Glass with modified surface regions on opposing sides and methods and apparatuses for forming the same via electro-thermal poling
A glass substrate according to one or more embodiments is disclosed. The glass substrate includes an alkali-containing bulk, at least one first alkali-depleted region, and at least one second alkali-depleted region. The alkali-containing bulk has a first surface and a second surfaces with the first and second surfaces opposing one another. The at least one first alkali-depleted region extends into the alkali-containing bulk from the first surface. The at least one second alkali-depleted region extends into the alkali-containing bulk from the second surface. The first alkali-depleted region and the second alkali-depleted region are amorphous and have a substantially homogenous composition. The first alkali-depleted region in some embodiments is a first alkali-depleted surface layer that extends across the alkali-containing bulk. The first alkali-depleted region in some embodiments is plurality of first alkali-depleted regions that are spaced apart from one another.
1. A method of forming a glass substrate with modified surface regions, comprising:
providing a glass substrate having a concentration of alkali and opposing surfaces that include a first surface and a second surface;
reducing the concentration of alkali in at least one first region extending for a first thickness from the first surface via thermal poling and, near-simultaneously, reducing the concentration of alkali in at least one second region extending for a second thickness from the second surface via thermal poling,
wherein, after thermal poling, each of the at least one first region and the at least one second region has a substantially homogenous composition,
wherein thermal poling comprises contacting a first electrode to the first surface, contacting a second electrode to the second surface, and applying an alternating electrical potential difference to the glass substrate such that the first and second electrodes are alternatingly positively-biased relative to the glass substrate to induce alkali depletion in the at least one first and second regions, respectively,
wherein applying an alternating electrical potential difference to the glass substrate comprises using an alternating current (AC) waveform,
wherein using the (AC) waveform includes increasing a total voltage to the first and second electrodes as a function of time, and
wherein the AC waveform defines a duty cycle with a first half cycle in which the first electrode is positively biased and a second half-cycle in which the second electrode is positively biased, the duty cycle controlled to induce asymmetry between the first thickness and the second thickness.
2. The method of claim 1 , wherein the AC waveform has a working frequency in a range that corresponds to an electrode polarization regime of the glass substrate.
3. The method of claim 1 , wherein increasing a total voltage to the first and second electrodes further includes one or more of stepping up the total voltage in discrete intervals over a period of time and ramping up the total voltage in a linear manner as a function of time.
4. The method of claim 1 , wherein thermal poling comprises heating the glass substrate to a temperature below a glass transition temperature (Tg) of the glass substrate prior to applying the alternating electrical potential difference to the glass substrate.
5. The method of claim 1 , wherein thermal poling is performed under vacuum, in an inert gas environment, or in a permeable gas environment.
6. The method of claim 1 , wherein a material of at least one of the first electrode and the second electrode is selected from carbon, stainless steel, one or more noble metals, one or more oxidation-resistant, conductive films, or combinations thereof.
7. The method of claim 1 , wherein thermal poling comprises contacting a first portion of the first electrode to a portion of the first surface corresponding to the at least one first region and contacting a second portion of the second electrode to a portion of the second surface corresponding to the at least one second region.
8. The method of claim 7 , further comprising, while reducing the concentration of alkali in the at least one first region, simultaneously reducing the concentration of alkali in at least one third region extending from the first surface via thermal poling, the at least one third region spaced from the at least one first region.
9. The method of claim 8 , wherein thermal poling comprises contacting a third portion of the first electrode to a portion of the first surface corresponding to the at least one third region, the first and third portions of the first electrode spaced apart from one another.
10. The method of claim 1 , wherein increasing a total voltage to the first and second electrodes includes ramping up the total voltage in a non-linear manner as a function of time.