Một số vấn đề động học trong tiếp xúc chất bán dẫn (cấu trúc nano) với môi trường điện giải

MUC
LUC
'i
Trang
I
Loi cam doan
Muc
luc
Danh muc cac ky hieu, cac
chu
viet tit
M6DAU
. 1
PHANI:
TONG QUAN QUA TRINH DIEN
HOA,
PHUONG
PHAP
CHE TAG VA NGHIEN
CtJlI
DBEN ClTC
BAN
DAN.
Chirong
1:
Qua trinh dien hoa dien
cue
ban
Akn
cau
true

nano-xop
5
U
Qua trinh dien hod cua dien
cue
ban
dan
5
1.1.1 Tiep
xiic
chat ban din
v6i
dung dich dien giai 5
1.1.2 Qua trinh trao doi
dien
tich ban din-dien giai 9
1.1.3 Hieu ling quang dien hoa dien cue ban din 13
L2
Dien
cue
ban
ddn
cdu
true
Nano-xop 16
1.2.1
Hieu ling
kich
thuoc hat luong tu 17
1.2.2 He hat ban din

kich
thu6c nho
18
7.2.2.7 Che tao vat lieu
18
12.2.2
Muc nang
luang
vo
cache
tdch hat tai 20
122.3
Phdn
bo'dien
the'trong
dien
cue
nano-xop 22
12.2.4
Cc^
che
ddn
hat tai
trong
dien
cue
nano-xop 24
Chuang
2 : Cong nghe
che

tao va
phuong
phap dien hoa
nghien cuu dien
cue
TiO,
cau
true
Nano-xop 28
2.1 Phuong phdp
soUgel
che tao ban ddn
TiO,
nano-xop 28
22 Phuong phdp 3 dien
cue
nghien cuu dien hod ehdt bdn
ddn
31
2.2.1
Dae
tinh Dong - The phan cue (dac
tinh
1-V)
31
2.2.2 Phep do
dien dung-ihe
phan
cue
(dac tinh

C-V)
32
2.22.1
Dien cue kim loqi
33
2.2.2.2 Dien
cue bdn
dan 35
PHAN
n
: NHUNG
KET
QUA NGHIEN
ClTU
THUC NGHIEM VA LY
THUYET TREN DIEN CUC
BAN
DAN CAU TRUC NANO-XOP TI02
Chuong
3 : Xay dung mo hinh
chuyen
tiep ban din-dien giai
(SEI)
va dac trung dien dung dien hoa he dien
cue
ban dan nano-xop 40
3d Mo hinh thiet lap can bang
bdn
ddn - dien giai (SEI)
41

3.1.1 Mo hinh tiep
xiic
ban din dien giai he nano-xop 41
3.1.2
Phuong trinh mo ta qua trinh thiet lap can bing 46
3.1.3 Trao doi dien
tich iren
tiep
xiic
ban din-dien giai 49
3.1.4
Diiu
kien trung hoa dien
tich ciia
be mat tiep
xiic
52
3.1.5 Dang loan hoc mo hinh tiep
xiic
ban din-dien giai 54
3.1.5.1
He phuong trinh mo td qua trinh can bang 54
3.1.5.2 Dieu kien bien tai tiep
xiic
bdn ddn-dien giai 56
3.1.5.3 Dieu kien bien tai goc
tog dp
x=0 (R=0) 57
3.1.5.4
Dieu kien tai thoi diem ban ddu

t=0
58
3.1.6 Phuong phap so giai he phuong trinh phi tuyen 58
3.1.7 Luu do quy trinh mo phong thiet lap can bing SEI 62
32 Phuong phdp so tinh dien dung dien hod dien
cue
nano-xop 63
3.2.1 Cac lop dien
tich
cua tiep xuc ban din-dien giai (SEI) 63
3.2.2 Cong thuc ciia dien dung cac lop dien tich tren SEI 64
3.2.3 Quy trinh mo phong dac
irung
dien dung dien hoa 67
Kef luan
73
Chuotig
4 : Dien
cue
TIO.
cau
true
nano-xop 74
4.1
Cdu
true
vd hinh thdi hoc cua dien cue
TiO^
74
4.1.1 Dien

cue Ti02
che tao bing phuong phap sol-gel
4.i.2DiencircTi02chelaotirbolP25
(DEGUSSA)
4.1.3 Dien
cue
TiO^
dac che tao bing phuong phap dot Ti
42 Dae tinh quang dien hod cua dien
cue Ti02
4.2.1 Cau true tinh
the'
va boat tinh quang dien hoa
4.2.2
Hinh
thai hoe va boat tinh quang dien hoa
4.2.3
Kfch
thude hat va boat tinh quang dien hoa
4.2.4 Thay doi dong hoc phan
ling
Redox trong dien cue
ciu true nano-xop khi bi kich
thich
anh sang
Ketbian
Chuong
5 : Dien dnng dien hoa dien
cue Ti02
nano-xop.

Co
che
tang
toe
do phan umg Redox
5.1 Qua trinh thiet lap can bang bdn ddn-dien giai
5.1.1 Cac thong so su dung trong mo phong he
Ti02:171'^
5.1.2
Ki6m chiing
doi v6i tiep
xiic
kim
loai-ban
din
5.1.3 Mo phong qua trinh thiet lap can bing SEI
52 Dien dung dien hod cua dien cue
Ti02
5.2.1 Dien dung dien hoa cua dien
cue Ti02
dac
5.2-2 Dien dung dien hoa dien
cue Ti02
nano-xop
5.2.3 Hien
tuong
dich
chuyen
bien vung cua he dien cue
ban din cau tnic nano-xop khi bi kich

thich
quang
Kit luan
KET
LUAN CHUNG VA
KEEN NGHl
DANH MUC CAC CONG TRINH CUA TAC GIA
TAI
LIEU THAM KHAO
PHU LUC
DANH
ML
C CAC KY HIEU VA
CHlT VTET
TAT
Cac ky hieu
C(o
- Dien dung Warburg .
C(,oni
- Dien dung diem cue doi
Cgc
- Dien dung
xoing dien
tich khong gian
ciia
b^
mat ban
dkn
Qs'
R-ss

"
Dien dung va
trd thuSn ciia
cac trang thai
h6
mat dien
cue
ban din
CH
- Dien dung lop dien
tich
kep be mat Helmholtz
CQX
-
Nong do trang thai oxy hoa (oxydized species) cua cap Redox
Cred"
N6ng do trang thai khtr (Reduced species) cua cap Redox dung dich
De,
Df,
- He so
khuecii
tan cua dien tu va
16
trong trong ban dkn
Ecs - Miic
bien vung cua
viing dSn
trong ban
din
Evs - Miic

bien vung
ciia viing
hoa tri trong ban
dSn
Ep
-
Miic
Fermi trong ban din
ERedox"
Muc
Redox
ciia
cap oxy hoa khtr
EQX
- Miic
oxy hoa
coa
cap oxy hoa khu
-
ERed • Muc
khu ciia cap oxy hoa
khii
ER
- Nang luong cau
tmic
lai (Reorganized Energy) cua cap Redox
G^,
Gp
-
Toe

do
kich
thich dien tu,
16
trong trong ban din
K^, K^
- Nhan
to'
chu\'en
doi (Transfer factor) doi
voi vxing
din
\'a
hoa tri
Loebyc • ^9 dai
Debye cua chat ban din
Loebye " Do
d^i
Dcby^
ciia dung dich dien giai
rn*,
nip
- Khoi luong hieu dung ciia dien tu va
16
trong
n^)
- Nong do pha tap
irong
ban din
no,

Po
- Nong do dien
lu
\'a
16
trong trong trang thai vung
ph^ng
Q^
- Dien
lich ducua
lop dien
li'ch
khong gian
Qsuri •
^i?"
^^^^ du
cua lop
b^
mat ngoai ban dan
rjj
- Ban
kinh
Bor
Rj.on,
- Dien
trd thuSn ciia
dien
cue
d6i
R^,

Rp
-
Toe
do tai hop cua dien tir,
16
trong trong ban din
Rsc -
Dien
tra
than viing dien
tich
kh6ng gian
ciia
hi mat ban din
T/,T^^
- Hang so
toe
do (rate constant) trao doi
dien
tich
ciia
dien
tu,
16 trong
Vg
- Do cao rao the be mat ban din
^Bias -
Th^
ph^
cue

Vft,
- The vung phing ciia ban din
(flatband
potential)
Eo
- Hing so dien m6i ciia chan khong
8 - Hing so dien m6i cua ciia vat
heu
H^,
|ih *
E^9
1"^
dong cua dien
tir
va
16
trong trong ban din
T]„,
Tip
- Do cao rao the trao doi dien
tich
cap Redox vdi ban din
p
-
Nong d6
di6n tieh du
trong vung dien tich kh6ng gian cua ban din
ID
-
Thdi

gian song nho nhat cua hat tai kh6ng
co
ban trong ban din
Cac chu viet tat
AFM - Hien vi luc nguyen tir
Cap Redox : Cap oxy hoa- khu
DTA -
Phan
tich
nhi6t
vi sai (Differential
Thermo-Analysis)
GCS - lop Gouy - Chapman - Stem : lop khuech tan Ion
a
gin bi mat dien cue
khi
CO
dien truong du tren hi mat dien cue (con goi la L6p Helmholtz ngoai -
outer Helmholtz layer)
NHE - Normal Hydrogen Electrode = SHE : The dien cue
chu^n
NHE
PBP - Gia the phan cue (Pseudo Bias Potential)
PEC - Quang dien hoa (PhotoElectroChemistry)
SCE
-
The dien
cue
chuin SCE (Saturated Calomel Electrode)
SEI - Chuyen tiep ban din - dien giai (Semiconductor-Electrolyte Interface)

SEM - Hien vi dien tu quet
MO
DAU
Nhung
hien
tuong dien hoa. quang dien hoa
(PhotoElectroChemistry
-
PEC) da
duoc
biet den va umg dung
tir
nhung nam diu the ky.
Nhimg
phai den
nam 1954 Brattain va
Garren
[8] moi chi ra ban chat
ciia
hieu
ling
quang dien
tren tiep
xiic
chat
rin-dien
giai dac biet la tiep
xiic
Ban
din-Dien

giai
dal niu
mong cho
linh
vuc quang dien hoa (PEC)
hien
dai. Nam 1970 Honda \'a cac
cong su [38] da phat hien ra hien tuong phan ly
nude
thanh Oxy va Hydro khi
chieu sang vao dien cue anode bing ban
din
oxit Titan
loai
n. Tir do
ti^m
nang
ling
dung ciia he PEC moi thuc su duoc quan tarn.
Nhung ling dung
ciia
he PEC de
chuydn
hoa nang luong mat
trdi
thanh
dien nang
ciing
nhu nhung dang nang luong khac da thu
hiit

n6 lac nghien cuu
ciia nhieu phong
thi
nghiem cung nhu cac hang c6ng nghiep trong mot thoi
gian dai. Tuy nhien he PEC dien
cue
ban din phai doi mat v6i
nhung \'an
di
vi ky thuat nhu hieu suit, do bin
\^
cua dien cue trong m6i truong nude.
Buoc dot pha thuc su chi xay ra vao nhung nam cu6'i thap ky 80 khi mot
linh \arc
m6i
ciia
khoa hoc
vai lieu
xuat hien : Vat heu c6 kich
thudc
Nanomet
(vat
lieu cau
triic
Nano). He PEC vai cac dien
cue
ban din c6 cau tnic Nano
da lam thay doi
each
nhin ve tinh chat Vat ly cung nhu hieu qua

ciia
cac ung
dung hieu
ling
PEC
Chi
trong khoang 10 nam
nhiing ung
dung
ciia
cac he
PEC dien cue ban din c6 cau
iriic
Nano (hay cau
triic
Meso)
tir
nhiing
Ilnh \aic
ky thuat cao nhu Pin mat
troi
PEC,
ciia
so d6i
mau,
Pin
Li, \^
den nhimg ung
dung lam sach m6i truong bang quang
xiic

tac.
son chong moc va diet vi
khuin, dieu tri ung thu. my pham
\^^
da trd nen rat quen thuoc.
Tuy
dugc
ung dung ngay cang rong
rai,
nhung ban chat cac qua trinh
val ly cua he tiep
xiic
chat ban dan (dac biet la he c6
kich ihudc
hat c6
Nanomet) voi moi truong dien giai (SEI) da va dang la muc tieu nghien cuu
ciia
nhidu
phong thi nghiem tren the
gioi.
Su hap din ciia van de
6
dav la
iinh
cap bach ve ling dung va tinh hoc thuat
ciia
cac qua trmh hoa ly tren bien
giira
Vat ly ban
dSn.

tinh chit dien-hoa cac qua trinh hi mat va vat ly cac vat lieu
CO
kich thuoc nho (he c6 cau triic nano).
Muc tieu luan dn tap trung vao nghien
cuai
mot so qua trinh dong hoc
cua4ie^en-euc-ban
din c6 cau tnic nano-xop trong m6i truong dien giai
nhim lam sang to nhiing van di sau : kich thuoc hat bdn ddn co anh huong
den tinh chat
vT mo
hay khong ? Neu co
thi
lam the ndo de
dinh
luon2
dugc
tic
kit qua do thuc nghiem vi du
C-V?.
Tinh chat vi mo co bi anh huong
bdi
tinh
nano-xop (morphology) cua dien
cue
khong ?. Moi quan he
giixa sU
thay doi
tinh chat vi mo vd
nhiing

hieu ung
vTmo
?.
Lam the ndo
detdc
dong
len
he vat
ly
nhdm
tao ra
nhiing
dac tinh co loi cho
ling
dung.
Doi tuong nghien
cim
ciia luan an la
v^t
lieu
Ti02
co cau tnic dang
Anatase va Rutile. Cac dien cue
TiOj
chii yeu la dang
mang,
cau tnic Nano-
Xop (NanoPorous), che tao bing phuong phap sol-gel va
tir
bpt thuong phim

P25 (DEGUSSA) co do hat trung binh
-15nxr\.
Mot so nghien cuu tren mang
TiOj
dang dac khit (Compact), che tao bdi phuong phap dot (Pyrolysis) Ti
6
nhiet do cao duoc tieh hanh nhim so sanh tinh chat ciia hai loai dien cue nay.
Phqm vi nghien ciiu ciia luan an g6m nhimg nghien
cixu
thuc nghiem
va ly thuyet m6 phong thuc nghiem ap dung cho doi tuong vat lieu
Ti02:
*/
Cac mang dien cue
dugc
che tao va khao sat cau tnic pha bing
nhi^u
xa tia X ; hinh thai hoc (morphology) bing
hi6n
vi dien
tii
quet (SEM) va
hi6n
\i luc nguyen ttr (AFM). Dac trung quang dien hoa dugc khao sat thong qua
ket qua do dac tnmg dong-the phan cue
(I-V)
va dien dung dien hoa-the phan
c\ic
iC-W)
trong

di6u
kien khong
va
co
kich
thich bing anh sang tii ngoai.
NhiJng
nghien cuu nay
nhAm
he thong tfnh chat nhay hoa, nhay quang co lien
quan den cau tnic, hinh thai hoc
ciia
mang dien cue TiOn trong nhiing moi
truong hoa hoc khac nhau. Kel qua thu dugc la co so khoa hoc cho viec trien
khai ling dung cac dien
CUQ
loai nay.
*/
Luan an xay dung ly thuyet mo phong qua trinh
thiei
lap can
bang
va
dac trung dien dung
dien
hoa cua he ban din cau tnic nano-xop tiep
xiic
voi
dung dich dien
giai.

Qua trmh khop (Fitting) ly thuyet vdi so do thuc nghiem
C-V
ciia
he dien
cue
TiO^
dang nano-xop va dac. trong cac moi truong
dien
—giai,
che dp kich thich khac nhau da dugc tien hanh.
Y
nghia khoa hoc vd thuc
tiSn ciia
di
tai
: luan an da xay dung dugc
phuong phap ly thuyet di
six
ly phep do thuc nghiem C-V cho he dien
cue
ban
din cau tnic nano-xop, la huong nghien cuu dang dugc quan tam tren the gioi.
Su dung phuong phap nay de nghien cuu vat lieu
Ti02
(la val lieu
rat
dugc
quan tarn vi kha nang ung dung rgng rai) cho chiing ta nhiing
hieiu
biet ve hoc

thuat doi
vdi
tinh chat vi mo cua he hat nho,
nh^m
ly giai
ca
che mot so tinh
chat
vat
ly, d6ng thoi ggi y cho nhiing dinh hudng
ling
dung he dien cue ban
dSn
nano-xop.
Ngoai phan mo
dau,
ket
luan,
kien nghi huong nghien cuu
liep
theo,
danh
muc tai lieu tham khao va phu luc, noi dung luan an dugc trinh bay trong 5
chuong :
Chuong 1: Tong quan ve cac qua
trinh
dien hoa
ciia
dien
cue

ban din
cau tnic nano-xop.
Chuong 2: Trinh bay phuong phap sol-gel che tao dien cue
T1O2
nano-
xop va phuong phap dien hoa 3 dien
cue dd
nghien cuu tinh chat ciia dien cue
ban dan.
Chuong 3: Xay dung m6 hinh ly thuyet mo ta qua trinh thiet lap can
bang ciia tiep
xiic
ban
dan-dien
giai (SEI) cho he hat kich thuoc nho. Xac lap
quy trinh tinh dien dung dien hoa bang phuong phap so de' mo phong dac
trung C-V
cLia
dien cue ban dan nano-xop.
Chuong 4: Trinh bay kei qua nghien cuu thuc nghiem
\i
cau tnic, hinh
thai hoc (morphology),
hoai
tfnh quang hoa ciia dien cue
TiO^
nano-xop trong
cac moi truong hoa hoc va anh huong
ciia
che do kfch thich khac nhau.

Chuong 5: Trinh bay ket qua mo phong qua trinh thiet lap can bang
cii<
tiep
xiic
SEI d6'i voi he hat ban dan kich thuoc nho ; Ket qua nghien cuu
v^
dien dung dien hoa dien cue
Ti02
cau tnic Nano-Xop ; Khop (Fitting)
I3
thuyet voi ket qua do thuc nghiem C-V cua chuong 4, nit ra nhiing th6ng tir
dinh
lugng
ve tinh chat ciia dien cue nano-xop.
Luan an dugc thuc hien tai Vien
Vai
ly ung dung & Thiet bi Khoa
hoc
Trung tarn
KHTN
&
CNQG
va bg m6n Vat ly Chat ran, khoa Vat ly,
trudng
Dai hoc Khoa hoc Tu nhien , Dai hoc Quoc gia Ha noi.
Noi dung
chinh
ciia luan an dugc trinh bay tai cac Seminar khoa hoc
ciia khoa Vat ly, truong Dai hoc Khoa hoc Tu
nhifen,

Dai hoc
quo'c
gia Ha
n6i,
tap
chi
chuyen nganh , cac hoi nghi khoa hoc trong va ngoai nude
.
CHUONG
1.
QUA TRINH DIEN HOA DIEN
CUC
BAN DAN
CAU TRUC NANO-XOP
1.1 Qua trinh dien hoa ciia dien cue ban
d^n.
I.IJ
Tiep xuc chat bdn ddn
vdi
chat dien giai.
Xet chat ban din loai
n
va chat dien giai chi
chiia
cap oxy hoa
khii
(cap
Redox)
AVA^"".
Khi chit ban dan va dien giai

each
ly
nhau trong chan kh6ng
(hinh
1.1
a/),
miic
Redox
nam
dudi
miic
Fermi cua ban dan. Muc chan khong
ciia ban
din
tuong ling vdi muc -4,5V
so
voi
the
dien
hoa
chuan NHE.
Khi
cho hai pha tiep
xiic
v6i nhau, trang thai can bang dugc thiet lap. Khi do
miic
CB
VB
Bvidanloiin
-4.5

Ec
•Er
CMnkh6ng
• Hdt
chin khong
A7A'
Oiini
U
Ivs
NHE)
4
^'B
,
T
CB
VB
X
i
\T»H
^fb
A*/A'*
1
U
Ban dan loai n
Dien giai —
Hinh
LI:
al
Trang thdi chan khong
hi

Tiep xuc bdn
ddn-dien
gidi
Fermi
cua
ban
din se
bang
miic
Redox cua dung dich
(Hinh
Lib/),
Trang
thai
can
bang dugc thiet lap
la do
qua trinh
chuydn
doi
dien tich
tir
ban
dan
vao dung
djch.
Su chuyen doi dien
tu
(electron transfer) thong
qua

phan
img
hoa (phan
ling
Redox)
A '
+ e >
A^
,
Qua trinh
nay lay
bot
dien
lu
tu
do,
tao ra lop ngheo hat tai co ban
6
vung
hi
mat tiep
xiic
cua ban
dSn
(con goi
la
vung dien tich khong gian). Cac dien tfch khong gian trong ban dan va cac ion
irai
dau trong dung dich tao thanh lop dien
tich

kep cua
chuyen
tiep SEI
.
Phan bo dien the (nang lugng
ciia
dien tU) tai vung dien tfch kh6ng gian
(Hinh 1.1 b/ )
ciia
tiep
xiic
ban dan
-
dien giai (SEI) khong khac gi rao the
Schottky trong tiep xuc ban
dSn-kim
loai. Phan bo dien truong va n6ng do hat
lai 6
trang thai chuan dirng trong viing nay da la bai toan kmh diin [7
J
1,76].
Do rong lop ngheo dugc tinh qua do cao rao the
b6
mat
V^^
[71,76]
:
W=
fe^ (1.1)
"V eN

d
Vg
- dp cao rao the be mat ban dan .
Nj
- n6ng do pha tap lai vung dien tich khong gian
ciia
chat ban
din
.
£o
- hang so dien m6i chan khong ; s - hang
so'
dien m6i tuong doi cua ban dan
e - dien
tieh
cua dien
tu.
Kich thuoc viing dien tich kh6ng gian co the thay doi ttr vai nanomet den vai
micromet. Ngugc lai do rgng lop dien tich kep hi mat Helmholtz
chi
vai A ,
do do sut the se roi chu yeu tren
Idp
dien tich kh6ng gian.
Da\^
la luan
cii
de
ap dung gan
diing

Mott-Schottky [4,63,64].
Cap Redox trong dung dich dac trung
boi miic
the Redox va phan bo
mat do trang thai ciia cac trang thai oxy hoa (OX) va khu (Red).
Miic
Redox dugc coi la
miic
the hoa
(miic
Fermi)
ciia
dien tu trong cap
Redox, the hien xu the cho cho hay nhan dien
tir.
Miic
Redox dugc tinh theo
chuan NHE (Normal Hydrogen Electrode) [24] ;
E'(H, /H*) - -4.5
±
O.OSeV
so voi
miic
chan kh6ng.
Miic
chuan thuong
ha}-
dugc dung la SCE (Saturated
Calomel Electrode) co the
+0,24V

so voi
\HE
tai
25°C.
W(E) la
h'liu
d'lin
xac suat ton tai
miic
nang lugng E cua trang thai
E^
(trang thai
E,
co
the
la trang thai oxy hoa
E^^
hoac trang thai
khii
E^.^
^ua
cap
Redox
E^edox)'
W(E)
=
AnE^kT
(
(E
exp

-
4E„kT
(1.2)
ER
-
nang lugng tai tao
lai
(Reorganization Energy) xac dinh thong qua
ca^
thong so m6i truong theo Marcus
[57]
va Doganadze [87] :
ER
=
STts^a
(
(1.3
q- so dien ttr
ctia
qua trinh tai tao ; a- ban kinh ion ;
CQ
hang
so dien m6i
chai
kh6ng ;
£,
- hang so dien m6i
tinh
dien (static dielectric constant);
s^p

-
han^
so'
dien m6i quang hoc .
H. Gerischer [22] coi nhung
miic nhiiu
loan theo thoi gian
(time
fluctuating energy levels) cua phan bo mat do trang thai cap Redox nhu
viinj
ciia
cac
miic
nang lugng trong chat ran. Mo hinh nhu vay rat tien
Igi
trong
tini
toan [49].
Tuong tu nhu su dich chuyen
miic
nang lugng giua trang thai trong
v^
lap day dien tu trong
\'at
ly ban dan. nang lugng tai tao
Ej^
(reorgamzatior
energy) doi voi cap Redox chinh la dich
chuyen miic
nang lugng giua

tran^
thai oxy hoa
EQX
va khir
E^^
(hinh 1.2):
EQX
-
E^ed
=
2ER
(1.4)
Th6ng thuong gia tri ciia
E^
khoang vai tram eV.
1 rang
thai
UNOC
noox
OC
M&t
do
tranc
thai
Hinh
12:
Phdn
bo
mat do trang thdi vd muc
Ef^^j^,^

khi
nong do
C„=C,,j(duongl)
vd
C,,j=20C„,
(du&ng
2)
^
redox
^
l^OX
"*" ^
rec
Miic
Redox chuan (Standard Redox Potential)
•'^ redox
khi nong do
trang hai trang thai
ciia
cap Redox nhu nhau :
^=d) .
(1.5)
Hinh 1.2 la phan bo mat do trang thai phu thuoc vao n6ng do cua trang
thai
oxy hoa va khir.
Di^m
cat
ciia
phan bo trang thai oxy hoa va trang thai khu
tuong ling voi vi tri the Redox. Vi

tri
the Redox
ERe^ox
tuong
ling
voi trang thai
CO
do lap day dien ttr la 0,5 va phu thuoc vao ty
le
mat do ciia cac trang thai.
Di6m
khac biet giiia tiep
xiic
ban din-dien giai (SEI) va ban
din-kim
loai
la lop dien tich kep Helmholtz tren hi mat tiep
xiic.
Do dien giai la dung dich,
nen tinh
cha't
phan cue ciia cac phan
tir
dung m6i gan be mat se rat
phiic
tap.
Hinh 1.3 minh hoa cau tnic
Idip
Helmholtz tren hi mat oxide kim loai. Hang
so dien m6i thay doi phu thuoc vao khoang each den hi mat chat ran.

Neu kh6ng gian ciia
chat dien giai bi gioi ban ca
kich thude
Idp
Helmholtz
Be
mat Ovide
kim loai
—Ldrp
Helmholtz trong
lAfp
Helmholtz ngoai
(doi
vdd
cac nano - channel
cua mang nano - xop ), rat
CO
th^
cau triic dien
tir
ciia
be mat ban dan se bi thay
d6i.
Tinh
chat
Idp
Helmholtz anh huong manh
den qua trinh trao doi dien
tich tren hi mat tiep
xiic

nen
su thay d6i cau
iriic
vi m6
ciia no trong cac dien cue
nano-xop se dong vai tro
kh6ng nho trong he nay.
Cac Cation bi hoa
tan
Cac Anion bi hap phu
^
Cau tnic
nuoc
thong
thirc
(E=
71.4)
L(yp
nuoc
Ihtr
hai
(c-32}
Lap
nifoc
dau
lien
((-6)
(H\
grr
CalKtn

Hinh 1.3: Mo hinh
l&p
Hclmhoh: tren be mat
oxide kim loai
Sut the tren 16p Helmholtz do dien tich cua cac ion pha tap (Donor)
trong chat ban dan voi nong dp
N^
=
10'^ -10"'
cm"^
se khong
vugi
qua
0,1
V
[63].
Do vay anh huong
ciia
sut the tren lop Helmholtz den vi
tri
bien
viang
ban din trong truong hgp nay coi nhu kh6ng dang
ki.
— Doi
vdi
ban din oxide kim
loai,
sut the do thay d6i do pH
ciia

dung
dich
Ion
hon
nhi6u.
Phu thuoc cua dien the Helmholtz vao pH nhu sau : Tren
be mat oxide ton tai
nhi6u
tam luong tinh (Amphoteric Sites) co the tich dien
duong hoac am. Nhu vay ion
H"
co the
h^p
phu len cac tam do tao ra cac dien
tich bi mat, lam thay doi the
Hehnholtz:
M-0-
+
H"
< > MOH ; M-OH
+
H''
< >
MOHs^
(1.6)
Theo
[18]
phu thuoc the Helmholtz vao do pH (59 mV/ pH) co dang :
Aij)H =
const - 0,059xpH

(L7)
Do do, thay d6i bien
viing Ec
,
Ey ctia
ban din oxide kim loai tiep
xiic
vdi
dung dich dien giai, gay ra bdi pH co kha nang len toi vai tram meV
[28].
Hien tugng dich chuyen bien
viing
ciia chat ban din do anh huong cua
pH len the Helmholtz do'i vdi oxide kim loai ve ban chat hoan toan khac hien
tugng dich chuyen do thay doi
c^u
tnic dien
tir
be mat trong diiu kien dac biet
(sir
ly quang hoa dien cue kim cuong [19] hay trong dien cue cau tnic nano-
xop khi bi chieu sang [27] ) . Hien tugng nay co ihi gay ra cac tinh chat
kh6ng binh thuong
ciia
dien cue ban din nhu : phan ung Redox xay ra trong
d\iu
kien ma theo quan
di6m
c6 diin la kh6ng
Xhi

; thay d6i tinh chat dong
hoc ciia phan ung Redox trong dien cue
nano-xop w
. Van de ve cac qua
trinh vi mo tren tiep
xiic
ban din dien giai vin con gay nhieu tranh cai [49]
nhat la doi voi vat lieu co ca'u tnic Nano.
7.7.2
Qud trinh trao doi dien tich bdn ddn - dien gidi (Charge
Transfer Processes)
Trong tiep
xiic
ban din-ban din hay ban
din-kim
loai qua trinh trao doi
dien lich xay ra khi dien tir (16 trong)
chuye'n
dai giua hai pha va di chuyen
10
theo cac dinh
luat
vat ly kh6ng co su thay doi dong hat mang dien tich. Nhung
vol liep
xiic
ban din-dien giai. qua trinh trao doi dien tich xay ra cimg vdi
phan ling hoa hoc. lam thay doi cac phan
tii
(spices) tham
gia

qua trinh.
Vi
du
dien tu viing din cua ban din
chuy6n
doi (transfer) sang trang thai oxy hoa
(OX) ciia cap Redox gay ra phan
ling,
bien trang thai oxy hoa thanh trang thai
khu (Red). Khi do dong dien di
chuyen
trong mach
(uong
dien giai) la dong
ion. Tai dien cue doi, cac ion lam lai qua trinh phan ung trao doi dien tu va
dong dien trong mach ngoai la dong dien tu. Dong dien tich trong chat rin la
dien
tir
va trong dung dich la dong ion se lu6n kem theo phan ung hoa hoc
tren be mat tiep
xiic.
Mo hinh
miic
nang lugng (Energy Level Model of Charge Transfer) m6
ta qua trinh trao doi dien tich (kh6ng tinh den cac phan
ling
hoa tren hi mat)
th6ng qua cac th6ng so hien tugng
(phenbmeno
parameters) [22,49]

.
Vi du
mat do dong dien tich J chuyen
ddi
den phin tir thu dien
tich
A (acceptor)
nong do [A] co dang nhu sau:
J
= -e.k,,.n,.[A]
(1-8)
n,
-nong do dien tir (ban din loai n) be mat dien
cue
(cm"^);
e dien tich dien
tir.
k^t
- hang
s6'
toe
do (Rate constant) dac tnmg cho phan ling trao doi dien tu
ciia he cha't
ran
dung dich. Don vi ciia
k^i
la
cm"*
.s"^
.

Theo m6 hinh va cham c6 dien
(Qassical
Collisional model) ciia
Marcus [58] hing so t6'c do ciia tiep
xiic
SEI to'i da
k^Lmax
=
10''^cm'^
.s''.
M6
hinh va cham
nira
c6 dien ciia Morrison [63] va N. S. Lewis [50] cung nhu ciia
H. Gerischer [23] diu cho gia tri hing so t6'c do cung cap voi m6 hinh co
dien»
Ngay den nhung ly thuyet lugng ttr chinh xac hon [59.75] cung co
ciing
danh
gia vi
cue
dai ciia hing so toe do
(10''"'
-
10"'^
cm^.s"') ciia
qua trinh trao doi
dien tich tren tiep
xiic
ban din-dien giai.

Nhung
CO
mot so ket qua thuc nghiem [60] tren ban din
AIII-BV
nhu
GaAs
n-type
hay
GalnP
n-type
lai cho gia tri
k,,^,,
len den
10'*°
cm^s'.
Di6u
11
do cho thay anh huong cua
cau
"tnic dien tu be mat ban din den phan
ling
trao
d6i dien tfch
(toe
do phan
ling) chua phai da dugc lam
sang to hoan toan.
Xet ban din loai n va
miic
Redox nim gan

viing
din (trao d6i dien tir vdi
viing din) tren hinh 1.4 .
Bie'u
diin mat do dong J
(gia thuyet the Helmholtz
rat nho so vcri sut the roi
tren ban din ) co dang rat
don gian :
Kkh thirdc
Nong do trang thai
J
=
J,
exi
kT
-I
(1-9)
Hinh 1.4
:
Mo hinh phdn
bd
trang thdi
cua tiep
xiic
bdn ddn - Redox
rjcs
- vugt the (Overvoltage) giiia do cao rao the be mat khi phan cue
V^
va khi

canbing
VSO:T1SC=(VS-Vgo).
Dong
JQ
trong (1.9) ggi la dong trao doi
(exchange current). Cong
thiic
(1.9) hoan toan gi6ng Schottky diode vi mat
hinh
thiic
toan hgc. Tuy nhien ban
chait
hien tugng vat ly thi rat khac nhau.
Ve nguyen tic, neu xac dinh dugc
JQ
ta hoan toan co the dinh lucmg
dugc hanh vi cua dien cue ban din. Nhung thuc te, viec xac dinh dong trao d6i
kh6ng hi don gian do su
phiic
tap cua cau tnic dien
tii
be mat chat ban
din,
nhat la khi tiep
xiic
vdi dung dich
chiia
cac hoa chat. Doi voi dong trao d6i
JQ
giiia

ly thuyet va thuc nghiem cho den nay vin chua co su thong nhat.
M6 hinh ph6 bien di danh gia dong trao
ddi
la mo hinh
nhidu
loan nhiet
ciia
Gerischer [22,54] tom tat nhu sau : Su
chuyen
dcri dien tich
(Qiarge
Transfer) dugc mo ta la su trao doi dien
tir
giiia trang thai lap day va trang thai
12
trong tai hai phia
ciia
bien tiep
xiic.
Toe
do chuydn doi dien tir dugc mo ta :
o = V£T jx(E)Docc(E)DvAc(E)dE (i.lO)
"^ETT ^^
X(E)"
th6ng so dong hoc dac trung co che phan ling trao doi dien
tic±.
DQCC
' DvAC
"
^^t ^P ^3ng

thai lap day va trong tai hai phia ciia bien tiep
xiic.
Dong trao doi co
th6
biin diin qua cac thong so ciia tiep
xiic
nhu sau :
-(E-Eox)
Jo =q Jv(E)N(E){47iE,kTr^'cox.exp
Ecs
4ERkT
dE
(1.11)
Gia thiet ring phan
bd
cua dien
tir nSm a
day vung
d^n
do rong ~2kT ta co :
Jo=-q-v(Ecs)-nso-c,
/ \l/2
^
kT
^
7lE
exp
R
/
4E,kT

(1.12)
Tur
(1.10), (1.12) suy ra
ring hSng
so
toe
do trao doi dien
tich
co lien quan
vdi
do cao rao the trao ddi 6 =
(Ecs
-
ER^dox)
(Hinh
1.5)
:
k^
-v.exp
-(E
CS
redox
4ERkT
(1.13)
Thong so v(E) trong
(1.13)
dac tnmg cho co che trao doi dien tfch.
Chang han voi
m6
hinh va cham nhiet (Collison Model) v(E) la

tan
so"
\^
cham nhiet. Con m6 hinh trao doi qua tam hay co su tham gia ciia sai hong
b^
mat thi v(E) co dang khac.
Ham e - mu
bi6u
diin
su phu thuoc ciia hing so toe
do vao do cao rao the. Su phu
thuoc nay
rai
manh nen hien
tuong
dich
chuy6n
bien vung
Ecs CO
the gay ra thay doi
dang ke hang so
idc
do. Hien
tugng
nay se
dugc
di cap lai
irons noi duns luan an.
SEI
Ecs

V^.
Ban
dan
VvsNi
Dien giai
Hinh 1,5: Mo hinh muc nang luong cua tiep xu
Bdn ddn(n) - Dien gidi
13
1J3
Hieu ung quang dien hod dien cue bdn ddn
Hieu ung quang dien hoa dien
cue
ban din co the ly giai tren m6 hinh
miic
nang lugng (hmh 1.6) nhu sau : Trong
toi,
khi tiep
xiic
voi chat dien
giai,
-E:
RwJo*
Trong toi
Chieu sang
Hinh
1.6:
Co
che
hieu
iing

quang
dien
hod dien
cue
Bdn ddn loai n
tren
Idp
bi mat chat ban dan hinh thanh vung dien
tich
khong gian trong do
t6n tai dien
trudng
noi. Khi kich thich anh sang co nang lugng
Idn
hon do
rong vung cam cua ban din, se tao ra cac cap dien
tir-l6
trong. Do tac dong
cua dien truong, cac cap dien tir
16
trong bi tach ra tao thanh cac hat tai tu do
kh6ng can bang (qua trinh tach hat tai - Qiarge Separation Process). Dien tir tu
do (kh6ng can bang)
chuyfen
dong vi
phia
de din tao ra ngu6n hat tai trong
ban din.
L6
trong (kh6ng can bang) duoi lac dong ciia dien trudng trong

\aing
dien tfch khong gian,
chuy6n
dong len be mat ban din, tham gia phan umg
trao doi dien
ifch
vdi cac ion
ciia
dung dich. Cac hat tai khong
can
bang neu
tren tao ra suat dien dong quang dien trong dien cue ban din.
The quang dien dugc xac dinh thong qua muc gia Fermi
ciia
hat tai
kh6ng can bing
Up
E' -E
AE:
(1.14)
14
va lien quan den cuong do chieu sang
I:
Up
^kT^
ln(I) (1-15)
Khi chieu sang cuong do
Ion,
do cong ciia
viing

nang lugng chi co the dat
miic
gin phing, do do gia tri
cue
dai cua the quang dien chi co the bing chenh lech
giua
miic
Fermi ciia ban din va
miic
Redox ciia dung dich trong chan khong
(hinh 1.1) hay do cong
V^
ciia vung nang lugng (hinh 1.5).
Theo lap
lu^n
tren, the quang dien ciia tiep
xiic
SEI xac dinh theo nhiet
dong hgc (thermodynamic). Nhung
u-en
thuc te [48,50,72] cho thay the quang
dien
U^
khong chi lien quan dao
tinh
chit
nhiat
d6ng (cac
miic
nang lugng)

ma con hen quan den tinh chit dong hgc (kinetic) ciia cac qua trinh hen quan
nhu toe do trao doi dien tfch tren be mat hay qua trinh tai hgp. The quang
dien co
tinh
den dong hgc trao d6i dien tich ban
din-Redox
[48] nhu sau :
(1.16)
q
^nso.k^[OX]
Tih •
hieu suat lugng
tir ciia 16
trong kh6ng can bing co
Ihi
phan
utig
trao doi
dien tich vdi trang trai
khir
(RED) ciia cap Redox tren be mat tiep
xiic.
nso
nong do dien
rix
bi mat ban din khi can bing :
<t>Q -
cuong do photon ;
kET[OX]
hing

so'
toe do trao d6i dien tich ban din
—>
trang thai oxy hoa [OX]
Dong quang dien ciia hieu
iing
quang dien hoa tuong tu nhu doi vdi rao
the Schottky (kim loai- ban din).: la tong ciia dong di
dcfi
(migration current)
tir viing
dien tich khong gian
Jw
va khuech tan tu \iing trung hoa dien tfch
Jjif,-
Jph.x =Jw + Jd.fr =q^x
1-
1
l
+
a-L
(1.17)
X
- budc song don sic ;
Oi
- cuong do anh sang ;
O;.
- he so hap thu don sic ;
w - do rgng vimg dien tich khong gian ; L - do dai khuech tan .
15

Hieu
siid'l h(0ig tit
fp,
(quantum efficiency) duac xac dinh nhu sau :
J
h-
Jniw
I^A/cm"
(1.18
SEI
A*
A
—1
A
- - VTA/A-*)
Ban dan
VvsNHE
0ien
eiai
•
'• '*
//m/21.7
: Cac qud trinh tdi hop
vd
phdn
iing
cua
hat tdi khong can bang
Hieu suat qud trinh quang dien bi anh huong bai cac qua trinh tai hgp
va cac phan ling hi mat khac nhau :

1/
Tai
hcfp
viing-viing,
nhat la
viing
trung hoa dien tfch.
2/
Tai hgp qua tam
a
trong va tren bi mat ban din
(Vi
du bien hat cua dien
cue da tinh the
T1O2
dong vai tro tam tai hgp [69,82] ).
3/
Hat tai dong vai tro trong qua trinh an mon hi mat, dac biet la ban din
viing
cam hep.
•4/
Phan ling trao doi dien tfch voi cac ion trong dung dich, dong vai tro trong
he hat kfch
thude
nho va roi rac (dispersion) khi ty le be mat tren the' tfch
(surface-lo-volume
ratio) la
idn.
He sir dung hieu ung quang dien hoa (PEC Cell - PhotoElectroChemical
Cell) dugc ting dung rgng rai de bien doi nang lugng mat troi thanh cac dang

nhu dien nang (pin
PEC),
quang nang (Smart windows
),
hoa nang trong cac
ling dung quang
xiic
tac
de"
lam
sach moi truong vv.
1.2 Dien cure ban
dkn
caiu triic nano - xop
Nhung ling dung
ciia
he PEC
Ian
diu tien dugc de cap
boi
nhom Honda
va A. Fujishima [38] vao nhung nam diu thap ky 70 khi nghien
ciiu
qua trinh
quang dien hoa phan buy
nude
cua dien
cue Ti02
. Trong thap ky 80,
nhiing

van dd kh6ng giai
quy^'t
dugc vi do b6n cung nhu hieu suit cua dien
cue
ban
din trong m6i
trudng
hoa da
timg
lam nan long nhieu nhom nghien
ciiu.
Nhirng
budc dot pha thuc su trong
iing
dung he PEC chi suit hien khi
nhiing
vat lieu ban din cau tnic Nano dugc
sir
dung. Nhung
iing
dung cua he PEC sir
dung dien
cue
ban din cau tnic Nano trong cac
linh
vuc nhu pin mat trdi [70],
phan buy cac chit doc, lam sach moi trudng [52,73], phan buy chit hiru co
nhu diu mo
loang
trong

nude bi^n
[39], chua tri ung thu [20]
v\'
da va dang
thu
hiit
n6
lire
cua
nhi^u
nhom nghien
ciiu
tren the gidi.
Thoi gian gin day, nhdm vat lieu rit dugc quan tam la cac oxide kim
loai boi do bin va nhung dac tinh be mat thfch hgp cho qua trinh quang
xiic
tac,
dac biet la trong
iing
dung sir ly m6i trudng [25]. Han che ciia oxide kim
loai la vung cam rgng nen hieu suit pho thap. Phuong an to hgp tinh chat
b6n
ciia oxide va hieu suit ph6 ciia chat mau (ph6 hip thu rgng)
phii
len dien
cue
cau triic nano-xop da tao ra
nhimg iing
dung hieu suit cao. Dien hinh la pin
mat

udi
phu chat mau
[27,28.33]
(Dye Sensitized Solar cells) tren dien
cue
TiOn
nano-xop co hieu suit tren 10%. Mac dii dugc
iing
dung ngay cang rgng
rai nhung ban chat cac qua trinh
hoa-ly
trong he ban din nano-xop vin la
nhung van di tranh cai.
Trong he ciu tnic nano-xop, khi cac hat ban din co kfch thuoc nho hon
nhung kfch thuoc dac trung ciia vat lieu nhu do dai che chin
tinh
dien, do dai
khuech tan, do rgng
Idp
dien tfch kep
w
rat co the tfnh chat hoa ly
ciia
vat
lieu sc bi thay d6i. Phan nay se de cap tdi mot so van de
ciia
dien
cue
ban din
cau

true nano-xop trong he PEC , tap trung
chii
yeu vao anh huong
ciia
kfch
thuoc
hai
den cac
linh
chat hoa
Iv.
.
17
12.1 Hieu ung kich thuoc hat luong
tu
(Quantum size effect)
Hat
CO
kich thuoc lugng tir (Q particle) thuong dugc xem nhu mot trang
thai mdi
ciia
chat rin: la trung gian giira trang thai phan tir (phan bo
miic
nang
lugng roi rac) va tinh
th^
rin (hmh thanh vimg nang lugng).
Hieu ling kich thuoc lugng
tu^iy
ra khi ban kinh Bohr cua trang thai

exciton
thii
nhat (Bohr radius of the first exciton) trong ban din co the' so sanh
dugc hay 16n hon kich
thude
hat. Ban kinh Bohr
bi6u di6n
qua cac thong so
_
h^S£o
ciia
vat lieu nhu sau :
^B
~ 1 T (1-19)
c
Ttm^
m^
- kh6'i lugng hieu dung ciia dien tir trong ban din ;
s
- hing so dien mdi.
Vf du d6'i vdi
Ti02
:
m*
=
9m^
va s = 170 hieu ling kfch
thude
lugng tu xay
khi kich thuoc hat nho hon

lOA.
Tren thuc te Kormann [47] da t6ng hgp dugc
nhiing
hat
Ti02
co kich
thude
d<3 nm cd hieu
iing
kich thuoc lugng
tir
(md
rgng do rgng viing cim len 0,15 eV so vdi kfch thuoc
Ion).
Trong nghien
ciiu va miic
nang lugng ciia hat ban din kfch thuoc lugng
tir, Brus [9] va Henglein [34] da sir dung m6 hinh exciton de tfnh nhirng trang
thai nang lugng ciia cap dien tir - 16 trong bi nhdt trong hat tinh the hinh ciu
nho.
Nang lugng trang thai kich thfch
thii
nhat ciia hat ban din cd ban kinh R
I8e^
bieu
d\ir\
nhu sau : E =
E^(R
-
00)

+
1 1
—
+
—
m; m;
£R
(1.20)
8R-
Thanh phin
thii
nhat trong (1.19) la ciia ban din kfch thude
Idn
. Thanh phin
thii
hai la hieu
iing
lugng
tir ciia
dien tu va 16 trong . Phin
cudi
la tuong tac
Coulomb. Tuong tac Coulomb lam giam rgng viing cam ty le vdi
R'",trong
khi
dd hieu
iing
lugng
lir
ty le vdi

Rl
Nhu vay do rgng vung cam se tang khi ban
kfnh R
dii
nho.
Tuong tu nhu hien tugng dich
chuyen
bien hap thu (blue shift) do hieu
ling kfch thuoc lugng
lir
trinh bay d tren, nhung nghien
ciiu
ve phat quang
18
(photoluminescence) ciia
hat nho cung cho
nhirng
bang chiing ve hieu
iing
kfch thuoc. Su dich bien pho phat quang vi phia budc song ngin khi kfch
thuoc hat nho dugc
ki6m
chiing tren
nhi6u
vat lieu nhu CdS [67]
,
ZnO [45] ,
PbSe [61] ,
Cd^As2
[21] ,

Zn3P2
[84] w . Hieu
iing
kich thuoc lugng tu gidi
ban do
Idn
kich thude hat la ban kfnh Bohr din den nhirng tranh luan ve cac
hien tugng vat ly khi hat cd kich
thude Idn
hon
nhi6u
ban kinh Bohr .
122 He hat bdn ddn kich
thu&c
nho (Mesoscopic Semiconductor)
Cac nhdm nghien curu
d6u
rit than trgng trong viec dua ra gia tri
tuy6t
do'i ciia kfch thude hat ap dung cho cac hien tugng hieu
iing
kfch thude nho.
Do'i vdi hieu
iing
kfch
thude
lugng ttr nhu tren, ban kinh Bohr ciia cac chit ban
din nhu
Ti02
c5

Inm,
CdS - 2,4 nm , ZnO - 3nm w . Trong khi dd kich
thude
hat cho nhiing tinh chit quang dien hoa tot lai
Idn
hon nhieu ban kinh
Bohr . Vf du ddi vdi
Ti02
lam dien cue pin quang dien hoa, kfch thuoc ma
hieu suit tot nhit co vai
chue
nm [27,33] hay ddi vdi ZnO
' 150
nm [31].
Hieu ling kfch thude lugng
tir khdng
phai la
tinh
chit duy nhat chiu anh
huong
ciia
kich thude hat nho. Khi kich thuoc hat
Idn
hon ban kinh Bohr, hieu
ling bat giir lugng
tir
(quantum confinement)
khdng
con tac dung, thong ke co
dien cd the ap dung dugc de nghien

ciiu
cac tinh chat vat ly. Nhung doi vdi he
nay, mot
s6'
do dai dac tnmg ciia vat lieu nhu do dai che chin
tinh
dien (do dai
Debye), do dai khuech tan, do rgng
viing
dien tfch
khdng
gian hay kfch thude
Idp
dien tfch kep Helmholtz ciia be mat tiep
xiic
ban din dien giai lai cd the so
sanh dugc vdi kich thude hat.
Di6u
dd din den nhirng thay doi tfnh chit
cda
he
hat nho so vdd vat lieu ciing loai kich thude
Idn.
122.1 Che'tao
vat lieu
Nhung
tie'n
bg trong phuong phap
tdng
hgp va kha nang nghien

ciiu
cac
hat ban din
6
kich thude Nanomet da kfch thfch nhung nghien
ciiu
ve tfnh
chat vat ly ciia cac hat kfch
thude
lugng
tii
[79], cung nhu cac hien tugng khac
19
trong vung kfch
thude
Nanomet. Nghien
ciiu
cac tfnh chit val ly phu thuoc
kfch
thude
hat khong don
gian.
la do phan bo khong deu cua kfch thuoc hat
cung nhu ciu tnic pha tinh the trong cac miu nghien
ciiu.
Nhirng cd ging vi
cong nghe di
kiim
soat kfch thuoc cung nhu hinh dang hat da dugc dua ra
nhu

kiem
soat
chiim
nguyen tu [40], ket
tiia
hoa hgc cd kiem soat [47]. Nhung
phuong phap tao hat kich
thude
nho
phii
hgp nhit ca vi chat lugng cung nhu
kha nang kha thi la phuong phap sol-gel [88].
Quy trinh che tao dien cue ban din nano-xop thuong dung la phuong
phap
sol-gel : H6n hgp dugc tong hgp tir dung dich chiia cac chat ti6n dinh
phan ttr (Precursors) trong cac dieu kien nhiet d6, m6i trudng thich hgp. Mang
dien cue de nghien
ciiu
thuong dugc
phii
tren cac de din dien khac
nhau.
Quy
trinh tao miu hudng tdi
nhimg
muc dich sau :
- Do sach va
ddng nhit
pha. Nhin chung quy trinh sol-gel cho do sach
va ddng nhit pha tuong ddi tot. Do'i vdi

Ti02
[1,65] sin pham thu dugc cho do
sach tot va pha dong nhit Anatase 100%. Ngudi ta cd the
dieu
chinh ty le pha
Anatase va Rutile bing each thay doi nhiet do thieu ket sin pham.
-
Do hat thfch hgp va cd phan bd tap trung. Mot trong
nhirng
each
di6u
khien do hat trong qua trinh che tao
TiOj
la hip ap suit (Autoclaving). Theo
[65],
neu hap sol d nhiet do
200^C
se thu dugc sin pham 100% pha Anatase
cd phan bd kich thude hat rit diu
-'15nm.
Tang nhiet do
iSn 250^C
sin phim
cd phan bd kich thude
khdng
deu : xuat hien cac hat kfch thude >
1 OOnm
.
- Do xop thfch hgp. Do phan
iing

cd fch d day la qua trinh dien hoa tren
be mat tiep
xiic
ban din dien giai, nen tang so lugng hi mat phan
iing
cung la
muc dich cua ciia cong nghe che tao dien cue loai nay [27]. Phuong an tang hi
mat n6i (internal surfaces) la tang do xop den
miic
thfch hgp
(nhidu
hi mat noi
dong thdi tiep
xiic
giiia cac hat tot). Giai phap la
dijng
phu gia dang polymer
dua them vao sol
de'
khi thieu ket cac goc
huu
co bay di tao ra cac 16 xop va
chgn nhiet do thieu kei tao mang thfch hgp .
20
-
Dp
day thich hgp. Cac
iing
dung khac nhau doi hoi do day cua
dien

cue
khac nhau. Ddi vdi ciia s6 dien sic. do day mang dien
cue
TiO.
khoang 3-
4
|im
de dam bao su trong su6t [29]. Nhimg dien
cue
cho quang
xiic
tac
khi
do
trong sudt kh6ng phai cot yeu, ddi hoi do day
Idn
hon. Dien
cue loai
nay cd
the day vai
\xxn
den vai chue
^m.
De
che tao mang day vai
|im
ma vin trong
sudt ddi hoi cac sol cd do dam dac cao (ma vin trong sudt) [26] ; quy trinh
phu mang
i*ai

lap lai nhieu
lin.
Theo c6ng bd [43,29,33]
,
ke't qua cho mang
cd do day tir 5-10
|im,
cd do xop khoang 1/ 2 va do trong sudt tot.
1222
Muc ndn2
luons
vd co che tdch hat tdi
Ddi vdi ban din kich thude
Idn,
co che tach hat tai la do dien trudng tai
vimg tiep
xiic
vdd dien giii nhu trinh bay d phin tren. Nhung ddi vdi hat ban
din
kich
thude nho vin de se khac.
Phan bd the trong hat ban din dang hinh ciu cd kich thude nho dugc
Albery
\'a Bartlen
[3] tfnh toan dua tren phuong trinh Poisson-Boltzmann dugc
tuyeh tinh hoa. Bieu dien do cong
vimg
theo kh6ng gian cd dang :
A^
*^T

6e
r-(ro-W)
1
+
2(r,-W)
(1-21)
r-
kfch
thude
tinh tu tam
(r=0)
;
ro
ban kinh
ciia
hinh ciu chat ban din
LD
- do dai Debye ban din (
L^
=
{zz^kT/le^'N^f^):
W- do rgng viing ngheo.
Trong hat kfch thude
Idn,
toan bg do cong viing (Total Band Bending):
AA
^^
2e
Ddi vdi hat ban kfnh
ro

nho hon W
W_
A<|»o =
kT
6e
V^D
y
(1.22)
(1.23)
De cd 50 mV sut the trong hat
Ti02
6nm doi hoi nong do pha tap
-5.10'"
cm
'.
Khi dd hieu qua tach hat tai ciia dien trudng thap, nen co che chuyen hoa nang
lugng quang-dien trong he hat nho cd the
khdng
gidng he hat
Idn.