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Cde nhd khoa hgc a PTN Berkeley (My) vd cde ddng nghiep da khdm phd ra mdi quan he mdi giita cde trudng dien vd trudng tir'vd nhung chenh lech nhiet do, cd thed&n den che tgo ra nhdng thiet bi nhiet dien hieu qua han chuyen hda nhiet thdnh dien hay nguac lgi, dien thdnh nhiet.
"Trong cudc tim kiem nguon nSng lugng mdi, nang lugng nhiet - kha nang bien nhiing chenh l?ch nhiet dp true tiep thinh dien ma khdng can cac biroc trung gian - la vd cung hua hen," Junqiao Wu d Phdng Khoa hoc Vat lieu thudc PTN Berkeley, ndi.
"Nhung hi^u ung mk ehung tdi mdi phat hien da dugc cdng dong nSng lugng nhiet tim hiiu, va cd thi tac dpng m^nh den hieu qua cua ning lugng nhiet vi cac thilt bi khac."
Wu va cac dong nghiep da tim thay ring cac gradient nhiet dp d ban din, khi mdt mat ndng hon mat kia, cd the sinh ra cac vdng xoay dien tir - cac vdng xoiy ciia ddng dien - vi dong thdi cd the tao ra cic tir tnrdng d gdc phii d ci cac ddng dien phing va xoiy vi hudng cua gradient nhiet
Wu ndi, cd 4 hieu ung ndi tieng lien quan den cac trudng dien, tir va nhiet. Thi du, hieu ung Hall quen thudc md ta chenh lech dien ap tren chat din dien trong mdt tu trudng vudng gdc. Nhung trong tat ca cac hieu ung nay tir trudng la mdt dau vao, chu khdng phai san pham. Chiing tdi tu hdi tai sao khdng sir dung dien trudng va cac gradient nhi?t lim dau vao de sinh ra tir trudng?
De kiem tra cac kha nang, cac nha nghien cuu lip md hinh mdt thiet bi thuc te dugc lam tu 2 ldp silic: ldp mdng dugc kich thich am (kieu N) cd sd du dien tu va ldp day hon dugc kich thich duong (kieu P) cd du cic Id, khdng cd cac dien tu vi hanh xu gid'ng nhu cac hat tich dien duong.
6 chd ndi khi cac ldp kich thich ngugc
B^n din kilu N 6 tren b^n din ki^u P tao ra di0n trucmg thing (E) eon su khuech tan tao ra lop hao hyt gin phin noi (vach giua), khi di?n tnrang mgnh nhat. Gia nhi?t mOt d i u thiet bi nay tao ra gradient nhi?t d g6c phai cua dien tnr!mg (del T).
Cac dien va 16 chuyen dong trong cac truong nay bj ep vao cac dong dien vong tron, va tir truong dupc sinh ra o ben cgnh (B) b goc ph^i cua ca eae tnrong di$n va tnrong nhi$t.
Anh: Jinqiao Wu, Lawrence Berkeley National Laboratory
gap nhau, mdt loai ldp thu 3 gpi la cic dang khdp P-N, khdng phai ndi vdi nhau ve vat ly mi vl dien tu: cic dien tir tir ldp kieu N khuech tan vao ldp kieu P cdn cac 16 di chuyen theo hudng ngugc lai, tao thanh mdt ldp hao hut d chd cic dien tich "bay hof di".
Vdi mat dp cao cac dien tu di ddng d bl m^t ldp N va mat dp cao cic 16 d bl mat ldp P, nhung cd it dien tich di chuyen d ldp hao hut, dien trudng manh nhat se d gan chd tiep xiic.
Wu giai thich, cac dien tich cd the di chuyen theo 3 each - tiic la cd 3 loai ddng dien. Mdt la ddng khuyen tin, trong dd cac hat di chuyen tir nhirng viing dam dac sang nhirng virng it dam dac hon. Chung ta khdng the lim gi vdi dien tich niy. Lay vi du chai sam-panh, chiing ta bat nut va mdt luc sau cd the ngui thay miii rugu sam-panh, dd la do
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THANH TUU MUI - CdNG NGHE MUI - SAN PHAM MUI
cac phan tu khuech tin tir ndng dp cao trong chai vao khdng khi."
Loai ddng dien thu hai dugc ggi la ddng dien trdi. "Neu trong phong cd su trdi hudng vl phia ban, ban cd the ngui thay mui sam- panh sdm hon mpt chut, hoac se mupn hon neu trdi ra xa phia ban. Trong thiet hi dien ddng trdi dugc gay ra bdi dp nghieng dien ap, tlie la dien trudng," Wu ndi.
"Nhu vay trong mpt thiet hi dien tu ehung ta cd ddng dien khuech tan khdi nhirng viing dien tich mat dp cao, vi ddng trdi do dien trudng. Cdn ddng thii 3, ddng nhiet dien, la mpt dang ddng trdi khac trong dd cac dien tich di chuyen tu diu ndng hon cua thiet hi den dau lanh hon."
Cac ket qua se khdng cd gi thu vi ca neu nhu tat ca cac ddng deu di theo cung mdt hudng. Nhung ehung lai khdng nhu the.
Trudng dien sip dat ddng trdi tir ldp tich dien am phia tren hudng tdi ldp dudi tich dien duong ciia thiet hi - di chuyen girgc vdi cac ddng khuech tan ciia cac vat mang dien tich.
Trong khi dd gradient xic dinh ddng trdi d gdc phai cua dien trudng.
"Trong cac luc vudng gdc xung dot nhau niy, cac dien tii va Id khdng the duy tri
chuyen ddng thang ma bi hut vao cac vdng xoat," Wu ndi.
Thay vi mpt vdng xoay thang dung trong thiet hi, cac vdng xoay dugc hinh thanh trong moi ldp va dugc tach biet bdi ldp hao hut. Trong ldp N, cac dien tu tach biet ldn gin ldp hao hut di chuyen theo gradient nhiet, tir ndng sang lanh, nhung di chuyen theo chilu ngugc lai d gin bl mat, noi cac dien tu chum lai gin nhau hon. Cac vdng xoay tao thanh bdi cac Id trong ldp P gan nhu la anh guang cua cac vdng xoay dien tir.
Ket qua bat thudng thuan tuy la khi dua nhiet vio mdt dau cua thiet bi sUic don gian, cac nha nghien ciiu cd the tao ra tir trudng vudng gdc vdi 2 vdng xoay ddi - tir trudng xu^
hien d gdc phai ciia mat phang ciia 2 ldp silic.
Wu ndi rang, ung dung tire thi khdng phai la ehung ta cd the tao ra tii trudng, chiing tuong dd'i yeu, ma ehung minh rang hieu suat cua nhilu thiet bi ban din, gom ca cac san pham thuong mai, cd the hieu qua hon neu ehung ta lam dung each. Thi du, thiet ke dam bao rang cic tnrdng dien cua chiing dugc xep dung vdi cic gradient nhiet se tranh dugc nhiing vdng xoay ddng lang phi nang lugng.
M.Q. (theo Physical Review B., 28/7/2011)
PIIXI O U A I M G D I E I M . . . (Tiip theo trong phd mat trdi, va cic vat lieu quang dien "khe bang thap" dugc phat minh trong thap ky trirdc cd the hap thu biic xa hong ngoai nhilu hon so vdi cac quang dien silic lieu chuan. Nhung nhiet van hi lang phi rat nhilu, nen hieu suat cdn thap.
Giai phap d day, Celanovic ndi, l i thiet ke chat phat nhiet chi biic xa cac budc sdng ma diot quang dien cd the hap thu vi chuyen hda Ihanh dien, trong khi han che cac budc sdng khac. Nhung lam the nao de tim ra dugc vai lieu cd linh chat than ky nhu mong mudn do?
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Cau tra ldi li lam ra tinh the photon bing each lay mdt miu vat lieu va tao ra mdt sd dac tinh d cap nano tren b l mat cua chiing - tiic la lap lai cac kieu hdc va ranh - sao cho anh sing trai khip mlu theo mdt each hoan toan khac.
Bing each chpn each thiet ke cau tnic nano, cac nha nghien ciiu cd the tao ra cac vat lieu cd cac tinh chat quang hpe mdi. Dilu nay cho phep hp cd kha nang kiem soit va dieu khien hanh vi cua anh sang.
M.Q. (theo PhyOrg, 29/7/2011)
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