Ionized Cluster Beam Deposition Technique Research Articles

Growth of CdTe on Si(100) surface by ionized cluster beam technique: Experimental and molecular dynamics simulation

II–VI semiconductor CdTe was grown on the Si(100) substrate surface by the ionized cluster beam (ICB) technique. In the ICB method, when vapors of solid materials such as CdTe were ejected through a nozzle of a heated crucible into a vacuum region, nanoclusters were created by an adiabatic expansion phenomenon. The clusters thus obtained were partially ionized by electron bombardment and then accelerated onto the silicon substrate at 473K by high potentials. The cluster size was determined using a retarding field energy analyzer. The results of X-ray diffraction measurements indicate the cubic zinc blende (ZB) crystalline structure of the CdTe thin film on the silicon substrate. The CdTe thin film prepared by the ICB method had high crystalline quality. The microscopic processes involved in the ICB deposition technique, such as impact and coalescence processes, have been studied in detail by molecular dynamics (MD) simulation.

Low-temperature synthesis of C 60 thin films by ionized cluster beam deposition technique

C 60 films on Si(1 1 1) have been grown at low substrate temperature of 100°C by ionized cluster beam deposition technique. Fourier transform infrared (FTIR) transmission spectroscopy, Raman measurements and X-ray diffraction are employed to investigate the structure of deposited films. The results show that the acceleration voltage plays an important role in the growth of the films. As the acceleration voltage is moderate (∼100 V), a pristine C 60 film with face-centered-cubic (fcc) crystal structure can be grown. Further increase of the acceleration voltage leads to the formation of amorphous carbon (a-C) in the grown films. When the acceleration voltage is increased to 600 V, the deposited film has a complete amorphous carbon (a-C) structure.

Deconvolution of tip affected atomic force microscope images and comparison to Rutherford backscattering spectrometry

There is distortion in atomic force microscope (AFM) images caused by a nonideal shape and size of the probe tip. This is called tip effect and is due to the convolution of the tip and sample. AFM images of nanometer size islands of zinc deposited on silicon substrates by the ionized cluster beam deposition technique were used to investigate this effect. The number of zinc atoms per unit area determined by each of two methods, the AFM images and Rutherford backscattering spectrometry (RBS) are compared and the AFM reported more zinc than RBS. A partial explanation for this difference is that the convolution of the tip and sample makes the islands appear larger in the AFM data. Previously reported convolution and deconvolution algorithms were implemented to study and simulate the interaction between tip and sample in the AFM. The deconvolution algorithm removes part of the distortion by taking into account the physical volume occupied by the tip which exposes a more accurate image. After deconvolution of the zinc islands images there was better agreement between AFM and RBS results. Deconvolution of other images will also be discussed.

Comparison of atomic force microscope and Rutherford backscattering spectrometry data of nanometre size zinc islands

Atomic force microscopes (AFM) form images by sliding a sharp tip over a surface in a raster pattern and recording the height of the tip at each position. There is distortion in these images caused by a non-ideal shape and the size of the probe tips. Previously reported convolution and deconvolution algorithms have been implemented to study and simulate the interaction between the tip and the sample. The first part of this work is a comparison between AFM and Rutherford backscattering spectrometry (RBS) data taken on nanometre size zinc islands on a flat substrate. Zinc islands were deposited on a silicon substrate using the ionized cluster beam deposition technique. An algorithm was developed to calculate the volume of the islands and the number of zinc atoms present from AFM images. The number of zinc atoms per unit area of the same samples was also measured by RBS. The AFM and RBS results agree qualitatively but there is an offset with AFM reporting more zinc than RBS. A possible explanation for this difference is a convolution of the tip and sample making the islands appear larger. After deconvolution of the AFM images there was better agreement between AFM and RBS on the number of zinc atoms per unit area.

Raman scattering studies on the C 60 films deposited by ionized cluster beam deposition (ICBD) technique

Experimental results on Raman-scattering spectra taken at room temperature of C 60 films deposited by ionized cluster beam deposition (ICBD) technique are presented. The Raman spectra show 10 strong Raman lines, consistent with the 10 Raman-allowed (2A g+8H g) modes predicted for isolated C 60 molecule. A broad feature at high frequency, which varies with acceleration voltage (Va), is also observed and is attributed to amorphous carbon (a-C). The formation and influence of a-C in the ICBD C 60 films are discussed. We think the ICBD technique is very useful in preparing dense and homogeneous pristine C 60 films with stable properties in air.

Investigation of silver in the ionized cluster beam deposition technique

Ionized cluster beam deposition uses a beam of ionized, accelerated atom clusters to grow thin films. Late in 1991, following nearly 20 years of development, synthesis of large clusters of zinc by homogeneous nucleation was achieved through significant changes in two source parameters. Crucible pressure was increased from 2 Torr to over 1000 Torr and the nozzle was changed from cylindrical (1 mm*1 mm) to converging-diverging (18 mm long and 0.4 mm in diameter at the throat). Such high vapour pressure is presently impractical for materials of industrial interest such as gold, silver, copper and aluminium. Recent results using gold with the converging-diverging nozzle at a pressure of less than 1 Torr showed no significant synthesis of large clusters. The work presented here describes results using silver at an intermediate pressure of around 100 Torr. The deposition rate was intermediate (2.2 nm s-1) between that for gold (0.02 nm s-1) and that for zinc (4.3 nm s-1). Significant numbers of large clusters were not detected. The purity of the silver influenced the appearance of the beam. X-ray and roughness analyses of deposited films are presented.

Formation of Te clusters in ionized cluster beam deposition technique

A retarding field method is used to measure the size distribution and the average size of Te clusters at various temperatures. From the dependence of the net ion current on the retarding voltage, we find the distribution of cluster sizes. The average cluster size is determined by the atom flux of ionized clusters and their charge flux. The experimental results show that the average size altered from 30 to 281 atoms when the crucible temperature changed from 650 to 790 K.

Combined EPMA and AES depth profiling of a multilayer Ti-Al-O-N coating

In order to compare thin-film electron probe microanalysis (EPMA) and Auger electron spectroscopy (AES) regarding reliability in quantifying chemical compositions of Ti-Al-O-N coatings with depth, a multilayer was prepared on a silicon wafer by using reactive ionized cluster beam deposition technique. Within a total thickness of about 25 nm the composition of the multilayer varied step by step from Ti-Al-O-N at the bottom to Al-O at the top. AES and, as an innovation, EPMA crater edge profiling was applied to measure the composition with depth. For quantification special thin-film EPMA techniques based on Monte Carlo simulations were applied. The chemical binding states of Al and Ti with depth were analysed using a high resolution energy analyser (MAC 3) for the AES investigations working in the direct mode. According to the deposition procedure the concentration profiles of the components varied with depth for both AES and EPMA measurements. AES provided a better depth resolution than EPMA. To get a true calibration of the depth scale an in-situ measurement method like an optical interferometry will be required. Assuming that the relative sensitivity factors are available AES depth profiling delivers concentration profiles with good accuracy. The new EPMA application provided quantitative depth profiles concerning concentration and coverage. For EPMA crater edge profiling the coating needs to be deposited on a foreign substrate because depth distributions of elements being present in both the layer and the substrate cannot be resolved. The combination of AES-depth profiling with EPMA crater edge profiling techniques is a powerful tool to analyse heterostructures quantitatively.

Structural and electronic studies of C60 films deposited using ionized cluster beam deposition

Films of a new form of carbon allotrope, C60, also known as fullerenes are deposited on Si(111) substrates by the ionized cluster beam deposition technique under an accelerating field less than 100 V. Raman spectra and X-ray photoelectron spectroscopy measurements are carried out to analyse the electronic properties of the films, to indicate the existence of C60 soccer-balls in the films. The resistance of this C60 film deposited here to oxygen contamination is better than that deposited by molecular beam epitaxy. Binding energies of C 1s peaks for C60 and highly oriented pyrolytic graphite are 284.7 and 284.3 eV, respectively. X-ray theta -2 theta diffraction investigations show that C60 films deposited under Va=0 V have highly textured close-packed structure with X-ray diffraction assignment (110), while those deposited under Va=65 V turn out to be more polycrystalline. C60 soccer-balls are found to be broken into fragments as accelerating field exceeds about 400 V, indicated by the results of X-ray photoelectron spectroscopy, Raman spectra, X-ray diffraction, and ultraviolet visible absorption spectra.

Study of zinc thin films formed using large clusters in the ionized cluster beam deposition technique

Ionized cluster beam (ICB) deposition uses a beam of ionized, accelerated atom clusters to grow thin films. It has been shown that in ICB efforts prior to late 1991, significant numbers of large clusters were not present in depositing beams. Since that time, formation of such large clusters of zinc by homogeneous nucleation has been demonstrated by Gspann using radiation crucible heating and pulsed ionizer time of flight cluster size measurement and in our laboratory using electron bombardment heating and deflected deposition cluster measurement. Crucible pressure was increased from 2 to over 1000 Torr and a converging–diverging nozzle 18 mm long and 0.4 mm in diameter at the throat was used in place of the older 1 mm×1 mm nozzles. Increasing source pressure from 2.8 to 11.3 atm (280–1130 kPa) is accompanied by an increase in peak average cluster size from a few hundred to over 2000 atoms/cluster. Surface roughness of cluster formed films increases with increasing incident cluster energy using a cluster beam peaking at ∼2200 atoms/cluster in average size for cluster energies from thermal to approximately thermal plus 700 eV.

Synthesis of crystalline polyimide film by ionized cluster-beam deposition

Polyimide thin films were deposited by the ionized cluster-beam deposition technique. Imidization and crystallization of polyimide films were investigated using transmission electron microscopy and Fourier transform infrared spectroscopy. Polyimide films deposited under optimum conditions showed a maximum imidization and good crystal structure, which is superior to that of films fabricated by other techniques.

Polyethylene crystal lamella growth on the mica

The polyethylene thin films on the mica (001) plane have been prepared by the ionized cluster beam deposition technique and analyzed by the transmission electron microscope. We have found that the polyethylene crystal lamellar structures are obviously affected by the crystal mica substrate. We have observed the Moire fringe pattern and the overlap diffraction spot array for both crystal thin films, as well as explained that the polyethylene subunit cell grows along, the direction which rotates 60° relative to the unit cell of the mica (001) plane.

Epitaxial growth of zincblende MnTe films as a new magneto-optical material

Epitaxial films of MnTe with a zincblende structure have been successfully grown on GaAs (100) and sapphire (0001) substrates using the ionized-cluster beam deposition technique. The values of the lattice constant, 6.34 Å, and the optical band gap, 2.92 eV (300 K), reveal that the MnTe films obtained have the previously hypothetical zincblende MnTe structure. In the Faraday rotation spectrum of the zincblende MnTe film, a large dispersion is observed near the band gap energy, and the peak value of the Verdet constant is about 0.6 deg/cm·G. From the X-ray photoelectron spectroscopy and the intra-Mn absorption, we investigate the Mn3d states of zincblende MnTe.

Electronic properties of ion implanted crystalline polymer thin film deposited by ionized cluster beam

Polyethylene thin film deposited by the ionized cluster beam deposition technique shows preferential crystal orientation at optimum deposit condition, and the lattice parameters of the crystalline PE film are in good agreement with those of the single crystal PE. The crystalline PE film reveals that the number of side chains is reduced. The conductivity of Li +, Na + and K + implanted crystalline PE films has a close correlation with defects generated by ion irradiation, and the conduction mechanism turns out to be the one-dimensional hopping conduction.

Fabrication of AIN thin films by reactive ionized cluster beam deposition technique

Low temperature and low damage deposition of insulating films on III–V compound semiconductors is of great importance for high speed devices and optoelectronic devices. The Reactive Ionized Cluster Beam (R-ICB) deposition technique is expected to provide such a process. We have modified the R-ICB deposition technique by using activated neutral species from rf plasma beam gun to obtain AIN films without damage, instead of using a reactive gas environment of 10 −4 Pa. The plasma beam gun has been utilized also for the cleaning pre-treatment. We have found that the combination of the modified R-ICB deposition technique and proper pre-treatment is promising to provide a MIS structure of a good electric property for GaAs. We have also shown that in-situ ellipsometry is a powerful tool to investigate the pre-treatment and the deposition process.

Formation of gold clusters in the ionized clusterbeam deposition technique

The unique aspect of the ionized cluster beam (ICB) thin film depositionmethod is that material is deposited from a beam of atom clusters, a fraction of which are ionized and accelerated to the substrate. A large number of different material films have been deposited to research the ICB method and advantages in film formation have been claimed. However, because methods for measuring cluster size distribution in film deposition instruments have been under development, the presence of clusters in the depositing beam normally has been inferred from theory rather than measured directly. Thus it is not yet clear whether interesting ICB film effects were due to clusters or other factors. A new measurement method which overcomes many of the difficulties of previous methods is developed in this work. Gold clusters up to an average of 3 gold atoms per ionized cluster have been formed and detected. Cluster size increased with crucible pressure and attempts to achieve larger clusters are underway.

Faraday Effects Due to Excitons in Cd1-xMnxTe Films

The authors performed a theoretical investigation of the Faraday effect in Cd 1-x Mn x Te epitaxial films prepared by the ionized-cluster beam deposition technique. Splitting energies and oscillator strengths of an exciton level are calculated by taking account of a nondegenerate second-order perturbation. The wavelength dispersion of the calculated Faraday rotation spectra is compared with experimental data for Cd 1-x Mn x Te films. The results suggest that the Faraday rotation is closely related to the magneto-optical transitions to Zeeman splitting levels of excitons.

Magneto-optical properties of Cd 1−xMn xTe multilayered structures prepared by ionized-cluster beams

The film growth of Cd 1− x Mn x Te with a multilayered structure was performed by the ionized-cluster beam deposition technique, and its magneto-optical properties have been investigated. The results of X-ray diffraction measurements showed that the films had a periodical structure, as designed artificially. In the Faraday rotation spectra of the multilayered structures, two band edge dispersions, corresponding to the well and barrier layers, were observed. As the well width decreased, the wavelength dispersion of the well layer was found to shift toward higher photon energies with an increase of the peak height, while that of the barrier layer was unchanged. This could be qualitatively explained by a quantum size effect in a superlattice.

Electro-optical effects of Cd1−xMnxTe films prepared by ionized-cluster beams

We report the first investigation of electro-optical properties of Cd1−xMnxTe films, prepared by the ionized-cluster beam deposition technique. Measurements of the birefringence Δn of the films were performed under applied electric field in the wavelength region from 800 to 450 nm. Major results obtained are as follows: The value of Δn rises to second power against the applied electric field, and for a film with x=0.77 a large quadratic electro-optical coefficient of 3.5×10−12 cm2/V2 is obtained at 633 nm. The wavelength dispersion of Δn is observed near its band gap, suggesting that the electro-optical properties of these films are caused by the Franz–Keldysh effect.

Ｃｄ１−ｘＭｎｘＴｅ薄膜の励起子による磁気光学効果

Theoretical investigation has been performed on the Faraday effect of Cd1-xMnxTe epitaxial films prepared by ionized-cluster beam deposition technique. Splitting energies and oscillator strengths of an exciton level are calculated by taking account of a nondegenerate second order perturbation. The wavelength dispersion of the calculated Faraday rotation spectra is compared with the experimental data of Cd1-xMnxTe films. This suggests that the Faraday rotation is closely related to the magnetooptical transitions to Zeeman splitting levels of exciton.