Nihad K. Ali

Nanoporous silicon as drug delivery systems for cancer therapies

Porous silicon nanoparticles have been established as excellent candidates for medical applications as drug delivery devices, due to their excellent biocompatibility, biodegradability, and high surface area. The simple fabrication method by electrochemical anodization of silicon and its photoluminescent properties are some of the merits that have contributed to the increasing interest given to porous silicon. This paper presents the methods of fabrication, which can be customized to control the pore size, various chemical treatments used for the modification of silicon surfaces, and the characterization and pore morphology of silicon structures. Different approaches used for drug loading and the variety of coatings used for the controlled released are revised. The monitoring of the toxicity of silicon degradation products and the in vivo release of a drug in a specific site are described taking into account its significance on medical applications, specifically on cancer therapy.

Morphological and optical characteristics of porous silicon structure formed by electrochemical etching

Porous silicon (PS) is defined as a composition of a silicon skeleton permeated by a network of pores or in other word, PS is a network of silicon nanowires and nanoholes which are formed when the crystalline silicon wafers are etched electrochemically in electrolyte solution such as hydrofluoric (HF) acid [1,2]. PS shows different features in comparison to the bulk silicon such as shifting of fundamental absorption edge into the short wavelength and photoluminescence visible region. The PS material possesses interesting characteristics such as larger surface to volume ratio, high-intensity of nano porous structure and low refractive index which lead to the potential application like filter, catalyst support, chemical sensor, anti reflection coating in solar cell and light emitting diode (LED) [3–6].

Growth and characterization of tree-like crystalline structures during electrochemical formation of porous GaN

Electrochemical etching of crystalline n-GaN in H 2 SO 4 :H 2 O 2 results in the formation of porous GaN. Scanning electron microscopy images revealed the presence of branches on the surface of porous GaN and showed the varying stages with etching time. The branches on the surface of the porous GaN that have been associated with Ga 2 O 3 have a significant enhancing effect on the photoluminescence intensity. Raman spectra of both as-grown and porous GaN exhibit phonon mode E 2 (high), A I (LO), A, (TO) and E 2 (low). There is a red shift in E 2 (high), indicating a relaxation of compressive stress in the porous GaN surface with respect to the underlying single-crystalline epitaxial GaN.

Effect of dopant concentration on the pore formation of porous silicon on n-type silicon

This paper investigated the effect of different doped n-type silicon on pores formation. We found that star-like shape pores occurred when low doped concentration n-type silicon sample was used while high doped concentration produced normal pores hole-shape on the surface. By increasing etching time will cause the neighbouring star-like shape branches to combine and produced bigger pores. Reasons related on this star-like shape pores formation such as the effect of materials impurities, dynamic stress and space charge region effect (SCR) were discussed.

Electrical properties of electrolyte-GaN junction during photoelectrical etching processing

Recently porous semiconductors have stimulated much of interests, because they exhibit different physical properties relative to those of bulk crystals. The high surface area, band gap shift, and efficient luminescence promised the use of porous semiconductor over a wide range, from optoelectronics to chemical and biochemical sensors applications. One of the most common techniques to fabricate porous GaN is the photo-assisted electrochemical etching. The main factor in the photo-assisted electrochemical etching is the electrolyte. When immersed in an electrolyte, the semiconductor exchanges electrons with the electrolyte along the surface because the Fermi level in the semiconductor is different from that of the electrolyte. As in the semiconductor-metal contacts, an energy barrier is formed, the effective height of which is often fixed by the distribution of surface states in the semiconductor. This paper investigates the use of four different electrolytes to study the electrical properties of the electrolyte-GaN contacts in the photoelectrochemical etching processes. Thermionic emission theory is used to investigate the mechanism of the current transport through metal-semiconductor interfaces. From I-V characterization, the Schottky barrier height, ideality factor, and series resistance are calculated.

Hydrogen sensor based on Schottky barriers of Pd/GeO 2 using a low cost electrochemically deposited thin GeO 2 film

Conductometric semi-conducting metal oxide gas sensors have been widely used and investigated in the detection of gases. They have attracted much attention in the field of gas sensing under atmospheric conditions due to their low cost and flexibility in production, simplicity of their use, and large number of detectable gases. One of such materials is (GeO2) [1]. In this work, we present a method of synthesis of sub micro-sized germanium dioxide (GeO2) on porous silicon (PS) by electrochemical deposition. An n-type Si (100) wafer was used to fabricate (PS) where PS was electrochemically anodized in HF based electrolyte, at current density of 50 mA/cm2 for 30 min. In the mean time pure GeO2 is produced through hydrolization of GeCl4 by hydrogen peroxide and then electrochemically deposited on PS. Palladium (Pd) is deposited on the GeO2 /PS using RF sputtering technique to produce Schottky contact. The grown GeO2 crystals were characterized using SEM, EDX, (Fig. 1). Corresponding I–V (Fig. 2) characteristics of the Schottky diodes were measured for different flow rates of hydrogen gas. Thermionic emission model was used to analysis I-V data. The barrier height could be seen to increase significantly with hydrogen flow rate. Sensitivity and response time of the sensor will be discussed.

Quantum Confinement of Integrated Pulse Electrochemical Etching of Porous Silicon for Metal Semiconductor Metal Photodetector

Porous silicon (PS) was successfully synthesized via novel integrated pulsed electrochemical etching of an n-type (100) silicon (Si) substrate under various condition. The PS was etched using hydrofluoric acid (HF) based solution and the porosity was optimized by introducing electroless chemical etching process prior to photo electrochemical (PEC) anodization. In the electroless etching, a delay time (TD) of 2 min was applied. After that a cycle time (T) and pause time () of pulsed current were supplied throughout the 30 min PEC etching process. As grown Si and PS through conventional direct current (DC) anodization were also included for comparison. The result obtained showed that applying delay time helps to improve the uniformity and density of the porous structures. AFM indicated that the roughness of the Si increases as the dissolution of the Si occurred. Raman spectroscopy showed that an improvement in the crystalline quality of PS under pulse etching method compared to DC method indicated by the reduction of full width at half maximum (FWHM). A broad visible photoluminescence (PL) was observed from green to red with blue shift as nanocrystallite size decreases which constituted quantum confinement effect from the PS structures. Nickel (Ni) finger contact was deposited onto the PS to form metal semiconductor metal (MSM) photodetector. Ni/PS MSM photodetector by pulse method exhibited higher gain (2 times) compared to conventional Si device at 5 V bias.

DNA hybridization detection on porous silicon: A review

In modern society, the application of biosensor gains its popularity in various fields such as biomedical diagnostic, food technology, cancer therapies, pharmaceutics and environmental monitoring. New biosensing technology is needed to accommodate low cost sensor, able to give fast response, versatile technique and eventually more stable products. During the past decades, various researches work focusing on how to immobilize biomolecules on compatible nanomaterial for the purpose of creating a sensing element. Among all of the nanomaterials that have been used, porous silicon (PS) exhibits great advantages on genetic research for instance the DNA detection. DNA based research became popular since the Genome Human Project (GHP) has been completed in year 2003. In this paper, the fabrication and properties of PS as a function of nanomaterial biosensing will be discussed especially for DNA detection application.

Hydrogen Sensor Based on Pd/GeO2 Using a Low Cost Electrochemical Deposition

This work reports on a synthesis of sub micron germanium dioxide (GeO2) on porous silicon (PS) by electrochemical deposition. n‐type Si (100) wafer was used to fabricate (PS) using conventional method of electrochemical etching in HF based solution. A GeCl4 was directly hydrolyzed by hydrogen peroxide to produce pure GeO2, and then electrochemically deposited on PS. Followed by palladium (Pd) contact on GeO2 /PS was achieved by using RF sputtering technique. The grown GeO2 crystals were characterized using SEM and EDX. I–V characteristics of Pd/ GeO2 were recorded before and after hydrogen gas exposure as well as with different H2 concentrations and different applied temperatures. The sensitivity of Pd/ GeO2 also has been investigated it could be seen to increase significantly with increased hydrogen concentration while it decreased with increase temperature.

Properties of contact resistance towards realization of graphene-based three-branch junction device

A three‐branch junction (TBJ) nanowire device is shown to exhibit a unique nonlinear input‐output characteristics. The effect of contact resistance on such characteristics is investigated. It is shown that metal contact having small contact resistance is required so that such nonlinear characteristics of TBJ device can be maintained. The graphene‐based back‐gated FET device structure and transmission line method are proposed and discussed in order to determine the contact resistance of metal/graphene interface. The preparation of graphene layer and its characterization using conventional methods are presented and discussed. These basic preliminary results provide useful guidance and information for the fabrication of actual devices which are on the way.