U.S. patent application number 12/280641 was filed with the patent office on 2008-12-18 for coating with carbon nitride and carbon nitride coated product.
This patent application is currently assigned to PICODEON LTD OY. Invention is credited to Reijo Lappalainen, Juha Makitalo, Vesa Myllymaki, Lasse Pulli, Jari Ruuttu.
Application Number | 20080311345 12/280641 |
Document ID | / |
Family ID | 38291318 |
Filed Date | 2008-12-18 |
United States Patent
Application |
20080311345 |
Kind Code |
A1 |
Ruuttu; Jari ; et
al. |
December 18, 2008 |
Coating With Carbon Nitride and Carbon Nitride Coated Product
Abstract
The invention relates in general level to a method for coating
various products including large surface areas with carbon nitride
material. The invention also relates to carbon nitride coated
products manufactured by the method. The coating is carried out by
employing ultra short pulsed laser deposition wherein pulsed laser
beam is scanned with a rotating optical scanner including at least
one mirror for reflecting the laser beam. The invention has several
both industrially and qualitatively advantageous effects such as
high coating production rate, excellent coating properties and
overall low manufacturing costs.
Inventors: |
Ruuttu; Jari; (Billnas,
FI) ; Lappalainen; Reijo; (Hiltulanlahti, FI)
; Myllymaki; Vesa; (Helsinki, FI) ; Pulli;
Lasse; (Helsinki, FI) ; Makitalo; Juha;
(Tammisaari, FI) |
Correspondence
Address: |
YOUNG & THOMPSON
209 Madison Street, Suite 500
ALEXANDRIA
VA
22314
US
|
Assignee: |
PICODEON LTD OY
Helsinki
FI
|
Family ID: |
38291318 |
Appl. No.: |
12/280641 |
Filed: |
February 23, 2007 |
PCT Filed: |
February 23, 2007 |
PCT NO: |
PCT/FI07/50105 |
371 Date: |
August 25, 2008 |
Current U.S.
Class: |
428/138 ;
427/596; 428/332; 428/336 |
Current CPC
Class: |
A61F 2/34 20130101; B23K
2103/05 20180801; B23K 26/0624 20151001; B23K 2103/50 20180801;
B23K 2103/52 20180801; Y10T 428/265 20150115; A61F 2002/30929
20130101; A61L 27/30 20130101; B23K 26/0821 20151001; C23C 14/0036
20130101; A61F 2002/3097 20130101; B23K 26/34 20130101; A61F
2310/0073 20130101; A61F 2310/00574 20130101; A61F 2/30767
20130101; B23K 2103/26 20180801; B23K 2103/08 20180801; B23K
2103/18 20180801; A61F 2002/3611 20130101; C23C 14/0658 20130101;
A61B 17/86 20130101; A61F 2/3094 20130101; A61F 2310/00395
20130101; B23K 26/324 20130101; A61B 2017/00836 20130101; C23C
14/083 20130101; C23C 14/28 20130101; A61F 2310/00856 20130101;
A61F 2/38 20130101; Y10T 428/24331 20150115; A61F 2310/00598
20130101; C23C 14/16 20130101; B23K 2103/14 20180801; B23K 26/32
20130101; B23K 2103/42 20180801; Y10T 428/26 20150115; C23C 14/0611
20130101 |
Class at
Publication: |
428/138 ;
427/596; 428/332; 428/336 |
International
Class: |
B32B 3/24 20060101
B32B003/24; C23C 14/30 20060101 C23C014/30; B32B 5/00 20060101
B32B005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 23, 2006 |
FI |
20060177 |
Feb 23, 2006 |
FI |
20060178 |
Feb 23, 2006 |
FI |
20060181 |
Feb 23, 2006 |
FI |
20060182 |
Claims
1-24. (canceled)
25. A method for coating a certain surface of a product with carbon
nitride by laser ablation, characterized in that the uniform
surface area to be coated comprises at least 0.2 dm.sup.2 and the
coating is carried by employing ultra short pulsed laser deposition
wherein pulsed laser beam is scanned with a rotating optical
scanner comprising at least one mirror for reflecting said laser
beam.
26. A method according to claim 25, characterized in that said
uniform surface area comprises at least 0.5 dm.sup.2, preferably at
least 1.0 dm.sup.2.
27. A method according to claim 25, characterized in that the
employed pulse frequency of said laser deposition is at least 1
MHz.
28. A method according to claim 25, characterized in that the
average surface roughness of produced coating on said uniform
surface area is less than 100 nm as scanned from an area of 1
.mu.m.sup.2 with Atomic Force Microscope (AFM).
29. A method according to claim 25, characterized in that the said
produced coating on said uniform surface area contains less than
one pinhole per 1 mm.sup.2, preferably less than one pinhole per 1
cm.sup.2 and most preferably no pinholes at said uniform surface
area.
30. A method according to claim 25, characterized in that said
uniform surface area of coated product comprises crystallic
structure.
31. A method according to claim 25, characterized in that said
uniform surface area of coated product comprises graphitic
structure.
32. A method according to claim 25, characterized in that the
thickness of said coating on uniform surface of product is between
20 nm and 20 .mu.m, preferably between 100 nm and 5 .mu.m.
33. A product comprising a certain surface being coated with carbon
nitride by laser ablation, characterized in that the coated uniform
surface area comprises at least 0.2 dm.sup.2 and that the coating
has been carried by employing ultra short pulsed laser deposition
wherein pulsed laser beam is scanned with a rotating optical
scanner comprising at least one mirror for reflecting said laser
beam.
34. A product according to claim 33, characterized in that said
uniform surface area comprises at least 0.5 dm.sup.2, preferably at
least 1.0 dm.sup.2.
35. A product according to claim 33, characterized in that the
average surface roughness of produced coating on said uniform
surface area is less than 100 nm as scanned from an area of 1
.mu.m.sup.2 with Atomic Force Microscope (AFM).
36. A product according to claim 33, characterized in that the
optical transmission of produced coating on said uniform surface
area is no less than 88%, preferably no less than 90% and most
preferably no less than 92%.
37. A product according to claim 33, characterized in that the said
produced coating on said uniform surface area contains less than
one pinhole per 1 mm.sup.2, preferably less than one pinhole per 1
cm.sup.2 and most preferably no pinholes at said uniform surface
area.
38. A product according to claim 33, characterized in that said
uniform surface area is coated in a manner wherein the first 50% of
said coating on said uniform surface area does not contain any
particles having a diameter exceeding 1000 nm, preferably 100 nm
and most preferably 30 nm.
39. A product according to claim 33, characterized in that the
thickness of said coating on uniform surface of product is between
20 nm and 20 .mu.m, preferably between 100 nm and 5 .mu.m.
Description
FIELD OF INVENTION
[0001] The invention relates generally to a method for coating
various products comprising large surface areas with carbon nitride
by ultra short pulsed laser ablation. The invention also relates to
products manufactured by the method. The invention has many
advantageous effects such as high coating production rate,
excellent coating properties and low manufacturing costs.
BACKGROUND
Carbon Nitride
[0002] Carbon nitride materials have been the focus of considerable
experimental and theoretical attention since Cohen and co-workers
proposed that .beta.-C.sub.3N.sub.4, a carbon nitride material
analogous to .beta.-Si.sub.3N.sub.4, should have a hardness
comparable to that of diamond. Subsequent calculations have shown
that other crystalline C.sub.3N.sub.4 should have stabilities
comparable or greater to that of .beta.-C.sub.3N.sub.4, and that
many of these structures should be quite hard. The
C.sub.3N.sub.4-structures include .alpha.-, .beta.-, cubic-,
pseudocubic-, and graphitic carbon nitride. Additionally,
C.sub.2N.sub.2, although possessing different chemical structure,
is called carbon nitride.
[0003] The local structure property that distinguishes potentially
superhard and dense C.sub.3N.sub.4 structures from low-density,
softer material is carbon coordination: hard materials require
tetrahedral or sp.sup.3-bonded carbon in the
C.sub.3N.sub.4-network, while sp.sup.2-bonded carbon will lead to
much softer materials. This requirement of having sp.sup.3-bonded
carbon in a hard carbon nitride is completely analogous to that in
amorphous diamondlike carbon (DLC), Hu et al, Physical Rewiev B,
vol 57, 1997, number 6, pages 3185-3188, Nitrogen-driven sp3 to sp2
transformation in carbon nitride materials.
[0004] As various diamond coatings, also carbon nitride coatings
possess excellent wear- and scratch-free properties. Additionally,
carbon nitride materials are corrosion resistant and can act as
electrical insulators, optical coatings, and above all, thermal
resistance better than with corresponding DLC-coatings.
[0005] Although good results can already be achieved with amorphous
CN.sub.x-structures, the properties are overly enhanced once the
nitrogen content and thus, the crystallinity in the carbon nitride
are realized in the thin film/coating structure.
[0006] In general, the materials produced in these studies have
been amorphous with nitrogen content less than 50%, i.e. not
C.sub.3N.sub.4 structures.
[0007] Due to their easier availability, the amorphous
CN.sub.x-materials have already found a wide spread of
applications. It is for instance the most widely used material in
protective overcoats for hard disks, Widlow et al, Brazilian
Journal of Physics, 2000, vol 30, n:o 3, Recent Progress in the
synthesis and characterization of amorphous and crystalline carbon
nitride coatings. Such films are produced by sputtering of graphite
in pure nitrogen the resulting films comprising amorphous carbon
nitride having wear performance several times better than existing
coatings.
[0008] The other efforts to produce carbon nitride coatings have
been done by laser ablation, inductively coupled plasma chemical
vapor deposition, solvothermal method as well as electrodeposition
from organic liquid. Majority of the reports results wherein the
nucleation and growth of amorphous CN.sub.x-thin solid films takes
place. In general, the materials produced in these studies have
been amorphous with nitrogen content less than 50%, i.e. not
C.sub.3N.sub.4-structures.
Laser-Ablation
[0009] In the recent years, considerable development of the laser
technology has provided means to produce very high-efficiency laser
systems that are based on semi-conductor fibres, thus supporting
advance in so called cold ablation methods.
[0010] At the priority date of the current application, solely
fibrous diode-pumped semiconductor laser is competing with
light-bulb pumped one, which both have the feature according to
which the laser beam is lead first into a fibre, and then forwarded
to the working target. These fibrous laser systems are the only
ones to be applied in to the laser ablation applications in an
industrial scale.
[0011] The recent fibres of the fibre lasers, as well as the
consequent low radiation power seem to limit the materials to be
used in the vaporization/ablation as the vaporization/ablation
targets. Vaporizing/ablating aluminium can be facilitated by a
small-pulsed power, whereas the more difficult substances to be
vaporized/ablated as Copper, Tungsten, etc. need more pulsed power.
The same applies into situation in which new compounds were in the
interest to be brought up with the same conventional techniques.
Examples to be mentioned are for instance manufacturing diamond
directly from carbon (graphite) or alumina production straight from
aluminium and oxygen via the appropriate reaction in the
vapour-phase in post-laser-ablation conditions.
[0012] On one hand, one of the most significant obstacles to the
forwarding progress of fibre-laser technology seems to be the fibre
capability of the fibre to tolerate the high power laser pulses
without break-up of the fibre or without diminished quality of the
laser beam.
[0013] When employing novel cold-ablation, both qualitative and
production rate related problems associated with coating, thin film
production as well as cutting/grooving/carving etc. has been
approached by focusing on increasing laser power and reducing the
spot size of the laser beam on the target. However, most of the
power increase was consumed to noise. The qualitative and
production rate related problems were still remaining although some
laser manufacturers resolved the laser power related problem.
Representative samples for both coating/thin film as well as
cutting/grooving/carving etc. could be produced only with low
repetition rates, narrow scanning widths and with long working time
beyond industrial feasibility as such, highlighted especially for
large bodies.
[0014] If the energy content of a pulse is kept constant, the power
of the pulse increases in the decrease of the pulse duration, the
problem with significance increases with the decreasing laser-pulse
duration. The problems are significant even with the
nano-second-pulse lasers, although they are not applied as such in
cold ablation methods.
[0015] The pulse duration decrease further to femto or even to
atto-second scale makes the problem almost irresolvable. For
example, in a pico-second laser system with a pulse duration of
10-15 ps the pulse energy should be 5 .mu.J for a 10-30 .mu.m spot,
when the total power of the laser is 100 W and the repetition rate
20 MHz. Such a fibre to tolerate such a pulse is not available at
the priority date of the current application according to the
knowledge of the writer at the very date.
[0016] The production rate is directly proportional to the
repetition rate or repetition frequency. On one hand the known
mirror-film scanners (galvano-scanners or back and worth wobbling
type of scanners), which do their duty cycle in way characterized
by their back and forth movement, the stopping of the mirror at the
both ends of the duty cycle is somewhat problematic as well as the
accelerating and decelerating related to the turning point and the
related momentary stop, which all limit the utilizability of the
mirror as scanner, but especially also to the scanning width. If
the production rate were tried to be scaled up, by increasing the
repetition rate, the acceleration and deceleration cause either a
narrow scanning range, or uneven distribution of the radiation and
thus the plasma at the target when radiation hit the target via
accelerating and/or decelerating mirror.
[0017] If trying to increase the coating/thin film production rate
by simply increasing the pulse repetition rate, the present above
mentioned known scanners direct the pulses to overlapping spot of
the target area already at the low pulse repetition rates in
kHz-range, in an uncontrolled way. At worst, such an approach
results in release of particles from the target material, instead
of plasma but at least in particle formation into plasma. Once
several successive laser pulses are directed into the same location
of target surface, the cumulative effect seems to erode the target
material unevenly and can lead to heating of the target material,
the advantages of cold ablation being thus lost.
[0018] The same problems apply to nano-second range lasers, the
problem being naturally even more severe because of the long
lasting pulse with high energy. Here, the target material heating
occurs always, the target material temperature being elevated to
approximately 5000 K. Thus, even one single nano-second range pulse
erodes the target material drastically, with aforesaid
problems.
[0019] In the known techniques, the target may not only wear out
unevenly but may also fragment easily and degrade the plasma
quality. Thus, the surface to be coated with such plasma also
suffers the detrimental effects of the plasma. The surface may
comprise fragments, plasma may be not evenly distributed to form
such a coating etc. which are problematic in accuracy demanding
application, but may be not problematic, with paint or pigment for
instance, provided that defects can be below a certain level of the
very application.
[0020] The present methods wear out the target in a single use so
that same target is not available for a further use from the same
surface again. The problem has been tackled by utilising only a
virgin surface of the target, by moving target material and/or the
beam spot accordingly.
[0021] In machining or work-related applications the left-overs or
the debris comprising some fragments also can make the cut-line
uneven and thus inappropriate, as the case could be for instance in
flow-control drillings. Also the surface could be formed to have a
random bumpy appearance caused by the released fragments, which may
be not appropriate in certain semiconductor manufacturing
applications, for instance.
[0022] In addition, the mirror-film scanners moving back and forth
generate inertial forces that load the structure itself, but also
to the bearings to which the mirror is attached and/or which cause
the mirror movement. Such inertia little by little may loosen the
attachment of the mirror, especially if such mirror were working
nearly at the extreme range of the possible operational settings,
and may lead to roaming of the settings in long time scale, which
may be seen from uneven repeatability of the product quality.
Because of the stops, as well as the direction and the related
velocity changes of the movement, such a mirror-film scanner has a
very limited scanning width so to be used for ablation and plasma
production. The effective duty cycle is relatively short compared
to the whole cycle, although the operation is anyway quite slow. In
the point of view of increasing the productivity of a system
utilising mirror-film scanners, the plasma production rate is in
prerequisite slow, scanning width narrow, operation unstable for
long time period scales, but yield also a very high probability to
get involved with unwanted particle emission in to the plasma, and
consequently to the products that are involved with the plasma via
the machinery and/or coating.
SUMMARY OF THE INVENTION
[0023] The need and simultaneously maintenance cost for various
metal, glass, stone and plastic products is huge and steadily
increasing and there is a great need for coating technologies for
especially all products comprising large surface areas. The product
lifetime should be increased and the maintenance costs should be
lowered, sustainable development being a prerequisite. The coating
and especially uniform coating of large product surfaces with one
or several of the following properties: excellent optical
properties, chemical and/or wear resistance, thermal resistance and
conductivity, scratch-free properties, excellent coating adhesion,
electrical conductivity and tribological properties has remained an
unsolved problem.
[0024] Carbon nitride materials possess several of those properties
but the methods to manufacture carbon nitride coatings, especially
those of C.sub.3N.sub.4-coatings for large scale surfaces don't
exist.
[0025] Neither recent high-technological coating methods, nor
present coating techniques related to laser ablation either in
nanosecond or cold ablation range (pico-, femto-second lasers) can
provide any feasible method for industrial scale coating of
products comprising larger surfaces. The present CVD- and
PVD-coating technologies require high-vacuum conditions making the
coating process batch wise, thus non-feasible for industrial scale
coating of most of the present products. Moreover, the distance
between the metal material to be coated and the coating material to
be ablated is long, typically over 50 cm, making the coating
chambers large and vacuum pumping periods time- and
energy-consuming. Such high-volume vacuumed chambers are also
easily contaminated with coating materials in the coating process
itself, requiring continuous and time-consuming cleaning
processes.
[0026] While trying to increase the coating production rate in
present laser-assisted coating methods in general, various defects
such as pinholes, increased surface roughness, decreased or
disappearing optical properties, particulates on coating surface,
particulates in surface structure affecting corrosion pathways,
decreased surface uniformity, decreased adhesion, unsatisfactory
surface thickness and tribological properties etc. take place.
[0027] Where applicable, the target material surface is eroded in a
manner that only the outmost layer of the target material can be
employed for coating purposes. The rest of the material is either
wasted or must be subjected to reprocessing before reuse. An aim of
the current invention is to solve or at least to mitigate the
problems of the known techniques.
[0028] A first object of this invention is to provide a new method
how to solve a problem to coat a certain surface of a product with
carbon nitride by pulsed laser deposition that so that the uniform
surface area to be coated comprises at least 0.2 dm.sup.2.
[0029] A second object of this invention is to provide new products
being coated with carbon nitride by pulsed laser deposition so that
the coated uniform surface area comprises at least 0.2
dm.sup.2.
[0030] A third object of this invention is to provide at least a
new method and/or related means to solve a problem how to provide
available such fine plasma practically from carbon nitride target
to be used in coating of various products, so that the target
material do not form into the plasma any particulate fragments
either at all, i.e. the plasma is pure plasma, or the fragments, if
exist, are rare and at least smaller in size than the ablation
depth to which the plasma is generated by ablation from said
target.
[0031] A fourth object of the invention is to provide at least a
new method and/or related means to solve how to coat the uniform
surface area of a product with the fine plasma without particulate
fragments larger in size than the ablation depth to which the
plasma is generated by ablation from said target, i.e. to coat
substrates with pure plasma originating from carbon nitride
material.
[0032] A fifth object of this invention is to is to provide a good
adhesion of the coating to the uniform surface area of a product by
said pure plasma, so that wasting the kinetic energy to particulate
fragments is suppressed by limiting the existence of the
particulate fragments or their size smaller than said ablation
depth. Simultaneously, the particulate fragments because of their
lacking existence in significant manner, they do not form cool
surfaces that could influence on the homogeneity of the plasma
plume via nucleation and condensation related phenomena.
[0033] A sixth object of the invention is to provide at least a new
method and/or related means to solve a problem how to provide a
broad scanning width simultaneously with fine plasma quality and
broad coating width even for large product bodies in industrial
manner.
[0034] A seventh object of the invention is to provide at least a
new method and/or related means to solve a problem how to provide a
high repetition rate to be used to provide industrial scale
applications in accordance with the objects of the invention
mentioned above.
[0035] An eighth object of the invention is to provide at least a
new method and/or related means to solve a problem how to provide
fine plasma for coating of uniform product surfaces to manufacture
products according to the first to seven objects, but still save
target material to be used in the coating phases producing same
quality coatings/thin films where needed.
[0036] A further object of the invention is to use such method and
means according previous objects to solve a problem how to
cold-work and/or coat surfaces for coated products.
[0037] The present invention is based on the surprising discovery
that various products comprising large surfaces can be coated with
carbon nitride with industrial production rates and excellent
qualities regarding several technical features common to carbon
nitrides in general. The carbon nitride material is preferably
employed as C.sub.3N.sub.4H.sub.x-target material, but the other
carbon nitride materials or carbon based target materials are not
to be excluded.
[0038] Moreover, the present method accomplishes the economical use
of carbon nitride target materials, because they are ablated in a
manner accomplishing the reuse of already subjected material with
retained high coating results. The present invention further
accomplishes the coating of various products in relatively low
vacuum conditions with simultaneously high coating properties.
Moreover, the required coating chamber volumes are dramatically
smaller than in competing methods. Such features decrease
dramatically the overall equipment cost and increase the coating
production rate. In many preferable cases, the coating equipment
can be fitted into production-line in online manner.
[0039] The coating deposition rates with 20 W USPLD-apparatus are 2
mm.sup.3/min. While increasing the laser power to 80 W, the USPLD
coating deposition rate is increased to 8 mm.sup.3/min,
accordingly. According to the invention, the increase in deposition
rate can now be fully employed to high quality coating
production.
[0040] In this patent application the term "coating" means forming
material of any thickness on a substrate. Coating can thus also
mean producing thin films with thickness of e.g. <1 .mu.m.
[0041] Various embodiments of the inventions are combinable in
suitable part.
[0042] When read and understood the invention, the skilled men in
the art may know many ways to modify the shown embodiments of the
invention, however, without leaving the scope of the invention,
which is not limited only to the shown embodiments which are shown
as examples of the embodiments of the invention.
FIGURES
[0043] The described and other advantages of the invention will
become apparent from the following detailed description and by
referring to the drawings where:
[0044] FIG. 1. illustrates an exemplary galvano-scanner set-up
comprising two galvano-scanners employed in state of the art cold
ablation coating/thin-film production and in machining and other
work-related applications. The number of galvano-scanners directing
the laser beam varies but is typically limited to one single
galvano-scanner,
[0045] FIG. 2. illustrates ITO-coating on polycarbonate sheet
(.about.100 mm.times.30 mm) produced by employing a prior art
vibrating mirror (galvo-scanner), in different ITO thin-film
thicknesses (30 nm, 60 nm and 90 nm).
[0046] FIG. 3. illustrates the situation wherein prior art
galvanometric scanner is employed in scanning laser beam resulting
in heavy overlapping of pulses with repetition rate of 2 Mhz.
[0047] FIG. 4. illustrates on possible coated product according to
the invention,
[0048] FIG. 5. illustrates one possible turbine scanner mirror
employed in method according to the invention,
[0049] FIG. 6. illustrates the movement of the ablating beam
achieved by each mirror in the example of FIG. 5,
[0050] FIG. 7. illustrates beam guidance through one possible
rotating scanner to be employed according to the invention,
[0051] FIG. 8. illustrates beam guidance through one possible
rotating scanner to be employed according to the invention
[0052] FIG. 9. illustrates beam guidance through one possible
rotating scanner to be employed according to the invention
[0053] FIG. 10. illustrates on possible coated product according to
the invention,
[0054] FIG. 11. illustrates on possible coated product according to
the invention,
[0055] FIG. 12. illustrates on possible coated product according to
the invention,
[0056] FIG. 13a. illustrates an embodiment according to the
invention, wherein target material ablated by scanning the laser
beam with rotating scanner (turbine scanner).
[0057] FIG. 13b. illustrates an exemplary part of target material
of FIG. 13a,
[0058] FIG. 13c. illustrates an exemplary ablated area of target
material of FIG. 13b,
[0059] FIG. 14a. illustrates an exemplary way according to the
invention to scan and ablate target material with turbine scanner
(rotating scanner),
[0060] FIG. 15a. illustrates plasma-related problems of known
techniques,
[0061] FIG. 15b. illustrates plasma-related problems of known
techniques.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0062] According to the invention there is provided a method for
coating a certain surface of either metal, glass, stone, ceramic,
plastic, fiber, composite of virtually any product with carbon
nitride material by laser ablation in which method the uniform
surface area to be coated comprises at least 0.2 dm.sup.2 and the
coating is carried by employing ultra short pulsed laser deposition
wherein pulsed laser beam is scanned with a rotating optical
scanner comprising at least one mirror for reflecting said laser
beam.
[0063] According to one embodiment of the invention, with carbon
nitride material is hereby meant all CN.sub.x-materials, preferably
C.sub.3N.sub.4 or C.sub.2N.sub.2-materials and most preferably
C.sub.3N.sub.4-materials. The coating can include small amounts of
hydrogen, the nitrogen to carbon ratio being thus close to 4:3.
[0064] The target material comprises preferably
C.sub.3N.sub.4-material for example in graphitic form. Such
graphitic material comprises always variable but small contents of
hydrogen. Thus, also here the nitrogen to carbon ratio is not
precisely but close to 4:3.
[0065] According to one embodiment of the invention, the coating
stoichiometry is adjusted by conducting the coating in nitrogen
atmosphere.
[0066] With products is hereby meant but not limited to metal
products such as for construction as whole, interior and decorative
use, for machinery, vehicle parts such as in cars, trucks,
motorcycles and tractors, airplanes such as in aircraft propulsion,
ships, boats, trains, rails, tools, medical products, electronic
devices and their casings, various stone and ceramic products,
fiber based products, glass based products, plastic based products,
lightning, computer hard disks, profiles, frames, component parts,
process equipment, bearings, electrical insulators, pipes and tanks
for various industries such as chemical industries, power and
energy industries, solar cells, leds, space ships, plain metal,
plastic and sheets, military solutions, ventilation, mining,
screws, water pipes, drills and their parts etc.
[0067] Ultra Short Laser Pulsed Deposition is often shortened
USPLD. Said deposition is also called cold ablation, in which one
of the characteristic features is that opposite for example to
competing nanosecond lasers practically no heat transfer takes
place from the exposed target area to the surroundings of this
area, the laser pulse energies being still enough to exceed
ablation threshold of target material. The pulse lengths are
typically under 50 ps, such as 5-30 ps. i.e. ultra short, the cold
ablation being reached with pico-second, femto-second and
atto-second pulsed lasers. The material evaporated from the target
by laser ablation is deposited onto a substrate that is held near
room temperature. Still, the plasma temperature reaches 1.000.000 K
on exposed target area. The plasma speed is superior, gaining even
100.000 m/s and thus, better prospective for adequate adhesion of
coating/thin-film produced.
[0068] In another preferred embodiment of the invention, said
uniform surface area comprises at least 0.5 dm.sup.2. In a still
preferred embodiment of the invention, said uniform surface area
comprises at least 1.0 dm.sup.2. The invention accomplishes easily
also the coating of products comprising uniform coated surface
areas larger than 0.5 m.sup.2, such as 1 m.sup.2 and over. As the
process is especially beneficial for coating large surfaces with
high quality plasma, it meets an underserved or unserved market of
several different metal products.
[0069] In industrial applications, it is important to achieve high
efficiency of laser treatment. In cold ablation, the intensity of
laser pulses must exceed a predetermined threshold value in order
to facilitate the cold ablation phenomenon. This threshold value
depends on the target material. In order to achieve high treatment
efficiency and thus, industrial productivity, the repetition rate
of the pulses should be high, such as 1 MHz, preferably over 2 MHz
and more preferably over 5 MHz. As mentioned earlier, it is
advantageous not to direct several pulses into same location of the
target surface because this causes a cumulating effect in the
target material, with particle deposition leading to bad quality
plasma and thus, bad quality coatings and thin-films, undesirable
eroding of the target material, possible target material heating
etc. Therefore, to achieve a high efficiency of treatment, it is
also necessary to have a high scanning speed of the laser beam.
According to the invention, the velocity of the beam at the surface
of the target should generally be more than 10 m/s to achieve
efficient processing, and preferably more than 50 m/s and more
preferably more than 100 m/s, even such speeds as 2000 m/s.
However, in the optical scanners based on vibrating mirror the
moment of inertia prevents achieving sufficiently high angular
velocity of the mirror. The obtained laser beam at the target
surface is therefore just a few m/s, FIG. 1 illustrating an example
of such vibrating mirror, also called galvano-scanner.
[0070] As the present coating methods employing galvano-scanners
can produce scanning widths at most 10 cm, preferably less, the
present invention also accomplishes much more broader scanning
widths such as 30 cm and even over 1 meter with simultaneously
excellent coating properties and production rates.
[0071] According to one embodiment of the invention, rotating
optical scanner is here meant scanners comprising at least one
mirror for reflecting laser beam. Such a scanner and its
applications are described in patent application FI20065867.
According to another embodiment of the invention, rotating optical
scanner comprises at least three mirrors for reflecting laser beam.
In one embodiment of the invention, in the coating method employs a
polygonal prism illustrated in FIG. 5. Here, a polygonal prism has
faces 21, 22, 23, 24, 25, 26, 27 and 28. Arrow 20 indicates that
the prism can be rotated around its axis 19, which is the symmetry
axis of the prism. When the faces of the prism of the FIG. 5 are
mirror faces, advantageously oblique in order to achieve scanning
line, arranged such that each face in its turn will change, by
means of reflection, the direction of radiation incident on the
mirror surface as the prism is rotated around its axis, the prism
is applicable in the method according to an embodiment of the
invention, in its radiation transmission line, as part of a
rotating scanner, i.e. turbine scanner. FIG. 5 shows 8 faces, but
there may be considerably more faces than that, even dozens or
hundreds of them. FIG. 5 also shows that the mirrors are at the
same oblique angle to the axis, but especially in an embodiment
including several mirrors, the said angle may vary in steps so
that, by means of stepping within a certain range, a certain
stepped shift on the work spot is achieved on the target,
illustrated in FIG. 6, among other things. The different
embodiments of invention are not to be limited into various turbine
scanner mirror arrangements regarding for example the size, shape
and number of laser beam reflecting mirrors.
[0072] The structure of the turbine scanner, FIG. 5, includes at
least 2 mirrors, preferably more than 6 mirrors, e.g. 8 mirrors (21
to 28) positioned symmetrically around the central axis 19. As the
prism 21 in the turbine scanner rotates 20 around the central axis
19, the mirrors direct the radiation, a laser beam, for instance,
reflected from spot 29, accurately onto the line-shaped area,
always starting from one and the same direction (FIG. 6). The
mirror structure of the turbine scanner may be non-tilted (FIG. 7)
or tilted at a desired angle, e.g. FIGS. 8 and 9. The size and
proportions of the turbine scanner can be freely chosen. In one
advantageous embodiment of the coating method it has a perimeter of
30 cm, diameter of 12 cm, and a height of 5 cm.
[0073] In an embodiment of the invention it is advantageous that
the mirrors 21 to 28 of the turbine scanner are preferably
positioned at oblique angles to the central axis 19, because then
the laser beam is easily conducted into the scanner system.
[0074] In a turbine scanner according to be employed according to
an embodiment of the invention (FIG. 5) the mirrors 21 to 28 can
deviate from each other in such a manner that during one round of
rotational movement there are scanned as many line-shaped areas
(FIG. 6) 29 as there are mirrors 21 to 28.
[0075] According to the invention, the surface to be coated can
comprise whole or a part of the product surface.
[0076] In one preferred embodiment of the invention laser ablation
is carried out under vacuum of 10.sup.-1 to 10.sup.-12 atmospheres.
High vacuum conditions require quite long pumping times, and thus
prolonged production times of coatings. With certain high
end-products this is not so big problem, but with for example
commodity products especially comprising larger surfaces this
definitely is. If taking into account these novel wear- and
scratch-free coatings, chemically inert coatings, tribological
coatings, thermally resistant and/or thermally conductive coatings,
electrically conductive coatings and possibly simultaneously
excellent transparencies in general, there simply aren't any
coating methods available for said products, neither from
technological point of view and/or from economical point of
view.
[0077] Thus, in a specially preferred embodiment of invention, the
laser ablation is carried out under vacuum of 10.sup.-1 to
10.sup.-4 atmospheres. According to the invention, excellent
coating/thin-film properties can be achieved already in low
atmospheres, leading to dramatically decreased processing times and
enhanced industrial applicability.
[0078] According to the invention it is possible to conduct the
coating in a manner wherein the distance between the target
material and said uniform surface area to be coated is under 25 cm,
preferably under 15 cm and most preferably under 10 cm. This
accomplishes the development of coating chambers with drastically
diminished volumes, making the overall price of coating production
lines lower and decreasing further the time required for vacuum
pumping.
[0079] In a preferred embodiment of the invention the ablated
surface of said target material can be repeatedly ablated in order
to produce defect-free coating. In case of most of the present
coating technologies, the target material wears unevenly in a
manner that the affected area cannot be reused for ablation and
must thus be either discarded or sent for regeneration after
certain use. The problem has been tackled by developing different
techniques for feeding constantly new, non-ablated target surface
for coating purposes by for example moving the target material in
x/y-axis or by rotating a cylinder-formed target material. The
present invention accomplishes simultaneously excellent coating
properties and production rates as well as use of carbon nitride
target material in a way wherein the good quality plasma retains
its quality throughout the use of substantially whole piece of
target material. Preferably, more than 50% of the single target
material weight is consumed to production of good quality plasma
according to the invention. With good quality plasma is hear meant
plasma for producing defect-free coatings and thin-films, the high
quality of plasma plume being maintained at high pulse frequencies
and deposition rates. Some of such properties are described here
below.
[0080] Even though the present invention prefers the use of carbon
nitride materials as target material, in another embodiment it also
applies for producing certain carbon nitride coatings by ablating
graphite or pyrocarbon in various nitrogen containing
atmospheres.
[0081] According to one embodiment of the invention, the average
surface roughness of produced coating on said uniform surface area
is less than 100 nm as scanned from an area of 1 .mu.m.sup.2 with
Atomic Force Microscope (AFM). More preferably, the average surface
roughness is less than 30 nm. With average surface roughness is
here meant the average deviation from the centre line average curve
fitted by a proper procedure, such as those available in AFM or
profilemeter. The surface roughness affects amongst the other the
wear- and scratch-free properties, tribological properties as well
as the transparency of coating on metal products coated according
to the invention.
[0082] In a still preferable embodiment of the invention, the
optical transmission of produced coating on said uniform surface
area is no less than 88%, preferably no less than 90% and most
preferably no less than 92%. It can even be higher than 98%.
[0083] In another embodiment of the invention, produced coating on
said uniform surface area contains less than one pinhole per 1
mm.sup.2, preferably less than one pinhole per 1 cm.sup.2 and most
preferably no pinholes at said uniform surface area. Pinhole is a
hole going through or substantially through the coating. Pinholes
provide a platform for erosion of the originally coated material
for example by chemical or environmental factors. Single pinhole in
for instance coating of chemical reactor or tubing, medical
implant, space ship, different parts of different vehicles and
their mechanical parts or further, in metallic construction or
interior structure leads easily to dramatically lowered lifetime of
said product.
[0084] Thus, in another preferred embodiment said uniform surface
area is coated in a manner wherein the first 50% of said coating on
said uniform surface area does not contain any particles having a
diameter exceeding 1000 nm, preferably 100 nm and most preferably
30 nm. If the early stages of the coating manufacturing process
produce micrometer size particles, such particles can cause open
corrosion pathways in the next layers of produced coating.
Moreover, due to irregular shape of particles, it is extremely
difficult to seal the surface underneath such particles.
Additionally, such particles increase surface roughness
substantially. The present method allows even here increased
lifetime and lowered maintenance cost of different products.
[0085] According to one embodiment of invention, said uniform
surface of the product is coated with only one single coating.
According to another embodiment of the invention, said uniform
surface of the product is coated with multilayered coating. Several
coatings can be produced in for different reasons. One reason might
be to enhance the adhesion of certain coatings to product surfaced
by manufacturing a first set of coating having better adhesion to
surface and possessing such properties that the following coating
layer has better adhesion to said layer than to surface itself.
Additionally, the multilayered coating can possess several
functions not achievable without said structure. The present
invention accomplishes the production of several coatings in one
single coating chamber or in the adjacent chambers.
[0086] The present invention further accomplishes the production of
composite coatings to product surface by ablating simultaneously
one composite material target comprising carbon nitride or in
addition to carbon nitride material target on or more target
materials comprising one or more substances. On preferable
additional material comprise metals, such as titanium. In some
cases it is according to the invention advantageous to add for
example small amounts of nucleation agents such as Ni, Pt, Re, Rh
or Cr. Composites can also comprise polymers such as Teflon or
silicon.
[0087] According to invention the thickness of said coating on
uniform surface of product is between 20 nm and 20 .mu.m,
preferably between 100 nm and 5 .mu.m. The coating thicknesses must
not be limited to those, because the present invention accomplishes
the preparation of molecular scale coatings on the other hand, very
thick coatings such as 100 .mu.m and over, on the other hand.
[0088] The present invention further accomplishes the preparation
of 3D-structures employing the product component as a scaffold for
growing said 3D-structure.
[0089] According to the invention there is also provided a carbon
nitride coated product comprising a certain surface being coated by
laser ablation wherein the coated uniform surface area comprises at
least 0.2 dm.sup.2 and that the coating has been carried by
employing ultra short pulsed laser deposition wherein pulsed laser
beam is scanned with a rotating optical scanner comprising at least
one mirror for reflecting said laser beam. The benefits received
with these products are described in more detail in the previous
description of the method.
[0090] In one embodiment of the invention said uniform surface area
comprises at least 0.5 dm.sup.2. In a more preferable embodiment of
the invention said uniform surface area comprises at least 1.0
dm.sup.2. The invention accomplishes easily also the products
comprising uniform coated surface areas larger than 0.5 m.sup.2,
such as 1 m.sup.2 and over.
[0091] According to one embodiment of the invention the average
surface roughness of produced coating on said uniform surface area
is less than 100 nm as scanned from an area of 1 .mu.m.sup.2 with
Atomic Force Microscope (AFM). More preferably, the average surface
roughness is less than 30 nm. With average surface roughness is
here meant the average deviation from the centre line average curve
fitted by a proper procedure, such as those available in AFM or
profilemeter. The surface roughness affects amongst the other the
wear- and scratch-free properties, tribological properties as well
as the transparency of coating on metal products coated according
to the invention.
[0092] According to another embodiment of the invention the optical
transmission of produced coating on said uniform surface area is no
less than 88%, preferably no less than 90% and most preferably no
less than 92%. In some cases the optical transmission can exceed
98%.
[0093] According to still another embodiment of the invention said
produced coating on said uniform surface area contains less than
one pinhole per 1 mm.sup.2, preferably less than one pinhole per 1
cm.sup.2 and most preferably no pinholes at said uniform surface
area.
[0094] According to still another embodiment of the invention said
uniform surface area is coated in a manner wherein the first 50% of
said coating on said uniform surface area does not contain any
particles having a diameter exceeding 1000 nm, preferably 100 nm
and most preferably 30 nm.
[0095] The coating of carbon nitride coated product according to
the invention can comprise virtually whichever type of carbon
nitride. Preferably, carbon nitride comprises C.sub.2N.sub.2 or
C.sub.3N.sub.4, and most preferably carbon nitride comprises
C.sub.3N.sub.4. Here, it can be beneficial to have graphitic
coating in certain solutions, and crystallic coating in certain
other solutions. Graphitic C.sub.3N.sub.4 typically contains small
amounts of hydrogen. The crystallic carbon nitride can comprise one
crystallic form or mixtures of these. Such forms include .alpha.-,
.beta.-, cubic- and pseudocubic-forms. With carbon nitride can here
also be meant the various mixtures of both all these crystallic and
graphitic forms and, metal composites of these.
[0096] Especially affordable embodiments of inventions include
carbon nitride in .alpha.- and/or .beta.-crystallic form, either in
pure form or as composites of with each other or with various
metals.
[0097] According to another preferred embodiment of the invention
said uniform surface of product is coated with multilayered
coating. According to another preferred embodiment of the invention
said uniform surface of product is coated with single coating
layer.
[0098] According to one preferred embodiment of the invention the
thickness of said carbon nitride coating on uniform surface of
product is between 20 nm and 20 .mu.m, preferably between 100 nm
and 5 .mu.m. The invention accomplishes also carbon nitride coated
products comprising one or several atomic layer coatings and thick
coatings such as exceeding 100 .mu.m, for example 1 mm. The present
invention further accomplishes the 3D-structures prepared by
employing the coated component as a scaffold for growing said
3D-structure.
EXAMPLES
Example to Demonstrate Known Art Problems
Laser Technology
[0099] FIG. 2 represents the ITO-coating on polycarbonate sheet
(.about.100 mm.times.30 mm) produced by employing a prior art
optical scanner, namely vibrating mirror (galvo-scanner), in
different ITO thin-film thicknesses (30 nm, 60 nm and 90 nm).
Although the ITO-coating is not deposited on metal substrate, the
picture clearly demonstrates some of the problems associated with
employing vibrating mirror as an optical scanner especially in
ultra short pulsed laser deposition (USPLD) but also in laser
assisted coatings in general. As a vibrating mirror changes its
direction of angular movement at its end positions, and due to
moment inertia, the angular velocity of the mirror is not constant
near to its end positions. Due to vibrating movement, the mirror
continuously brakes up and stops before speeding up again, causing
thus irregular treatment of the target material at the edges of the
scanned area. As it can be seen from FIG. 2, this in turn results
in low quality plasma comprising particles especially in the edges
of the scanned area and finally, in low quality and seemingly
uneven coating result.
[0100] The coating parameters have been selected in order to
demonstrate the uneven distribution of ablated material due to the
nature of employed scanner. If selecting the parameters
appropriately, the film quality can be enhanced, problems becoming
invisible but not excluded.
Example to Demonstrate Known Art Problems
Laser Technology
[0101] Conventionally galvanometric scanners are used to scan a
laser beam with a typical maximum speed of about 2-3 m/s, in
practice about 1 m/s. This means that even 40-60 pulses are
overlapping with a repetition rate of 2 MHz (FIG. 3).
Example to Demonstate Known Art Problems
Laser Technology
[0102] Plasma related quality problems are demonstrated in FIGS.
15a and 15b, which indicate plasma generation according to known
techniques. A laser pulse .quadrature. 1114 hits a target surface
1111. As the pulse is a long pulse, the depth h and the beam
diameter d are of the same magnitude, as the heat of the pulse 1114
also heat the surface at the hit spot area, but also beneath the
surface 1111 in deeper than the depth h. The structure experiences
thermal shock and tensions are building, which while breaking,
produce fragments illustrated F. As the plasma may be in the
example quite poor in quality, there appears to be also molecules
and clusters of them indicate by the small dots 1115, as in the
relation to the reference by the numeral 1115 for the nuclei or
clusters of similar structures, as formed from the gases 1116
demonstrated in the FIG. 15b. The letter "o"s demonstrate particles
that can form and grow from the gases and/or via agglomeration. The
released fragments may also grow by condensation and/or
agglomeration, which is indicated by the curved arrows from the
dots to Fs and from the os to the Fs. Curved arrows indicate also
phase transitions from plasma 1113 to gas 1116 and further to
particles 1115 and increased particles 1117 in size. As the
ablation plume in FIG. 15b can comprise fragments F as well as
particles built of the vapours and gases, because of the bad plasma
production, the plasma is not continuous as plasma region, and thus
variation of the quality may be met within a single pulse plume.
Because of defects in composition and/or structure beneath the
deepness h as well as the resulting variations of the deepness
(FIG. 15a), the target surface 1111 in FIG. 15b is not any more
available for a further ablations, and the target is wasted,
although there were some material available.
[0103] Such problems are common with nanosecond-lasers in general,
and present pico-second lasers, if they were employing the state of
the art scanners.
Example of Invention-1
[0104] FIG. 13a demonstrates a target material ablated with
pico-second-range pulsed laser employing rotating scanner with
speed accomplishing the ablation of target material with slight
overlapping of adjacent pulses, avoiding the problems associated
with prior art galvano-scanners. FIG. 13b shows enlarged picture of
one part of the ablated material, clearly demonstrating the smooth
and controlled ablation of material on both x- and y-axis and thus,
generation of high quality, particle-free plasma and further, high
quality thin-films and coatings. FIG. 13c demonstrates one example
of possible x- and y-dimensions of one single ablation spot
achieved by one or few pulses. Here, it can be clearly seen, that
the invention accomplishes the ablation of material in a manner
wherein the width of the ablated spot is always much bigger than
the depth of the ablated spot area. Theoretically, the possible
particles (if they would be generated) could now have a maximum
size of the spot depth. The rotating scanner now accomplishes the
production of good quality, particle free plasma with great
production rate, with simultaneously large scanning width,
especially beneficial for substrates comprising large surface areas
to be coated. Furthermore, the FIGS. 13a, 13b and 13c clearly
demonstrate that opposite to present techniques, the already
ablated target material area can be ablated for new generation of
high class plasma--reducing thus radically the overall
coating/thin-film producing cost.
Example of Invention-2
[0105] FIG. 14a demonstrates an example wherein coating is carried
out by employing a pico-second USPLD-laser and scanning the laser
pulses with turbine scanner. Here, the scanning speed is 30 m/s,
the laser spot-width being 30 .mu.m. In this example, there is an
1/3 overlapping between the adjacent pulses.
Examples of Invention
Coated Products
[0106] The following samples were grown on various metal substrates
by employing ultra short pulsed laser deposition (USPLD) with a
picosecond-range laser (X-lase, 20-80 W) at 1064 nm. Substrate
temperature varied from room temperature to 400.degree. C. and
target temperature in the range of room temperature to 700.degree.
C. In coating applications sintered graphitic
C.sub.3N.sub.4H.sub.x-target materials (Carbodeon Ltd Oy) were
employed. When employing nitrogen atmosphere, the nitrogen pressure
varied in the range of 10.sup.-4 to 10.sup.-1 mbar. The employed
scanner was a rotating mirror scanner accomplishing tunable
velocity of the beam at the surface of the target between 1 m/s to
350 m/s. The employed repetition rates varied between 1 to 30 MHz,
clearly demonstrating the importance of both the scanner and high
repetition rates when producing high quality coatings in industrial
manner. Deposited films were characterized by confocal microscope,
FTIR and Raman spectroscopy, AFM, optical transmission
measurements, ESEM and in some cases, electrical measurements
(University of Kuopio, Finland; ORC, Tampere, Finland and Corelase
Oy, Tampere Finland). The employed spot sizes varied between 20 to
45 .mu.m. The wear tests were carried out by employing pin on
disk-method (University of Kuopio, Finland), the tests being
carried out at room temperature 22 C and 50% (AD-coatings) or 25%
(others) relative humidity (without lubrication) with loads in the
range 10-125 g using a hardened steel ball (AISI 420), 6 mm in
diameter, as a pin. For AD-coatings the rotation speed was 300-600
rpm and for lenses 1 rpm. All the coatings possessed excellent wear
properties as well as adhesions.
Example 1
[0107] A bone screw made of stainless steel was coated by ablating
hot-pressed C.sub.3N.sub.4H.sub.x with pulse repetition rate of 20
MHz, pulse energy 5 .mu.J, pulse length 20 ps and the distance
between the target material and surface to be coated was 10 mm. The
vacuum level was 10.sup.-5 atmospheres during the coating process.
The coating thickness was measured to 1 .mu.m. The average surface
roughness was determined to be under 3 nm as scanned from an area
of 1 .mu.m2 with Atomic Force Microscope (AFM). No pinholes were
found on any measured area of carbon nitride coating.
Example 2
[0108] A chromium metal coated crasp was coated with carbon nitride
by ablating sintered C.sub.3N.sub.4H.sub.x-material with pulse
repetition rate of 6 MHz, pulse energy 5 .mu.J, pulse length 24 ps
and the distance between the target material and surface to be
coated was 5 cm. The vacuum level was 10.sup.-4 atmospheres during
the coating process. The process resulted in a uniform coating. The
carbon nitride coating thickness was measured to 390 nm and the
average surface roughness was determined to be under 2 nm as
scanned from an area of 1 .mu.m.sup.2 with Atomic Force Microscope
(AFM). No pinholes were found on any measured area of carbon
nitride (C.sub.3N.sub.4) coating.
Example 3
[0109] A metallic motor valve according to FIG. 12 was coated with
carbon nitride by ablating sintered C.sub.3N.sub.4H.sub.x-material
with pulse repetition rate of 4 MHz, pulse energy 5 .mu.J, pulse
length 24 ps and the distance between the target material and
surface to be coated was 3 cm. Nitrogen pressure varied in the
range of 10.sup.-4 to 10.sup.-1 mbar. The process resulted in a
uniform C.sub.3N.sub.4-coating. The carbon nitride coating
thickness was measured to 500 nm and the average surface roughness
was determined to be under 2 nm as scanned from an area of 1 .mu.m2
with Atomic Force Microscope (AFM). No pinholes were found on any
measured area of carbon nitride (C.sub.3N.sub.4) coating.
Example 4
[0110] A laboratory glass tube according to FIG. 10 was coated by
ablating sintered, graphitic carbon nitride (C.sub.3N.sub.4Hx,
Carbodeon Ltd Oy) target material. The pulse repetition rate of was
2 MHz, pulse energy 5 .mu.J, pulse length 20 ps, and the distance
between the target material and surface to be coated was adjusted
to 15 mm. The glass-material was pre-heated into approximately
120.degree. C. The vacuum level was 10.sup.-5 atmospheres during
the coating process. The process resulted in C.sub.3N.sub.4-coating
possessing coating thickness of 19 nm. No pinholes were found on
any measured area of copper coating. The copper coating seemed to
be easily oxidized.
Example 5
[0111] A sheet of polycarbonate comprising 10 mm.times.25 mm was
coated by ablating hot-pressed C.sub.3N.sub.4H.sub.x with pulse
repetition rate of 1 MHz, pulse energy 5 .mu.J, pulse length 20 ps
and the distance between the target material and surface to be
coated was 65 mm. Nitrogen pressure varied in the range of
10.sup.-4 to 10.sup.-1 mbar. The coating thickness was measured to
100 nm. The average surface roughness was determined to be under 3
nm as scanned from an area of 1 .mu.m.sup.2 with Atomic Force
Microscope (AFM). No pinholes were found on any measured area of
carbon nitride coating.
Example 6
[0112] A polished granite tile according to FIG. 4 comprising 100
mm.times.100 mm was coated by ablating graphitic carbon nitride
with pulse repetition rate of 4 MHz in nitrogen atmosphere the
nitrogen pressure varying in the range of 10.sup.-4 to 10.sup.-1
mbar. The employed pulse energy was 5 .mu.J, pulse length 20 ps and
the distance between the target material and surface to be coated
was 40 mm. The vacuum level was hold at vacuum of 10.sup.-5
atmospheres prior the coating process. The coating thickness was
approximately 1 .mu.m and the average surface roughness was
determined to be lower than 10 nm as scanned from an area of 1
.mu.m.sup.2 with Atomic Force Microscope (AFM).
* * * * *