Cơ học lượng tử và vật liệu nano

7/31/2019 C hc lng t v vt liu nano

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C hc lng t v vt liu nano*Trng Vn Tn

If you think you understand quantum mechanics,then you don't understand quantum mechanics.

Richard P. Feynman (Nobel Vt l 1965)

Abstract

This article has been written in the style of popular science to exposethe exploitation of quantum mechanics in nano-structured materialsand the synergism of these two fields. A brief history of quantummechanics starting from Planck's law of black body radiation hasbeen described. The progress of nanotechnology in recent years hasprovided opportunities to fabricate and control the structure andcomposition of materials at nanoscale level optimizing theirproperties for products with higher degree of sophistication andperformances. One of the most striking effects of reducing materialsto nanoscale is dependence on size of their electronic, optical,optoelectronic, magnetic, physical, mechanical properties. In the

areas of electronics, optoelectronics and photonics, the dependenceon size is dominantly controlled by quantum laws in materials withnanoscale features or structures. Interactions betweenelectromagnetic waves, in particular, from far infrared (IR) to visiblelight and ultraviolet, and materials are used as an example tocompare the band gap properties of bulk materials and nano-structured materials. Quantization of electronic energy, which occursin quantum dots (nanoparticles) and quantum wells as a function ofsize according to Schrdinger's wave equation, is attributed tofluorescence in nanoparticles and quantum well IR detection.

Ni dung:E=h - Trc hai ng ng: c hc c in v lngt - nh hng ca s thu nh - Di nng lng in t v s phtquang - Chm lng t v ging lng t - Ht nano bn dn: spht hunh quang - Ht nano kim loi vng: plasmon v s phthunh quang - Ging lng t v tia hng ngoi - Tim nng ngdng - Thng x ngu!


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1. E=h

Vo nhng m ng khng g th v bng ngi bn cnhci l si nghe ting la reo t tch, nhn ngn la lung

linh cng vi vi ngi bn nhm nhp ly ru vang Penfolds bn v trit l cuc i, ni chuyn thin vn al, ng ty kim c. Nhng m ng s v cng lnh lov v v nu khng c ci l si vi nhng thi than hngthoang thong mi khi ca nhng khc g cn xanh,quyn theo lung khng kh c hm nng bng nhng tiahng ngoi. m chm trong mt khng gian m p, ngng men ru, thnh thong nh mt ca ta b li cun vonhng ngn la ang hng hc nhy nht, nhng khonhkhc y c khi no ta ngh n ngha.... vt l ca ci lsi khim tn? C khi no ta ngh rng ci l si kia cngc quan h "b con xa" n ci CD player t mt gcphng v ang pht ra nhng m thanh tuyt vi ca dngnhc giao hng c in Schubert, Mozart hay nhng bitnh ca Ng Thy Min, Trnh Cng Sn au xt cho mitnh gy mong manh hay tn tng mt tnh yu ang cln ngi?! Khi t ra nhng cu hi ny ngi i s chorng ta ang b "mo m ngh nghip", thch ngh ngimng lung, nhng thc s nu bo ci l si l m u v

ci CD player l h qu ca c hc lng t, thin nghcng khng phi l qu li.

Xut pht t gi thuyt lng t ca Planck, hn mt th ktri qua thuyt lng t nh mt con sng vt quanhiu khc quanh, ghnh thc, tp hp nhng pht hin vi theo dng chy ngy hm nay tr thnh mt dngsng to ln vo bin c khoa hc, duy tr s phn vinh vhnh phc ca nhn loi. Vo nm 1900, qua s quan st vbc x sng in t ca vt en (black body), Planck a ra

nh lut bc x din t s lin h gia nhit v bcsng ca bc x. Ni mt cch d hiu, khi lm nng mtthanh st, st bin thnh mu , nng hn thnh mu vngv nng hn na mu xanh trng nh ta thng thy khi st th lng. Cng nng bc sng ca bc x cng ngn (tmu tin n mu xanh trong trng hp thanh st). Dkhng phi l vt en l tng theo ng nh ngha trong


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vt l, vt en trong thc t c th l in tr ca bng n,thanh st, khc g trong l si, mt tri, phong nn v tr(cosmic background). T nh lut bc x Planck, da theoquang ph hay mu sc pht quang ta c th d on nhit

ca b mt mt tri trong khong 5.000 6.000 C, thanhng trong l si trn di 1.000 C, in tr bng ntrn 1.000 C. Vi ba (microwave) pht i t khong khnggian v tn cho ta bit nhit ca v tr l -270 C. Ngcli, t nhit ca mt vt ta c th bit bc sng pht rat vt . Nhit con ngi 37 C cho bit c th tapht tia hng ngoi.

chng minh nh lut bc x ca mnh, Planck tobo a ra gi thuyt lng t l nng lng bc x casng in t c pht ra khng lin tc theo tng "ginng lng"E=h ri rc, gi l lng t, trong h lhng s Planck, n l tn s ca sng in t. Nhng Plancktin ch mi l ci mo ton suy ra cng thc phnb nng lng bc x ca ng va tm thy sao cho honton ph hp vi kt qu th nghim. Vi nm sau (1905),da vo tng bc x nhit theo gi nng lng caPlanck, Einstein i thm mt bc quan trng khi a raquan nim rng nh sng c cu to bi cc ht gi l

photon (hay quang t, light quantum), mi ht mang nnglngE=h, v tng tc vi cc in t ca vt cht khichm vo. Bng cch ng nhanh chng hon ton giithch c hiu ng quang in m gii vt l ng thiphi b tay, v pht hin ny em li cho ng gii Nobelnm 1921. Tc l, tri vi quan nim sng ph bin lc bygi, Einstein cho rng nh sng cn mt s tn ti th hai, l ht. nh sng va l sng va l ht: khi nim nhnguyn sng/ht ra i.

Ngi Nht Bn dng ting Hn dch thut ng"quantum" l ryoshi, c ra m Hn Vit l "lng t"(lng: nng lng, t: con, phn nh), biu hin ng ngha ca quantum. Cng thc v i,E=h, hm cha tnhht ca sng, cng l khi im ca b mn c hc lngt. Tr s ca h rt nh (6,626 x 10-34J.s) nhng ng saucc ct tr quan trng ca c hc lng t, hng s Planck


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khng bao gi vng bng. N hin hu trong mi cng thcquan trng lin quan n c hc lng t v chi phi vic"i ng" ca cc vt cht cc nh ca th gii vi m. Chon ngy hm nay, c hc lng t cng ngy cng phc v

nhn loi mt cch c lc t chic radio, TV bnh thngn chic my tnh, CD player, iPod, in thoi cm tay vnhng thit b khoa hc, y hc, vin thng, ci thin isng v sc khe con ngi.

2. Trc hai ng ng: c hc c in v lng t

Khi gp phi mt vn khng r rt, ngi Nam B cmt cu ni d dm nhng mc mc, chn thnh: "coi dzym hng phi dzy". Trong vt l, n din t mt cch bnh

dn nhng c bn ca c hc lng t nh tnh xc sut,tnh bt nh v bn cht nh nguyn sng/ht ca vt chttrong th gii vi m ca phn t, nguyn t, in t v ccht s cp h nguyn t (subatomic particle). K t u thk 20, khi hng s Planck xut hin trong nh lut bc xv tip theo mt lot l thuyt nh hiu ng quang inEinstein, phng trnh sng Schrdinger, nh lut deBroglie, nguyn l bt nh Heisenberg, nhng iu hiubit da theo "thng thc" (common sense) ca th giii thng c l gii qua c hc c in Newton honton b o ln. Trc nhng pht hin v i ny, cmt thi gian di cc nh khoa hc tng hoang mang,thm ch ch diu trc nhng khm ph mang tnh trit v dt khot ca mt cuc cch mng khoa hc.

Trong th gii bt nh ca c hc lng t, hiu cs hin hu, di ng v tng tc ca vt cht cc nh tacn n mt t duy khc ph tan nhng xing xch tri bucca c hc c in. Khi mt chic xe hi chy vi vn tc100 km/h, th ta c th tin liu rng sau 1 ting ng hchic xe xut pht t im A s n im B cch 100km. y l kt qu tt nh ca chic xe. Nhng trong thgii ca cc ht nh, ta khng th xc nh v tr ca htchnh xc 100 %. Khc vi chic xe hi, vn tc v v trca vi ht khng th o c mt cch chnh xc cng mtlc v s nho lng t. Nguyn l bt nh Heisenberg


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nh lng ha nho ny bng mt cng thc n gincha hng s Planck.

Ci m mt v v tr hay tnh cht phi nh x (non-locality)

ca vi ht l mt c im khc ca c hc lng t. cng mt thi im chng nh bng ma c th nhiu nikhc nhau vi nhng xc sut nh v khc nhau. y lvic k l theo trc gic i thng nhng xy ra trong thgii vi m. Xc sut ny c th tnh c t phng trnhsng ni ting ca Schrdinger. Phng trnh c din tdi mt dng n gin,H= E, l hm s sng. Bnhphng ca l xc sut hin hu ca ht mt v tr no. Tnh ngu nhin t xc sut ca phng trnh

Schrdinger v s nhe m trong nguyn l bt nhHeisenberg ng tr th gii vi m ca c hc lng t. Ci"c c khng khng" ny cho con ngi mt v kh suylun v c tnh vt l ca nhng ci nh nht ni mnhng nh lut ca c hc c in phi li bc. C l khikhm ph ra phng trnh ny Schrdinger cn cao hnghn c Archimede khi pht hin c sc y ca nc lcngm trong bn tm; Archimede nhy o ra khi bn chyra ngoi ng trn trung nh nhng la ln "Eureka!" (tmra ri!). Erwin Schrdinger ngi o, vit ra phng

trnh ny trong nhng ngy m say ca mt cuc hn hlng mn vi ngi bn gi trong vng rng ni Alpsng qu l mt nh khoa hc lng t ho hoa, cng mt lcphng s cho c khoa hc v tnh yu!

Cng thc Planck,E=h, biu hin tnh ht ca sng; nnglng quang t, E, c biu th bi tn s sng n. Gn 20nm sau nh lut bc x Planck, nh vt l ngi Php,Louise de Broglie, to bo a ra mt xut ngc li chorng ht cng c th l sng. T cng thcE=h, ng cho

thy vi ht (in t v cc ht s cp) khi di chuyn vntc v s tng ng vi sng vi bc sng = h/mv (h lhng s Planck, m l khi lng ht v v l vn tc). Mtln na, ta thy lng tnh sng/ht xut hin trong cngthc de Broglie; bc sng ty thuc vo khi lng htm. Th nghim chng minh s di ng ca in t, vnl ht, sinh ra hin tng giao thoa, nhiu x ca sng. Th


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d khi in t di chuyn trong mt in trng c in p 1volt, in t c bc sng l 1,2 x 10-9 m (vng ca tia X)[1]. Nh vy, tri banh golf khi chuyn ng c tr thnhsng khng? Theo de Broglie, tri banh golf (hay nhng vt

di ng nh chim bay, c bay, xe chy, ngi i....) cng cdng sng. Ta hy dng con tnh cho d hiu. Dng cngthc de Broglie, ta tnh c "bc sng" ca banh dikhong 10-34 m [2], nhng tr s ny qu nh c nhnghin tng mang tnh cht sng nh nhiu x v giao thoaxy ra. V vy, theo nhng tri nghim thng ngy, mt cvt banh trn sn golf d nhn th no i na th banh vn lbanh!

Sau c vt, tri banh golf bay lc hng va vo mt gccy, theo nh lut tc lc v phn lc Newton tri banhgolf s b di tr li. Chuyn bnh thng khng g phingc nhin. Nhng ci ngc nhin l khi tri banh c thunh n kch c ca in t th tri banh c th i "xuyn"qua vt chn v "banh" by gi c tc dng nh sng. Lithm mt hin tng "ma qui" khc ca c hc lng tc gi l hiu ng ng hm (tunelling effect). Nhn licng thc bc sng ca de Broglie, ta nhn ra ngay ch cnhng vt cc nh vi khi lng cc nh mi cho bc

sng c mt con s ln hiu ng ny xy ra.Tnh nh nguyn sng/ht l mt c tnh tiu biu ca chc lng t. Schrdinger khi cp n bn cht canhng ht s cp tng ni "Khng nn nhn mt ht nh lmt thc th c nh m hy xem n nh l s kin nhtthi. i khi nhng s kin ny lin kt vi nhau cho ramt o gic ca nhng thc th c nh" (It is better not toview a particle as a permanent entity, but rather as aninstantaneous event. Sometimes these events link together

to create the illusion of permanent entities) [3]. Kh hiu?C l. Nhng ta ng nh gi thp kh nng t duy camnh v ta ang b cong hay phi i ngc vi trc gic c thnh hnh qua nhng tri nghim ca cuc sng ithng. Chnh v vy khi bn v lng t, gio s RichardFeynman tng ni "Nu bn ngh rng bn hiu c hclng t, th bn tht ra cha hiu g v n c". Tuy nhin,


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ci m mt lng t s sng t hn khi ta t ci o gic caSchrdinger trong ci nhn trit hc Pht gio, khi m bncht v ng, v thng ca vt cht - lc sng lc ht, "vym khng vy" - tht ra ch l kt qu ca ci ta b phn nh

iu kin th nghim v s o c ca ngi quan st.

Nh vy, u l ln ranh gia vt cht v m tun theo chc c in v vt cht vi m ca th gii lng t. Cc bctin bi nh Bohr, Heisenberg v von Neumann vn nhnmnh s phn chia gia hai phm tr c in v lng t,mc d cc ng cng tha nhn rng cha c qui lut vt lno c th nh v r rt ln ranh "i i" ny. Gn y(nm 2005), mt nhm nghin cu ti o v c [4] dnggiao thoa k phn t (molecular interferometry) tm kimln ranh ny qua s kim nhn vch giao thoa ca cc loiphn t trong chn khng bng cch tng dn ln phnt cho n khi cc vch ny bin mt. Cc phn t ln nhqu bng C70 (70 nguyn t carbon, ng knh 1 nm), phnt sinh hc C44H30N4 (ng knh 2 nm) v phn t nng kC60F48 (phn t lng = 1632, ng knh 1 nm), chothy vch giao thoa. Tnh nh nguyn sng/ht c xc lp.Phn t C60F48 l phn t c phn t lng cao nht t trcn gi c ghi nhn mang tnh nh nguyn sng/ht. Tuy

nhin, khi c s tc ng ca phn t kh ca mi trngxung quanh. Cc vch giao thoa b nho i nhanh chng.Tnh cht sng ca ht b suy gim ri tan bin. Th nghimny cho thy mt kt qu quan trng l ngoi kch thc, stng tc va chm vi vt cht trong mi trng nh hngn tnh nh nguyn sng/ht trong th gii vi m.

Ln ranh gia c hc c in v lng t, tt nh v btnh khng phi l mt ng bin r rt m ty thuc voiu kin th nghim v mi trng xung quanh. Ta li thy

bn cht v ng ca s vt. Thuyt duyn sinh trong Phtgio ni n s lin h h tng ca vn vt; "ci ny sinhci kia sinh, ci ny dit ci kia dit". V duyn sinh nn vng. Ln ranh m o gia c hc c in v c hc lng tlc n lc hin ty vo s tng tc ca vt c quan stv mi trng xung quanh, chng qua cng khng ngoi s


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chi phi ca duyn sinh bao trm v tr.

Vo thp nin 70 ca th k trc, nhng thit b thcnghim tinh vi ra i. Nhng nh lut lng t u th k

20 va mang tnh trit hc va mang tnh khoa hc n tngmt cht ma qui gi y c kim chng vi nhngthnh cng vt bc. Nhng pht hin bt ng t cc ktqu ca thc nghim lng t khng nhng gii ta cnhiu bn khon c xung quanh nhng cuc tranh lun giaEinstein v Bohr, m cn cho cc nh vt l mt khung trimi trong vic to lp c s cho mn tin hc lng t(quantum information) m nh cao s l my tnh lng tv cc phng tin vin thng lng t.

Mt khc, s xut hin ca nn cng ngh nano vo thpnin 90 tr thnh mt mc tiu cho cc ng dng tuntheo c hc lng t. Cc vt liu nano trong phm vi t 1dn 10 nm (nanomt) nm gia kch c ca cc loi phn tnh v vt liu khi. cho thy nh cng nh " ln"ca vt liu nano, 2 gram ht nano c ng knh 100 nmc th phn pht cho ton th 6 t ngi trn qu t nymi ngi 300.000 ht; 1 gram ng than nano c din tchb mt l 1.600 m2 rng tng ng vi 8 sn tennis.Tnh cht ca vt liu nano khng phi nh vt liu khi mcng khng ging cc hp cht phn t, va nm trongvng chi phi ca cc qui lut vt l c in va ty thucvo thuyt lng t. Nhng tnh cht ny bao gm c tnh,l tnh, quang tnh, t tnh, ha tnh, bin i ty vo lnca ht (dy, si) nano, khong cch cc ht (dy, si) vhnh dng ca n. Nh ta s thy phn k tip, nh hngca c hc lng t trn vt liu nano cho ta nhng hintng th v v nhng ng dng v cng to ln.

3. nh hng ca s thu nh

Hn 15 nm qua, vic ch to cc loi tinh th nano, htnano kim loi, kim loi t tnh v bn dn c kch thc tvi nm n vi chc nm c s tin b vt bc. Phngphp tng hp ht nano c kch thc vi nm v n phnb (monodispersion) c trnh by t m trong mt bi boco tng quan c sc gn y [5]. Trc khi kho st nh


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hng ca cc qui lut lng t n vt liu nano, ta hyxem s thu nh t bn thn mang li nhng thay i non cc c tnh ca vt liu.

S gia tng b mt cp triu ln n t ln khi vt chtthu nh t mc v m, trung m (m, cm, mm, m) n cpnanomt lm thay i l tnh, quang tnh, t tnh v cc ctnh nhit ng hc ca vt cht . Nhng "hng s tnhin" ca vt liu khi m ta ng l bt bin, khi mcnm tr thnh kh bin theo ln ht. Tht ra, cc c tnhca vt liu ty vo s ni kt, cu trc ca nguyn t gmnguyn t bn trong (bulk) v nguyn t b mt. kchthc i thng, s nguyn t b mt gn nh khng ngk so vi s nguyn t bn trong. Khi b thu nh nnanomt, b mt gia tng v s nguyn t b mt cng giatng. Ta hy xem vi th d n gin v nng chy, ttnh v c tnh ca mt s vt liu.

nng chy ca vng khi l 1.064 C. Khi vng lncm, mm, thm ch m, cc t l nguyn t vng b mt sovi nguyn t bn trong vt cht c th xem nh l khngng k. nng chy cn duy tr khong 1.000 C khiht vng c ln 50 nm v nguyn t b mt ch chim 6%. Tuy nhin, khi ht nh hn 5 nm (cha 3600 nguyn tvng) nguyn t b mt chim 20 %, nng chy gimn 900 C v n 350 C khi ht kch thc 2 nm (200nguyn t vng, nguyn t b mt 50 %). S chnh lch vitrm C do s khc bit ch vi nanomt gia 2 - 5 nm chothy tm quan trng ca nh hng ln th nguynnano. Khi ngoi suy n kch thc 1 nm (30 nguyn t,nguyn t b mt 80 %) th nng chy ch cn 200 C[6].

Mt th d khc quan trng hn l t tnh. Nhng kim loit nh st, nickel, cobalt cho thy vng t tr "c hu" giat trng, H, v t ha M (Hnh 1). Tuy nhin, dnght nano vng t tr khp li tr thnh mt ng cong cnht cho thy c tnh siu thun t (superparamagnetic)[7]. Nhm khng phi kim loi t nhng khi ht nano nhmcha 18 nguyn t c kch thc 0,8 nm th t tnh xut


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hin [8]. L do rt phc tp v c lin quan n s sp xpin t (electronic configuration) th nguyn nano. Tuyrng thi im hin ti t tnh ht nano vn cn nhiu unkhut cha c nghin cu trit v ton din, nhng c

tim nng rt ln cho vic tr liu y hc hch nhn, ti thucn t bo, b cm ng vi hiu ng t tr khng l (giantmagnetic resistive, GMR), tin hc lng t, tch tr d liu.

Hnh 1: nh hng ca s thu nh trn t tnh ca st,(a) vng t tr ca st khi v (b) ca ht nano st (Ngun:

Wikipedia).

C tnh v l tnh cng b nh hng ca s thu nh. c

nhiu cng trnh pht hin s gia tng c tnh v bn(strength) v dai (toughness) ca cc ht nano kim loiv ceramic. Ht nano ng vi kch thc 10 nm gia tng cng (hardness) 8 ln cao hn ng khi. Ngoi ra,nhng cu trc b mt nano cn em li nhng hiu qunh gia tng lc bm do lc van der Waals m phng bnchn thch sng hay to ra b mt cc ght nc(superhydrophobic) hay cc thch nc (superhydrophilic)ca mt s vt liu.

nh hng ca cc qui lut lng t trn s thu nh ca vtliu cp nanomt l mt hin tng ni bt c th quanst qua s tc ng ca sng in t trong vng hng ngoi,nh sng thy c v t ngoi trn cc loi ht v cu trcnano. Cc vt liu ng p tr li bng cch pht sinh ranh sng, dng in, chuyn hon nng lng ty vo ctnh ca khe di nng lng (energy bandgap) cho ta nhng


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ng dng nh s pht quang, pin mt tri, b cm ng sngin t, my nh hng ngoi v cc dng c quang hc,quang in t hu dng khc. S thnh hnh ca khe dinng lng, s bin ha ca khe di khi vt liu c thu

nh v cc ng dng s c kho st phn sau.

4. Di nng lng in t v s pht quang

Di nng lng in t (electronic energy band) v khe dil nhng c tnh khi rt quan trng ca cht rn. Trongcht rn, s thnh hnh ca di nng lng in t quytnh c tnh dn in, bn dn hay cch in ca cht rn. th rn, cc vn o nguyn t lin kt, chng chpln nhau mi phng hng to nn vn o phn t.

Ngi ta phng tnh 1 cm3 cht rn c 1022 (10 ngn tt) nguyn t to thnh. Trong qu trnh ny, theo c hclng t, nhng mc nng lng in t s c thnh hnhv cc in t s chim c cc mc nng lng ny. Nhvy, ta c 1022 vn o phn t v 1022 mc nng lngtng ng c to thnh. Cc mc nng lng ny chngchp ln nhau theo th t tr s ca chng, tr thnh dic gi l "di nng lng in t". Di nng lng thpgi l di ha tr (valence band) v di nng lng caohn gi l di dn in (conduction band) (Hnh 2). V cons 1022 l mt con s rt ln nhng mc nng lng chngchp nhau trng ging nh mt di lin tc (continuum).Nh b dy ca mt quyn t in, t xa nhn th trng nhmt khi lin tc, nhn gn th mi thy nhng trang giyri rc. S thnh hnh di nng lng ca cht rn c thkhng lin tc, khi s c mt "khong trng" xut hin,ging nh ci mng chia ra hai vng nng lng. Khongtrng gi l khe di nng lng (Hnh 2).


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Hnh 2 : Di nng lng in t : (a) kim loi (khe di = 0 eV), (b)

cht bn dn (khe di = 1 1,5 eV), (c) cht cch in (khe di > 3eV). Di en tng trng cho di ha tr v di trng cho di dnin.

Tr s ca khe di nng lng khng nhng cho bit ctnh dn in, bn dn v cch in ca vt liu m cnquyt nh quang tnh cho nhng ng dng nh s phtquang (n LED, light emitting diode), s hin th mu sc,pin mt tri ca cc cht bn dn v polymer dn in.Nguyn tc pht quang ca n LED l khi cho mt dngin chy qua, s kt hp gia in t v l trng mangin dng xy ra. Trong qu trnh kt hp in t "nhy"t di dn in (nng lng cao) xuyn qua khe di xungdi ha tr (nng lng thp) (Hnh 3). Nng lng d thas bin thnh nh sng c bc sng nh bi nng lngkhe di Egap [9]. Th d nu ta mun LED pht nh sng (bc sng = 720 nm, nng lng Egap = h= 1,7 eV) th tacn mt vt liu c khe di nng lng khong 1,7 eV.Hng lot hp cht bn dn nh GaAs, GaAsP, AlGaP,GaP, InGaN c ch to c tr s khe di t 1 eV n

3,5 eV pht ra nhiu mu sc khc nhau bao ph ton thph nh sng thy c (Bng 1). Tng t, n PLED(polymer light emitting diode) dng polymer dn in cngpht ra nhiu mu sc ty vo cc loi polymer c Egap khcnhau [9].


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Hnh 3: S pht quang in hc (electroluminescence) ca nLED. Nng lng d tha do s phi hp in t nng lng caovi l trng (+) c bin thnh nh sng. Mu (bc sng) ca

nh sng c quyt nh bi tr s ca khe di.

Bng 1: Bc sng v nng lng sng.

nh sng Bc sng (nm)

Nng lng sng E(eV)*

Tia t ngoi ngn hn 380 ln hn 3,3Tm 380 3,3

Xanh 450 2,8Xanh l cy 530 2,3Vng 580 2,1 720 1,7Tia hng ngoi di hn 720 nh hn 1,7

*Tnh t cng thc h = hc/, c: vn tc nh sng 300.000 km/s, : bcsng; 1 eV = 1,602 x 10-19 J

Khe di nng lng ca trng thi khi bin i khi kch ctin n nanomt. Ngi ta thng bo "ci b l ci khn",khi vt liu b "b" trong khng gian nano ta hy th xemchng s l ci "khn" lng t nh th no.

5. Chm lng t v ging lng t

Nhng ht vt cht chng hn nh ht kim loi c th nhnthy c bng mt (kch thc ~1 mm3) vn cn c nhng


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di nng lng in t gn nh lin tc v s nguyn t cuthnh cn rt ln. Thm ch, mt ht c th tch 1 m3 chc th nhn thy qua knh hin vi cng cha 1010 (10 t)nguyn t. Con s to ln ny cho bit di nng lng vn

khng khc g ht kch cmm3, cm3. V vy, cc c tnhca ht 1 m3 vn l c tnh khi (bulk properties). Nutip tc thu nh, mi vic s khc i th nguyn nanomt.Gi d nu ta c mt ht kim loi hnh lp phng c cnhdi 5 nm (nanomt) c th tch 125 nm3, ht kim loi scha trn di 1.000 nguyn t. th nguyn cc nh nyv con s 1.000 nh lm gia tng khong cch giacc bc nng lng in t. Ni mt cch khc, di nnglng khng cn nh mt quyn sch dy m tr thnhnhng trang giy ri rc. S "lin tc" ca di nng lngbiu hin c tnh khi tiu biu bin mt v c thay thbi nhng bc nng lng ring bit khi vt cht tin v thnguyn nanomt. Ta gi y l s "km ta lng t"(quantum confinement) hay l s lng t ha nng lngtrong mt khng gian cc nh. T th gii i thng cac hc Newton ta bc vo th gii sa m ca c hc lngt. V trong ci th gii sa m ny vt liu tr nn "thinbin vn ha" kch c nano v cho ta bit bao ng dngcc k th v.

hiu r s lng t ha nng lng trong mt khnggian cc nh ta hy xem p n phn Ph lc ca bi ton"ging lng t" (quantum well) ca phng trnh sngSchrdinger. Trong bi ton ny, khi kch thc tin nmt tr s cc nh nng lng ca in t khng cn l mtdi lin tc m nhng mc ri rc t thp n cao. "Ciging" tht ra l hnh nh ca nguyn t ni m in t bkm gi trong vng cng ta ca nguyn t. ng knh"ci ging" cng l ng knh ca nguyn t. Phi ni y

l bi ton n gin nhng cho ra mt kt qu cc k quantrng c tm thu bi cng thc sau (Ph lc),

E = n2h2/8ma2 (n= 1, 2, 3, .)

vi E l nng lng bc n, h l hng s Planck, m l khilng in t v a l ng knh ging hay chm lng t.


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T phng trnh sng Schrdinger v vi li gii ca biton "ging lng t", cc nh khoa hc ngh ra ciging lng t thc s bng cch to ra nhng "nguyn t"nhn to. "Nguyn t" ny tc l chm lng t (quantum

dot). Thut ng nghe hi l tai nhng n rt c ng vchnh xc trong vic din t hnh dng v chc nng ca n."Chm lng t" biu hin mt vt cc nh chu nh hngca cc qui lut lng t. Trn thc t, chm lng t l ccht nano cha vi nguyn t n vi ngn nguyn t c thc thnh hnh t dung dch colloid. Chm lng t cngc th c kch hot pht quang. Cng nh vt liukhi, s pht quang ca chm lng t cng ty thuc votr s khe di. Nhng khc vi vt liu khi, chm lng tpht ra nhiu mu sc khc nhau bng cch thay i kchthc ca n. Nhng phn k tip s gii thch c ch khcbit trong s pht quang gia vt liu khi v ht nano(chm lng t).

6. Ht nano bn dn: s pht hunh quang

Nghin cu v chm lng t dng tinh th (Hnh 4) haytrong dung dch huyn ph thot u xut pht t vic chto pin mt tri trong vic gia tng hiu sut bin hon tnng lng mt tri sang in nng. K t nm 1986,nghin cu v chm lng t gia tng mnh lit v cho nnm 2005 c gn 2.000 ng k pht minh (patent) chocc ng dng ca chm lng t. Vo thp nin 90 ca thk trc, cc nh khoa hc ti M v Nga pht hin cc tinhth nano bn dn pht ra nhng mu nh sng khc nhau tyvo kch c ca n. nh hng ca kch c vo s phtquang ca vt liu nano li cng lm gia tng ci k b cath gii nano.


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Hnh 4: Tp hp chm lng t (tinh th nano) silicon.Mi chm c ng knh 7 nm v cha 50-70 nguyn t silicon

(Ngun: Dr. Arthur Nozik, National Renewable Energy Laboratorry,B Nng lng, M).

S pht hunh quang (fluorescence) l hin tng xy rakhi ta dng sng in t (quang t) kch hot mt vt liu,y in t ca vt liu ny t di ha tr i xuyn qua khedi ln di dn in nng lng cao hn (Hnh 5). Sngkch hot thng l sng mang nng lng cao nh tia tngoi hay nh sng mu xanh. in t nng lng caovn khng n nh lc no cng mun tr li chn c cnng lng thp. Khi in t tr li di ha tr, s phtquang xy ra (Hnh 5). Cng ging nh s pht quang inhc (Hnh 3), nh sng pht quang c nng lng tng

ng vi tr s khe di. Tr s khc nhau s cho mu sckhc nhau.

Hnh 5: C ch ca s pht hunh quang.

(1): Sng kch hot; (2): Sng pht ra;; () : in t.


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S pht hunh quang ca dung dch colloid ht nano bndn CdSe (cadmium selenide) l mt th d v nh hngca s lng t ha nng lng trn c ch pht quang.Dung dch colloid ca ht nano CdSe c kho st vi

nhng ht c ng knh khc nhau. S thay i khe dinng lng ca ht nano CdSe do s bin i ca ngknh ht c th kho st qua cng thc sau,

E = Egap + Equantum

El khe di ca ht nano, Egap l khe di ca trng thikhi (= 1,74 eV) v Equantum l nng lng do hiu nglng t (Hnh 6). Hnh 7 cho thy s i mu ca dungdch colloid CdSe t mu xanh sang mu khi ng knh

ht gia tng t 2,3 n 5,5 nm. Mu pht quang cc k nhyvi ng knh ht, ch cn khc nhau vi nanomt l munh sng thay i. Li gii ca phng trnh sngSchrdinger cho ta thy r iu ny. Khi ng knh httng gp i, Equantum tng gp bn (cng thc 4, Ph lc).V nhy kh cao, qu trnh tng hp ht nano i hi ng nht v kch c phi tht chnh xc cho mt mu scpht quang nht nh.

Hnh 6: Khe di nng lng ca (a) trng thi khi v (b) ht nano;(1): Egap; (2): Ev (3): Equantum. DE c th gia gim ty vo ):

Equantum do s chi phi ca kch thc ht (xem chi tit trong bi).


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Hnh 7: Kch thc ht CdSe gim t 5,5 nm n 2,3 nm (t phisang tri) khin s pht hunh quang ca dung dch nc thay it mu n mu xanh bao ph ton b ph nh sng thy c

[10].

c mt sn phm thc dng, ht nano c ha ln vomt loi polymer trong sut. Tng t nh trong dung dch,ht nano trong polymer s pht cc loi nh sng khc nhauv cho ta n pht hunh quang. Cng ging nh n neonthy ngn gia dng, ngun tia t ngoi c dng trong nhunh quang ht nano kch hot cc in t ca ht. Loin ny gii quyt c nhng khuyt im n LED bvng mc. c nhng mu pht quang khc nhau, nLED cn nhng vt liu c khe di nng lng khc nhau.V im ny, ht nano dng c nht mt vt liu v chcn thay i kch thc. n LED rt kh pht ra nh sngxanh v nht l nh sng trng. n pht hunh quang htnano cng vt qua tr ngi ny. Cc nh khoa hc tiSandia National Laboratories thuc B Nng lng M(Department of Energy) ch to thnh cng n hunhquang pht nh sng trng bng cch trn ht nano cng knh khc nhau pht ra nh sng , xanh l cy,xanh. Tng hp ba loi mu ny s cho ra nh sng trng(Hnh 8). K thut quan trng trong qu trnh ch to nhunh quang ht nano l cn phi trnh s kt tp ca htnano, v khi c s kt tp xy ra, ng knh gia tng lmc tnh nano bin mt v vic iu chnh mu s mt hiuqu. Mt thng tin gn y [11] cho bit ng than nano -mt vt liu thn k v a nng - khi c ct thnh nhngng rt ngn s tr nn chm lng t pht quang khi c


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kch hot bi tia t ngoi do hiu ng ging lng t.

Hnh 8: n pht hunh quang mu xanh (tri) v mu trng (phi)

c ch to ti Sandia National Laboratories (M).(Ngun:http://www.physlink.com/News/071403QuantumDotLED.cfm)

n hunh quang ht nano pht nh sng trng hin nay vnl mt ti nghin cu quan trng nhm to ra loi n ctui th cao v t hao nng lng [12]. Mc d c nhng uim vt tri hn cc loi LED trn thng trng, victhng mi ha n hunh quang ht nano to ra mt snphm i tr hay ch to mn hnh TV vn cn nhiu kh

khn v ty thuc vo cch tng hp cc ht nano c kchthc ging nhau v cch ha ln ng u vo cc vt liunn khng c s kt tp ngoi mun.

7. Ht nano kim loi vng: plasmon v s pht hunhquang

T bui bnh minh ca lch s loi ngi, vng c th ni lb ni ca mt nn vn minh. Hn 3.000 nm trc, ti AiCp v Trung Quc con ngi thc vng l kim loi

qu, bit khai thc, gia cng vng to ra cc trang scqu gi v c xem nh mt th chp c th d tr cho sphn thnh ca mt triu i. Gi tr v m thut hay kinh tca vng cho n ngy hm nay vn khng c nhiu thayi, nhng trong nn cng ngh nano hin i vi nhngtim nng ng dng quan trng ca ht nano vng trongquang hc, quang in t v y hc, vng nano c l cn qu


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gi hn vng khi trn quan im thc dng nhm phng scho cuc sng v hnh phc con ngi.

trng thi khi, trong cc p dng quang hc hay quang

in t, vng hu dng cho lm th ch dng lm gngphn chiu, k d xem nh l "b i". Tuy nhin, vng nanocho con ngi mt lnh vc nghin cu v ng dng honton mi l. Khi sng in t tc dng ln ht nano vng,ty vo kch c ca ht sng in t s (1) c tc dng sngtun theo hiu ng "cng hng plasmon" ca cc in tt do b mt v (2) c tc dng ht khi kch c ca vngnh hn 2 nm v s pht hunh quang xy ra tun theo quilut lng t nh ht bn dn CdSe. Chng ta hy tun tkho st hai trng hp th v ny.

c im ca kim loi l s hin hu dy t ca nhngin t t do. y cng l nguyn nhn ca s bng longb mt, truyn in v truyn nhit u vit ca kim loi. Khikim loi nh vng v bc dng ht nano, ht khng cnmu vng hay bc "c hu" trng thi khi m pht ranhiu mu sc khc nhau ty vo kch c v hnh dng(Hnh 9). iu ny i ngc li nhng hiu bit thng thctrong cuc sng hng ngy. Hai chic nhn vng c nuchy v gia cng thnh mt chic nhn to gp i th vn lchic nhn mu vng. Tht ra, mu sc ca ht nano vngv bc t dung dch huyn ph c ngi La M pdng vo th k 4. Ngi ta cn pha ch ht nano vng vithy tinh lm knh mu "ruby" trang tr cho ca sthnh ng. Mc d ht nano vng c p dng hn1.700 nm, s i mu ca ht ch c lm sng t vonm 1908 bi nh khoa hc c, Gustav Mie, qua li giida trn phng trnh sng in t Maxwell cho bi ton vs hp th v tn x ca sng trn b mt ca cc ht hnh

cu. V vy, s hin th mu sc ca ht nano vng cng knh t vi chc n vi trm nanomt khng trctip lin quan n s lng t ha nng lng v sng int tc ng ln nhng in t t do b mt ht mang ctnh sng c c bn l thuyt da trn phng trnhMaxwell.


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Hnh 9: S thay i mu sc ca ht nano vng cc kch thckhc nhau

(Ngun: Dr. Michael Cortie, University of Technology, Sydney,Australia).

Mu vng quen thuc ca vng l s hp th nh sng muxanh ca ph mt tri v pht ra mu vng. Nhng khi vngc thu nh cho n kch c nh hn bc sng ca vngnh sng thy c (400 - 700 nm), theo Mie hin tng"cng hng plasmon b mt" (surface plasmon resonance,SPR) xy ra. y l do tc ng ca in trng ca sngin t (nh sng) vo cc in t t do trn b mt ca htnano. in trng lm phn cc ht, dn in t v mtpha to ra hai vng, vng mang in tch m v vng mangin tch dng (Hnh 10). V bn cht sng nn in

trng dao ng lm cho s phn cc b mt dao ngtheo. S dao ng ny c gi l "plasmon". m myin tch trn b mt ht cng s dao ng lc m lc dngtheo nhp iu v cng ca in trng. mt kchthc v hnh dng thch hp ca ht nano, dao ng(tn s) ca m my in tch s trng hp vi daong ca mt vng nh sng no . S cng hng xy rav vng nh sng ny s b cc ht nano hp th. y l mthin tng c bit cho vng v bc nhng khng thy cc kim loi khc nh st, bch kim hay palladium.


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hng ngoi (bc sng 800 - 2.200 nm). Phng php phvng ln ht thy tinh silica to ra mt vt liu lai vi khnng hp th sng bi SPR v pha vng ph ca nhngbc sng di hn vng hng ngoi, tin v sng terahertz,

vi ba, nhng di sng rt quan trng trong cng ngh truynthng. Trong di sng ny, tim nng ng dng ca loi htnano lai trong cc dng c quang in t gn nh v hn.

Hiu ng SPR s bin mt khi vt liu tr li trng thikhi. Khi cc ht nano vng tp tch n ln micromt,ci mu vng quyn r nguyn thy ca kim loi vng sxut hin tr li. Ngc li, hiu ng SPR cng s bin mtkhi ht nano nh hn 2 nm. th nguyn ny, ta i vo thgii lng t. Ging nh chm lng t bn dn c cp bn trn, nng lng c lng t ha thnh cc mcri rc. Sng in t gi y c tc dng ht (quang t).Nhm ca gio s Robert Dickson (Georgia Institute ofTechology, M) to ra nhng ht nano (chm lng t)vng vi kch thc tht chnh xc cha 5, 8, 13, 23 v 31nguyn t [15]. y l nhng ht pht hunh quang trong chm 31 nguyn t c ng knh ln nht khong 1nm. Nhng ht ny c x l b mt ha tan c trongnc. Trong dung dch nc, theo th t kch thc t nh

n ln khi c kch hot nhng ht ny c kh nng phtra tia t ngoi, nh sng xanh, xanh l cy, v tia hngngoi (Hnh 11). So vi chm lng t bn dn CdSe chavi trm n hn 1.000 nguyn t, chm lng t vng nhhn vi vi chc nguyn t v khng c c tnh nh Cd.V vy, tim nng p dng trong y hc rt ln.

Hnh 11: S pht hunh quang nh sng xanh ca ht nanovng cha 8 nguyn t vng [15].


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8. Ging lng t v tia hng ngoi

Tia hng ngoi (hng: , ngoi: ngoi) l vng sng phangoi nh sng , c bc sng di hn nh sng tri

di t 700 nm n 14.000 nm (14 m). Tia hng ngoi lvng sng in t v cng quan trng trong cc ng dngvin thng, khng gian, quc phng v dn dng. Nhng gta gi l "nhit" theo ngha thng thng pht t l si,ly nc nng, c th con ngi u nm trong vng snghng ngoi. Mc d tia hng ngoi c bng tn di rng(broadband), nhng phn ln b bu khng kh hp th chcha li nhng "ca s", tc l nhng vng sng tia hngngoi khng b hp th, c bit l vng sng 3 - 5 m v 8- 14 m. Hai vng ny theo nh lut bc x Planck tngng mt vt pht nhit c nhit 300 - 600 C (3 - 5m) v 30 40 C (8 - 14 m). Mt cch ngu nhin, ycng l vng nhit ca ng c n hay ng c phn lcv nhit con ngi. V vy, trong nhng dng c cmbin vi tia hng ngoi (infrared detector/sensor) ngi tathit k vt liu c th hp th hai vng sng ny.

Cng ngh tia hng ngoi t n mc trng thnhv sn xut nhng dng c v thit b quan trng. Bcm bin hng ngoi l mt b phn trung tm ca tn latm nhit dng truy lng nhng ngun nhit t my bayv tu chin i phng, iu khin tn la ph tung mctiu. B cm bin vin hng ngoi (bc sng 8 - 12 m) lmt trong nhng thit b quan trng trong cc v tinh dng quan st mt t cho mc ch qun s v dn s. Mttrong nhng dng c quan trng khc l my nh hngngoi chc thng mn m, xuyn qua bi rm chp nhngbc nh do s khc bit nhit gia mc tiu chp v mitrng xung quanh (Hnh 12). Thit b ny c gn vo

ng nhm hoc knh c nhn (goggle) x tot bng ti phthin d dng nhng k i ngang v tt, thch chui vo bilm nhng chuyn m m linh tinh!


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Hnh 12: Hai ngi lnh trong bi rm vi mn m dy thin ra trong my nh hng ngoi (Ngun: Wikipedia).

Mc d nn cng ngh hng ngoi trng thnh, nhngch to nhng vt liu cm ng hng ngoi nhng bcsng nht nh vi nhy cao vn l nhng th thch lntrong vt liu hc. Nhng vt liu cm th tia hng ngoithng l silicon hay l cc hp cht bn dn nh PtSi,InSb, InGaAs, HgCdTe. Gn y, vt liu hu c nh ngthan nano v polymer dn in c kho st cng cho thys cm ng i vi tia hng ngoi. Khi quang t hng ngoikch hot in t ca vt liu, dng in xut hin v quacng dng in s khc bit nhit ca mc tiu c

ghi nhn thnh hnh nh. Nguyn tc ny cng ging nhmy nh k thut s thng thng trong s xut hindng in l do cm ng vi nh sng thy c.

T thp nin 80 ca th k trc, cc nh khoa hc ghinhn kh nng hp th tia hng ngoi xy ra ti cc bcnng lng ca ging lng t. C quan NASA v JetPropulsion Laboratories (California Institute of Technology,M) t hai thp nin qua u t vo chng trnh nghincu "b cm ng hng ngoi ging lng t" (quantum well

infrared photodetector, QWIP) v ch to my nh QWIPcho v tinh v cho nhng trang b theo di tn la n o[16]. QWIP l chng trnh nghin cu c mt quc gia caM v ch mi c gii mt vo nm 1997. Nhu cu chto nhng "thin l nhn" dng trong cc v tinh ngoikhng gian quan st qu a cu cho vic tin on thitit, tm kim qung m, trinh st qun s i hi nhng vt


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liu c th cm ng tia vin hng ngoi vi bc sng rtdi (> 12 m). nhng bc sng di nng lng cng nh(E = h = hc/) v ci ging lng t ca phng trnhsng Schrdinger tr thnh mt nn tng c bn trong vic

thit k vt liu p ng nhu cu ny.

Vt liu tiu biu ca QWIP l hp cht bn dn GaAs vAlGaAs. GaAs l mt lp mng nanomt c kp gia hailp AlGaAs. AlGaAs c khe di nng lng to hn GaAs,nn khi kt hp li vi nhau ging lng t GaAs ving knh vi nanomt s c thnh hnh (Hnh 13). Kchthc ca ging GaAs c thit k sao cho in t trongging c quang t hng ngoi kch hot ln bc nnglng cao hn nhy thot ra khi ming ging tr thnhdng in (Hnh 13). Chiu cao ging c iu chnh binng nhm trong hp cht AlGaAs v khong cch giacc bc nng lng bi ng knh ging (cng thc 5, Phlc). Ging nh trng hp s pht hunh quang ca chmlng t, ta dng mt vt liu ging nhau ch cn iu chnhng knh v chiu cao nano ca ging, QWIP c th baotrm ton th vng hng ngoi, cm ng nhng vng sngt cn hng ngoi (1 - 3 m) n vin hng ngai (8 - 12m), cc vin hng ngoi (> 12 m). Cc nh vt liu hc

i xa hn, thit k cc loi ging lng t c th cm nhnquang t vng sng c bc sng di hn na tin nvng sng terahertz (bc sng 30 - 3000 m, nng lngmili eV) c nhiu p dng trong y hc v vic chng khngb, r sot v kh hay bom mang trong ngi.


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Hnh 13: C ch ca QWIP. in t () c kch hot trong ginglng t nhy ra ngoi tr thnh dng in. (a): AlGaAs; (b):GaAs;(1) (2): Khe di nng lng; (.....): Bc nng lng trong ging do

s lng t ha.

Nhng tin b trong cch to hnh chm lng t bn dntrong cng ngh nano a n vic p dng chm lng ttrong b cm ng hng ngoi (quantum dot infrareddetector, QDIP). Nhng nm gn y, rt nhiu kt qu cacc cng trnh QDIP c cng b trn cc tp chchuyn ngnh [17]. Theo l thuyt QDIP c nhy caohn QWIP v cc hp cht bn dn cm ng vng vinhng ngoi, nhng chng cn thi gian cho s nghin cu tr thnh cc sn phm in t v quang in t hudng.

Ch trong vng 20 nm QWIP c nhng bt ph k thutv tr thnh mt b mn quan trng trong cng ngh bndn. L thuyt v QWIP c vit thnh sch [18-19], vnhng phng thc trong cng ngh nano to ra vt liunano vi chnh xc cp nanomt s cho ta nhng dng chng ngoi, terahertz tha mn nhy v chc nng caotrong mt tng lai khng xa.

9. Tim nng ng dng


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Ngoi s pht quang, vic chuyn hon nng lng mt trithnh in nng l mt ng dng quan trng khc ca chmlng t vi hiu sut kinh ngc 300 %, vt tri hn tt cvt liu c bit t trc n nay (hiu sut ca pin mt

tri silicon trn thng trng ch c 15 %) [20]. Vt liunano cn c mt ng dng ni bt l tr liu, chn onbnh, ti thuc n t bo bnh v cc p dng trong khcnghin cu y sinh hc. S pht sng hunh quang khngngng vic to cc loi bng n nhiu mu sc. Chmlng t (ht nano) c "gn" vo cc phn t sinh hctrong t bo. Di s kch hot ca tia t ngoi, chm lngt pht quang ging nh cy thng Ging sinh trong t bo,gip ta phn bit phn t ta mun quan st vi cc phn txung quanh. Cc nh khoa hc tn dng hiu ng cnghng plasmon ca ht nano vng to ra b cm ng sinhhc v s pht hunh quang trong vic tr liu ung th.Thin l nhn QWIP bao trm c vng hng ngoi vsng terahertz l mt loi thit b cm ng a nng, khi pdng cho thin vn c kh nng "nhn" thy nhng hnhtinh lnh chi vi trong v tr, hay gn gi hn nhn a cut v tinh, v khi hng vo c th con ngi QWIP gip ys nh v khi u ung th, gia tng s chnh xc cho qutrnh phu thut.

Tt c nhng tim nng ng dng nhiu ha hn ny nmngoi khun kh bi vit v s c cp mt c hikhc.

10. Thng x ngu!

Mc d Einstein l ngi thy r hn ai ht trc ngnn tng xc sut ca cc nh lut vt l, v ng l ngitin phong trong cuc chin u chinh phc s hoang dca cc hin tng lng t (Max Born) [21], nhng cuicng Einstein khng tin vo tnh xc sut nh nn tng cath gii vi m. Cho n ngy ng qua i, Einstein khngtin c hc lng t l mt l thuyt hon chnh. ng hoi nghi nguyn l bt nh Heisenberg ri sau phicng nhn n, nhng vn bt ng kin vi Bohr v thgii quan lng t, c din t qua cu ni "Thng


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khng x ngu" (God does not play dice). Cu ni lmt m nh ln ca cc nh khoa hc nhiu thp nin lin,lm cho nhiu tr tu ln trong vt l phi ngp ngng, biri. Nhng nh l Bell (1964) v cc kim tra thc nghim

ni tip sau chng minh rng Thng qu tht x ngu [21]. V Thng chi tr ny rt gii v ngyhm nay bit bao ng dng in t, quang in t hu chcho con ngi xut hin nh vo tnh cht xc sut cath gii lng t.

Bc vo th k 21, c hc lng t khng cn mang musc huyn b ca trit hc hay ch l mt cuc chi ton hccao cp tha mn tnh hiu k hn lm, m n ckhot ln chic o thc dng vi nhng p dng quan trngtrong tin hc lng t (quantum information) v cng nghnano. Nh trong bi vit ny trnh by, s thu nh cavt liu n cp nanomt cho thy r s chi phi lngt, to ra nhng bc nng lng ri rc. Ch cn nhng quilut c bn nht trong c hc lng t cng cho ranhng ng dng cc k mi l qua s tc ng ca sngin t trn cc vt liu nano tri rng t sng terahertz,vin hng ngoi cho n vng nh sng thy c, tia tngoi, bao trm mt vng to ln ca sng in t vi bc

sng ko di t vi ngn micromt n vi trm nanomt.iu ny phn nh s thnh cng ln ca cm ng hngngoi trong nn cng nghip bn dn hin i.

Vt liu nano tr thnh mt sn chi c hc lng tthao tng v khng nh tim nng p dng ca mnh. Chc lng t cng l nh uc dn ng nh hng vicch to nhng vt liu nano mi cho cc ng dng tng laitrong in t, quang in t v quang t hc. Tinh th nano,ht nano, ng nano, que nano ca cc cht hu c, oxide

kim loi hay bn dn v c vi nhiu hnh dng v kchthc khc nhau, ln lt xut hin trong cc phng thnghim trn th gii. n LED, n hunh quang ht nanocho nhng tim nng ng dng v cng phong ph cacng ngh "xanh" theo tiu chun t tiu hao nng lng,gim thiu nhim v gn gi mi sinh. Lng t v nanocng l bn tay m du ca ngi hin mu. Chng l ct


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sng ca nhng p dng y khoa hin i cng lc cng emn nhiu thnh qu bt ng trong vic nh v, kt hp,cm ng vi phn t sinh hc, ti thuc, pht hin t boung th cho vic tr liu v phu thut.

Khi nhng cng trnh nghin cu thun l ca c hc lngt c kt hp vi cu cnh thc dng ca nn cng nghnano, nhiu tng mi s ny sinh, nng cao l lun vt lvt ra ngoi phm vi hin c, cng nh to ra nhiu c hicho cc nghin cu a ngnh hnh thnh cc loi vt liumi vi nhng ng dng siu vit cho cuc sng ithng. C th khng nh rng nhng iu ny s khngxy ra nu khng c hng s Planck; mt hng s khim tnc mt tr s rt nh nhng nh hng tht l v i. Nmang tnh ph qut bao trm v tr, ng tr th gii ca vtcht cc nh n th gii ca v s cc thin h bao la, lmthay i s hiu bit v v tr, v tip tc phong ph hacuc sng con ngi trn qu a cu nh b ny.

Trng Vn TnThng 8, 2008

Cui ng Nam bn cu

* ng thnh mt chng sch trong quyn "Max Planck:Ngi khai sng thuyt lng t" (2009). Ch bin: Phm XunYm - Nguyn Xun Xanh - Trnh Xun Thun - Chu Ho - oVng c. Nh xut bn: Tri Thc, H Ni.

Ph lc: Bi ton chm lng t v ging lng t caphng trnh sng Schrdinger

Chi tit v phng trnh sng Schrdinger c th tm thy cc sch gio khoa ha l ca nm th nht i hc. y,li gii v cc bc nng lng ca ging lng t s ctrnh by. Phng trnh sng Schrdinger l mt phngtrnh vi phn, cho trng hp mt th nguyn x, c vitnh sau,
http://www.erct.com/2-ThoVan/TruongVTan/Max%20Planck.htmhttp://www.erct.com/2-ThoVan/TruongVTan/Max%20Planck.htmhttp://www.erct.com/2-ThoVan/TruongVTan/Max%20Planck.htmhttp://www.erct.com/2-ThoVan/TruongVTan/Max%20Planck.htm


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(-h2/82m)(d2/dx2) = E (1)

h l hng s Plack(6,626 x 10-34 J.s), m l khi lngin t, E l cc bc nng lng in t, y l hm s sng.

Li gii ca phng trnh (1) cho ging hay chm lng tc ng knh a l,

= A sin(nx/a) n= 1, 2, 3, . (2)

A l mt hng s, n l s th t ca cc bc nng lng(Hnh P1)

Thay cng thc (2) vo (1), ta c

E = n2

h2

/8ma2

n= 1, 2, 3, . (3)

Khi n= 1 ta c

E1 = Equantum = h2/8ma2 (4)

sai bit nng lng gia bc n =1 v n = 2 l

E2 - E1 = 3h2/8ma2 (5)

Kt qu trn cho ta thy hng s Planck, h, chi phi tr snng lng v sai bit gia cc mc nng lng (cng thc4 v 5). V hng s Planck rt nh, theo cng thc trn ivi nhng vt c kch thc v m, trung m (m, cm, mm,m), cc tr s ny gn nh zero. V vy, di nng lngcho ta cm gic gn nh lin tc. Tuy nhin, khi a thnguyn nanomt nh trong trng hp ging lng t haychm lng t sai bit gia cc bc nng lng tng lnng k v khng th xem nh l zero na. Cc bc nnglng tr nn ri rc, ta gi y l s lng t ha nng

lng.


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Hnh P1: Cc bc nng lng in t ca chm lng t hay ginglng t c ng knh a.

Ti liu tham kho v ch thch

1. mt in t di chuyn trong in p 1 volt, ta cnnng lng 1 electron-volt (eV) (E= 1 eV = 1,602 x 10-19

J). Vn tc v c tnh t E = 1/2 (mv2), v= 5,93 x 105

m/s. Khi lng m ca electron l 9,1 x 10-28 g. T cngthc de Broglie, = h/mv, = 1,2 x 10-9 m.

2. Mt c vt s lm tri banh golf (khi lng m = 45 g)bay vi vn tc 30 m/s. Dng cng thc de Broglie, bcsng ca tri banh golf l 4,9 x 10-34 m. y l con s cck nh v v ngha.

3. Matthieu Ricards and Trinh Xuan Thuan, "The quantumand the lotus", Three Rivers Press, New York, 2001.

4. M. Arndt, K. Hornberger and A. Zeilinger, PhysicsWorld, March 2005, pp.35.

5. J. Park, J. Joo, S.G. Kwon, Y. Jang and T. Hyeon,Angnew. Chem. Int. Ed., 46 (2007) 4630.


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6. M.B. Cortie, Gold Bulletin, 37 (2004) 1.

7. K.S. Suslick, M. Fang, T. Hyeon, J. Am. Chem. Soc., 118(1996) 11960.

8. W. Eberhart, Surface Science, 500 (2002) 242.

9. Trng Vn Tn, "Vt liu tin tin: t polymer dn inn ng than nano", nxb Tr, TP HCM, 2008.

10. B.O. Dabbousi, J. Rodriguez Viejo, F.V. Mikulec, J.R.Heine, H. Mattoussi, R. Ober, K.F. Jensen and M.G.Bawendi, J. Phys. Chem. B, 101 (1997) 9463.

11. Photonics Spectra, June 2008, pp.98.

12. H.S. Jang, H. Yang, S.W. Kim, J.Y. Han, S.G. Lee andD.Y. Jeon, Adv. Mater, 20 (2008) 2696.

13. M.-C. Daniel and D. Astruc, Chem. Rev., 104 (2004)293.

14. S.J. Odenburg, J.B. Jacson, S.L. Westcott and N.J.Halas, Appl. Phys. Lett., 75 (1999) 2897.

15. J. Zheng, C. Zhang, R.M. Dickson, Phys. Rev. Lett., 93(2004) 077402-1.

16. S.D. Gunapala et al, Infrared Phys. & Tech., 42 (2001)267.

17. J. Jiang et al, Appl. Phys.Lett., 84 (2004) 2166.

18. K.K. Choi, "The physics of quantum well infrared

photodetectors", World Scientific, London, 1997.19. H. Schneider and H.C. Liu, "Quantum well infraredphotodetectors", Springer, Berlin New York, 2007.

20. R.J. Ellingson, M.C. Beard, J.C. Johnson, P. Yu, O.I.Micic, A.J. Nozik, A. Shabaev and A.L. Efros, Nano Lett., 5


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(2005) 865.

21. Nguyn Xun Xanh, "Einstein", Chng 7, nxb Tnghp TP HCM, 2007.

(*) Anh Trng Vn Tn sinh qun ti tnh Sa c, cu hcsinh trng trung hc Sa c v Tng Phc Hip (VnhLong). Anh Tn n Nht cui nm 1969. Anh tt nghipBachelor Eng. (1975), Master Eng. (1977) trng Tokodai(Tokyo Institute of Technology) v PhD (1980, University

of Adelaide, c).Anh Tn hin lm vic ti Vin Khoa Hc v Cng NghQuc Phng (Defence Science and TechnologyOrganisation) trc thuc Chnh Ph Lin Bang c. Anhchuyn v Vt Liu Hc v hin nghin cu v polymersdn in v ng nano carbon. Anh cng b hn 70 bibo co khoa hc trn cc tp ch khoa hc quc t. Xemthm nhng bi vit ca anh Trng Vn Tn trn ERCT

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