Latency effects and periodic structures in light-induced frustrated etching of Fe:doped LiNbO3

Abstract

Single crystals of z-cut 0.05% Fe:doped lithium niobate (Fe:LiNbO 3 ), have been etched in a mixture of HF and HNO 3 acids, under simultaneous illumination from a ϳ100 mW 488 nm wavelength Ar ion laser light source, focused to power densities of ϳ50 W cm Ϫ2 at the crystal surface exposed to the etchant. Etching is partially inhibited in illuminated regions, and the degree of inhibition shows a systematic latency: sites illuminated early in the etch run resist further etching even after the light is removed. Etched structures additionally exhibit regular periodic features of ϳ0.5 m scale length. Details of these structures are shown, and the latent etching effect is discussed. © 2000 American Institute of Physics. ͓S0003-6951͑00͒00844-5͔Structuring of photonic and optoelectronic materials at sub-m scale lengths continues to have considerable interest in areas such as photonic crystal solids, 1 Bragg grating fabrication, 2 tips for scanning probe microscopes, and the developing area of optical MEMS. 3 In all cases, such structuring requires methodologies for, and accurate control of, the patterning, processing and subsequent revealing stages for the features to be fabricated. In this letter, we report new results in the microstructuring of iron doped lithium niobate single crystals for which the normal etch characteristics are modified through a photoelectrochemical process at the lithium niobate/etchant interface. We observe a latent effect, in which illumination of the sample has a marked effect on subsequent etching behavior for periods of at least several hours after the illumination has been removed, and show arrays of periodic features of ϳ0.5 m scale lengths that result from this latent etch behavior.Initial results in light induced frustrated etching ͑LIFE͒ in Fe:doped LiNbO 3 have already been reported. 4 These preliminary results however were directed mainly at total suppression of etching, and additionally used more heavily doped (0.2%)Fe:LiNbO 3 . Details of the LIFE process can be found in Ref. 4, but for clarity we briefly review the etch frustration procedure, whose implementation is illustrated in Fig. 1.The etch cell is constructed from stainless steel and PTFE, which has good etch resistance from the 1:2 mixture of HF and HNO 3 acids used. The LiNbO 3 crystal was a z-cut oriented, 0.5 mm thick sample of dimensions 10 mm square, doped with 0.05 wt % Fe, and supplied by Castech, China, oriented with the Ϫz face uppermost. When exposed to the etchant, the Ϫz face will etch at a rate of ϳ1 m per hour at room temperature, while the ϩz face remains almost totally unaffected. However, when moderate cw visible laser power densities ͑ϳ1 W cm Ϫ2 ͒ are directed at the LiNbO 3 interface undergoing etching this normal etch rate can be drastically modified, yielding complete etch frustration at power densities of ϳ100 W cm Ϫ2 , and partial frustration for power levels down to ϳ1 W cm Ϫ2 . The laser light used here, unlike that reported for Ref. 4, was passed through a spatial filter assembly, consisting of two...

UV laser-induced ordered surface nanostructures in congruent lithium niobate single crystals

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Impact of the crystal orientation of Fe-doped lithium niobate on photo-assisted proton exchange and chemical etching

“…In addition, the [Fe 2+ ] of LN:Fe samples can be calculated by using the absorption at 532 nm in Fig. 1 15 , 16 . The redox state of the Fe ions, represented by the ratio [Fe 2+ ]/[Fe], is listed in Table 1 .…”

Fabrication of piezoelectric micro-cantilevers in domain-engineered LiNbO3single crystals

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