ƘANANAN LU'ULU'U MASU TSAGE DA KE WARKEWA SU SAKE KAMA HASKE

Na’urorin photonic suna ƙara ƙanƙanta: hanyoyin da ke ɗaukar haske, resonator da ke kama shi, laser. A wannan ma’auni, ƙaramar tsagewa ta isa ta ɓata su. Yadda tsagewa ke samuwa da warkewa a cikin lu’ulu’u na kwayoyin halitta (organic) masu aiki da haske, marubutan sun rubuta, har yanzu “ba a bincika shi sosai ba”.

Lu’ulu’u da ke gyara tsagewarsu da kansu, a kalmominsu, “wani al’amari ne da ba kasafai ake gani ba kuma abin al’ajabi”. Misalan baya da takardar ta ambata sun haɗa da gishirin dutse (rock salt), potassium chloride da alumina, da kuma wasu lu’ulu’u na molecule (molecular crystals). Amma galibinsu tsawonsu daga milimita ne zuwa santimita, ana sarrafa su da hanzaki (forceps) da allurai. Wasu sun warke a hankali: lu’ulu’u masu tsawon kusan milimita 3 sun farfaɗo da 6.7% kawai bayan an matse su na tsawon awa 24. Wasu kuma, masu siffar allura, sun sake haɗewa cikin millisecond.

Bakin microscope a matsayin guduma

Melchi Chosenyah, Rajadurai Chandrasekar da abokan aikinsu a University of Hyderabad da Central University of Karnataka, a Indiya, sun sauka zuwa ma’aunin da lu’ulu’u ke aiki a matsayin sassan na’urorin haske. Sun yi amfani da wani sinadari na kwayoyin halitta (organic compound) mai suna HDMAC, wanda ke haskakawa da launin lemu-ja a ƙarƙashin hasken ultraviolet, da hasken da yake fitarwa a tsakiyar nanometre 660. Idan aka ɗiga shi a matsayin ruwan magani (solution) a kan gilashi, yana samar da siraran lu’ulu’u masu siffar murabba’i da mai tsawo masu faɗin micrometre ’yan goma-goma.

Kayan aikinsu shi ne bakin cantilever na na’urar hangen ƙananan abubuwa ta ƙarfin zarra (atomic force microscope), wanda aka yi amfani da shi duka wajen tsaga lu’ulu’un ta hanyoyin da aka sarrafa da kuma tura gutsuttsuran su koma tare. Marubutan sun aro kalmominsu daga karayar ƙashi: tsagewar ratsawa (transverse) tana tafiya a faɗin lu’ulu’u, ta tsawo (longitudinal) tana bin tsawonsa, ta karkata (oblique) tana tafiya a tsallake; fizgewa (avulsion) kuma tana fizge ƙaramin gutsure.

Gutsuttsuran da ke haɗewa

• A cikin lu’ulu’u mai kusan micrometre 13.7 da 12.5, wata tsagewa mai karkata ta ɓace lokacin da aka tura gefen lu’ulu’un zuwa ciki. A ƙarƙashin na’urar hangen ƙananan abubuwa ta electron (electron microscope), gyaran ya kusan zama ba tare da alamar haɗi ba, sai wani siririn layi idan aka ƙara girman hoto sosai. Wurin da aka fizge wani gutsure ne kawai bai warke ba.
• An raba wani lu’ulu’u mai tsawon kusan micrometre 20 zuwa gutsure biyu daban-daban. Bayan an sake daidaita su aka matse su tare, sun warke nan take. Da aka tura shi daga baya da bakin, lu’ulu’un ya motsa a matsayin jiki ɗaya.
• Tsagewa a kan fannonin lu’ulu’u (crystal planes) biyu daban-daban duka sun warke. Kusan dukkan ƙananan lu’ulu’un sun warke lokacin da saman da suka karye suka zauna da tsabta; tarin ƙananan tarkace a wurin karayar ya hana warkewa.
• Wani babban lu’ulu’u mai kama da ɓawo (flake), mai irin tsarin jeruwar molecule ɗaya, ya farfashe maimakon ya tsage da kyau, kuma bai warke ba.

Yawan hasken da ke dawowa

Dogayen lu’ulu’u suna aiki a matsayin hanyoyin jagorantar haske (waveguides): hasken da aka fitar a ƙarshe ɗaya yana tafiya zuwa ɗayan ƙarshen. A cikin lu’ulu’u mai tsawon micrometre 271, ƙungiyar ta haska laser na nanometre 405 a ƙarshe ɗaya kuma ta tattara hasken da aka jagoranta a ɗayan ƙarshen, kafin tsagewa da bayan warkewa. Kwatanta su biyun ya ba da “ingancin warkewa” na kusan 80%. A cikin lu’ulu’u shida irin waɗannan, ya kasance daga 32% zuwa 99%. Asarar ta fito ne daga hasken da ya watse a tsagewar da aka gyara, musamman inda gutsuttsura suka ɓace.

Resonator da aka maido

Siraran lu’ulu’u suna kuma aiki a matsayin resonator: fuskokinsu na sama da na ƙasa suna aiki kamar madubai, don haka wasu launukan haske ne kawai ke taruwa a tsakaninsu. Gwargwadon siririn lu’ulu’un, gwargwadon faɗin tazarar da ke tsakanin waɗannan resonance. Wani lu’ulu’u mai micrometre 31 da 28, da kaurin micrometre 1.8, ya nuna resonance masu tazarar nanometre 17.8 tsakaninsu.

Ƙungiyar ta tsaga shi a tsawonsa ta tsakiya, ba tare da raba shi ba. A wurin tsagewar, resonance ɗin sun ragu ƙwarai. Bayan warkewa, sun dawo, da bakan haske (spectrum) da ya yi daidai da na lu’ulu’un da bai lalace ba. Hotunan haske mai sheƙi (fluorescence) da aka ɗauka yanki bayan yanki, kowane nanometre 257, sun nuna ɗan alamar tsagewar ne kawai a shimfiɗun sama; ƙasa da kusan nanometre 770, cikin lu’ulu’un ya yi kama da ya warke.

Ya fi laushi a wurin haɗin

Wani kaifin lu’u-lu’u (diamond) da aka danna cikin lu’ulu’un da ƙarfi iri ɗaya ya nutse nanometre 95 a yankunan da ba su lalace ba, da nanometre 115 a cikin wanda ya warke. Taurin yankin da ya warke, wato ma’aunin Young (Young’s modulus) ɗinsa, ya sauka daga gigapascal 2.15 zuwa 1.49, kusan kashi biyu bisa uku na na asali, kuma ƙarfinsa na jure wa huji (hardness) ya ragu kusan da rabi. Duk da haka ya ɗan koma yadda yake lokacin da aka cire nauyin.

Me ke riƙe gutsuttsuran tare? Lissafin ƙarfin da ke tsakanin molecule suna nuna sarƙoƙin jan hankali marasa yankewa a tsawon fannonin warkewa biyu: haɗin hydrogen (hydrogen bonds) tsakanin molecule da jan hankalin dipole tsakanin shimfiɗu maƙwabta, waɗanda marubutan ke gani a matsayin ɗaya daga cikin ƙarfin da ke tuƙa warkewar.

Marubutan sun nace cewa babu wata lamba ɗaya da ke bayyana ingancin warkewa: girman lu’ulu’u, irin tsagewa da yadda aka sake daidaita gutsuttsuran duka suna canza sakamakon. Burinsu shi ne sassan na’urorin haske da ke tsira daga lalacewa — lu’ulu’u masu haske waɗanda, da zarar sun karye, za a iya mayar da su bakin aiki.