FAQ

LUXOR coaters do not use rotating, planetary rotating or tilting stages. Such stages are used in some commercially available sputter coaters as an accessory to achieve more homogeneous coatings on three-dimensional samples. The unique A² technology that is part of every LUXOR coater creates a fine and homogeneous “cloud” of particles that deposit on and in three-dimensional structures and totally avoid charging of such samples. Tests on a large number of three-dimensional materials have shown that the use of a rotating or tilting stage does not improve the coating result in a LUXOR coater.

“Race tracking” is a spatially dependent erosion phenomenon of the sputter target that is influenced by, among other things, the relative positioning and dimensions of components such as the target and magnets, the strength of the cathode voltage, the strength and positioning of the magnetic field and the amount of process gas (argon). This erosion develops a ring or “race track” in the target that is devoid of material. Because of this selective erosion, only a small portion (typically 10-15%) of the total amount of target material is used for coating, before the “race track” erodes through the entire thickness of the target, requiring its replacement. “Race tracking” thus has a clear negative impact on the lifetime of the target, and also, if a target is not replaced in time, on the quality of the coating.
Although this phenomenon can never be completely avoided, the positioning, dimensions and construction of the various components in the plasma reactor of a LUXOR coater are optimized such that race tracking is reduced to a minimum. Also, the combination of low voltage and coating current together with the positioning of the magnetic field ensure that the lifetime of a LUXOR target is longer, which means a significant reduction in the cost of ownership.

The maximum area that can be coated during a sputter coating process is a 100 mm (4″) diameter circle, which corresponds to the surface of the sample holder. However, tests have shown that the requested coating thickness is obtained only in the middle 60 mm (2.4″) diameter circle of this surface. Outside this zone, the coating thickness is less than the requested value, decreasing further as the distance from the center point increases. However, for the vast majority of coated samples, charging is also prevented in this zone.
All types of LUXOR sample holders are designed in such a way that it is, in fact, not possible to position samples outside the 60 mm (2.4″) centering zone.

Check here for more info about our various sample holders.

Tests show that when coating a flat material in a LUXOR coater, the central area of the sample holder with a distance of 30 mm (2.4″) from the center point is uniformly coated with less than a few % deviation from the set coating thickness. The coating thickness decreases as the distance from the central point increases. The reason for this is the arrangement of the permanent magnetic field, which directs the plasma to the sample holder in a certain direction and orientation.
The morphology of the sample plays a very important role in the homogeneity of the coating. Especially for samples with a 3-dimensional structure such as e.g. nanofibers or powders, the coating thickness becomes very dependent on the position where one measures the thickness of the coating. For example, what does the coating thickness look like on the “back side” of a nanofiber, or inside the cell structure of a PE foam? Clearly, in these cases the use of a built-in coating thickness measurement system is pointless.

Au/Pd is often recommended to obtain smaller grain sizes. And Au/Pd does indeed result in smaller grain sizes when evaporated in high vacuum (by using a TMP), but when used in SEM sputter coaters, the difference between Au and Au/Pd is barely noticeable. The typical grain size for Au is 5 to 12 nm, and for Au/Pd 4 to 8 nm. Au/Pd is also less suitable for heat-sensitive specimens and for EDX analysis because of the extra set of peaks for Pd. LUXOR has a Au/Pd (80/20) target available, but we offer it only as an optional accessory with our gold or platinum coaters.

Coating with gold is mainly used at magnifications up to 50,000x. At higher magnifications, the structure of the gold coating becomes visible in the SEM images. Coating with platinum is possible for all magnifications, but is mainly used for magnifications above 50,000 x. So this means mainly imaging applications with FE-SEM or other high resolution (floor model) Electron microscopes. Shown below are 2 typical images of gold coating and platinum coating on nanofibers. At 100,000 x magnification, the structure of the gold coating is clearly visible.

No, a LUXOR Au coater cannot be upgraded to a LUXOR Pt. Although some of the hardware in a LUXOR Pt coater is identical to a LUXOR Au, the LUXOR Pt contains a number of unique hardware components and specific software algorithms that allow it to generate high-resolution platinum coatings. On the other hand, it is possible to work with a gold target in a LUXOR Pt.

At the start of a sputter coating process, a LUXOR coater controls the vacuum pump and built-in high frequency microvalve to achieve a stable initial vacuum for the plasma coating process. Depending on the metal being coated, this value ranges from 7 Pa to 12 Pa. When coating is performed in air, this part of the coating process takes about 2 minutes. When working in a process gas such as argon or nitrogen, a rinsing cycle is first performed, replacing the ambient air with the process gas. In this case, reaching the starting vacuum takes about 2.5 minutes.

A LUXOR coater uses a permanent magnetic field to avoid heat generation. During the glow discharge process, high-energy electrons are generated that can reach the sample and cause unwanted heating. In sputter coaters, the problem of heat generation is largely avoided by incorporating a system of permanent magnets that conduct the electrons away from the sample and contain the plasma in a doughnut shape above the target surface.

No, this is not possible because LUXOR sputter coater targets are different from all other targets on the market. The metal target disc (Au – Au/Pd – Pt) is pre-assembled on a push-fit holder.
Instead of having to replace a thin fragile metal disc, you can simply push the LUXOR target into place. No need for a screwdriver or other tools.
Moreover, LUXOR targets always ensure perfect and reproducible contact between the holder and the electrode surface.

LUXOR uses targets with a diameter of 30 mm (about 1.2″). This size, combined with the specific positioning of the magnetron and electrodes, mostly prevents “race-tracking” phenomena (often seen on the larger 57-60 mm targets) in which the outer part of the target is consumed much faster than the inner part.
This means that LUXOR targets need to be replaced less often than other targets.

LUXOR coaters also use very low sputter currents. This means that less material is consumed. Typically, we estimate about 1000 to 5000 coating cycles, depending on the required coating thickness and sample purity.

The number of cycles depends on the selected layer thickness per sputtering process. Theoretically, layer thickness can be set between 1 nm and 100 nm for LUXOR Au and Luxor Pt coaters. Multiplied by 5, this corresponds approximately to the actual ablation of the target per sputter cycle. In practice, for most SEM applications, a coating thickness between 2 nm and 10 nm is applied to prevent charging.

LUXOR sputter coaters work with fully automatic process parameters, which means that the layer thickness is reproducible and the target ablation is well calculable. The targets cannot be completely consumed because they are no longer stable if the residual thickness is too thin. Spent targets can be recognized by the holes that appear in the target film. Assuming replacement after 50% of the 100 µm thickness has been consumed, we calculate as follows:

• at 10 nm film thickness per cycle: 10 nm x 5 x 1000 coating cycles = 50 µm
• at 2 nm film thickness per cycle: 2 nm x 5 x 5000 coating cycles = 50 µm

So typically, we estimate about 1000 to 5000 coating cycles, depending on the required coating thickness.

For sputter coating, the “ideal” coating thickness range varies as a function of the coating material used. As an example, gold is typically coated with a layer thickness of 5 to 15 nm, while for platinum a layer thicknesses of 2 to 5 nm are applied. The reason for this is that, for equal plasma coating parameters such as vacuum, current, voltage and instrument configuration, the resulting gold particles are larger (typically 5-15 nm) than the platinum particles (typically 2-7 nm). It then follows that the layer of gold particles required to coat a surface to avoid charging will be thicker than a layer of platinum particles that avoids charging.

The attached pictures show a 10-nm gold coating on the left and a 2-nm platinum coating on the right. Both layers prevent charging of the nanofiber sample, but at this magnification (100k x) it is clear that platinum is the right solution.

The time for coating a 10 nm gold layer is typically 2 min and 1.5 min for a platinum layer of 5 nm. The entire coating process with the preliminary vacuum creation and return to atmospheric pressure after the process takes about 5 to 6 min.

In general, we do not recommend using LUXOR coaters with any model or type of pump other than those supplied as standard with the coater, or those recommended by LUXOR or a local LUXOR sales partner. This is because the pump is controlled directly from the LUXOR coater, and to ensure fully automatic operation of the coating process, the pump must operate within certain specifications in terms of pumping speed and ultimate pressure.

After the reactor of a sputter coater is placed under vacuum, the plasma is initiated by injecting a gas and applying a voltage. This gas is preferably inert (it does not decompose in the glow discharge) and it has a relatively high atomic weight. Argon, with an atomic weight of 39.95 is an ideal candidate. It is freely available from a large number of manufacturers and it is inert. The high-purity variant known as N4.8 (Zero Grade) with a purity of 99.998% is ideally suited for high-resolution imaging in SEM.

Other gases are also used for sputter coating with gold where the magnifications are moderate (< 50,000 x) and there is no danger of a reaction of decomposing gas with the samples. Sometimes nitrogen is used, which is available in many laboratories, or often just ambient air for magnifications up to 10,000 x where the contaminations present in the air do not affect the SEM images .

When using a process gas, an input pressure of min. 0.1 bar and max. 0.7 bar should be used. 0.6 bar is recommended. The gas cylinder should be equipped with a pressure regulator that reduces the pressure from (typically) 200 bar to 0.6 bar (for example, model HD 300 200-4-2 from Air Liquide). From this pressure regulator, a 6 mm outside diameter Teflon tubing runs to the connector piece (see image) supplied with each LUXOR coater.

Different types of sample holders for thin films exist on the market. They consist of a standard 3.1 mm diameter pin and a flat round surface with one or more sample clamps on the edges. These sample holders can hold round film samples with diameters up to 25, 50 or 75 mm (1, 2 or 3″) and thicknesses up to 2 mm.

Contact LUXOR or your local sales partner for more information.

The standard warranty period for a LUXOR coater is 12 months. On request and for an additional price, LUXOR offers second and third year warranty extensions.

A fully functioning LUXOR sputter coater configuration consists of the sputter coater (LU02-004-AU – LUXOR gold coater or LU02-001-PT – LUXOR platinum coater) combined with the vacuum pump (LU02-PUMP). Both coaters come with a sample holder for standard pin stubs.

Users of cylindrical stubs should order the following holder additionally: LU02-SHC – sample holder for cylindrical stubs, while for resin embedded samples the following holder should be ordered additionally: LU02-SHE – sample holder for mounted/embedded samples.

See also the accessories section for more information.

The serial number of your LUXOR coater can be found on the original packaging along with the LUXOR model. Furthermore, on the back of your LUXOR coater you will find a sticker with the serial number and coater type. A LUXOR coater serial number looks like this: CT-AA01-BBBB, where AA is the year of manufacture and BBBB is the serial number.

The list of parts supplied with a LUXOR coater is completely identical for a LUXOR Au gold coater and LUXOR Pt platinum coater, except for the target: the LUXOR Au is supplied with a gold target, while the LUXOR Pt is supplied with a platinum target.

The vacuum pump is supplied only with a bottle of 300 ml vacuum oil and an instruction manual. Furthermore, the input and output of the pump are already equipped with clamps and the corresponding centering rings, o-rings and one filter on the output. The metal vacuum hose and all fittings for connection to the coater and a funnel for filling the oil are supplied with the coater.

LUXOR coaters are available through the worldwide network of LUXOR distributors and sales partners.

Check the worldwide network page for details on a local sales partner near you.

More info on direct LUXOR overseas branches can be found here.