U.S. patent application number 10/959321 was filed with the patent office on 2006-04-13 for first surface mirror with chromium nitride layer.
This patent application is currently assigned to Guardian Industries Corp.. Invention is credited to Brent Boyce, Anton Dietrich, Gregory Scott, Francis Wuillaume.
Application Number | 20060077580 10/959321 |
Document ID | / |
Family ID | 36144973 |
Filed Date | 2006-04-13 |
United States Patent
Application |
20060077580 |
Kind Code |
A1 |
Wuillaume; Francis ; et
al. |
April 13, 2006 |
First surface mirror with chromium nitride layer
Abstract
A mirror (e.g., first surface mirror) is provided with a layer
of or including chromium nitride (CrN.sub.x). In certain example
embodiments, the CrN.sub.x layer may be the primary reflective
layer of the mirror. Surprisingly and unexpectedly, it has been
found the addition of nitrogen to the chromium to form CrN.sub.x
reduces pinhole formations in the resulting layer. In certain
example embodiments, the more nitrogen which is introduced into the
layer, the smaller the number and/or size of pinholes in the Cr
inclusive layer. In certain example embodiments, it has also been
found that the addition of nitrogen to Cr may improve
durability.
Inventors: |
Wuillaume; Francis;
(Plymouth, MI) ; Dietrich; Anton; (Fontnas,
CH) ; Boyce; Brent; (Novi, MI) ; Scott;
Gregory; (Shelby Township, MI) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
Guardian Industries Corp.
Aubum Hills
MI
C.R.V.C.
Grand Duche de
|
Family ID: |
36144973 |
Appl. No.: |
10/959321 |
Filed: |
October 7, 2004 |
Current U.S.
Class: |
359/883 |
Current CPC
Class: |
G02B 5/08 20130101 |
Class at
Publication: |
359/883 |
International
Class: |
G02B 5/08 20060101
G02B005/08 |
Claims
1. A mirror comprising: a substrate supporting a coating, wherein
the coating includes at least a reflective layer comprising
chromium nitride.
2. The mirror of claim 1, wherein the mirror has a visible
transmission of no greater than 5%.
3. The mirror of claim 1, wherein the mirror has a visible
transmission of no greater than 2.0%.
4. The mirror of claim 1, wherein the substrate is composed of
glass, and wherein the layer comprising chromium nitride is located
on and in direct contact with the substrate.
5. The mirror of claim 1, wherein a dielectric layer is provided
between the substrate and the layer comprising chromium
nitride.
6. The mirror of claim 1, wherein the chromium nitride is
represented by CrN.sub.x, where x is from 0.01 to 0.5.
7. The mirror of claim 1, wherein the chromium nitride is
represented by CrN.sub.x, where x is from 0.01 to 0.25.
8. The mirror of claim 1, wherein the chromium nitride is
represented by CrN.sub.x, where x is from 0.01 to 0.15.
9. The mirror of claim 1, wherein the layer comprising chromium
nitride is from 200 to 700 .ANG. thick.
10. The mirror of claim 1, wherein the layer comprising chromium
nitride is from 250 to 600 .ANG. thick.
11. The mirror of claim 1, wherein the mirror is a first surface
mirror.
12. The mirror of claim 1, wherein the mirror has film side
reflective a* color of from -2.0 to +2.0, and film side reflective
b* color of from -3.0 to +1.5.
13. The mirror of claim 1, wherein the mirror has film side
reflective a* color of from -1.0 to +1.0, and film side reflective
b* color of from -1.5 to +1.0.
14. The mirror of claim 1, wherein the layer comprising chromium
nitride is the only reflective layer of the mirror.
15. The mirror of claim 1, wherein the layer comprising chromium
nitride is nitrogen graded so that a first portion thereof contains
more nitrogen than a second portion thereof.
16. The mirror of claim 1, wherein a first portion of the layer
comprising chromium nitride located closer to the substrate
contains more nitrogen than does a second portion of the layer
comprising chromium nitride that is located further from the
substrate.
17. The mirror of claim 1, further comprising a metallic Cr layer
on the substrate, wherein the metallic Cr layer is located over the
layer comprising chromium nitride.
18. A mirror comprising: a glass substrate supporting a layer
comprising chromium nitride, and wherein the mirror has a visible
transmission of no greater than 5%.
19. The mirror of claim 18, wherein the mirror has a visible
transmission of no greater than 2.5%.
20. The mirror of claim 18, wherein the mirror has a visible
transmission of no greater than 2.0%.
21. The mirror of claim 18, wherein the layer comprising chromium
nitride is located on and in direct contact with the substrate.
22. The mirror of claim 18, wherein a dielectric layer is provided
between the glass substrate and the layer comprising chromium
nitride.
23. The mirror of claim 18, wherein the chromium nitride is
represented by CrN.sub.x, where x is from 0.01 to 0.5.
24. The mirror of claim 18, wherein the chromium nitride is
represented by CrN.sub.x, where x is from 0.01 to 0.25.
25. The mirror of claim 18, wherein the chromium nitride is
represented by CrN.sub.x, where x is from 0.01 to 0.15.
26. The mirror of claim 18, wherein the layer comprising chromium
nitride is from 200 to 700 .ANG. thick.
27. The mirror of claim 18, wherein the mirror is a first surface
mirror.
28. The mirror of claim 18, wherein the mirror has film side
reflective a* color of from -2.0 to +2.0, and film side reflective
b* color of from -3.0 to +1.5.
29. The mirror of claim 18, wherein the mirror has film side
reflective a* color of from -1.0 to +1.0, and film side reflective
b* color of from -1.5 to +1.0.
30. The mirror of claim 18, wherein the layer comprising chromium
nitride is the only reflective layer of the mirror.
31. The mirror of claim 18, wherein a first portion of the layer
comprising chromium nitride located closer to the substrate
contains more nitrogen than does a second portion of the layer
comprising chromium nitride located further from the substrate.
32. The mirror of claim 18, further comprising a metallic Cr layer
on the substrate, wherein the metallic Cr layer is located over the
layer comprising chromium nitride.
33. A method of making a mirror, the method comprising: providing a
glass substrate; sputtering a target comprising Cr in an atmosphere
comprising nitrogen gas in order to form a layer comprising
chromium nitride on the glass substrate; and wherein said
sputtering comprises using a nitrogen gas flow in the atmosphere
which represents from about 1-21% of total gas flow in the
atmosphere.
34. The method of claim 33, wherein said sputtering comprises using
a nitrogen gas flow in the atmosphere which represents from about
3-19% of total gas flow in the atmosphere.
35. The method of claim 33, wherein said sputtering comprises using
a nitrogen gas flow in the atmosphere which represents from about
5-18% of total gas flow in the atmosphere.
36. The method of claim 33, further comprising forming another
layer on the substrate, so that said another layer is located
between the substrate and the layer comprising chromium
nitride.
37. The method of claim 33, wherein the mirror has a visible
transmission of no greater than 5%.
38. The method of claim 33, wherein the mirror is a first surface
mirror.
39. The method of claim 33, wherein the sputtering is performed so
as to cause the mirror to have a film side reflective a* color of
from -2.0 to +2.0, and a film side reflective b* color of from -3.0
to +1.5.
40. A mirror comprising: a substrate supporting a coating, wherein
the coating includes at least a reflective layer comprising a metal
nitride, wherein the metal is nitrided sufficiently so as to reduce
pinholes and so that the mirror has a film side reflective a* color
of from -2.0 to +2.0, and a film side reflective b* color of from
-3.0 to +1.5.
41. The mirror of claim 40, wherein the metal is one of chromium
and aluminum.
Description
[0001] This application is related to a first-surface mirror
including a layer of or including chromium nitride (CrN.sub.x). In
certain example embodiments, a reflective layer of the mirror
comprises chromium nitride, and is nitrided to an extent so as to
reduce undesirable pinhole formation and/or improve adhesion. In
certain example non-limiting instances, such first surface mirrors
may be used in the context of a projection television (PTV)
apparatus, automotive mirrors, or in any other suitable
application.
BACKGROUND OF THE INVENTION
[0002] Mirrors for various uses are known in the art. For example,
see U.S. Pat. Nos. 5,923,464 and 4,309,075 (all hereby incorporated
herein by reference). Mirrors are also known for use in projection
televisions and other suitable applications. In the projection
television context, see for example U.S. Pat. Nos. 6,275,272,
5,669,681 and 5,896,236 (all hereby incorporated herein by
reference).
[0003] One type of mirror is a second or back surface mirror (most
common), while another type of mirror is a first or front surface
mirror (less common). Back surface mirrors typically include a
glass substrate with a reflective coating on a back surface thereof
(i.e., not on the front surface which is first hit by incoming
light). Incoming light passes through the glass substrate before
being reflected by the coating in a second surface mirror. Thus,
reflected light passes through the glass substrate twice in back or
second surface mirrors; once before being reflected and again after
being reflected on its way to a viewer. In certain instances,
passing through the glass substrate twice can create ambiguity in
directional reflection and imperfect reflections may sometimes
result. Mirrors such as bathroom mirrors, bedroom mirrors, and
architectural mirrors are typically back or second surface mirrors
so that the glass substrate can be used to protect the reflective
coating provided on the rear surface thereof.
[0004] In applications where more accurate reflections are desired,
front (or first) surface mirrors (FSMs) are often used. In
front/first surface mirrors, a reflective coating is provided on
the front surface of the glass substrate so that incoming light is
reflected by the coating before it passes through the glass
substrate. Since the light to be reflected does not have to pass
through the glass substrate in first surface mirrors (in contrast
to rear surface mirrors), first surface mirrors generally have
higher reflectance than do rear surface mirrors, and no or less
double reflected image. Example front surface mirrors (or first
surface mirrors) are disclosed in U.S. Pat. Nos. 6,783,253,
5,923,464 and 4,780,372 (all incorporated herein by reference).
[0005] It has been proposed to use a metallic chromium (Cr)
reflective layer in a first surface mirror. In particular, the
proposed mirror includes a layer of metallic Cr located directly on
and contacting a glass substrate. Unfortunately, such first surface
mirrors with a structure of glass/Cr suffer from pinhole related
problems. In particular, such a mirror structure is susceptible to
pinhole formation in the metallic Cr layer, especially as the Cr
layer thickness increases in applications where lower transmission
(e.g., 0.5% visible transmission) are desired. Light tends to leak
through such pinholes making large numbers of them especially
undesirable in mirror applications where reflectance (not
transmission) of light is desired.
[0006] It will be apparent from the above that there exists a need
in the art for a first/front surface mirror, or other type of
mirror, that is less susceptible to significant amounts of pinhole
formations.
BRIEF SUMMARY OF EXAMPLE EMBODIMENTS OF INVENTION
[0007] In certain embodiments of this invention, a mirror such as a
front surface mirror (FSM) is provided with a layer of or including
chromium nitride (CrN.sub.x). In certain example embodiments, the
CrN.sub.x layer may be the primary reflective layer of the
mirror.
[0008] Surprisingly and unexpectedly, it has been found the
addition of nitrogen to the chromium to form CrN.sub.x reduces
pinhole formations in the resulting layer, without strongly
affecting the mirror's reflective properties. In certain example
embodiments, the more nitrogen which is introduced into the layer,
the smaller the number and/or size of pinholes in the Cr inclusive
layer. In certain example embodiments, it has also been found that
the addition of nitrogen to Cr may improve durability of the
mirror.
[0009] In certain example embodiments of this invention, first
surface mirrors including such a layer may be used in projection
televisions, copiers, scanners, bar code readers, overhead
projectors, automotive mirrors (e.g., rearview mirrors, interior or
exterior), and/or any other suitable applications.
[0010] In certain example embodiments of this invention, there is
provided a mirror comprising a substrate supporting a coating,
wherein the coating includes at least a reflective layer comprising
fully or partially nitridic chromium.
[0011] In other example embodiments of this invention, there is
provided a mirror comprising a glass substrate supporting a layer
comprising chromium nitride, and wherein the mirror has a visible
transmission of no greater than 5%.
[0012] In still further example embodiments of this invention,
there is provided a method of making a mirror, the method
comprising providing a glass substrate; sputtering a target
comprising Cr in an atmosphere comprising nitrogen gas (and
possibly other gas or gases such as argon) in order to form a layer
comprising chromium nitride on the glass substrate; and wherein
said sputtering comprises using a nitrogen gas flow in the
atmosphere which represents from about 1-21% of total gas flow in
the atmosphere.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a cross sectional view of a first surface mirror
according to an example embodiment of this invention.
[0014] FIG. 2 is a graph illustrating that pinholes in a CrN.sub.x
layer decrease in number as nitrogen content increases in a
CrN.sub.x layer in a mirror.
[0015] FIG. 3 is a graph illustrating that the adhesion force of
protective tape to a Cr inclusive layer in a mirror decreases as
nitrogen content in the layer increases, thereby indicating that
durability of an exposed CrN.sub.x layer increases as nitrogen
content increases since the protective tape is less likely to pull
off parts of the layer when the tape is removed.
[0016] FIG. 4 is a cross sectional view if a first surface mirror
according to another example embodiment of this invention.
[0017] FIG. 5 is a cross sectional view of a first surface mirror
according to another example embodiment of this invention.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION
[0018] The instant invention relates to a mirror that may be used
in the context of projection televisions (PTVs), copiers, scanners,
bar code readers, overhead projectors, and/or any other suitable
applications. In certain embodiments, the mirror includes a layer
of or including CrN.sub.x. The CrN.sub.x layer may be used as the
only or primary reflective layer of the mirror in certain example
embodiments of this invention. In certain example embodiments, a
front surface mirror (FSM) is provided with a layer of or including
chromium nitride (CrN.sub.x). The CrN.sub.x layer may be formed by
physical vapor deposition such as sputtering, or in any other
suitable manner in different embodiments of this invention.
[0019] Most in the art would not add nitrogen to a reflective layer
in a mirror, because nitrogen tends to degrade reflection
characteristics which are of course highly desirable in mirrors.
However, surprisingly and unexpectedly, it has been found the
addition of nitrogen to the chromium to form CrN.sub.x reduces
pinhole formations in the resulting layer, without significantly
adversely affecting the mirror's reflective properties. In certain
example embodiments, the more nitrogen which is introduced into the
layer, the smaller the number and/or size of pinholes in the Cr
inclusive layer. In certain example embodiments, it has also been
found that the addition of nitrogen to Cr may also improve
durability of the mirror.
[0020] It has also been found that the addition of nitrogen tends
to reduce stress of the Cr inclusive layer thereby making it closer
to zero (compared to if no nitrogen was present given a Cr layer of
the same thickness). Thus, the stress in layer 3 tends to be less
when nitrogen is added (resulting in a CrN.sub.x layer), so that
the adhesive force of layer 3 to the glass is less likely to be
overcome causing delamination. Durability is improved in this
respect, and this may lead to less pinholes due to improved
adhesion.
[0021] Introduction of nitrogen during physical vapor deposition
(e.g., sputtering) of a metal-based first surface mirror on either
a bulk or graded basis has been found to significantly reduce the
formation of pinholes. Nitrogen may have multiple effects which
reduce the formation of pinholes, such as stress reduction of the
Cr inclusive layer, reduced adhesion to any optional protective
tape applied to the Cr inclusive layer surface, and/or increased
adhesion of the Cr inclusive layer to the underlying glass
substrate. Although nitrogen would typically be thought to have a
strong adverse effect on reflective properties, it has surprisingly
been found that it is possible to choose nitrogen flow levels which
reduce pinholes and/or improve durability while at the same time do
not sacrifice desired mirror-like reflection properties. For
instances, in certain example embodiments, the Cr inclusive layer
is only partially nitrided, and/or is nitrided only at a portion
thereof such as a bottom portion thereof, thereby permitting less
pinholes and/or improved durability to be achieved in combination
with satisfactory mirror optical properties such as reflection
and/or color.
[0022] FIG. 1 is a cross sectional view of a first surface mirror
(FSM) according to an example embodiment of this invention. The
first surface mirror of FIG. 1 includes glass substrate 1 and
reflective layer 3 of or including CrN.sub.x. Glass substrate 1 may
be from about 1-10 mm thick in different embodiments of this
invention, and may be any suitable color (e.g., grey, clear, green,
blue, etc.). In certain example instances, glass (e.g., soda lime
silica type glass) substrate 1 is from about 1-5 mm thick, most
preferably from about 2 to 3 mm thick. When substrate 1 is glass,
it may have an index of refraction value "n" of from about 1.48 to
1.53 (most preferably about 1.51 to 1.52). In FIG. 1, incident
light is represented by I, and reflected light by R.
[0023] Reflective layer 3 may be composed of or comprise CrN.sub.x
in certain example embodiments of this invention. Reflective layer
3 reflects the majority of incoming light before it reaches glass
substrate 1 and directs it toward a viewer away from the glass
substrate, so that the mirror is referred to as a first surface
mirror. In certain example embodiments of this invention, the
reflective CrN.sub.x layer 3 may be formed on glass substrate 1 by
sputtering a Cr target in an atmosphere including argon (Ar) and
nitrogen (N) gas, although other methods may instead be used in
alternative embodiments. The nitrogen content in the layer 3 may be
uniformly provided throughout the layer, or alternatively may be
graded (e.g., see discussion with respect to FIG. 5 below).
[0024] In certain example embodiments of this invention (e.g.,
embodiments of FIGS. 1-5), CrN.sub.x layer 3 may be from about 200
to 700 .ANG. thick, more preferably from about 250 to 600 .ANG.
thick. The thickness of layer 3 can be tuned based on the
reflection (and thus inversely transmission) desired. For purposes
of example only, when a visible transmission of light through the
mirror of about 2.5% is desired, CrN.sub.x layer 3 may be about 300
.ANG. thick. However, when a visible transmission of light through
the mirror of about 0.5% is desired, CrN.sub.x layer 3 may be about
525 .ANG. thick. Pinholes in metallic Cr layers are particularly
problematic at higher thicknesses. Thus, when lower visible
transmission are desired, and thus higher thicknesses, the addition
of nitrogen to the Cr inclusive reflective layer is especially
beneficial. The use of nitrogen in a Cr inclusive layer may be used
at any thickness in different embodiments of this invention.
However, in view of the above, the addition of nitrogen to the Cr
inclusive reflective layer to form a CrN.sub.x layer 3 is
especially beneficial, for example, at layer 3 thicknesses of at
least about 300 .ANG., more preferably of at least about 350 .ANG.,
and most preferably of at least about 400 .ANG..
[0025] The mirror, in certain example embodiments of this invention
(e.g., FIGS. 1-5), has a visible light transmission of no greater
than 10%, more preferably no greater than 5%, even more preferably
no greater than 3%, still more preferably no greater than 2.5%,
sometimes no greater than 1.5%, and possibly no greater than about
0.5% in certain example instances. Moreover, the mirror in certain
example embodiments of this invention (e.g., FIGS. 1-5) has a
reflectance (e.g., from the film side, Hunter measured as Rf Y) of
at least 50%, more preferably of at least 60%.
[0026] Moreover, in certain example embodiments of this invention
(e.g., embodiments of FIGS. 1-5), the mirror has a reflective a*
color (film side, Hunter measured) of from -2 to +2, more
preferably from -1.5 to +1.5, and most preferably from -1 to +1.
Also, in certain example embodiments of this invention, the mirror
has a reflective b* color (film side, Hunter measured) of from -3
to +2, more preferably from -3 to +1.5, and even more preferably
from -1.5 to +1.0.
[0027] While only layer 3 is provided on the substrate 1 in the
FIG. 1 embodiment, this invention is not so limited. For example,
and without limitation, other layer(s) may be provided between
layer 3 and the substrate 1 in certain example embodiments of this
invention. For instance, a dielectric layer may be provided between
reflective layer 3 and glass substrate 1. Moreover, other layer(s)
such as a dielectric layer(s) may be provide on the glass substrate
1 over reflective layer 3. As another alternative embodiment(s) of
this invention, Cr may be replaced in the reflective layer 3 by Al,
Ag, or any other reflective material whose film stress is reduced
by addition of nitrogen in any embodiment of this invention.
[0028] FIG. 2, based on example data, is a graph plotting the
number of pinholes in layer 3 per square foot (vertical axis of
graph) versus nitrogen flow in the sputtering of CrN.sub.x layer 3
from a Cr sputtering target. The nitrogen flow % (horizontal axis
of graph) is the percentage of the overall gas flow (using only Ar
and N.sub.2) made up of nitrogen. For example, if the gas flow used
in sputtering CrN.sub.x layer 3 was 162 sccm nitrogen gas and 788
sccm argon gas (i.e., 17% nitrogen and 83% argon), then the
nitrogen gas flow amount would be 17% (i.e., 162/950=17%).
[0029] Still referring to FIG. 2, it can be seen that the addition
of nitrogen to the Cr inclusive layer reduces the number of
pinholes which end up therein. For example, as shown in FIG. 2,
when no nitrogen is used in the layer (i.e., for a metallic Cr
layer, where the intentional gas flow was 100% argon), in a 300
.ANG. Cr layer there were about 18 pinholes per square foot and in
a 525 .ANG. Cr layer there were about 23 pinholes per square foot.
However, when nitrogen gas was added to the gas in the sputtering
chamber to form a CrN.sub.x layer 3, the number of pinholes
significantly dropped. For instance, at about a 9% nitrogen gas
flow for the CrN.sub.x layer 3, when the layer was about 300 .ANG.
thick on the glass substrate there were about 11 pinholes per
square foot (down from about 18 pinholes at 0% nitrogen gas flow
for a layer of similar thickness) and in a 525 .ANG. thick
CrN.sub.x layer 3 there were about 7 pinholes (down from about 23
pinholes at 0% nitrogen gas flow for a layer of similar thickness)
per square foot. As another example shown in FIG. 2, at about a 17%
nitrogen gas flow (i.e., 17% of the gas in the sputtering chamber
was nitrogen, and the rest was argon) for the CrN.sub.x layer 3,
when the layer was about 300 .ANG. thick on the glass substrate
there were no pinholes per square foot (down from about 18 pinholes
at 0% nitrogen gas flow for a layer of similar thickness) and in a
525 .ANG. thick CrN.sub.x, layer 3 there were about 4 pinholes
(down from about 23 pinholes at 0% nitrogen gas flow for a layer of
similar thickness) per square foot. Thus, it can be seen from FIG.
2 that the addition of nitrogen to the Cr inclusive layer, to form
a CrN.sub.x layer 3, significantly reduces the number of pinholes
in a Cr inclusive layer in an unexpected and surprising manner.
[0030] Protective tape is sometimes applied to the surface of a
mirror during shipment, handling, and the like, and is then removed
upon installation of the mirror. Sometimes, pinholes form in
layer(s) of the mirror when the tape is removed. It is believed
that this may be due to the tape pulling off some material of the
coating when the tape is removed. Thus, it may be advantageous to
reduce the adhesion strength of tape to a coating. In this regard,
FIG. 3 is a graph based on example data illustrating that the
adhesion force of protective tape to a Cr inclusive layer in a
mirror decreases as nitrogen content in the layer increases,
thereby indicating that durability of an exposed CrN.sub.x layer 3
can increase as nitrogen content increases since the protective
tape is less likely to pull off parts of the layer when the tape is
removed. The horizontal axis in FIG. 3 is the same as the
horizontal axis in FIG. 2. Thus, FIG. 3 illustrates that the mirror
may become more durable as nitrogen content in CrN.sub.x layer 3
increases.
[0031] FIG. 4 illustrates another example embodiment of this
invention. In the FIG. 4 embodiment, the first surface mirror
includes glass substrate 1, CrN.sub.x layer 3 (discussed above),
and metallic or substantially Cr layer 7. Each of layers 3 and 7
may act as reflective layers in the FIG. 4 embodiment. In the FIG.
4 embodiment, the CrN.sub.x layer 3 helps reduce the number of
pinholes in the coating thereby improving characteristics of the
mirror, and the metallic Cr layer 7 may provide excellent
reflection characteristics. In the FIG. 4 embodiment, it is
possible that the CrN.sub.x layer 3 may be thinned relative to the
thicknesses for the layer discussed above.
[0032] FIG. 5 illustrates another example embodiment of this
invention. In the FIG. 5 embodiment, the CrN.sub.x layer 3 is
nitrogen graded so as to include more nitrogen at one portion
thereof than at another portion thereof. The use of "N" in the
layer 3 in FIG. 5 is illustrate of nitrogen content. Thus, in the
FIG. 5 embodiment, a portion of the CrN.sub.x layer 3 closer to the
glass substrate 1 includes more nitrogen than does a portion of the
layer 3 further from the glass substrate. This grading may be
continuous of step-wise in different embodiments of this invention.
In certain example instances of the FIG. 5 embodiment, the portion
of CrN.sub.x layer 3 furthest from the substrate 1 has less
nitrogen content (e.g., little or no nitrogen) than does the
portion of the layer 3 closest to the glass substrate 1.
[0033] In certain example embodiments of this invention, it has
been found that the amount of nitrogen added to the Cr inclusive
layer leads to unexpected results. In particular, as shown in FIG.
2 for example, if too little (e.g., 0% or very little) nitrogen is
added to the Cr inclusive layer, then there may be a pinhole
problem relating to large numbers of pinholes. Moreover, if too
much nitrogen is added to the Cr inclusive layer, then reflectance
suffers and/or film side reflective b* color becomes undesirable
(e.g., b* becomes too large and significant yellow color can
result). Thus, a particular amount of nitrogen is added in certain
example non-limiting embodiments of this invention. For example, in
certain example embodiments layer 3 comprises CrN.sub.x, where x is
from 0.01 to 0.5, more preferably from 0.01 to 0.4, still more
preferably from 0.01 to 0.25, even more preferably from 0.01 to
0.20, and still more preferably from 0.05 to 0.15 (with respect to
atomic percentage).
[0034] Moreover, in certain example embodiments of this invention
the percentage of nitrogen gas (of the total gas flow used in
sputtering the CrN.sub.x layer 3) used in sputtering is from about
1-21%, more preferably from about 3-19%, and even more preferably
from 5-18%.
EXAMPLES
[0035] The following example first surface mirrors were made and
tested, but are not intended to be limiting. Example 1 had a layer
stack of glass/Cr, whereas the other examples all had a layer stack
of glass/CrN.sub.x as shown in FIG. 1. The glass substrate 1 was
about 2.3 mm thick. The examples were made by sputtering the Cr
inclusive layer on the substrate using a Cr sputtering target in a
gas atmosphere, using the following process parameters. Lower
linespeeds were used for thicker layers and thus less visible
transmission if desired. TABLE-US-00001 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex.
5 Ex. 6 Ex. 7 N.sub.2 gas flow (sccm): 0 92 131 131 160 198 94 Ar
gas flow (sccm): 970 878 825 825 790 747 878 Total gas (sccm): 970
970 956 956 950 945 972 % N gas flow: 0 9% 14% 14% 17% 21% 10%
Linespeed (ipm): 160 160 142 150 142 85 90 pressure (mTorr): 2.6
2.5 2.4 2.4 2.3 2.2 2.5
[0036] It was found that the mirrors of Examples 2-6 (which
included nitrogen in the Cr inclusive layer 3) had much fewer
pinholes than did the mirror of Example 1 (which had a metallic Cr
layer 3--thus, no nitrogen). Certain of these examples, and others,
were used to accumulate the data shown in FIGS. 2-3, evidencing the
unexpected results with respect to less pinholes and improved
durability.
[0037] Moreover, Examples 1-6 had the following optical
characteristics (the optical data was measured using a Hunter
Ultrascan XE during the run; reflectance/color was film side
reflective): TABLE-US-00002 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex.
7 Reflectance 65.88 64.96 64.24 63.97 63.64 62.68 65.13 (Rf Y %):
a*: -1.05 -0.52 -0.15 -0.12 0.12 0.55 -0.15 b*: -1.02 0.31 0.67 0.7
1.08 1.64 0.43 Visible Trans- 2.55 2.53 2.28 2.52 2.53 0.69 0.43
mission (TY %):
[0038] It can be seen that Examples 6-7 had lower visible
transmissions since lower linespeeds and thus higher layer
thicknesses were used. Moreover, it can be seen from the above that
higher nitrogen flows cause the b* value to increase toward yellow
which may be undesirable in certain example non-limiting
instances.
[0039] While the invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not to be
limited to the disclosed embodiment, but on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims. For
example, the coatings discussed herein may in some instances be
used in back surface mirror applications, different materials may
be used, additional or fewer layers may be provided, and/or the
like.
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