Physical Vapor Deposition
We deposit thin films using physical vapor deposition (PVD). In PVD, the material (in the form of powder or pellets) is evaporated to make the thin film. The material can be evaporated using three techniques:
· Electron beam evaporation
· Thermal evaporation using resistive heating of a metallic boat
· Thermal evaporation using a ceramic crucible.
The choice of any of these three techniques depends on the material to be deposited. The thickness of the film can be controlled using a thickness monitor. The substrates can be rotated and heated up to 300 oC.
In addition, reactive evaporation (using controlled atmospheres of oxygen, nitrogen and other gases) can be achieved. Moreover, co-evaporation (simultaneous evaporation from more than one source) can be achieved. All PVD process take place in the fully-automated Leybold L-560 box coater.
Pulsed Laser Ablation
Thin films can also be deposited using pulsed laser ablation (evaporation). In this technique, the energy required to evaporate the material is supplied by powerful laser pulses. The most important advantage of this technique is that it is versatile, it can work with almost any material. In addition, the chemical composition of the film is very close to the starting material. Currently, we use a UV pulsed excimer laser (Lambda Physik COMPEX Pro 102).
Sputtering is a versatile technique for the preparation of thin solid films of various classes of materials. In this technique, a solid target is bombarded with ions that eject atomic and molecular species of the desired material; and subsequently these are deposited on the surface of the substrate. Our system can perform DC or RF sputtering, as well as co-sputtering and reactive sputtering. Additionally, the substrates can be heated to as high as 600 oC. Currently, we use an Oerlikon (Leybold) Univex 350 Sputtering system.
Atomic Force Microscope
The atomic force microscope (AFM) or scanning force microscope (SFM) is a very high-resolution type of scanning probe microscope, with demonstrated resolution of fractions of a nanometer, more than 1000 times better than the optical diffraction limit. The AFM is one of the foremost tools for imaging, measuring and manipulating matter at the nanoscale. The term 'microscope' in the name is actually a misnomer because it implies looking, while in fact the information is gathered by "feeling" the surface with a mechanical probe. Piezoelectric elements that facilitate tiny but accurate and precise movements on (electronic) command enable the very precise scanning. (© Wikipedia the free encyclopedia)
We are using the Veeco Innova diSPM.
Stylus profilers employ a simple measurement technique.
A conical diamond tip stylus (with a radius ranging from 0.2µm to 25µm) scans across the surface at a very light stylus force. As a sample moves under the stylus and the stylus encounters various surface features, vertical motion of the stylus is detected by an LVDT, and this signal is converted into two-dimensional data. This data is presented as a profile or cross section of the sample surface, and provides extremely accurate and repeatable step height measurements of vertical features.
We are using an AMBIOS XP-2 surface profilometer to measure the thickness of films.
The Jasco V-570 is a double beam scanning spectrometer with two monochromators which cover the wavelength range of 190-2500 nm. Both gratings and detectors are changed automatically and the user can select the wavelength at which the changeover occurs. The spectrometer is capable of performing transmittance, absorption and reflectance measurements of solid and liquid sample. These measurements are used to extract the optical properties of the materials.
Fluorescence is the emission of light. This emission can be stimulated by heat, electron bombardment, or high-energy photons. This process may also be referred to as luminescence. Luminescence of thin films can yield information on their bandgaps and defects. Luminescence processes are especially important in thin films intended for optoelectronic applications, such as light detectors and emitters. In our lab, we use the Shimadzu RF-5301 PC spectrofluorometer. It can also be used with liquid sample. For high resolution spectra, we have installed an MMR refrigerator to cool the samples down to 80 K.
In addition to the spectrofluorometer, we have a cryogenic photoluminescence system, where the excitation source is a He-Cd laser (Kimmon IK3501R-G) with a wavelength of 325 nm. Photoluminescence spectra are acquired using a Newport 74085 spectrograph coupled to a Newport 78236 CCD camera. The samples can be cooled down to a temperature of 4K using a Janis cryostat.
This system is used to measure the resistivity, sheet resistance and carrier concentration. It can work both at room temperature as well as liquid nitrogen temperature (77 K).
The system is fully automated and computer-controlled.
This system is used to measure the sheet resistance and resistivity. It is computer-controlled with variable load to insure contact to the sample surface.
A gas-mixing chamber wherein the monitored gas (e.g. CO) could be mixed with normal air to a controlled concentration (i.e. parts per million of the monitored gas) has been fabricated and is in use (see the image here). The chamber is coupled to another chamber wherein measurement of change in resistance of the sensor can be carried out as a function of the concentration of the monitored gas.
The resistance measurement chamber coupled to the gas-mixing chamber is also shown on the right. The gas sensor and the heater for the sensor has been mounted on a common flange as shown in the second figure. Varying the magnitude of the applied voltage to the heating element controls the temperature of the sensor.
Measurement of sensitivity and selectivity of pure and catalyst added metal oxide thin film gas sensors for different gas such as CO, CO2, SO2 etc. at various temperatures and different concentrations of the monitored gas mixed with normal air can be carried out.
In addition to the above facilities, we benefit form various facilities available at KFUPM. These include: X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), X-ray fluorescence (XRF), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR).