Half mirror, method for manufacturing the same and lighting unit using the same
A half mirror, a method for manufacturing the half mirror and a lighting unit using the half mirror can include a base material and a half mirror layer formed on the base material. The half mirror layer can include a chrome oxide layer, which is made by only a sputtering method, and can be configured to perform a high thermal resistance. Accordingly, the half mirror cannot crack even under various circumstances such that repeat low/high temperatures. Thus, the disclosed subject matter can provide half mirrors having a high durability such as a thermal resistance and methods for manufacturing such the half mirrors in simple manufacturing processes, and also can provide lighting units using the half mirror having a high durability, which can maintain a stable reflectivity for a long term and which can also maintain a good appearance for a long-term use because the half mirror can prevent cracking therein.
1. A half mirror which receives light and reflects a part of the light while transmitting another part of the light from a base material, the half mirror comprising:
the base material, which has a first surface and a second surface formed in a substantially planar shape, the base material being made from a transparent material and comprising a polycarbonate resin; and
a half mirror layer formed on at least one of the first surface and the second surface of the base material as a chromium oxide layer of only one layer having a layer thickness,
wherein a minimum of a ratio of oxygen to chromium in a thickness direction of the half mirror layer toward the base material is at least 0.55, and a maximum of the ratio of oxygen to chromium in the thickness direction of the half mirror layer toward the base material is at most 0.86, and
wherein a minimum amount of oxygen in the chromium oxide layer in the thickness direction of the half mirror layer toward the base material is at least 35 atomic percent, and a maximum amount of oxygen in the chromium oxide layer in the thickness direction of the half mirror layer toward the base material is at most 46 atomic percent.
2. The half mirror according to claim 1 , wherein a ratio of oxygen to chromium on a central line in the thickness direction of the half mirror layer toward the base material is at least 0.67.
3. A lighting unit using the half mirror according to claim 2 , the lighting unit comprising:
a casing having an opening and an inner surface, the opening of the casing being attached to the half mirror; and
a light source attached to the casing and facing the half mirror.
4. The lighting unit according to claim 3 , wherein the inner surface of the casing is a reflective surface.
5. The half mirror according to claim 3 , wherein the layer thickness of the chromium oxide layer of only one layer is 26 to 65 nm, and the chromium oxide layer of only one layer is exposed from the half mirror.
6. A method for manufacturing the half mirror according to claim 1 , the method comprising:
preparing the base material;
forming a chromium layer on the base material by a sputtering method, wherein a pressure of argon gas in a coating chamber of a sputtering equipment is more than 1.5 Pa, and a power is less than 1,500 watts when a direct current (DC) is applied between a positive electrode connecting the base material and a negative electrode connecting a chromium target; and
forming the chromium oxide layer on the base material by injecting oxygen or a gas including the oxygen in the coating chamber of the sputtering equipment.
7. A lighting unit using the half mirror according to claim 1 , the lighting unit comprising:
a casing having an opening and an inner surface, the opening of the casing being attached to the half mirror; and
a light source attached to the casing and facing the half mirror.
8. The lighting unit according to claim 7 , wherein the inner surface of the casing is a reflective surface.
9. The half mirror according to claim 7 , wherein the layer thickness of the chromium oxide layer of only one layer is 26 to 65 nm.