LI CAM OAN Tụi xin cam oan õy l cụng trỡnh nghiờn cu ca riờng tụi Cỏc s liu, kt qu lun ỏn l trung thc, cha tng c tỏc gi khỏc cụng b Tụi xin cam oan rng mi s giỳp cho vic thc hin lun ỏn ó c cm n, cỏc thụng tin trớch dn lun ỏn ny u c ch rừ ngun gc H Ni, Ngy thỏng nm Tỏc gi lun ỏn i LI CM N Trc tiờn, tụi xin by t lũng bit n sõu sc ti thy hng dn GS.TS Trn Trung, ngi ó nh hng, hng dn, giỳp tụi hon thnh cỏc nhim v t cho lun ỏn Tụi xin chõn thnh cm n cỏc thnh viờn Nhúm iSensor Vin o to Quc t v Khoa hc Vt liu (ITIMS) nhng ngi ó ch bo cho tụi cỏch nghiờn cu khoa hc, nh hng nghiờn cu cho tụi c bit tụi xin gi li cm n sõu sc n cỏc thy GS.TS Nguyn Vn Hiu v PGS TS Nguyn c Hũa ó giỳp tụi rt nhiu tụi cú th hon thin lun ỏn ca mỡnh Tụi xin chõn thnh cm n ti Ban giỏm c, B mụn Vt liu in t & cm bin thuc Vin o to Quc t v Khoa hc Vt liu (ITIMS), Vin o to sau i hc - Trng i hc Bỏch khoa H Ni ó to iu kin giỳp tụi sut thi gian hc v thc hin ti Tụi xin chõn thnh cm n Lónh o Trng i hc S phm K thut Hng Yờn ó to iu kin thun li v thi gian, cng nh cỏc s giỳp ng h khỏc giỳp tụi hon thnh bn lun ỏn ny Xin chõn thnh cm n n tt c cỏc ng nghip, bn bố v gia ỡnh ó ng viờn giỳp thi gian qua v chuyờn mụn cng nh v vt cht ln tinh thn cú liờn quan trc tip hoc giỏn tip giỳp tụi hon thnh bn lun ỏn ny Tỏc gi lun ỏn Hong Vn Hỏn ii DANH MC CC Kí HIU V CH VIT TT Ký hiu Tờn ting Anh Tờn ting Vit CVD Chemical vapor deposition Lng ng hi húa hc EDX Energy-Dispersive X-ray Tỏn sc nng lng tia X FE-SEM Field Emission Scanning Electron Kớnh hin vi in t quột phỏt x Microscope trng Nb Niobium Niobi NO2 Nitrogen (IV) Oxide Ni - t (IV) ụ - xớt P123 Pluronic Pluronic ppm parts per million Mt phn triu PID Proportional integral derivative B iu khin vi tớch phõn t l PL Photoluminescence Phỏt x hunh quang R Resistance in tr SLS Solid Liquid Solid Rn Lng Rn sccm standard cubic centimeter per Centi-một trờn phỳt minute (ml trờn phỳt) MFC Mass flow controler Thit b iu khin lu lng khớ SAED Selected area electron diffraction Nhiu x in t vựng c chn SEM Scanning Electron Microscope Kớnh hin vi in t quột TEM Transmission Electron Microscope Kớnh hin vi in t truyn qua Ultravioletvisible spectroscopy Ph t ngoi-kh kin XRD X-ray diffraction Nhiu x tia X ZnO Zinc Oxide Km ụ-xớt UV-Vis iii MC LC CHNG 1: TNG QUAN 1.1 Gii thiu tng quan v ZnO 1.1.1 Cu trỳc tinh th ca vt liu ZnO .1 1.1.2 Mt s c tớnh ni bt ca vt liu ZnO cu trỳc mt chiu 1.1.3 Mt s ng dng ca vt liu ZnO mt chiu 1.2 Cỏc phng phỏp ch to s lng ln v dõy nano dng t 10 1.2.1 Ch to nano ZnO bng phng phỏp bc bay nhit .10 1.2.2 Ch to nano ZnO bng phng phỏp thy nhit 15 1.2.3 Ch to nano ZnO bng quỏ trỡnh nhit 21 1.3 Cm bin khớ dng dn 25 1.3.1 Khỏi nim v cm bin 25 1.3.2 Cỏc i lng c trng ca cm bin .26 1.3.3 Cu to ca cm bin khớ kiu thay i in tr 29 1.3.4 Cỏc dng vt liu s dng ca cm bin khớ 30 1.3.5 Cỏc yu t nh hng n c tớnh ca cm bin khớ .32 1.3.6 Nguyờn lý hot ng ca cm bin khớ 37 CHNG 2: THC NGHIM V PHNG PHP NGHIấN CU 40 2.1 Tng hp vt liu nano ZnO 40 2.1.1 Ch to nano ZnO bng phng phỏp thy nhit 40 2.1.2 Ch to vt liu nano ZnO mt chiu bng phng phỏp bc bay nhit 43 2.2 Ch to cm bin trờn c s vt liu nano ZnO 46 2.2.1 in cc s dng cho cm bin .46 2.2.2 Ch to cm bin 46 2.2.3 Ch to cm bin s dng dõy nano bin tớnh bng Nb2O5 .47 2.3 o cỏc c trng ca vt liu 48 2.3.1 Kho sỏt cỏc tớnh cht c bn 48 2.3.2 Kho sỏt cỏc c trng ca cm bin .48 iv 2.3.3 Quy trỡnh o .49 2.3.4 Cỏc tớnh toỏn cho cỏc c trng ca cm bin 50 CHNG 3: KT QU V THO LUN 52 3.1 ỏnh giỏ quy trỡnh ch to v nghiờn cu cỏc tớnh cht c bn ca vt liu nano ZnO 52 3.1.1 Thanh nano ZnO ch to bng phng phỏp thy nhit 52 3.1.2 Nano ZnO ch to bng phng phỏp bc bay nhit .58 3.2 c trng nhy khớ ca vt liu nano ZnO 72 3.2.1 La chn nhit ca cm bin 72 3.2.2 Tớnh cht nhy khớ ca cm bin s dng nano ZnO ch to bng phng phỏp thy nhit 74 3.2.3 Tớnh cht nhy khớ ca cm bin s dng dõy nano ZnO ch to bng phng phỏp bc bay nhit 79 3.2.4 Tớnh cht nhy khớ ca cm bin nano tetrapod ZnO ch to bng phng phỏp bc bay nhit 84 3.3 c trng nhy khớ ca cm bin dõy nano ZnO bin tớnh Nb2O5 87 3.3.1 c trng c bn ca dõy nano ZnO bin tớnh 88 3.3.2 Tớnh cht nhy khớ ca cm bin dõy nano ZnO bin tớnh theo nng Nb2O5 khỏc 89 3.4 Phõn tớch, ỏnh giỏ v so sỏnh cỏc loi vt liu nano ZnO ch to c v c trng nhy khớ ca chỳng 93 3.4.1 Vt liu nano ZnO 93 3.4.2 Tớnh cht nhy khớ ca cỏc vt liu nano ZnO 96 KT LUN CHUNG 105 TI LIU THAM KHO 106 DANH MC CC CễNG TRèNH CễNG B CA LUN N 107 v DANH MC HèNH V Hn Mụ hỡnh minh cu trỳc tinh th bn vng ca ZnO theo kiu Wurzite (a) v Zincblende (b) Hn Ph phỏt quang ca cỏc nano ZnO vi kớch thc tinh th khỏc Hn : Ph hunh quang ca ZnO vi cỏc cu trỳc nano mt chiu cú hỡnh dng khỏc .4 Hn Gin mc nng lng ca ZnO Hn c trng I V ca dõy nano ZnO (a), s ph thuc ca in tr dõy nano ZnO theo nhit (b) Hn Minh cu to chung ca FET (MOSFET) .7 Hn : c trng IDS-VDS (A), IDS-Vg ca FET s dng dõy nano ZnO (B) Hn Cu trỳc ca mt cm bin húa hc s dng vt liu nano ZnO Hn Sn phm ZnO c tng hp bng phng phỏp bc bay (a,) nh FE-SEM ca sn phm (b,c) v nh HR-TEM (d) 12 Hn nh HR TEM ca vt liu ZnO (a,b), SEAD ca ZnO (c,d) .13 Hn : Quy trỡnh ch to vt liu bng phng phỏp thy nhit 16 Hn : nh SEM (a,b), nh HR-TEM ca vt liu nano ZnO (c,d) .17 Hn : nh TEM ca cỏc sn phm ZnO thờm Na2CO3 vi cỏc lng khỏc nhau: 5g (a) v 10 g (b) .18 Hn C ch hỡnh thnh dõy nano ZnO bng phng phỏp thy nhit 19 Hn : nh SEM vựng nhit trung bỡnh 800 850 C (a, b, c), vựng nhit trung bỡnh 700- 800 C (d, e, f) 22 Hn : nh TEM (a), HR- TEM (b), SEAD (c) ca nano ZnO .23 Hn S s ca bn c ch cú th cú ca chuyn ion phn ng ụ - xi húa, s chuyn ca cỏc ion ụ - xi ca c ch k ụ - xi (a), s chuyn ca cỏc ion ụ - xi ca c ch trng ụ - xi (b), s chuyn ca cỏc ion kim loi bng c ch in k kim loi (c), chuyn ca cỏc ion kim loi bng c ch kim loi trng (d) 24 Hn S ph thuc ca ỏp ng vo nng o (Ethanol) [ỏp ng khớ ca cm bin mó s TGS2611 ca hóng Figaro c ng ti trờn trang web ca hóng] .27 vi Hn : c tuyn mụ t quỏ trỡnh hi ỏp cm bin tng tỏc vi khớ o .28 Hn Cu to ca cm bin khớ 29 Hn Cu to cm bin dng 30 Hn Kt cu dng mng 31 Hn : Kt cu dng dõy 32 Hn Hỡnh mụ t lp tip xỳc gia dõy nano trờn cm bin 33 Hn : nh hng ca kớch thc dõy n ỏp ng ca cm bin 34 Hn S ph thuc ca ỏp ng vo nhit .35 Hn : S nng lng ti b mt ca ht tinh th 37 Hn : C ch hp ph khớ thụng qua s gim vựng dn ca dõy nano 38 Hn Hỡnh nh mt s thit b s dng quỏ trỡnh ch to vt liu nano ZnO bng phng phỏp thy nhit 41 Hn S ch to vt liu ZnO bng phng phỏp thu nhit 42 Hn : S minh h ch to vt liu ZnO bng phng phỏp bc bay nhit 44 Hn nh ca lũ dựng ch to dõy nano ZnO bng phng phỏp bc bay nhit 45 Hn Minh cu trỳc in cc rng lc ca cm bin .46 Hn Chu trỡnh nhit ca linh kin cm bin nano ZnO .47 Hn : S nguyờn lý ca h trn khớ 49 Hn Giao din phn mm VEE Pro ghi nhn s thay i in tr ca cm bin theo thi gian thay i nng khớ 49 Hn : Minh vic tớnh toỏn thi gian ỏp ng v thi gian hi phc ca cm bin 50 Hn nh SEM ca vt liu ZnO ch to bng phng phỏp thu nhit vi pH khỏc pH = (a), pH = (b), pH = 10 (c) v pH = 11 (d) 53 Hn nh SEM (a), nh HR-TEM (b,c,d) v nh bin i Fourier hai chiu - FFT (e) ca nano ZnO c ch to vi pH = 10 54 Hn nh TEM (a), phõn b EDS ca cỏc nguyờn t C (b), O(c) v Zn (d) ca nano ZnO c ch to iu kin vi pH = 10 55 vii Hn Gin nhiu x XRD ca vt liu nano ZnO ch to bng phng phỏp thy nhit vi pH =10 56 Hn Ph hp th UV-Vis ca vt liu nano ZnO ch to bng phng phỏp thy nhit vi pH =10 56 Hn : Ph hunh quang (PL) ca vt liu nano ZnO c ch to bng phng phỏp thy nhit vi pH =10 57 Hn : nh minh dõy nano ZnO thu c trờn cc thy tinh v h mu I (a), h mu II (b) v h mu III (c) 60 Hn : nh SEM mu M11 vi phúng i khỏc ca cỏc cu trỳc dng dõy (a, b) v dng cú cỏc tetrapod (c, d) .62 Hn : nh SEM mu M12 vi phúng i khỏc ca cỏc cu trỳc dng dõy (a, b) v dng cú cỏc tetrapod (c, d) .62 Hn : nh SEM mu M13 vi phúng i khỏc ca cỏc cu trỳc dng dõy (a, b) v dng cú cỏc tetrapod (c, d) .63 Hn : nh SEM mu M14 vi phúng i khỏc ca cỏc cu trỳc dng dõy (a, b) v dng cú cỏc tetrapod (c, d) .63 Hn : nh SEM mu M15 vi phúng i khỏc ca cỏc cu trỳc dng dõy (a, b) v dng cú cỏc tetrapod (c, d) .64 Hn nh TEM ca dõy nano ZnO 65 Hn : nh HR-TEM (a,b), bin i Fourier hai chiu-FFT (c) v ph biu din s phõn b 38 mt phng 10 nm (d) ca dõy nano ZnO .65 Hn : nh SEM (a), nh TEM (b,c); bin i Fourier hai chiu - FFT (d), HRTEM (e,f), ph biu din s phõn b 38 mt phng 10 nm (g) ca vt liu nano ZnO cú cu trỳc tetrapod 66 Hn Gin nhiu x tia X ca dõy nano ZnO ch to bng phng phỏp bc bay nhit 68 Hn Ph phỏt x hunh quang ( PL) ca dõy nano ZnO ch to bng phng phỏp bc bay nhit 69 Hn 18: Ph hunh quang ca dõy nano ZnO vi cỏc nhit mu khỏc t 400 700 oC ti vựng t ngoi 381 nm (a) v vựng kh kin 514 nm (b) .70 Hn S minh quỏ trỡnh hỡnh thnh dõy nano ZnO bng phng phỏp bc bay khụng s dng mm xỳc tỏc ban u 71 viii Hn Minh c ch hỡnh thnh nano tetrapod ZnO bng phng phỏp bc bay nhit 72 Hn : ỏp ng ca cm bin s dng dõy nano ZnO ti nhit hot ng l 250 oC vi nng NO2 khớ t 0,5 n 10 ppm ng ti nhit mu khỏc l 400 oC (a), 500 oC (b), 600 oC (c) v 700 oC (d) .73 Hn : in tr ca cm bin dõy nano ZnO o 10 ppm NO2 nhit t 400 oC n 700 oC 73 Hn : S ỏp ng in tr ca cm bin nano ZnO vi nng khớ NO2 t 0.5 ppm n 10 ppm ti nhit lm vic khỏc 200 oC (a), 250 oC (b), 300 oC (c) v 350 oC (d) 75 Hn ỏp ng ca cm bin nano ZnO ph thuc vo nng khớ NO2 ti cỏc nhit t 200 n 350 oC 76 Hn hi ỏp ca cm bin nano ZnO vi v 10 ppm khớ NO2 ph thuc vo nhit hot ng 76 Hn in tr ca cm bin nano ZnO ỏp ng vi ppm khớ NO2 ti cỏc nhit lm vic t 200 oC n 350 oC 77 Hn S ph thuc thi gian ỏp v thi gian hi phc ca cm bin nano ZnO vi nng khớ NO2 l ppm vo nhit lm vic t 200 oC n 350 oC .78 H nh 3.28: ỏp ng ca cm bin nano ZnO theo chu k o vi ppm NO2/khụng khớ ti nhit hot ng 250 oC 79 Hn ỏp ng ca cm bin dõy nano ZnO theo nng khớ NO2 ti nhit hot ng 200 oC (a), 250 oC (b), 300 oC (c) v 350 oC (d) 80 Hn : S ph thuc ỏp ng ỏp ng khớ vo nng khớ NO2 ti cỏc nhit hot ng t 200 n 350 oC 80 Hn : ỏp ng ca cm bin dõy nano ZnO vi v 10 ppm khớ NO2 ph thuc vo nhit hot ng 81 Hn : S ph thuc ca in tr cm bin dõy nano ZnO ỏp ng vi 1ppm NO2 ti cỏc nhit hot ng t 200 350 oC 82 Hn Thi gian ỏp ng v thi gian hi phc ca cm bin dõy nano ZnO vi nng ppm ph thuc vo nhit hot ng t 200 350 oC .83 Hn : ỏp ng ca cm bin dõy nano ZnO vi chu kỡ ca ppm khớ NO2/khụng khớ 83 ix Hn ỏp ng ca cm bin nano tetrapod ZnO vi cỏc nng NO2 ti nhit hot ng 200 oC (a), 250 oC (b), 300 oC (c) v 350 oC (d) .84 H nh 3.36: ỏp ng ca cm bin nano tetrapod ZnO ph thuc vo nng khớ NO2 ti cỏc nhit hot ng khỏc .85 Hn ỏp ng ca cm bin nano tetrapod ZnO theo nhit vi nng khớ v 10 ppm NO2 85 Hn S thay i in tr ca cm bin nano tetrapod ZnO vi nng khớ ppm ti cỏc nhit hot ng 200 oC (a),250 oC (b), 300 oC (c) v 350 oC (d) .86 Hn Thi gian ỏp ng v thi gian hi phc ca cm bin nano tetrapod ZnO vi nng ppm ph thuc vo nhit hot ng 87 Hn nh SEM ca cỏc mu dõy nano ZnO bin tớnh bng Nb2O5: M4 (a), M3 (b), M2 (c) v M1 (d) .88 Hn : Ph tỏn x nng lng EDS ca dõy nano ZnO bin tớnh bng Nb2O5 89 Hn : ỏp ng ca cm bin M1 (a), M0 (b) vi nng khớ NO2; ỏp ng ca cỏc cm bin ph thuc vo nng khớ NO2 (c); biu ỏp ng ca cỏc cm bin M0, M1, M2, M3 v M4 vi 10 ppm NO2 (d) hot ng ti 200 oC .90 Hn : ỏp ng ca cm bin M vi khớ NO2 ti nhit hot ng 200 oC (a), 250oC (b), 300 oC (c) v 350 oC (d) 91 Hn : ỏp ng ca cm bin M2 ph thuc nng khớ NO2 (a), ph thuc nhit hot ng vi ppm v 10 ppm khớ NO2 (b) 91 H n 3.45: in tr cm bin M2 ỏp ng vi ppm NO2 ti cỏc nhit hot ng 92 Hn : Thi gian ỏp ng v hi phc ca cm bin M2 vi ppm NO2 ph thuc vo nhit hot ng t 200 n 350 oC .92 Hn nh SEM, TEM, HR - TEM ca cỏc loi vt liu nano ZnO ch to bng phng phỏp thy nhit v bc bay nhit 94 Hn Gin nhiu x tia X (a), v ph phỏt x hunh quang (b) ca nano v dõy nano ZnO 95 Hn Minh cỏc mc nng lng vựng cm gõy bi cỏc sai hng cu trỳc vt liu ZnO [102] 95 x O2 + 2e 2O- (ads) (3.16) Trong dõy nano ZnO, in t cng c bt ngun t cỏc nguyờn t km in k Zni2 + hoc khuyt thiu oxy (VO) úng vai trũ l ngun cung cp in t Trong ú khớ NO2 b hp ph v tng tỏc vi b mt dõy ZnO nh ó trỡnh by trờn Nb2O5 O2 Vựng nghốo H Nb2O5 Vựng dn Nano ZnO 3.52: Minh s m rng kờnh dn in ca dõy nano ZnO cú bin tớnh cỏc ht Nb2O5 Khi cú cỏc vt liu nn oxit kim loi c bin tớnh cỏc cht xỳc tỏc trờn b mt (c th õy l dõy nano ZnO bin tớnh ht Nb2O5) Khi cha tng tỏc vi cỏc khớ, ZnO c bin tớnh trờn b mt bng Nb2O5 thỡ cú th to s thay i v dn in mnh Chi tit, s gia tng dn in ca ZnO bin tớnh Nb2O5 l c ch th hỡnh thnh cỏc ht ti in c mụ t nh l [85]: NbZn NbZn 3e (3.17) Nb2O5 (ZnO) 2Nb+Zn + 2O- + 3/2 O2 (g) (3.18) Nh cỏc phng trỡnh trờn, s lng ca cỏc in t vựng dn ca dõy nano ZnO s tng, rng kờnh dn in dõy nano ZnO s m rng nh th hin trờn Hỡnh 3.52 Hn na, bin tớnh thỡ tn ti nhiu im m cỏc ht Nb2O5 ni cỏc dõy nano vi Do vy, in tr tng cng cm bin s gim mnh so vi trng hp khụng bin tớnh (nh kt qu ó trỡnh by trc õy Mc 3.3.2) T cỏc hiu ng trờn, cm bin dõy nano ZnO bin tớnh Nb2O5 tng tỏc vi khớ NO2 thỡ cht xỳc tỏc úng vai trũ phõn ly cỏc phn t khớ hp ph v phõn tỏn chỳng trờn b mt ca vt liu cm bin theo nguyờn tc trn spill-over [89].Do ú, in tr ca cm bin tng mnh lm cho t s in tr sau v trc tng tỏc khớ ( ỏp ng) thay i mnh 100 c) ỏ iỏ tớ c t ca cỏc cm bin nano ZnO Nhm tỡm mi liờn h gia hỡnh thỏi hc, cu trỳc tớnh th, tớnh cht quang vi cỏc c trng nhy khớ tng ng ca cỏc vt liu nano ZnO ch to t hai phng phỏp thy nhit v bc bay nhit, chỳng tụi ỏnh giỏ phõn tớch v so sỏnh mt cỏch h thng cỏc kt qu nhy khớ NO2 thu c t cỏc cm bin ny Độ đáp ứng RG/RA 50 40 30 20 10 Thanh nano Dây nano Nano tetrapod 150 200 250 300 350 o Nhiệt độ ( C) H 3.53: ỏp ng ca cỏc cm bin nano ZnO dng thanh, dõy v tetrapod vi 10 ppm NO2 ph thuc vo nhit hot ng Hỡnh 3.53 ch ỏp ng ca cỏc cm bin nano ZnO dng thanh, dõy v tetrapod vi 10 ppm NO2 ph thuc vo nhit hot ng Kt qu ny ch rng ỏp ng ca cm bin nano ZnO cú cc i ti nhit hot ng 250 oC cũn cm bin dõy nano hay nano tetrapod ZnO thỡ ti nhit hot ng c 200 oC Cm bin nano ZnO dng dõy hoc nano tetrapod cú ỏp ph thuc vo nhit l rt ging cú kiu dỏng cng nh ln, kt qu ny cho thy minh chng hai vt liu cú cựng ngun gc hỡnh thnh ỏp ng ca hai cm bin ny gim khỏ nhanh theo chiu tng nhit hot ng (ti 350 oC thỡ ỏp ng RG/RA ca cm bin ch khong l 6) Khi so sỏnh thỡ cm bin nano ZnO th hin ỏp ng khỏ ln vựng nhit hot ng cao, ti 350 oC thỡ ỏp ng l RG/RA = 16 Theo chỳng tụi, kt qu ny th hiờn trờn Hỡnh 3.53 ny v cỏc cm bin cú th l liờn 101 quan n hon ho ca tinh th cng nh tớnh nh hng tinh th u tiờn ca cỏc vt liu nano ZnO ch to lun ỏn C th nh sau: - Thụng thng, nano ụ-xớt kim loi cú nh hng tớnh th u tiờn s tn ti mt s trng thỏi nng lng riờng bit no ú tng ng vi nh hng tinh th [41, 42] Vỡ vy, vt liu cú ng nht cao v tớnh nh hng tớnh th tt thỡ s cú tớnh chn lc tng tỏc vi mt loi khớ no ú iu ny s tng ng vi cm bin da trờn vt liu ú s cú mt vựng nhit hot ng hp Trờn c s ú xột cho cỏc cm bin nano ZnO lun ỏn ny, chỳng ta cú dõy nano ZnO hay nano tetrapod ZnO cú tớnh ng nht, hon ho tinh th v nh hng tinh th tt hn nhiu so vi nano ZnO Vỡ th, hiu ng ny cú th l nguyờn nhõn m cm bin dõy nano ZnO hay cm bin nano tetrapod ZnO cú nh ca ng ỏp ng vi khớ NO2 ph thuc vo nhit hot ng nhn hn, cng nh vựng nhit hot ng ti u thp hn so vi ca cm bin nano ZnO - Chỳng ta ý rng khớ NO2 cú xu hng t phõn hy mt phn thnh NO nhit cao Do vy, hot ng nhit cao nano ụ-xit kim loi m cú nhiu trng thỏi nng lng b mt (vớ d nh nano ZnO ch to lun ỏn ó bit cú tớnh hon ho tinh th v nh hng tinh th kộm hn) thỡ cú th tng tỏc khớ s phc v cựng lỳc vi nhiu loi khớ (NO2 v NO), dn n vựng nhit hot ng ca cm bin nano ZnO ny m rng v vựng nhit cao Khi xột cho cỏc cm bin dõy nano ZnO hoc nano tetrapod cỏc vt liu cú th ch cú mt s nng lng riờng bit m ti u cho tng tỏc vi khớ NO2 nhit thp Ngoi ra, minh chng thờm cho lp lun trờn v mi liờn h gia c trng nhy khớ vi tớnh cht tinh th v ng nht ca cỏc nano ZnO, chỳng tụi xem xột n thi gian hi ỏp ca cỏc cm bin Bng 3.3 lit kờ thi gian ỏp ng v thi gian hi phc ca cỏc cm bin vi 2,5 ppm khớ NO2 ti hai nhit hot ng l 200 v 350 oC T cỏc kt qu ny chỳng tụi nhn thy rng: Cỏc cm bin nano ZnO u th hin s tng i phự hp gia thi gian ỏp ng v hi phc Nu cm bin cú thi gian ỏp ng di thỡ cng cú thi gian hi phc di Cm bin dõy nano ZnO v nan tetrapod ZnO cú giỏ tr thi gian hi ỏp gn nh ti mi nhit hot ng Khi so sỏnh thỡ cm bin nano ZnO cú thi gian hi ỏp cú xu hng l nh hn ti cỏc nhit hot ng Kt qu ny cú th c gii thớch nh sau: 102 - Vt liu nhy khớ cú nhiu sai hng (thanh nano ZnO) dn n tn ti nhiu mc nng lng vựng cm iu ny lm cho vt liu cú nng ht ti (in t) ln, ú rng vựng nghốo (hoc rng Debye LD) trờn b mt gim Nh chỳng ta ó bit c ch nhy khớ ca oxit kim loi bỏn dn l quỏ trỡnh trao i in t vựng dn vi cỏc khớ hp ph trờn b mt qua mt lp cỏch in (hay cũn gi vựng nghốo) Vy, vựng nghốo ca vt liu gim thỡ quỏ trỡnh trao i in t dn gia vt liu v khớ (NOx) d dng, tc l thi gian hi ỏp gim - Tuy vy, nu vt liu cú nhiu mc nng lng vựng cm sai hng thỡ in t tr v sau quỏ trỡnh tng tỏc vi NO2 (cm bin hi phc sau quỏ trỡnh ngt khớ NO2) s cú th dch chuyn qua nhiu trng thỏi nng lng Chớnh vỡ vy hiu ng ny cú th l nguyờn nhõn m thi gian hi phc ca cm bin nano ZnO ti nhit hot ng thp 200 oC cú thi gian di so vi cỏc cm bin khỏc 3.3: Bng lit kờ thi gian hi ỏp ca cỏc cm bin nano ZnO vi 2,5 ppm khớ NO2 ti nhit hot ng 200 v 350 oC Vt liu N it ot T i gian ỏp ng T i gian i p c ng ( C) ti , ppm NO2 ti , ppm NO2 200 76 76 350 46 16 200 81 62 350 49 19 200 92 56 350 53 21 200 91 34 350 16 o Thanh nano ZnO Dõy nano ZnO Nano tetrapod ZnO Dõy nano ZnO bin tớnh Nb2O5 Cỏc gii thớch v lp lun ny mt ln na minh chng mi liờn h cht ch gia tớnh cht nhy khớ v cỏc c trng v cu trỳc tớnh th, s sai hng, ng nht ca vt liu nano ZnO lun ỏn 103 Trong lun ỏn ny, vic chỳng tụi th nghim bin tớnh dõy nano ZnO bng Nb2O5 ó cho thy nhng kt qu rt kh quan so sỏnh vi cm bin dõy nano ZnO khụng bin tớnh v ỏp ng tng lờn hng trm ln v thi gian hi ỏp cng c gim khỏ nhiu (thi gian ỏp ng gim t 53 giõy n 16 giõy, thi gian hi phc gim t 21 giõy v giõy ti nhit hot ng 350 oC) Kt lun c ng Thanh nano ZnO vi kớch thc 50 nm ì 500 nm ó c ch to thnh cụng bng phng phỏp thy nhit iu kin pH=10, nhit 160 oC, v khụng s dng mm kt tinh ban u Dõy nano ZnO v nano tetrapod ZnO vi kớch thc ng kớnh c 30 nm ó c ch to bng phng phỏp bc nhit iu kin ỏp sut khớ quyn, nhit phn ng 1100 oC, thi gian ngn (15 phỳt), v khụng s dng mm kt tớnh ban u Hai quy trỡnh dựng ch to vt liu nano ZnO, dõy nano ZnO v nano tetrapod ZnO u cho hiu sut cao tng ng c 80% v 10 % Cỏc cm bin trờn c s vt liu nano ZnO ch to c kho sỏt nhy khớ NO2 vi nng t 0,5 n 10 ppm ti vựng nhit hot ng t 150 n 350 oC Cỏc cm bin ny u cú ỏp ng khớ tt v khỏ ging nhau, t giỏ cao nht khong 50 ln vi 10 ppm NO2 c trng nhy khớ ca cỏc cm bin nano ZnO ó c gii thớch liờn quan n nh hng ca cỏc tham s v nh hng tớnh th u tiờn, tớnh hon ho tinh th, v tớnh ng nht kớch thc Cm bin dõy nano ZnO bin tớnh Nb2O5 th hin ỏp ng tng vt bc (t giỏ tr i 371 ln) so vi khụng bin tớnh ln (giỏ tr ln nht l 53 ln), v thi gian hi ỏp gim khỏ mnh Lun ỏn a mụ hỡnh gii thớch v s bin tớnh Nb2O5 nh hng n c trng nhy khớ ca NO2 104 KT LUN CHUNG KT LUN CHUNG Trong quỏ trỡnh thc hiờn ti lun ỏn tin s, tỏc gi v th hng dn ó thu c nhng kt qu nht nh Cỏc kt qu nghiờn cu ca lun ỏn ó c tỏc gi v th hng dn cụng b trờn cỏc chuyờn ngnh nc v quc t Trong ú, cỏc kt qu cú nhiu ý ngha khoa hc v cú tớnh mi ó c cụng b hai bi bỏo quc t thuc h thng SCI Cỏc kt qu chớnh lun ỏn c kt lun nh sau: Cỏc vt liu nano ZnO dng thanh, dõy v tetrapod c ch to thnh cụng t cỏc phng phỏp thy nhit v bc bay nhit Cỏc quy trỡnh ch to ca hai phng phỏp ny u n gin, hiu qu v cho hiu sut cao Mi vt liu nano ZnO ch to c u cú ng nht cao v hỡnh thỏi hc, kớch thc v cú phm cht tinh th tt Vt liu nano ZnO dng dõy v tetrapod cú hon ho n tớnh th v ng u v hỡnh thỏi l tt hn nhiu so vi vt liu dng c trng nhy khớ ca cỏc cm bin s dng nano ZnO, dõy nano ZnO, v nano tetrapod ZnO u th hin tớnh cht nhy khớ tt vi NO2 v khỏ ging im khỏc bit gia cỏc cm bin l ỏp ng khớ NO2 l v vựng nhit hot ng ti u v thi gian hi ỏp, cm bin dõy nano ZnO v nano tetrapod ZnO cú vựng nhit hot ng ti u nh hn v hp hn so vi cm bin nano ZnO Mi liờn h mt thit gia cỏc c trng nhy khớ ca cỏc cm bin vi nh hng cu trỳc tinh th u tiờn, hon ho tinh th v tớnh cht ng nht ca cỏc dng nano ZnO ó c gii thớch chi tit lun ỏn Cm bin dõy nano ZnO bin tớnh bng cỏc ht Nb2O5 cho ỏp ng tng vt bc hng trm ln v thi gian hi ỏp gim 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International Conference on Advanced Materials and Nanotechnologies ICAMN Hoang Van Han, Nguyen Duc Hoa, Pham Van Tong, Hugo Nguyen, Nguyen Van Hieu (2013) Single-crystal zinc oxide nanorods with nanovoids as highly sensitive NO2 nanosensors Materials Letters vol 94 Pp 41-43 Hoang Van Han1, 2, Nguyen Van Hieu2, and Tran Trung1, (2014) A Simple Method for Production of High Aspect Ratio ZnO Nanowires with Uniform Structure for NO2 Gas Sensors Science of Advanced Materials Vol 6, Tran Trung, Hoang Van Han, Nguyen Van Hieu (2016) New insights on the mechanism of semiconductor nanostructures formed during vapor transport at atmospheric pressure Jounal of sciencs and technology Vol 54-5A, 107-117 Hoang Van Han, Chu Van Tuan, Tran Trung (2016) Study the response of gas sensor using ZnO nanorod synthesized by hydrothermal method Jounal of sciencs and technology Vol 54-5A, 201-207 114 ... tạo cảm biến sở vật liệu nano ZnO đồng thời khảo sát đặc trưng nhạy khí cảm biến với khí NO2 - Biến tính vật liệu nano ZnO Nb2O5 cho nghiên cứu đặc trưng nhạy khí NO2 - Phân tích, đánh giá kết nghiên. .. điện cực .Cho đến nay, nhiều nghiên cứu tập trung chế tạo dây nano ZnO ứng dụng cho cảm biến khí Bảng 1-1 liệt kê dây/thanh nano ZnO nghiên cứu gần cho số loại khí Kết cho thấy vật liệu nano ZnO có... dung vật viết nano ZnO có đường kính 200 nm ứng dụng cho cảm biến khí Trong nước có nhiều nhóm nghiên cứu PGS TS Nguyễn Ngọc Toàn nghiên cứu tính chất vật liệu perovskite ô-xít ứng dụng cho cảm biến