Highly photoconductive oxide films functionalized with GeSi nanoparticles

Growth of self-assembled quantum dots is of great interest due to their potential quantum confinement effect and numerous applications in optoelectronics and nano-sized structures. Semiconducting Si, Ge and SiGe nanocrystals (NCs), embedded in a dielectric-oxide matrix have for instance been found to exhibit strong quantum confinement. For SiGe nano-based structures in addition to strong quantum confinement effect they offer the advantage of fine tuneability of energy-band structure via quantum confinement, strain engineering and varying the Si/Ge ratio. Among the most common methods to obtain NCs embedded in oxide systems is deposition with magnetron sputtering, followed by subsequent anneal treatments. However, the device performance obtained are lower in production line than obtained for research devices. This has mainly been attributed to the thermal treatment used, which causes strain accumulation within the structure, dislocations and dangling bonds, clustering and phase separation of Ge in Si1-xGex system, diffusion and formation of unwanted insulating oxide. All of these side-effects cause degradation of optical and electrical properties of the fabricated structures. In this study, structures comprising of SiO2/SiGe/SiO2 and TiO2/SiGe/TiO2 were fabricated by utilizing radio frequency (rfMS), direct current (dcMS) and/or high power impulse magnetron sputtering (HiPIMS). The structures were then subjected to thermal and/or hydrogen (H2) plasma treatment. Their photocurrent intensity was increased by up to several orders of magnitude along with wider spectral coverage into near infra-red regime by controlling the sputter discharge and anneal parameters. Moreover, as a proof of concept, a control over the HiPIMS discharge parameters have exhibited the possibility of obtaining as-grown crystalline structures, consisting of SiGe NCs without the need of annealing, along with a viable control over the size of NCs. The annealing of such structure prepared via HiPIMS method, have shown an interesting self-organization of periodically arranged columnar SiGe NCs. Exposure to hydrogen plasma of both as-grown samples and annealed samples ensued amplification in photoconductivity by neutralization of dangling bonds and passivation of non-radiative defects in the oxide matrix and/or at SiGe/matrix interfaces.Ræktun sjálfsamsettra skammtapunkta er mjög áhugavert rannsóknaverkefni vegna margvíslegra notkunarmöguleika í ljósnæmum rafeindatækjum og ýmsum örsmáum skynjurum. Hálfleiðandi Si, Ge og SiGe öragnir í þunnhúðum úr torleiðiefnum (einkum málmoxíðum) hafa til dæmis reynst hafa sterka skammtaeiginleika. Sökum skammtahrifa má fínstilla þá ljós-öldulengd sem þarf til að gera þá leiðandi með því að stýra stærð öragnanna, hlutfalli milli Si og Ge og álagi sem þeir verða fyrir í þunnhúðinni. Algengasta leiðin til að búa til ofangreind kerfi er þunnhúðun með segulspætun og hitameðhöndlun í kjölfarið. Hefðbundin hitameðferð veldur hinsvegar ákveðnum skemmdum í Si1-xGex kerfinu, s.s. lausum efnatengjum, efnis-aðskilnaði, myndun þyrpinga og útsveimi. Þessar aukaverkanir rýra ljós- og rafeiginleika efnisins. Framleiðslu aðferðir sem valda ekki slíkum skemmdum geta því haft mikla þýðingu. Í þessari rannsókn voru riðspennu (rfMS)-, jafnspennu (dcMS) - og háaflpúlsuð segulspætun (HiPIMS) aðferðir notaðar til að rækta lög af SiO2/SiGe/SiO2 og TiO2/SiGe/TiO2 kerfum. Í kjölfarið var mildum hita- og vetnis rafgasmeðferðum beitt til að framkalla SiGe og Ge öragnir í húðinni sem sýndu breytilega ljósnæmni. Með þessum hætti tókst að auka ljósnæmnina um nokkrar stærðargráður auk þess sem næmnisvið litrófsins var víkkað. Önnur megin niðurstaða er að með notkun HiPIMS aðferðarinnar tóks að útbúa sýni með háa ljósnæmni án þess að hitameðhöndla þau. Meðhöndlun með vetnis-rafgasi leiddi til mikillar (stærðargráðu) aukningar á ljósnæmni húðanna, bæði fyrir og eftir hitaneðhöndlun.Technology Development Fund of the Icelandic Center for Research (RANNIS) grant no. 159006-0611, through the M-ERA NET program

Germanium coated silicon nanowires as human respiratory sensing device

Post-print (lokagerð höfundar)We report on germanium coated silicon nanowires structures synthesized with metal assisted chemical etching and qualify their functionality as human respiratory sensor. The sensors were made from p-type single-crystalline (100) silicon wafers using a silver catalyzed top-down etching, afterwards coated by 50 nm germanium thin layer using a magnetron sputtering. The germanium post-treatment was performed by rapid thermal annealing at 450 and 700◦C. The sensors were characterized by X-ray diffraction diffractogram and scanning electron microscopy. It is demonstrated that the sensors are highly sensitive as human breath detectors, with rapid response and frequency detectability. They are also shown to be a good candidate for human respiratory disease diagnoses.This work was supported by Reykjavik University Ph.D. fund no. 220006 and the Icelandic Research Fund Grant no. 218029-051. We are grateful to Rodica Plugaru and Neculai Plugaru for discussions.Peer review

Photoluminescence study of Si_1-xGe_x nanoparticles in various oxide matrices

We investigate the photoluminescence properties of structures comprising of Si1-xGex nanoparticles (NPs) within SiO2, GeO2, TiO2 and Ta2O5 oxide matrices. Of the investigated structures, it was observed that the structures with GeO2 and TiO2 matrices provide increased spectral response (at ~907 and 844 nm respectively) and increased PL intensity. The improved PL characteristic have been attributed to increased diffusion barrier against oxygen which otherwise would result in formation of unwanted oxide at the film-oxide interface, thereby deteriorating the optical properties.This work is partially funded by the Icelandic Research Fund Grants nos. 218029 and 196141.Pre-print (óritrýnt handrit

Structural and magnetic changes in CoAlZr thin films upon post annealing

We present a study of the effect of annealing amorphous ferromagnetic thin films of Co0.85(Al0.7Zr0.3)0.15, post deposition. The annealing was done in vacuum with no applied magnetic field. We find that already at a relatively low annealing temperature of 130 ◦C there is crystallite formation that introduces both structural and magnetic inhomogeneity. This does not affect the saturation magnetization strongly, but strongly affects the switching behavior and the overall effective anisotropy of the films. Further, there is a dramatic increase in magnetization damping. Thus, the annealing has a profound effect on both static and dynamic magnetic properties of the material. This is important to keep in mind for potential applications using these materials.Icelandic Research Fund Grants No. 228951, 218029 and 217843.Peer Reviewe

SiGe nanocrystals in SiO2 with high photosensitivity from visible to short-wave infrared

Publisher's version (útgefin grein)Films of SiGe nanocrystals (NCs) in oxide have the advantage of tuning the energy band gap by adjusting SiGe NCs composition and size. In this study, SiGe-SiO2 amorphous films were deposited by magnetron sputtering on Si substrate followed by rapid thermal annealing at 700, 800 and 1000 °C. We investigated films with Si:Ge:SiO2 compositions of 25:25:50 vol.% and 5:45:50 vol.%. TEM investigations reveal the major changes in films morphology (SiGe NCs with different sizes and densities) produced by Si:Ge ratio and annealing temperature. XPS also show that the film depth profile of SiGe content is dependent on the annealing temperature. These changes strongly influence electrical and photoconduction properties. Depending on annealing temperature and Si:Ge ratio, photocurrents can be 103 times higher than dark currents. The photocurrent cutoff wavelength obtained on samples with 25:25 vol% SiGe ratio decreases with annealing temperature increase from 1260 nm in SWIR for 700 °C annealed films to 1210 nm for those at 1000 °C. By increasing Ge content in SiGe (5:45 vol%) the cutoff wavelength significantly shifts to 1345 nm (800 °C annealing). By performing measurements at 100 K, the cutoff wavelength extends in SWIR to 1630 nm having high photoresponsivity of 9.35 AW−1.This work was supported by TE Contract no.30/2018 (PN-III-P1-1.1-TE-2016-2050, within PNCDI III), M-ERA.NET PhotoNanoP Contract No. 33/2016, PCE Contract No. 122/2017, PCCDI Contract No. 75/2018, and financed by CNCS-UEFISCDI, and by Romanian Ministry of Research and Innovation through NIMP Core Program PN19-03 (Contract No. 21N/08.02.2019)."Peer Reviewed

Piezoresistance characterization of silicon nanowires in uniaxial and isostatic pressure variation

Publisher's version (útgefin grein)Silicon nanowires (SiNWs) are known to exhibit a large piezoresistance (PZR) effect, making them suitable for various sensing applications. Here, we report the results of a PZR investigation on randomly distributed and interconnected vertical silicon nanowire arrays as a pressure sensor. The samples were produced from p-type (100) Si wafers using a silver catalyzed top-down etching process. The piezoresistance response of these SiNW arrays was analyzed by measuring their I-V characteristics under applied uniaxial as well as isostatic pressure. The interconnected SiNWs exhibit increased mechanical stability in comparison with separated or periodic nanowires. The repeatability of the fabrication process and statistical distribution of measurements were also tested on several samples from different batches. A sensing resolution down to roughly 1 mbar pressure was observed with uniaxial force application, and more than two orders of magnitude resistance variation were determined for isostatic pressure below atmospheric pressure.Reykjavík UniversityPeer reviewe

Fabrication and characterization of Si1−xGex nanocrystals in as-grown and annealed structures: a comparative study

Publisher's version (útgefin grein)Multilayer structures comprising of SiO2/SiGe/SiO2 and containing SiGe nanoparticles were obtained by depositing SiO2 layers using reactive direct current magnetron sputtering (dcMS), whereas, Si and Ge were co-sputtered using dcMS and high-power impulse magnetron sputtering (HiPIMS). The as-grown structures subsequently underwent rapid thermal annealing (550-900 degrees C for 1 min) in N-2 ambient atmosphere. The structures were investigated using X-ray diffraction, high-resolution transmission electron microscopy together with spectral photocurrent measurements, to explore structural changes and corresponding properties. It is observed that the employment of HiPIMS facilitates the formation of SiGe nanoparticles (2.1 +/- 0.8 nm) in the as-grown structure, and that presence of such nanoparticles acts as a seed for heterogeneous nucleation, which upon annealing results in the periodically arranged columnar self-assembly of SiGe core-shell nanocrystals. An increase in photocurrent intensity by more than an order of magnitude was achieved by annealing. Furthermore, a detailed discussion is provided on strain development within the structures, the consequential interface characteristics and its effect on the photocurrent spectra.M-ERA. NET project PhotoNanoP UEFISCDI Contract no. 33/2016, PCE project UEFISCDI Contract no. 122/2017 and by Romanian Ministry of Research and Innovation through NIMP Core Program PN19-03, contract no. 21 N/08.02.2019 and by the Technology Development Fund of the Icelandic Centre for Research, grant no. 159006-0611."Peer Reviewed

Impact of opioid-free analgesia on pain severity and patient satisfaction after discharge from surgery: multispecialty, prospective cohort study in 25 countries

Background: Balancing opioid stewardship and the need for adequate analgesia following discharge after surgery is challenging. This study aimed to compare the outcomes for patients discharged with opioid versus opioid-free analgesia after common surgical procedures.Methods: This international, multicentre, prospective cohort study collected data from patients undergoing common acute and elective general surgical, urological, gynaecological, and orthopaedic procedures. The primary outcomes were patient-reported time in severe pain measured on a numerical analogue scale from 0 to 100% and patient-reported satisfaction with pain relief during the first week following discharge. Data were collected by in-hospital chart review and patient telephone interview 1 week after discharge.Results: The study recruited 4273 patients from 144 centres in 25 countries; 1311 patients (30.7%) were prescribed opioid analgesia at discharge. Patients reported being in severe pain for 10 (i.q.r. 1-30)% of the first week after discharge and rated satisfaction with analgesia as 90 (i.q.r. 80-100) of 100. After adjustment for confounders, opioid analgesia on discharge was independently associated with increased pain severity (risk ratio 1.52, 95% c.i. 1.31 to 1.76; P < 0.001) and re-presentation to healthcare providers owing to side-effects of medication (OR 2.38, 95% c.i. 1.36 to 4.17; P = 0.004), but not with satisfaction with analgesia (beta coefficient 0.92, 95% c.i. -1.52 to 3.36; P = 0.468) compared with opioid-free analgesia. Although opioid prescribing varied greatly between high-income and low- and middle-income countries, patient-reported outcomes did not.Conclusion: Opioid analgesia prescription on surgical discharge is associated with a higher risk of re-presentation owing to side-effects of medication and increased patient-reported pain, but not with changes in patient-reported satisfaction. Opioid-free discharge analgesia should be adopted routinely