Gábor Pető

Electronic structure of gold nanoparticles deposited on SiOx/Si(100)

Nanosize gold particles were prepared by Ar+ ion sputtering of island-like 10-nm-thick film deposited onto Si/SiOx substrate. The valence band of the gold particles was measured by means of photoelectron spectroscopy and infrared (IR) absorbance. The size of the particles was determined by transmission electron microscopy (TEM). The valence band of Au nanoparticles is strongly redistributed with decreasing size, involving mostly the lowest and the highest binding energy part of the Au 5d valence states. This effect can be attributed more to the redistribution than to the narrowing of the 5d states.

Combination of CVD Diamond and DLC Film Growth with Pulsed Laser Deposition to Enhance the Corrosive Protection of Diamond Layers

CVD diamond layers are often used as protective layers. One of the most important of these applications requires pinhole-free layers to protect against fluid materials, such as found in chemically aggressive environment. These pinholes are present even in very good quality CVD diamond films. In this work we combined the Pulsed Laser Deposition (PLD) technique with Microwave assisted Chemical Vapor Deposition (MW-CVD). We used CVD diamond films prepared under different conditions and layer thicknesses. Both of these proceses produced inperfect protective layers, but we proved that a PLD DLC film over the diamond layer does reduce the number of pinholes in the coating. We used special chemical alcaline etching to detect the remaining pinholes, and to test the corrosion protective properties of the layers. As a result we were able to prepare samples of 1 x 1cm2 with only 0.2 micron thickness without any pinholes, while in CVD diamond layers a thickness of 2,5 micron was needed for the same level of compactness.

Properties of high-density amorphous carbon films deposited by laser ablation

The properties of carbon films deposited by high intensity pulsed Nd:G lass laser are reported. Different measurements like TEM, SIMS, EELS, XPS and A FM showed the formation of a high-density amorphous carbon layer with good protection against che mically aggressive alkaline solutions. We demonstrated that instead of excimer lase rs, Nd-based solid state lasers can be used successfully for preparation of high quality amorphous carbon films. Introduction Carbon layers have growing importance because of the wide range of applications. The wide variety of carbon materials based on the unique bonding property of t he carbon atoms. Carbon has 4 valence electrons (2s 2 p). Chemical bonds may include both π or σ bonds. In case of ideal diamond crystal all 4 bonds are σ, which is known as sp 3 hybridization. In this form the carbon crystal has extreme physical and chemical par meters. In case of graphite crystal 3 σ and 1 π bonds exist (it is called sp 2 hybridization). The difference in only one bond changes the properties of the material drastically. In amorphous carbon structures both of the two hybrid states (sp 2 and sp) can exist. Therefore a wide scale of properties of the a morphous carbon materials can be achieved. Preparation of sp 3 rich diamond-like carbon (DLC) or sp 2 rich graphite-like carbon (GLC) films in high quality is a great challenge now adays. Multi-technique investigation of these layers can result in enhancing their qualit y. The commonly used methods for producing DLC layers are PVD [1], plasma CVD [2-4] ion beam de position [5,6], sputtering [7] and pulsed laser deposition (PLD) [8-14]. Many of the PLD studies concentrate on excimer laser deposition techniques. Our aim was to produce good quality carbon f ilms for protective purpose with a Nd:Glass laser, which doesn’t use any toxic gase s in contrast to the excimer lasers. It may be a very important fact in environmentally friendly industri al applications. Experiment The carbon thin films were deposited on both silicon and silicon dioxide s ubstrates at room temperature in 10 -6 mbar pressure. The laser wavelength was 1054nm with 1Hz repetiti on rate. The 40ns long laser pulses were focused onto a spot of 5mm , which resulted in 10 W/cm power density. Using an excimer laser at so high energies w ll lead to formation of a predominantly graphitic layer [15] due to the high level of multiphoton i onization and inverse bremsstrahlung heating in the plasma. The dimensions of the samples were 1cm x 5cm, but larger areas can also be covered using this method. Materials Science Forum Online: 2003-01-15 ISSN: 1662-9752, Vols. 414-415, pp 127-132 doi:10.4028/www.scientific.net/MSF.414-415.127

Nanoindentation of Silicon

The nanoindentation behaviours of single crystalline silicon samples has gained wide attention in recent years, because of the anomaly effects in the loading curve, caused by the pressure induced phase transformation of silicon. To further enlighten the phenomenon bulk, ion-implanted, single crystalline Si samples have been studied by nanoindentation and by atomic force microscopy. The implantation of Si wafers was carried out by P+ ions at 40 KeV accelerating voltage and 80 ions/cm2 dose, influencing the defect density and structure of the Si material in shallow depth at the surface. Our experiments provide Young’s modulus and hardness data measured with Berkovich-, spherical- and cube corner indenters, statistics of the pop-in and pop-out effects in the loading- and unloading process, and interesting results about the piling-up behaviour of the Si material.

Formation and characterization of electric contacts on CVD diamond films prepared by ion implantation

Diamond layers have a potential application as the highest band-gap semiconductor for electronic devices. One of the major problems is to form electric contact on the diamond surface useful for an electronic device. This paper shows the properties of the contacts formed by the very promising ion implantation technique. The diamond layers were deposited with Microwave Assisted Chemical Vapor Deposition (MW-CVD) equipped with special extra features like High Voltage Bias and Heated Substrate Holder [1]. Phosphoruos ion implantation and gold deposition were used for the contact formation. This technique resulted graphitization the top of the diamond film and intermixing of gold with the graphite or diamond surface. The properties of the contacts were tested with surface conduction characterization methods, and the properties of the contact to diamond interface was investigated with SIMS (Secondary Ion Mass Spectroscopy ) and XPS (X-ray Photoelectron Spectroscopy).