va ket qua nghien curu 4.L Noi dung cac bao cao chuyen de Chuyen de 1 ''Cong nghe chitm tia dien tu vd che tao mang mong nhiet quang " Trinh bay tdng quan cac phuong phap che

DAI HOC QUOC GIA HA NOI

NGHIEN CtJU CHE TAO CHUYEN MACH

NHIET QUANG VA UNG DUNG

(Bao cao tong hgp

De tai Nghien ciiu khoa hoc dac biet cap Dai hoc Qu6c gia Ha Noi)

OAI HOC QUOC GIA HA NOI TI^UNG TAM THONG TIN THU VIEN

PT/5r>^

Ma so: QG-04.01 Chu nhiem de tai:

PGS-TS NGUYfiN NANG DINH

Ha Noi 2005

MUC lUC

« « ' ^^

I PHAN MODAU

LI Cac chu viet tat

1.2 Danh sach nhihig ngudi tham gia thuc hien

1.3 Danh muc cac hinh

1.4 Tom tdt nhung ket qua chinh

II NOI DUNG CHINH

1 Dat va'n de

2 Tong quan cac va'n de nghien cun

3 Dia diem, thoi gian va phuong phap nghien cihi

4 Noi dung va ket qua nghien cun

4.1 Noi dung cac bao cao chuyen de

4.2 Cong nghe che tao mlu va phuong phap nghien ciiu 4.3 Ket qua nghien cun

4.3.1 Che tao mSu

4.3.2 Nghien cun tinh chat

5 Thao luan va kien nghi

L PHAN Md DAU

L I Cac chur viet tdt

KHVL: Khoa hoc vat lieu DHCN: Dai hoc Cong nghe BDKL: Ban dan - Kim loai

NDP: Nhiet d6 phong

NDCP: Nhiet do chuyen pha SEM: Scanning Electron Microscope (Hien vi dien tu quet) XRD: X-ray diffraction (Nhieu xa tia X)

1.2 Danh sach nhOmg nguoi tham gia thuc hien

TS Tran Thi Tam

Th.S.Vu Ngoc Cham

TS.Nguyen Phuong Hoai Nam

PGS-TS Nguyln Thi Bao Ngoc

HVCH Le Ha Chi

TS Pham Duy Long

KS D6 Xuan Mai

CN- Dang Van Thanh

KSC Dang Quoc Trung

KSC Tran Anh Vu

KS Le Huu Minh

NCS Th.S.Le Dinh Trong

Co quan cong tac Trucmg DHCN, DHQGHN

1.3 Danh muc cac hinh

Hinh 1 So d6 he chan khong co chum tia dien tir

1 Sling dien tu, 2 Chen va vat lieu goc, 3 De va ga de co be'p d6t, Van dieu chinh d5ng khi 6xy, 5 Tu dieu khien

Hmh 2 Anh SEM be mat mang mong oxyt vanadi hoc bay bangky thuat chu

tia dien tu

Hinh 3 Gian do XRD tren mang VO2 tai NDP (A), dot nong 80°C (B) va Sc

khi de ngu6i vl NDP (C), Hmh 4 Pho tan xa Raman cua mang mong VO2 tai nhiet do 25 **C-NDP (1), t

90 '^C (2) va tra lai NDP (3)

Hinh 5 Anh SEM mat cat vuong goc cua mang mong VOj

Hinh 6 Dien trd suat phu thuoc vao nhiet do cua mang mong VO2

Hinh 7 Pho truyen qua cua mang mong VO2 tai nhiet do 27 '^C (< x^) va 90'

Hmh 8 Anh SEM chyp be mat cua mang VO2 truac (phan tren) va sau khi 1

ket tinh (phan duoi) Hmh 9 Pho truyen qua cua mang VO2 nano tai hai vung nhiet do thap hi

NDCP (30°C) va cao hon NDCP (80°C) Hmh 10 Pho truyen qua ciia mang VO2 nano tai hai vung nhiet do thap b

NDCP (30°C) va cao hon NDCP (80°C) Hmh 11 So do cau tao cam bien nhiet quang

1- Dau sgi quang co phu lop mang mong VO2 2- Bg phat, thu laser va so sanh tin hieu nhiet-quang 3- Vi tinh va hien thi so sanh pho

1.4 Tom tdt nhOmg ket qua chinh

1 Ten de tai:

Nghien curu che tao chuyen mach nhiet quang va ung dung

2 Ma so: QG-04.01

3 Nhufng ket qua chinh

a, Ket qua ve khoa hpc (nhirng dong gop cua de tai, cac cong trinh khoa hoc cong bo)

Xay dung phuong phap cong nghe che' tao mang VO2 micro va nano co tinh chSit

cam bien nhiet quang Cac ke't qua chinh dugc tong ke't a 5 cong trinh va bao cao khoa

hoc dudi day:

1 Nguyln Nang Dinh, Linh kien quang dien tu tren ca sa mang mong VO2 che tao bang chum tia dien tii Tap chi Khoa hoc DHQGHN, KHTN&CN, T.XXI, so 2AP

(2005)tr.8-15

2 Nguyln Nang Dinh, Le Dinh Trgng, Ifng dung phd tdng trd de nghien cicu tinh chat ddn ion cua mang mong chat ran Tap chi khoa hgc va cong nghe, Vien

KH&CN Viet Nam , nhan dang 12/2005

3 N.N.Dinh, T.T.Tam, V.X.Huong, D.H.Thanh, Electrical and Optical properties of nano-structured VO2 thin films prepared by e-beam deposition, Gui dang trong

Coom.in Physics, nhan dang 12/2005,

4 Nguyen Nang Dinh, Do Phuong Anh, Le Dinh Trong, Electrochromic properties

of vanadium oxide films made by high voltage spraying Advances in Nat.Sci.,

nhan dang 12/2005

5 Nguyln Nang Dinh, Tran Thi Tam, Nghien cihi che tao cam bien nhiet quang tren casdmdng mong VO2 cau trite nano, B/c tai Hoi nghi Vat ly toan quoc lan thii

6, Ha Noi, 23-25/11/2005

b, Ket qudphiic vu thitc te(cAc san pham cong nghe, kha nang ung dung thuc it)

Che tao thu cam bien nhiet quang, co hieu ung cam bien tot, Co the ap dung vao thuc te giam sat nhiet do moi truong chat long, khi doc lai

K^iU UlZ-t/i^-Nl^V^iT^ ,

c Ket qua dao tao (s6' lugng sinh vien, hgc vien cao hgc, NCS lam viec trong de tai)

Le Binh Trgng NCS nam thii hai; da co ket qua tdt ve che' tao mSu bang

chum tia dien tir, khao sat tinh chsft nhiet sac va cam bien nhiet quang

Trdn Quang Trung NCS nam cu6'i; da hoan thanh Ban thao luan an TS, se bao

ve luan an trong nam 2006

12 nam 2005

d Kit qua ndng cao tiem luc khoa hgc (nang cao trinh do can bg va tang cucmg tran^

thiet bi cho don vi)

Nang cao trinh do NCKH cho tap the khoa hgc, giang vien trong nhom Dl tai Trong do mot s6' can bg tiir trinh d6 cut nhan thanh thac sy, tijr thac sy thanh tien sy

Gop phan nang ca'p mot sd he thuc nghiem phuc vu do dac tinh cha't dien

e Tinh hinh sii diing kinh phi

Da thanh quyet toan dSy dia va dung theo quy dinh cua Phong Ke toan-Tai vu Trucmg Dai hgc Cong nghe, DHQGHN

CHU NHIEM DE TAI

PGS-TS Nguyln Nang Dinh

XAC NHAN CUA DON VI

L Titlle of the project:

Investigation of preparation of thermo-optical switching and application

2 Project code: QG-04.01

3 Main results

a Scientific results (contributions and pubhcations)

Developing technological method for preparation of micro- and nanostructured vanadium dioxide films with thermo-optical switching properies The results have been reported in 5 published scientific works, as follows:

1 N N Dinh, Opto-electronic devices based on VO2 thin films made by beam-deposition, J Sci.VNUH, Nat.Sci.&Tech., V.XXI, No.2AR (2005) pp.8-15

electron-2 N N Dinh, L D Trong, Application of impedance technique for investigation oi ionic conducting properties of tliin solid films, J Sci & Tech VAST, to be pubhsbed in Dec 2005

3 N.N.Dinh, T.T.Tam, V.X.Huong, D.H.Thanh, Electrical and Optical properties oj

nano-structured VO2 thin films prepared by e-beam deposition, J Coom ir

Physics, to be published in Dec 2005

4 Nguyen Nang Dinh, Do Phuong Anh, Le Dinh Trong, Electrochromic properties

of vanadium oxide films made by high voltage spraying Advances in Nat.Sci., tc

be pubhshed in Dec 2005

5 N N Dinh, T T Tam, Investigation of preparation of thermo-optical sensors based on nanostructured VO2 thin films, Proc the 6-th Nat.Conf.on Physics Hanoi 23-25/11/2005

b Application results (produces, application potentials)

Preparation of prototype thermo-optical svv^itching devices used for monitoring temperature change in oil or/and gaseous toxic storages

c Education results (number of students of BS, MSc and doctors working in tht subject)

Le Dinh Trong, Mr Ph.D student in the second academic year; having good

results in electron-beam technique for samples preparation and characterisation of theirs properties

Tran Quang Trung, Ph.D student in the last year; fulfilled the dissertation

Mr being defended in next year (2006)

Le Ha Chi, Mrs MSc student -¥1^ Cao hgc KION; se bao ve luan van

trong thang 12 nam 2005

d Results in the improvement of scientific power (scientific staff-members and equipments)

Improvement of science and technology experiences of the team, some of them have been got higher degree in science, e.g from BS to MSc., from MSc to Ph.D degrees

Partial contribution in up-grading some characterization set-ups

e Financial expenditures

Efficient use of the provided finacial sum of 60 milion VND and this sum has been completely cleared up

Director of the Project

Assoc.Prof Nguyen Nang Dinh

n NOI DUNG CHINH

1 D a t v ^ n d e

Vat ueu nhiet quang hay con ggi la nhiet sdc (thermochromic) dugc nhieu tap the khoa hgc tren the gidi chii trgng nghien cun la do vat lieu nay co nhieu tinh cha't dac biet ly thu va kha nang ung dung vao thuc tiln rat tilm tang, Trong so vat lieu nhiet quang thi mang mong VO2 la vat lieu thich hgp nhat de thie't ke' che' tao b6 dong ngat trong he vi chuyen mach th6ng minh Oxyt vanadi khong hgp thu'e co tinh cha't nhay khi, nhit la ddi vdi loai khi doc hai hay dl chay nhu hcfi con Khi mang mong 6xyt vanadi tiep xiic vdi loai khi nay thi dien tro bl mat thay doi dang ke Vi vay, mang mong 6xyt vanadi con co trien vgng ung dung trong linh vuc sensor khi de bao d6c, bao chay gop ph^n gin giu va bao ve moi trucmg Mot tinh cha't quan trgng khac

cua VO2 the hien a ch6 khi nhiet d6 ciia mang dat den diem chuyen pha ban din kim

loai thi ca tinh chat dien va quang ciia chung deu bie'n d6i mot each dot nggt va mang tinh thuan nghich Do vay, viec nghien cun cong nghe che' tao chuyen mach nhiet quang khong nhung gop phSn nang cao trinh d6 khoa hgc cong nghe vl quang dien tu

va quang tu cho can bg khoa hgc, giang vien ma con md ra kha nang ung dung vao thuc tiln che' tao cam bien nhiet quang su dung de phat hien nguong nhiet d6 cua moi trucmg gay chay no, doc hai ciia cha't long, xang ddu hay cha't khi

2 Tong quan cac van de nghien cihi

- Nhu cSu bao chay tai cac kho tang khi gidi hay cac tram xang dau ngay cang tro nen cap bach Hien nay viec bao chay dugc thuc hien thong qua cac cam bien nhiet do va

bao khoi chi thuc hien dugc tai cac cong trinh cong cong, nha a, kho kho De bao nguong nhiet do nguy hiem ngay trong tec xang dau hay a nhung khu vuc kho tang khi

gidi bi mat dat each xa tram quan sat thi cac cam bie'n hien dang su dung la khong thich hgp Do la do phan Idn cam bien nhiet dien diu phai dung den dien truong (dien the') hay dong dien, khi phai nhung chim trong xang dau se gay nguy hiem hoac do khoang each tCr noi dat cam bie'n den may do qua Idn khie'n do chinh xac giam nhanh

- De khac phuc cac nhugc diem tren co the su dung loai senso nhiet-quang, senso nay lam viec tren nguyen ly khi nhiet do tang den mot nguong nhat dinh thi chiet suat cua vat lieu trong senso thay doi, dan den do truyen qua/phan xa thay doi Qua viec giam sat do truyen qua, phan xa cua vat lieu co the phat hien-chinh xac su thay d6i cua nhiet

do trong moi truong (chat khi hoac chat long) Loai cam bien nay co uu diim:

• Su dung cap quang truyin tin hieu cho nen co the dat dau cam bien vao trong chat long hay tai cac dia diim each xa tram theo doi;

• La m6t loai cam bien nhiet - quang cho nen d^ duy tri hoat dong ciia senso

- i „ khong cdn co dong dien

- Dl tai nghien ciiu mang tinh cong nghe cao, tap trung giai quyet cac va'n dl vl sii

dung ky thuat bdc bay chiam tia dien tit di che' tao mang mong VO2 co tinh chit nhiet

sac, CO kha nang cam bie'n nhiet quang; nghien cun cac tinh cha't chuyin mach nhiet quang ciia mSu mang mong VO2 ctfu tnic micro, nano va kha nang iing dung ciia cam bi^n nhiet quang

Che tao mang mong VO2 nhiet sac tren co s6 oxyt vanadi co thi tien hanh bang nhilu phuong phap khac nhau, tuy nhien ky thuat chan kh6ng dung chum tia dien tii (bdc bay chiim tia dien tii) vSn la mdt trong sd phuong phap mang lai ket qua tdt va hieu qua Cac budc cong nghe trong phuong phap chiim tia dien tii va anh hudng ciia che' d6 cong nghe len tinh chat vat ly ciia mang mong VO2, dac biet la tinh chat nhiet-quang la cac va'n de chinh trong nghien cun cong nghe che' tao mlu Trong do, cac tham sd cong nghe nhu tdc d6 bdc bay, nhiet d6 de, dieu kien xir ly nhiet, cac loai de' khac nhau nhu thuy tinh phang, cap quang, dugc chii trgng nghien cun

Trong phan nghien ciiu tinh cha't, di tai tap trung vao dac trung tinh cha't chuyen

mach nhiet dien va nhiet quang ciia mang VO2 che' tao bang chiim tia dien tii Co che'

va tinh cha't nhiet sdc, kha nang cam bie'n nhiet quang cua vat lieu mang mong nay

3 Dia diem, thcri gian va phuong phap nghien curu

Cac nghien ciiu cong nghe dugc tien hanh tai PTN lien ke't giiia Trucmg Dai hgc Cong nghe (DHQGHN) va Vien Khoa hgc Vat lieu (Vien KHCNVN)

Nghien ciiu va dac trung tfnh cha't dugc tien hanh tai Khoa Vat ly ky thuat va Cong nghe nano, Truong DHCN Sii dung cac trang thiet bi trong Khoa va ciia Trung tam KHVL, Trucmg DHKHTN (DHQGHN) , Vien KHVL, Vien KHCNVN

dl phan tich ca'u triic vat lieu, do dac cac thong sd va dac trung cac tinh chat ciia mang mong VO2

Thoi gian nghien cun dugc bat dau tii 5/2004 va ket thiic vao thang 12/2005

4 Noi dung va ket qua nghien curu

4.L Noi dung cac bao cao chuyen de

Chuyen de 1 ''Cong nghe chitm tia dien tu vd che tao mang mong nhiet quang "

Trinh bay tdng quan cac phuong phap che tao mang mong nhiet s k tren co so oxyt vanadi, trong do co ky thuat chan khong dung chiim tia dien tir (phuong phap

10

chiim tia dien tii) Cac budc c6ng nghe trong phucmg phap chiim tia dien tii va su anh hudng ciia chd d6 cong nghe len tinh chit vat ly cua mang mong VO2, dac biet la tinh chit nhiet-quang Dd la tdc d6 bdc bay, nhiet do dd, dieu kien xii ly nhiet, cac loai de' khac nhau nhu Si, thach anh, thuy tinh ciu hinh phang, ciu hinh tru (cap quang),

Chuyen dl 2: 'Tinh chat chuyen mach nhiet quang trong ban ddn oxyt"

Nghien Clin tinh chit chuyin mach nhiet dien va nhiet quang ciia cac chit ban dan thdng thudng va ban dSn 6xyt (ban dan viing cim rong), dac biet nhin manh den loai di-6xit vanadi (VO2) Trinh bay co che' va tinh chit nhiet quang ciia mang mong nhiet sac

Neu ra cac linh vuc ung dung trong ky thuat va ddi sdng ciia vat lieu bien ddi nhiet quang, do la

• Tu dong hoa va dieu khien: sir dung trong viec chd tao may dieu nhiet, thie't bi chdng lai su qua tai nhiet, qua dien ap, dilu khiln tdc do mo to, bg kich xuit hien plazma va role nhiet

• Quang - dien tii: mang mong nhiet sac co trien vgng iing dung trong linh vuc ciia s6 th6ng minh

• Chuyen mach nhiet-quang: ke't hgp sir dung he laser ban dSn va cap quang, vat lieu phun phii nhiet quang dugc sir dung de che tao thiet bi bao nguong nhiet do ciia xang dau, chit long va chat khi doc hai

4.2 Cong nghe che tao mau va phuorng phap nghien curu

Tien hanh thuc nghiem che tao vat lieu mang mong VO2 tren cac de trong sudt nhu thuy tinh chiu nhiet, thach anh, sgi quang, v.v Nhan tha'y thuy tinh Corning glass 2476 va sgi quang co the dung lam de thich hgp de che tao senso nhiet quang;

Khao sat ciu true tinh the bang phuong phap nhilu xa tia X, cau true phan tii bang phd tan xa Raman cua cac mSu che tao dugc;

Nghien ciiu tinh chat nhiet quang cua vat lieu thong qua cac phep do phd truyen qua, phan xa phu thuoc nhiet do, tim ra dieu kien tdi un trong cong nghe tao mau CO nhiet cam bien viing thich hgp;

11

4.3 Ket qua nghien curu

4.3.1 Che tao mdu

Mang mong 6xyt vanadi dugc lang dgng tren de thuy tinh bang ky thuat chum ti dien tii thuc hien tren he YBH-75-PI (Hinh 1) Vat lieu gdc diing dl bdc bay la be dxyt vanadi V2O3 hoac VO2 hay hdn hgp cac oxyt V2O3 va V2O5 dugc ep than vien ( 0 = 10 mm; 1 = 8 mm) Vat lieu gdc nay dugc dat vao bdc dung vat lieu tron budng chan khong, ap suit cd thi dat tir 10^ den lO'^Torr Khoang each tir vat lieu gd den de' ket tinh tii 30 den 50 cm Nhiet do dd dugc giu" cd dinh tai nhung gia tri tron khoang tijt 200 ddn 400 "C Dong catdt c6 8 den 10 A; Dong tai (andt) dat tii 40 den 8

mA Thdi gian bdc bay tii 10 de'n 15 phiit Ngudn nang lugng diing de kich thich ca phin tii bay hoi la chiim tia dien tii co nang lugng cao dugc hoi tu tren bia vat liei D6ng nang ciia dien tii co the dat tir 7 den 10 keV tuy thuoc vao dien the' cao ap Chiir tia CO kich thudc tieu diem vao co Imml Khi hoi tu vao ngudn vat lieu, nd tao nen mc viing nhiet do rit cao lam cho cac phin tii ciia vat lieu bi thang hoa hay bdc hoi Chiin tdi dd lien ket tao thanh mang

mong tren dd Trong trucmg hgp

vat lieu gdc la V2O3, mang mong

hinh thanh sau khi lang dgng

thudng cd mau den, the hien mau

ciia vat lieu giau kim loai vanadi

Mau ciia mang chuyen sang mau

xanh sSm khi vat lieu gdc dugc six

dung tuong la VO2 va vang nau

ddi vdi vat lieu gdc V20g Do

sang dan ciia mang lang dgng the

hien miic do thieu hut oxy ft hon

Dudi day la anh SEM chup be mat

mau mang mong oxit vanadi

(Hinh 2) lang dgng tii vat lieu gdc

V2O3, cho tha'y kich thudc micro

mang cd do min tuong ddi cao

Hinh 1 So do he chan khong co chiim tia dien

1 Sung dien tii, 2 Chen vd vat lieu goc, 3 De

gd deed hep dot, 4 Van dieu chinh ddng hhi

5 Tu dieu khien

12

.':-•: \ r-ik V^'i

Hinh 2 Anh SEM bl mat mang mong oxyt vanadi bdc bay bang

ky thuat chiim tia dien tii

4.3.2 Nghien cthi tinh chat

a Can true tinh the Bang cong nghe chiim tia dien tii ket hgp vdi quy trinh tai ket

tinh thich hgp chiing tdi da nhan dugc mang mong dcm pha VO2 tai nhiet do phong cd ciu true mang tinh the thudc he don ta VO2 co chuyin pha BDKL tai nhiet do trong khoang 65°C -^ 68"C, do thang giang ciia NDCP phu thudc vao phuong phap che tao va ban chit vat lieu de Dl khao sat mdt each tudng minh su thay ddi ciu tnic tinh the trong qua trinh chuyen pha BDKL, chiing tdi su dung phuong phap phan tich nhilu xa tia X ngay tren miu dugc ddt ndng MSu dugc ga dat tren phie'n thuy tinh dan dien In203: Sn (ITO) kich thudc 10 x 20 cm^ che tao tai phong VL&CN Mang mong, dien trd bl mat ciia ITO la 50 Q/^, khi dat dien ap mot chieu tir 5 V de'n 20 V len hai dai tiep xuc thi VO2 dugc cung cap mdt nhiet lugng dii Idn de dat nhiet do trong khoang tir 30"CdenlOO"C

NDCP cua VO2 nam trong dai nhiet do nay Do vay bang viec ghi cac gian dd nhilu xa tia X tren m4u ddt ndng d nhiet do khac nhau cd the khao sat su thay ddi cau triic ciia mang VO2 theo nhiet do

13

i

Tren hinh 3 trinh bay ba gian dd nhilu xa tia X ghi dugc tren miu d NDP, tai 80"C va sau khi de ngudi ve NDP Tii cac gian dd nay cd thi nhan thiy su bien ddi thuan nghich cua ciu triic tinh thi VOj tii pha dcm ta sang pha tii giac Thuc vay, tren

hinh 3A la gian dd nhilu xa tia X ciia mang d NDP (<x^) cd hai dinh nhilu xa tai gdc

20 = 39,96 va 40,35 do, tuong ung vdi cac mat mang tinh thi cd khoang each d = 2,253; 2,233 A" thudc ciu triic mang don ta ciia tinh the VO2 Ddt ndng miu den nhiet

dd 80 "C (> x j , hai dinh nhilu xa nay dich vl vi tri tuong iing vdi goc 20 = 39,81 va 40,05 do vdi mat mang co khoang each d = 2,262; 2,248 A° thudc ciu triic mang tii giac cua tinh thi VO2 (Hinh 3B) Nhu vay hai dinh nhilu xa tai gdc 29 = 39,96 va 40,35 do da dich tuong iing 0,15 do va 0,30 do ve phfa gdc nhd, nghia la khoang each d

da tang len mot lirgng Ad « 0,0125 A°, ciu true mang tinh thi VO2 dugc sip xep lai vdi bac ddi xiing cao hon De miu ngudi trd vl NDP, hai dinh nhilu xa nay lai dich ve vi tri ban dau (Hinh 3C) Tren co sd phan tfch ban chit ciia hai pha ciu true mang tinh the VO2 nhan thay, sir dich thay ddi Idioang each mang tinh thi nhu tren la hoan toan phii hgp vdi su dich chuyen khdng Idn lim ciia cac vi trf nut mang tii dcm ta sang tii giac

Hjnh :> Gian do XRD ciia mang mong VO2 tai NDP (A), tai 80 "C (B)

va sau khi dl ngudi trd ve NDP (C)

14

Ke't qua nay chiing td chuyin pha BDKL trong VO2 thuc chit la chuyin pha loai I - gin liln vdi su thay ddi ciu tnic mang tinh thi Nhu da bidt ciu true mang tinh thi d trang thai bin vfing khi nang lugng tu do trong lien ket cd gia tri nhd nhit Dilu nay chiing

td tai nhiet dd cao hem x^ nang luong tu do ciia mang tii giac nhd, ngugc lai tai nhiet dd

thip hem Tc thi mang dcm ta lai cho gia tri nang lugng tu do nhd hem

b Cau triic phan tit Chiing tdi cung dung ngudn ddt mlu tuong tu nhu tren gin vdi he

do phd tan xa micro-Raman LABRAM-IB de khao sat su thay ddi ciu true phan tii ciia lien ke't VO2 trong chuyin pha BDKL Day la phep do phd Raman tiic thi ("in situ Raman scattering spectra") khao sat su thay ddi phd dao dgng phan tii phu thudc vao nhiet dd

1 8 0 0

*<o D) 1 2 0 0

c

§

- 900 D) 6 0 0

15

phan tii ciia cac lien kdt V-O trong mang tii giac ciia tinh the VO2 Khi miu ngudi vl NDP phd tan xa Raman lai dugc thidt lap nhu phd ban diu Phd tan xa Raman ciia mang mong VO2 phu thudc nhiet dd cung mang tinh thuan nghich, gidng nhu trong phep do ciu true tinh thi d phin tren Su thay ddi phd Raman d nhiet dd cao cung ndi len ring, mang tinh thi VO2 da dugc cung cip mot nhiet lucmg cin thiet lam dich chuyin cac nguyen tii vanadi vl vi tri cin bang iing vdi nang lugng tu do thip nhit trong lien kdt mang

Nhu vay, bang hai phep do in situ ve ciu true tinh thi va phd tan xa Raman diu nhin dugc hien tugng chuyin pha BDKL mang tinh thuan nghich

c Tinh chat dien vd qiians

cl Tinh chat dien Dl xac dinh chinh xac NDCP, chiing tdi da thuc hien phep

do dien trd bl mat (dien trd vudng) phu thudc vao nhiet dd MSu dugc dat trong thermostat, cac tiep xiic dmic kim loai tren VO2 dugc ndi vdi may do dien trd Gia tri ciia dien trd vudng dugc tinh ra dien trd suit theo cdng thiic p = Rn x d Chilu day d ciia mang mdng VO2 dugc kilm tra khdng chi bang thie't Ellipsometer tren co sd phuong phap do triet tieu anh sang ma con dugc do bang ca phuong phap hien vi dien tii quet (SEM), chup mat cat vudng gdc ciia miu SEM cho thiy, mang cd do day vao khoang 230 nm (Hinh 5)

Hinh 5 Anh SEM mat cat vudng goc

ciia mang mdng VO2

Ke't qua do dudng tri nhiet dien (trd suit - nhiet do) ciia miu dugc trinh bay tren hinh 6, cd thi nhin thiy cac dac diim quan trgng sau day cua dudng tri nhiet:

- Tir NDP ddn 66°C dien trd suit giam tuan theo quy luat ciia chit ban din, gia tri nang lugng kich boat dat 0,35 eV;

- Tii 90 °C trd len dien trd suit hiu nhu khdng thay ddi va cd xu hudng tang theo chilu tang ciia nhiet do, thi hien qui luat vat lieu thudc pha kim loai Trong dai nhiet

dd nay mdt kim loai thuin nhit nhu nhdm hay ddng se thi hien rd su giam do din (dien trd suit tang) do do linh ddng ciia dien tu giam Bieu hien nay quan sat thiy khi miu dugc ddt ndng tii 100 °C trd len thi dien trd suit tuong ling tang tii p = 3 x 10^ Q.cm de'n p = 3,5 x 10"* Q.cm

- Tai nhiet dd 67,0°C ± 0 , 1 ^C gia tri dien trd suit ciia mang giam rit nhanh,

"budc nhay" (tiic la ty sd p^J PKJ vao cd bang 10^ vdi dd Idn ciia dien trd suit p = 2 x

10" Q.cm (tai nhiet dd 66°C) giam xudng den p = 1,2 x 10"^ Q.cm (tai nhiet do 76"C)

va do rdng dudng tri nhiet la 8°C Dieu nay chiing td qua trinh chuyin pha BDKL da xayratai67"C

- Qua trinh xay ra ngugc lai khi miu dl ngudi, tai nhiet do 67"C gia tri dien trd suit ciia mang tang dot ngdt (PKL/PBD ^ 10"^)» cudi ciing nd dugc thie't lap lai gia tri dien trd suit ciia pha ban dSn

c2 Tinh chat quang Trong chuyen pha BDKL chiet suit ciia VO2 giam do ciu triic tinh the thay ddi tii mang don ta sang mang tii giac lam cho do phan xa tang (do truyin qua giam), nhit la trong viing hong ngoai Tfnh chit nay rat co y nghia iing dung thuc tiln bdi vi trong tdng nang lugng ciia biic xa mat trdi chieu tren mat dit thi

biic xa vung hong ngoai chiem tdi tren 50 %

De khao sat do truyen qua phu thudc nhiet do ciia mang trong vung biic xa hdng ngoai, mau can dugc dot ndng lien tuc trong sudt thdi gian do

Do truyin qua phu thudc vao nhiet do cua VO2 tai budc sdng X = 1^50 nm cung

da dugc khao sat, nhiet do cua miu dugc tang tir thap len cao (tii NDP den 90"C) va giam ngugc lai tii cao xudng thip Trong khoang NDP den 66"C, do truyen qua gan nhu khdng thay ddi va dat co 65 % Dieu nay cd the dugc giai thich la do d nhiet dd

17

OAI HOC QUOC G\A MA NOt TRUNG TAM THONG TIN 'W ^/'EM

PT / 51?F

thip hem Tc VO2 thudc pha ban din cd dd phin cue ion Idn do dd cd chidt suit Idn Khi nhiet do tang len cao hem 67 °C, dd truyin qua giam ddt ngdt do mang VO2 da chuyin sang pha kim loai Dd truyin qua giam xudng thip cdn 15 % va gin nhu khdng thay ddi sudt dai nhiet dd tir 75°C den 90°C Dd truyen qua giam phan anh do phan xa tang (vi dd hip thu ciia mang mdng VO2 trong chuyin pha hiu nhu bang khdng) Vdi tinh chit phan xa cao trong viing hdng ngoai, mang mdng VO2 d nhiet do cao da thi hien ro dac trung cua pha kim loai Khi giam din nhiet do cua miu vl NDP, qua trinh xay ra ngugc lai Kdt qua cho thiy mang mdng VO2 con cd tinh chit bien dieu nhiet - quang thuan nghich

Nhu da biet, biic xa mat trdi la

tap hgp Idn cac phdtdn vdi nhung

dai nang lugng khac nhau Tuy

nhien, dai sdng tur 300 den 2500 nm

la viing dugc quan tam nhilu hon

ca Hieu iing nhiet sic cua mang

mdng VO2 dugc khao sat trong

vung nay (hinh 7) O viing kha

kien, do truyin qua cua miu ddt

ndng (T90 > Tc), Idn hon khoang 10

500 1000 1500 2000 2500 Bu6c song (nm)

Hinh 7 Pho truyin qua ciia mang mdng VOj tai nhiet do 27 °C (< T,) va 90 "C (> T,)

% so vdi do truyen qua ciia miu tai nhiet do phong (T^^p < TJ Ngugc lai, d vung budc

sdng hdng ngoai, tii 750 nm den 2500 nm, khi T > T^, do truyen qua da giam xudng

dang kl, vi du tai budc sdng A, = 2300 nm do truyen qua giam til 65 % xudng con 15

% Khi ha nhiet do xudng dudi T^, phd truyen qua dugc lap lai hoan toan triing vdi phd ban dau Hieu iing nhiet sic mang tinh thuan nghich

d Cam bien nhiet ciuans tren casaVO-y can true nano

dl Cau true be mat Mang VO2 cau tnic nano cQng dugc che tao tir phucmg phap

bdc bay chiim tia dien tii, nhung de khong dugc dot ndng va tdc do bdc bay nhd hon Tiep theo cung la qua trinh li nhiet, vdi tdc do tang nhiet do Idn hon so vdi qua trinh u trudc day

18

Tir anh SEM ciia mat cit miu da xac dinh chieu day cua mang, vao khoang 210 nm Sau khi u, mang dugc kSt tinh, chiSu day tang len khoang 20 - 25 % Vi mang bdc bay len tren dS ngugi thudng la vd dinh hinh va giau vanadi (thi6u dxy), do trong qua trinh tai ket tinh, cau tnic vd dinh hinh bien ddi thanh cau tnic tinh the, cimg vdi viec nhan them dxy tir mdi trudng li (dxy hda nhiet) Trong cac thi nghiem trudc day, binh thudng chieu day chi tang len cd 15 % DiSu nay chiing td mang VO2 nano cd do xdp cao hon thudng le Ciing tir anh SEM, nhung la anh be mat, cau tnic nano cua mang VO2 the hien rat ro rang (hinh 8) Kich thudc trung binh ciia cac hat xac dinh tir anh SEM la llOnm Nghia la Idp mang mong VO2, mdt each gan dung, co the coi nhu mdt Idp cau tao tir hai Idp don hat nand

* Tinh chat chuyen mach nhiet quang

Mang mdng cau tnic nand co tinh chat

chuyen pha KLBD the hien rat rd tai nhiet

do 63°C (hinh 9), thip hon NDCP cua mang

VO2 thdng thudng hay VO2 tinh the khdi

Dieu nay c6 the giai thich la do nang lugng

tu do trong vat lieu nand thap hon (bdi sir

sap xep mat trat tu ciia cac hat nand dat miic

do cao) Pha cau tnic ben viing ciia mdt vat

ran tdn tai ung vdi nang lugng tir do thap H*"*^ ^- ^^^ SEM chup bl mat ciia

mang VO2 trudc (phan tren) va sau nhat Qua trinh chuyen pha KLBD xay ra khi tai kit tinh (phk dudi)

khi nhiet do ciia mau tang len den gia tri tdi

ban nhat dinh Nang lugng can thiet cho qua trinh chuyin pha ty le thuan vdi nang lugng tu do

ve mat ciu tnic tinh the, c6 the ndi, dd chinh la nang lugng tdi thilu dl "dich" chuyen cac nguyen tir trong mang tinh the tir vi tri ciia mang don ta (img vdi pha ban din) sang vi tri ciia mang tii giac (img vdi pha kim loai) Do do tai NDCP dien trd suit ciia mang VO2 ha dot ngdt, gia tri dien trd suit giam gin ba bac Tai viing nhiet do cao hon NDCP, VO2 cd cau tnic tii giac thudc pha kim loai Do mang mdng cho nen 0 vimg nhin thiy VO2 vin trong sudt, nhung d viing hdng ngoai he sd phan xa tang len -tinh chat dac trung ciia pha kim loai Vi vay, do truyin qua giam

19

Tren hinh 10 la pho truyin qua ciia mang VO2 phu thudc nhiet do Tai budc sdng

2500 nm, do truyin qua cua mang V02-nhiet do cao giam xudng dudi 10% (trong khi

T cua VO2-NDP cao din 60%) Gia tri sai khac trong do truyin qua dat 50% Tuy nhien, budc sdng ma chiing ta quan tam lai la 1550 nm, dd la budc sdng phat ra ciia laser sgi quang Tai budc sdng nay, do sai khac trong phd truyin qua dat gia tri 35% Vdi sir khac biet nay, VO2 cd thi sii dung vdi tu each mot sensor nhiet-quang trong cdng nghe che tao cam bien nhiet-quang

Hinh 9 So sanh dudng tre nhiet cua VO2

ciu tnic nano (dudng lien) va VO2 thong

thudng (dudng net diit)

500 1000 1500 2000 2500

Budc song (nm)

Hinh 10 Pho truyen qua cua mang VO2 nano tai hai vung nhiet do thap hon NDCP (30°C) va cao hon NDCP (80°C)

So dd cau tao ciia cam bien nhiet-quang dugc trinh bay tren hinh 11 Nguyen ly boat dgng ciia cam bien nay dugc md ta nhu sau Tia laser hdng ngoai dugc truyen vao sgi quang ma phia dau cua nd da dugc phu lop mang mdng VO2 Khi nhiet do ciia dau sgi quang cdn thap, tia laser xuyen qua lop mang hau nhu hoan toan, do do phd phan

xa rit thap Khi nhiet do tang len den 63 °C (NDCP cua V02-nand), tia laser dugc phan xa ngugc lai vdi phd phan xa cao hon han So sanh hai phd phan xa nay, bg phan hiln thi cua may cho chiing ta biet nhiet do ciia mdi trudng da tang len den nguong cao blng NDCP ciia dau sensor Tren thuc te, khao sat tren he cam bien nhiet quang thii nghiem, da nhan dugc hieu img chuyen mach Tin hieu phat ra tir laser din dau sgi quang dang 0 65*^0 da dugc phan xa lai vdi he sd phan xa vao khoang 25%, Idn hon bin tin hieu phan xa khi dau sgi quang d nhiet do phong

20

I K'.-v? ^•.:^^.^'

•

Hinh II Sa do cau tao cam bien nhiet quang

1- Dau sai quang co phii lap mdng mong VO2 2- Bo phdt, thu laser vd so sanh tin hieu nhiet-quang 3- Vi tinh vd hien thi so sanh pho

5 Thao luan va kien nghi

- Tun ra quy trinh che tao vat lieu mang mdng don pha VO2 cd tfnh chat cam bien nhiet-quang;

- Hinh thanh hudng nghien ciiu ung dung trong ITnh vuc quang dien tir va quang tir trong Trudng DHCN, vdi ddi tugng cu the la vat lieu dxit cau tnic nano Thdng qua de tai nay nhieu sinh vien, hgc vien cao hgc va nghien ciiu sinh da dugc true tiep thuc hanh, thuc tap va nghien ciiu khoa hgc ve chuyen nganh vat

ly ky thuat va cdng nghe nano;

- Ddng gdp cac cdng trinh khoa hgc cd chit lugng tdt cung nhu cac bao cao khoa hgc tai cac hdi nghi chuyen nganh

Viec cap kinh phi (tuy khdng Idn llm, sau muoi trieu dong) mot each kip thdi cua DHQGHN da tao dilu kien thuan Igi cho nhdm de tai hoan thanh tdt cac muc tieu va ndi dung dang ky Ddng thdi dieu nay cung chiing td nhdm de tai da sir dung kinh phi dugc cap mot each cd hieu qua

21

5.2 Kien nghi

Trong tinh hinh hien nay, tren the' gidi khoa hgc va cdng nghe nano dang dugc diu tu rit Idn, cho nen chiing tdi cho ring cac dl tai vl linh vuc nay trong DHQGHN cung cin cd su uu tien hon vl kinh phi Miic cip kinh phi nen ning Idn 100 trieu ddng cho cac dl tai dac biet va 500 trieu ddng cho cac dl tai trgng diim

IIL TAI LEU THAM KHAO

Tai lieu tieng Viet

[1] Dd Hdng Thanh, Phan Van anh, Pham Gia Ngir, Vd Vgng, Nguyln Nang Dinh,

Nghien citu su hinh thanh cau triic tinh the vd ca che chuyen mach cua mdng mong VO2 che tao bang chum tia dien tit, Hdi nghi Vat ly Chit ran toan qudc lin

thii III - Nha Trang ^ M ^ P

[2] Nguyln Nang Dinh, Nguyln Thi Tii Oanh, Pham Duy Long, Dd Hdng Thanh,

Mdng mong bien ddi nhiet - dien - quang: cong nghe, tinh chat vd ITnh vuc itng diing, Hdi nghi Vat ly Chit rin toan qudc lin thii III - Nha Trang 8/2001

[3] Nguyln Nang Dinh, Linh kien quang dien tit tren ca sd mdng mong VO2 chef go

bang chiim tia dien tit, Tap chi Khoa hgc DHQGHN, KHTN&CN, T.XXI, sd

2AR(2005)tr.8-15

[4] Nguyln Nang Dinh, Le Dinh Trgng, Ung dung phd tdng trd de nghien cicu tinh

chat dan ion ciia mdng mong chat ran Tap chi khoa hgc va cdng nghe, Vien

KH&CN Viet Nam , nhan dang 12/2005

[5] Nguyln Nang Dinh, Trdn Thi Tam, Nghien citu che tao cam bien nhiet quang

tren cd sd mdng mdng VO2 cau triic nano, B/c tai Hdi nghi Vat ly toan qudc ISn

thii 6, Ha Ndi, 23-25/11/2005

Tai lieu tieng nude ngoai

[1] Chipindale A.M., Dicken P.G and Powell A V "Synthesic Characterization and Inelastic Neutron Scattering Study of Hydrogen Insertion Compounds of

VO2 iRuXilQy',Journal of solid State chemistry 93 (2001) pp 526-533

[2] Dachuan - Yin, Niankan- Xu, Jingyu - Zhang "Vanadium dioxide films with

good electrical switching property" Journal of Physics, D, Applied Physics V.29

(1996) pp 1051-1057

[3] David Rauh R and Cogan Stuart F "Counter electrodes in transmissive Electro

chromic hght modulators" Solid State ionics, 28/30 (1988) pp 1707-1714

[4] Duplan Carole Alfred, Masso Jean, Gavarri Jean-Raymond and Cesari Claude

"Variable electrical properties in composites: Application to vanadium dioxide

22

pigments in a polyethylene host" Journal of Solid state Chemistry 110 (2000)

pp 6-14

[5] Gerbstein Yu M Smimova T.V and and Chudnovskii F A "Light absorption

by droplets of metalUc phase near the Semeconductor - metal transition in VO2", Pisma V Zh Eksp Teor Fiz., 25 (2001) pp 474-476

[6] D.H Thanh, P.D.Long, V.T.Bich and N.N.Dinh, Structural formation and Raman scattering spectrum of vanadium oxide thin films made by electron beam deposition Communications in Physics, Vol 8 (1998) N.3, pp 152-158 [7] D H Thanh, P D Long, P.V Anh and N, N Dinh, Characterization of VO2 and V2O5 thin films made by electron beam deposition and high dc-voltage spraying, "Trends in Materials Science and Technology", Proc IWOMS-III, Hanoi, November 2-4, 1999, p 415

[8] D H Thanh, P.V Anh and N.N.Dinh, Gas sensing properties of vanadium oxides films made by high Dc-vohage spraying Communications in Physics, Vol.10 (2000) N.l, 39-45

[9] Do Hong Thanh, Phan Van Anh and Nguyen Nang Dinh, Characterisation of thermochromic VO2 made by re-crystallisation from vanadium-rich thin films,

Communications in Physics Vol.10 (2000) N.3, 143-149

[10] N.N.Dinh, T.T.Tam, V.X.Huong, D.H.Thanh, Electrical and Optical properties

of nano-structured VO2 thin films prepared by e-beam deposition, Giri dang

trong Coom.in Physics, nhan dang 12/2005

[11] Nguyen Nang Dinh, Do Phuong Anh, Le Dinh Trong, Electrochromic

properties of vanadium oxide films made by high voltage spraying Advances in

Nat.Sci., nhan dang 12/ 2005

23

IV PHU LUC

5.1 CHUYEN DE 1 Phuong phap bdc bay chiim tia dien tu va cdng nghe che

tao mang mdng oxyt vanadi

5.2 CHUYEN DE 2 Tfnh chat chuyin mach cua mang mdng dxyt vanadi

5.3 CAC CONG TRINH KHOA HOC

24

CHUYEN DE 1

PHl/ONG PHAP BOG BAY CHUM TIA DIEN TLf

VA CONG NGHE CHE TAO MANG MONG OXYT VAVADI

PHUONG PHAP BOG BAY CHUM TIA DIEN j(S

*

* *

I NHUNG NET CHUNG

1.1 Uu diem ciia phuong phap

Co the nhan thiy nhirng uu diim chinh ciia phuong phap nay la:

- Mdi trudng che' tao mlu sach nhd co chan khdng cao;

- Do tinh khiei cua mang so vdi vat lieu gdc dugc dam bao do cac phan tir gan nhu bay hoi tiic thdi dudi tac dung nhiet nhanh cua chiim tia dien tir;

- Bdc bay dugc hau hei cac loai vat lieu vi chum tia dien tir hdi tu co nang lugng rat Idn;

- Dl dilu chinh ap suat va thanh phSn khf va nhiet do, cung nhu dl theo ddi qua trinh lang dgng;

- Co the sir dung rat it vat lieu gdc (dudi 100 mg) di bdc bay, cho nen trong

cac trudng hgp tie'n hanh nhilu thuc nghiem dl tim kiem cdng nghe che tao vat lieu mdi se tiet kiem dang ke nguyen vat lieu quy hiem

1.2 Ca sd ly thuyet va mo ta thuc nghiem

a) Co sd ly thuyet

Dac diem ndi bat ciia phuong phap chiim tia dien tir khac vdi cac phuong phap bdc bay nhiet hay phiin xa catdt la sir dung nang lugng ciia chiim dien tir dugc hdi tu true tiep tren vat lieu Khi chum electron nang lugng cao ban pha len vat lieu thi toan bd dgng nang cua chung dugc chuyin thanh nhiet nang do bi dimg dot ngdt Nguyen ly hoat dgng ciia siing dien tir trong chan khdng hoan toan gidng nhu mot den dien tir ba cue (tridt): catdt la sgi volfram co dien ap cao tdi 10 kV, dien ap tren dien cue ludi dugc dilu khien co do chenh dien ap can thiet so vdi catdt va andt thudng la toan bd thanh chuong thep khdng ri Khac vdi tridt la trong thiet bi chan khdng con co nam cham dien vdi tir trudng c6 hudng song song vdi sgi catdt (vudng goc vdi hudng bay ra ctia dien tir), dilu khiln do Idn ciia tir trudng se chinh dugc khoang each hoi tu ciia chum dien tir

Quy dao bay ciia chiim electron dugc quyei dinh bdi hai yeu td quan trong la van tdc ban dau thoat ra khdi catdt va do Idn ciia tir trudng, theo dinh luat Lorentz:

F = -qvxB (1.1)

Mat dd dong electron j e sinh ra do phat xa nhiet bdi ddt nong bd day catdt

dugc the hien bang phucmg trinh Richardson:

ie=AT^exp[(-qO)/kT] (1-2)

6 day A la hing sd Richardson, q la do Idn dien tich electron va O la cdng

thoat, T - nhiet do sgi ddt

Khi ngudn phat xa dugc boat ddng tai miic bao hoa thi ddng catdt cue dai dugc

dilu khiln bang viec lua chgn dong ddt, Dudi miic bao hoa, mat do dong phu thudc

vao the' gia tdc Ddng nang ban dau cua electron phat xa la 3kT/2, khdng dang ke so

vdi dgng nang cudi cung chung dat dugc sau khi dugc gia tdc trong dien trudng mdt

chilu dien ap cao (tii 7 de'n 10 kV)

Chiim electron ban ra tir sung dien tir dugc dilu khiln vdi cung tron khac nhau

va hdi tu vao bia vat lieu da dugc tham do mdt each dinh lugng Qui dao cua

electron cung da dugc tfnh toan bang tich phan cac phuong trinh chuyen ddng Cac

ket qua da chi ra rang: tuy vao vi trf ban dau cua electron ddi vdi sgi phat xa trong

dien trudng va tir trudng, chung phat ra tir sgi phat xa, dugc dilu khiln va ban chinh

xac vao bia vat lieu theo cung tron Nhung electron nam d ben dudi sgi phat xa dugc

dieu khien va hdi tu vao bia vat lieu hoan toan chinh xac Chuyen ddng do da dugc

thie't lap hinh anh qui dao chuyen dgng cua electron ban vao trong chen nung, cho

tha'y nhiing electron xuat phat tir vi trf d ben dudi sgi phat xa ban vao chen nung

chinh xac hon electron xua't phat ben trai sgi phat xa va kem chinh xac ddi vdi vi tri

xuat phat a ben tren sgi phat xa Ddi vdi vi tri ben phai sgi phat xa, nghia la vi tri

nam giua sgi phat xa va chen nung, electron chuyin ddng vdi qui dao khdng on dinh

roi bien mat Vl vay, khe chum cau tao mong mudn sao cho thu dugc nhimg electron

ban vao bia vat lieu dat hieu qua cao [I]

Chiim tia dien tii dugc gia tdc trong dien trudng co nang lugng cao va hdi tu

vao bia vat lieu nhd tac dung ciia tir trudng dieu khiln, rdi lang dgng len de nong la

phuong phap che tao mang mdng co do tinh khiei cao Vai qua trinh lang dgng bang

chiim tia dien tir phiic tap hon, chiing chiing td tinh da dang ve qua trinh lai ghep va

kha nang bien ddi trong che tao mang mdng cijng vdi nhung tfnh chat dang chii y

[2] Trong qua trinh bay hoi phan iing (reactive evaporation processes), ca hoi kim

loai va khi phan iing deu dugc ion hoa trong mdi trudng plazma tang cudng phan

Khoang each tir bia vat lieu den de ket tinh tir 36 den 50 cm Nhiet do de dugc gia

cd dinh tai nhiing gia tri trong khoang tir 200 den 400 °C Dong catdt cd 8 de'n 10 A; Dong tai (andt) dat tir 40 den 80 mA Thdi gian bdc bay tir 10 den 15 phut

Hinh 2.1 So d6 bdc bay bang chum tia dien tir che tao mang mong oxyt vanadi

I- Sdng dien tit; 2- bia; 3- de ket tinh; 4- bep nung; 5- cap nhiet dien; 6- Cdng tdc dieu khien he quay de ; 7- Cong tdc mang; 8- Ngdt dien; 9- Van khi lam viec; 10- Van xd khi; II- Van sa cap thong vdi van khuyech tdn; 12- Van bam khityech tdn; 13- Cong tdc bam ca hgc, 14- He quay de; 15- Cong tdc bep bam khuyech tdn; 16- khi ; 17- Cong tdc cung cap nhiet dp cho bep Id; 18- Dong ho do dp sudt

'^^ Ngudn nang lugng dijng de kich thfch cac phdn tir bay hoi la chiim tia dien tir

cd nang lugng cao dugc hdi tu tren bia vat lieu Ddng nang ciia dien tir co thi dat 10 key tuy thudc vao thd gia tdc Churn tia co kich thudc tieu diim vao cd Imm^ Khi hdi tu vao ngudn vat lieu, nd tao nen mdt vung nhiet do rit cao lam cho cac phan tir cua vat lieu bi thang hoa hay bdc hoi Chung tdi de' lien kdt tao thanh mang mdng tren do

2.3 Ke't qua lang dgng

Tir bia vat lieu V2O3, mang mdng dugc hinh thanh sau khi lang dgng co mau den sim, thi hien mau ciia vat lieu giau kim loai vanadi Mau ciia mang chuyin sang mau xanh sim hay xanh vang khi bia vat heu dugc sir dung tuong iing la bdt VO2 hoac V2O5 SEM bl mat mang mdng dxyt vanadi do tren mSu lang dgng tir V2O3 cho thiy mang co sdd min cao ciing vdi su xuit hien cua ddm la co thi la hat tinh the dugc hinh thanh trong khi lang dgng

Tai ket tinh trong dxy ap suat thap

• Ndng luong dxy hoa

Trong qua trinh tai kei tinh, nang lugng cung cip cho mau dudi dang nhiet nang Nang lugng dugc tfnh bang nhiet do va thdi gian tai kei tinh Nguon cung cip nang lugng nhiet co thi sir dung 15 nung hoac ngudn biic xa nhiet (tia laser) Tuy vao, ciu triic (nang lugng lien ket) giua cac ph£n tir tao nen tinh thi hoac nhiing sai hdng mang cu thi trong chung ma xac dinh nang lugng tai kei tinh cho phii hgp Lfng vdi mdi che do lang dgng, tinh the VO2 co the dugc hinh thanh ngay sau khi lang dgng [3], hoac phai qua tai ket tinh tdi hang tram gid [4], hoac vai chuc giay [5]

Mang mdng ngay sau khi lang dgng bang phuong phap bdc bay chiim tia dien tir CO cau true vd dinh hinh hoac da co dinh nhilu xa thudc dinh hudng ciia tinh thi V2O5 he true giao, dugc tai ke't tinh d cac che do trong khoang nhiet do tir 300 den

500 "C, thdi gian 1/2 gid den 6 gid

• Moi tru&ng tdi ket tinh

Mdi trudng nay dugc xac dinh bang cac thdng sd ap suit va thanh phan khi quyen bao xung quanh mau Co thi thuc hien mdi trudng tai kei tinh hd hoac trong dng kin Trong qua trinh tai kei linh, giu-a mau vdi thanh phan khi quyin bao xung

quanh ludn co su tuong tac Bdi vay, mau mudn khdng hi dxy hoa do dxygen ciia khi quyen d nhiet đ cao, cd the sir dung cac khf tro nhu Argon hoac Nitrogen [5,6] Mau mudn thay đi thanh p h ^ hop thiic thi thanh phdn khi tai ket tinh dugc sir dung CO the la khf ma miu dang thidu hoac cd kha nang hoa hgp dugc vdi thanh phdn khi khudch tan t^ mau vao mdi trudng [7]

Do ban chit da dang vl hoa tri ciia vanadi va su phiic tap ve thanh phin hoa hgc cua dxyt vanadi, mang mdng V02dugc hinh thanh trong dieii kien rat hep [85] Ldp phii giau kim loai vanadi va tinh the V2O5 co dinh hudng da dugc hinh thanh sau khi lang dgng Dl hinh thanh tinh thi mang mdng VO2, ldp phii nay can dugc tai ket tinh tiep trong dilu kien co khdng che vl ap suit thap

• Qui trinh tdi ket tinh

La each thay đi nhiet do, ap suat va thanh phin khi quyen theo thdi gian, tdc

do tang nhiet do lam sinh ra hoac mit di nhirng sai hdng mang, gop phin vao sir tuong tac ciia miu vdi mdi trudng Duy tri nang lugng va mdi trudng tai ket tinh trong khoang thdi gian nhat dinh, de tinh the mong mudn dugc hinh thanh Giam nhiet do sau khi tai ket tinh, gop phin on dinh trang thai cua tinh thẹ Giam din

nhiet do di giai phdng nang lugng du trong miu gop phin hinh thanh trang thai can

bang bin Su giam nhiet do tai kei tinh mdt each dot ngdt con dugc ggi la tdi nhiet, mau dugc hinh thanh d trang thai khdng can bang, do con ton tai nang lugng du dudi dang the nang

Qui trinh tai kei tinh trong dxy ap suit thap lÓ^Torr, dl tinh the mang mdng VO2 dugc hinh thanh can tién hanh theo ba giai doan: i- tang nhiet do tir nhiet do phong den 450"C trong thdi gian 1 gid 30 phut; ii- duy tri nhiet do nay trong thdi gian tir 2 dén 6 gid; iii- giam dan nhiet do 450"C vl NDP trong thdi gian 2 gid

U nhiet trong khdng khi

• Ndng luong u nhiet

Bang phuong phap phun dien cao ap mdt chieu, tinh the mang mdng V2O5 dugc hinh thanh tai che do thích hgp hoac con tdn tai mdt ham lugng nhd V2O5 3H2O hay dxyt giau dxy V^Ộ Bdi vay ngay sau khi dugc ling dgng, mang mdng dxyt vanadi cin dugc cung cap tiep nang lugng cho qua trinh khuyéch tan dxy vao miu va bay hoi nudẹ Nang lugng LI nay cung dugc xac dinh bang nhiet đ va thdi

gian ii Thdng thudng, mang mdng nay chi cin u trong thdi gian ngin va nhiet do ii nhd hon nhiet dd lang dgng, do ciu tnic tinh the trong mang da kha ddng nhit

• Moi tru&ng u

Miu va mdi trudng bao xung quanh ludn xay ra su khuech tan khi trong qua trinh ii Khf ii cd kha nang kdt hgp vdi thanh phin khi khue'ch tan tir miu vao mdi trudng ap suit thip, giam bdt lugng khi trong miu, nhung qua trinh lai xay ra ngugc lai neu ap suit dii Idn Bdi vay, mang mdng dien sac V2O5 mudn dugc che' tao ma phai ii nhiet thi sir dung mdi trudng hd trong khdng khi dudi dilu kien ap suit khi quyen thdng thudng

• Qui trinh ii

Ngay sau khi ling dgng, mang mdng dxyt vanadi dugc ii nhiet ngay Qua trinh ii nhiet dl tinh thi V2O5 hinh hanh ddng nhit ciing dugc tie'n hang theo ba giai doan: i- Giam nhiet do tir nhiet do ling dgng xudng de'n 250°C trong thdi gian 1 gid; ii- duy tri nhiet dd nay trong thdi gian 2 gid; iii- giam din nhiet do ii vl NDP trong thdi gian 1 gid

i n PHUONG PHAP DO DAC VA KHAO SAT TINH CHAT

3.1- Khao sat cau triic tinh the bing nhieu xa tia X

Phuong phap nhilu xa tia X dugc sir dung phd bie'n nhit de nghien ciiu cau true vat rin, vi tia X co budc song ngin, nhd hon khoang each giQa cac nguyen tir trong vat rin Khao sat ciu true tinh the ciia miu bang nhilu xa tia X se gop phin dilu chinh che do cdng nghe che tao vat lieu de nhan dugc ciu true tinh the mong mudn

Ban chit cua hien tugng nhilu xa tia X tren mang tinh the dugc thi hien d dinh luat nhilu xa Laue va phuong trinh Bragg

Tren Hinh 3.1 trinh bay hien tugng nhilu xa tia X tren hg mat mang tinh thi

(mat phang Bragg) co khoang each giira hai mat liln kl d Dl nhan thay hieu quang

trinh giua hai tia phan xa tir hai mat phang nay la 2dsin0, trong do 0 la goc giua tia tdi va mat phing mang Cac song phan xa tir nhiing mat phang Bragg thoi man dilu kien ciia song ket hgp: ciing tin sd va lech pha Cudng do ciia chung se dugc nhan len theo dinh luat giao thoa Cdng thu'e diln ta dinh luat nay chinh la ndi dung co ban ciia phuong trinh Bragg [8]:

2dsine = nA (3.1)

trong do X la budc sdng ngudn tia X sir dung; n = 1, 2, 3, la bac nhilu xa Thdng

thuong trong thuc nghiem chi nhan dugc cac nhilu xa iing vdi n = 1

B

BI=BK= d sinO

Hinh 3.1 Su phan xa ciia tia X tren cac mat phing Bragg

Tir phuong trinh Bragg, nhan thay ddi vdi mdt he mat phang tinh thi (d da biet) thi ling vdi gia tri nhit dinh ciia budc song tia X se co gia tri 0 tuong iing thoa man dilu kien nhilu xa Noi each khac, bang thuc nghiem tren may nhilu xa tia X chung

ta se nhan dugc td hgp ciia cac gia tri d^ki ^^^ trung cho cac khoang each mat mang

theo cac hudng khac nhau ciia mdt ciu true tinh the Bing each so sanh td hgp nay vdi bang tra ciiu ciu true trong cac tep dir lieu vl cau true tinh thi hoac ciia cac miu chuan co the xac lap cau true tinh the ciia miu nghien ciiu

Khao sat ciu true cua mang mdng dxyt vanadi cung dugc tien hanh bing phuong phap nhilu xa tia X tai Vien Khoa hgc Vat lieu sir dung may SIEMENS D-

5000 vdi su hd trg ciia "buong mang mdng" va bd ddt miu nhiet do cao Mot sd gian

do thuc nghiem vl cau triic ciia mang cung dugc ghi tren may SIEMENS D-5005 ciia khoa Vat ly, Dai hgc Khoa hgc tu nhien-Dai hgc Qudc gia Ha Ndi

3.2 Phuong phap hien vi dien tii truyen qua

Kinh hien vi dien tir diu tien ra ddi thudc loai kinh hien vi dien tir truyin qua (TEM-Transmission Electron Microscope) hoat ddng theo nguyen tic phong dai nhd cac thau kinh, tuong tu kinh hien vi quang hgc, diim khac la anh sang dugc thay the' bang chiim tia dien tir

Hinh 3.2 So d6 nguyen ly cua kinh hien vi dien tir truyen qua

khi chup anh hien vi didn tii

S la mang mong oxyt vanadi; 1,2,3- siing dien tit; 4-kinh tu; 5-kinh vat; 6-kinh phong thic nha't; 7- kinh phong thit hai; 8,10,12- dnh nhieu dien tit;

9,11, 13- dnh hien vi dien titvdM - mdn dnh

Hinh 3.2 la so do nguyen ly ciia kinh hiln vi dien tir truyen qua [2], khi chup anh hien vi dien tir Chieu mdt chum tia dien tir vao miu, sau vat kinh ludn cho hai anh: anh hien vi d mat phing anh cua thiu kinh (theo qui tic 1/d +l/d = 1/f); anh nhilu xa d mat phing tieu dien ciia thau kinh (theo qui tic tia song song tap trung vl tieu diem) Thau kinh dien tir co the thay ddi tieu cu (bing each thay ddi dong dien kich thich), nen co thi kich thich tieu cu ciia thau kinh sau vat kfnh dl tren man anh

CO anh hien vi (hoac anh nhilu xa)

Mudn chup anh nhilu xa dien tir, nguyen ly tuong tu nhu tren chi khac la kich thich dong dien de tieu dien ciia kfnh phong 6 triing vdi vat 8 va man anh M dat triing vdi tieu dien anh ciia kinh phong 7 Thi du, anh nhilu xa dien tir va TEM ciia mang VO2 dugc trinh bay tren hinh 3.3 va 3.4

10

d*.? w ^i^ H^

• 1 * 1

f t

Hinh 3.3 Anh nhilu xa dien tii cua mang

dugc tai kei tinh trong ap su^t

thip do tren miu V245

Hinh 3.4 Anh TEM ciia mang mong dugc tai kei tinh trong ap suit thap

do tren miu V245

Uu diim quan trgng ciia hien vi dien tir truyin qua la co the dilu chinh dl dang de thiy dugc ca anh hien vi va anh nhilu xa ciia miu, nhd do ma phdi hgp biei dugc nhilu thdng tin vl ciu true, each sip xe'p cac nguyen tir cua miu

Nhugc diim co ban ciia phuong phap nay la miu nghien ciiu phai dugc lat cue rit mdng (dudi 0,1 micromet), nhung lai phai du day dl ton tai dugc d dang rin (vai chuc den vai tram nguyen tir) Nhu vay iing vdi nhimg diem tren anh hiln vi dien tir truyin qua la nhung cot nguyen tir tren miu co chilu cao bang chieu day ciia mang Anh liiln vi dien tir truyen qua va nhilu xa dien tir ciia mang mdng dxyt vanadi dugc chup tren he EM-125K ciia Vien Khoa hgc Vat lieu, Trung tam Khoa hgc tu nhien va cdng nghe Qudc gia

3.3 - Phuong phap hien vi dien tu quet

Kinh hien vi dien tir quet (scaning electron microscope-SEM) hoat ddng theo nguyen tic, electron thii cap phat xa nhd cac electron ciia sung dien tir co nang lugng cao bin pha vao be mat cua miu khao sat Sd lugng electron thii cap phat xa cang nhilu neu bl mat miu bi phong len cang Idn va ngugc lai khi be mat bi Idm xudng, tuong iing vdi nhirng diem sang - tdi duoc ghi tren anh

11

Tren hinh 3.5 la kfnh hiln vi dien tir quet [8] chup vi anh bl mat Electron duoc gia tdc trong dien trudng tao bdi cao ap c ^ ^ PR H- A V hoac Idn tdi

CRT CRT

L, AS

SC

L-Hinh 3.5 Gian d6 kfnh hiln vi dien tii quet chup anh be mat miu

G - la sung di6n tu; Lj- kfnh tu; AS- lua chpn dp md; SC- cu6n quet;

SGmay quet; Lj kfnh vat; S miu nghien cuu; C dng gop; e electron; A

-may khue'ch dai; CRT- dng tia catdt; PR- dng tia catdt ghi anh; LT- dng tia

catdt hien thi thdi gian hoat dpng; VP- bom chan khong

60 KV tuy thudc vao thiet bi va miu khao sat dugc hdi tu vao cira AS nhd thiu kinh L, Chiim electron di qua cudn quet SC hdi tu nhd kinh vat Lj vao miu S phat xa ra electron thd cip di vao dng gop C Qua trinh dugc thuc hien trong buong chan khdng ap suit cd 10'"^ Torr Nhd may khuech dai A thdng tin dugc truyin vao thiet

bi ghi anh PR ciia dng tia catdt CRT Nang suit phan giai ciia kinh hien vi dien tir quet bi gidi han bdi kich thudc ciia chiim tia dien tir chieu vao miu Nang suat phan giai ciia SEM dat vao cd 6 -r 3 nm tuy thudc vao loai ngudn phat xa electron

3.3 Khao sat phd truyen qua va phan xa

Phd truyin qua va phd phan xa dugc do tren he quang pho ke JASCO-V 570/UV-VIS-NIR CO d Trudng DHCN, DHQGHN Tuy thudc vung phd khao sat, mdt trong hai ngudn sang dugc diing la den co phd lien tuc vdi budc song trong viing kha kien hay trong vimg hdng ngoai

Chum sang vdi pho lien tuc tir den dugc phan xa tren guong M tdi thiet bi loc sic Sau khi qua thiet bi Igc sic chiim sang tdi each tir Thiei bi Igc sic F va each tir

G tao ra tia vai do don sic nhat dinh Tia nay phan xa tdi guong ban ma, mdt phan

12

truyin qua guong, phan con lai phan xa dugc dua de'n miu chuan R va miu do S

Trong phep do do truyin qua, mdt tia truyin qua miu rdi tdi detector, chiim kia

truyin qua miu chuin (de' thuy tinh chua co mang) rdi tdi detector Cac detector D

la ciing mdt loai photodiode Silic Trong phep do do phan xa, cac chum tia dugc

phan xa tuong iing tren miu va tren miu chuan Trong trudng hgp nay miu chuan

dugc diing la mdt guong co dd phan xa cao (guong ma nhdm hoac ma vang) Cac tin

hieu quang tir hai chum tia dugc bien ddi thanh tin hieu dien nhd cac detector va

dugc so sanh di cho do truyin qua hoac do phan xa tuong icng vdi phep do tai mdi

budc song trong viing pho khao sat nhd may tfnh

3.4 Tinh chat dien

• Do dien trd be mat

Tren bl mat ciia mang, tao tiep xuc ohmic bing each bay hoi mdt ldp vang

mdng lam thanh hai dai dien cue song song Mang co dien tich mdt hinh vudng,

canh d Vdi t la chilu day ciia mang, dien trd suit ciia mang la p, thi dien trd bl mat

RQ ciia mang dugc xac dinh theo cdng thiic :

Rr =pxl/S = p/t (3.2) Dien trd suit p ciia mang dugc xac dinh khi biet dien trd bl mat R va chilu

day t ciia mang bing cdng thiic:

Gia tri dien trd R- theo nhiet do ciia mang dugc xac dinh nhd he do gdm thiet

bi dilu nhiet hoac mot be'p hinh tru khep kin on nhiet (tu tao) de chiia miu, ddng ho

KIETHLEY va may tinh COMPAQ Chieu day t ciia mang mdng do bing thiet bi

Ellipsometer va phuong phap SEM d tren

Nhu tren da trinh bay, mang mdng nhiet sic VO2 la ddi tugng de nghien ciiu ly

thuyet va iing dung rat co triln vgng Tuy nhien, viec che' tao mang VO2 don pha lai

la van de cdng nghe het siic kho khan, den miic co thi noi giai phap cdng nghe nay

mang tinh bi quyei doi hdi su tim toi va nghien ciiu rat cdng phu

Di dam bao do tin cay ciia cac sd lieu thuc nghiem, mot sd phep do tire

thi can dugc tien hanh tren cac he thiet bi ghep ndi hai hay nhilu may hoat

ddng ddng thdi

13

TAI Ll£U THAM KHAO

[1] Mahan Jon E., (2000), "Physical vapor deposition of thin films", Jon Wiley &

Sons INC, AWiley Interscience Publication, New York Chichester Weinheim- Brisbance - Singapo -Toronto, pp 115-132

-[2] Milton Ohring (1992), "The Materials Science of Thin Films", Harcourt Brace

Jovanovich Pubhshers, Academic Press INC., 79-190

[3] Micocci G., Serra A., Tepore A., Capone S., Rella R and Siciliano P (1997),

"Properties of vanadium oxide thin films for ethanol sensor", / Vac Sci Tecnol.A.l5 {l),pp,34-3S

[4] Babulanam S.M., Ericssion T.S., Niklasson G.A and Granqvist CG (1986),

"Thermochromic VOj films for energy-efficient window", SPIE Vol 692 Material and optics for solar energy conversion and Advanced Lighting tecnology, pp 8-18

[5] Lee Moon-He, Kim Myoung- Geun, Song Hyung-Keun (1996),

"Thermochromism of rapid thermal annealed VO2 and Sn -doped VO2 thin

films", Thin solid films 290-291, pp 30-33

[6] Takahushi Yasutaka, Kanamori Masaki, Hashimoto Hiroyuki, Moritani Yoshimitsu, Masuda Yoshiro (1989), "Preparation of VO2 films by

Organometallic chemical vapour deposition and dip-coating", Journal of Material als Science 24, pp 192-198

[7] Long Pham Duy, Hung Nguyen Van (1994), Toan Nguyen Ngoc and Dinh Nguyen Nang, "Enhacement of the thermochromic properties of VO2 thin

films by annealing", Communications in Physics, 4 (2) pp 90-96

[8] Flewitt P E J and Wild R K (1994), ''Physical Methods for Materials Chracterisation", Institute of Physics Publishing, Bristol and Philadelphia, pp

75-395

14

TINH CHAT CHUYEN MACH

Trong dilu kien ap suit va nhiet do binh thudng dxyt vanadi co the tdn tai dudi cac dang cdng thiic hoa hgc nhu: VO, V2O3, VO2, V2O5 tuong iing vdi hoa tri ciia vanadi la; 2, 3, 4, 5 va cac dxyt cd dang cdng thLi:c Vn02n.i, (vdi n = 3 -^ 9); Vn02n+i (vdi n = 3 -H 6) (xem bang 1.1) [1,2] Mdi loai dxyt vanadi co nhimg kha nang iing dung dac thii trong cac linh vuc khoa hgc ky thuat, an ninh qudc phdng hay cudc sdng dan sinh la tuy thudc vao kha nang khai thac cac tfnh chit ciia chiing Tuy nhien, trong tap hgp Idn cac dxyt vanandi kl tren chiing ta nhan thiy co ba loai dxyt

da va dang dugc chii trgng nghien ciiu va trien khai ung dung, dd la didxyt (VO2), peta-dxyt (V2O5) va hdn hgp dxyt vanadi khdng hgp thiic VO^ (1,5 < x < 2,5; x^ 2) Didxyt vanadi (VO2) cd chuyen pha BDKL tai nhiet do 67°C, gan vdi nhiet do phong hon ca [3] Bdi vay, VO2 co triln vgng ung dung rat phong phii va dugc quan tam nghien ciiu ngay cang nhilu V2O3 cd nhiet do chuyen pha (NDCP) tai -105"C

va cd thi chuyin NDCP nay ve gin nhiet do phong trong dilu kien cd tac dung ciia dien trudng cao [1] NDCP cua V2O5 la 240*^0 [4], cau triic mang tinh thi xep ldp la

CO sd cho nhilu iing dung

Bang 1.1: Nhiet dd chuyin pha va budc nhay dd din dien ciia 6xyt vanadi

10'"

10^

10^

10' 10' Kim loai

68

80

340

-205 -193

67

10' 10' 10^

dl chay Do dd chiing la vat lieu cd nhilu trien vgng iing dung trong viec che tao cac sensor nhay khf dl phat hien va xac dinh nong do ciia mdt sd chat khi cd hai trong mdi trudng [12,13]