Characterization of undoped ZnO layers grown by molecular beam epitaxy towards biosensing devices

Abstract

Undoped ZnO layers grown by molecular beam epitaxy (MBE) were investigated aiming at biosensing devices based on organic/inorganic hybrid structures. Clear observation of free exciton emission in low temperature photoluminescence (PL) spectra and electron mobility as high as 114 cm 2 /Vs at room temperature indicate that the quality of the ZnO layers is applicable for biosensors. Surface bonding of the ZnO the layers, which is one of the key issues for hybridization, was examined by means of xray photoelectron spectroscopy (XPS). The XPS spectra of O 1s revealed that formation and desorption of hydroxyl (OH) bonds can be controlled by air exposure and thermal treatments. , establishment of hybridization between biofunctionalized molecules and inorganic semiconductor systems is of high importance. Until now, Si-based FETs are mainly utilized for them, however, compound semiconductors should be another candidates. In termes of fabrication of hybridized structures, their controllability of bandgap energies and lattice constants, which resulted in realization of laser diodes and high electron mobility transistors (HEMTs), would possess several potential. Among lots of compounds, i.e., numerous combinations of elements, we have chosen zinc oxide (ZnO) based semiconductors as materials for EnFET and biochemical sensors from the following reasons.One of the advantages of ZnO is expected to easily form direct bonding between organic molecules and the oxide surface. In case of non-oxide compounds, surface cleaning is necessary for precise bonding control, which can be realized by the removal of unintentionally formed amorphous oxide layer at the surface, while oxide surfaces are free from that. Considering that direct binding of biofunctional molecules on insulating gate layers in FETs is preferable for signal processing, availability of crystalline insulating layers of oxides is crucial for hybridization. Also it is expected that the techniques of selfassembled monolayer formation using organothiols on gold [3] would be applicable on oxide surfaces by the reaction between cation in oxide and S in molecules. In addition, multi-functionality of ZnO, such as large bandgap energy of 3.3eV for transparent electronics [4] and piezoelectricity for actuator [5], would be interesting for hybridization devices. From the viewpoint of biomedical applications, less hazardousness of oxides has attracted a great deal of attention, where other compound semiconductors cannot work.Recent progress on epitaxial growth of ZnO based semiconductors has been performed by molecular beam epitaxy (MBE) [6,7], pulsed laser deposition (PLD) [8,9] and metalorganic vapor phase epitaxy

A Microwave-Assisted Synthesis of Zinc Oxide Nanocrystals Finely Tuned for Biological Applications

“…Also the O1s region shows an almost perfect overlap between the three samples. From the deconvolution procedures (not reported) three components are obtained and are due to: O-Zn bond (529.7 eV), O-H bond (531.0 eV) and H 2 O residue (532.0 eV) as already reported in literature both theoretically [29] and experimentally [30]. Moreover, we have also checked the N1s region for the functionalized ZnO-mw sample, finding out that the experimental signal (reported in the inset of Figure 6c) is due to the imine group –N= (398.6 eV; 22.3 %) and amine group –NH– (399.7 eV; 77.7%).…”

Enzyme-conjugated ZnO nanocrystals for collisional quenching-based glucose sensing

“…15 Ogata et al analysed the relationship between mercaptopropionic acid (MPA) and ZnO surface and they proposed that ZnO is expected to easily form direct bonding with the organic molecules. 16 Despite the direct synthesis of water soluble ZnO nanoparticles, so far optical glucose sensing based upon ZnO has not been reported. Recently, many research groups have been developing electrochemical biosensors based upon metal and semiconductor nanostructures that can give many advantages such as increased sensitivity and accuracy.…”

Study on the annealing-dependent photoluminescence properties of SnO2 cluster-system structures

“…Figure 6 are XPS spectra of the product. The O1 peak corresponds to the oxygen ions in SnO2 lattice of rutile structure and the O2 peak at the range of 531-532 eV is attributed to loosely bound oxygen on the surface [30][31][32]. No peak at 533 eV from free water is observed [31,32].…”

“…However, the XPS measurement result gives a contrary result for product annealed 30 minutes, which indicates the increasing of VO as theoretical reckoning above. It is well established that water adsorption on SnO2 results in the formation of OH surface species [31,32]. Considering the exposure of product in air before and during annealing process, the origin of O2 peak is explained as to be arising from such OH surface species [32,33] provided by coordinated water existing in the SnO2 lattice shown in Figure 8c.…”