## 2 Materials and Methods
### Oxygen-Free Atmosphere  
In order to be able to carry out tests on the influence of the metal oxide layer on a bond, it must be ensured that the test environment can be used technically free of oxygen. Various methods are available for this purpose: the contact point can be kept free of oxygen locally, or the individual process step can be placed in an oxygen-free environment. Since the bonding process, the specimen preparation, and the subsequent strength tests are to take place in an oxygen-free environment, using a glove box is a suitable and simple method as sufficient test space is available [24]. In this case, the entire process takes place entirely  
Figure 1: Schematic representation of the test sequence with different oxygen contents in the environment as well as bonding with and without an intermediate oxide layer and subsequent measurement of the tensile strength. in an oxygen-free environment. A consideration for the influence on the strength is thus ensured for each environment. An indicator of the oxygen content is the oxygen partial pressure, which represents the proportion of oxygen in the total pressure of the gas mixture. A common method for reducing the partial pressure of oxygen in a glove box is to create a vacuum using a vacuum pump. However, the generation of low oxygen partial pressures, as is the case in the technically producible ultra-high vacuum (UHV), is an energy-intensive and time-consuming process with correspondingly high-priced equipment. In addition, neither vacuum pumps nor standard gas purification systems achieve the low oxygen partial pressures required to bond a pure metal surface. Conventional methods are, therefore, not practical. In the applied method, two steps enable an oxygen-free process environment in a commercial glovebox. In the first step, the air in the glove box is displaced by rinsing the box with inert gas argon. Since argon is not technically sufficient to completely eliminate oxygen, a mixture of argon doped with 1% silane is added to the inert gas atmosphere. In this low concentration, the highly reactive silane is harmless and unproblematic to handle. Silane, as a highly reactive gas, reacts with the residual oxygen contained in the inertgas (specified by the manufacturer \(<2\) ppmv) according to Equation (1) to form amorphous silicon dioxide SiO\({}_{2}\) and water H\({}_{2}\)O.  
\[\text{SiH}_{4}+2\text{O}_{2}\rightarrow\text{SiO}_{2}+2\text{H}_{2}\text{O} \tag{1}\]  
This reaction gives rise to oxygen partial pressures of less than \(10^{-15}\) mbar at ambient pressure, which is adequate to oxygen partial pressures in extremely high vacuum (XHV). In comparison, the oxygen partial pressure in the technically producible UHV is many orders of magnitude higher, with values between \(10^{-7}\) and \(10^{-1}\) mbar. Table 1 shows the times required for forming a monolayer of oxide. It is noticeable that processing of the pure metal layer can only be assumed for the XHV-adequate atmosphere. From a kinetic point of view, there is thus complete freedom from oxygen. For atmospheres with a higher oxygen partial pressure, it has to be assumed that oxide has already formed. A detailed description of the mechanism of silane for generating an oxygen-free environment and its use in the field of soldering can be found in the paper by [PERSON] et al. [21]. Since requirements such as free handling and an unrestricted view of the complete test environment are ensured, the glove box GS MEGA Line is used as a flushing box with pressure maintenance from the company GS GLOVEBOX Systemtechnik GmbH for providing the oxygen-free test environment (see Figure 2). The glove box used is operated with an overpressure of approx. 2.5 mbar for product protection. The gas is introduced into the glove box via a gas curtain to ensure good atmosphere mixing. A fixed fan on the glove box's ceiling and a portable fan further enhance the mixing and ensure that the residual oxygen or moisture comes into contact with the silane completely and reacts off.