Avishai Ofan

Origin of highly spatially selective etching in deeply implanted complex oxides

The origin of the rate of anomalously high spatially selective etching of a buried heavily implanted region in complex oxides is studied. Single-crystal LiNbO3 samples are prepared with a 0.4μm wide implanted region at depth of 10μm, using 5×1016cm−2 fluence of 3.8MeV He+, and wet etched after a low-temperature anneal. An etch-rate enhancement of 104 is found after implantation and low-temperature 175–275°C post-implantation annealing. Experiments using time-resolved optical microscopy, x-ray diffraction, and proximal-probe microscopy show that this enhancement arises from the more rapid etch-solution transport in the microdomain network formed in the implanted region after annealing.The origin of the rate of anomalously high spatially selective etching of a buried heavily implanted region in complex oxides is studied. Single-crystal LiNbO3 samples are prepared with a 0.4μm wide implanted region at depth of 10μm, using 5×1016cm−2 fluence of 3.8MeV He+, and wet etched after a low-temperature anneal. An etch-rate enhancement of 104 is found after implantation and low-temperature 175–275°C post-implantation annealing. Experiments using time-resolved optical microscopy, x-ray diffraction, and proximal-probe microscopy show that this enhancement arises from the more rapid etch-solution transport in the microdomain network formed in the implanted region after annealing.

Large-area regular nanodomain patterning in He-irradiated lithium niobate crystals

Large-area ferroelectric nanodomain patterns, which are desirable for nonlinear optical applications, were generated in previously He-implanted lithium niobate crystals by applying voltage pulses to the tip of a scanning force microscope. The individual nanodomains were found to be of uniform size, which depended only on the inter-domain spacing and the pulse amplitude. We explain this behavior by the electrostatic repulsion of poling-induced buried charges between adjacent domains. The domain patterns were imaged by piezoresponse force microscopy and investigated by domain-selective etching in conjunction with focused ion beam etching followed by scanning electron microscopy imaging. In order to optimize the He-irradiation parameters for easy and reliable nanodomain patterning a series of samples subjected to various irradiation fluences and energies was prepared. The different samples were characterized by investigating nanodomains generated with a wide range of pulse parameters (amplitude and duration). In addition, these experiments clarified the physical mechanism behind the facile poling measured in He-irradiated lithium niobate crystals: the damage caused by the energy loss that takes place via electronic excitations appears to act to stabilize the domains, whereas the nuclear-collision damage degrades the crystal quality, and thus impedes reliable nanodomain generation.

Low-voltage nanodomain writing in He-implanted lithium niobate crystals

A scanning force microscope tip is used to write ferroelectric domains in He-implanted single-crystal lithium niobate and subsequently probe them by piezoresponse force microscopy. Investigation of cross-sections of the samples showed that the buried implanted layer, ∼1 μm below the surface, is nonferroelectric and can thus act as a barrier to domain growth. This barrier enabled stable surface domains of <1 μm size to be written in 500 μm thick crystal substrates with voltage pulses of only 10 V applied to the tip.

Fabrication of freestanding LiNbO3 thin films via He implantation and femtosecond laser ablation

The authors report using a combination of ion-implantation exfoliation and femtosecond laser ablation to fabricate thin (micrometers-thick) single-crystal films of a complex oxide, LiNbO3. The process physics for the method is bounded by the threshold for ablation and the onset of laser thermal outdiffusion of the implanted He used in exfoliation selective etching.

Second harmonic generation in single-crystal thin membranes of LiNbO 3 fabricated by patterned He + ion implantation

We demonstrate room-temperature phase matching of second-harmonic generation by waveguide dispersion (WGD) in 3-mum-thick LiNbO3 membranes. The membranes were made using patterned deep-ion-implantation-guided etching.

Femtosecond laser milling of ultrathin films of LiNbO3

We report femtosecond laser cutting of ultrathin ferroelectric sheets. This process enables one to do rapid patterning of microns-thick films of complex oxides such as LiNbO3, which are obtained via ion-beam exfoliation from standard wafers. Cutting these fragile samples is extremely difficult using standard methods but can be done effectively with ultrafast lasers. To achieve fast writing speed, we employ a high-repetition-rate amplified Ti:sapphire laser system with a pulse peak power of ~100MW. Optimization of the depth and quality of cut were determined as a function of laser pulse energy, crystallographic axes, optical polarization, and pre- and post-ablation chemical treatments.