ultra-sensitive graphene sensor for measuring high vacuum pressure
Samples can be separated from the GNR mixture synthesized by conventional methods.
The square resistance of the purified GNR decreases gradually with the decrease of the pressure of 30 °c, while increases at the pressure of 100 °c.
To explain this finding, the hypothesis of attraction interaction between GNR sheets based on Van der Valls was introduced.
The main peak of displacement in vacuum X-verifies this hypothesis
Ray diffraction spectrum: 0. 022u2009nm and 0.
For the reduced graphene oxide, 041 nm movement is observed (RGO)
They are GNR.
Theoretical calculations show that the moving distance is similar to the calculated distance for RGO.
The response of GNR sensors to pressure changes occurs rapidly (in seconds).
The normalized response time for each sample indicates that the sensor using GNR reduces the tail of the response time by shortening the diffusion path of the gas molecule.
Within a given pressure range, the sensitivity of the GNR sensor is three times that of the RGO.
In addition, the sensitivity of the GNR is much greater than the most popular pressure sensor using the pressure resistance effect, which can detect the vacuum pressure of the 8 × 10-7 tortorr.
Many pressure sensors using graphene and its derivatives have been studied, such as field emission pressure sensors, graphene extrusion-
Film pressure sensor and Microelectro-
The mechanical system pressure resistance type pressure sensor is used to determine the strain generated by the external pressure in graphene.
Most of the previous reports on pressure sensors focused on high-voltage measurements.
In addition to a few cases, sensors are rarely used to measure pressure below 1 tortorr.
Vacuum technology is a technology widely used in many industries and scientific research such as semiconductor, surface engineering and space science.
Therefore, accurate measurement of vacuum pressure is essential and fundamental for advanced research and production.
The figure shows several vacuum gauges commonly used in industry.
The capacitor meter is a direct vacuum meter that can measure the vacuum pressure most accurately by measuring the differential pressure between the vacuum and the ambient pressure.
However, the measurable vacuum range of the meter is limited to three or four orders of magnitude of the vacuum range (
For example, 10 to 1, 1 to 1000 or 10 to 100 tortorr)
, It is difficult to measure the pressure below 10 u2009 torr.
The next most popular meter is hotconductivity-
Indirect vacuum gauge and ionization-
Type meters for pressure ranges of 1 to 10 tortorr and 10 to 10 Torr, respectively.
The measurement error of these meters is very high, about 30%. conductivity-
Type meters for ionization meters and more than 10%.
In addition, the size and power consumption of the existing sensors in the meter are too large to be used for wireless measurement, or for the measurement of isolated thin devices and small devices.
For example, the current vacuum meter cannot directly measure the diffusion speed of gas molecules from outside the device to inside through the protective layer, nor can it measure equipment isolated from the atmosphere, including display equipment.
We have previously investigated the use of Van der Valls (VDW)
The attraction between reducing graphene oxide (RGO)
Paper applied in the vacuum pressure sensor.
Compared to the size of the current vacuum sensor, based on the effective area of the sensor, the volume size of the sensor using RGO can be reduced by only a few μm.
The VDW-based vacuum pressure sensor will provide high durability and low power consumption as it is based on RGO\'s Nano
Scale physical motion according to vacuum pressure.
VDW forces, especially attractive interactions between molecules, are responsible for many physical properties of carbon compounds such as carbon nanotubes (CNTs)
, Graphite, graphene derivatives.
Due to the large kinetic energy of molecules, VDW attraction is usually too weak to attract small molecules, while very large carbon compounds are greatly affected by VDW force, even at high temperatures
Based on the VDW force and thermal vibration mode of graphene sheets, we propose two different physical motions of carbon clusters on adjacent RGO sheets with gaps in the film, resulting in an electrical response to vacuum pressureSee Fig. and ).
Assuming that the RGO sheet in the film is ideally coated and aligned, the most likely size of the void in the vertical direction is about the size of an sp carbon atom.
In addition, the defect structure of the RGO board and the random stacking of the RGO board can form a smaller or larger void size.
Because the VDW attraction appears below the distance 2. 5u2009×u2009σ (
One of the Lennard-jones parameters, 0.
34 nm graphite)
, This force affects the carbon clusters in the RGO sheet located above and below the film gap.
However, due to the gas molecules in the void of the film, the distance from these carbon clusters to other carbon clusters remains the same.
Due to the VDW interaction, the reduction of the number of gas molecules to a certain content will lead to a decrease in the distance between RGO films, resulting in an increase in the conductivity of RGO films.
Due to VDW interaction, vibration energy, further reduction of gas content may result in various movements of carbon clusters or RGO sheets, as well as various elastic forces generated according to the shape and size of the RGO sheet.
At low temperature, the spacing of the RGO sheet is reduced in a large range, because the vertical oscillation of the carbon cluster on the RGO sheet is too small to deform the cluster through VDW interaction (See Fig. ).
In contrast, at high temperatures, the attractive interaction of VDW can occur in local rather than extensive areas due to the large vibration distance of carbon clusters (See Fig. ).
According to a report on the vibration mode of graphene
Graphene sheets of size can allow local fluctuations in carbon clusters, while nanometers
Size sheet including graphene nanoribbon (GNR)
Different vibration movements of carbon clusters are allowed.
Based on this discovery, we can speculate
Different sizes of graphene have different sensor properties depending on the size.
As shown in the figure. (
Note that the actual GNR film can have a wide variety of pore structures, as shown in the figure, with a TEM image of the concentrated GNR sample. ), nano-
The size of graphene also has an advantage over Micron-grade graphene in the diffusion of gas molecules.
The size of graphene and allows for a faster response to changing pressures.
In this study, we made sensor devices using graphene samples of various types and sizes and studied the electrical behavior under vacuum pressure.
We also use X-to provide evidence of VDW interaction in the sample
Ray diffraction (XRD)
Spectrum measured at different temperatures in vacuum.
In a previous study, there was no direct evidence of vacuum pressure-
Sensing principle of RGO (
Or insert RGO).
On the contrary, theoretical calculations are provided to support the sensing principle of RGO based on the experimental results.
In addition, when GNR is synthesized from MWCNT, we prove that
With simple pH control, a synthetic GNR mixture containing a small amount of carbon nanotubes can be purified.